[dpdk-dev] [PATCH] vhost: Introduce vhost-user's REPLY_ACK feature

[Maxime Coquelin]

REPLY_ACK features provide a generic way for QEMU to ensure both
completion and success of a request.

As described in vhost-user spec in QEMU repository, QEMU sets
VHOST_USER_NEED_REPLY flag (bit 3) when expecting a reply_ack from
the backend. Backend must reply with 0 for success or non-zero
otherwise when flag is set.

Currently, only VHOST_USER_SET_MEM_TABLE request implements reply_ack,
in order to synchronize mapping updates.

This patch enables REPLY_ACK feature generally, but only checks error
code for VHOST_USER_SET_MEM_TABLE.

Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
Hi,

The intend of this patch is not to fix a known issue, but it is
nice to have this feature, and it will be used by upcoming MTU
feature if it remains in its current form.

Thanks,
Maxime

 lib/librte_vhost/vhost_user.c | 11 ++++++++++-
 lib/librte_vhost/vhost_user.h |  5 ++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 6b83c15..9ce80cb 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -903,6 +903,7 @@ send_vhost_message(int sockfd, struct VhostUserMsg *msg)
 		return 0;
 
 	msg->flags &= ~VHOST_USER_VERSION_MASK;
+	msg->flags &= ~VHOST_USER_NEED_REPLY;
 	msg->flags |= VHOST_USER_VERSION;
 	msg->flags |= VHOST_USER_REPLY_MASK;
 
@@ -938,6 +939,7 @@ vhost_user_msg_handler(int vid, int fd)
 		return -1;
 	}
 
+	ret = 0;
 	RTE_LOG(INFO, VHOST_CONFIG, "read message %s\n",
 		vhost_message_str[msg.request]);
 	switch (msg.request) {
@@ -967,7 +969,7 @@ vhost_user_msg_handler(int vid, int fd)
 		break;
 
 	case VHOST_USER_SET_MEM_TABLE:
-		vhost_user_set_mem_table(dev, &msg);
+		ret = vhost_user_set_mem_table(dev, &msg);
 		break;
 
 	case VHOST_USER_SET_LOG_BASE:
@@ -1025,9 +1027,16 @@ vhost_user_msg_handler(int vid, int fd)
 		break;
 
 	default:
+		ret = -1;
 		break;
 
 	}
 
+	if (msg.flags & VHOST_USER_NEED_REPLY) {
+		msg.payload.u64 = !!ret;
+		msg.size = sizeof(msg.payload.u64);
+		send_vhost_message(fd, &msg);
+	}
+
 	return 0;
 }
diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
index ba78d32..179e441 100644
--- a/lib/librte_vhost/vhost_user.h
+++ b/lib/librte_vhost/vhost_user.h
@@ -46,10 +46,12 @@
 #define VHOST_USER_PROTOCOL_F_MQ	0
 #define VHOST_USER_PROTOCOL_F_LOG_SHMFD	1
 #define VHOST_USER_PROTOCOL_F_RARP	2
+#define VHOST_USER_PROTOCOL_F_REPLY_ACK	3
 
 #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_RARP) | \
+					 (1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK))
 
 typedef enum VhostUserRequest {
 	VHOST_USER_NONE = 0,
@@ -98,6 +100,7 @@ typedef struct VhostUserMsg {
 
 #define VHOST_USER_VERSION_MASK     0x3
 #define VHOST_USER_REPLY_MASK       (0x1 << 2)
+#define VHOST_USER_NEED_REPLY		(0x1 << 3)
 	uint32_t flags;
 	uint32_t size; /* the following payload size */
 	union {
-- 
2.9.3