lkml.org 
[lkml]   [2010]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] VFS: fix recent breakage of FS_REVAL_DOT
On Mon, 24 May 2010 12:59:03 +0100
Al Viro <viro@ZenIV.linux.org.uk> wrote:

> On Mon, May 24, 2010 at 04:57:56PM +1000, Neil Brown wrote:
> >
> > Commit 1f36f774b22a0ceb7dd33eca626746c81a97b6a5 broke FS_REVAL_DOT semantics.
> >
> > In particular, before this patch, the command
> > ls -l
> > in an NFS mounted directory would always check if the directory on the server
> > had changed and if so would flush and refill the pagecache for the dir.
> > After this patch, the same "ls -l" will repeatedly return stale date until
> > the cached attributes for the directory time out.
> >
> > The following patch fixes this by ensuring the d_revalidate is called by
> > do_last when "." is being looked-up.
> > link_path_walk has already called d_revalidate, but in that case LOOKUP_OPEN
> > is not set so nfs_lookup_verify_inode chooses not to do any validation.
> >
> > The following patch restores the original behaviour.
> >
> > Cc: stable@kernel.org
> > Signed-off-by: NeilBrown <neilb@suse.de>
>
> Applied, but I really don't like the way you do it; note that e.g. foo/bar/.
> gets that revalidation as well, for no good reason. If anything, shouldn't
> we handle that thing in the _beginning_ of pathname resolution, not in
> the end? For now it'd do, and it's a genuine regression, but...
>

Thanks.

I think I see what you mean by "at the beginning" - the problem path is
simply ".", and both the start and end of that are "." so we can handle at
either end... But I don't think there is any other special handling of the
'start' of a path, so I imagine it would be a fairly ugly special case.

We could avoid the extra GETATTR in "foo/bar/." by allowing NFS to keep some
state in the namei_data to record that it has valid attributes for a given
dentry so if it sees the same dentry again it doesn't need to revalidate.

I must confess though that I don't feel I understand VFS name lookup properly
any more. Since intents were added it seems to have become much more obscure
and complex. I cannot help thinking that there must be a better way:
distinguish between the various cases at a higher level so we don't need as
many flags being passed around and interpreted by widely separate pieces of
code. I don't have a concrete proposal but I would certainly be interested
to work on one if there were any hope of real change.
Thoughts?

Thanks,
NeilBrown

> BTW, here's a question for nfs client folks: is it true that for any two
> pathnames on _client_ resolving to pairs (mnt1, dentry) and (mnt2, dentry)
> resp., nfs_devname(mnt1, dentry, ...) and nfs_devname(mnt2, dentry, ...)
> should yield the strings that do not differ past the ':' (i.e. that the
> only possible difference is going to be in spelling the server name)?



\
 
 \ /
  Last update: 2010-05-25 03:17    [W:0.062 / U:5.664 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site