Re: [PATCH] btrfs: extend BTRFS_IOC_SNAP_CREATE_V2 to snapshot by subvolid

[David Sterba <dsterba@suse.cz>]

On Wed, May 14, 2014 at 08:51:30AM -0400, Chris Mason wrote:
> On 03/24/2014 07:58 PM, Jeff Mahoney wrote:
> > The BTRFS_IOC_SNAP_CREATE_V2 ioctl is limited by requiring that a file
> > descriptor be passed in order to create the snapshot. This means that
> > snapshots may only be created of trees that are available in the mounted
> > namespace. We have a need to create snapshots from subvolumes outside
> > of the namespace. This is already possible by mounting the numbered
> > subvolume by ID on a separate mount point, creating the snapshot, and
> > unmounting it. That's a tedious and unnecessary process since the ioctl
> > can be extended so easily.
> > 
> > This patch adds a new BTRFS_SUBVOL_CREATE_SUBVOLID flag that instructs
> > the ioctl to use the fd argument (which is now a union) as a subvolume
> > id instead. The subvolume ID is used to look up the root and instantiate
> > the inode so proper permission checking takes place.
> 
> Can you please make this root only?  The file handle makes sure the
> admin hasn't intentionally hidden the subvol from the user, and this
> bypasses those permission checks.

I'll take care of this and send an updated patch.