ovs-brcompatd: Fix sending replies to kernel requests.

Commit 7d7447 (netlink: Postpone choosing sequence numbers until send
time.) broke ovs-brcompatd because it prevented userspace replies to
kernel requests from using the correct sequence numbers.  This commit fixes
it.

Atzm Watanabe found the root cause and provided an alternative patch to
avoid the problem.

Reported-by: André Ruß <andre.russ@hybris.com>
Reported-by: Atzm Watanabe <atzm@stratosphere.co.jp>
Tested-by: Atzm Watanabe <atzm@stratosphere.co.jp>
Signed-off-by: Ben Pfaff <blp@nicira.com>

2 files changed, 29 insertions, 6 deletions

diff --git a/lib/netlink-socket.c b/lib/netlink-socket.c
index 713049aa..3bdbbd73 100644
--- a/lib/netlink-socket.c
+++ b/lib/netlink-socket.c
@@ -253,13 +253,14 @@ nl_sock_leave_mcgroup(struct nl_sock *sock, unsigned int multicast_group)
 }
 
 static int
-nl_sock_send__(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
+nl_sock_send__(struct nl_sock *sock, const struct ofpbuf *msg,
+               uint32_t nlmsg_seq, bool wait)
 {
     struct nlmsghdr *nlmsg = nl_msg_nlmsghdr(msg);
     int error;
 
     nlmsg->nlmsg_len = msg->size;
-    nlmsg->nlmsg_seq = nl_sock_allocate_seq(sock, 1);
+    nlmsg->nlmsg_seq = nlmsg_seq;
     nlmsg->nlmsg_pid = sock->pid;
     do {
         int retval;
@@ -274,8 +275,9 @@ nl_sock_send__(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
 }
 
 /* Tries to send 'msg', which must contain a Netlink message, to the kernel on
- * 'sock'.  nlmsg_len in 'msg' will be finalized to match msg->size, and
- * nlmsg_pid will be set to 'sock''s pid, before the message is sent.
+ * 'sock'.  nlmsg_len in 'msg' will be finalized to match msg->size, nlmsg_pid
+ * will be set to 'sock''s pid, and nlmsg_seq will be initialized to a fresh
+ * sequence number, before the message is sent.
  *
  * Returns 0 if successful, otherwise a positive errno value.  If
  * 'wait' is true, then the send will wait until buffer space is ready;
@@ -283,11 +285,29 @@ nl_sock_send__(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
 int
 nl_sock_send(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
 {
+    return nl_sock_send_seq(sock, msg, nl_sock_allocate_seq(sock, 1), wait);
+}
+
+/* Tries to send 'msg', which must contain a Netlink message, to the kernel on
+ * 'sock'.  nlmsg_len in 'msg' will be finalized to match msg->size, nlmsg_pid
+ * will be set to 'sock''s pid, and nlmsg_seq will be initialized to
+ * 'nlmsg_seq', before the message is sent.
+ *
+ * Returns 0 if successful, otherwise a positive errno value.  If
+ * 'wait' is true, then the send will wait until buffer space is ready;
+ * otherwise, returns EAGAIN if the 'sock' send buffer is full.
+ *
+ * This function is suitable for sending a reply to a request that was received
+ * with sequence number 'nlmsg_seq'.  Otherwise, use nl_sock_send() instead. */
+int
+nl_sock_send_seq(struct nl_sock *sock, const struct ofpbuf *msg,
+                 uint32_t nlmsg_seq, bool wait)
+{
     int error = nl_sock_cow__(sock);
     if (error) {
         return error;
     }
-    return nl_sock_send__(sock, msg, wait);
+    return nl_sock_send__(sock, msg, nlmsg_seq, wait);
 }
 
 /* This stress option is useful for testing that OVS properly tolerates
@@ -770,7 +790,8 @@ nl_dump_start(struct nl_dump *dump,
     }
 
     nl_msg_nlmsghdr(request)->nlmsg_flags |= NLM_F_DUMP | NLM_F_ACK;
-    dump->status = nl_sock_send__(sock, request, true);
+    dump->status = nl_sock_send__(sock, request, nl_sock_allocate_seq(sock, 1),
+                                  true);
     dump->seq = nl_msg_nlmsghdr(request)->nlmsg_seq;
 }
 
diff --git a/lib/netlink-socket.h b/lib/netlink-socket.h
index e74bc983..78dd7b23 100644
--- a/lib/netlink-socket.h
+++ b/lib/netlink-socket.h
@@ -52,6 +52,8 @@ int nl_sock_join_mcgroup(struct nl_sock *, unsigned int multicast_group);
 int nl_sock_leave_mcgroup(struct nl_sock *, unsigned int multicast_group);
 
 int nl_sock_send(struct nl_sock *, const struct ofpbuf *, bool wait);
+int nl_sock_send_seq(struct nl_sock *, const struct ofpbuf *,
+                     uint32_t nlmsg_seq, bool wait);
 int nl_sock_recv(struct nl_sock *, struct ofpbuf *, bool wait);
 int nl_sock_transact(struct nl_sock *, const struct ofpbuf *request,
                      struct ofpbuf **replyp);