docs/devel/qgraph.rst - qemu - Git at Google

 .. _qgraph:

 ========================================
 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 compability 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.

 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/raspi2``
 - **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.

 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-raspi2``) 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/raspi2`` machine node. This machine ``contains``
   a ``generic-sdhci`` memory mapped ``sdhci`` driver node, representing
   ``QSDHCI_MemoryMapped``.

   ``arm/raspi2 --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-raspi2`` 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/raspi2\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/raspi2\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/raspi2 --contains--> generic-sdhci */
         qos_node_create_machine("arm/raspi2",
                                  qos_create_machine_arm_raspi2);
         qos_node_contains("arm/raspi2", "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/raspi2 --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/raspi2 --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/raspi2 --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/raspi2 --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/raspi2/generic-sdhci/sdhci/sdhci-test``

 Additional examples are also in ``test-qgraph.c``

 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``

 Qgraph API reference
 ^^^^^^^^^^^^^^^^^^^^

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

	========================================
	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 compability 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.

	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/raspi2``
	- 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.

	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-raspi2``) 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/raspi2`` machine node. This machine ``contains``
	a ``generic-sdhci`` memory mapped ``sdhci`` driver node, representing
	``QSDHCI_MemoryMapped``.

	``arm/raspi2 --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-raspi2`` 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/raspi2\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/raspi2\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/raspi2 --contains--> generic-sdhci */
	qos_node_create_machine("arm/raspi2",
	qos_create_machine_arm_raspi2);
	qos_node_contains("arm/raspi2", "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/raspi2 --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/raspi2 --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/raspi2 --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/raspi2 --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/raspi2/generic-sdhci/sdhci/sdhci-test``

	Additional examples are also in ``test-qgraph.c``

	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``

	Qgraph API reference
	^^^^^^^^^^^^^^^^^^^^

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