Re: [PATCH -V3] Generic name to handle and open by handle syscalls

[Christoph Hellwig <hch@infradead.org>]

On Sat, Apr 24, 2010 at 11:08:12AM +1000, Neil Brown wrote:
> Maybe map the filesystem part of the handle from UUID (or whatever) to devno
> in userspace, then pass the devno+file-part-of-handle to the kernel to
> perform, the final mapping.

The device number is not a useful kernel interface at all.  Getting a
uuid really is easy in kernelspace as it's available in the superblock
for every reasonable fs.  What's more difficult is finding the right
vfsmount instance of a superblock to use - not just due to read only
but also things like no* per-vfsmount flags.

If you look at libhandle in xfsprogs which wraps the existing xfs handle
ioctls for use in application you'll see such a hash table to map to
open file descriptors per filesystems due to the limits of the ioctl
interface.  Doing the uuid lookup in kernelspace sounds much saner as
we have a list of mounts there anyway.