[PATCH] Add man page for vfs_syncops

[Ira Cooper]

On Fri, Aug 9, 2013 at 5:12 AM, Christoph Hellwig <hch at infradead.org> wrote:

> On Fri, Aug 09, 2013 at 11:08:03AM +0200, Karolin Seeger wrote:
> > +     Some filesystems (even some journaled filesystems) require that a
> > +     fsync() be performed on many meta data operations to ensure that
> the
> > +     operation is guaranteed to remain in the filesystem after a power
> > +     failure. This is particularly important for some cluster
> filesystems
> > +     which are participating in a node failover system with clustered
> > +     Samba. On those filesystems the <command>vfs_syncops</command> VFS
> module
> > +     provides a way to perform those operations safely.
>
> I don't know a single Unix filesystems from the last 40 years where this
> is not true.  Why isn't this the default behaviour in Samba instead of
> having it in a module that very few people are going to use?
>

ZFS behaves correctly here.  And fsync only guarantees a file is correct,
not the filesystem.

(Taken from OS X's man fsync.)

FSYNC(2)                    BSD System Calls Manual
FSYNC(2)

NAME
     fsync -- synchronize a file's in-core state with that on disk

So, I 100% see the need for this.  And I'd want there to at least be a flag
to disable it.

Thanks,

-Ira