Re: [PATCH V14 06/16] xfs: Check for extent overflow when renaming dir entries

["Darrick J. Wong" <djwong@kernel.org>]

On Sun, Jan 10, 2021 at 09:37:10PM +0530, Chandan Babu R wrote:
> A rename operation is essentially a directory entry remove operation
> from the perspective of parent directory (i.e. src_dp) of rename's
> source. Hence the only place where we check for extent count overflow
> for src_dp is in xfs_bmap_del_extent_real(). xfs_bmap_del_extent_real()
> returns -ENOSPC when it detects a possible extent count overflow and in
> response, the higher layers of directory handling code do the following:
> 1. Data/Free blocks: XFS lets these blocks linger until a future remove
>    operation removes them.
> 2. Dabtree blocks: XFS swaps the blocks with the last block in the Leaf
>    space and unmaps the last block.
> 
> For target_dp, there are two cases depending on whether the destination
> directory entry exists or not.
> 
> When destination directory entry does not exist (i.e. target_ip ==
> NULL), extent count overflow check is performed only when transaction
> has a non-zero sized space reservation associated with it.  With a
> zero-sized space reservation, XFS allows a rename operation to continue
> only when the directory has sufficient free space in its data/leaf/free
> space blocks to hold the new entry.
> 
> When destination directory entry exists (i.e. target_ip != NULL), all
> we need to do is change the inode number associated with the already
> existing entry. Hence there is no need to perform an extent count
> overflow check.
> 
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>

Looks good,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_bmap.c |  3 +++
>  fs/xfs/xfs_inode.c       | 44 +++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 6c8f17a0e247..8ebe5f13279c 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5160,6 +5160,9 @@ xfs_bmap_del_extent_real(
>  		 * until a future remove operation. Dabtree blocks would be
>  		 * swapped with the last block in the leaf space and then the
>  		 * new last block will be unmapped.
> +		 *
> +		 * The above logic also applies to the source directory entry of
> +		 * a rename operation.
>  		 */
>  		error = xfs_iext_count_may_overflow(ip, whichfork, 1);
>  		if (error) {
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 4cc787cc4eee..f0a6d528cbc4 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -3116,6 +3116,35 @@ xfs_rename(
>  	/*
>  	 * Check for expected errors before we dirty the transaction
>  	 * so we can return an error without a transaction abort.
> +	 *
> +	 * Extent count overflow check:
> +	 *
> +	 * From the perspective of src_dp, a rename operation is essentially a
> +	 * directory entry remove operation. Hence the only place where we check
> +	 * for extent count overflow for src_dp is in
> +	 * xfs_bmap_del_extent_real(). xfs_bmap_del_extent_real() returns
> +	 * -ENOSPC when it detects a possible extent count overflow and in
> +	 * response, the higher layers of directory handling code do the
> +	 * following:
> +	 * 1. Data/Free blocks: XFS lets these blocks linger until a
> +	 *    future remove operation removes them.
> +	 * 2. Dabtree blocks: XFS swaps the blocks with the last block in the
> +	 *    Leaf space and unmaps the last block.
> +	 *
> +	 * For target_dp, there are two cases depending on whether the
> +	 * destination directory entry exists or not.
> +	 *
> +	 * When destination directory entry does not exist (i.e. target_ip ==
> +	 * NULL), extent count overflow check is performed only when transaction
> +	 * has a non-zero sized space reservation associated with it.  With a
> +	 * zero-sized space reservation, XFS allows a rename operation to
> +	 * continue only when the directory has sufficient free space in its
> +	 * data/leaf/free space blocks to hold the new entry.
> +	 *
> +	 * When destination directory entry exists (i.e. target_ip != NULL), all
> +	 * we need to do is change the inode number associated with the already
> +	 * existing entry. Hence there is no need to perform an extent count
> +	 * overflow check.
>  	 */
>  	if (target_ip == NULL) {
>  		/*
> @@ -3126,6 +3155,12 @@ xfs_rename(
>  			error = xfs_dir_canenter(tp, target_dp, target_name);
>  			if (error)
>  				goto out_trans_cancel;
> +		} else {
> +			error = xfs_iext_count_may_overflow(target_dp,
> +					XFS_DATA_FORK,
> +					XFS_IEXT_DIR_MANIP_CNT(mp));
> +			if (error)
> +				goto out_trans_cancel;
>  		}
>  	} else {
>  		/*
> @@ -3283,9 +3318,16 @@ xfs_rename(
>  	if (wip) {
>  		error = xfs_dir_replace(tp, src_dp, src_name, wip->i_ino,
>  					spaceres);
> -	} else
> +	} else {
> +		/*
> +		 * NOTE: We don't need to check for extent count overflow here
> +		 * because the dir remove name code will leave the dir block in
> +		 * place if the extent count would overflow.
> +		 */
>  		error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
>  					   spaceres);
> +	}
> +
>  	if (error)
>  		goto out_trans_cancel;
>  
> -- 
> 2.29.2
>