Commit f79e2abb authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

[PATCH] sys_sync_file_range() 

Remove the recently-added LINUX_FADV_ASYNC_WRITE and LINUX_FADV_WRITE_WAIT
fadvise() additions, do it in a new sys_sync_file_range() syscall instead.
Reasons:

- It's more flexible.  Things which would require two or three syscalls with
  fadvise() can be done in a single syscall.

- Using fadvise() in this manner is something not covered by POSIX.

The patch wires up the syscall for x86.

The sycall is implemented in the new fs/sync.c.  The intention is that we can
move sys_fsync(), sys_fdatasync() and perhaps sys_sync() into there later.

Documentation for the syscall is in fs/sync.c.

A test app (sync_file_range.c) is in
http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz

.

The available-to-GPL-modules do_sync_file_range() is for knfsd: "A COMMIT can
say NFS_DATA_SYNC or NFS_FILE_SYNC.  I can skip the ->fsync call for
NFS_DATA_SYNC which is hopefully the more common."

Note: the `async' writeout mode SYNC_FILE_RANGE_WRITE will turn synchronous if
the queue is congested.  This is trivial to fix: add a new flag bit, set
wbc->nonblocking.  But I'm not sure that we want to expose implementation
details down to that level.

Note: it's notable that we can sync an fd which wasn't opened for writing.
Same with fsync() and fdatasync()).

Note: the code takes some care to handle attempts to sync file contents
outside the 16TB offset on 32-bit machines.  It makes such attempts appear to
succeed, for best 32-bit/64-bit compatibility.  Perhaps it should make such
requests fail...

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent d6dfd131

arch/i386/kernel/syscall_table.S

+1 −0
Original line number Diff line number Diff line
@@ -313,3 +313,4 @@ ENTRY(sys_call_table) 
	.long sys_set_robust_list

	.long sys_get_robust_list

	.long sys_splice

	.long sys_sync_file_range

fs/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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 splice.o

		ioprio.o pnode.o drop_caches.o splice.o sync.o



obj-$(CONFIG_INOTIFY)		+= inotify.o

obj-$(CONFIG_EPOLL)		+= eventpoll.o

fs/sync.c

0 → 100644
+164 −0
Original line number Diff line number Diff line 
/*

 * High-level sync()-related operations

 */



#include <linux/kernel.h>

#include <linux/file.h>

#include <linux/fs.h>

#include <linux/module.h>

#include <linux/writeback.h>

#include <linux/syscalls.h>

#include <linux/linkage.h>

#include <linux/pagemap.h>



#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \

			SYNC_FILE_RANGE_WAIT_AFTER)



/*

 * sys_sync_file_range() permits finely controlled syncing over a segment of

 * a file in the range offset .. (offset+nbytes-1) inclusive.  If nbytes is

 * zero then sys_sync_file_range() will operate from offset out to EOF.

 *

 * The flag bits are:

 *

 * SYNC_FILE_RANGE_WAIT_BEFORE: wait upon writeout of all pages in the range

 * before performing the write.

 *

 * SYNC_FILE_RANGE_WRITE: initiate writeout of all those dirty pages in the

 * range which are not presently under writeback.

 *

 * SYNC_FILE_RANGE_WAIT_AFTER: wait upon writeout of all pages in the range

 * after performing the write.

 *

 * Useful combinations of the flag bits are:

 *

 * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages

 * in the range which were dirty on entry to sys_sync_file_range() are placed

 * under writeout.  This is a start-write-for-data-integrity operation.

 *

 * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which

 * are not presently under writeout.  This is an asynchronous flush-to-disk

 * operation.  Not suitable for data integrity operations.

 *

 * SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER): wait for

 * completion of writeout of all pages in the range.  This will be used after an

 * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait

 * for that operation to complete and to return the result.

 *

 * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER:

 * a traditional sync() operation.  This is a write-for-data-integrity operation

 * which will ensure that all pages in the range which were dirty on entry to

 * sys_sync_file_range() are committed to disk.

 *

 *

 * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any

 * I/O errors or ENOSPC conditions and will return those to the caller, after

 * clearing the EIO and ENOSPC flags in the address_space.

 *

 * It should be noted that none of these operations write out the file's

 * metadata.  So unless the application is strictly performing overwrites of

 * already-instantiated disk blocks, there are no guarantees here that the data

 * will be available after a crash.

 */

asmlinkage long sys_sync_file_range(int fd, loff_t offset, loff_t nbytes,

					int flags)

{

	int ret;

	struct file *file;

	loff_t endbyte;			/* inclusive */

	int fput_needed;

	umode_t i_mode;



	ret = -EINVAL;

	if (flags & ~VALID_FLAGS)

		goto out;



	endbyte = offset + nbytes;



	if ((s64)offset < 0)

		goto out;

	if ((s64)endbyte < 0)

		goto out;

	if (endbyte < offset)

		goto out;



	if (sizeof(pgoff_t) == 4) {

		if (offset >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {

			/*

			 * The range starts outside a 32 bit machine's

			 * pagecache addressing capabilities.  Let it "succeed"

			 */

			ret = 0;

			goto out;

		}

		if (endbyte >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {

			/*

			 * Out to EOF

			 */

			nbytes = 0;

		}

	}



	if (nbytes == 0)

		endbyte = -1;

	else

		endbyte--;		/* inclusive */



	ret = -EBADF;

	file = fget_light(fd, &fput_needed);

	if (!file)

		goto out;



	i_mode = file->f_dentry->d_inode->i_mode;

	ret = -ESPIPE;

	if (!S_ISREG(i_mode) && !S_ISBLK(i_mode) && !S_ISDIR(i_mode) &&

			!S_ISLNK(i_mode))

		goto out_put;



	ret = do_sync_file_range(file, offset, endbyte, flags);

out_put:

	fput_light(file, fput_needed);

out:

	return ret;

}



/*

 * `endbyte' is inclusive

 */

int do_sync_file_range(struct file *file, loff_t offset, loff_t endbyte,

			int flags)

{

	int ret;

	struct address_space *mapping;



	mapping = file->f_mapping;

	if (!mapping) {

		ret = -EINVAL;

		goto out;

	}



	ret = 0;

	if (flags & SYNC_FILE_RANGE_WAIT_BEFORE) {

		ret = wait_on_page_writeback_range(mapping,

					offset >> PAGE_CACHE_SHIFT,

					endbyte >> PAGE_CACHE_SHIFT);

		if (ret < 0)

			goto out;

	}



	if (flags & SYNC_FILE_RANGE_WRITE) {

		ret = __filemap_fdatawrite_range(mapping, offset, endbyte,

						WB_SYNC_NONE);

		if (ret < 0)

			goto out;

	}



	if (flags & SYNC_FILE_RANGE_WAIT_AFTER) {

		ret = wait_on_page_writeback_range(mapping,

					offset >> PAGE_CACHE_SHIFT,

					endbyte >> PAGE_CACHE_SHIFT);

	}

out:

	return ret;

}

EXPORT_SYMBOL_GPL(do_sync_file_range);

include/asm-i386/unistd.h

+2 −1
Original line number Diff line number Diff line
@@ -319,8 +319,9 @@ 
#define __NR_set_robust_list	311

#define __NR_get_robust_list	312

#define __NR_sys_splice		313

#define __NR_sys_sync_file_range 314



#define NR_syscalls 314

#define NR_syscalls 315



/*

 * user-visible error numbers are in the range -1 - -128: see

include/linux/fadvise.h

+0 −6
Original line number Diff line number Diff line
@@ -18,10 +18,4 @@ 
#define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */

#endif



/*

 * Linux-specific fadvise() extensions:

 */

#define LINUX_FADV_ASYNC_WRITE	32	/* Start writeout on range */

#define LINUX_FADV_WRITE_WAIT	33	/* Wait upon writeout to range */



#endif	/* FADVISE_H_INCLUDED */

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