linux-ext4 - Re: Is this a bug?

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Date:	Sat, 2 Apr 2011 09:32:49 -0700
From:	Amir Goldstein <amir73il@...il.com>
To:	Ding Dinghua <dingdinghua85@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Is this a bug?

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.

> 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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