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: <20110123062900.GA7436@noexit>
Date:	Sat, 22 Jan 2011 22:29:01 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	Ted Ts'o <tytso@....edu>
Cc:	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 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.

> 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.

Joel

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