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SubjectRe: [PATCH v3] introduce sys_syncfs to sync a single file system
Date
On Thu, 10 Mar 2011 11:31:30 -0800 (PST), Sage Weil <sage@newdream.net> wrote:
> 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 <sage@newdream.net>

Reviewed-by: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>



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