linux-ext4 - Re: [PATCH 2/5] ext4: let ext4 journal deletion of data blocks

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Date:	Fri, 30 Dec 2011 22:59:48 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/5] ext4: let ext4 journal deletion of data blocks

Hi Ted,

The 2nd and 3rd patch aim to let ext4_free_blocks work with journal
mode.  Consider that journal mode of a file is changed from ordered
mode to journal mode and several data blocks are deleted, then bh
passed in is NULL and sb_find_get_block returns NULL, but we need
ext4_forget to handle the data blocks to record them in revoke table.

I am not sure status of ext4 with journal mode, according code here it
seems that ext4 with journal mode does not work.

Yongqiang.

On Thu, Dec 29, 2011 at 1:23 AM, Ted Ts'o <tytso@....edu> wrote:
> On Tue, Nov 15, 2011 at 04:07:51PM +0800, Yongqiang Yang wrote:
>> This patch lets ext4 journal deletion of data blocks. Besides this,
>> a unnecessary variable is removed.
>>
>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
>
> I don't see the point of this patch; it seems to be a code
> simplification, but in fact it introduces a bug which has to get fixed
> in patch 3/5 of this series.
>
> The code here is a little arcane, because if bh is non-null, then
> count must be 1.  This is expressed in the BUG_ON found in the
> function:
>
>>               BUG_ON(bh && (count > 1));
>
> The reason for this bit of complexity is to avoid needing to call
> sb_find_get_block() in those places where we have the buffer_head
> already.  This happens in exactly two locations: in an error cleanup
> path in fs/ext4/indirect.c, and when releasing an xattr block in
> ext4_xattr_release_block().
>
> The better way of dealing with this is to drop the bh argument from
> ext4_free_blocks() completely, and explicitly call ext4_forget() on
> the bh in those two functions.
>
> This will require changing all of the call sites of
> ext4_free_blocks(), but it simplifies the function signature as well
> as simplifying the code.
>
>                                        - Ted
>
>>  fs/ext4/mballoc.c |    7 ++-----
>>  1 files changed, 2 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index e2d8be8..2529efc 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -4562,19 +4562,16 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
>>       trace_ext4_free_blocks(inode, block, count, flags);
>>
>>       if (flags & EXT4_FREE_BLOCKS_FORGET) {
>> -             struct buffer_head *tbh = bh;
>>               int i;
>>
>>               BUG_ON(bh && (count > 1));
>>
>>               for (i = 0; i < count; i++) {
>>                       if (!bh)
>> -                             tbh = sb_find_get_block(inode->i_sb,
>> +                             bh = sb_find_get_block(inode->i_sb,
>>                                                       block + i);
>> -                     if (unlikely(!tbh))
>> -                             continue;
>>                       ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
>> -                                 inode, tbh, block + i);
>> +                                 inode, bh, block + i);
>>               }
>>       }
>>
>> --
>> 1.7.5.1
>>



-- 
Best Wishes
Yongqiang Yang
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