linux-ext4 - Re: Is this a bug?

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Message-ID: <BANLkTimEAtVeHge52Sj9F6=mh6jo2KB5hQ@mail.gmail.com>
Date:	Sun, 3 Apr 2011 17:24:02 +0800
From:	Ding Dinghua <dingdinghua85@...il.com>
To:	Amir Goldstein <amir73il@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Is this a bug?

2011/4/3 Amir Goldstein <amir73il@...il.com>:
> On Sat, Apr 2, 2011 at 1:05 AM, Ding Dinghua <dingdinghua85@...il.com> wrote:
>> When truncate files and free blocks, the following codes make me puzzled:
>>
>> void ext4_free_blocks(handle_t *handle, struct inode *inode,
>>                      struct buffer_head *bh, ext4_fsblk_t block,
>>                      unsigned long count, int 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,
>>                                                        block + i);
>>                        if (unlikely(!tbh))
>>                                continue;
>>                        ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
>>                                    inode, tbh, block + i);
>>                }
>>        }
>> }
>>
>> I notice that ext4_forget mainly do two things:
>>    a)  call jbd2_journa_forget to forget the modification of some buffer head
>>    b)  or deal with the revoke issue
>> however, if we are freeing data blocks && ext4_forget get into branch a),
>
> Simple. we don't pass the FORGET flag when freeing data blocks,
> only when freeing metadata blocks, which may have been journalled
> already.
> I am not sure about the journal=data case through.
Thanks for reply. The reason for me to dip into this issue is journal=data mode.
>
>> tbh is not the buffer_head which journal took care of in ext4_write_begin,
>> so i'm puzzled with this.
>>
>> Could anyone explain it to me? Thanks.
>>
>> --
>> Ding Dinghua
>> --
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>



-- 
Ding Dinghua
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