Re: [PATCH v2 1/5] fat: allocate persistent inode numbers

From: J. Bruce Fields
Date: Wed Sep 12 2012 - 13:45:54 EST


On Thu, Sep 13, 2012 at 02:38:11AM +0900, OGAWA Hirofumi wrote:
> "J. Bruce Fields" <bfields@xxxxxxxxxxxx> writes:
>
> >> On other view (as server side solution), we are thinking there is
> >> possible to make the stable filehandle on FAT if we disabled some
> >> operations (e.g. rename(), unlink()) which change inode location in FAT.
> >>
> >> Yes, it would be stable, but supporting limited operations.
> >>
> >> This is server side solution, and we comparing it with client solution.
> >
> > Is that useful to anyone?
>
> Good question. I'm not sure though, Namjae is asking. And I was asked
> about stable read-only export in past.
>
> >> >> LOOKUP return NFS FH->[inode number changed at NFS Server] ->
> >> >> But we still use old NFS FH returned from LOOKUP for any file
> >> >> operation(write,read,etc..)
> >> >> -> ESTALE will be returned.
> >>
> >> Yes. And I'm expecting as client side solution,
> >>
> >> -> ESTALE will be returned -> discard old FH -> restart from LOOKUP ->
> >> make cached inode -> use returned new FH.
> >>
> >> Yeah, I know this is unstable (there is no perfect solution for now),
> >
> > You may end up with a totally different file, of course:
> >
> > client: server:
> >
> > open "/foo/bar"
> > rename "/foo/baz"->"/foo/bar"
> > write to file
> >
> > And now we're writing to the file that was originally named /foo/baz
> > when we should have gotten ESTALE.
>
> I see. So, client can't solve the ESTALE if inode cache was evicted,
> right? (without application changes)

I don't see how.


As another server-side workaround: maybe they could try tuning the inode
caching to make eviction less likely?

Grepping around... Documentation/sysctl/vm.txt mentions a
vfs_cache_pressure parameter.

--b.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/