On 02/29/2012 12:19 PM, Daniel P. Berrange wrote: > On Wed, Feb 29, 2012 at 12:05:32PM +0200, Avi Kivity wrote: > > On 02/29/2012 11:58 AM, Daniel P. Berrange wrote: > > > > > > > > How about using a virtio-serial channel for this? You can transfer any > > > > amount of information (including the dump itself). > > > > > > When the guest OS has crashed, any dumps will be done from the host > > > OS using libvirt's core dump mechanism. The guest OS isn't involved > > > and is likely too dead to be of any use anyway. Likewise it is > > > quite probably too dead to work a virtio-serial channel or any > > > similarly complex device. We're really just after the simplest > > > possible notification that the guest kernel has paniced. > > > > If it's alive enough to panic, it's alive enough to kexec its kdump > > kernel. After that it can do anything. > > > > Guest-internal dumps are more useful IMO that host-initiated dumps. In > > a cloud, the host-initiated dump is left on the host, outside the reach > > of the guest admin, outside the guest image where all the symbols are, > > and sometimes not even on the same host if a live migration occurred. > > It's more useful in small setups, or if the problem is in the > > hypervisor, not the guest. > > I don't think guest vs host dumps should be considered mutually exclusive, > they both have pluses+minuses. True. > Configuring kexec+kdump requires non-negligable guest admin configuration > work before it's usable, and this work is guest OS specific, if it is possible > at all. I think it's on by default on Windows and requires installing a package on Linux, which may be part of the default configuration on many distros. > A permanent panic notifier that's built in the kernel by default > requires zero guest admin config, and can allow host admin to automate > collection of dumps across all their hosts/guests. The KVM hypercall > notification is fairly trivially ported to any OS kernel, by comparison > with a full virtio + virtio-serial impl. That's the path of least resistance. But it's not necessarily the best path. We end up with a wide set of disconnected ABIs instead of a narrow set that is more flexible. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
