linux-kernel - Re: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

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Message-ID: <AANLkTikdCRfgDRLHZ7zr-ZALU8g8LwWc5We-CgbcQ8mF@mail.gmail.com>
Date:	Wed, 21 Jul 2010 10:42:51 -0700
From:	"Patrick J. LoPresti" <lopresti@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

On Wed, Jul 21, 2010 at 10:27 AM, Jan Kara <jack@...e.cz> wrote:
>> Signed-off-by: Patrick LoPresti <lopresti@...il.com>
>>
>> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
>> index bc2ff59..c5a864f 100644
>> --- a/fs/jbd2/journal.c
>> +++ b/fs/jbd2/journal.c
>> @@ -1365,6 +1365,8 @@ int jbd2_journal_check_used_features (journal_t *journal, unsigned long compat,
>>
>>       if (!compat && !ro && !incompat)
>>               return 1;
>> +     if (journal_get_superblock(journal))
>> +             return 0;
>>       if (journal->j_format_version == 1)
>>               return 0;
>
> This looks OK in principle. It would be even nicer to avoid all the checks
> journal_get_superblock() when the superblock is actually loaded so that we
> don't do them each time jbd2_journal_check_used_features is called...

How about this?

         if (!compat && !ro && !incompat)
                return 1;
+        if (journal->j_format_version == 0 &&
journal_get_superblock(journal) != 0)
+               return 0;
        if (journal->j_format_version == 1)
                return 0;

journal_init_common() uses kzalloc() to allocate the journal_t, and
journal_get_superblock() fills it in, so I believe this is a valid
test.

 - Pat
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