[Xen-devel] [PATCH RFC 1/3] virtio infrastructure

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

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 details of probing the device are left to hypervisor-specific
code: it simple constructs the "struct virtio_device" and hands it to
the probe function (eg. virtnet_probe() or virtblk_probe()).

The virtio drivers add and detach input and output buffers; as the
buffers are used up their associated "used" pointers are filled in.

I have written two virtio device drivers (net and block) and two
virtio implementations (for lguest): a read-write socket-style
implementation, and a more efficient descriptor-based implementation).

Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
 include/linux/virtio.h |   69 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff -r 2db2135723b0 include/linux/virtio.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/include/linux/virtio.h    Thu May 31 17:52:19 2007 +1000
@@ -0,0 +1,66 @@
+#ifndef _LINUX_VIRTIO_H
+#define _LINUX_VIRTIO_H
+#include <linux/types.h>
+#include <linux/scatterlist.h>
+
+/**
+ * virtio_device - description and routines to drive a virtual device.
+ * @dev: the underlying struct device.
+ * @ops: the operations for this virtual device.
+ */
+struct virtio_device {
+       struct device *dev;
+       struct virtio_ops *ops;
+};
+
+/**
+ * virtio_ops - virtio abstraction layer
+ * @add_outbuf: prepare to send data to the other end:
+ *     vdev: the virtio_device
+ *     sg: the description of the buffer(s).
+ *     num: the size of the sg array.
+ *     used: the length sent (set once sending is done).
+ *      Returns an identifier or an error.
+ * @add_inbuf: prepare to receive data from the other end:
+ *     vdev: the virtio_device
+ *     sg: the description of the buffer(s).
+ *     num: the size of the sg array.
+ *     used: the length sent (set once data received).
+ *      Returns an identifier or an error (eg. -ENOSPC).
+ * @sync: update after add_inbuf/add_outbuf
+ *     vdev: the virtio_device we're talking about.
+ *     Use the virtio_sync wrapper, to avoid unnecessary calls.
+ * @detach_outbuf: make sure sent sg can no longer be read.
+ *     vdev: the virtio_device we're talking about.
+ *     id: the identifier returned from add_outbuf.
+ * @detach_inbuf: make sure sent sg can no longer be written to.
+ *     vdev: the virtio_device we're talking about.
+ *     id: the identifier returned from add_inbuf.
+ */
+struct virtio_ops {
+       unsigned long (*add_outbuf)(struct virtio_device *vdev,
+                                   const struct scatterlist sg[],
+                                   unsigned int num,
+                                   unsigned long *used);
+
+       unsigned long (*add_inbuf)(struct virtio_device *vdev,
+                                  struct scatterlist sg[],
+                                  unsigned int num,
+                                  unsigned long *used);
+
+       void (*sync)(struct virtio_device *vdev);
+
+       void (*detach_outbuf)(struct virtio_device *vdev, unsigned long id);
+       void (*detach_inbuf)(struct virtio_device *vdev, unsigned long id);
+};
+
+/**
+ * virtio_sync - start sending/receiving data from the other end.
+ * @vdev: the virtio_device we're talking about.
+ */
+static inline void virtio_sync(struct virtio_device *vdev)
+{
+       if (vdev->ops->sync)
+               vdev->ops->sync(vdev);
+}
+#endif /* _LINUX_VIRTIO_H */



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