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Date: Tue, 30 Apr 2019 09:45:02 +0200
From: Jens Freimann <jfreimann@...hat.com>
To: Yoni Bettan <ybettan@...hat.com>
Cc: virtualization@...ts.linux-foundation.org, ehabkost@...hat.com,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC-PATCH] Introducing virtio-example.
On Mon, Apr 29, 2019 at 03:40:03PM +0300, Yoni Bettan wrote:
>The main goal is to create an example to be used as template or
>guideline for contributors when they wish to create a new virtio
>device and to document "the right way" to do so.
>
>It consists of several parts:
Thanks for doing this, I think it's a good idea.
> 1. The device specification
> * it can be found in the device header of the implementation
> * it will hopefully be added to the official virtio specification
>
> 2. The device implementation for Qemu-KVM hypervisor
> * it can be found at https://github.com/ybettan/qemu/blob/virtio\
> /hw/virtio/virtio-example.c
>
> 3. The device driver for linux
> * this patch content
>
> 4. A blog on virtio
> * introducing the virtio concept
> * gives some motivation for virtio-devices to be used
> * bring extra documentation on "how to write":
> - device specification
> - device implementation
> - device driver for linux
> * it can be found at https://howtovms.wordpress.com
Maybe add a link to the blog in the example code? Or better put a
text-only version of it into Documentation/ (Not sure it's a good
idea, just thinking out loud...)
>
>Signed-off-by: Yoni Bettan <ybettan@...hat.com>
>---
> samples/virtio/Makefile | 1 +
> samples/virtio/virtio_example_driver.c | 239 +++++++++++++++++++++++++
> 2 files changed, 240 insertions(+)
> create mode 100644 samples/virtio/Makefile
> create mode 100644 samples/virtio/virtio_example_driver.c
>
>diff --git a/samples/virtio/Makefile b/samples/virtio/Makefile
>new file mode 100644
>index 000000000000..6f3cc811ca89
>--- /dev/null
>+++ b/samples/virtio/Makefile
>@@ -0,0 +1 @@
>+obj-m := virtio_example_driver.o
>diff --git a/samples/virtio/virtio_example_driver.c b/samples/virtio/virtio_example_driver.c
>new file mode 100644
>index 000000000000..2f5a354009a1
>--- /dev/null
>+++ b/samples/virtio/virtio_example_driver.c
>@@ -0,0 +1,239 @@
>+/*
>+ * Virtio example implementation.
>+ *
>+ * Copyright 2019 Yoni Bettan Red Hat Corporation
>+ *
>+ * This program is free software; you can redistribute it and/or modify
>+ * it under the terms of the GNU General Public License as published by
>+ * the Free Software Foundation; either version 2 of the License, or
>+ * (at your option) any later version.
>+ *
>+ * This program is distributed in the hope that it will be useful,
>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>+ * GNU General Public License for more details.
>+ */
>+
>+#include <linux/virtio.h>
>+#include <linux/module.h>
>+#include <linux/device.h>
>+#include <linux/pci.h>
>+#include <linux/interrupt.h>
>+#include <linux/io.h> /* io map */
>+#include <linux/dma-mapping.h> /* DMA */
>+#include <linux/kernel.h> /* kstrtoint() func */
>+#include <linux/virtio_config.h> /* find_single_vq() func */
>+
>+
>+#define VIRTIO_ID_EXAMPLE 21
>+/* big enough to contain a string representing an integer */
>+#define MAX_DATA_SIZE 20
>+
>+struct virtexample_info {
>+ struct virtqueue *vq;
>+ /*
>+ * in - the data we get from the device
>+ * out - the data we send to the device
>+ */
>+ int in, out;
>+};
>+
>+
>+
>+//-----------------------------------------------------------------------------
>+// sysfs - give user access to driver
>+//-----------------------------------------------------------------------------
>+
>+static ssize_t
>+virtio_buf_store(struct device *dev, struct device_attribute *attr,
>+ const char *buf, size_t count)
>+{
>+ char tmp_buf[MAX_DATA_SIZE];
>+ int retval;
>+ struct scatterlist sg_in, sg_out;
>+ struct scatterlist *request[2];
>+ /* cast dev into a virtio_device */
>+ struct virtio_device *vdev = dev_to_virtio(dev);
>+ struct virtexample_info *vi = vdev->priv;
Indentation is off here and in many other places.
>+
>+ /* copy the user buffer since it is a const buffer */
>+ sprintf(tmp_buf, "%s", buf);
>+
>+ /* convert the data into an integer */
>+ retval = kstrtoint(tmp_buf, 10, &vi->out);
>+ if (retval) {
>+ pr_alert("string converstion failed with error: %d\n", retval);
>+ }
>+
>+ /* initialize a single entry sg lists, one for input and one for output */
>+ sg_init_one(&sg_out, &vi->out, sizeof(int));
>+ sg_init_one(&sg_in, &vi->in, sizeof(int));
>+
>+ /* build the request */
>+ request[0] = &sg_out;
>+ request[1] = &sg_in;
>+
>+ /* add the request to the queue, in_buf is sent as the buffer idetifier */
>+ virtqueue_add_sgs(vi->vq, request, 1, 1, &vi->in, GFP_KERNEL);
>+
>+ /* notify the device */
>+ virtqueue_kick(vi->vq);
>+
>+ return count;
>+}
>+
>+static ssize_t
>+virtio_buf_show(struct device *dev, struct device_attribute *attr, char *buf)
>+{
>+ /* cast dev into a virtio_device */
>+ struct virtio_device *vdev = dev_to_virtio(dev);
>+ struct virtexample_info *vi = vdev->priv;
>+
>+ return sprintf(buf, "%d\n", vi->in);
>+}
>+
>+/*
>+ * struct device_attribute dev_attr_virtio_buf = {
>+ * .attr = {
>+ * .name = "virtio_buf",
>+ * .mode = 0644
>+ * },
>+ * .show = virtio_buf_show,
>+ * .store = virtio_buf_store
>+ * }
>+ */
>+static DEVICE_ATTR_RW(virtio_buf);
>+
>+
>+/*
>+ * The example_attr defined above is then grouped in the struct attribute group
>+ * as follows:
>+ */
>+struct attribute *example_attrs[] = {
>+ &dev_attr_virtio_buf.attr,
>+ NULL,
>+};
>+
>+static const struct attribute_group example_attr_group = {
>+ .name = "example", /* directory's name */
>+ .attrs = example_attrs,
>+};
>+
>+
>+
>+//-----------------------------------------------------------------------------
>+// IRQ functions
>+//-----------------------------------------------------------------------------
>+
>+static void example_irq_handler(struct virtqueue *vq)
>+{
>+
>+ struct virtexample_info *vi = vq->vdev->priv;
>+ unsigned int len;
>+ int *res = NULL;
>+
>+ /* get the buffer from virtqueue */
>+ res = virtqueue_get_buf(vi->vq, &len);
check for res!=NULL?
>+
>+ vi->in = *res;
>+}
>+
>+
>+//-----------------------------------------------------------------------------
>+// driver functions
>+//-----------------------------------------------------------------------------
>+
>+
>+static int example_probe(struct virtio_device *vdev)
>+{
>+ int retval;
>+ struct virtexample_info *vi = NULL;
>+
>+ /* create sysfiles for UI */
>+ retval = sysfs_create_group(&vdev->dev.kobj, &example_attr_group);
>+ if (retval) {
>+ pr_alert("failed to create group in /sys/bus/virtio/devices/.../\n");
Should an error value be returned here?
>+ }
>+
>+ /* initialize driver data */
>+ vi = kzalloc(sizeof(struct virtexample_info), GFP_KERNEL);
>+ if (!vi)
>+ return -ENOMEM;
>+
>+ /* We expect a single virtqueue. */
>+ vi->vq = virtio_find_single_vq(vdev, example_irq_handler, "input");
>+ if (IS_ERR(vi->vq)) {
>+ pr_alert("failed to connect to the device virtqueue\n");
same here
regards,
Jens
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