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>

4 files changed, 228 insertions, 0 deletions

diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 7588345..e5208f2 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -343,6 +343,7 @@ unifdef-y += user.h
 unifdef-y += utsname.h
 unifdef-y += videodev2.h
 unifdef-y += videodev.h
+unifdef-y += virtio_config.h
 unifdef-y += wait.h
 unifdef-y += wanrouter.h
 unifdef-y += watchdog.h
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 522b0dd..e9fddb4 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -361,4 +361,10 @@ struct ssb_device_id {
 #define SSB_ANY_ID		0xFFFF
 #define SSB_ANY_REV		0xFF
 
+struct virtio_device_id {
+	__u32 device;
+	__u32 vendor;
+};
+#define VIRTIO_DEV_ANY_ID	0xffffffff
+
 #endif /* LINUX_MOD_DEVICETABLE_H */
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
new file mode 100644
index 0000000..14e1379
--- /dev/null
+++ b/include/linux/virtio.h
@@ -0,0 +1,110 @@
+#ifndef _LINUX_VIRTIO_H
+#define _LINUX_VIRTIO_H
+/* Everything a virtio driver needs to work with any particular virtio
+ * implementation. */
+#include <linux/types.h>
+#include <linux/scatterlist.h>
+#include <linux/spinlock.h>
+#include <linux/device.h>
+#include <linux/mod_devicetable.h>
+
+/**
+ * virtqueue - a queue to register buffers for sending or receiving.
+ * @callback: the function to call when buffers are consumed (can be NULL).
+ *    If this returns false, callbacks are suppressed until vq_ops->restart
+ *    is called.
+ * @vdev: the virtio device this queue was created for.
+ * @vq_ops: the operations for this virtqueue (see below).
+ * @priv: a pointer for the virtqueue implementation to use.
+ */
+struct virtqueue
+{
+	bool (*callback)(struct virtqueue *vq);
+	struct virtio_device *vdev;
+	struct virtqueue_ops *vq_ops;
+	void *priv;
+};
+
+/**
+ * virtqueue_ops - operations for virtqueue abstraction layer
+ * @add_buf: expose buffer to other end
+ *	vq: the struct virtqueue we're talking about.
+ *	sg: the description of the buffer(s).
+ *	out_num: the number of sg readable by other side
+ *	in_num: the number of sg which are writable (after readable ones)
+ *	data: the token identifying the buffer.
+ *      Returns 0 or an error.
+ * @kick: update after add_buf
+ *	vq: the struct virtqueue
+ *	After one or more add_buf calls, invoke this to kick the other side.
+ * @get_buf: get the next used buffer
+ *	vq: the struct virtqueue we're talking about.
+ *	len: the length written into the buffer
+ *	Returns NULL or the "data" token handed to add_buf.
+ * @restart: restart callbacks after callback returned false.
+ *	vq: the struct virtqueue we're talking about.
+ *	This returns "false" (and doesn't re-enable) if there are pending
+ *	buffers in the queue, to avoid a race.
+ * @shutdown: "unadd" all buffers.
+ *	vq: the struct virtqueue we're talking about.
+ *	Remove everything from the queue.
+ *
+ * Locking rules are straightforward: the driver is responsible for
+ * locking.  No two operations may be invoked simultaneously.
+ *
+ * All operations can be called in any context.
+ */
+struct virtqueue_ops {
+	int (*add_buf)(struct virtqueue *vq,
+		       struct scatterlist sg[],
+		       unsigned int out_num,
+		       unsigned int in_num,
+		       void *data);
+
+	void (*kick)(struct virtqueue *vq);
+
+	void *(*get_buf)(struct virtqueue *vq, unsigned int *len);
+
+	bool (*restart)(struct virtqueue *vq);
+
+	void (*shutdown)(struct virtqueue *vq);
+};
+
+/**
+ * virtio_device - representation of a device using virtio
+ * @index: unique position on the virtio bus
+ * @dev: underlying device.
+ * @id: the device type identification (used to match it with a driver).
+ * @config: the configuration ops for this device.
+ * @priv: private pointer for the driver's use.
+ */
+struct virtio_device
+{
+	int index;
+	struct device dev;
+	struct virtio_device_id id;
+	struct virtio_config_ops *config;
+	void *priv;
+};
+
+int register_virtio_device(struct virtio_device *dev);
+void unregister_virtio_device(struct virtio_device *dev);
+
+/**
+ * virtio_driver - operations for a virtio I/O driver
+ * @driver: underlying device driver (populate name and owner).
+ * @id_table: the ids serviced by this driver.
+ * @probe: the function to call when a device is found.  Returns a token for
+ *    remove, or PTR_ERR().
+ * @remove: the function when a device is removed.
+ */
+struct virtio_driver {
+	struct device_driver driver;
+	const struct virtio_device_id *id_table;
+	int (*probe)(struct virtio_device *dev);
+	void (*remove)(struct virtio_device *dev);
+};
+
+int register_virtio_driver(struct virtio_driver *drv);
+void unregister_virtio_driver(struct virtio_driver *drv);
+#endif /* _LINUX_VIRTIO_H */
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
new file mode 100644
index 0000000..bcc0188
--- /dev/null
+++ b/include/linux/virtio_config.h
@@ -0,0 +1,111 @@
+#ifndef _LINUX_VIRTIO_CONFIG_H
+#define _LINUX_VIRTIO_CONFIG_H
+/* Virtio devices use a standardized configuration space to define their
+ * features and pass configuration information, but each implementation can
+ * store and access that space differently. */
+#include <linux/types.h>
+
+/* Status byte for guest to report progress, and synchronize config. */
+/* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */
+#define VIRTIO_CONFIG_S_ACKNOWLEDGE	1
+/* We have found a driver for the device. */
+#define VIRTIO_CONFIG_S_DRIVER		2
+/* Driver has used its parts of the config, and is happy */
+#define VIRTIO_CONFIG_S_DRIVER_OK	4
+/* We've given up on this device. */
+#define VIRTIO_CONFIG_S_FAILED		0x80
+
+/* Feature byte (actually 7 bits availabe): */
+/* Requirements/features of the virtio implementation. */
+#define VIRTIO_CONFIG_F_VIRTIO 1
+/* Requirements/features of the virtqueue (may have more than one). */
+#define VIRTIO_CONFIG_F_VIRTQUEUE 2
+
+#ifdef __KERNEL__
+struct virtio_device;
+
+/**
+ * virtio_config_ops - operations for configuring a virtio device
+ * @find: search for the next configuration field of the given type.
+ *	vdev: the virtio_device
+ *	type: the feature type
+ *	len: the (returned) length of the field if found.
+ *	Returns a token if found, or NULL.  Never returnes the same field twice
+ *	(ie. it's used up).
+ * @get: read the value of a configuration field after find().
+ *	vdev: the virtio_device
+ *	token: the token returned from find().
+ *	buf: the buffer to write the field value into.
+ *	len: the length of the buffer (given by find()).
+ *	Note that contents are conventionally little-endian.
+ * @set: write the value of a configuration field after find().
+ *	vdev: the virtio_device
+ *	token: the token returned from find().
+ *	buf: the buffer to read the field value from.
+ *	len: the length of the buffer (given by find()).
+ *	Note that contents are conventionally little-endian.
+ * @get_status: read the status byte
+ *	vdev: the virtio_device
+ *	Returns the status byte
+ * @set_status: write the status byte
+ *	vdev: the virtio_device
+ *	status: the new status byte
+ * @find_vq: find the first VIRTIO_CONFIG_F_VIRTQUEUE and create a virtqueue.
+ *	vdev: the virtio_device
+ *	callback: the virqtueue callback
+ *	Returns the new virtqueue or ERR_PTR().
+ * @del_vq: free a virtqueue found by find_vq().
+ */
+struct virtio_config_ops
+{
+	void *(*find)(struct virtio_device *vdev, u8 type, unsigned *len);
+	void (*get)(struct virtio_device *vdev, void *token,
+		    void *buf, unsigned len);
+	void (*set)(struct virtio_device *vdev, void *token,
+		    const void *buf, unsigned len);
+	u8 (*get_status)(struct virtio_device *vdev);
+	void (*set_status)(struct virtio_device *vdev, u8 status);
+	struct virtqueue *(*find_vq)(struct virtio_device *vdev,
+				     bool (*callback)(struct virtqueue *));
+	void (*del_vq)(struct virtqueue *vq);
+};
+
+/**
+ * virtio_config_val - get a single virtio config and mark it used.
+ * @config: the virtio config space
+ * @type: the type to search for.
+ * @val: a pointer to the value to fill in.
+ *
+ * Once used, the config type is marked with VIRTIO_CONFIG_F_USED so it can't
+ * be found again.  This version does endian conversion. */
+#define virtio_config_val(vdev, type, v) ({				\
+	int _err = __virtio_config_val((vdev),(type),(v),sizeof(*(v))); \
+									\
+	BUILD_BUG_ON(sizeof(*(v)) != 1 && sizeof(*(v)) != 2		\
+		     && sizeof(*(v)) != 4 && sizeof(*(v)) != 8);	\
+	if (!_err) {							\
+		switch (sizeof(*(v))) {					\
+		case 2: le16_to_cpus((__u16 *) v); break;		\
+		case 4: le32_to_cpus((__u32 *) v); break;		\
+		case 8: le64_to_cpus((__u64 *) v); break;		\
+		}							\
+	}								\
+	_err;								\
+})
+
+int __virtio_config_val(struct virtio_device *dev,
+			u8 type, void *val, size_t size);
+
+/**
+ * virtio_use_bit - helper to use a feature bit in a bitfield value.
+ * @dev: the virtio device
+ * @token: the token as returned from vdev->config->find().
+ * @len: the length of the field.
+ * @bitnum: the bit to test.
+ *
+ * If handed a NULL token, it returns false, otherwise returns bit status.
+ * If it's one, it sets the mirroring acknowledgement bit. */
+int virtio_use_bit(struct virtio_device *vdev,
+		   void *token, unsigned int len, unsigned int bitnum);
+#endif /* __KERNEL__ */
+#endif /* _LINUX_VIRTIO_CONFIG_H */