Features/qtest driver framework

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-host ───────→ QPCIBusPC  ───────→ QPCIBus ───────→ QSDHCI_PCI
             contains             contains            produces        consumed by   │ produces
                                                                                    │
                                                                                    ↓
                                                           (driver)             (interface)
                                                           QSDHCI_MM ────────────→ QSDHCI
                                                           produces                 │ consumed by
                                                                                    ↓
                                                                                 register-test

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-host/pcibus-pci/sdhci-pci/sdhci/registers-test":

  /x86_64/pc/i440FX-host/pcibus-pc/pci-bus/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-host"
        │  │       ╰──────────────────────────────────────────────── Device embedded by "pc"
        │  ╰──────────────────────────────────────────────────────── QEMU machine
        ╰─────────────────────────────────────────────────────────── Target architecture

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

  /x86_64/pc/i440FX-host/pcibus-pc/pci-bus/sdhci-pci/sdhci/registers-test
        │  │       │          │       │      │        │       ╰────── 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-host" 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-host");
 qos_node_create_driver("i440FX-host");
 qos_node_create_driver("pci-bus-pc");
 qos_node_contains("i440FX-host", "pci-bus-pc");
 qos_node_create_interface("pci-bus");
 qos_node_produces("pci-bus-pc", "pci-bus");
 qos_node_create_driver("sdhci-pci");
 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("sdhci-mm");
 qos_node_produces("sdhci-mm", "sdhci");

Here is how another machine could be added:

 qos_node_create_machine("arm/raspi", qos_create_machine_arm_raspi3);
 qos_node_contains(raspi3, "sdhci-mm");

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)