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fscache: Implement raw I/O interface 

Provide a pair of functions to perform raw I/O on the cache.  The first
function allows an arbitrary asynchronous direct-IO read to be made against
a cache object, though the read should be aligned and sized appropriately
for the backing device:

        int fscache_read(struct netfs_cache_resources *cres,
                         loff_t start_pos,
                         struct iov_iter *iter,
                         enum netfs_read_from_hole read_hole,
                         netfs_io_terminated_t term_func,
                         void *term_func_priv);

The cache resources must have been previously initialised by
fscache_begin_read_operation().  A read operation is sent to the backing
filesystem, starting at start_pos within the file.  The size of the read is
specified by the iterator, as is the location of the output buffer.

If there is a hole in the data it can be ignored and left to the backing
filesystem to deal with (NETFS_READ_HOLE_IGNORE), a hole at the beginning
can be skipped over and the buffer padded with zeros
(NETFS_READ_HOLE_CLEAR) or -ENODATA can be given (NETFS_READ_HOLE_FAIL).

If term_func is not NULL, the operation may be performed asynchronously.
Upon completion, successful or otherwise, (*term_func)() will be called and
passed term_func_priv, along with an error or the amount of data
transferred.  If the op is run asynchronously, fscache_read() will return
-EIOCBQUEUED.

The second function allows an arbitrary asynchronous direct-IO write to be
made against a cache object, though the write should be aligned and sized
appropriately for the backing device:

        int fscache_write(struct netfs_cache_resources *cres,
                          loff_t start_pos,
                          struct iov_iter *iter,
                          netfs_io_terminated_t term_func,
                          void *term_func_priv);

This works in very similar way to fscache_read(), except that there's no
need to deal with holes (they're just overwritten).

The caller is responsible for preventing concurrent overlapping writes.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819613224.215744.7877577215582621254.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906915386.143852.16936177636106480724.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967122632.1823006.7487049517698562172.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021521420.640689.12747258780542678309.stgit@warthog.procyon.org.uk/ # v4
This commit is contained in:
David Howells 2021-10-20 14:06:34 +01:00
parent 3a11b3a863
commit 9af1c6c308
2 changed files with 76 additions and 0 deletions
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74
include/linux/fscache.h
View File

@ -429,4 +429,78 @@ int fscache_begin_read_operation(struct netfs_cache_resources *cres,
return -ENOBUFS;
}
/**
* fscache_read - Start a read from the cache.
* @cres: The cache resources to use
* @start_pos: The beginning file offset in the cache file
* @iter: The buffer to fill - and also the length
* @read_hole: How to handle a hole in the data.
* @term_func: The function to call upon completion
* @term_func_priv: The private data for @term_func
*
* Start a read from the cache. @cres indicates the cache object to read from
* and must be obtained by a call to fscache_begin_operation() beforehand.
*
* The data is read into the iterator, @iter, and that also indicates the size
* of the operation. @start_pos is the start position in the file, though if
* @seek_data is set appropriately, the cache can use SEEK_DATA to find the
* next piece of data, writing zeros for the hole into the iterator.
*
* Upon termination of the operation, @term_func will be called and supplied
* with @term_func_priv plus the amount of data written, if successful, or the
* error code otherwise.
*
* @read_hole indicates how a partially populated region in the cache should be
* handled. It can be one of a number of settings:
*
* NETFS_READ_HOLE_IGNORE - Just try to read (may return a short read).
*
* NETFS_READ_HOLE_CLEAR - Seek for data, clearing the part of the buffer
* skipped over, then do as for IGNORE.
*
* NETFS_READ_HOLE_FAIL - Give ENODATA if we encounter a hole.
*/
static inline
int fscache_read(struct netfs_cache_resources *cres,
loff_t start_pos,
struct iov_iter *iter,
enum netfs_read_from_hole read_hole,
netfs_io_terminated_t term_func,
void *term_func_priv)
{
const struct netfs_cache_ops *ops = fscache_operation_valid(cres);
return ops->read(cres, start_pos, iter, read_hole,
term_func, term_func_priv);
}
/**
* fscache_write - Start a write to the cache.
* @cres: The cache resources to use
* @start_pos: The beginning file offset in the cache file
* @iter: The data to write - and also the length
* @term_func: The function to call upon completion
* @term_func_priv: The private data for @term_func
*
* Start a write to the cache. @cres indicates the cache object to write to and
* must be obtained by a call to fscache_begin_operation() beforehand.
*
* The data to be written is obtained from the iterator, @iter, and that also
* indicates the size of the operation. @start_pos is the start position in
* the file.
*
* Upon termination of the operation, @term_func will be called and supplied
* with @term_func_priv plus the amount of data written, if successful, or the
* error code otherwise.
*/
static inline
int fscache_write(struct netfs_cache_resources *cres,
loff_t start_pos,
struct iov_iter *iter,
netfs_io_terminated_t term_func,
void *term_func_priv)
{
const struct netfs_cache_ops *ops = fscache_operation_valid(cres);
return ops->write(cres, start_pos, iter, term_func, term_func_priv);
}
#endif /* _LINUX_FSCACHE_H */

2
include/trace/events/fscache.h
View File

@ -79,6 +79,7 @@ enum fscache_access_trace {
fscache_access_io_not_live,
fscache_access_io_read,
fscache_access_io_wait,
fscache_access_io_write,
fscache_access_lookup_cookie,
fscache_access_lookup_cookie_end,
fscache_access_lookup_cookie_end_failed,
@ -149,6 +150,7 @@ enum fscache_access_trace {
EM(fscache_access_io_not_live, "END io_notl") \
EM(fscache_access_io_read, "BEGIN io_read") \
EM(fscache_access_io_wait, "WAIT io ") \
EM(fscache_access_io_write, "BEGIN io_writ") \
EM(fscache_access_lookup_cookie, "BEGIN lookup ") \
EM(fscache_access_lookup_cookie_end, "END lookup ") \
EM(fscache_access_lookup_cookie_end_failed,"END lookupf") \