net-test: packetdrill: run_all: add --capture option

This new option is useful to capture packet traces per test for debug
purposes.

With the new parameter, we can specify to capture packets with TCPDump
and write the .pcap files in the given directory without modifying
in_netns.sh or re-launching the tests manually outside the netns.

e.g. to write .pcap files in the home directory:

  $ run_all.py -c ~

Files will be generated using the name of the test and its variant.

Note that this adds some delay: one second before starting not to miss
the first packets and one second at the end to make sure the last
packets will be captured by TCPDump.

Signed-off-by: Matthieu Baerts <[email protected]>

gtests/net/packetdrill/in_netns.sh

@@ -6,12 +6,24 @@ set -e
 
 readonly NETNS="ns-$(mktemp -u XXXXXX)"
 
+TCPDUMP_PID=
+
 setup() {
 	ip netns add "${NETNS}"
 	ip -netns "${NETNS}" link set lo up
+	if [ -n "${TCPDUMP_OUTPUT}" ]; then
+		ip netns exec "${NETNS}" tcpdump -i any -s 150 -w "${TCPDUMP_OUTPUT}" &
+		TCPDUMP_PID=$!
+		sleep 1 # give some time to TCPDump to start
+	fi
 }
 
 cleanup() {
+	if [ -n "${TCPDUMP_PID}" ]; then
+		sleep 1 # give some time to TCPDump to process the packets
+		kill "${TCPDUMP_PID}"
+		wait "${TCPDUMP_PID}" 2>/dev/null || true
+	fi
 	ip netns del "${NETNS}"
 }
 

gtests/net/packetdrill/run_all.py

@@ -50,7 +50,7 @@ def CmdTest(self, path, variant, extra_args=None):
       cmd.append('-' + 'v' * (self.args['verbose'] - 1))
     cmd.append(basename)
 
-    return (cmd, execdir, path, variant)
+    return (cmd, execdir, path, variant, basename)
 
   def CmdTestIPv4(self, path):
     """Return a command to run a packetdrill test over ipv4."""
@@ -116,13 +116,19 @@ def Log(self, outfile, errfile):
     errfile.seek(0)
     sys.stderr.write(errfile.read())
 
-  def StartTest(self, cmd, execdir, path, variant):
+  def StartTest(self, cmd, execdir, path, variant, basename):
     """Run a packetdrill test"""
     outfile = tempfile.TemporaryFile(mode='w+')
     errfile = tempfile.TemporaryFile(mode='w+')
 
+    env = os.environ
+    if self.args['capture'] is not None:
+      fname = os.path.splitext(basename)[0] +  "_" + variant + ".pcap"
+      env = dict(env, TCPDUMP_OUTPUT=os.path.join(self.args['capture'], fname))
+
     time_start = time.time()
-    process = subprocess.Popen(cmd, stdout=outfile, stderr=errfile, cwd=execdir)
+    process = subprocess.Popen(cmd, stdout=outfile, stderr=errfile, cwd=execdir,
+                               env=env)
 
     return (process, path, variant, outfile, errfile, time_start)
 
@@ -254,6 +260,8 @@ def ParseArgs():
   """Parse commandline arguments."""
   args = argparse.ArgumentParser()
   args.add_argument('path', default='.', nargs='?')
+  args.add_argument('-c', '--capture', metavar='DIR',
+                    help='capture packets in the specified directory')
   args.add_argument('-l', '--log_on_error', action='store_true',
                     help='requires verbose')
   args.add_argument('-L', '--log_on_success', action='store_true',