Re: [PATCH 07/11] xfs: fully initialise temp leaf in xfs_attr3_leaf_compact

Ben Myers
2013-05-22T21:59:34Z

On Tue, May 21, 2013 at 06:02:06PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> xfs_attr3_leaf_compact() uses a temporary buffer for compacting the
> the entries in a leaf. It copies the the original buffer into the
> temporary buffer, then zeros the original buffer completely. It then
> copies the entries back into the original buffer. However, the
> original buffer has not been correctly initialised, and so the
> movement of the entries goes horribly wrong.
>
> Make sure the zeroed destination buffer is fully initialised, and
> once we've set up the destination incore header appropriately, write
> is back to the buffer before starting to move entries around.
it

>
> While debugging this, the _d/_s prefixes weren't sufficient to
> remind me what buffer was what, so rename then all _src/_dst.

Yeah, it helps.

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_attr_leaf.c | 42 ++++++++++++++++++++++++++----------------
> 1 file changed, 26 insertions(+), 16 deletions(-)
>
> diff --git a/fs/xfs/xfs_attr_leaf.c b/fs/xfs/xfs_attr_leaf.c
> index 79ece72..5b03d15 100644
> --- a/fs/xfs/xfs_attr_leaf.c
> +++ b/fs/xfs/xfs_attr_leaf.c
> @@ -1445,11 +1445,12 @@ xfs_attr3_leaf_add_work(
> STATIC void
> xfs_attr3_leaf_compact(
> struct xfs_da_args *args,
> - struct xfs_attr3_icleaf_hdr *ichdr_d,
> + struct xfs_attr3_icleaf_hdr *ichdr_dst,
> struct xfs_buf *bp)
> {
> - xfs_attr_leafblock_t *leaf_s, *leaf_d;
> - struct xfs_attr3_icleaf_hdr ichdr_s;
> + struct xfs_attr_leafblock *leaf_src;
> + struct xfs_attr_leafblock *leaf_dst;
> + struct xfs_attr3_icleaf_hdr ichdr_src;
> struct xfs_trans *trans = args->trans;
> struct xfs_mount *mp = trans->t_mountp;
> char *tmpbuffer;
> @@ -1457,29 +1458,38 @@ xfs_attr3_leaf_compact(
> trace_xfs_attr_leaf_compact(args);
>
> tmpbuffer = kmem_alloc(XFS_LBSIZE(mp), KM_SLEEP);
> - ASSERT(tmpbuffer != NULL);
> memcpy(tmpbuffer, bp->b_addr, XFS_LBSIZE(mp));
> memset(bp->b_addr, 0, XFS_LBSIZE(mp));
> + leaf_src = (xfs_attr_leafblock_t *)tmpbuffer;
> + leaf_dst = bp->b_addr;
>
> /*
> - * Copy basic information
> + * Copy the on-disk header back into the destination buffer to ensure
> + * all the information in the header that is not part of the incore
> + * header structure is preserved.
> */
> - leaf_s = (xfs_attr_leafblock_t *)tmpbuffer;
> - leaf_d = bp->b_addr;
> - ichdr_s = *ichdr_d; /* struct copy */
> - ichdr_d->firstused = XFS_LBSIZE(mp);
> - ichdr_d->usedbytes = 0;
> - ichdr_d->count = 0;
> - ichdr_d->holes = 0;
> - ichdr_d->freemap[0].base = xfs_attr3_leaf_hdr_size(leaf_s);
> - ichdr_d->freemap[0].size = ichdr_d->firstused - ichdr_d->freemap[0].base;
> + memcpy(bp->b_addr, tmpbuffer, xfs_attr3_leaf_hdr_size(leaf_src));
> +
> + /* Initialise the incore headers */
> + ichdr_src = *ichdr_dst; /* struct copy */
> + ichdr_dst->firstused = XFS_LBSIZE(mp);
> + ichdr_dst->usedbytes = 0;
> + ichdr_dst->count = 0;
> + ichdr_dst->holes = 0;
> + ichdr_dst->freemap[0].base = xfs_attr3_leaf_hdr_size(leaf_src);
> + ichdr_dst->freemap[0].size = ichdr_dst->firstused -
> + ichdr_dst->freemap[0].base;
> +
> +
> + /* write the header back to initialise the underlying buffer */
> + xfs_attr3_leaf_hdr_to_disk(leaf_dst, ichdr_dst);

I can see that the memcpy is necessary but again I'm having a hard time
understanding what field was messed up for moveents.

The patch looks fine in general... I must be blind.