2010-07-11 17:03:19

by Patrick J. LoPresti

Subject: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

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 <[email protected]>

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;

2010-07-21 17:27:21

by Jan Kara

Subject: Re: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

> 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 <[email protected]>
>
> 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 <[email protected]>
SuSE CR Labs

2010-07-21 17:42:53

by Patrick J. LoPresti

Subject: Re: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

On Wed, Jul 21, 2010 at 10:27 AM, Jan Kara <[email protected]> wrote:
>> Signed-off-by: Patrick LoPresti <[email protected]>
>>
>> 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

2010-07-21 17:50:24

by Jan Kara

Subject: Re: [PATCH 1/2] JBD2: Allow feature checks before journal recovery

> On Wed, Jul 21, 2010 at 10:27 AM, Jan Kara <[email protected]> wrote:
> >> Signed-off-by: Patrick LoPresti <[email protected]>
> >>
> >> 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 <[email protected]>
SuSE CR Labs