On Sat, Apr 2, 2011 at 1:05 AM, Ding Dinghua <dingdinghua85@xxxxxxxxx> 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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