Re: [PATCH v3] xfs: Add check for unsupported xflags

[Dave Chinner <david@fromorbit.com>]

On Thu, Sep 03, 2020 at 11:57:13AM +0800, Xiao Yang wrote:
> Current ioctl(FSSETXATTR) ignores unsupported xflags silently
> so it is not clear for user to know unsupported xflags.
> For example, use ioctl(FSSETXATTR) to set dax flag on kernel
> v4.4 which doesn't support dax flag:
> --------------------------------
> # xfs_io -f -c "chattr +x" testfile;echo $?
> 0
> # xfs_io -c "lsattr" testfile
> ----------------X testfile
> --------------------------------
> 
> Add check to return -EOPNOTSUPP as ext4/f2fs/btrfs does.
> 
> Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_ioctl.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 6f22a66777cd..59f9a86f29f7 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1425,6 +1425,14 @@ xfs_ioctl_setattr_check_projid(
>  	return 0;
>  }
>  
> +#define XFS_SUPPORTED_FS_XFLAGS \
> +	(FS_XFLAG_REALTIME | FS_XFLAG_PREALLOC | FS_XFLAG_IMMUTABLE | \
> +	 FS_XFLAG_APPEND | FS_XFLAG_SYNC | FS_XFLAG_NOATIME | FS_XFLAG_NODUMP | \
> +	 FS_XFLAG_RTINHERIT | FS_XFLAG_PROJINHERIT | FS_XFLAG_NOSYMLINKS | \
> +	 FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT | FS_XFLAG_NODEFRAG | \
> +	 FS_XFLAG_FILESTREAM | FS_XFLAG_DAX | FS_XFLAG_COWEXTSIZE | \
> +	 FS_XFLAG_HASATTR)
> +
>  STATIC int
>  xfs_ioctl_setattr(
>  	xfs_inode_t		*ip,
> @@ -1439,6 +1447,10 @@ xfs_ioctl_setattr(
>  
>  	trace_xfs_ioctl_setattr(ip);
>  
> +	/* Check if fsx_xflags has unsupported xflags */
> +	if (fa->fsx_xflags & ~XFS_SUPPORTED_FS_XFLAGS)
> +                return -EOPNOTSUPP;

I don't think we can do this as it may break existing applications
that have been working on XFS for many, many years that don't
correctly initialise fsx_xflags....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com