On 08/22/13 21:19, Paolo Bonzini wrote: > Il 22/08/2013 19:15, Laszlo Ersek ha scritto: >>> 2) On all versions, <on_crash> will only work if the element is there. >> >> I like this, because, if on_crash doesn't work without panic_notifier >> *at all*, then we can just drop panic_notifier, and make on_crash mean >> (on_crash && panic_notifier) in the original sense. >> >> IOW, drop "panic_notifier", and make "on_crash" work *always*. > > No, we cannot because of backwards compatibility. VMs could have no > on_crash element (which means <on_crash>destroy</on_crash>) and yet the > guest admin could expect them to reboot on panic. Ah. I thought "no on_crash" meant <on_crash>ignore</on_crash>, or something like that -- if on_crash was absent, the guest wouldn't see a working pvpanic device in ACPI, and wouldn't trigger the event in qemu. >>> 2b) QEMU will provide a way for libvirt to detect that no machine type >>> has the builtin pvpanic. If some machine type may have the builtin >>> pvpanic, and <panic-notifier/> is absent, libvirt will add >>> "-global pvpanic.iobase=0" to neutralize it. Otherwise, libvirt >>> will create the device normally. >>> >>> A possible way for libvirt to detect "good" machine types is a >>> dummy property. This is a bit ugly in that the property would not >>> affect the behavior of the device. The property would remain in >>> the long term. >>> >>> Another possibility is for QEMU to rename the device, e.g. to >>> isa-pvpanic. This is also somewhat gross, but not visible in the >>> long term when the "pvpanic" name will be lost in history. >>> >>> Advantage 1: libvirt has no knowledge of the pvpanic port number >>> >>> Disadvantage 1: same as above >>> >>> Disadvantage 2: need a somewhat gross change in QEMU >>> >>> >>> This method also provides an (also somewhat gross on the QEMU side) >>> way to detect other changes in the pvpanic semantics. One example >>> mentioned below, is making the panicked state temporary. >> >> Too much work in qemu, in order to introduce ugliness, to hide older >> ugliness. > > Is it too much work? s/"pvpanic"/"isa-pvpanic"? ... I probably skipped the rename option because you called it gross (and maybe because I (erroneously?) recall Michael's opposition). I think I meant the dummy property under "too much work" (it may not be, in retrospect, but properties always imply compat stuff for me, and *that* is scary). Laszlo -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list