* Daniel P. Berrangé (berra...@redhat.com) wrote: > On Thu, Jan 14, 2021 at 04:27:28PM -0800, Dongli Zhang wrote: > > The virtio device/driver (e.g., vhost-scsi and indeed any device including > > e1000e) may hang due to the lost of IRQ or the lost of doorbell register > > kick, e.g., > > > > https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01711.html > > > > The virtio-net was in trouble in above link because the 'kick' was not > > taking effect (missed). > > > > This RFC adds a new debug interface 'DeviceEvent' to DeviceClass to help > > narrow down if the issue is due to lost of irq/kick. So far the new > > interface handles only two events: 'call' and 'kick'. Any device (e.g., > > e1000e or vhost-scsi) may implement (e.g., via eventfd, MSI-X or legacy > > IRQ). > > > > The 'call' is to inject irq on purpose by admin for a specific device (e.g., > > vhost-scsi) from QEMU/host to VM, while the 'kick' is to kick the doorbell > > on purpose by admin at QEMU/host side for a specific device. > > I'm really not convinced that we want to give admins the direct ability to > poke at internals of devices in a running QEMU. It feels like there is way > too much potential for the admin to make a situation far worse by doing > the wrong thing here,
We already do have commands to write to an iport, and to inject MCEs for example; is this that much different? > and people dealing with support tickets will have > no idea that the admin has been poking internals of the device and broken > it by doing something wrong. You could add a one time log entry to say that this mischeivous command had been used. > You pointed to bug that hit where this could conceivably be useful, but > that's a one time issue and should not a common occurrance that justifies > making an official public API to poke at devices forever more IMHO. I think where it might be practically useful is if you were debugging a hung customers VM and need to find a way to get it to move again. THat's something I'm not familiar with on the virtio side; mst - is this useful from a virtio side? Dave > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
