netlink-socket: Make caller provide message receive buffers.

Typically an nl_sock client can stack-allocate the buffer for receiving
a Netlink message, which provides a performance boost.

Signed-off-by: Ben Pfaff <blp@nicira.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/utilities/nlmon.c b/utilities/nlmon.c
index 1b2f1e21..e6cf0235 100644
--- a/utilities/nlmon.c
+++ b/utilities/nlmon.c
@@ -39,7 +39,9 @@ static const struct nl_policy rtnlgrp_link_policy[] = {
 int
 main(int argc OVS_UNUSED, char *argv[])
 {
+    uint64_t buf_stub[4096 / 64];
     struct nl_sock *sock;
+    struct ofpbuf buf;
     int error;
 
     set_program_name(argv[0]);
@@ -55,9 +57,8 @@ main(int argc OVS_UNUSED, char *argv[])
         ovs_fatal(error, "could not join RTNLGRP_LINK multicast group");
     }
 
+    ofpbuf_use_stub(&buf, buf_stub, sizeof buf_stub);
     for (;;) {
-        struct ofpbuf *buf;
-
         error = nl_sock_recv(sock, &buf, false);
         if (error == EAGAIN) {
             /* Nothing to do. */
@@ -95,19 +96,17 @@ main(int argc OVS_UNUSED, char *argv[])
             struct ifinfomsg *iim;
             int i;
 
-            nlh = ofpbuf_at(buf, 0, NLMSG_HDRLEN);
-            iim = ofpbuf_at(buf, NLMSG_HDRLEN, sizeof *iim);
+            nlh = ofpbuf_at(&buf, 0, NLMSG_HDRLEN);
+            iim = ofpbuf_at(&buf, NLMSG_HDRLEN, sizeof *iim);
             if (!iim) {
                 ovs_error(0, "received bad rtnl message (no ifinfomsg)");
-                ofpbuf_delete(buf);
                 continue;
             }
 
-            if (!nl_policy_parse(buf, NLMSG_HDRLEN + sizeof(struct ifinfomsg),
+            if (!nl_policy_parse(&buf, NLMSG_HDRLEN + sizeof(struct ifinfomsg),
                                  rtnlgrp_link_policy,
                                  attrs, ARRAY_SIZE(rtnlgrp_link_policy))) {
                 ovs_error(0, "received bad rtnl message (policy)");
-                ofpbuf_delete(buf);
                 continue;
             }
             printf("netdev %s changed (%s):\n",
@@ -132,7 +131,6 @@ main(int argc OVS_UNUSED, char *argv[])
                 }
                 printf("\tmaster=%"PRIu32" (%s)\n", idx, ifname);
             }
-            ofpbuf_delete(buf);
         }
 
         nl_sock_wait(sock, POLLIN);