linux-kernel - Re: [PATCH v2] ext4: fix hole punch failure when depth is greater than 0

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Date:	Fri, 22 Jun 2012 09:49:00 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	sandeen@...hat.com,
	Lukáš Czerner <lczerner@...hat.com>
Cc:	Ted Tso <tytso@....edu>, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org,
	Ashish Sangwan <ashish.sangwan2@...il.com>,
	Ashish Sangwan <ashishsangwan2@...il.com>
Subject: Re: [PATCH v2] ext4: fix hole punch failure when depth is greater
 than 0

Hi. Eric.

This is the patch for punch hole issue.

Thanks.

2012/6/14, Ashish Sangwan <ashishsangwan2@...il.com>:
> The current implementation of hole punch uses the same code path as for
> truncate in which the block removal starts from the end of the file and
> continue backwards removing extents and in the process decreases the
> count of valid entries in the extent header of extent index.
> If all the extents under current extent index are removed than this index
> is also removed and the number of valid entries in the "depth -1"
> extent header is decreased by 1.
>
> Whether to continue removing extents or not is decided by the return value
> of function ext4_ext_more_to_rm() which checks 2 conditions:
> a) if there are no more indexes to process.
> b) if the number of entries are decreased in the header of "depth -1".
>
> In case of hole punch, if the last block to be removed is not part of the
> last extent index than this index will not be deleted, hence the number of
> valid entries in the extent header of "depth - 1" will remain as it is and
> ext4_ext_more_to_rm will return 0 although the required blocks are not
> yet removed.
>
> This patch fixes the above mentioned problem as instead of removing the
> extents from the end of file, it starts removing the blocks from the
> particular extent from which removing blocks is actually required and
> continue backward until done.
>
> Signed-off-by: Ashish Sangwan <ashish.sangwan2@...il.com>
> Signed-off-by: Namjae Jeon <linkinjeon@...il.com>
> ---
>  fs/ext4/extents.c |   43 +++++++++++++++++++++++++++----------------
>  1 files changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 91341ec..27c3a30 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2570,10 +2570,10 @@ static int ext4_ext_remove_space(struct inode
> *inode, ext4_lblk_t start,
>  {
>  	struct super_block *sb = inode->i_sb;
>  	int depth = ext_depth(inode);
> -	struct ext4_ext_path *path;
> +	struct ext4_ext_path *path = NULL;
>  	ext4_fsblk_t partial_cluster = 0;
>  	handle_t *handle;
> -	int i, err;
> +	int i = 0, err;
>
>  	ext_debug("truncate since %u to %u\n", start, end);
>
> @@ -2606,8 +2606,12 @@ again:
>  		}
>  		depth = ext_depth(inode);
>  		ex = path[depth].p_ext;
> -		if (!ex)
> +		if (!ex) {
> +			ext4_ext_drop_refs(path);
> +			kfree(path);
> +			path = NULL;
>  			goto cont;
> +		}
>
>  		ee_block = le32_to_cpu(ex->ee_block);
>
> @@ -2637,8 +2641,6 @@ again:
>  			if (err < 0)
>  				goto out;
>  		}
> -		ext4_ext_drop_refs(path);
> -		kfree(path);
>  	}
>  cont:
>
> @@ -2647,19 +2649,27 @@ cont:
>  	 * after i_size and walking into the tree depth-wise.
>  	 */
>  	depth = ext_depth(inode);
> -	path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 1), GFP_NOFS);
> -	if (path == NULL) {
> -		ext4_journal_stop(handle);
> -		return -ENOMEM;
> -	}
> -	path[0].p_depth = depth;
> -	path[0].p_hdr = ext_inode_hdr(inode);
> +	if (path) {
> +		int k = i = depth;
> +		while (--k >= 0)
> +			path[k].p_block =
> +			le16_to_cpu(path[k].p_hdr->eh_entries)+1;
> +	} else {
> +		path =
> +		kzalloc(sizeof(struct ext4_ext_path) * (depth + 1), GFP_NOFS);
> +		if (path == NULL) {
> +			ext4_journal_stop(handle);
> +			return -ENOMEM;
> +		}
> +		path[0].p_depth = depth;
> +		path[0].p_hdr = ext_inode_hdr(inode);
>
> -	if (ext4_ext_check(inode, path[0].p_hdr, depth)) {
> -		err = -EIO;
> -		goto out;
> +		if (ext4_ext_check(inode, path[0].p_hdr, depth)) {
> +			err = -EIO;
> +			goto out;
> +		}
>  	}
> -	i = err = 0;
> +	err = 0;
>
>  	while (i >= 0 && err == 0) {
>  		if (i == depth) {
> @@ -2773,6 +2783,7 @@ cont:
>  out:
>  	ext4_ext_drop_refs(path);
>  	kfree(path);
> +	path = NULL;
>  	if (err == -EAGAIN)
>  		goto again;
>  	ext4_journal_stop(handle);
> --
> 1.7.2.3
>
>
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