Re: [PATCH 1/2] xfs: disable xfs_ioc_space for always COW inodes

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

On Fri, Oct 11, 2019 at 03:03:15PM +0200, Christoph Hellwig wrote:
> If we always have to write out of place preallocating blocks is
> pointless.  We already check for this in the normal falloc path, but
> the check was missig in the legacy ALLOCSP path.

This function handles other things than preallocation, such as
XFS_IOC_ZERO_RANGE and XFS_IOC_UNRESVSP, which call xfs_zero_file_space
and xfs_free_file_space, respectively.  We don't prohibit fallocate
from calling those two functions on an always_cow inode, so why do that
here?

--D

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_ioctl.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index d58f0d6a699e..abf7a102376f 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -33,6 +33,7 @@
>  #include "xfs_sb.h"
>  #include "xfs_ag.h"
>  #include "xfs_health.h"
> +#include "xfs_reflink.h"
>  
>  #include <linux/mount.h>
>  #include <linux/namei.h>
> @@ -607,6 +608,9 @@ xfs_ioc_space(
>  	if (!S_ISREG(inode->i_mode))
>  		return -EINVAL;
>  
> +	if (xfs_is_always_cow_inode(ip))
> +		return -EOPNOTSUPP;
> +
>  	if (filp->f_flags & O_DSYNC)
>  		flags |= XFS_PREALLOC_SYNC;
>  	if (filp->f_mode & FMODE_NOCMTIME)
> -- 
> 2.20.1
>