fuzz: run the main-loop in fork-server process

Without this, the time since the last main-loop keeps increasing, as the
fuzzer runs. The forked children need to handle all the "past-due"
timers, slowing them down, over time. With this change, the
parent/fork-server process runs the main-loop, while waiting on the
child, ensuring that the timer events do not pile up, over time.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200512030133.29896-5-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/qtest/fuzz/i440fx_fuzz.c

@@ -151,6 +151,7 @@ static void i440fx_fuzz_qos_fork(QTestState *s,
         i440fx_fuzz_qos(s, Data, Size);
         _Exit(0);
     } else {
+        flush_events(s);
         wait(NULL);
     }
 }

tests/qtest/fuzz/virtio_net_fuzz.c

@@ -122,6 +122,7 @@ static void virtio_net_fork_fuzz(QTestState *s,
         flush_events(s);
         _Exit(0);
     } else {
+        flush_events(s);
         wait(NULL);
     }
 }
@@ -134,6 +135,7 @@ static void virtio_net_fork_fuzz_check_used(QTestState *s,
         flush_events(s);
         _Exit(0);
     } else {
+        flush_events(s);
         wait(NULL);
     }
 }

tests/qtest/fuzz/virtio_scsi_fuzz.c

@@ -145,6 +145,7 @@ static void virtio_scsi_fork_fuzz(QTestState *s,
         flush_events(s);
         _Exit(0);
     } else {
+        flush_events(s);
         wait(NULL);
     }
 }
@@ -164,6 +165,7 @@ static void virtio_scsi_with_flag_fuzz(QTestState *s,
         }
         _Exit(0);
     } else {
+        flush_events(s);
         wait(NULL);
     }
 }