[PATCH 0/2] hoist btrfs' label set/get ioctls to vfs, and document

I'm planning to add online label set/get support to xfs, and to do so
I plan to re-use the existing btrfs ioctls, BTRFS_IOC_[SG]ET_FSLABEL

We're still working out minor details on the xfs side, but I'd like to
start the conversation regarding the new more generic interface ASAP,
so here goes - patches to move the ioctls to the vfs and document them.

(Other filesystems may wish to use this interface in the future as well)

Thanks,
-Eric