[dpdk-dev] [PATCH 01/28] vhost: introduce vhost transport operations structure

[Nikos Dragazis]

This is the first of a series of patches, whose purpose is to add
support for the virtio-vhost-user transport. This is a vhost-user
transport implementation that is different from the default AF_UNIX
transport. It uses the virtio-vhost-user PCI device in order to tunnel
vhost-user protocol messages over virtio. This lets guests act as vhost
device backends for other guests.

File descriptor passing is specific to the AF_UNIX vhost-user protocol
transport.  In order to add support for additional transports, it is
necessary to extract transport-specific code from the main vhost-user
code.

This patch introduces struct vhost_transport_ops and associates each
device with a transport.  Core vhost-user code calls into
vhost_transport_ops to perform transport-specific operations.

Notifying callfd is a transport-specific operation, so it belongs to
trans_af_unix.c.

Several more patches follow this one to complete the task of moving
AF_UNIX transport code out of core vhost-user code.

Signed-off-by: Nikos Dragazis <ndragazis at arrikto.com>
Signed-off-by: Stefan Hajnoczi <stefanha at redhat.com>
---
 lib/librte_vhost/Makefile        |  2 +-
 lib/librte_vhost/trans_af_unix.c | 20 ++++++++++++++++++++
 lib/librte_vhost/vhost.c         |  1 +
 lib/librte_vhost/vhost.h         | 34 +++++++++++++++++++++++++++++-----
 4 files changed, 51 insertions(+), 6 deletions(-)
 create mode 100644 lib/librte_vhost/trans_af_unix.c

diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
index 8623e91..5ff5fb2 100644
--- a/lib/librte_vhost/Makefile
+++ b/lib/librte_vhost/Makefile
@@ -23,7 +23,7 @@ LDLIBS += -lrte_eal -lrte_mempool -lrte_mbuf -lrte_ethdev -lrte_net
 
 # all source are stored in SRCS-y
 SRCS-$(CONFIG_RTE_LIBRTE_VHOST) := fd_man.c iotlb.c socket.c vhost.c \
-					vhost_user.c virtio_net.c vdpa.c
+					vhost_user.c virtio_net.c vdpa.c trans_af_unix.c
 
 # install includes
 SYMLINK-$(CONFIG_RTE_LIBRTE_VHOST)-include += rte_vhost.h rte_vdpa.h
diff --git a/lib/librte_vhost/trans_af_unix.c b/lib/librte_vhost/trans_af_unix.c
new file mode 100644
index 0000000..3f0c308
--- /dev/null
+++ b/lib/librte_vhost/trans_af_unix.c
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2010-2018 Intel Corporation
+ * Copyright(c) 2017 Red Hat, Inc.
+ * Copyright(c) 2019 Arrikto Inc.
+ */
+
+#include "vhost.h"
+
+static int
+af_unix_vring_call(struct virtio_net *dev __rte_unused,
+		   struct vhost_virtqueue *vq)
+{
+	if (vq->callfd >= 0)
+		eventfd_write(vq->callfd, (eventfd_t)1);
+	return 0;
+}
+
+const struct vhost_transport_ops af_unix_trans_ops = {
+	.vring_call = af_unix_vring_call,
+};
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 981837b..a36bc01 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -507,6 +507,7 @@ vhost_new_device(void)
 	dev->vid = i;
 	dev->flags = VIRTIO_DEV_BUILTIN_VIRTIO_NET;
 	dev->slave_req_fd = -1;
+	dev->trans_ops = &af_unix_trans_ops;
 	dev->vdpa_dev_id = -1;
 	dev->postcopy_ufd = -1;
 	rte_spinlock_init(&dev->slave_req_lock);
diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 884befa..077f213 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -286,6 +286,30 @@ struct guest_page {
 	uint64_t size;
 };
 
+struct virtio_net;
+
+/**
+ * A structure containing function pointers for transport-specific operations.
+ */
+struct vhost_transport_ops {
+	/**
+	 * Notify the guest that used descriptors have been added to the vring.
+	 * The VRING_AVAIL_F_NO_INTERRUPT flag and event idx have already been checked
+	 * so this function just needs to perform the notification.
+	 *
+	 * @param dev
+	 *  vhost device
+	 * @param vq
+	 *  vhost virtqueue
+	 * @return
+	 *  0 on success, -1 on failure
+	 */
+	int (*vring_call)(struct virtio_net *dev, struct vhost_virtqueue *vq);
+};
+
+/** The traditional AF_UNIX vhost-user protocol transport. */
+extern const struct vhost_transport_ops af_unix_trans_ops;
+
 /**
  * Device structure contains all configuration information relating
  * to the device.
@@ -312,6 +336,7 @@ struct virtio_net {
 	uint16_t		mtu;
 
 	struct vhost_device_ops const *notify_ops;
+	struct vhost_transport_ops const *trans_ops;
 
 	uint32_t		nr_guest_pages;
 	uint32_t		max_guest_pages;
@@ -544,12 +569,11 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		if ((vhost_need_event(vhost_used_event(vq), new, old) &&
 					(vq->callfd >= 0)) ||
 				unlikely(!signalled_used_valid))
-			eventfd_write(vq->callfd, (eventfd_t) 1);
+			dev->trans_ops->vring_call(dev, vq);
 	} else {
 		/* Kick the guest if necessary. */
-		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-				&& (vq->callfd >= 0))
-			eventfd_write(vq->callfd, (eventfd_t)1);
+		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
+			dev->trans_ops->vring_call(dev, vq);
 	}
 }
 
@@ -601,7 +625,7 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		kick = true;
 kick:
 	if (kick)
-		eventfd_write(vq->callfd, (eventfd_t)1);
+		dev->trans_ops->vring_call(dev, vq);
 }
 
 static __rte_always_inline void
-- 
2.7.4