> Watches work in kernel space in domU (the frontends to the split device
> drivers use them), but they don't work in userspace there.  The problem is
> that there is no support in xenbus for blocking a userspace process waiting
> for a watch to fire.
> 
> In domain 0, Xend uses a unix domain socket straight to Xenstored: it can
> block on that, as it's not going through the Xenbus kernel-level driver.

Huh?  Sleeping on the unix socket and sleeping on the /proc/xen/xenbus
filehandle should work equally well, shouldn't it?  Well, right now
there is no poll support, so you can't stuff the filehandle into
select()-loop.  But that is trivially fixable, patch below
(compile-tested only though).  Or did I miss the real problem?

cheers,

  Gerd

-- 
Gerd 'just married' Hoffmann <kraxel@suse.de>
I'm the hacker formerly known as Gerd Knorr.
http://www.suse.de/~kraxel/just-married.jpeg