On Wed, Mar 14, 2012 at 03:21:14PM +0530, Amit Shah wrote: > On (Wed) 14 Mar 2012 [16:29:50], Wen Congyang wrote: > > At 03/13/2012 06:47 PM, Avi Kivity Wrote: > > > On 03/13/2012 11:18 AM, Daniel P. Berrange wrote: > > >> On Mon, Mar 12, 2012 at 12:33:33PM +0200, Avi Kivity wrote: > > >>> On 03/12/2012 11:04 AM, Wen Congyang wrote: > > >>>> Do you have any other comments about this patch? > > >>>> > > >>> > > >>> Not really, but I'm not 100% convinced the patch is worthwhile. It's > > >>> likely to only be used by Linux, which has kexec facilities, and you can > > >>> put talk to management via virtio-serial and describe the crash in more > > >>> details than a simple hypercall. > > >> > > >> As mentioned before, I don't think virtio-serial is a good fit for this. > > >> We want something that is simple & guaranteed always available. Using > > >> virtio-serial requires significant setup work on both the host and guest. > > > > > > So what? It needs to be done anyway for the guest agent. > > > > > >> Many management application won't know to make a vioserial device available > > >> to all guests they create. > > > > > > Then they won't know to deal with the panic event either. > > > > > >> Most administrators won't even configure kexec, > > >> let alone virtio serial on top of it. > > > > > > It should be done by the OS vendor, not the individual admin. > > > > > >> The hypercall requires zero host > > >> side config, and zero guest side config, which IMHO is what we need for > > >> this feature. > > > > > > If it was this one feature, yes. But we keep getting more and more > > > features like that and we bloat the hypervisor. There's a reason we > > > have a host-to-guest channel, we should use it. > > > > > > > I donot know how to use virtio-serial. > > > > I start vm like this: > > qemu ...\ > > -device virtio-serial \ > > -chardev socket,path=/tmp/foo,server,nowait,id=foo \ > > -device virtserialport,chardev=foo,name=port1 ... > > This is sufficient. On the host, you can open /tmp/foo using a custom > program or nc (nc -U /tmp/foo). On the guest, you can just open > /dev/virtio-ports/port1 and read/write into it. > > See the following links for more details. > > https://fedoraproject.org/wiki/Features/VirtioSerial#How_To_Test > http://www.linux-kvm.org/page/Virtio-serial_API > > > You said that there are too many channels. Does it mean /tmp/foo is a channel? > > You can have several such -device virtserialport. The -device part > describes what the guest will see. The -chardev part ties that to the > host-side part of the channel. > > /tmp/foo is the host end-point for the channel, in the example above, > and /dev/virtio-ports/port1 is the guest-side end-point. If we do choose to use virtio-serial for panics (which I don't think we should), then we should not expose it in the host filesystem. The host side should be a virtual chardev backend internal to QEMU, in the same way that 'spicevmc' is handled. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- 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
