linux-kernel - Re: [PATCH] vfs: allow FILE_EXTENT_SAME (dedupe_file

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Date:	Mon, 18 Jul 2016 19:41:30 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Adam Borowski <kilobyte@...band.pl>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, Mark Fasheh <mfasheh@...e.de>
Subject: Re: [PATCH] vfs: allow FILE_EXTENT_SAME (dedupe_file_range) on a
 file opened ro

On Mon, Jul 18, 2016 at 12:13:38AM +0200, Adam Borowski wrote:
> Instead of checking the mode of the file descriptor, let's check whether it
> could have been opened rw.  This allows fixing intermittent exec failures
> when deduping a live system: anyone trying to exec a file currently being
> deduped gets ETXTBSY.
> 
> Issuing this ioctl on a ro file was already allowed for root/cap.
> 
> Tested on btrfs and not-yet-merged xfs, as only them implement this ioctl.
> 
> Signed-off-by: Adam Borowski <kilobyte@...band.pl>

Could you please send an xfstest to test this aspect of the dedupe ioctl?

--D

> ---
>  fs/read_write.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 933b53a..df59dc6 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1723,7 +1723,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
>  
>  		if (info->reserved) {
>  			info->status = -EINVAL;
> -		} else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) {
> +		} else if (!(is_admin || !inode_permission(dst, MAY_WRITE))) {
>  			info->status = -EINVAL;
>  		} else if (file->f_path.mnt != dst_file->f_path.mnt) {
>  			info->status = -EXDEV;
> -- 
> 2.8.1
>