linux-ext4 - Re: [PATCH 1/3] jbd2 : Make jbd2 transaction handle allocation to return errors and handle them gracefully.

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Message-ID: <20110124133143.GA5058@quack.suse.cz>
Date:	Mon, 24 Jan 2011 14:31:43 +0100
From:	Jan Kara <jack@...e.cz>
To:	Joel Becker <jlbec@...lplan.org>
Cc:	Ted Ts'o <tytso@....edu>, Manish Katiyar <mkatiyar@...il.com>,
	Jan Kara <jack@...e.cz>, ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 1/3] jbd2 : Make jbd2 transaction handle allocation to
 return errors and handle them gracefully.

On Sat 22-01-11 22:29:01, Joel Becker wrote:
> On Sun, Jan 23, 2011 at 12:40:49AM -0500, Ted Ts'o wrote:
> > On Sat, Jan 22, 2011 at 07:32:44PM -0800, Manish Katiyar wrote:
> > >  Hi Jan,
> > > 
> > > This is the follow up from https://lkml.org/lkml/2011/1/17/154
> > > Following patches make jbd2 to use GFP_KERNEL for transaction
> > > allocation if the caller can handle the errors. Following is the list
> > > of functions that I updated to pass the new flag. Also below is the
> > > list of functions which still have the old behavior and pass the old
> > > flags (either because they can't deal with errors, or I wasn't too
> > > sure so I did conservatively). Appreciate your feedback. The other
> > > callers of jbd2_journal_start() are from ocfs2, they still pass the
> > > old flag.
> > 
> > Hmm, I wonder if it would be better to use
> > 
> > jbd2_journal_start(...)
> > 
> > and
> > 
> > jbd2_journal_start_nofail(...)
> 
> 	This API is markedly better to read.  Btw, does _nofail() mean no
> possible failures, or just no memory errors?  If it is no failures, I'd
> love to see the function become void.
  jbd2_journal_start can always fail e.g. because the journal is aborted.
So it really just means no memory failures...

> > The tradeoff is that long-term, the code is more readable (as opposed
> > to having people look up what a random "true" or "false" value means).
> > But short-term, while it will make the patch smaller, it also makes
> > the patch harder audit, since we need to look at all of the places
> > where we _haven't_ made a change to make sure those call sites can
> > tolerate an error return.
> 
> 	I think we should start with jbd2_journal_start_can_fail() or
> something like it, and change it back to jbd2_journal_start() in the
> next window.  It's a silly name, but it catches exactly what you are
> worried about.
  Yes, I think this would be nice for auditting (but for that matter
current interface with additional argument isn't bad either and we can
just do the rename to _nofail in the final patch...).

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