Re: [PATCH 2/4] Btrfs: use cross mount point check for cloning and deduplication

[David Sterba <dsterba@suse.cz>]

On Wed, Dec 12, 2018 at 06:05:57PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> There is no reason why this check was performed for clone operations but
> not for deduplication operations, after all deduplication is a special
> case of cloning. So make the check happen for deduplication as well.
> 
> This check used to be done and got removed by accident in commit
> 2b3909f8a7fe9 ("btrfs: use new dedupe data function pointer").
> 
> Fixes: 2b3909f8a7fe9 ("btrfs: use new dedupe data function pointer").
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  fs/btrfs/ioctl.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 1e90d10b5638..ffe940ceb80a 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3912,12 +3912,12 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
>  
>  		if (btrfs_root_readonly(root_out))
>  			return -EROFS;
> -
> -		if (file_in->f_path.mnt != file_out->f_path.mnt ||
> -		    inode_in->i_sb != inode_out->i_sb)
> -			return -EXDEV;
>  	}
>  
> +	if (file_in->f_path.mnt != file_out->f_path.mnt ||
> +	    inode_in->i_sb != inode_out->i_sb)
> +		return -EXDEV;

I'm checking if this is or is not a change in the dedupe behaviour
regarding dedupe on different mont points.

I can't see the f_path.mnt check anywhere in the VFS calls so after that
patch deduping stops to work in some cases.