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From: Jan Kara on 21 Jul 2010 13:30
> Before we start accessing a huge (> 16 TiB) OCFS2 volume, we need to
> confirm that its journal supports 64-bit offsets. So we need to check
> the journal's feature bits before recovering the journal.
>
> This is not possible with JBD2 at present, because the journal
> superblock (where the feature bits reside) is not loaded from disk until
> the journal is recovered.
>
> This patch loads the journal superblock in
> jbd2_journal_check_used_features() if it has not already been loaded,
> allowing us to check the feature bits before journal recovery.
>
> Signed-off-by: Patrick LoPresti <lopresti(a)gmail.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...

Honza
--
Jan Kara <jack(a)suse.cz>
SuSE CR Labs
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From: Patrick J. LoPresti on 21 Jul 2010 13:50
On Wed, Jul 21, 2010 at 10:27 AM, Jan Kara <jack(a)suse.cz> wrote:
>> Signed-off-by: Patrick LoPresti <lopresti(a)gmail.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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From: Jan Kara on 21 Jul 2010 14:00
> On Wed, Jul 21, 2010 at 10:27 AM, Jan Kara <jack(a)suse.cz> wrote:
> >> Signed-off-by: Patrick LoPresti <lopresti(a)gmail.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.
Yes, this looks OK. Just add a comment before the check like
/* Load journal super block if it isn't loaded yet */

Honza
--
Jan Kara <jack(a)suse.cz>
SuSE CR Labs
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