[Libguestfs] [Qemu-devel] debugging qemu-nbd.c
Richard W.M. Jones
rjones at redhat.com
Tue Apr 9 14:33:19 UTC 2013
On Tue, Apr 09, 2013 at 10:18:50AM -0400, Skippy VonDrake wrote:
> Hello,
>
> Apologies upfront if posting to this list is inappropriate.
>
> I have an app that forks a process with calls qemu-nbd with an offset
> into an image.
> The app then uses libguestfs to attach the nbd device.
> But it appears that qemu is failing.
When you say "qemu is failing", do you mean qemu-nbd, or the qemu
subprocess that libguestfs uses? Does it print any error?
> I'm using the latest qemu sources and placed file log statements within
> qemu-nbd.c to pinpoint the problem.
>
> The statement: " if (chdir("/") < 0)"
> appears to be the culprit.
>
> But the subsequent err() call is never reached. If I pull 'chdir' out of
> the 'IF' and assign a local var to its return - execution still seems to
> stop on the 'chdir'. So there is no opportunity to examine its return.
>
> What is the best approach to debugging this section of code?
As a first step I would just add 'fprintf (stderr, ...)' straight into
the qemu-nbd.c file. Or run it under gdb.
Rich.
--
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