[RFC v3 4/8] virtio: Define the pasta vhost interface

[Ammar Yasser <aerosound161@gmail.com>]

- Include the ioctls needed in opening, initializing and registering
  queues and fds with vhost-net
- Create the vq_state type which represents from pasta's perspective our
  state of virtqueue processing
- Define the structures that will represent the actual descriptor
  queues: vring_desc (the actual descriptor chain), vring_used_all (used
  ring for each queue), vring_avail_all (available ring for each queue),
  vhost_memory (the structure that carries the shape of the memory
  region as it should be shared with the kernel)
- Increase PKT_BUF_BYTES by 1536 because the byte array that carries
  the frames needs to also account for virtio_net_hdr_mrg_rxbuf header
  sizes per each frame.
- Define the signatures of functions that will be used in setting up the
  virtqueues with the kernel (set_vring_for_queue, setup_memory_table,
  setup_vhost_net, setup_eventfds).
- Define the signature of rx_descriptor_handoff, which will be used to
  mark descriptors as available again to the driver, and vhost_kick so
  we can notify the driver of our updates

Signed-off-by: Ammar Yasser <aerosound161@gmail.com>
---
 passt.h  |  2 +-
 virtio.h | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/passt.h b/passt.h
index c729316..88a1b03 100644
--- a/passt.h
+++ b/passt.h
@@ -36,7 +36,7 @@ union epoll_ref;
 	((uint8_t [ETH_ALEN]){0x9a, 0x55, 0x9a, 0x55, 0x9a, 0x55})
 
 /* Large enough for ~128 maximum size frames */
-#define PKT_BUF_BYTES		(8UL << 20)
+#define PKT_BUF_BYTES		((8UL << 20) + 1536)	/* 128 * sizeof(virtio_net_hdr_mrg_rxbuf) */
 
 extern char pkt_buf		[PKT_BUF_BYTES];
 
diff --git a/virtio.h b/virtio.h
index 8f2ae06..2d1eef1 100644
--- a/virtio.h
+++ b/virtio.h
@@ -9,14 +9,82 @@
 #ifndef VIRTIO_H
 #define VIRTIO_H
 
+#include <assert.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <linux/vhost_types.h>
 
+struct ctx;
+
 /* Maximum size of a virtqueue */
 #define VIRTQUEUE_MAX_SIZE 1024
 
 #define VNET_HLEN	(sizeof(struct virtio_net_hdr_mrg_rxbuf))
 
+/* Keep in sync with PKT_BUF_BYTES in passt.h */
+#define PKT_BUF_BYTES		((8UL << 20) + 1536)	/* 128 * sizeof(virtio_net_hdr_mrg_rxbuf) */
+
+#define VHOST_NDESCS (PKT_BUF_BYTES / 65520)
+static_assert(!(VHOST_NDESCS & (VHOST_NDESCS - 1)),
+			 "Number of vhost descs must be a power of two by standard");
+
+
+#define VIRTQUEUE_MAX_SIZE 1024
+
+#define VHOST_VIRTIO         0xAF
+#define VHOST_GET_FEATURES   _IOR(VHOST_VIRTIO, 0x00, __u64)
+#define VHOST_SET_FEATURES   _IOW(VHOST_VIRTIO, 0x00, __u64)
+#define VHOST_SET_OWNER	     _IO(VHOST_VIRTIO, 0x01)
+#define VHOST_SET_MEM_TABLE  _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory)
+#define VHOST_SET_VRING_NUM  _IOW(VHOST_VIRTIO, 0x10, struct vhost_vring_state)
+#define VHOST_SET_VRING_ADDR _IOW(VHOST_VIRTIO, 0x11, struct vhost_vring_addr)
+#define VHOST_SET_VRING_KICK _IOW(VHOST_VIRTIO, 0x20, struct vhost_vring_file)
+#define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file)
+#define VHOST_SET_VRING_ERR  _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
+#define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
+#define VHOST_NET_SET_BACKEND _IOW(VHOST_VIRTIO, 0x30, struct vhost_vring_file)
+
+/**
+ * struct vq_state - Per-virtqueue local descriptor tracking
+ * @num_free:		Number of descriptors ready to be announced
+ *			to the kernel as available via rx_descriptor_handoff()
+ * @last_used_idx:	Number of used-ring entries consumed so far;
+ *			lagging read cursor vs. vring_used->idx (the
+ *			kernel's write cursor)
+ */
+extern struct vq_state {
+	uint16_t num_free;
+	uint16_t last_used_idx;
+	uint16_t next_free;
+} vqs[2];
+
+
+extern struct vring_desc vring_desc[2][VHOST_NDESCS];
+union vring_avail_u {
+	struct vring_avail avail;
+	char buf[offsetof(struct vring_avail, ring[VHOST_NDESCS])];
+};
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpedantic"
+extern union vring_avail_u vring_avail_all[2];
+#pragma GCC diagnostic pop
+
+union vring_used_u {
+	struct vring_used used;
+	char buf[offsetof(struct vring_used, ring[VHOST_NDESCS])];
+};
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpedantic"
+extern union vring_used_u vring_used_all[2];
+#pragma GCC diagnostic pop
+
+#define N_VHOST_REGIONS 12
+union vhost_memory_u {
+	struct vhost_memory mem;
+	char buf[offsetof(struct vhost_memory, regions[N_VHOST_REGIONS])];
+};
+extern union vhost_memory_u vhost_memory;
+
 /**
  * struct vu_ring - Virtqueue rings
  * @num:		Size of the queue
@@ -147,6 +215,7 @@ struct vu_virtq_element {
 	struct iovec *out_sg;
 };
 
+void vu_queue_notify(const struct vu_dev *dev, struct vu_virtq *vq);
 /**
  * has_feature() - Check a feature bit in a features set
  * @features:	Features set
@@ -199,4 +268,11 @@ void vu_queue_fill(const struct vu_dev *vdev, struct vu_virtq *vq,
 		   unsigned int idx);
 void vu_queue_flush(const struct vu_dev *vdev, struct vu_virtq *vq,
 		    unsigned int count);
+void set_vring_for_queue(struct ctx *c, int queue_idx, int tap_fd);
+int setup_memory_table(struct ctx *c);
+void setup_vhost_net(struct ctx *c);
+void setup_eventfds(struct ctx *c, int queue_idx);
+void rx_descriptor_handoff(struct ctx *c);
+void vhost_kick(struct vring_used *used, int kick_fd);
+
 #endif /* VIRTIO_H */
-- 
2.34.1