Re: [PATCH 06/11] xfs: fully initialise temp leaf in xfs_attr3_leaf_unbalance

Ben Myers
2013-05-22T20:51:02Z

On Tue, May 21, 2013 at 06:02:05PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> xfs_attr3_leaf_unbalance() uses a temporary buffer for recombining
> the entries in two leaves when the destination leaf requires
> compaction. The temporary buffer ends up being copied back over the
> original destination buffer, so the header in the temporary buffer
> needs to contain all the information that is in the destination
> buffer.
>
> To make sure the temporary buffer is fully initialised, once we've
> set up the temporary incore header appropriately, write is back to
> the temporary buffer before starting to move entries around.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
>
> ---
> fs/xfs/xfs_attr_leaf.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/xfs_attr_leaf.c b/fs/xfs/xfs_attr_leaf.c
> index 0bce1b3..79ece72 100644
> --- a/fs/xfs/xfs_attr_leaf.c
> +++ b/fs/xfs/xfs_attr_leaf.c
> @@ -2181,14 +2181,24 @@ xfs_attr3_leaf_unbalance(
> struct xfs_attr_leafblock *tmp_leaf;
> struct xfs_attr3_icleaf_hdr tmphdr;
>
> - tmp_leaf = kmem_alloc(state->blocksize, KM_SLEEP);
> - memset(tmp_leaf, 0, state->blocksize);
> - memset(&tmphdr, 0, sizeof(tmphdr));
> + tmp_leaf = kmem_zalloc(state->blocksize, KM_SLEEP);
> +
> + /*
> + * Copy the header into the temp leaf so that all the stuff
> + * not in the incore header is present and gets copied back in
> + * once we've moved all the entries.
> + */
> + memcpy(tmp_leaf, save_leaf, xfs_attr3_leaf_hdr_size(save_leaf));
>
> + memset(&tmphdr, 0, sizeof(tmphdr));
> tmphdr.magic = savehdr.magic;
> tmphdr.forw = savehdr.forw;
> tmphdr.back = savehdr.back;
> tmphdr.firstused = state->blocksize;
> +
> + /* write the header to the temp buffer to initialise it */
> + xfs_attr3_leaf_hdr_to_disk(tmp_leaf, &tmphdr);
> +

Hrm. It seemed like the memset 0 for the incore temp header should have been
enough for the purposes of moveents. Why did you have to add this additional
hdr_to_disk?

-Ben