[PATCH v2 2/2] vhost: add reconnection support to VDUSE

[Maxime Coquelin <maxime.coquelin@redhat.com>]

This patch enables VDUSE reconnection support making use of
the newly introduced reconnection mechanism in Vhost
library.

At DPDK VDUSE device creation time, there are two
possibilities:
 1. The Kernel VDUSE device does not exist:
  a. A reconnection file named after the VUDSE device name
     is created in VDUSE tmpfs.
  b. The file is truncated to 'struct vhost_reconnect_data'
     size, and mmapped.
  c. Negotiated features, Virtio status... are saved for
     sanity checks at reconnect time.
 2. The Kernel VDUSE device already exists:
  a. Exit with failure if no reconnect file exists for
     this device.
  b. Open and mmap the reconnect file.
  c. Perform sanity check to ensure features are compatible.
  d. Restore virtqueues' available indexes at startup time.

Then at runtime, the virtqueues' available index are logged by
the Vhost reconnection mechanism.

At DPDK VDUSE device destruction time, there are two
possibilities:
 1. The Kernel VDUSE device destruction succeed, which
    means it is no more attached to the vDPA bus. The
    reconnection file is unmapped and then removed.
 2. The Kernel VDUSE device destruction failed, meaning it
    is no more attached to the vDPA bus. The reconnection
    file is unmapped but not removed to make possible later
    reconnection.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/vduse.c | 308 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 268 insertions(+), 40 deletions(-)

diff --git a/lib/vhost/vduse.c b/lib/vhost/vduse.c
index c66602905c..f9ac317438 100644
--- a/lib/vhost/vduse.c
+++ b/lib/vhost/vduse.c
@@ -136,7 +136,7 @@ vduse_control_queue_event(int fd, void *arg, int *remove __rte_unused)
 }
 
 static void
-vduse_vring_setup(struct virtio_net *dev, unsigned int index)
+vduse_vring_setup(struct virtio_net *dev, unsigned int index, bool reconnect)
 {
 	struct vhost_virtqueue *vq = dev->virtqueue[index];
 	struct vhost_vring_addr *ra = &vq->ring_addrs;
@@ -152,6 +152,19 @@ vduse_vring_setup(struct virtio_net *dev, unsigned int index)
 		return;
 	}
 
+	if (reconnect) {
+		vq->last_avail_idx = vq->reconnect_log->last_avail_idx;
+		vq->last_used_idx = vq->reconnect_log->last_avail_idx;
+	} else {
+		vq->last_avail_idx = vq_info.split.avail_index;
+		vq->last_used_idx = vq_info.split.avail_index;
+	}
+	vq->size = vq_info.num;
+	vq->ready = true;
+	vq->enabled = vq_info.ready;
+	ra->desc_user_addr = vq_info.desc_addr;
+	ra->avail_user_addr = vq_info.driver_addr;
+	ra->used_user_addr = vq_info.device_addr;
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "VQ %u info:", index);
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tnum: %u", vq_info.num);
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tdesc_addr: %llx",
@@ -160,17 +173,9 @@ vduse_vring_setup(struct virtio_net *dev, unsigned int index)
 			(unsigned long long)vq_info.driver_addr);
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tdevice_addr: %llx",
 			(unsigned long long)vq_info.device_addr);
-	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tavail_idx: %u", vq_info.split.avail_index);
+	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tavail_idx: %u", vq->last_avail_idx);
+	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tused_idx: %u", vq->last_used_idx);
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "\tready: %u", vq_info.ready);
-
-	vq->last_avail_idx = vq_info.split.avail_index;
-	vq->size = vq_info.num;
-	vq->ready = true;
-	vq->enabled = vq_info.ready;
-	ra->desc_user_addr = vq_info.desc_addr;
-	ra->avail_user_addr = vq_info.driver_addr;
-	ra->used_user_addr = vq_info.device_addr;
-
 	vq->kickfd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
 	if (vq->kickfd < 0) {
 		VHOST_CONFIG_LOG(dev->ifname, ERR, "Failed to init kickfd for VQ %u: %s",
@@ -267,7 +272,7 @@ vduse_vring_cleanup(struct virtio_net *dev, unsigned int index)
 }
 
 static void
-vduse_device_start(struct virtio_net *dev)
+vduse_device_start(struct virtio_net *dev, bool reconnect)
 {
 	unsigned int i, ret;
 
@@ -287,6 +292,15 @@ vduse_device_start(struct virtio_net *dev)
 		return;
 	}
 
+	if (reconnect && dev->features != dev->reconnect_log->features) {
+		VHOST_CONFIG_LOG(dev->ifname, ERR,
+				"Mismatch between reconnect file features 0x%" PRIx64 " & device features 0x%" PRIx64,
+				dev->reconnect_log->features, dev->features);
+		return;
+	}
+
+	dev->reconnect_log->features = dev->features;
+
 	VHOST_CONFIG_LOG(dev->ifname, INFO, "Negotiated Virtio features: 0x%" PRIx64,
 		dev->features);
 
@@ -300,7 +314,7 @@ vduse_device_start(struct virtio_net *dev)
 	}
 
 	for (i = 0; i < dev->nr_vring; i++)
-		vduse_vring_setup(dev, i);
+		vduse_vring_setup(dev, i, reconnect);
 
 	dev->flags |= VIRTIO_DEV_READY;
 
@@ -373,6 +387,7 @@ vduse_events_handler(int fd, void *arg, int *remove __rte_unused)
 				req.s.status);
 		old_status = dev->status;
 		dev->status = req.s.status;
+		dev->reconnect_log->status = dev->status;
 		resp.result = VDUSE_REQ_RESULT_OK;
 		break;
 	case VDUSE_UPDATE_IOTLB:
@@ -398,7 +413,7 @@ vduse_events_handler(int fd, void *arg, int *remove __rte_unused)
 
 	if ((old_status ^ dev->status) & VIRTIO_DEVICE_STATUS_DRIVER_OK) {
 		if (dev->status & VIRTIO_DEVICE_STATUS_DRIVER_OK)
-			vduse_device_start(dev);
+			vduse_device_start(dev, false);
 		else
 			vduse_device_stop(dev);
 	}
@@ -407,10 +422,64 @@ vduse_events_handler(int fd, void *arg, int *remove __rte_unused)
 			vduse_req_id_to_str(req.type), req.type);
 }
 
+static char vduse_reconnect_dir[PATH_MAX];
+static bool vduse_reconnect_path_set;
+
+static int
+vduse_reconnect_path_init(void)
+{
+	const char *directory;
+	int ret;
+
+	/* from RuntimeDirectory= see systemd.exec */
+	directory = getenv("RUNTIME_DIRECTORY");
+	if (directory == NULL) {
+		/*
+		 * Used standard convention defined in
+		 * XDG Base Directory Specification and
+		 * Filesystem Hierarchy Standard.
+		 */
+		if (getuid() == 0)
+			directory = "/var/run";
+		else
+			directory = getenv("XDG_RUNTIME_DIR") ? : "/tmp";
+	}
+
+	ret = snprintf(vduse_reconnect_dir, sizeof(vduse_reconnect_dir), "%s/vduse",
+			directory);
+	if (ret < 0 || ret == sizeof(vduse_reconnect_dir)) {
+		VHOST_CONFIG_LOG("vduse", ERR, "Error creating VDUSE reconnect path name");
+		return -1;
+	}
+
+	ret = mkdir(vduse_reconnect_dir, 0700);
+	if (ret < 0 && errno != EEXIST) {
+		VHOST_CONFIG_LOG("vduse", ERR, "Error creating '%s': %s",
+				vduse_reconnect_dir, strerror(errno));
+		return -1;
+	}
+
+	VHOST_CONFIG_LOG("vduse", INFO, "Created VDUSE reconnect directory in %s",
+			vduse_reconnect_dir);
+
+	return 0;
+}
+
+static void
+vduse_reconnect_handler(int fd, void *arg, int *remove)
+{
+	struct virtio_net *dev = arg;
+
+	vduse_device_start(dev, true);
+
+	close(fd);
+	*remove = 1;
+}
+
 int
 vduse_device_create(const char *path, bool compliant_ol_flags)
 {
-	int control_fd, dev_fd, vid, ret;
+	int control_fd, dev_fd, vid, ret, reco_fd;
 	uint32_t i, max_queue_pairs, total_queues;
 	struct virtio_net *dev;
 	struct virtio_net_config vnet_config = {{ 0 }};
@@ -418,6 +487,9 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 	uint64_t features;
 	struct vduse_dev_config *dev_config = NULL;
 	const char *name = path + strlen("/dev/vduse/");
+	char reconnect_file[PATH_MAX];
+	struct vhost_reconnect_data *reconnect_log = NULL;
+	bool reconnect = false;
 
 	if (vduse.fdset == NULL) {
 		vduse.fdset = fdset_init("vduse-evt");
@@ -427,6 +499,20 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 		}
 	}
 
+	if (vduse_reconnect_path_set == false) {
+		if (vduse_reconnect_path_init() < 0) {
+			VHOST_CONFIG_LOG(path, ERR, "failed to initialize reconnect path");
+			return -1;
+		}
+		vduse_reconnect_path_set = true;
+	}
+
+	ret = snprintf(reconnect_file, sizeof(reconnect_file), "%s/%s", vduse_reconnect_dir, name);
+	if (ret < 0 || ret == sizeof(reconnect_file)) {
+		VHOST_CONFIG_LOG(name, ERR, "Failed to create vduse reconnect path name");
+		return -1;
+	}
+
 	control_fd = open(VDUSE_CTRL_PATH, O_RDWR);
 	if (control_fd < 0) {
 		VHOST_CONFIG_LOG(name, ERR, "Failed to open %s: %s",
@@ -441,14 +527,6 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 		goto out_ctrl_close;
 	}
 
-	dev_config = malloc(offsetof(struct vduse_dev_config, config) +
-			sizeof(vnet_config));
-	if (!dev_config) {
-		VHOST_CONFIG_LOG(name, ERR, "Failed to allocate VDUSE config");
-		ret = -1;
-		goto out_ctrl_close;
-	}
-
 	ret = rte_vhost_driver_get_features(path, &features);
 	if (ret < 0) {
 		VHOST_CONFIG_LOG(name, ERR, "Failed to get backend features");
@@ -469,23 +547,118 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 	else
 		total_queues += 1; /* Includes ctrl queue */
 
-	vnet_config.max_virtqueue_pairs = max_queue_pairs;
-	memset(dev_config, 0, sizeof(struct vduse_dev_config));
+	if (access(path, F_OK) == 0) {
+		VHOST_CONFIG_LOG(name, INFO, "Device already exists, reconnecting...");
+		reconnect = true;
+
+		reco_fd = open(reconnect_file, O_RDWR, 0600);
+		if (reco_fd < 0) {
+			if (errno == ENOENT)
+				VHOST_CONFIG_LOG(name, ERR, "Missing reconnect file (%s)",
+						reconnect_file);
+			else
+				VHOST_CONFIG_LOG(name, ERR, "Failed to open reconnect file %s (%s)",
+						reconnect_file, strerror(errno));
+			ret = -1;
+			goto out_ctrl_close;
+		}
 
-	strncpy(dev_config->name, name, VDUSE_NAME_MAX - 1);
-	dev_config->device_id = VIRTIO_ID_NET;
-	dev_config->vendor_id = 0;
-	dev_config->features = features;
-	dev_config->vq_num = total_queues;
-	dev_config->vq_align = sysconf(_SC_PAGE_SIZE);
-	dev_config->config_size = sizeof(struct virtio_net_config);
-	memcpy(dev_config->config, &vnet_config, sizeof(vnet_config));
+		reconnect_log = mmap(NULL, sizeof(*reconnect_log), PROT_READ | PROT_WRITE,
+				MAP_SHARED, reco_fd, 0);
+		close(reco_fd);
+		if (reconnect_log == MAP_FAILED) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to mmap reconnect file %s (%s)",
+					reconnect_file, strerror(errno));
+			ret = -1;
+			goto out_ctrl_close;
+		}
 
-	ret = ioctl(control_fd, VDUSE_CREATE_DEV, dev_config);
-	if (ret < 0) {
-		VHOST_CONFIG_LOG(name, ERR, "Failed to create VDUSE device: %s",
-				strerror(errno));
-		goto out_free;
+		if (reconnect_log->version != VHOST_RECONNECT_VERSION) {
+			VHOST_CONFIG_LOG(name, ERR,
+					"Version mismatch between backend (0x%x) & reconnection file (0x%x)",
+					VHOST_RECONNECT_VERSION, reconnect_log->version);
+		}
+
+		if ((reconnect_log->features & features) != reconnect_log->features) {
+			VHOST_CONFIG_LOG(name, ERR,
+					"Features mismatch between backend (0x%" PRIx64 ") & reconnection file (0x%" PRIx64 ")",
+					features, reconnect_log->features);
+			ret = -1;
+			goto out_ctrl_close;
+		}
+
+		if (reconnect_log->nr_vrings != total_queues) {
+			VHOST_CONFIG_LOG(name, ERR,
+					"Queues number mismatch between backend (%u) and reconnection file (%u)",
+					total_queues, reconnect_log->nr_vrings);
+			ret = -1;
+			goto out_ctrl_close;
+		}
+	} else {
+		reco_fd = open(reconnect_file, O_CREAT | O_EXCL | O_RDWR, 0600);
+		if (reco_fd < 0) {
+			if (errno == EEXIST) {
+				VHOST_CONFIG_LOG(name, ERR, "Reconnect file %s exists but not the device",
+						reconnect_file);
+			} else {
+				VHOST_CONFIG_LOG(name, ERR, "Failed to open reconnect file %s (%s)",
+						reconnect_file, strerror(errno));
+			}
+			ret = -1;
+			goto out_ctrl_close;
+		}
+
+		ret = ftruncate(reco_fd, sizeof(*reconnect_log));
+		if (ret < 0) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to truncate reconnect file %s (%s)",
+					reconnect_file, strerror(errno));
+			close(reco_fd);
+			goto out_ctrl_close;
+		}
+
+		reconnect_log = mmap(NULL, sizeof(*reconnect_log), PROT_READ | PROT_WRITE,
+					MAP_SHARED, reco_fd, 0);
+		close(reco_fd);
+		if (reconnect_log == MAP_FAILED) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to mmap reconnect file %s (%s)",
+					reconnect_file, strerror(errno));
+			ret = -1;
+			goto out_ctrl_close;
+		}
+
+		reconnect_log->version = VHOST_RECONNECT_VERSION;
+
+		dev_config = malloc(offsetof(struct vduse_dev_config, config) +
+				sizeof(vnet_config));
+		if (!dev_config) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to allocate VDUSE config");
+			ret = -1;
+			goto out_ctrl_close;
+		}
+
+		vnet_config.max_virtqueue_pairs = max_queue_pairs;
+		memset(dev_config, 0, sizeof(struct vduse_dev_config));
+
+		rte_strscpy(dev_config->name, name, VDUSE_NAME_MAX - 1);
+		dev_config->device_id = VIRTIO_ID_NET;
+		dev_config->vendor_id = 0;
+		dev_config->features = features;
+		dev_config->vq_num = total_queues;
+		dev_config->vq_align = sysconf(_SC_PAGE_SIZE);
+		dev_config->config_size = sizeof(struct virtio_net_config);
+		memcpy(dev_config->config, &vnet_config, sizeof(vnet_config));
+
+		ret = ioctl(control_fd, VDUSE_CREATE_DEV, dev_config);
+		if (ret < 0) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to create VDUSE device: %s",
+					strerror(errno));
+			goto out_free;
+		}
+
+		memcpy(&reconnect_log->config, &vnet_config, sizeof(vnet_config));
+		reconnect_log->nr_vrings = total_queues;
+		free(dev_config);
+		dev_config = NULL;
 	}
 
 	dev_fd = open(path, O_RDWR);
@@ -519,10 +692,15 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 	strncpy(dev->ifname, path, IF_NAME_SZ - 1);
 	dev->vduse_ctrl_fd = control_fd;
 	dev->vduse_dev_fd = dev_fd;
+	dev->reconnect_log = reconnect_log;
+	if (reconnect)
+		dev->status = dev->reconnect_log->status;
+
 	vhost_setup_virtio_net(dev->vid, true, compliant_ol_flags, true, true);
 
 	for (i = 0; i < total_queues; i++) {
 		struct vduse_vq_config vq_cfg = { 0 };
+		struct vhost_virtqueue *vq;
 
 		ret = alloc_vring_queue(dev, i);
 		if (ret) {
@@ -530,6 +708,12 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 			goto out_dev_destroy;
 		}
 
+		vq = dev->virtqueue[i];
+		vq->reconnect_log = &reconnect_log->vring[i];
+
+		if (reconnect)
+			continue;
+
 		vq_cfg.index = i;
 		vq_cfg.max_size = 1024;
 
@@ -549,7 +733,32 @@ vduse_device_create(const char *path, bool compliant_ol_flags)
 		goto out_dev_destroy;
 	}
 
-	free(dev_config);
+	if (reconnect && dev->status & VIRTIO_DEVICE_STATUS_DRIVER_OK)  {
+		/*
+		 * Make vduse_device_start() being executed in the same
+		 * context for both reconnection and fresh startup.
+		 */
+		reco_fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+		if (reco_fd < 0) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to create reco_fd: %s",
+					strerror(errno));
+			ret = -1;
+			goto out_dev_destroy;
+		}
+
+		ret = fdset_add(vduse.fdset, reco_fd, vduse_reconnect_handler, NULL, dev);
+		if (ret) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to add reconnect fd %d to vduse fdset",
+					reco_fd);
+			goto out_dev_destroy;
+		}
+
+		ret = eventfd_write(reco_fd, (eventfd_t)1);
+		if (ret < 0) {
+			VHOST_CONFIG_LOG(name, ERR, "Failed to write to reconnect eventfd");
+			goto out_dev_destroy;
+		}
+	}
 
 	return 0;
 
@@ -587,6 +796,9 @@ vduse_device_destroy(const char *path)
 	if (vid == RTE_MAX_VHOST_DEVICE)
 		return -1;
 
+	if (dev->reconnect_log)
+		munmap(dev->reconnect_log, sizeof(*dev->reconnect_log));
+
 	vduse_device_stop(dev);
 
 	fdset_del(vduse.fdset, dev->vduse_dev_fd);
@@ -597,10 +809,26 @@ vduse_device_destroy(const char *path)
 	}
 
 	if (dev->vduse_ctrl_fd >= 0) {
+		char reconnect_file[PATH_MAX];
+
 		ret = ioctl(dev->vduse_ctrl_fd, VDUSE_DESTROY_DEV, name);
-		if (ret)
+		if (ret) {
 			VHOST_CONFIG_LOG(name, ERR, "Failed to destroy VDUSE device: %s",
 					strerror(errno));
+		} else {
+			/*
+			 * VDUSE device was no more attached to the vDPA bus,
+			 * so we can remove the reconnect file.
+			 */
+			ret = snprintf(reconnect_file, sizeof(reconnect_file), "%s/%s",
+					vduse_reconnect_dir, name);
+			if (ret < 0 || ret == sizeof(reconnect_file))
+				VHOST_CONFIG_LOG(name, ERR,
+						"Failed to create vduse reconnect path name");
+			else
+				unlink(reconnect_file);
+		}
+
 		close(dev->vduse_ctrl_fd);
 		dev->vduse_ctrl_fd = -1;
 	}
-- 
2.46.0