* David Hildenbrand (da...@redhat.com) wrote: > On 21/09/2018 18:55, Dr. David Alan Gilbert wrote: > > * David Hildenbrand (da...@redhat.com) wrote: > >> On 21/09/2018 18:00, Dr. David Alan Gilbert wrote: > >>> * David Hildenbrand (da...@redhat.com) wrote: > >>>> Compile virtio-pmem for x86 and properly hotplug virtio-pmem devices > >>>> (memory-device part) from our pc machine hotplug handler. > >>>> > >>>> Signed-off-by: David Hildenbrand <da...@redhat.com> > >>> > >>> I see a few other places in the pc subdir that have checks for > >>> TYPE_NVDIMM; can you just explain why they are untouched: > >>> i386/pc.c: pc_memory_unplug_request > >> > >> I think I had an answer why that isn't needed, but for unplug we might > >> still be missing something. > >> > >> In general: unplug requests are always directed at the proxy device (via > >> qdev_unplug()) (e.g. virtio-pmem-pci, see below). virtio-pmem is a child > >> device of virtio-pmem-pci. Once virtio-pmem-pci is finally unrealized, > >> the virtio-mem device will be unrealized. > >> > >> Now, there are no hotplug handlers getting called as far as I can see > >> for that child device. there would have to be an proper call to a > >> hotplug handler somewhere when setting the device to unrealized. (and > >> that's the place where a unplug requests does not make really sense, but > >> only a straight unplug - because we are half way through removing the > >> hierarchy of devices - one of the reason why also failures of unrealize > >> are usually ignored). > >> > >> I'll look into the details. Thanks for pointing that out, this stuff > >> always messes with my head. > >> > >>> acpi/ich9.c: ich9_pm_device_plug_cb > >>> acpi/piix4.c:piix4_device_plug_cb > >> > >> virtio-pmem is not an acpi device, that's why these don't apply. > >> > >> E.g. if virtio-pmem-pci is plugged, it will most probably trigger these > >> hotplug handlers for the proxy virtio pci device. The proxy device > >> creates and realized the virtio-mem (memory-device) - without any > >> hotplug handlers involved. That#s the point where we can jump in and > >> realize the device via the machine instead. > > > > Does not being an acpi-device make life easier or harder? > > My opinion is: easier. > > Being an acpi device, we would have devices that are both, ACPI and > virtio. Or you have to create separate device and somehow link them > together (both in QEMU and in Linux) > > I don't like gluing virtio devices to different, unrelated technologies. > Especially, you could never support architectures that don't support > ACPI. (with virtio-pmem, we could eventually even support architectures > that don't support something like nvdimm or acpi). > > > Again, not > > knowing anything about the pmem acpi; if it looked like a normal nvdimm > > through ACPI would OSs be able to boot off it? > > As far as I remember, booting from NVDIMM is not implemented anywhere. I > guess if it would be, we could also realize booting from virtio-pmem > (e.g. via grub extension).
OK, that's fair enough; I was just curious about why there was the difference. Dave > > > > Dave > > > -- > > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
