Changeset f9df20e

Timestamp:

06/19/18 16:48:33 (2 years ago)

Author:

Shane Alcock <salcock@…>

Branches:

cachetimestamps, develop, master, rc-4.0.4, ringdecrementfix, ringperformance

Children:

528a27c, 95ca714

Parents:

86b365b

Message:

Fix bug where two ring: trace inputs had same fanout group.

We use rand() to assign the fanout group when we create the
input, but the rand() seed state is usually equal in both threads
at the point where we call rand().

So we end up with two inputs trying to be assigned to the same
fanout group, which fails and the second input will immediately
halt.

Also added code to try incrementing the fanout group number if
we end up clashing with another existing group. This will also
resolve any issues with the RNG producing one-off clashes.

Location:

lib

Files:

• format_linux_common.c (modified) (2 diffs)
• format_linux_common.h (modified) (1 diff)

lib/format_linux_common.c

@@ -49 +49 @@
 
 #include "format_linux_common.h"
+
+unsigned int rand_seedp = 0;
 
 #ifdef HAVE_NETPACKET_PACKET_H
@@ -201 +203 @@
         /* Some examples use pid for the group however that would limit a single
          * application to use only int/ring format, instead using rand */
-        FORMAT_DATA->fanout_group = (uint16_t) rand();
+        FORMAT_DATA->fanout_group = (uint16_t) (rand_r(&rand_seedp) % 65536);
         return 0;
 }

lib/format_linux_common.h

@@ -421 +421 @@
                                         struct linux_per_stream_t *stream)
 {
-        int fanout_opt = ((int)FORMAT_DATA->fanout_flags << 16) |
-                         (int)FORMAT_DATA->fanout_group;
-        if (setsockopt(stream->fd, SOL_PACKET, PACKET_FANOUT,
-                        &fanout_opt, sizeof(fanout_opt)) == -1) {
-                trace_set_err(libtrace, TRACE_ERR_INIT_FAILED,
+        int fanout_opt;
+        int attempts = 0;
+        while (attempts < 5) {
+                fanout_opt = ((int)FORMAT_DATA->fanout_flags << 16) |
+                                 (int)FORMAT_DATA->fanout_group;
+
+                if (setsockopt(stream->fd, SOL_PACKET, PACKET_FANOUT,
+                                &fanout_opt, sizeof(fanout_opt)) == -1) {
+                        trace_set_err(libtrace, TRACE_ERR_INIT_FAILED,
                               "Converting the fd to a socket fanout failed %s",
                               libtrace->uridata);
-                return -1;
+                        FORMAT_DATA->fanout_group ++;
+                        attempts ++;
+                        continue;
+                }
+                return 0;
         }
-        return 0;
+        return -1;
 }
 #endif /* HAVE_NETPACKET_PACKET_H */