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

[Daniel P. Berrange]

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"

Regards,
Daniel
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