On Tue, Jan 25, 2022 at 09:12:28PM +0000, Jag Raman wrote: > > > > On Jan 25, 2022, at 5:44 AM, Stefan Hajnoczi <stefa...@redhat.com> wrote: > > > > On Wed, Jan 19, 2022 at 04:41:56PM -0500, Jagannathan Raman wrote: > >> Signed-off-by: Elena Ufimtseva <elena.ufimts...@oracle.com> > >> Signed-off-by: John G Johnson <john.g.john...@oracle.com> > >> Signed-off-by: Jagannathan Raman <jag.ra...@oracle.com> > >> --- > >> hw/remote/machine.c | 57 +++++++++++++++++++++++++++++++++++++++++++++ > >> 1 file changed, 57 insertions(+) > >> > >> diff --git a/hw/remote/machine.c b/hw/remote/machine.c > >> index 220ff01aa9..221a8430c1 100644 > >> --- a/hw/remote/machine.c > >> +++ b/hw/remote/machine.c > >> @@ -22,6 +22,60 @@ > >> #include "hw/pci/pci_host.h" > >> #include "hw/remote/iohub.h" > >> > >> +static bool remote_machine_get_bus(const char *type, BusState **bus, > >> + Error **errp) > >> +{ > >> + ERRP_GUARD(); > >> + RemoteMachineState *s = REMOTE_MACHINE(current_machine); > >> + BusState *root_bus = NULL; > >> + PCIBus *new_pci_bus = NULL; > >> + > >> + if (!bus) { > >> + error_setg(errp, "Invalid argument"); > >> + return false; > >> + } > >> + > >> + if (strcmp(type, TYPE_PCI_BUS) && strcmp(type, TYPE_PCI_BUS)) { > >> + return true; > >> + } > >> + > >> + root_bus = qbus_find_recursive(sysbus_get_default(), NULL, > >> TYPE_PCIE_BUS); > >> + if (!root_bus) { > >> + error_setg(errp, "Unable to find root PCI device"); > >> + return false; > >> + } > >> + > >> + new_pci_bus = pci_isol_bus_new(root_bus, type, errp); > >> + if (!new_pci_bus) { > >> + return false; > >> + } > >> + > >> + *bus = BUS(new_pci_bus); > >> + > >> + pci_bus_irqs(new_pci_bus, remote_iohub_set_irq, remote_iohub_map_irq, > >> + &s->iohub, REMOTE_IOHUB_NB_PIRQS); > >> + > >> + return true; > >> +} > > > > Can the user create the same PCI bus via QMP commands? If so, then this > > I think there is a way we could achieve it. > > When I looked around, both the command line and the QMP didn’t have a direct > way to create a bus. However, there are some indirect ways. For example, the > TYPE_LSI53C895A device creates a SCSI bus to attach SCSI devices. Similarly, > there are some special PCI devices like TYPE_PCI_BRIDGE which create a > secondary PCI bus. > > Similarly, we could implement a PCI device that creates a PCI bus with > isolated address spaces.
Exactly. device_add instantiates DeviceStates, not busses, so there needs to be a parent device like a SCSI controller, a PCI bridge, etc that owns and creates the bus. > > is just a convenience that saves the extra step. Or is there some magic > > that cannot be done via QMP device_add? > > > > I'm asking because there are 3 objects involved and I'd like to > > understand the lifecycle/dependencies: > > 1. The PCIDevice we wish to export. > > 2. The PCIBus with isolated address spaces that contains the PCIDevice. > > 3. The vfio-user server that exports a given PCIDevice. > > > > Users can already create the PCIDevice via hotplug and the vfio-user > > server via object-add. So if there's no magic they could also create the > > PCI bus: > > 1. device_add ...some PCI bus stuff here...,id=isol-pci-bus0 > > 2. device_add ...the PCIDevice...,bus=isol-pci-bus0,id=mydev > > 3. object-add x-vfio-user-server,device=mydev > > We are able to do 2 & 3 already. We could introduce a PCI device that > creates an isolated PCI bus. That would cover step 1 outlined above. I wonder if a new device is needed or whether it's possible to add an isol_as=on|off (default: off) option to an existing PCI bridge/expander? Hopefully most of the code is already there. Stefan
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