stream-unix: Give accepted sockets distinct names for log messages.

At least on Linux, when process A connects to process B over a Unix
domain socket, unless process A bound its socket to a name before
it made the connection, process B gets an empty peer name.  Until
now, OVS has just reported the name of the connection as "unix".
This is not meaningful, of course.  I do not know of a good general
solution to this problem, but this commit attempts a step in the
right direction by at least giving each connection of this kind a
number: "unix#1", "unix#2", and so on.  That way, in log messages
one can at least see which messages are related to a particular
connection.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>

lib/stream-unix.c

@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include "ovs-atomic.h"
 #include "packets.h"
 #include "openvswitch/poll-loop.h"
 #include "socket-util.h"
@@ -112,9 +113,17 @@ punix_accept(int fd, const struct sockaddr_storage *ss, size_t ss_len,
 {
     const struct sockaddr_un *sun = (const struct sockaddr_un *) ss;
     int name_len = get_unix_name_len(sun, ss_len);
-    char *bound_name = (name_len > 0
-                        ? xasprintf("unix:%.*s", name_len, sun->sun_path)
-                        : xstrdup("unix"));
+    char *bound_name;
+
+    if (name_len > 0) {
+        bound_name = xasprintf("unix:%.*s", name_len, sun->sun_path);
+    } else {
+        /* When a Unix socket connects to us without first binding a name, we
+         * don't get any name for it.  It's useful nevertheless to be able to
+         * distinguish separate sockets in log messages, so use a counter. */
+        static atomic_count next_idx = ATOMIC_COUNT_INIT(0);
+        bound_name = xasprintf("unix#%u", atomic_count_inc(&next_idx));
+    }
     return new_fd_stream(bound_name, fd, 0, AF_UNIX, streamp);
 }
 

tests/ofproto-macros.at

@@ -32,6 +32,7 @@ prt==1 { sub(/[ \t]*$/, ""); print $0 }
 vconn_sub() {
     sed '
 s/tcp:127.0.0.1:[0-9][0-9]*:/unix:/
+s/unix#[0-9]*:/unix:/
 '
 }
 ]

tests/ofproto.at

@@ -5219,7 +5219,7 @@ vconn|DBG|unix: sent (Success): NXST_FLOW reply:
  in_port=2,dl_src=00:66:77:88:99:aa actions=drop
 ])
 
-AT_CHECK([grep " flow_mods in the last " ovs-vswitchd.log | sed -e 's/^.*connmgr|INFO|//'], [0], [dnl
+AT_CHECK([grep " flow_mods in the last " ovs-vswitchd.log | sed -e 's/^.*connmgr|INFO|//' | vconn_sub], [0], [dnl
 br0<->unix: 1 flow_mods in the last 0 s (1 deletes)
 br0<->unix: 9 flow_mods in the last 0 s (7 adds, 2 deletes)
 br0<->unix: 2 flow_mods in the last 0 s (2 modifications)