linux-kernel - Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries

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Date:	Mon, 09 Jul 2012 12:09:18 -0500
From:	"Steven J. Magnani" <steve@...idescorp.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted
 inodes/dentries

On Mon, 2012-07-09 at 11:27 -0500, Steven J. Magnani wrote: 
> On Tue, 2012-07-10 at 01:10 +0900, OGAWA Hirofumi wrote: 
> > "Steven J. Magnani" <steve@...idescorp.com> writes:
> > 
> > > On Mon, 2012-07-09 at 22:43 +0900, OGAWA Hirofumi wrote: 
> > >> "Steven J. Magnani" <steve@...idescorp.com> writes:
> > >> 
> > >> >> We need the key, possible key is - if it is only directory, FAT may be
> > >> >> able to use i_start as additional search key.
> > >> >
> > >> > Interesting idea. I think this, and reformulating the FAT NFS file
> > >> > handle to include the parent's i_ino, will greatly simplify (and speed
> > >> > up) the code.
> > >> 
> > >> Does it work even if the inode was rename()'ed?
> > >
> > > AFAICT. I don't see why it wouldn't; on a rename, the inode's i_pos
> > > changes but its i_ino stays the same, right?
> > 
> > If the inode is not on cache anymore, is there the possibility that
> > selects the wrong parent? IIRC, NFS Server can be rebooted at any time
> > while the client using the same file handle.
> 
> True, but it's looking like we can just use the default handle
> constructed by export_encode_fh(), namely (i_ino, i_generation,
> parent->i_ino, parent->i_generation). None of those components should
> change in a server reboot.

I think I misunderstood you when I wrote this. I assumed we were talking
about a restart of nfsd, not the entire machine it was running on. If
there is a danger of mismapping on a reboot isn't that present in the
existing mainline code, i.e. fat_fh_to_dentry()? Ideally, the (i_ino,
i_generation) signature would be different on a reboot, although with
only 2-second granularity in i_generation I suppose that's less likely
than we would prefer. Also I would think that many inodes simply
wouldn't exist in the cache, in which case we would fail the operation
with ESTALE.

------------------------------------------------------------------------
Steven J. Magnani               "I claim this network for MARS!
www.digidescorp.com              Earthling, return my space modulator!"

#include <standard.disclaimer>

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