Virtio interface

This attempts to implement a "virtual I/O" layer which should allow
common drivers to be efficiently used across most virtual I/O
mechanisms.  It will no-doubt need further enhancement.

The virtio drivers add buffers to virtio queues; as the buffers are consumed
the driver "interrupt" callbacks are invoked.

There is also a generic implementation of config space which drivers can query
to get setup information from the host.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Dor Laor <dor.laor@qumranet.com>
Cc: Arnd Bergmann <arnd@arndb.de>

drivers/virtio/Kconfig

@@ -0,0 +1,3 @@
+# Virtio always gets selected by whoever wants it.
+config VIRTIO
+	bool

drivers/virtio/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_VIRTIO) += virtio.o

drivers/virtio/config.c

@@ -0,0 +1,13 @@
+/* Configuration space parsing helpers for virtio.
+ *
+ * The configuration is [type][len][... len bytes ...] fields.
+ *
+ * Copyright 2007 Rusty Russell, IBM Corporation.
+ * GPL v2 or later.
+ */
+#include <linux/err.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/bug.h>
+#include <asm/system.h>
+

drivers/virtio/virtio.c

@@ -0,0 +1,171 @@
+#include <linux/virtio.h>
+#include <linux/spinlock.h>
+#include <linux/virtio_config.h>
+
+static ssize_t device_show(struct device *_d,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtio_device *dev = container_of(_d,struct virtio_device,dev);
+	return sprintf(buf, "%hu", dev->id.device);
+}
+static ssize_t vendor_show(struct device *_d,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtio_device *dev = container_of(_d,struct virtio_device,dev);
+	return sprintf(buf, "%hu", dev->id.vendor);
+}
+static ssize_t status_show(struct device *_d,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtio_device *dev = container_of(_d,struct virtio_device,dev);
+	return sprintf(buf, "0x%08x", dev->config->get_status(dev));
+}
+static struct device_attribute virtio_dev_attrs[] = {
+	__ATTR_RO(device),
+	__ATTR_RO(vendor),
+	__ATTR_RO(status),
+	__ATTR_NULL
+};
+
+static inline int virtio_id_match(const struct virtio_device *dev,
+				  const struct virtio_device_id *id)
+{
+	if (id->device != dev->id.device)
+		return 0;
+
+	return id->vendor == VIRTIO_DEV_ANY_ID || id->vendor != dev->id.vendor;
+}
+
+/* This looks through all the IDs a driver claims to support.  If any of them
+ * match, we return 1 and the kernel will call virtio_dev_probe(). */
+static int virtio_dev_match(struct device *_dv, struct device_driver *_dr)
+{
+	unsigned int i;
+	struct virtio_device *dev = container_of(_dv,struct virtio_device,dev);
+	const struct virtio_device_id *ids;
+
+	ids = container_of(_dr, struct virtio_driver, driver)->id_table;
+	for (i = 0; ids[i].device; i++)
+		if (virtio_id_match(dev, &ids[i]))
+			return 1;
+	return 0;
+}
+
+static struct bus_type virtio_bus = {
+	.name  = "virtio",
+	.match = virtio_dev_match,
+	.dev_attrs = virtio_dev_attrs,
+};
+
+static void add_status(struct virtio_device *dev, unsigned status)
+{
+	dev->config->set_status(dev, dev->config->get_status(dev) | status);
+}
+
+static int virtio_dev_probe(struct device *_d)
+{
+	int err;
+	struct virtio_device *dev = container_of(_d,struct virtio_device,dev);
+	struct virtio_driver *drv = container_of(dev->dev.driver,
+						 struct virtio_driver, driver);
+
+	add_status(dev, VIRTIO_CONFIG_S_DRIVER);
+	err = drv->probe(dev);
+	if (err)
+		add_status(dev, VIRTIO_CONFIG_S_FAILED);
+	else
+		add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
+	return err;
+}
+
+int register_virtio_driver(struct virtio_driver *driver)
+{
+	driver->driver.bus = &virtio_bus;
+	driver->driver.probe = virtio_dev_probe;
+	return driver_register(&driver->driver);
+}
+EXPORT_SYMBOL_GPL(register_virtio_driver);
+
+void unregister_virtio_driver(struct virtio_driver *driver)
+{
+	driver_unregister(&driver->driver);
+}
+EXPORT_SYMBOL_GPL(unregister_virtio_driver);
+
+int register_virtio_device(struct virtio_device *dev)
+{
+	int err;
+
+	dev->dev.bus = &virtio_bus;
+	sprintf(dev->dev.bus_id, "%u", dev->index);
+
+	/* Acknowledge that we've seen the device. */
+	add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
+
+	/* device_register() causes the bus infrastructure to look for a
+	 * matching driver. */
+	err = device_register(&dev->dev);
+	if (err)
+		add_status(dev, VIRTIO_CONFIG_S_FAILED);
+	return err;
+}
+EXPORT_SYMBOL_GPL(register_virtio_device);
+
+void unregister_virtio_device(struct virtio_device *dev)
+{
+	device_unregister(&dev->dev);
+}
+EXPORT_SYMBOL_GPL(unregister_virtio_device);
+
+int __virtio_config_val(struct virtio_device *vdev,
+			u8 type, void *val, size_t size)
+{
+	void *token;
+	unsigned int len;
+
+	token = vdev->config->find(vdev, type, &len);
+	if (!token)
+		return -ENOENT;
+
+	if (len != size)
+		return -EIO;
+
+	vdev->config->get(vdev, token, val, size);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__virtio_config_val);
+
+int virtio_use_bit(struct virtio_device *vdev,
+		   void *token, unsigned int len, unsigned int bitnum)
+{
+	unsigned long bits[16];
+
+	/* This makes it convenient to pass-through find() results. */
+	if (!token)
+		return 0;
+
+	/* bit not in range of this bitfield? */
+	if (bitnum * 8 >= len / 2)
+		return 0;
+
+	/* Giant feature bitfields are silly. */
+	BUG_ON(len > sizeof(bits));
+	vdev->config->get(vdev, token, bits, len);
+
+	if (!test_bit(bitnum, bits))
+		return 0;
+
+	/* Set acknowledge bit, and write it back. */
+	set_bit(bitnum + len * 8 / 2, bits);
+	vdev->config->set(vdev, token, bits, len);
+	return 1;
+}
+EXPORT_SYMBOL_GPL(virtio_use_bit);
+
+static int virtio_init(void)
+{
+	if (bus_register(&virtio_bus) != 0)
+		panic("virtio bus registration failed");
+	return 0;
+}
+core_initcall(virtio_init);