[Libguestfs] launch failure of appliance with nbd drive

[Richard W.M. Jones]

On Thu, Apr 04, 2013 at 10:48:54AM -0400, Skippy VonDrake wrote:
> I'm using qemu-nbd to setup the device with an offset
> into the image. Using libguestfs version 1.21.22
>
> Code for adding the drive:
>   char *server[] = { "localhost:3000", NULL };
>   if (guestfs_add_drive_opts (g, "" /* export name - see below */,
>      GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
>      GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "nbd",
>      GUESTFS_ADD_DRIVE_OPTS_SERVER, server,
>      -1)

Glad someone is trying it!

> Here is some of the stdout. A mix of libguestfs and
> qemu-nbd messages.
> 
> 	\ libguestfs: child_cleanup: 0xbc4ba0: child process died
> 	libguestfs: sending SIGTERM to process 23981
[...]

Are you sure that qemu itself isn't crashing?

I've only tested this on qemu 1.4.0.

> 	/build/buildd/qemu-kvm-1.2.0+noroms/nbd.c:nbd_trip():L836: requested
> operation past EOF--bad client?
> 	/build/buildd/qemu-kvm-1.2.0+noroms/nbd.c:nbd_receive_request():L516:
> read failed
> 
> So I peppered some fprintfs in launch-appliance.c to try and narrow
> down the problem. Just below the comment:
>    * does not mean the daemon is up until we read the
>    * GUESTFS_LAUNCH_FLAG below.  Failures in qemu startup can still
> Is the call where it fails:
>   r = guestfs___recv_from_daemon (g, &size, &buf);
> r is -1 and size is zero

This would indicate that qemu is exiting or crashing early.

> How can I debug this problem further?
> I suppose I could build/debug the qemu side of this process...

If qemu is crashing then enabling core dumps might be a good idea, ie:

  ulimit -c unlimited

But even if you get a coredump, no one in qemu-land will care since
1.2.0 is an old version.  You could try a locally compiled copy of
qemu from git:

  http://libguestfs.org/guestfs.3.html#qemu-wrappers

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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