Re: [PATCH 2/2 V3] xfs: don't take addresses of packed xfs_rmap_key member

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Jan 29, 2020 at 12:35:21PM -0600, Eric Sandeen wrote:
> gcc now warns about taking an address of a packed structure member.
> 
> This happens here because of how be32_add_cpu() works; just open-code
> the modification instead.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> V2: fix key-> vs rec-> derp derp thinko
> V3: drop local temp variable, add comment
> 
> diff --git a/fs/xfs/libxfs/xfs_rmap_btree.c b/fs/xfs/libxfs/xfs_rmap_btree.c
> index fc78efa52c94..c6f6a7ec6121 100644
> --- a/fs/xfs/libxfs/xfs_rmap_btree.c
> +++ b/fs/xfs/libxfs/xfs_rmap_btree.c
> @@ -187,7 +187,9 @@ xfs_rmapbt_init_high_key_from_rec(
>  	adj = be32_to_cpu(rec->rmap.rm_blockcount) - 1;
>  
>  	key->rmap.rm_startblock = rec->rmap.rm_startblock;
> -	be32_add_cpu(&key->rmap.rm_startblock, adj);
> +	/* do this manually to avoid gcc warning about alignment */
> +	key->rmap.rm_startblock =
> +		cpu_to_be32(be32_to_cpu(key->rmap.rm_startblock) - adj);

<blink>

This should be getting the value from rec->rmap, not key->rmap.

This should be adding adj, not subtracting it, since that's what the
original code did.

And finally, there's no need to set the value twice.

--D

>  	key->rmap.rm_owner = rec->rmap.rm_owner;
>  	key->rmap.rm_offset = rec->rmap.rm_offset;
>  	if (XFS_RMAP_NON_INODE_OWNER(be64_to_cpu(rec->rmap.rm_owner)) ||
> 
>