test: Test and example how to dump namespace with macvlan

One note -- the macvlan's index _does_ change. We should
either patch iproute2 or use raw kernel API to preserve it.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/ext-links/Makefile

+all: mvlink.so
+
+mvlink.so: mvlink.c
+	gcc -g -Werror -Wall -shared -nostartfiles mvlink.c -o mvlink.so -iquote ../../include -fPIC

test/ext-links/addmv.sh

+#!/bin/bash
+# $1 -- link name
+# $2 -- file with namespace pid
+if [ "$CRTOOLS_SCRIPT_ACTION" == "setup-namespaces" ]; then
+	$(dirname $0)/addmv_raw.sh $1 $(cat $2)
+else
+	exit 0
+fi

test/ext-links/addmv_raw.sh

+#!/bin/bash
+# $1 -- link name
+# $2 -- pid of task in namespace
+set -x
+$ip link add link eth0 name $1 type macvlan || exit 1
+$ip link set $1 netns $2

test/ext-links/mvlink.c

+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "criu-plugin.h"
+#include "criu-log.h"
+
+extern cr_plugin_init_t cr_plugin_init;
+extern cr_plugin_dump_ext_link_t cr_plugin_dump_ext_link;
+
+int cr_plugin_init(void)
+{
+	pr_info("Initialized macvlan dumper\n");
+	return 0;
+}
+
+int cr_plugin_dump_ext_link(int index, int type, char *kind)
+{
+	if (strcmp(kind, "macvlan"))
+		return -ENOTSUP;
+	else {
+		pr_info("Dump %d macvlan\n", index);
+		return 0;
+	}
+}

test/ext-links/run.sh

+#!/bin/bash
+
+ip=${CR_IP_TOOL:-xip}
+mvln="mv0"
+finf="finish"
+outf="ns_output"
+pidf="ns_pid"
+criu="../../criu"
+
+export ip
+export mvln
+export finf
+export outf
+export pidf
+
+function fail {
+	$ip link del $mvln
+	touch $finf
+	echo $@
+	exit 1
+}
+
+# Build the mvlink plugin
+make
+
+set -x
+
+rm -f "$finf" "$outf" "$pidf"
+rm -rf "dump"
+
+# Unshare netns. The run_ns will exit once ns is spawned.
+unshare --net ./run_ns.sh
+nspid=$(cat $pidf)
+ps $nspid
+
+# Create and push macvlan device into it. CRIU doesn't support
+# macvlans treating them as external devices.
+./addmv_raw.sh $mvln $nspid || fail "Can't setup namespace"
+
+# Dump
+sleep 1
+mkdir dump
+$criu dump -t $nspid -D dump/ -o dump.log -v4 --lib $(pwd) || fail "Can't dump namespace"
+
+# Restore
+# Ask for the pid (shouldn't change, so just as an example), ask to call
+# script that will put macvlan device back into namespace
+sleep 1
+rm -f $pidf
+$criu restore -D dump/ -o restore.log -v4 --pidfile $(pwd)/$pidf --action-script "$(pwd)/addmv.sh $mvln $(pwd)/$pidf" -d || fail "Can't restore namespaces"
+
+# Finish and check results
+touch $finf
+set +x
+while ! egrep 'PASS|FAIL' $outf; do
+	echo "Waiting"
+	sleep 1
+done

test/ext-links/run_ns.sh

+#!/bin/bash
+set -x
+echo "NS: $$" >> $outf
+echo "Links before:" >> $outf
+$ip link list >> $outf 2>&1
+# Detach from session, terminal and parent
+setsid ./run_wait.sh < /dev/null >> $outf 2>&1 &
+# Keep pid for future reference :)
+echo "$!" > $pidf
+exit 0

test/ext-links/run_wait.sh

+#!/bin/bash
+
+echo "Wait: $$"
+while [ ! -e "$finf" ]; do
+	echo "WAIT ($$)"
+	sleep 1;
+done
+
+echo "Links after:"
+$ip link list
+
+# The mvln device (exported from run.sh) should exits in
+# namespace after we get restored
+echo "Check for $mvln:"
+$ip link list $mvln && echo "PASS" || echo "FAIL"