Re: [Xen-devel] Xen blktap driver for Ceph RBD : Anybody wants to test ? :p

From: Sylvain Munaut <s.munaut@whatever-company.com>
To: Frederik Thuysbaert <frederik.thuysbaert@gmail.com>
Cc: "James Harper" <james.harper@bendigoit.com.au>,
	"Pasi Kärkkäinen" <pasik@iki.fi>,
	"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [Xen-devel] Xen blktap driver for Ceph RBD : Anybody wants to test ? :p
Date: Wed, 14 Aug 2013 17:03:39 +0200	[thread overview]
Message-ID: <CAF6-1L43p76keEosc+RfP0yzGfFFn==b9FTUKwYSU5xski4pTw@mail.gmail.com> (raw)
In-Reply-To: <520B4339.6090209@gmail.com>

Hi Frederik,

>> A traceback would be great if you can get a core file. And possibly
>> compile tapdisk with debug symbols.
>
> I'm not quite sure what u mean, can u give some more information on how I do
> this? I compiled tapdisk with ./configure CFLAGS=-g, but I'm not sure this
> is what u meant.

Yes, ./configure CFLAGS=-g LDFLAGS=-g  is a good start.

Then when it crashes, if will leave a 'core' time somewhere. (not sure
where, maybe in / or in /tmp)
If it doesn't you may have to enable it. When the process is running,
use this on the tapdisk PID :

http://superuser.com/questions/404239/setting-ulimit-on-a-running-process

Then once you have a core file, you can use gdb along with the tapdisk
executable to generate a meaningful backtrace of where the crash
happenned :

See for ex http://publib.boulder.ibm.com/httpserv/ihsdiag/get_backtrace.html
for how to do it.

> When halting the domU after the errors, I get the following in dom0 syslog:

It's not really unexpected. If tapdisk crashes the IO ring is going to
be left hanging and god knows what weird behaviour will happen ...

Cheers,

    Sylvain