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

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Date:	Sat, 29 Jan 2011 21:40:03 -0800
From:	Manish Katiyar <mkatiyar@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>,
	Joel Becker <jlbec@...lplan.org>, "Ted Ts'o" <tytso@....edu>,
	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 Tue, Jan 25, 2011 at 3:46 AM, Jan Kara <jack@...e.cz> wrote:
> On Mon 24-01-11 18:06:24, Andreas Dilger wrote:
>> >  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...).
>>
>> The reason I don't like the "true" and "false" arguments is that it isn't
>> at all clear which functions have "false" because they cannot fail, and
>> which ones just haven't been updated yet.
>>
>> In that light, I'd prefer to add _two_ new functions, one that indicates
>> the function needs to retry (as it does now), and one that indicates that
>> the caller will handle the error.  That way it is clear which functions
>> have been investigated, and which ones haven't been looked at yet.  Once
>> all of the functions have been changed, we can remove the old
>> jbd2_journal_start() function to catch any patches that have not been
>> updated to the new functions.
>  I agree this would be good for the transition period but once we go
> through all the callsites, I'd prefer to do a rename and have just
> jbd2_journal_start() be the one which does not retry.
>
>> Maybe jbd2_journal_start_canfail() and jbd2_journal_start_retry()?
>  As I said above, I'd like the first one to live only temporarily so
> I don't care about the name. The second one is probably better than
> _nofail() but I still don't feel it describes well what the function
> does...

Hi all,

Have we reached on any conclusion yet on the function name which I can
use to send my updated patch ? My preference from the above list is to
use ext4_journal_start_nofs() as that seems the closest match, but I
would like hear the conclusion from experts.

-- 
Thanks -
Manish
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