Qtest Driver Framework

In order to test a specific driver, plain libqos tests need to take care of booting QEMU with the right machine and devices. This makes each test "hardcoded" for a specific configuration, reducing the possible coverage that it can reach.

For example, the sdhci device is supported on both x86_64 and ARM boards, therefore a generic sdhci test should test all machines and drivers that support that device. Using only libqos APIs, the test has to manually take care of covering all the setups, and build the correct command line.

This also introduces backward compatibility issues: if a device/driver command line name is changed, all tests that use that will not work properly anymore and need to be adjusted.

The aim of qgraph is to create a graph of drivers, machines and tests such that a test aimed to a certain driver does not have to care of booting the right QEMU machine, pick the right device, build the command line and so on. Instead, it only defines what type of device it is testing (interface in qgraph terms) and the framework takes care of covering all supported types of devices and machine architectures.

Following the above example, an interface would be sdhci, so the sdhci-test should only care of linking its qgraph node with that interface. In this way, if the command line of a sdhci driver is changed, only the respective qgraph driver node has to be adjusted.

QGraph concepts

The graph is composed by nodes that represent machines, drivers, tests and edges that define the relationships between them (CONSUMES, PRODUCES, and CONTAINS).

Nodes

A node can be of four types:

QNODE_MACHINE: for example arm/raspi2b
QNODE_DRIVER: for example generic-sdhci
QNODE_INTERFACE: for example sdhci (interface for all -sdhci drivers). An interface is not explicitly created, it will be automatically instantiated when a node consumes or produces it. An interface is simply a struct that abstracts the various drivers for the same type of device, and offers an API to the nodes that use it ("consume" relation in qgraph terms) that is implemented/backed up by the drivers that implement it ("produce" relation in qgraph terms).
QNODE_TEST: for example sdhci-test. A test consumes an interface and tests the functions provided by it.

Notes for the nodes:

QNODE_MACHINE: each machine struct must have a QGuestAllocator and implement get_driver() to return the allocator mapped to the interface "memory". The function can also return NULL if the allocator is not set.
QNODE_DRIVER: driver names must be unique, and machines and nodes planned to be "consumed" by other nodes must match QEMU drivers name, otherwise they won't be discovered

Edges

An edge relation between two nodes (drivers or machines) X and Y can be:

X CONSUMES Y: Y can be plugged into X
X PRODUCES Y: X provides the interface Y
X CONTAINS Y: Y is part of X component

Execution steps

The basic framework steps are the following:

All nodes and edges are created in their respective machine/driver/test files
The framework starts QEMU and asks for a list of available devices and machines (note that only machines and "consumed" nodes are mapped 1:1 with QEMU devices)
The framework walks the graph starting from the available machines and performs a Depth First Search for tests
Once a test is found, the path is walked again and all drivers are allocated accordingly and the final interface is passed to the test
The test is executed
Unused objects are cleaned and the path discovery is continued

Depending on the QEMU binary used, only some drivers/machines will be available and only test that are reached by them will be executed.

Command line

Command line is built by using node names and optional arguments passed by the user when building the edges.

There are three types of command line arguments:

in node : created from the node name. For example, machines will have -M <machine> to its command line, while devices -device <device>. It is automatically done by the framework.
after node : added as additional argument to the node name. This argument is added optionally when creating edges, by setting the parameter after_cmd_line and extra_edge_opts in QOSGraphEdgeOptions. The framework automatically adds a comma before extra_edge_opts, because it is going to add attributes after the destination node pointed by the edge containing these options, and automatically adds a space before after_cmd_line, because it adds an additional device, not an attribute.
before node : added as additional argument to the node name. This argument is added optionally when creating edges, by setting the parameter before_cmd_line in QOSGraphEdgeOptions. This attribute is going to add attributes before the destination node pointed by the edge containing these options. It is helpful to commands that are not node-representable, such as -fdsev or -netdev.

While adding command line in edges is always used, not all nodes names are used in every path walk: this is because the contained or produced ones are already added by QEMU, so only nodes that "consumes" will be used to build the command line. Also, nodes that will have { "abstract" : true } as QMP attribute will loose their command line, since they are not proper devices to be added in QEMU.

Example:

QOSGraphEdgeOptions opts = {
    .before_cmd_line = "-drive id=drv0,if=none,file=null-co://,"
                       "file.read-zeroes=on,format=raw",
    .after_cmd_line = "-device scsi-hd,bus=vs0.0,drive=drv0",

    opts.extra_device_opts = "id=vs0";
};

qos_node_create_driver("virtio-scsi-device",
                        virtio_scsi_device_create);
qos_node_consumes("virtio-scsi-device", "virtio-bus", &opts);

Will produce the following command line: -drive id=drv0,if=none,file=null-co://, -device virtio-scsi-device,id=vs0 -device scsi-hd,bus=vs0.0,drive=drv0

Troubleshooting unavailable tests

If there is no path from an available machine to a test then that test will be unavailable and won't execute. This can happen if a test or driver did not set up its qgraph node correctly. It can also happen if the necessary machine type or device is missing from the QEMU binary because it was compiled out or otherwise.

It is possible to troubleshoot unavailable tests by running:

$ QTEST_QEMU_BINARY=build/qemu-system-x86_64 build/tests/qtest/qos-test --verbose
# ALL QGRAPH EDGES: {
#   src='virtio-net'
#      |-> dest='virtio-net-tests/vhost-user/multiqueue' type=2 (node=0x559142109e30)
#      |-> dest='virtio-net-tests/vhost-user/migrate' type=2 (node=0x559142109d00)
#   src='virtio-net-pci'
#      |-> dest='virtio-net' type=1 (node=0x55914210d740)
#   src='pci-bus'
#      |-> dest='virtio-net-pci' type=2 (node=0x55914210d880)
#   src='pci-bus-pc'
#      |-> dest='pci-bus' type=1 (node=0x559142103f40)
#   src='i440FX-pcihost'
#      |-> dest='pci-bus-pc' type=0 (node=0x55914210ac70)
#   src='x86_64/pc'
#      |-> dest='i440FX-pcihost' type=0 (node=0x5591421117f0)
#   src=''
#      |-> dest='x86_64/pc' type=0 (node=0x559142111600)
#      |-> dest='arm/raspi2b' type=0 (node=0x559142110740)
...
# }
# ALL QGRAPH NODES: {
#   name='virtio-net-tests/announce-self' type=3 cmd_line='(null)' [available]
#   name='arm/raspi2b' type=0 cmd_line='-M raspi2b ' [UNAVAILABLE]
...
# }

The virtio-net-tests/announce-self test is listed as "available" in the "ALL QGRAPH NODES" output. This means the test will execute. We can follow the qgraph path in the "ALL QGRAPH EDGES" output as follows: '' -> 'x86_64/pc' -> 'i440FX-pcihost' -> 'pci-bus-pc' -> 'pci-bus' -> 'virtio-net-pci' -> 'virtio-net'. The root of the qgraph is '' and the depth first search begins there.

The arm/raspi2b machine node is listed as "UNAVAILABLE". Although it is reachable from the root via '' -> 'arm/raspi2b' the node is unavailable because the QEMU binary did not list it when queried by the framework. This is expected because we used the qemu-system-x86_64 binary which does not support ARM machine types.

If a test is unexpectedly listed as "UNAVAILABLE", first check that the "ALL QGRAPH EDGES" output reports edge connectivity from the root ('') to the test. If there is no connectivity then the qgraph nodes were not set up correctly and the driver or test code is incorrect. If there is connectivity, check the availability of each node in the path in the "ALL QGRAPH NODES" output. The first unavailable node in the path is the reason why the test is unavailable. Typically this is because the QEMU binary lacks support for the necessary machine type or device.

Creating a new driver and its interface

Here we continue the sdhci use case, with the following scenario:

sdhci-test aims to test the read[q,w], writeq functions offered by the sdhci drivers.
The current sdhci device is supported by both x86_64/pc and ARM (in this example we focus on the arm-raspi2b) machines.
QEMU offers 2 types of drivers: QSDHCI_MemoryMapped for ARM and QSDHCI_PCI for x86_64/pc. Both implement the read[q,w], writeq functions.

In order to implement such scenario in qgraph, the test developer needs to:

Create the x86_64/pc machine node. This machine uses the pci-bus architecture so it contains a PCI driver, pci-bus-pc. The actual path is

x86_64/pc --contains--> 1440FX-pcihost --contains--> pci-bus-pc --produces--> pci-bus.

For the sake of this example, we do not focus on the PCI interface implementation.
Create the sdhci-pci driver node, representing QSDHCI_PCI. The driver uses the PCI bus (and its API), so it must consume the pci-bus generic interface (which abstracts all the pci drivers available)

sdhci-pci --consumes--> pci-bus
Create an arm/raspi2b machine node. This machine contains a generic-sdhci memory mapped sdhci driver node, representing QSDHCI_MemoryMapped.

arm/raspi2b --contains--> generic-sdhci
Create the sdhci interface node. This interface offers the functions that are shared by all sdhci devices. The interface is produced by sdhci-pci and generic-sdhci, the available architecture-specific drivers.

sdhci-pci --produces--> sdhci

generic-sdhci --produces--> sdhci
Create the sdhci-test test node. The test consumes the sdhci interface, using its API. It doesn't need to look at the supported machines or drivers.

sdhci-test --consumes--> sdhci

arm-raspi2b machine, simplified from tests/qtest/libqos/arm-raspi2-machine.c:

#include "qgraph.h"

struct QRaspi2Machine {
    QOSGraphObject obj;
    QGuestAllocator alloc;
    QSDHCI_MemoryMapped sdhci;
};

static void *raspi2_get_driver(void *object, const char *interface)
{
    QRaspi2Machine *machine = object;
    if (!g_strcmp0(interface, "memory")) {
        return &machine->alloc;
    }

    fprintf(stderr, "%s not present in arm/raspi2b\n", interface);
    g_assert_not_reached();
}

static QOSGraphObject *raspi2_get_device(void *obj,
                                            const char *device)
{
    QRaspi2Machine *machine = obj;
    if (!g_strcmp0(device, "generic-sdhci")) {
        return &machine->sdhci.obj;
    }

    fprintf(stderr, "%s not present in arm/raspi2b\n", device);
    g_assert_not_reached();
}

static void *qos_create_machine_arm_raspi2(QTestState *qts)
{
    QRaspi2Machine *machine = g_new0(QRaspi2Machine, 1);

    alloc_init(&machine->alloc, ...);

    /* Get node(s) contained inside (CONTAINS) */
    machine->obj.get_device = raspi2_get_device;

    /* Get node(s) produced (PRODUCES) */
    machine->obj.get_driver = raspi2_get_driver;

    /* free the object */
    machine->obj.destructor = raspi2_destructor;
    qos_init_sdhci_mm(&machine->sdhci, ...);
    return &machine->obj;
}

static void raspi2_register_nodes(void)
{
    /* arm/raspi2b --contains--> generic-sdhci */
    qos_node_create_machine("arm/raspi2b",
                             qos_create_machine_arm_raspi2);
    qos_node_contains("arm/raspi2b", "generic-sdhci", NULL);
}

libqos_init(raspi2_register_nodes);

x86_64/pc machine, simplified from tests/qtest/libqos/x86_64_pc-machine.c:

#include "qgraph.h"

struct i440FX_pcihost {
    QOSGraphObject obj;
    QPCIBusPC pci;
};

struct QX86PCMachine {
    QOSGraphObject obj;
    QGuestAllocator alloc;
    i440FX_pcihost bridge;
};

/* i440FX_pcihost */

static QOSGraphObject *i440FX_host_get_device(void *obj,
                                            const char *device)
{
    i440FX_pcihost *host = obj;
    if (!g_strcmp0(device, "pci-bus-pc")) {
        return &host->pci.obj;
    }
    fprintf(stderr, "%s not present in i440FX-pcihost\n", device);
    g_assert_not_reached();
}

/* x86_64/pc machine */

static void *pc_get_driver(void *object, const char *interface)
{
    QX86PCMachine *machine = object;
    if (!g_strcmp0(interface, "memory")) {
        return &machine->alloc;
    }

    fprintf(stderr, "%s not present in x86_64/pc\n", interface);
    g_assert_not_reached();
}

static QOSGraphObject *pc_get_device(void *obj, const char *device)
{
    QX86PCMachine *machine = obj;
    if (!g_strcmp0(device, "i440FX-pcihost")) {
        return &machine->bridge.obj;
    }

    fprintf(stderr, "%s not present in x86_64/pc\n", device);
    g_assert_not_reached();
}

static void *qos_create_machine_pc(QTestState *qts)
{
    QX86PCMachine *machine = g_new0(QX86PCMachine, 1);

    /* Get node(s) contained inside (CONTAINS) */
    machine->obj.get_device = pc_get_device;

    /* Get node(s) produced (PRODUCES) */
    machine->obj.get_driver = pc_get_driver;

    /* free the object */
    machine->obj.destructor = pc_destructor;
    pc_alloc_init(&machine->alloc, qts, ALLOC_NO_FLAGS);

    /* Get node(s) contained inside (CONTAINS) */
    machine->bridge.obj.get_device = i440FX_host_get_device;

    return &machine->obj;
}

static void pc_machine_register_nodes(void)
{
    /* x86_64/pc --contains--> 1440FX-pcihost --contains-->
     * pci-bus-pc [--produces--> pci-bus (in pci.h)] */
    qos_node_create_machine("x86_64/pc", qos_create_machine_pc);
    qos_node_contains("x86_64/pc", "i440FX-pcihost", NULL);

    /* contained drivers don't need a constructor,
     * they will be init by the parent */
    qos_node_create_driver("i440FX-pcihost", NULL);
    qos_node_contains("i440FX-pcihost", "pci-bus-pc", NULL);
}

libqos_init(pc_machine_register_nodes);

sdhci taken from tests/qtest/libqos/sdhci.c:

/* Interface node, offers the sdhci API */
struct QSDHCI {
    uint16_t (*readw)(QSDHCI *s, uint32_t reg);
    uint64_t (*readq)(QSDHCI *s, uint32_t reg);
    void (*writeq)(QSDHCI *s, uint32_t reg, uint64_t val);
    /* other fields */
};

/* Memory Mapped implementation of QSDHCI */
struct QSDHCI_MemoryMapped {
    QOSGraphObject obj;
    QSDHCI sdhci;
    /* other driver-specific fields */
};

/* PCI implementation of QSDHCI */
struct QSDHCI_PCI {
    QOSGraphObject obj;
    QSDHCI sdhci;
    /* other driver-specific fields */
};

/* Memory mapped implementation of QSDHCI */

static void *sdhci_mm_get_driver(void *obj, const char *interface)
{
    QSDHCI_MemoryMapped *smm = obj;
    if (!g_strcmp0(interface, "sdhci")) {
        return &smm->sdhci;
    }
    fprintf(stderr, "%s not present in generic-sdhci\n", interface);
    g_assert_not_reached();
}

void qos_init_sdhci_mm(QSDHCI_MemoryMapped *sdhci, QTestState *qts,
                    uint32_t addr, QSDHCIProperties *common)
{
    /* Get node contained inside (CONTAINS) */
    sdhci->obj.get_driver = sdhci_mm_get_driver;

    /* SDHCI interface API */
    sdhci->sdhci.readw = sdhci_mm_readw;
    sdhci->sdhci.readq = sdhci_mm_readq;
    sdhci->sdhci.writeq = sdhci_mm_writeq;
    sdhci->qts = qts;
}

/* PCI implementation of QSDHCI */

static void *sdhci_pci_get_driver(void *object,
                                  const char *interface)
{
    QSDHCI_PCI *spci = object;
    if (!g_strcmp0(interface, "sdhci")) {
        return &spci->sdhci;
    }

    fprintf(stderr, "%s not present in sdhci-pci\n", interface);
    g_assert_not_reached();
}

static void *sdhci_pci_create(void *pci_bus,
                              QGuestAllocator *alloc,
                              void *addr)
{
    QSDHCI_PCI *spci = g_new0(QSDHCI_PCI, 1);
    QPCIBus *bus = pci_bus;
    uint64_t barsize;

    qpci_device_init(&spci->dev, bus, addr);

    /* SDHCI interface API */
    spci->sdhci.readw = sdhci_pci_readw;
    spci->sdhci.readq = sdhci_pci_readq;
    spci->sdhci.writeq = sdhci_pci_writeq;

    /* Get node(s) produced (PRODUCES) */
    spci->obj.get_driver = sdhci_pci_get_driver;

    spci->obj.start_hw = sdhci_pci_start_hw;
    spci->obj.destructor = sdhci_destructor;
    return &spci->obj;
}

static void qsdhci_register_nodes(void)
{
    QOSGraphEdgeOptions opts = {
        .extra_device_opts = "addr=04.0",
    };

    /* generic-sdhci */
    /* generic-sdhci --produces--> sdhci */
    qos_node_create_driver("generic-sdhci", NULL);
    qos_node_produces("generic-sdhci", "sdhci");

    /* sdhci-pci */
    /* sdhci-pci --produces--> sdhci
     * sdhci-pci --consumes--> pci-bus */
    qos_node_create_driver("sdhci-pci", sdhci_pci_create);
    qos_node_produces("sdhci-pci", "sdhci");
    qos_node_consumes("sdhci-pci", "pci-bus", &opts);
}

libqos_init(qsdhci_register_nodes);

In the above example, all possible types of relations are created:

x86_64/pc --contains--> 1440FX-pcihost --contains--> pci-bus-pc
                                                          |
             sdhci-pci --consumes--> pci-bus <--produces--+
                |
                +--produces--+
                             |
                             v
                           sdhci
                             ^
                             |
                             +--produces-- +
                                           |
             arm/raspi2b --contains--> generic-sdhci

or inverting the consumes edge in consumed_by:

x86_64/pc --contains--> 1440FX-pcihost --contains--> pci-bus-pc
                                                          |
          sdhci-pci <--consumed by-- pci-bus <--produces--+
              |
              +--produces--+
                           |
                           v
                          sdhci
                           ^
                           |
                           +--produces-- +
                                         |
          arm/raspi2b --contains--> generic-sdhci

Adding a new test

Given the above setup, adding a new test is very simple. sdhci-test, taken from tests/qtest/sdhci-test.c:

static void check_capab_sdma(QSDHCI *s, bool supported)
{
    uint64_t capab, capab_sdma;

    capab = s->readq(s, SDHC_CAPAB);
    capab_sdma = FIELD_EX64(capab, SDHC_CAPAB, SDMA);
    g_assert_cmpuint(capab_sdma, ==, supported);
}

static void test_registers(void *obj, void *data,
                            QGuestAllocator *alloc)
{
    QSDHCI *s = obj;

    /* example test */
    check_capab_sdma(s, s->props.capab.sdma);
}

static void register_sdhci_test(void)
{
    /* sdhci-test --consumes--> sdhci */
    qos_add_test("registers", "sdhci", test_registers, NULL);
}

libqos_init(register_sdhci_test);

Here a new test is created, consuming sdhci interface node and creating a valid path from both machines to a test. Final graph will be like this:

x86_64/pc --contains--> 1440FX-pcihost --contains--> pci-bus-pc
                                                          |
             sdhci-pci --consumes--> pci-bus <--produces--+
                |
                +--produces--+
                             |
                             v
                           sdhci <--consumes-- sdhci-test
                             ^
                             |
                             +--produces-- +
                                           |
             arm/raspi2b --contains--> generic-sdhci

or inverting the consumes edge in consumed_by:

x86_64/pc --contains--> 1440FX-pcihost --contains--> pci-bus-pc
                                                          |
          sdhci-pci <--consumed by-- pci-bus <--produces--+
              |
              +--produces--+
                           |
                           v
                          sdhci --consumed by--> sdhci-test
                           ^
                           |
                           +--produces-- +
                                         |
          arm/raspi2b --contains--> generic-sdhci

Assuming there the binary is QTEST_QEMU_BINARY=./qemu-system-x86_64 a valid test path will be: /x86_64/pc/1440FX-pcihost/pci-bus-pc/pci-bus/sdhci-pc/sdhci/sdhci-test

and for the binary QTEST_QEMU_BINARY=./qemu-system-arm:

/arm/raspi2b/generic-sdhci/sdhci/sdhci-test

Additional examples are also in test-qgraph.c

Qgraph API reference

.. kernel-doc:: tests/qtest/libqos/qgraph.h

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