[dpdk-dev] [PATCH v2] vhost: workaround MQ fails to startup

[Zhiyong Yang <zhiyong.yang@intel.com>]

  vhost since dpdk17.02 + qemu2.7 and above will cause failures of
new connection when negotiating to set MQ. (one queue pair works
well).
   Because there exist some bugs in qemu code when introducing
VHOST_USER_PROTOCOL_F_REPLY_ACK to qemu. when dealing with the vhost
message VHOST_USER_SET_MEM_TABLE for the second time, qemu indeed
doesn't send the messge (The message needs to be sent only once)but
still will be waiting for dpdk's reply ack, then, qemu is always
freezing. DPDK code indeed works in the right way.
   The feature VHOST_USER_PROTOCOL_F_REPLY_ACK has to be disabled
by default at the dpdk side in order to avoid the feature support of
DPDK + qemu at the same time. if doing like that, MQ can works well.

Cc: stable@dpdk.org

Reported-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
Tested-by: Ciara Loftus <ciara.loftus@intel.com>
---

changes in V2
1. modify "workaround" instead of "fix" in the title.
2. add a simple comment suggested by yuanhan

 lib/librte_vhost/vhost_user.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
index 2ba22db..35ebd71 100644
--- a/lib/librte_vhost/vhost_user.h
+++ b/lib/librte_vhost/vhost_user.h
@@ -49,10 +49,14 @@
 #define VHOST_USER_PROTOCOL_F_REPLY_ACK	3
 #define VHOST_USER_PROTOCOL_F_NET_MTU 4
 
+/*
+ * disable REPLY_ACK feature to workaround the buggy QEMU implementation.
+ * Proved buggy QEMU includes v2.7 - v2.9.
+ */
 #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) | \
+					 (0ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
 					 (1ULL << VHOST_USER_PROTOCOL_F_NET_MTU))
 
 typedef enum VhostUserRequest {
-- 
2.7.4