modem: Move modem iface to its netns before using it

We used to do that once after ofono startup for all iface
(modem-netns-setup.py), but then if a modem crashes the interface is
re-created on the default netns, and tests fail until manual re-run of
modem-netns-setup.py.

This way now we always make sure the iface is moved to the expected
netns before it is used.

Related: OS#3881
Change-Id: I506309c424aa46684c4516a1a0217343ecbf32c6

src/osmo_gsm_tester/modem.py

@@ -677,6 +677,7 @@ class Modem(MS):
         iface = ctx_settings.get('Interface', None)
         if not iface:
             raise log.Error('%s Settings contains no iface! %r' % (ctx_id, repr(ctx_settings)))
+        util.move_iface_to_netns(iface, self.netns(), self.run_dir.new_dir('move_netns'))
         self.run_netns_wait('ifup', ('ip', 'link', 'set', 'dev', iface, 'up'))
         self.run_netns_wait('dhcp', ('udhcpc', '-q', '-i', iface))
 

src/osmo_gsm_tester/util.py

@@ -100,6 +100,17 @@ def setcap_net_admin(binary, run_dir):
     proc = Process(SETCAP_NET_ADMIN_BIN, run_dir, ['sudo', SETCAP_NET_ADMIN_BIN, binary])
     proc.launch_sync()
 
+def move_iface_to_netns(ifname, netns, run_dir):
+    '''
+    Moves an iface to a netns. It creates the netns if it doesn't exist.
+    fail_iface_not_found=False is handy in order to assume the iface is already
+    in another netns and thus cannot be foud.
+    '''
+    from .process import Process
+    NETNS_SETUP_BIN = 'osmo-gsm-tester_netns_setup.sh'
+    proc = Process('move_netns', run_dir, ['sudo', NETNS_SETUP_BIN, ifname, netns])
+    proc.launch_sync()
+
 def import_path_prepend(pathname):
     dir = os.path.realpath(pathname)
     if dir not in sys.path:

utils/osmo-gsm-tester_netns_setup.sh

@@ -0,0 +1,22 @@
+#!/bin/bash -e
+
+ifname="$1"
+netns="$2"
+shift
+shift
+
+
+
+if [ -f "/var/run/netns/${netns}" ]; then
+    echo "netns $netns already exists"
+else
+    echo "Creating netns $netns"
+    ip netns add "$netns"
+fi
+
+if [ -d "/sys/class/net/${ifname}" ]; then
+    echo "Moving iface $ifname to netns $netns"
+    ip link set $ifname netns $netns
+else
+    ip netns exec $netns ls "/sys/class/net/${ifname}" >/dev/null && echo "iface $ifname already in netns $netns"
+fi