From b7ed78f56575074f29ec99d8984f347f6c99c914 Mon Sep 17 00:00:00 2001 From: Sage Weil Date: Thu, 10 Mar 2011 11:31:30 -0800 Subject: introduce sys_syncfs to sync a single file system It is frequently useful to sync a single file system, instead of all mounted file systems via sync(2): - On machines with many mounts, it is not at all uncommon for some of them to hang (e.g. unresponsive NFS server). sync(2) will get stuck on those and may never get to the one you do care about (e.g., /). - Some applications write lots of data to the file system and then want to make sure it is flushed to disk. Calling fsync(2) on each file introduces unnecessary ordering constraints that result in a large amount of sub-optimal writeback/flush/commit behavior by the file system. There are currently two ways (that I know of) to sync a single super_block: - BLKFLSBUF ioctl on the block device: That also invalidates the bdev mapping, which isn't usually desirable, and doesn't work for non-block file systems. - 'mount -o remount,rw' will call sync_filesystem as an artifact of the current implemention. Relying on this little-known side effect for something like data safety sounds foolish. Both of these approaches require root privileges, which some applications do not have (nor should they need?) given that sync(2) is an unprivileged operation. This patch introduces a new system call syncfs(2) that takes an fd and syncs only the file system it references. Maybe someday we can $ sync /some/path and not get sync: ignoring all arguments The syscall is motivated by comments by Al and Christoph at the last LSF. syncfs(2) seems like an appropriate name given statfs(2). A similar ioctl was also proposed a while back, see http://marc.info/?l=linux-fsdevel&m=127970513829285&w=2 Signed-off-by: Sage Weil Signed-off-by: Al Viro --- fs/sync.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'fs') diff --git a/fs/sync.c b/fs/sync.c index ba76b9623e7..92ca208777d 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -128,6 +129,29 @@ void emergency_sync(void) } } +/* + * sync a single super + */ +SYSCALL_DEFINE1(syncfs, int, fd) +{ + struct file *file; + struct super_block *sb; + int ret; + int fput_needed; + + file = fget_light(fd, &fput_needed); + if (!file) + return -EBADF; + sb = file->f_dentry->d_sb; + + down_read(&sb->s_umount); + ret = sync_filesystem(sb); + up_read(&sb->s_umount); + + fput_light(file, fput_needed); + return ret; +} + /** * vfs_fsync_range - helper to sync a range of data & metadata to disk * @file: file to sync -- cgit v1.2.3