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

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Message-ID: <1341865572.31078.2.camel@iscandar.digidescorp.com>
Date:	Mon, 09 Jul 2012 15:26:12 -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 Tue, 2012-07-10 at 04:10 +0900, OGAWA Hirofumi wrote: 
> "Steven J. Magnani" <steve@...idescorp.com> writes:
> 
> >> > >> > 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.
> 
> Ah, i_ino. I was talking about i_pos. Well, so, what happens if the
> child was renamed to other parent on NFS server machine (not via nfs
> client)? The file handle would be including the old i_ino, and the old
> i_ino on file handle is still vaild as old parent. So, it returns the
> wrong parent?

Yes, but I believe exportfs_decode_fh() handles that case:

  /*
   * Now that we've got both a well-connected parent and a
   * dentry for the inode we're after, make sure that our
   * inode is actually connected to the parent.
   */


Really, the FAT NFS code will pretty much parallel that of ext2.
------------------------------------------------------------------------
Steven J. Magnani               "I claim this network for MARS!
www.digidescorp.com              Earthling, return my space modulator!"

#include <standard.disclaimer>



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