[PATCH] xfs: fail ->bmap for reflink inodes

[Avi Kivity]

On 05/26/2016 04:02 PM, Christoph Hellwig wrote:
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>   fs/xfs/xfs_aops.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index a955552..d053a9e 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1829,6 +1829,17 @@ xfs_vm_bmap(
>   
>   	trace_xfs_vm_bmap(XFS_I(inode));
>   	xfs_ilock(ip, XFS_IOLOCK_SHARED);
> +
> +	/*
> +	 * The swap code (ab-)uses ->bmap to get a block mapping and then
> +	 * bypasseѕ the file system for actual I/O.  We really can't allow
> +	 * that on reflinks inodes, so we have to skip out here.  And yes,
> +	 * 0 is the magic code for a bmap error..
> +	 */
> +	if (xfs_is_reflink_inode(ip)) {
> +		xfs_iunlock(ip, XFS_IOLOCK_SHARED);
> +		return 0;
> +	}
>   	filemap_write_and_wait(mapping);
>   	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
>   	return generic_block_bmap(mapping, block, xfs_get_blocks);

Don't you also have to prevent a swapfile from being reflinked after 
it's bmapped?  Or is that already taken care of?