Re: [libvirt] [RFC 00/15] qmp: Report supported device types on 'query-machines'

The Problem =========== Currently management software has no way to find out which device types can be plugged in a machine, unless the machine is already initialized. Even after the machine is initialized, there's no way to map existing bus types to supported device types unless management software hardcodes the mapping between bus types and device types. Example: floppy support on q35 vs i440fx ---------------------------------------- There's no way for libvirt to find out that there's no floppy controller on pc-q35-* machine-types by default. With this series, pc-i440fx-* will report "floppy" as a supported device type, but pc-q35-* will not. Example: Legacy PCI vs vs PCIe devices -------------------------------------- Some devices require a PCIe bus to be available, others work on both legacy PCI and PCIe, while others work only on a legacy PCI bus. Currently management software has no way to know which devices can be added to a given machine, unless it hardcodes machine-type names and device-types names.

The Proposed Interface ====================== This series adds a new field to the output of 'query-machines': 'supported-device-types'. It will contain a list of QOM type names, that can be used to find the list of device types that can be plugged in the machine by default. The type names reported on the new field can then be used as the 'implements' argument on the 'qom-list-types' command, to find out which device types can be plugged on the machine. Example output -------------- (QEMU) query-machines { "return": [ [...] { "supported-device-types": [ "sys-bus-device" ], "cpu-max": 1, "hotpluggable-cpus": false, "name": "none" }, [...] { "supported-device-types": [ "sys-bus-device" ], "cpu-max": 1, "hotpluggable-cpus": false, "name": "xenpv" }, [...] { "supported-device-types": [ "sys-bus-device", "floppy", "i2c-slave", "pci-device", "isa-device", "ide-device" ], "name": "pc-i440fx-2.8", "alias": "pc", "is-default": true, "cpu-max": 255, "hotpluggable-cpus": true }, [...] { "supported-device-types": [ "sys-bus-device", "floppy", "isa-device", "ide-device" ], "cpu-max": 1, "hotpluggable-cpus": true, "name": "isapc" }, [...] { "supported-device-types": [ "sys-bus-device", "floppy", "i2c-slave", "pci-device", "isa-device", "ide-device" ], "cpu-max": 128, "hotpluggable-cpus": true, "name": "xenfv" }, [...] { "alias": "q35", "supported-device-types": [ "sys-bus-device", "i2c-slave", "PCIE-device", "isa-device", "ide-device" ], "cpu-max": 288, "hotpluggable-cpus": true, "name": "pc-q35-2.8" }, [...] ] } Considered alternatives ======================= Indirect mapping (machine => bus => device) ------------------------------------------- This RFC implements a mechanism to implement ax machine-type => supported-device-types mapping. An alternative solution I considered was to expose an indirect mapping: machine-type => default-bus-types followed by bus-type => supported-device-types. But exposing only the resulting supported device-types list imposes less restrictions on how the device and bus type hierarchy is implemented inside QEMU. There's still a machine-type => bus-type => device-type mapping implemented internally, but it is an implementation detail on the current version, and not part of the externally-visible interface. The Implementation ================== This add a new field to MachineClass: default_bus_types, and a new field to BusClass: supported_device_type. The two fields are used to build the list of supported device types for a given machine. On most cases, the normal QOM type hierarchy is used to define the set of supported devices for a bus. On the case of PCIe buses, a INTERFACE_PCIE_DEVICE interface name was introduced, to indicate PCIe-capable devices. This means we are duplicating information in some cases: * BusClass::supported_device_type duplicates knowlege that is already encoded in DeviceClass::bus_type. To make sure both fields agree with each other, a new device_class_set_bus_type() wrapper was added, to perform additional validation. * MachineClass::default_bus_type duplicates knowledge that is already encoded in the machine init function. To make sure the information is correct, a qmp-machine-info.py test case is added, that will validate the supported-device-types field based on the buses created by the machine. * PCIDeviceClass::is_express and INTERFACE_PCIE_DEVICE both encode the same information about a PCI device class. A future version of this series may include a class_base_post_init hook that will allow TYPE_PCI_DEVICE to validate/update is_express and the interface list to ensure both are always consistent. Test Code --------- qdev-based test code for the new field was implemented in a Python script. Some extra support was implemented in tests/Makefile.include, scripts/qemu.py and scripts/qtest.py to allow the test to be implemented. Limitations ===========

TYPE_SYS_BUS_DEVICE is too generic ---------------------------------- Currently all machines have a TYPE_SYS_BUS bus, meaning all TYPE_SYS_BUS_DEVICE subclasses are reported as supported. The current solution in this series is to report TYPE_SYS_BUS_DEVICE as supported by all machines. But we could gradually add arch-specific or machine-family-specific interface names that can be used on devices that are meant to work with only a subset of TYPE_SYS_BUS_DEVICE subclasses. A future version of this series may remove TYPE_SYS_BUS_DEVICE from the supported-device-types output, and return a arch-specific or machine-family-specific interface name to restrict management software to a subset of TYPE_SYS_BUS_DEVICE subclasses. PCI vs PCIe ----------- Machines with PCIe buses will report INTERFACE_PCIE_DEVICE on supported-device-types. Machines with legacy PCI buses will report TYPE_PCI_DEVICE on supported-device-types. The problem with the current approach is that PCIe devices are TYPE_PCI_DEVICE subclasses. The allows PCI device classes to indicate they are PCIe-capable, but there's no obvious way to indicate that a device is PCIe-only. This needs to be addressed in a future version of this series. Suggestions are welcome.

Incomplete bus lists on some machines ------------------------------------- With this series, not all machines classes are changed to add the full list of device types on the 'supported-device-types'. To allow the code to be updated gradually, qmp-machine-info.py has a STRICT_ARCHES variable, that will make the test code require a complete device type list only on some architectures. Out of scope: Configurable buses -------------------------------- There's no way to map machine options like "usb=on|off" to device-types or buses. I plan to propose a new interface that allows machine options to be mapped to buses/device-types later. Out of scope: Deciding where to plug devices -------------------------------------------- Once management software discovers which devices can be plugged to a machine, it still has to discover or define where devices can/should/will be plugged. This is out of the scope of this series. Out of scope: Hotplug --------------------- The proposed interface is supposed to help management software find which device types can be used when creating the VM. Device hotplug is out of the scope of this series. However, the new 'device-types' QOM property on bus objects could be used to find out which device types can be plugged on the existing buses. --- Cc: libvir-list(a)redhat.com Cc: Laine Stump <laine(a)redhat.com&gt; Eduardo Habkost (15): qemu.py: Make logging optional qtest.py: Support QTEST_LOG environment variable qtest.py: make logging optional qtest.py: Make 'binary' parameter optional tests: Add rules to non-gtester qtest test cases qdev: Add device_type field to BusClass machine: Add MachineClass::default_buses field qmp: Add 'supported-device-types' field to 'query-machines' pci: Introduce INTERFACE_PCIE_DEVICE interface name pc: Initialize default bus lists s390x: Initialize default bus lists arm: Initialize default bus lists mips: Initialize default bus lists ppc: Initialize default bus lists qdev: Add device_class_set_bus_type() function hw/arm/aspeed.c | 2 + hw/arm/collie.c | 1 + hw/arm/cubieboard.c | 1 + hw/arm/exynos4_boards.c | 5 ++ hw/arm/gumstix.c | 7 ++ hw/arm/highbank.c | 4 ++ hw/arm/imx25_pdk.c | 1 + hw/arm/kzm.c | 1 + hw/arm/musicpal.c | 1 + hw/arm/nseries.c | 2 + hw/arm/palm.c | 1 + hw/arm/realview.c | 1 + hw/arm/spitz.c | 10 +++ hw/arm/stellaris.c | 4 ++ hw/audio/intel-hda.c | 9 ++- hw/block/fdc.c | 17 +++-- hw/block/nvme.c | 4 ++ hw/char/virtio-serial-bus.c | 3 +- hw/core/bus.c | 9 +++ hw/core/machine.c | 18 ++++- hw/core/qdev.c | 8 +++ hw/core/sysbus.c | 3 +- hw/i2c/core.c | 9 ++- hw/i386/pc_piix.c | 13 ++++ hw/i386/pc_q35.c | 4 ++ hw/ide/qdev.c | 3 +- hw/input/adb.c | 9 ++- hw/ipack/ipack.c | 9 ++- hw/isa/isa-bus.c | 3 +- hw/mips/mips_malta.c | 7 ++ hw/mips/mips_r4k.c | 2 + hw/misc/auxbus.c | 3 +- hw/net/e1000e.c | 4 ++ hw/net/vmxnet3.c | 4 ++ hw/pci-bridge/ioh3420.c | 4 ++ hw/pci-bridge/xio3130_downstream.c | 4 ++ hw/pci/pci.c | 16 ++++- hw/ppc/e500plat.c | 3 + hw/ppc/mac_newworld.c | 4 ++ hw/ppc/mac_oldworld.c | 3 + hw/ppc/mpc8544ds.c | 4 ++ hw/ppc/ppc440_bamboo.c | 1 + hw/ppc/prep.c | 4 ++ hw/ppc/spapr_vio.c | 3 +- hw/s390x/css-bridge.c | 2 + hw/s390x/event-facility.c | 3 +- hw/s390x/s390-pci-bus.c | 9 ++- hw/s390x/s390-virtio-ccw.c | 6 ++ hw/s390x/virtio-ccw.c | 2 +- hw/scsi/megasas.c | 7 ++ hw/scsi/scsi-bus.c | 3 +- hw/scsi/vmw_pvscsi.c | 1 + hw/sd/core.c | 7 ++ hw/sd/sd.c | 2 +- hw/ssi/ssi.c | 9 ++- hw/usb/bus.c | 3 +- hw/usb/dev-smartcard-reader.c | 9 ++- hw/usb/hcd-xhci.c | 4 ++ hw/vfio/pci.c | 4 ++ hw/virtio/virtio-bus.c | 1 + hw/virtio/virtio-pci.c | 4 ++ hw/virtio/virtio.c | 2 +- include/hw/boards.h | 5 ++ include/hw/pci/pci.h | 3 + include/hw/qdev-core.h | 4 ++ qapi-schema.json | 9 ++- scripts/qemu.py | 25 +++++-- scripts/qtest.py | 15 +++- tests/Makefile.include | 39 ++++++++++- tests/qmp-machine-info.py | 138 +++++++++++++++++++++++++++++++++++++ vl.c | 11 +++ 71 files changed, 518 insertions(+), 37 deletions(-) create mode 100755 tests/qmp-machine-info.py -- 2.7.4