[Qemu-devel] [RFC-PATCH] Introducing virtio-example device.

[Yoni Bettan]

The main goal is to add an example device to Qemu to be used as template or
guideline for contributors when they wish to create a new virtio device.

Another reason for this device is to document "the right way" to write
a new virtio device in Qemu.

This device is a simple device and its functionality is to increase its input
by 1.

The device driver is located at:
https://github.com/ybettan/QemuDeviceDrivers.git

In addition I am writing a blog to give a logical overview of the virtio
protocol and a step-by-step guide to write a new virtio device.
This blog can be found at https://howtovms.wordpress.com.

scripts/checkpatch.pl have some errors do to "//" (old style one line comment),
those lines contains FIXMEs for the next version and will be removed.

Signed-off-by: Yoni Bettan <address@hidden>
---
 hw/virtio/Makefile.objs                       |   1 +
 hw/virtio/virtio-example.c                    | 121 ++++++++++++++++++
 hw/virtio/virtio-pci.c                        |  49 +++++++
 hw/virtio/virtio-pci.h                        |  14 ++
 include/hw/pci/pci.h                          |   1 +
 include/hw/virtio/virtio-example.h            |  31 +++++
 .../standard-headers/linux/virtio_example.h   |   8 ++
 include/standard-headers/linux/virtio_ids.h   |   1 +
 8 files changed, 226 insertions(+)
 create mode 100644 hw/virtio/virtio-example.c
 create mode 100644 include/hw/virtio/virtio-example.h
 create mode 100644 include/standard-headers/linux/virtio_example.h

diff --git a/hw/virtio/Makefile.objs b/hw/virtio/Makefile.objs
index 1b2799cfd8..7a6fb2505c 100644
--- a/hw/virtio/Makefile.objs
+++ b/hw/virtio/Makefile.objs
@@ -7,6 +7,7 @@ common-obj-$(CONFIG_VIRTIO_PCI) += virtio-pci.o
 common-obj-$(CONFIG_VIRTIO_MMIO) += virtio-mmio.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio-balloon.o
 obj-$(CONFIG_VIRTIO_CRYPTO) += virtio-crypto.o
+obj-$(CONFIG_VIRTIO_CRYPTO) += virtio-example.o
 obj-$(call land,$(CONFIG_VIRTIO_CRYPTO),$(CONFIG_VIRTIO_PCI)) += 
virtio-crypto-pci.o
 
 obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o
diff --git a/hw/virtio/virtio-example.c b/hw/virtio/virtio-example.c
new file mode 100644
index 0000000000..3c170f8022
--- /dev/null
+++ b/hw/virtio/virtio-example.c
@@ -0,0 +1,121 @@
+/*
+ * A virtio device example.
+ *
+ * Copyright 2019 Red Hat, Inc.
+ * Copyright 2019 Yoni Bettan <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/iov.h"
+#include "hw/virtio/virtio.h"
+#include "hw/virtio/virtio-example.h"
+
+#define MAX_DATA_SIZE 10
+
+
+/*
+ * this function is called when the driver 'kick' the virtqueue.
+ * since we can have more than 1 virtqueue we need the vq argument in order to
+ * know which one was kicked by the driver.
+ */
+static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtQueueElement *elem;
+    int data, len;
+    char buf[MAX_DATA_SIZE];
+
+    /* check that virtqueue have at least 2 elements, input and output */
+    //FIXME: implement
+
+    /* get the virtqueue input element sent from the driver */
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+
+    /* read the input element (sg) into a buffer */
+    len = iov_to_buf(elem->in_sg, elem->out_num, 0, buf, MAX_DATA_SIZE);
+    //FIXME: should i check buffer overflow, or iov_to_buf() is safe ?
+    if (len > MAX_DATA_SIZE) {
+        goto error;
+    }
+
+    /* process the data */
+    data = atoi(buf);
+    sprintf(buf, "%d", ++data);
+
+    /* get the virtqueue output element sent from the driver */
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+
+    /* write the result to the output element (sg) */
+    len = iov_from_buf(elem->in_sg, elem->in_num, 0, buf, MAX_DATA_SIZE);
+    //FIXME: should i check buffer overflow, or iov_from_buf() is safe ?
+
+    /* push back the result into the virtqueue */
+    virtqueue_push(vq, elem, /*len=*/1);
+
+    /* interrupt the driver */
+    virtio_notify(vdev, vq);
+
+    return;
+
+error:
+    printf("ERROR: buffer overflow\n");
+    //FIXME: can we make the request fail ?, if iov_*_buf is safe we don't 
need it
+}
+
+/*
+ * There is no currently defined feature bits, we still need this function
+ * because the backend driver checks that VirtioDeviceClass.get_features is
+ * initialized
+ */
+static uint64_t get_features(VirtIODevice *vdev, uint64_t features, Error 
**errp)
+{
+    return features;
+}
+
+static void virtio_example_device_realize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtIOEXAMPLE *vexmp = VIRTIO_EXAMPLE(dev);
+
+    /* base class initialization */
+    virtio_init(vdev, "virtio-example", VIRTIO_ID_EXAMPLE, /*config_size=*/0);
+
+    /* this device suppot 1 virtqueue */
+    vexmp->vq = virtio_add_queue(vdev, 8, handle_input);
+}
+
+static void virtio_example_device_unrealize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+
+    /* base class cleanup */
+    virtio_cleanup(vdev);
+}
+
+static void virtio_example_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
+
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+    vdc->realize = virtio_example_device_realize;
+    vdc->unrealize = virtio_example_device_unrealize;
+    vdc->get_features = get_features;
+}
+
+static const TypeInfo virtio_example_info = {
+    .name = TYPE_VIRTIO_EXAMPLE,
+    .parent = TYPE_VIRTIO_DEVICE,
+    .instance_size = sizeof(VirtIOEXAMPLE),
+    .class_init = virtio_example_class_init,
+};
+
+static void virtio_register_types(void)
+{
+    type_register_static(&virtio_example_info);
+}
+
+type_init(virtio_register_types)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 3a01fe90f0..99fc6ce79b 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2521,6 +2521,54 @@ static const TypeInfo virtio_rng_pci_info = {
     .class_init    = virtio_rng_pci_class_init,
 };
 
+/* virtio-example-pci */
+
+static void virtio_example_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
+{
+    VirtIOExamplePCI *vexmp = VIRTIO_EXAMPLE_PCI(vpci_dev);
+    DeviceState *vdev = DEVICE(&vexmp->vdev);
+    Error *err = NULL;
+
+    qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
+    object_property_set_bool(OBJECT(vdev), true, "realized", &err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+
+}
+
+static void virtio_example_pci_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
+    PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
+
+    k->realize = virtio_example_pci_realize;
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+
+    pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
+    pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_EXAMPLE;
+    pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
+    pcidev_k->class_id = PCI_CLASS_OTHERS;
+}
+
+static void virtio_example_initfn(Object *obj)
+{
+    VirtIOExamplePCI *dev = VIRTIO_EXAMPLE_PCI(obj);
+
+    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
+                                TYPE_VIRTIO_EXAMPLE);
+}
+
+static const TypeInfo virtio_example_pci_info = {
+    .name          = TYPE_VIRTIO_EXAMPLE_PCI,
+    .parent        = TYPE_VIRTIO_PCI,
+    .instance_size = sizeof(VirtIOExamplePCI),
+    .instance_init = virtio_example_initfn,
+    .class_init    = virtio_example_pci_class_init,
+};
+
 /* virtio-input-pci */
 
 static Property virtio_input_pci_properties[] = {
@@ -2693,6 +2741,7 @@ static const TypeInfo virtio_pci_bus_info = {
 static void virtio_pci_register_types(void)
 {
     type_register_static(&virtio_rng_pci_info);
+    type_register_static(&virtio_example_pci_info);
     type_register_static(&virtio_input_pci_info);
     type_register_static(&virtio_input_hid_pci_info);
     type_register_static(&virtio_keyboard_pci_info);
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index 813082b0d7..db3f5ec17d 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -19,6 +19,7 @@
 #include "hw/virtio/virtio-blk.h"
 #include "hw/virtio/virtio-net.h"
 #include "hw/virtio/virtio-rng.h"
+#include "hw/virtio/virtio-example.h"
 #include "hw/virtio/virtio-serial.h"
 #include "hw/virtio/virtio-scsi.h"
 #include "hw/virtio/virtio-balloon.h"
@@ -51,6 +52,7 @@ typedef struct VHostSCSIPCI VHostSCSIPCI;
 typedef struct VHostUserSCSIPCI VHostUserSCSIPCI;
 typedef struct VHostUserBlkPCI VHostUserBlkPCI;
 typedef struct VirtIORngPCI VirtIORngPCI;
+typedef struct VirtIOExamplePCI VirtIOExamplePCI;
 typedef struct VirtIOInputPCI VirtIOInputPCI;
 typedef struct VirtIOInputHIDPCI VirtIOInputHIDPCI;
 typedef struct VirtIOInputHostPCI VirtIOInputHostPCI;
@@ -339,6 +341,18 @@ struct VirtIORngPCI {
     VirtIORNG vdev;
 };
 
+/*
+ * virtio-example-pci: This extends VirtioPCIProxy.
+ */
+#define TYPE_VIRTIO_EXAMPLE_PCI "virtio-example-pci"
+#define VIRTIO_EXAMPLE_PCI(obj) \
+        OBJECT_CHECK(VirtIOExamplePCI, (obj), TYPE_VIRTIO_EXAMPLE_PCI)
+
+struct VirtIOExamplePCI {
+    VirtIOPCIProxy parent_obj;
+    VirtIOEXAMPLE vdev;
+};
+
 /*
  * virtio-input-pci: This extends VirtioPCIProxy.
  */
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 990d6fcbde..c69d5997b7 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -83,6 +83,7 @@ extern bool pci_available;
 #define PCI_DEVICE_ID_VIRTIO_CONSOLE     0x1003
 #define PCI_DEVICE_ID_VIRTIO_SCSI        0x1004
 #define PCI_DEVICE_ID_VIRTIO_RNG         0x1005
+#define PCI_DEVICE_ID_VIRTIO_EXAMPLE     0x1006 //FIXME: update to valid ID
 #define PCI_DEVICE_ID_VIRTIO_9P          0x1009
 #define PCI_DEVICE_ID_VIRTIO_VSOCK       0x1012
 
diff --git a/include/hw/virtio/virtio-example.h 
b/include/hw/virtio/virtio-example.h
new file mode 100644
index 0000000000..c08db28e8f
--- /dev/null
+++ b/include/hw/virtio/virtio-example.h
@@ -0,0 +1,31 @@
+/*
+ * Virtio EXAMPLE Support
+ *
+ * Copyright Red Hat, Inc. 2019
+ * Copyright Yoni Bettan <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#ifndef QEMU_VIRTIO_EXAMPLE_H
+#define QEMU_VIRTIO_EXAMPLE_H
+
+#include "standard-headers/linux/virtio_example.h"
+
+#define TYPE_VIRTIO_EXAMPLE "virtio-example-device"
+#define VIRTIO_EXAMPLE(obj) \
+        OBJECT_CHECK(VirtIOEXAMPLE, (obj), TYPE_VIRTIO_EXAMPLE)
+#define VIRTIO_EXAMPLE_GET_PARENT_CLASS(obj) \
+        OBJECT_GET_PARENT_CLASS(obj, TYPE_VIRTIO_EXAMPLE)
+
+typedef struct VirtIOEXAMPLE {
+    VirtIODevice parent_obj;
+
+    /* Only one vq - guest puts buffer(s) on it when it needs computation */
+    VirtQueue *vq;
+
+} VirtIOEXAMPLE;
+
+#endif
diff --git a/include/standard-headers/linux/virtio_example.h 
b/include/standard-headers/linux/virtio_example.h
new file mode 100644
index 0000000000..6321c60c5c
--- /dev/null
+++ b/include/standard-headers/linux/virtio_example.h
@@ -0,0 +1,8 @@
+#ifndef _LINUX_VIRTIO_EXAMPLE_H
+#define _LINUX_VIRTIO_EXAMPLE_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers. */
+#include "standard-headers/linux/virtio_ids.h"
+#include "standard-headers/linux/virtio_config.h"
+
+#endif /* _LINUX_VIRTIO_EXAMPLE_H */
diff --git a/include/standard-headers/linux/virtio_ids.h 
b/include/standard-headers/linux/virtio_ids.h
index 6d5c3b2d4f..30c189303b 100644
--- a/include/standard-headers/linux/virtio_ids.h
+++ b/include/standard-headers/linux/virtio_ids.h
@@ -43,5 +43,6 @@
 #define VIRTIO_ID_INPUT        18 /* virtio input */
 #define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
 #define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
+#define VIRTIO_ID_EXAMPLE      21 /* virtio example */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
-- 
2.17.2