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

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

On Mon, Oct 10, 2011 at 11:34:44AM +0200, Jan Kiszka wrote:
> On 2011-10-10 11:10, Daniel P. Berrange wrote:
> > On Mon, Oct 10, 2011 at 10:08:26AM +0100, Daniel P. Berrange wrote:
> >> On Mon, Oct 10, 2011 at 10:21:02AM +0800, Wen Congyang wrote:
> >>> At 10/09/2011 06:23 PM, Richard W.M. Jones Write:
> >>>> On Sun, Oct 09, 2011 at 10:49:57AM +0200, Jan Kiszka wrote:
> >>>>> As explained in the other replies: It is way more future-proof to use an
> >>>>> interface for this which was designed for it (remote gdb) instead of
> >>>>> artificially relaxing reasonable constraints of the migration mechanism
> >>>>> plus having to follow that format with the post-processing tool.
> >>>>
> >>>> Any interface that isn't "get this information off my production
> >>>> server *now*" so that I can get the server restarted, and send it to
> >>>> an expert to analyse -- is a poor interface, whether it was designed
> >>>> like that or not.  Perhaps we don't have the right interface at all,
> >>>> but remote gdb is not it.
> >>>
> >>> What about the following idea?
> >>>
> >>> Introduce a new monitor command named dump, and this command accepts a filename.
> >>> We can use almost all migration's code. We use this command to dump guest's
> >>> memory, so there is no need to check whether the guest has a unmigratable device.
> >>
> >> I think it would be a good idea of QEMU had a dedicated 'dump' command
> >> for this purpose, even if it was just an alias for 'migrate' initially.
> >> I have never really liked the fact that we abuse the 'migrate' command
> >> to generate a core dump. The resulting data file from this is more
> >> complex than it really needs to be, causing complexity for post-processing
> >> it. The needs of migration, are not entirely aligned with the needs of
> >> core dumping in the long term, so we should allow the possibility of
> >> their impls diverging without impacting apps using them.
> >>
> >> So adding a 'dump' command which wrote out data in a format that was
> >> optimized for offline processing by tools like 'crash' (or the windows
> >> equivalent) would be a good improvement, even if it just reuses the
> >> migrate code for now.
> > 
> > The other reason why it would be good, is that we would then have a clearly
> > defined standard "QEMU dump format", instead of "libvirt dump format for QEMU"
> 
> A core file would be that format - for direct gdb processing. No
> proprietary re-inventions please.

I have no personal attachment to any particular format, so if the standard
core file format is possible, then we should definitely try to use it in
QEMU.


Daniel
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