Re: [PATCH] quota: handle io errors in dquot_transfer

[Jan Kara <jack@suse.cz>]

On Wed 07-04-10 11:22:00, Dmitry Monakhov wrote:
> Jan Kara <jack@suse.cz> writes:
> 
> > On Mon 05-04-10 13:44:54, Dmitry Monakhov wrote:
> >> Currently quota is able to return real error code to caller.
> >> Now it is possible to fix long standing bug with silent quota
> >> corruption in dquot_transfer.
> >
> >> From 5e529864261c7bffe32a8b3d45d7b51749b4512f Mon Sep 17 00:00:00 2001
> >> From: Dmitry Monakhov <dmonakhov@openvz.org>
> >> Date: Mon, 5 Apr 2010 13:02:18 +0400
> >> Subject: [PATCH] quota: handle io errors in dquot_transfer
> >> 
> >> Currently if one of dquot structures absent due to some io errors
> >> dquot_transfer will ignore corresponding quotatype. Which is very
> >> bad because result in silent quota inconsistency.
> >   But because we were unable to read some quota structure, quota already
> > *is* inconsistent. So it's not like this particular operation would
> > introduce the inconsistency.
> Ohh... This is another type of error which is not handled at all.
> dquot_initialize() may fail to read dquot from a disk and live
> corresponding inode's structures semi-initialized. Before  Christoph's
> cleanup it was almost impossible to solve this issue because init()
> was called from semi_random places. I'm tried to make it one but
> give up this idea due to lack of perspective.
> The good things is what since fs itself is now responsible for dquot
> init it is possible to solve this issue.
  Yes, it shouldn't be too hard to handle errors from dquot_init now.

> >> Sane implementation must return corresponding error to caller.
> >   But sure I agree we should return the fact that we stumbled on quota
> > inconsistency the same way we do it for dquot_alloc_space or
> > dquot_free_space.
> I'll combine init and transfer patches to one patchset.
> The way i see it now:
> 1) dquot_initialize() return eio to caller
> 2) dquot_transfer() return eio to caller
> 3-5) dquot_(alloc/free/claim/...) must check that corresponding
>      ->i_dquot[type] was initialized.
> 5) fs: handle error from dquot_initialize (this one will be huge)
  Yes, this looks like a good plan.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR