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[PATCH] Introduce sys_splice() system call 

This adds support for the sys_splice system call. Using a pipe as a
transport, it can connect to files or sockets (latter as output only).

From the splice.c comments:

   "splice": joining two ropes together by interweaving their strands.

   This is the "extended pipe" functionality, where a pipe is used as
   an arbitrary in-memory buffer. Think of a pipe as a small kernel
   buffer that you can use to transfer data from one end to the other.

   The traditional unix read/write is extended with a "splice()" operation
   that transfers data buffers to or from a pipe buffer.

   Named by Larry McVoy, original implementation from Linus, extended by
   Jens to support splicing to files and fixing the initial implementation
   bugs.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Jens Axboe 2006-03-30 15:15:30 +02:00 committed by Linus Torvalds
parent 5d4fe2c1ce
commit 5274f052e7
15 changed files with 669 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/i386/kernel/syscall_table.S
View File

@ -312,3 +312,4 @@ ENTRY(sys_call_table)
.long sys_unshare /* 310 */
.long sys_set_robust_list
.long sys_get_robust_list
.long sys_splice

1
arch/ia64/kernel/entry.S
View File

@ -1605,5 +1605,6 @@ sys_call_table:
data8 sys_ni_syscall // reserved for pselect
data8 sys_ni_syscall // 1295 reserved for ppoll
data8 sys_unshare
data8 sys_splice
.org sys_call_table + 8*NR_syscalls // guard against failures to increase NR_syscalls

2
fs/Makefile
View File

@ -10,7 +10,7 @@ obj-y := open.o read_write.o file_table.o buffer.o bio.o super.o \
ioctl.o readdir.o select.o fifo.o locks.o dcache.o inode.o \
attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
seq_file.o xattr.o libfs.o fs-writeback.o mpage.o direct-io.o \
ioprio.o pnode.o drop_caches.o
ioprio.o pnode.o drop_caches.o splice.o
obj-$(CONFIG_INOTIFY) += inotify.o
obj-$(CONFIG_EPOLL) += eventpoll.o

2
fs/ext2/file.c
View File

@ -53,6 +53,8 @@ const struct file_operations ext2_file_operations = {
.readv = generic_file_readv,
.writev = generic_file_writev,
.sendfile = generic_file_sendfile,
.splice_read = generic_file_splice_read,
.splice_write = generic_file_splice_write,
};
#ifdef CONFIG_EXT2_FS_XIP

2
fs/ext3/file.c
View File

@ -119,6 +119,8 @@ const struct file_operations ext3_file_operations = {
.release = ext3_release_file,
.fsync = ext3_sync_file,
.sendfile = generic_file_sendfile,
.splice_read = generic_file_splice_read,
.splice_write = generic_file_splice_write,
};
struct inode_operations ext3_file_inode_operations = {

33
fs/pipe.c
View File

@ -15,6 +15,7 @@
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <asm/uaccess.h>
#include <asm/ioctls.h>
@ -94,11 +95,20 @@ static void anon_pipe_buf_release(struct pipe_inode_info *info, struct pipe_buff
{
struct page *page = buf->page;
if (info->tmp_page) {
__free_page(page);
/*
* If nobody else uses this page, and we don't already have a
* temporary page, let's keep track of it as a one-deep
* allocation cache
*/
if (page_count(page) == 1 && !info->tmp_page) {
info->tmp_page = page;
return;
}
info->tmp_page = page;
/*
* Otherwise just release our reference to it
*/
page_cache_release(page);
}
static void *anon_pipe_buf_map(struct file *file, struct pipe_inode_info *info, struct pipe_buffer *buf)
@ -152,6 +162,11 @@ pipe_readv(struct file *filp, const struct iovec *_iov,
chars = total_len;
addr = ops->map(filp, info, buf);
if (IS_ERR(addr)) {
if (!ret)
ret = PTR_ERR(addr);
break;
}
error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars);
ops->unmap(info, buf);
if (unlikely(error)) {
@ -254,8 +269,16 @@ pipe_writev(struct file *filp, const struct iovec *_iov,
struct pipe_buf_operations *ops = buf->ops;
int offset = buf->offset + buf->len;
if (ops->can_merge && offset + chars <= PAGE_SIZE) {
void *addr = ops->map(filp, info, buf);
int error = pipe_iov_copy_from_user(offset + addr, iov, chars);
void *addr;
int error;
addr = ops->map(filp, info, buf);
if (IS_ERR(addr)) {
error = PTR_ERR(addr);
goto out;
}
error = pipe_iov_copy_from_user(offset + addr, iov,
chars);
ops->unmap(info, buf);
ret = error;
do_wakeup = 1;

2
fs/reiserfs/file.c
View File

@ -1576,6 +1576,8 @@ const struct file_operations reiserfs_file_operations = {
.sendfile = generic_file_sendfile,
.aio_read = generic_file_aio_read,
.aio_write = reiserfs_aio_write,
.splice_read = generic_file_splice_read,
.splice_write = generic_file_splice_write,
};
struct inode_operations reiserfs_file_inode_operations = {

612
fs/splice.c Normal file
View File

@ -0,0 +1,612 @@
/*
* "splice": joining two ropes together by interweaving their strands.
*
* This is the "extended pipe" functionality, where a pipe is used as
* an arbitrary in-memory buffer. Think of a pipe as a small kernel
* buffer that you can use to transfer data from one end to the other.
*
* The traditional unix read/write is extended with a "splice()" operation
* that transfers data buffers to or from a pipe buffer.
*
* Named by Larry McVoy, original implementation from Linus, extended by
* Jens to support splicing to files and fixing the initial implementation
* bugs.
*
* Copyright (C) 2005 Jens Axboe <axboe@suse.de>
* Copyright (C) 2005 Linus Torvalds <torvalds@osdl.org>
*
*/
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/pipe_fs_i.h>
#include <linux/mm_inline.h>
/*
* Passed to the actors
*/
struct splice_desc {
unsigned int len, total_len; /* current and remaining length */
unsigned int flags; /* splice flags */
struct file *file; /* file to read/write */
loff_t pos; /* file position */
};
static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
page_cache_release(buf->page);
buf->page = NULL;
}
static void *page_cache_pipe_buf_map(struct file *file,
struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
lock_page(page);
if (!PageUptodate(page)) {
unlock_page(page);
return ERR_PTR(-EIO);
}
if (!page->mapping) {
unlock_page(page);
return ERR_PTR(-ENODATA);
}
return kmap(buf->page);
}
static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
unlock_page(buf->page);
kunmap(buf->page);
}
static struct pipe_buf_operations page_cache_pipe_buf_ops = {
.can_merge = 0,
.map = page_cache_pipe_buf_map,
.unmap = page_cache_pipe_buf_unmap,
.release = page_cache_pipe_buf_release,
};
static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
int nr_pages, unsigned long offset,
unsigned long len)
{
struct pipe_inode_info *info;
int ret, do_wakeup, i;
ret = 0;
do_wakeup = 0;
i = 0;
mutex_lock(PIPE_MUTEX(*inode));
info = inode->i_pipe;
for (;;) {
int bufs;
if (!PIPE_READERS(*inode)) {
send_sig(SIGPIPE, current, 0);
if (!ret)
ret = -EPIPE;
break;
}
bufs = info->nrbufs;
if (bufs < PIPE_BUFFERS) {
int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS - 1);
struct pipe_buffer *buf = info->bufs + newbuf;
struct page *page = pages[i++];
unsigned long this_len;
this_len = PAGE_CACHE_SIZE - offset;
if (this_len > len)
this_len = len;
buf->page = page;
buf->offset = offset;
buf->len = this_len;
buf->ops = &page_cache_pipe_buf_ops;
info->nrbufs = ++bufs;
do_wakeup = 1;
ret += this_len;
len -= this_len;
offset = 0;
if (!--nr_pages)
break;
if (!len)
break;
if (bufs < PIPE_BUFFERS)
continue;
break;
}
if (signal_pending(current)) {
if (!ret)
ret = -ERESTARTSYS;
break;
}
if (do_wakeup) {
wake_up_interruptible_sync(PIPE_WAIT(*inode));
kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO,
POLL_IN);
do_wakeup = 0;
}
PIPE_WAITING_WRITERS(*inode)++;
pipe_wait(inode);
PIPE_WAITING_WRITERS(*inode)--;
}
mutex_unlock(PIPE_MUTEX(*inode));
if (do_wakeup) {
wake_up_interruptible(PIPE_WAIT(*inode));
kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
}
while (i < nr_pages)
page_cache_release(pages[i++]);
return ret;
}
static int __generic_file_splice_read(struct file *in, struct inode *pipe,
size_t len)
{
struct address_space *mapping = in->f_mapping;
unsigned int offset, nr_pages;
struct page *pages[PIPE_BUFFERS], *shadow[PIPE_BUFFERS];
struct page *page;
pgoff_t index, pidx;
int i, j;
index = in->f_pos >> PAGE_CACHE_SHIFT;
offset = in->f_pos & ~PAGE_CACHE_MASK;
nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (nr_pages > PIPE_BUFFERS)
nr_pages = PIPE_BUFFERS;
/*
* initiate read-ahead on this page range
*/
do_page_cache_readahead(mapping, in, index, nr_pages);
/*
* Get as many pages from the page cache as possible..
* Start IO on the page cache entries we create (we
* can assume that any pre-existing ones we find have
* already had IO started on them).
*/
i = find_get_pages(mapping, index, nr_pages, pages);
/*
* common case - we found all pages and they are contiguous,
* kick them off
*/
if (i && (pages[i - 1]->index == index + i - 1))
goto splice_them;
/*
* fill shadow[] with pages at the right locations, so we only
* have to fill holes
*/
memset(shadow, 0, i * sizeof(struct page *));
for (j = 0, pidx = index; j < i; pidx++, j++)
shadow[pages[j]->index - pidx] = pages[j];
/*
* now fill in the holes
*/
for (i = 0, pidx = index; i < nr_pages; pidx++, i++) {
int error;
if (shadow[i])
continue;
/*
* no page there, look one up / create it
*/
page = find_or_create_page(mapping, pidx,
mapping_gfp_mask(mapping));
if (!page)
break;
if (PageUptodate(page))
unlock_page(page);
else {
error = mapping->a_ops->readpage(in, page);
if (unlikely(error)) {
page_cache_release(page);
break;
}
}
shadow[i] = page;
}
if (!i) {
for (i = 0; i < nr_pages; i++) {
if (shadow[i])
page_cache_release(shadow[i]);
}
return 0;
}
memcpy(pages, shadow, i * sizeof(struct page *));
/*
* Now we splice them into the pipe..
*/
splice_them:
return move_to_pipe(pipe, pages, i, offset, len);
}
ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,
size_t len, unsigned int flags)
{
ssize_t spliced;
int ret;
ret = 0;
spliced = 0;
while (len) {
ret = __generic_file_splice_read(in, pipe, len);
if (ret <= 0)
break;
in->f_pos += ret;
len -= ret;
spliced += ret;
}
if (spliced)
return spliced;
return ret;
}
/*
* Send 'len' bytes to socket from 'file' at position 'pos' using sendpage().
*/
static int pipe_to_sendpage(struct pipe_inode_info *info,
struct pipe_buffer *buf, struct splice_desc *sd)
{
struct file *file = sd->file;
loff_t pos = sd->pos;
unsigned int offset;
ssize_t ret;
void *ptr;
/*
* sub-optimal, but we are limited by the pipe ->map. we don't
* need a kmap'ed buffer here, we just want to make sure we
* have the page pinned if the pipe page originates from the
* page cache
*/
ptr = buf->ops->map(file, info, buf);
if (IS_ERR(ptr))
return PTR_ERR(ptr);
offset = pos & ~PAGE_CACHE_MASK;
ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,
sd->len < sd->total_len);
buf->ops->unmap(info, buf);
if (ret == sd->len)
return 0;
return -EIO;
}
/*
* This is a little more tricky than the file -> pipe splicing. There are
* basically three cases:
*
* - Destination page already exists in the address space and there
* are users of it. For that case we have no other option that
* copying the data. Tough luck.
* - Destination page already exists in the address space, but there
* are no users of it. Make sure it's uptodate, then drop it. Fall
* through to last case.
* - Destination page does not exist, we can add the pipe page to
* the page cache and avoid the copy.
*
* For now we just do the slower thing and always copy pages over, it's
* easier than migrating pages from the pipe to the target file. For the
* case of doing file | file splicing, the migrate approach had some LRU
* nastiness...
*/
static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
struct splice_desc *sd)
{
struct file *file = sd->file;
struct address_space *mapping = file->f_mapping;
unsigned int offset;
struct page *page;
char *src, *dst;
pgoff_t index;
int ret;
/*
* after this, page will be locked and unmapped
*/
src = buf->ops->map(file, info, buf);
if (IS_ERR(src))
return PTR_ERR(src);
index = sd->pos >> PAGE_CACHE_SHIFT;
offset = sd->pos & ~PAGE_CACHE_MASK;
find_page:
ret = -ENOMEM;
page = find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
if (!page)
goto out;
/*
* If the page is uptodate, it is also locked. If it isn't
* uptodate, we can mark it uptodate if we are filling the
* full page. Otherwise we need to read it in first...
*/
if (!PageUptodate(page)) {
if (sd->len < PAGE_CACHE_SIZE) {
ret = mapping->a_ops->readpage(file, page);
if (unlikely(ret))
goto out;
lock_page(page);
if (!PageUptodate(page)) {
/*
* page got invalidated, repeat
*/
if (!page->mapping) {
unlock_page(page);
page_cache_release(page);
goto find_page;
}
ret = -EIO;
goto out;
}
} else {
WARN_ON(!PageLocked(page));
SetPageUptodate(page);
}
}
ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
if (ret)
goto out;
dst = kmap_atomic(page, KM_USER0);
memcpy(dst + offset, src + buf->offset, sd->len);
flush_dcache_page(page);
kunmap_atomic(dst, KM_USER0);
ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
if (ret < 0)
goto out;
set_page_dirty(page);
ret = write_one_page(page, 0);
out:
if (ret < 0)
unlock_page(page);
page_cache_release(page);
buf->ops->unmap(info, buf);
return ret;
}
typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
struct splice_desc *);
static ssize_t move_from_pipe(struct inode *inode, struct file *out,
size_t len, unsigned int flags,
splice_actor *actor)
{
struct pipe_inode_info *info;
int ret, do_wakeup, err;
struct splice_desc sd;
ret = 0;
do_wakeup = 0;
sd.total_len = len;
sd.flags = flags;
sd.file = out;
sd.pos = out->f_pos;
mutex_lock(PIPE_MUTEX(*inode));
info = inode->i_pipe;
for (;;) {
int bufs = info->nrbufs;
if (bufs) {
int curbuf = info->curbuf;
struct pipe_buffer *buf = info->bufs + curbuf;
struct pipe_buf_operations *ops = buf->ops;
sd.len = buf->len;
if (sd.len > sd.total_len)
sd.len = sd.total_len;
err = actor(info, buf, &sd);
if (err) {
if (!ret && err != -ENODATA)
ret = err;
break;
}
ret += sd.len;
buf->offset += sd.len;
buf->len -= sd.len;
if (!buf->len) {
buf->ops = NULL;
ops->release(info, buf);
curbuf = (curbuf + 1) & (PIPE_BUFFERS - 1);
info->curbuf = curbuf;
info->nrbufs = --bufs;
do_wakeup = 1;
}
sd.pos += sd.len;
sd.total_len -= sd.len;
if (!sd.total_len)
break;
}
if (bufs)
continue;
if (!PIPE_WRITERS(*inode))
break;
if (!PIPE_WAITING_WRITERS(*inode)) {
if (ret)
break;
}
if (signal_pending(current)) {
if (!ret)
ret = -ERESTARTSYS;
break;
}
if (do_wakeup) {
wake_up_interruptible_sync(PIPE_WAIT(*inode));
kill_fasync(PIPE_FASYNC_WRITERS(*inode),SIGIO,POLL_OUT);
do_wakeup = 0;
}
pipe_wait(inode);
}
mutex_unlock(PIPE_MUTEX(*inode));
if (do_wakeup) {
wake_up_interruptible(PIPE_WAIT(*inode));
kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
}
mutex_lock(&out->f_mapping->host->i_mutex);
out->f_pos = sd.pos;
mutex_unlock(&out->f_mapping->host->i_mutex);
return ret;
}
ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
size_t len, unsigned int flags)
{
return move_from_pipe(inode, out, len, flags, pipe_to_file);
}
ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
size_t len, unsigned int flags)
{
return move_from_pipe(inode, out, len, flags, pipe_to_sendpage);
}
static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
unsigned int flags)
{
loff_t pos;
int ret;
if (!out->f_op || !out->f_op->splice_write)
return -EINVAL;
if (!(out->f_mode & FMODE_WRITE))
return -EBADF;
pos = out->f_pos;
ret = rw_verify_area(WRITE, out, &pos, len);
if (unlikely(ret < 0))
return ret;
return out->f_op->splice_write(pipe, out, len, flags);
}
static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
unsigned int flags)
{
loff_t pos, isize, left;
int ret;
if (!in->f_op || !in->f_op->splice_read)
return -EINVAL;
if (!(in->f_mode & FMODE_READ))
return -EBADF;
pos = in->f_pos;
ret = rw_verify_area(READ, in, &pos, len);
if (unlikely(ret < 0))
return ret;
isize = i_size_read(in->f_mapping->host);
if (unlikely(in->f_pos >= isize))
return 0;
left = isize - in->f_pos;
if (left < len)
len = left;
return in->f_op->splice_read(in, pipe, len, flags);
}
static long do_splice(struct file *in, struct file *out, size_t len,
unsigned int flags)
{
struct inode *pipe;
pipe = in->f_dentry->d_inode;
if (pipe->i_pipe)
return do_splice_from(pipe, out, len, flags);
pipe = out->f_dentry->d_inode;
if (pipe->i_pipe)
return do_splice_to(in, pipe, len, flags);
return -EINVAL;
}
asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
{
long error;
struct file *in, *out;
int fput_in, fput_out;
if (unlikely(!len))
return 0;
error = -EBADF;
in = fget_light(fdin, &fput_in);
if (in) {
if (in->f_mode & FMODE_READ) {
out = fget_light(fdout, &fput_out);
if (out) {
if (out->f_mode & FMODE_WRITE)
error = do_splice(in, out, len, flags);
fput_light(out, fput_out);
}
}
fput_light(in, fput_in);
}
return error;
}

3
include/asm-i386/unistd.h
View File

@ -318,8 +318,9 @@
#define __NR_unshare 310
#define __NR_set_robust_list 311
#define __NR_get_robust_list 312
#define __NR_sys_splice 313
#define NR_syscalls 313
#define NR_syscalls 314
/*
* user-visible error numbers are in the range -1 - -128: see

3
include/asm-ia64/unistd.h
View File

@ -285,12 +285,13 @@
#define __NR_faccessat 1293
/* 1294, 1295 reserved for pselect/ppoll */
#define __NR_unshare 1296
#define __NR_splice 1297
#ifdef __KERNEL__
#include <linux/config.h>
#define NR_syscalls 273 /* length of syscall table */
#define NR_syscalls 274 /* length of syscall table */
#define __ARCH_WANT_SYS_RT_SIGACTION

3
include/asm-powerpc/unistd.h
View File

@ -301,8 +301,9 @@
#define __NR_pselect6 280
#define __NR_ppoll 281
#define __NR_unshare 282
#define __NR_splice 283
#define __NR_syscalls 283
#define __NR_syscalls 284
#ifdef __KERNEL__
#define __NR__exit __NR_exit

4
include/asm-x86_64/unistd.h
View File

@ -609,8 +609,10 @@ __SYSCALL(__NR_unshare, sys_unshare)
__SYSCALL(__NR_set_robust_list, sys_set_robust_list)
#define __NR_get_robust_list 274
__SYSCALL(__NR_get_robust_list, sys_get_robust_list)
#define __NR_splice 275
__SYSCALL(__NR_splice, sys_splice)
#define __NR_syscall_max __NR_get_robust_list
#define __NR_syscall_max __NR_splice
#ifndef __NO_STUBS

4
include/linux/fs.h
View File

@ -1032,6 +1032,8 @@ struct file_operations {
int (*check_flags)(int);
int (*dir_notify)(struct file *filp, unsigned long arg);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct inode *, struct file *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, struct inode *, size_t, unsigned int);
};
struct inode_operations {
@ -1609,6 +1611,8 @@ extern ssize_t generic_file_sendfile(struct file *, loff_t *, size_t, read_actor
extern void do_generic_mapping_read(struct address_space *mapping,
struct file_ra_state *, struct file *,
loff_t *, read_descriptor_t *, read_actor_t);
extern ssize_t generic_file_splice_read(struct file *, struct inode *, size_t, unsigned int);
extern ssize_t generic_file_splice_write(struct inode *, struct file *, size_t, unsigned int);
extern void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
extern ssize_t generic_file_readv(struct file *filp, const struct iovec *iov,

2
include/linux/syscalls.h
View File

@ -569,5 +569,7 @@ asmlinkage long compat_sys_newfstatat(unsigned int dfd, char __user * filename,
asmlinkage long compat_sys_openat(unsigned int dfd, const char __user *filename,
int flags, int mode);
asmlinkage long sys_unshare(unsigned long unshare_flags);
asmlinkage long sys_splice(int fdin, int fdout, size_t len,
unsigned int flags);
#endif

6
net/socket.c
View File

@ -119,6 +119,9 @@ static ssize_t sock_writev(struct file *file, const struct iovec *vector,
static ssize_t sock_sendpage(struct file *file, struct page *page,
int offset, size_t size, loff_t *ppos, int more);
extern ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
size_t len, unsigned int flags);
/*
* Socket files have a set of 'special' operations as well as the generic file ones. These don't appear
@ -141,7 +144,8 @@ static struct file_operations socket_file_ops = {
.fasync = sock_fasync,
.readv = sock_readv,
.writev = sock_writev,
.sendpage = sock_sendpage
.sendpage = sock_sendpage,
.splice_write = generic_splice_sendpage,
};
/*