Re: [Qemu-devel] [Question] dump memory when host pci device is used by guest

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, Oct 07, 2011 at 02:56:56PM +0200, Jan Kiszka wrote:
> On 2011-10-07 14:25, Wen Congyang wrote:
> > 于 2011/10/7 18:16, Jan Kiszka 写道:
> >> On 2011-10-07 11:46, Wen Congyang wrote:
> >>> Currently, virsh dump uses monitor command migrate to dump guest's memory
> >>> to file, and we can use crash to analyze the file.
> >>>
> >>> Unfortunately, virsh dump can not work if guest uses host pci device. The
> >>> reason is that the device's status is also needed to migrate to remote machine,
> >>> and the host pci device's status is not stored in qemu. So it is unmigratable.
> >>>
> >>> I think we can  we can add a option to qmp command migrate(eg: skip) to allow
> >>> the user to skip the check, and this option should be used only when dumping
> >>> the guest's memory.
> >>
> >> Why not simply attach gdb? That works independently of migration.
> > 
> > If qemu has some problem, we can use gdb to debug it. But if guest os 
> > has problem
> > (eg:kernel panic and kdump does not work), we should dump guest's memory 
> > and use
> > crash to analyze.
> 
> qemu-system-xxx -s (or "gdbserver" via monitor if qemu is already
> running), gdb vmlinux, then "target remote :1234".

That is already possible, but that is not what we need for 'virsh dump'.

The goal of that API is to provide a coredump of the guest, which can
then be analysed off-node/site. While in theory you could attach GDB
to the QEMU process and use GDB commands to then write out a coredump
this isn't really satisfactory because too many large companies have
security/audit compliance rules which forbid installation of developer
tools (compilers, debuggers, etc) on production servers. So we cannot
assume GDB is available.

We need to be able to create a coredump natively from either QEMU or
libvirt, with minimal of external tools.

Daniel
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