[PATCH] ext4: fix callers of ext4_handle_release_buffer() API

[PATCH] ext4: fix callers of ext4_handle_release_buffer() API

[Amir Goldstein]

ext4_handle_release_buffer() is an API, which is not being used properly.
This is not so bad considering that it calls jbd2_journal_release_buffer(),
which does nothing, but the snapshots implementation of this API does
something.

ext4_jbd2.h defines 2 identical wrapper functions:
ext4_journal_release_buffer() and ext4_handle_release_buffer().
The former has no callers, so it was removed.

There are 2 users of the API:
ext4_new_inode() calls ext4_handle_release_buffer() and
ext4_xattr_block_set() calls jbd2_journal_release_buffer() directly.
The latter was chagned to call the wrapper API.

Signed-off-by: Amir Goldstein <amir73il@users.sf.net>
---
 fs/ext4/ext4_jbd2.h |    7 -------
 fs/ext4/xattr.c     |    2 +-
 2 files changed, 1 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index d8b992e..e25e99b 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -202,13 +202,6 @@ static inline int
ext4_handle_has_enough_credits(handle_t *handle, int needed)
 	return 1;
 }

-static inline void ext4_journal_release_buffer(handle_t *handle,
-						struct buffer_head *bh)
-{
-	if (ext4_handle_valid(handle))
-		jbd2_journal_release_buffer(handle, bh);
-}

Re: [PATCH] ext4: fix callers of ext4_handle_release_buffer() API

[Ted Ts'o]

On Tue, Mar 01, 2011 at 03:30:24PM +0200, Amir Goldstein wrote:
> ext4_handle_release_buffer() is an API, which is not being used properly.
> This is not so bad considering that it calls jbd2_journal_release_buffer(),
> which does nothing, but the snapshots implementation of this API does
> something.
> 
> ext4_jbd2.h defines 2 identical wrapper functions:
> ext4_journal_release_buffer() and ext4_handle_release_buffer().
> The former has no callers, so it was removed.

Note that there are some commented-out calls to
ext4_journal_release_buffer() in resize.c; they're probably commented
out because at least today, jbd2_journal_release_buffer() is indeed a
no-op.

I'll update resize.c to use the preferred call.  Speaking of which,
how does on-line resize work in the face of the snapshot feature?  Is
that something that is or isn't supported?

Note also that there may be places where a buffer has
get_write_access() called on it, only for it to be never modified.
resize.c is an example of that.

> There are 2 users of the API:
> ext4_new_inode() calls ext4_handle_release_buffer() and
> ext4_xattr_block_set() calls jbd2_journal_release_buffer() directly.
> The latter was chagned to call the wrapper API.
> 
> Signed-off-by: Amir Goldstein <amir73il@users.sf.net>

I'll apply this patch the changes.

						- Ted
		

Re: [PATCH] ext4: fix callers of ext4_handle_release_buffer() API

[Amir Goldstein]

On Mon, Mar 21, 2011 at 4:43 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Tue, Mar 01, 2011 at 03:30:24PM +0200, Amir Goldstein wrote:
>> ext4_handle_release_buffer() is an API, which is not being used properly.
>> This is not so bad considering that it calls jbd2_journal_release_buffer(),
>> which does nothing, but the snapshots implementation of this API does
>> something.
>>
>> ext4_jbd2.h defines 2 identical wrapper functions:
>> ext4_journal_release_buffer() and ext4_handle_release_buffer().
>> The former has no callers, so it was removed.
>
> Note that there are some commented-out calls to
> ext4_journal_release_buffer() in resize.c; they're probably commented
> out because at least today, jbd2_journal_release_buffer() is indeed a
> no-op.
>
> I'll update resize.c to use the preferred call.  Speaking of which,
> how does on-line resize work in the face of the snapshot feature?  Is
> that something that is or isn't supported?

Yes, it is supported. (offline resize isn't supported).
The old snapshots sizes (i_disksize) represent the file system
size at the time of the snapshot.

>
> Note also that there may be places where a buffer has
> get_write_access() called on it, only for it to be never modified.
> resize.c is an example of that.

Those places can be a problem (since COW does happen and use
up transaction credits) and calling buffer_release can help
(it tries to extend the transaction), but specifically, resize.c is not
a problem, since blocks outside the active snapshot's i_disksize
are never COWed.

>
>> There are 2 users of the API:
>> ext4_new_inode() calls ext4_handle_release_buffer() and
>> ext4_xattr_block_set() calls jbd2_journal_release_buffer() directly.
>> The latter was chagned to call the wrapper API.
>>
>> Signed-off-by: Amir Goldstein <amir73il@users.sf.net>
>
> I'll apply this patch the changes.
>
>                                                - Ted
>
>
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