ignoring xenbus state transitions during shutdown

[David Lively <dlively@virtualiron.com>]

Hi Folks -
  In otherend_changed() in xenbus_probe.c, the driver is trying to 
ignore xenbus state transitions while the guest OS is shutting down.  It 
currently does this by looking for system_state > SYSTEM_RUNNING.  But 
system_state is not exported by some kernels that use it (e.g., SLES9 
running in a HVM guest), so the xenbus driver can't be loaded. 
  The comments indicate we're trying to avoid a failure that occurs when 
there is no rootfs.  I haven't yet seen this failure (after removing the 
code my shutdowns with PV drivers seemed to work fine, though I haven't 
pushed hard yet), but I suspect I shouldn't be ignoring it.  I was 
thinking it might be better to test for the screw condition (no rootfs) 
directly, perhaps something like try vfs_stat("/", &stat) and see 
whether it fails (??).  (These state transitions are relatively rare, so 
it doesn't need to be a particularly cheap test.)
  Any other suggestions?  I've heard of the old global 'system_running', 
but that's not used SLES9, at least.

Thanks in Advance,
Dave