On Mon, Sep 20, 2010 at 01:05:33PM +0200, Michal Novotny wrote: > On 09/20/2010 12:53 PM, Daniel P. Berrange wrote: > >On Mon, Sep 20, 2010 at 12:48:50PM +0200, Michal Novotny wrote: > > > >>On 09/20/2010 12:34 PM, Paolo Bonzini wrote: > >> > >>>On 09/20/2010 11:47 AM, Michal Novotny wrote: > >>> > >>>>Hi, > >>>> > >>>>this is the patch to introduce a NIC model fallback to default when > >>>>model > >>>>specified is not supported. It's been tested on i386-softmmu target on > >>>>i386 host using the Windows XP x86 virtual machine and by trying to > >>>>setup > >>>>the invalid (unsupported) model of NIC device. Also, the new constant in > >>>>the net.h called the DEFAULT_NIC_MODEL has been introduced to be able to > >>>>change the default NIC model easily. This variable is being used to set > >>>>the default NIC model when necessary. > >>>> > >>>Why? If it's not supported, it shouldn't run. > >>> > >>>Paolo > >>> > >>I don't think so. It makes sense it shouldn't run for case of pure qemu > >>but since there's newly added support for xen (and also there's support > >>for other virtualization platforms to be used with the qemu device > >>model) it should fallback with just a warning since otherwise those > >>platforms, like e.g. mentioned Xen, will leave defunct device models > >>there and the guests won't run be running at all ending up with no > >>state. If there's a warning with information it's falling back to > >>default the user can notice if he wants to but it won't leave the > >>defunct device models anymore which can be pretty hard to determine > >>what's going on there for standard user that doesn't have much > >>experience with e.g. Xen yet. > >> > >IMHO this is just a bug in the xen mgmt layer. If the QEMU device model > >dies/quits, then XenD should teardown the guest, since you can't do any > >useful work once the device model has crashed. Silently switching to a > >different NIC model than the one requested is definitely a wrong approach. > > > >Daniel > > > When the qemu-dm has crashed we can't do anything with the guest, that's > correct. Nevertheless do you think that we should bail with error and > just fix the layer of xen management to check whether there's a device > model still running or not? It's being spawned by XenD itself so we > would need to check whether this process is not a zombie using the > /proc/$PID/stat or use some better way to get the state. Unfortunately > using /proc/$PID/stat would kill the portability of the code. > > The other way is to implement the thread that will be (periodically or > "on change") checking the device model state and that will be > terminating the domain when device model dies/quits. I'm not saying this > is the bad approach but we've been talking with Mirek about at least > RHEL-5 version and he told me that he recommends to implement a fallback > to the default NIC.
If XenD holds open a connection to the QEMU monitor socket, then it can easily receive a POLLHUP when QEMU dies. This is the approach most mgmt tools use for detecting QEMU death. > Daniel, if you consider RHEL-5 version, what do you prefer to do with > this one? Fix it somehow in the XenD or is altering the device model OK > for this version? Also, the patch has been already sent upstream Xen for > consideration about an hour ago. RHEL5 Xen maintenance isn't a concern of qemu-devel really, so this is not the place to decide that. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|
