[dpdk-dev] [RFC 2/2] vhost-user: add support for VHOST_USER_SET_QUEUE_NUM

[Maxime Coquelin]

With some guest drivers, the number of queues setup by the
guest driver can be less than the number of queues declared in Qemu.

This is the case for example with Windows virtio-net driver, which
only setups as much queue pairs as the number of vCPUs.

When it happens, depending on QEMU version, the vhost-user port can:
- Either be started with some uninitialized queues, which ends up
corrupting GPA at 0 when guest notifications get disabled,
- Or be stuck forever, waiting for uninitialized rings to be ready.

This patch implements handling of VHOST_USER_SET_QUEUE_NUM new
protocol request, which is sent by QEMU to report the number
of queue pairs initialized by the guest driver.

When received, all unused queues get removed from the vhost-user
port, taking care that it is not already running.

Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
 lib/librte_vhost/vhost_user.c | 30 ++++++++++++++++++++++++++++++
 lib/librte_vhost/vhost_user.h |  5 ++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index f94fd16cf..73388027e 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -50,6 +50,7 @@ static const char *vhost_message_str[VHOST_USER_MAX] = {
 	[VHOST_USER_NET_SET_MTU]  = "VHOST_USER_NET_SET_MTU",
 	[VHOST_USER_SET_SLAVE_REQ_FD]  = "VHOST_USER_SET_SLAVE_REQ_FD",
 	[VHOST_USER_IOTLB_MSG]  = "VHOST_USER_IOTLB_MSG",
+	[VHOST_USER_SET_QUEUE_NUM] = "VHOST_USER_SET_QUEUE_NUM",
 };
 
 static uint64_t
@@ -1137,6 +1138,32 @@ vhost_user_iotlb_msg(struct virtio_net **pdev, struct VhostUserMsg *msg)
 	return 0;
 }
 
+static int
+vhost_user_set_queue_num(struct virtio_net *dev, struct VhostUserMsg *msg)
+{
+	uint64_t queue_num = msg->payload.u64 * 2; /* Payload is nr of qpairs */
+
+	if (dev->nr_vring > queue_num && dev->flags & VIRTIO_DEV_RUNNING) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+				"Cannot remove queues while device is running\n");
+		return -1;
+	}
+
+	while (dev->nr_vring > queue_num) {
+		struct vhost_virtqueue *vq;
+
+		vq = dev->virtqueue[--dev->nr_vring];
+		if (!vq)
+			continue;
+
+		dev->virtqueue[dev->nr_vring] = NULL;
+		cleanup_vq(vq, 1);
+		free_vq(vq);
+	}
+
+	return 0;
+}
+
 /* return bytes# of read on success or negative val on failure. */
 static int
 read_vhost_message(int sockfd, struct VhostUserMsg *msg)
@@ -1389,6 +1416,9 @@ vhost_user_msg_handler(int vid, int fd)
 	case VHOST_USER_IOTLB_MSG:
 		ret = vhost_user_iotlb_msg(&dev, &msg);
 		break;
+	case VHOST_USER_SET_QUEUE_NUM:
+		vhost_user_set_queue_num(dev, &msg);
+		break;
 
 	default:
 		ret = -1;
diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
index d4bd604b9..ab6557d9e 100644
--- a/lib/librte_vhost/vhost_user.h
+++ b/lib/librte_vhost/vhost_user.h
@@ -20,13 +20,15 @@
 #define VHOST_USER_PROTOCOL_F_REPLY_ACK	3
 #define VHOST_USER_PROTOCOL_F_NET_MTU 4
 #define VHOST_USER_PROTOCOL_F_SLAVE_REQ 5
+#define VHOST_USER_PROTOCOL_F_SET_QUEUE_NUM 7
 
 #define VHOST_USER_PROTOCOL_FEATURES	((1ULL << VHOST_USER_PROTOCOL_F_MQ) | \
 					 (1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD) |\
 					 (1ULL << VHOST_USER_PROTOCOL_F_RARP) | \
 					 (1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
 					 (1ULL << VHOST_USER_PROTOCOL_F_NET_MTU) | \
-					 (1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ))
+					 (1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ) | \
+					 (1ULL << VHOST_USER_PROTOCOL_F_SET_QUEUE_NUM))
 
 typedef enum VhostUserRequest {
 	VHOST_USER_NONE = 0,
@@ -52,6 +54,7 @@ typedef enum VhostUserRequest {
 	VHOST_USER_NET_SET_MTU = 20,
 	VHOST_USER_SET_SLAVE_REQ_FD = 21,
 	VHOST_USER_IOTLB_MSG = 22,
+	VHOST_USER_SET_QUEUE_NUM = 24,
 	VHOST_USER_MAX
 } VhostUserRequest;
 
-- 
2.14.3