linux-sg2042/fs/eventfd.c

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signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
/*
* fs/eventfd.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
*
*/
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-24 16:04:11 +08:00
#include <linux/slab.h>
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/anon_inodes.h>
#include <linux/syscalls.h>
#include <linux/module.h>
#include <linux/kref.h>
#include <linux/eventfd.h>
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
struct eventfd_ctx {
struct kref kref;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
wait_queue_head_t wqh;
/*
* Every time that a write(2) is performed on an eventfd, the
* value of the __u64 being written is added to "count" and a
* wakeup is performed on "wqh". A read(2) will return the "count"
* value to userspace, and will reset "count" to zero. The kernel
* side eventfd_signal() also, adds to the "count" counter and
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
* issue a wakeup.
*/
__u64 count;
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00
unsigned int flags;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
};
/**
* eventfd_signal - Adds @n to the eventfd counter.
* @ctx: [in] Pointer to the eventfd context.
* @n: [in] Value of the counter to be added to the eventfd internal counter.
* The value cannot be negative.
*
* This function is supposed to be called by the kernel in paths that do not
* allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
* value, and we signal this as overflow condition by returining a POLLERR
* to poll(2).
*
* Returns @n in case of success, a non-negative number lower than @n in case
* of overflow, or the following error codes:
*
* -EINVAL : The value of @n is negative.
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
*/
int eventfd_signal(struct eventfd_ctx *ctx, int n)
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
{
unsigned long flags;
if (n < 0)
return -EINVAL;
spin_lock_irqsave(&ctx->wqh.lock, flags);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
if (ULLONG_MAX - ctx->count < n)
n = (int) (ULLONG_MAX - ctx->count);
ctx->count += n;
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLIN);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
return n;
}
EXPORT_SYMBOL_GPL(eventfd_signal);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
static void eventfd_free_ctx(struct eventfd_ctx *ctx)
{
kfree(ctx);
}
static void eventfd_free(struct kref *kref)
{
struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
eventfd_free_ctx(ctx);
}
/**
* eventfd_ctx_get - Acquires a reference to the internal eventfd context.
* @ctx: [in] Pointer to the eventfd context.
*
* Returns: In case of success, returns a pointer to the eventfd context.
*/
struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
{
kref_get(&ctx->kref);
return ctx;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_get);
/**
* eventfd_ctx_put - Releases a reference to the internal eventfd context.
* @ctx: [in] Pointer to eventfd context.
*
* The eventfd context reference must have been previously acquired either
* with eventfd_ctx_get() or eventfd_ctx_fdget()).
*/
void eventfd_ctx_put(struct eventfd_ctx *ctx)
{
kref_put(&ctx->kref, eventfd_free);
}
EXPORT_SYMBOL_GPL(eventfd_ctx_put);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
static int eventfd_release(struct inode *inode, struct file *file)
{
struct eventfd_ctx *ctx = file->private_data;
wake_up_poll(&ctx->wqh, POLLHUP);
eventfd_ctx_put(ctx);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
return 0;
}
static unsigned int eventfd_poll(struct file *file, poll_table *wait)
{
struct eventfd_ctx *ctx = file->private_data;
unsigned int events = 0;
unsigned long flags;
poll_wait(file, &ctx->wqh, wait);
spin_lock_irqsave(&ctx->wqh.lock, flags);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
if (ctx->count > 0)
events |= POLLIN;
if (ctx->count == ULLONG_MAX)
events |= POLLERR;
if (ULLONG_MAX - 1 > ctx->count)
events |= POLLOUT;
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
return events;
}
static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
{
*cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
ctx->count -= *cnt;
}
/**
* eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
* @ctx: [in] Pointer to eventfd context.
* @wait: [in] Wait queue to be removed.
* @cnt: [out] Pointer to the 64bit conter value.
*
* Returns zero if successful, or the following error codes:
*
* -EAGAIN : The operation would have blocked.
*
* This is used to atomically remove a wait queue entry from the eventfd wait
* queue head, and read/reset the counter value.
*/
int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
__u64 *cnt)
{
unsigned long flags;
spin_lock_irqsave(&ctx->wqh.lock, flags);
eventfd_ctx_do_read(ctx, cnt);
__remove_wait_queue(&ctx->wqh, wait);
if (*cnt != 0 && waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLOUT);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return *cnt != 0 ? 0 : -EAGAIN;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
/**
* eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
* @ctx: [in] Pointer to eventfd context.
* @no_wait: [in] Different from zero if the operation should not block.
* @cnt: [out] Pointer to the 64bit conter value.
*
* Returns zero if successful, or the following error codes:
*
* -EAGAIN : The operation would have blocked but @no_wait was nonzero.
* -ERESTARTSYS : A signal interrupted the wait operation.
*
* If @no_wait is zero, the function might sleep until the eventfd internal
* counter becomes greater than zero.
*/
ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
{
ssize_t res;
DECLARE_WAITQUEUE(wait, current);
spin_lock_irq(&ctx->wqh.lock);
*cnt = 0;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
res = -EAGAIN;
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00
if (ctx->count > 0)
res = 0;
else if (!no_wait) {
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
__add_wait_queue(&ctx->wqh, &wait);
for (;;) {
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
set_current_state(TASK_INTERRUPTIBLE);
if (ctx->count > 0) {
res = 0;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
break;
}
if (signal_pending(current)) {
res = -ERESTARTSYS;
break;
}
spin_unlock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
schedule();
spin_lock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
}
__remove_wait_queue(&ctx->wqh, &wait);
__set_current_state(TASK_RUNNING);
}
if (likely(res == 0)) {
eventfd_ctx_do_read(ctx, cnt);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLOUT);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
}
spin_unlock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
return res;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_read);
static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct eventfd_ctx *ctx = file->private_data;
ssize_t res;
__u64 cnt;
if (count < sizeof(cnt))
return -EINVAL;
res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
if (res < 0)
return res;
return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
}
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
loff_t *ppos)
{
struct eventfd_ctx *ctx = file->private_data;
ssize_t res;
__u64 ucnt;
DECLARE_WAITQUEUE(wait, current);
if (count < sizeof(ucnt))
return -EINVAL;
if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
return -EFAULT;
if (ucnt == ULLONG_MAX)
return -EINVAL;
spin_lock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
res = -EAGAIN;
if (ULLONG_MAX - ctx->count > ucnt)
res = sizeof(ucnt);
else if (!(file->f_flags & O_NONBLOCK)) {
__add_wait_queue(&ctx->wqh, &wait);
for (res = 0;;) {
set_current_state(TASK_INTERRUPTIBLE);
if (ULLONG_MAX - ctx->count > ucnt) {
res = sizeof(ucnt);
break;
}
if (signal_pending(current)) {
res = -ERESTARTSYS;
break;
}
spin_unlock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
schedule();
spin_lock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
}
__remove_wait_queue(&ctx->wqh, &wait);
__set_current_state(TASK_RUNNING);
}
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00
if (likely(res > 0)) {
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
ctx->count += ucnt;
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLIN);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
}
spin_unlock_irq(&ctx->wqh.lock);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
return res;
}
static const struct file_operations eventfd_fops = {
.release = eventfd_release,
.poll = eventfd_poll,
.read = eventfd_read,
.write = eventfd_write,
};
/**
* eventfd_fget - Acquire a reference of an eventfd file descriptor.
* @fd: [in] Eventfd file descriptor.
*
* Returns a pointer to the eventfd file structure in case of success, or the
* following error pointer:
*
* -EBADF : Invalid @fd file descriptor.
* -EINVAL : The @fd file descriptor is not an eventfd file.
*/
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
struct file *eventfd_fget(int fd)
{
struct file *file;
file = fget(fd);
if (!file)
return ERR_PTR(-EBADF);
if (file->f_op != &eventfd_fops) {
fput(file);
return ERR_PTR(-EINVAL);
}
return file;
}
EXPORT_SYMBOL_GPL(eventfd_fget);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
/**
* eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
* @fd: [in] Eventfd file descriptor.
*
* Returns a pointer to the internal eventfd context, otherwise the error
* pointers returned by the following functions:
*
* eventfd_fget
*/
struct eventfd_ctx *eventfd_ctx_fdget(int fd)
{
struct file *file;
struct eventfd_ctx *ctx;
file = eventfd_fget(fd);
if (IS_ERR(file))
return (struct eventfd_ctx *) file;
ctx = eventfd_ctx_get(file->private_data);
fput(file);
return ctx;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
/**
* eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
* @file: [in] Eventfd file pointer.
*
* Returns a pointer to the internal eventfd context, otherwise the error
* pointer:
*
* -EINVAL : The @fd file descriptor is not an eventfd file.
*/
struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
{
if (file->f_op != &eventfd_fops)
return ERR_PTR(-EINVAL);
return eventfd_ctx_get(file->private_data);
}
EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
/**
* eventfd_file_create - Creates an eventfd file pointer.
* @count: Initial eventfd counter value.
* @flags: Flags for the eventfd file.
*
* This function creates an eventfd file pointer, w/out installing it into
* the fd table. This is useful when the eventfd file is used during the
* initialization of data structures that require extra setup after the eventfd
* creation. So the eventfd creation is split into the file pointer creation
* phase, and the file descriptor installation phase.
* In this way races with userspace closing the newly installed file descriptor
* can be avoided.
* Returns an eventfd file pointer, or a proper error pointer.
*/
struct file *eventfd_file_create(unsigned int count, int flags)
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
{
struct file *file;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
struct eventfd_ctx *ctx;
/* Check the EFD_* constants for consistency. */
BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00
if (flags & ~EFD_FLAGS_SET)
return ERR_PTR(-EINVAL);
flag parameters: eventfd This patch adds the new eventfd2 syscall. It extends the old eventfd syscall by one parameter which is meant to hold a flag value. In this patch the only flag support is EFD_CLOEXEC which causes the close-on-exec flag for the returned file descriptor to be set. A new name EFD_CLOEXEC is introduced which in this implementation must have the same value as O_CLOEXEC. The following test must be adjusted for architectures other than x86 and x86-64 and in case the syscall numbers changed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <sys/syscall.h> #ifndef __NR_eventfd2 # ifdef __x86_64__ # define __NR_eventfd2 290 # elif defined __i386__ # define __NR_eventfd2 328 # else # error "need __NR_eventfd2" # endif #endif #define EFD_CLOEXEC O_CLOEXEC int main (void) { int fd = syscall (__NR_eventfd2, 1, 0); if (fd == -1) { puts ("eventfd2(0) failed"); return 1; } int coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if (coe & FD_CLOEXEC) { puts ("eventfd2(0) sets close-on-exec flag"); return 1; } close (fd); fd = syscall (__NR_eventfd2, 1, EFD_CLOEXEC); if (fd == -1) { puts ("eventfd2(EFD_CLOEXEC) failed"); return 1; } coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if ((coe & FD_CLOEXEC) == 0) { puts ("eventfd2(EFD_CLOEXEC) does not set close-on-exec flag"); return 1; } close (fd); puts ("OK"); return 0; } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [akpm@linux-foundation.org: add sys_ni stub] Signed-off-by: Ulrich Drepper <drepper@redhat.com> Acked-by: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@googlemail.com> Cc: <linux-arch@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-24 12:29:25 +08:00
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return ERR_PTR(-ENOMEM);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
kref_init(&ctx->kref);
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
init_waitqueue_head(&ctx->wqh);
ctx->count = count;
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00
ctx->flags = flags;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
if (IS_ERR(file))
eventfd_free_ctx(ctx);
return file;
}
SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
{
int fd, error;
struct file *file;
error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
if (error < 0)
return error;
fd = error;
file = eventfd_file_create(count, flags);
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto err_put_unused_fd;
}
fd_install(fd, file);
return fd;
err_put_unused_fd:
put_unused_fd(fd);
return error;
signal/timer/event: eventfd core This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 13:23:19 +08:00
}
SYSCALL_DEFINE1(eventfd, unsigned int, count)
flag parameters: eventfd This patch adds the new eventfd2 syscall. It extends the old eventfd syscall by one parameter which is meant to hold a flag value. In this patch the only flag support is EFD_CLOEXEC which causes the close-on-exec flag for the returned file descriptor to be set. A new name EFD_CLOEXEC is introduced which in this implementation must have the same value as O_CLOEXEC. The following test must be adjusted for architectures other than x86 and x86-64 and in case the syscall numbers changed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <sys/syscall.h> #ifndef __NR_eventfd2 # ifdef __x86_64__ # define __NR_eventfd2 290 # elif defined __i386__ # define __NR_eventfd2 328 # else # error "need __NR_eventfd2" # endif #endif #define EFD_CLOEXEC O_CLOEXEC int main (void) { int fd = syscall (__NR_eventfd2, 1, 0); if (fd == -1) { puts ("eventfd2(0) failed"); return 1; } int coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if (coe & FD_CLOEXEC) { puts ("eventfd2(0) sets close-on-exec flag"); return 1; } close (fd); fd = syscall (__NR_eventfd2, 1, EFD_CLOEXEC); if (fd == -1) { puts ("eventfd2(EFD_CLOEXEC) failed"); return 1; } coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if ((coe & FD_CLOEXEC) == 0) { puts ("eventfd2(EFD_CLOEXEC) does not set close-on-exec flag"); return 1; } close (fd); puts ("OK"); return 0; } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [akpm@linux-foundation.org: add sys_ni stub] Signed-off-by: Ulrich Drepper <drepper@redhat.com> Acked-by: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@googlemail.com> Cc: <linux-arch@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-24 12:29:25 +08:00
{
return sys_eventfd2(count, 0);
}
eventfd: improve support for semaphore-like behavior People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-01 06:24:18 +08:00