At 03/14/2012 06:57 PM, Daniel P. Berrange Wrote: > 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. Yes. But we don't decide to choose which now. I prefer to use vmcall. It is simple and more reliable. Thanks Wen Congyang > > Regards, > Daniel -- 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
