Re: exception looking up device number f,or hda

[Mike Wray <mike.wray@hp.com>]

Arun Sharma wrote:
> Hi Mike,
> 
> I have the following line in my config file:
> 
> disk = [ 'file:/var/images/min-el3-i386.img,hda,w' ]
> 
> and my host doesn't have a /dev/hda (it has a SATA disk which shows up 
> as /dev/sda).
> 
> But I would like the guest to see a /dev/hda. Sounds reasonable?
> 
> Now, when I try to create this domain, I get:
> 
> [2005-08-05 14:40:53 xend] DEBUG (blkif:24) exception looking up device 
> number for hda: [Errno 2] No such file or directory: '/dev/hda'
> 2005-08-05 14:40:53 xend] DEBUG (blkif:449) Destroying blkif domain=1
> [2005-08-05 14:40:53 xend] DEBUG (blkif:337) Destroying vbd domain=1 id=0
> 
> The code in util/blkif.py that tries to convert name to device number 
> doesn't seem to be new, but I don't know why it started showing up 
> suddenly.
> 
> I worked around by manually creating /dev/hda, but I don't think it's 
> reasonable to expect that host's /dev contains entries for all guest 
> devices.

No, and the blkdev_name_to_number() function should convert names like /dev/hda
without the device existing. This code should be trapping the error:

     try:
         return os.stat(n).st_rdev
     except Exception, ex:
         log.debug("exception looking up device number for %s: %s", name, ex)
         pass

The code then uses regexps to analyse the device name (though you will see
the debug message in the log).


What xen version are you using?

> 
> Also, the effect of having a bad "disk=" line in xmdefconfig (such as 
> pointing to a non-existent file) results in a xend crash. We probably 
> need to add a few checks at the python level so that the user sees a 
> more useful stack trace.

All errors during domain construction are intended to be trapped and returned
to the caller - so maybe something got broken.
Did you see anything in the xend log?
Might be worth causing the error using xend with tracing on (xend trace_start)
and having a look at the trace (/var/log/xend.trace).

Mike