Re: [PATCH] xfs: Forbid FIEMAP on RT devices

[Eric Sandeen <sandeen@sandeen.net>]

On 11/19/19 9:44 AM, Carlos Maiolino wrote:
> By now, FIEMAP users have no way to identify which device contains the
> mapping being reported by the ioctl, so, let's forbid FIEMAP on RT
> devices/files until FIEMAP can properly report the device containing the
> returned mappings.

I'm not sure I agree with this - we don't return any device information with
any mapping, ever. It's always up to the caller to understand what they have
asked to have mapped. I'm not sure why RT files should be singled out, as long
as the mapping is correct.

-Eric

> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
> 
> Hi folks, this change has been previously suggested by Christoph while the
> fibmap->fiemap work was being discussed on the last version [1] of that set.
> And after some thought I do think RT devices shouldn't allow fiemap calls
> either, giving the file blocks will actually be on a different device than that
> displayed on /proc/mounts which can lead to erroneous assumptions.
> 
>  fs/xfs/xfs_iops.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index e532db27d0dc..ec7749cbd3ca 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1138,6 +1138,9 @@ xfs_vn_fiemap(
>  {
>  	int			error;
>  
> +	if (XFS_IS_REALTIME_INODE(XFS_I(inode)))
> +		return -EOPNOTSUPP;
> +
>  	xfs_ilock(XFS_I(inode), XFS_IOLOCK_SHARED);
>  	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) {
>  		fieinfo->fi_flags &= ~FIEMAP_FLAG_XATTR;
>