virtio: Introduce vringh wrappers in virtio_config

Add wrappers for the host vrings to support loose
coupling between the virtio device and driver.

A new struct vringh_config_ops with the functions
find_vrhs() and del_vrhs() is added to the virtio_device
struct. This enables virtio drivers to manage virtio
host rings without detailed knowledge of how the
vrings are created and deleted.

The function vringh_notify() is added so vringh clients
can notify the other side that buffers are added to the
used-ring.

Cc: Ohad Ben-Cohen <ohad@wizery.com>
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (constified vringh_config)

include/linux/virtio.h

@@ -8,6 +8,7 @@
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
 #include <linux/gfp.h>
+#include <linux/vringh.h>
 
 /**
  * virtqueue - a queue to register buffers for sending or receiving.
@@ -70,6 +71,7 @@ static inline unsigned int virtqueue_get_queue_index(struct virtqueue *vq)
  * @dev: underlying device.
  * @id: the device type identification (used to match it with a driver).
  * @config: the configuration ops for this device.
+ * @vringh_config: configuration ops for host vrings.
  * @vqs: the list of virtqueues for this device.
  * @features: the features supported by both driver and device.
  * @priv: private pointer for the driver's use.
@@ -79,6 +81,7 @@ struct virtio_device {
 	struct device dev;
 	struct virtio_device_id id;
 	const struct virtio_config_ops *config;
+	const struct vringh_config_ops *vringh_config;
 	struct list_head vqs;
 	/* Note that this is a Linux set_bit-style bitmap. */
 	unsigned long features[1];

include/linux/vringh.h

@@ -47,6 +47,28 @@ struct vringh {
 
 	/* The vring (note: it may contain user pointers!) */
 	struct vring vring;
+
+	/* The function to call to notify the guest about added buffers */
+	void (*notify)(struct vringh *);
+};
+
+/**
+ * struct vringh_config_ops - ops for creating a host vring from a virtio driver
+ * @find_vrhs: find the host vrings and instantiate them
+ *	vdev: the virtio_device
+ *	nhvrs: the number of host vrings to find
+ *	hvrs: on success, includes new host vrings
+ *	callbacks: array of driver callbacks, for each host vring
+ *		include a NULL entry for vqs that do not need a callback
+ *	Returns 0 on success or error status
+ * @del_vrhs: free the host vrings found by find_vrhs().
+ */
+struct virtio_device;
+typedef void vrh_callback_t(struct virtio_device *, struct vringh *);
+struct vringh_config_ops {
+	int (*find_vrhs)(struct virtio_device *vdev, unsigned nhvrs,
+			 struct vringh *vrhs[], vrh_callback_t *callbacks[]);
+	void (*del_vrhs)(struct virtio_device *vdev);
 };
 
 /* The memory the vring can access, and what offset to apply. */
@@ -193,4 +215,11 @@ void vringh_notify_disable_kern(struct vringh *vrh);
 
 int vringh_need_notify_kern(struct vringh *vrh);
 
+/* Notify the guest about buffers added to the used ring */
+static inline void vringh_notify(struct vringh *vrh)
+{
+	if (vrh->notify)
+		vrh->notify(vrh);
+}
+
 #endif /* _LINUX_VRINGH_H */