[PATCH] Enable coredumps to be captured from the appliance (RHBZ#619334).
by Richard W.M. Jones
https://bugzilla.redhat.com/show_bug.cgi?id=619334
This is a slightly unsatisfactory patch which allows coredumps to be
captured when they occur inside the appliance. You can capture
coredumps by doing:
export LIBGUESTFS_COREDUMP=/sysroot/core.%t.%p.%e
or equivalently:
g.set_coredump ("/sysroot/core.%t.%p.%e")
or variations thereof, see the manual page.
When a coredump occurs, a core file will be dropped into the root
directory of the currently mounted guest disk. If it is guestfsd
which crashes, then the appliance will exit, but I have checked that
the coredump is written and synched first. You can then copy this out
of the guest disk using guestfish and debug using gdb:
$ guestfish --ro -a guest_disk -m /dev/vg/lv_root
><fs> ll /
><fs> download /core.xxx.yyy.zzz core
$ gdb daemon/guestfsd core
http://fedoraproject.org/wiki/StackTraces#Obtaining_a_stack_trace_from_a_...
Clearly you need to have a writable guest disk mounted for this to
work, and you have to not care too much about having large core files
written to it.
Ideally we would have liked to use a special capture disk, but it
turns out that the kernel contains code which disallows using a /dev
device (or any non-regular file) for coredumps:
http://lxr.linux.no/linux+v2.6.34.1/fs/exec.c#L1930
We could do it using a coredump-to-pipe, but I think it would be
better to just remove this limitation in the kernel.
Another shortcoming is that a coredump isn't a stack trace, and to get
a stack trace you really need a copy of the daemon around with
debugging enabled. It is possible we could change the RPM packaging
to ship this.
Luckily the suspected bug in Augeas which we are chasing (RHBZ#613967)
happens in aug_init or aug_save when the conditions above are
satisfied and we should be able to get a useful coredump. However
since I am unable to reproduce this bug at all, I cannot help with
this, so it's over to Marek and Matt.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines. Boot with a
live CD or over the network (PXE) and turn machines into Xen guests.
http://et.redhat.com/~rjones/virt-p2v
13 years, 9 months
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