Features/qtest driver framework

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Status: qgraph was merged in QEMU 4.0

Through a driver framework, libqos can expose a description of QEMU's supported machine types and a set of drivers; unit tests can request a driver, and the framework takes care of starting QEMU with options that provide that driver.

For example, the framework could provide:

  1. an interface for SD-HCI (SD Host Controller Interface) devices (abstract class QSDHCI)
  2. a driver for PCI SD-HCI devices (a subclass of QSDHCI, for example QSDHCI_PCI)
  3. a description of how QEMU's "sdhci-pci" device maps to QSDHCI_PCI (for simplicity this can be part of QSDHCI_PCI)
  4. an interface for a PCI bus (abstract class QPCIBus)
  5. a driver for the PCI bus in an x86 PC machine (a subclass of QPCIBus, for example QPCIBusPC)
  6. a description of QEMU's "pc" machine (a subclass of QOSMachine) and its embedded devices (in this case a QPCIBusPC)

(Right now libqos provides items 4 and 5 only).

You can construct a graph where the nodes are interfaces, drivers and unit tests, connected by relations such as "X produces Y" or "X consumes Y":

 (machine)           (driver)             (driver)          (interface)       (driver)
 x86_64/pc  ────────→ i440FX-pcihost ───────→ QPCIBusPC  ───────→ QPCIBus ───────→ QSDHCI_PCI
             contains                contains            produces        consumed by   │ produces
                                                              (driver)             (interface)
                                                              QSDHCI_MM ────────────→ QSDHCI
                                                                          produces     │ consumed by

The above is a subset of a potentially very large graph. The relations are hard-coded and even include some unused classes such as QSDHCI_MM (a memory-mapped SD-HCI device). That's okay: if there is no incoming edge, simply there will be no way to test the device. Another machine can add the required node and then QSDHCI_MM will be tested too.

After the graph is built, tests can be discovered by walking the graph: each test to run corresponds to a path from the root of the graphs to a unit test. Let's look at the path from pc to register-test, a unit test for the SD-HCI device. The above path could represent a test like "/x86_64/pc/i440FX-pcihost/pcibus-pci/sdhci-pci/sdhci/registers-test":

        │  │       │             │         │     │      │       ╰────── Test name
        │  │       │             │         │     │      ╰────────────── Interface provided by "sdhci-pci"
        │  │       │             │         │     ╰───────────────────── Device on the PCI bus
        │  │       │             │         ╰─────────────────────────── Interface provided by "pcibus-pc"
        │  │       │             ╰───────────────────────────────────── Driver provided by "i440FX-pcihost"
        │  │       ╰─────────────────────────────────────────────────── Device embedded by "pc"
        │  ╰─────────────────────────────────────────────────────────── QEMU machine
        ╰────────────────────────────────────────────────────────────── Target architecture

or reading it in the other direction (right to left):

        │  │       │             │       │      │        │       ╰────── Test name
        │  │       │             │       │      │        ╰────────────── Driver or interface consumed by the test
        │  │       │             │       │      ╰─────────────────────── Driver providing the "sdhci" interface
        │  │       │             │       ╰────────────────────────────── Interface consumed by "sdhci-pci"
        │  │       │             ╰────────────────────────────────────── Driver providing the "pcibus" interface
        │  │       ╰──────────────────────────────────────────────────── Driver embedding a "pcibus-pc" device
        │  ╰──────────────────────────────────────────────────────────── QEMU machine embedding an "i440FX-pcihost" device
        ╰─────────────────────────────────────────────────────────────── Target architecture

At run-time, a lot of steps are hidden in the framework, and are realized by walking the path:

  • All the drivers and tests register themselves into the graph.
  • libqos runs QEMU to detect machine types
  • libqos takes machine types that it knows about and adds them to the graph.
  • libqos walks the graph and registers a testcase for each path (from machine to test).
  • for each test:
    • libqos walks the path and builds the QEMU command line
    • libqos starts QEMU
    • libqos creates the machine object
    • starting from the machine object, libqos walks the path to obtain the object needed for the test function
    • libqos passes the interface to the test function

When register-test runs, for example, the command line is built like this:

  • the machine itself adds "-M pc" to the command line
  • QPCIBusPC need not add anything to the command line because the device is embedded
  • QSDHCI_PCI adds "-device sdhci-pci" to the command line

And then when the test function runs:

  • It asks QSDHCI_PCI to start the device
    • QSDHCI_PCI sets up the PCI device using the methods of QPCIBus
  • The function tests the SDHCI device

Creating the graph

The test would add itself to the graph like this:

 qos_add_test("register-test", "sdhci", sdhci_register_test_func);
                    │             │            ╰─────── Function invoked to the run test
                    │             ╰──────────────────── Interface consumed by the test
                    ╰────────────────────────────────── Test name

and likewise all the edges in the graph would be hard coded:

 qos_node_create_machine("x86_64/pc", qos_create_machine_x86_pc);
 qos_node_contains("x86_64/pc", "i440FX-pcihost");
 qos_node_create_driver("i440FX-pcihost", NULL); // created via "contains" only
 qos_node_create_driver("pci-bus-pc", NULL);
 qos_node_contains("i440FX-pcihost", "pci-bus-pc");
 qos_node_produces("pci-bus-pc", "pci-bus");
 qos_node_create_driver("sdhci-pci", sdhci_pci_create);
 qos_node_consumes("sdhci-pci", "pci-bus");   // "consumed by" edge from pci-bus to sdhci-pci
 qos_node_produces("sdhci-pci", "sdhci");
 qos_node_create_driver("generic-sdhci", NULL);
 qos_node_produces("generic-sdhci", "sdhci");

Here is how another machine could be added:

 qos_node_create_machine("arm/raspi2", qos_create_machine_arm_raspi2);
 qos_node_contains("arm/raspi2", "generic-sdhci");

Sample data structures

contains the name of a driver/machine/test/interface and possibly extra data depending on the kind of object (e.g. the "constructor" function if needed---machines need it because they're the root, and also anything that is reached by a "consumes" edge). QOSGraphNode could also take care of creating the command line. We'll get to the command line later but (for now) suffice to say that for example QSDHCI_PCI will add "-device sdhci-pci" to the command line.
joins two QOSGraphNode with a "produces" or "consumed by" relationship
a struct that is common to all "instances" created during the walk of a graph path. The most important function pointer in the struct is the one that returns the sub-objects (pci-device, sdhci, etc.) of the QOSGraphObject.

Note the asymmetry between "producer" (outgoing "produces" edge) and "consumer" (incoming "consumed by" edge). Whenever there is a "produces" relationship, an object is asked to return the next step in the graph. This is a method in QOSGraphObject. Whenever there is a "consumed by" relationship, the parent doesn't know what the next step in the graph will be. It can be a test, a driver, whatever. So it is up to the framework to create the object, using the constructor in QOSGraphNode itself.

QOSGraphObject example

In QEMU we have right now the following code (tests/sdhci-test.c):

   static uint16_t sdhci_readw(QSDHCI *s, uint32_t reg)
       uint16_t val;

       if (s->pci.dev) {
           val = qpci_io_readw(s->pci.dev, s->mem_bar, reg);
       } else {
           val = qtest_readw(global_qtest, s->addr + reg);

       return val;

The two arms of the "if" basically correspond to two drivers, respectively "sdhci-pci" and "sdhci-memory-mapped". Both of them implements QSDHCI which looks like this:

   struct QSDHCI {
       uint16_t (*sdhci_readw)(QSDHCI *s, uint32_t reg);

The first would have an implementation like:

   struct QSDHCI_PCI {
       QOSGraphObject obj;
       QPCIDevice dev;
       QSDHCI sdhci;

   static uint16_t sdhci_pci_readw(QSDHCI *s, uint32_t reg)
       QSDHCI_PCI *spci = container_of(s, QSDHCI, sdhci);

       return = qpci_io_readw(&spci->dev, spci->mem_bar, reg);

   static void *sdhci_pci_get_driver(void *object,
                                     const char *interface)
       QSDHCI_PCI *spci = obj;
       if (!strcmp(interface, "pci-device")) {
           return &spci->dev;
       if (!strcmp(interface, "sdhci")) {
           return &spci->sdhci;

and the constructor (pointed to by the QOSGraphNode) initializes the function pointers when it creates the object:

   void *sdhci_pci_create(void *pci_bus)
       QPCIBus *bus = pci_bus;
       qpci_device_init(&spci->dev, bus, QPCI_DEVFN(4, 0));
       spci->obj.get_driver = sdhci_pci_get_driver;
       spci->sdhci.readw = sdhci_pci_readw;

The second would have:

   struct QSDHCI_MemoryMapped {
       QOSGraphObject obj;
       QSDHCI sdhci;

   static uint16_t sdhci_mm_readw(QSDHCI *s, uint32_t reg)
       QSDHCI_MemoryMapped *smm = container_of(smm, QSDHCI, sdhci);

       return qtest_readw(global_qtest, smm->addr + reg);

   static void *sdhci_mm_get_driver(void *object,
                                    const char *interface)
       QSDHCI_MemoryMapped *spci = obj;
       if (!strcmp(interface, "sdhci")) {
           return &spci->sdhci;

with similar initialization (a bit different because this device would be "contained" in the machine, rather than a "consumer" of a bus:

   void qos_create_sdhci_mm(QSDHCI_MemoryMapped *sdhci, uint32_t addr)
       sdhci->obj.get_driver = sdhci_mm_get_driver;
       sdhci->sdhci.readw = sdhci_mm_readw;
       sdhci->addr = addr;

   static QOSGraphObject *raspi2_get_device(void *obj, const char *device)
       QRaspi2Machine *machine = obj;
       if (!strcmp(device, "generic-sdhci")) {
           return &machine->sdhci.obj;

   QOSGraphObject *qos_create_machine_arm_raspi2(void)
       QRaspi2Machine *machine = calloc(sizeof(QRaspi2Machine), 1);

       machine->obj.get_device = raspi2_get_device;
       qos_create_sdhci_mm(&machine->sdhci, 0x300000);
       return &machine->obj;

Possible milestones

  1. Create graph framework and write unit tests
  2. Convert all PC-based PCI device tests to use the graph framework
  3. Convert all PCI device tests to use the graph framework, so that all PC-based PCI device tests can work on more than one machine
  4. Create more drivers (e.g. SD-HCI)