wwan: T9350: move session re-dial from cron into vyos-netlinkd

/etc/cron.d/vyos-wwan re-ran the conf_mode script every 5 minutes via
op-mode "connect interface wwanN" to re-establish a session lost to RF
signal loss. Re-entering conf_mode from cron is unsafe: the cron job knows
nothing about the boot commit or about a commit in flight, so when a tick
lands before the running config is populated, get_config() returns nothing
but {'ifname', 'deleted'} and apply() takes the teardown branch instead of
dialling. It then stops the DHCP clients, stops ModemManager and unlinks its
own cron file, leaving wwan0 down with no way to recover until the next
commit:

  CRON[1869]: (root) CMD (/usr/libexec/vyos/vyos-check-wwan.py)
  systemd[1]: Stopping DHCP client on wwan0...
  systemd[1]: Stopping Modem Manager...

This is timing dependent - it only bites when a */5 tick coincides with
boot - which is why it presents as an intermittently dead WWAN interface.

Move the re-dial into vyos-netlinkd, which already tracks these interfaces
for DHCP and already gates all of its work behind boot_configuration_complete()
and commit_in_progress2(). A re-dial can therefore no longer land on a
half-applied configuration. It also dials ModemManager directly rather than
re-entering conf_mode, so the teardown branch is no longer reachable from
the recovery path at all.

1 files changed, 124 insertions, 0 deletions

diff --git a/python/vyos/utils/wwan.py b/python/vyos/utils/wwan.py
new file mode 100644
index 000000000..fd8cd4f2e
--- /dev/null
+++ b/python/vyos/utils/wwan.py
@@ -0,0 +1,124 @@
+# Copyright (C) VyOS Inc.
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+
+"""ModemManager helpers shared between the WWAN conf_mode script and
+vyos-netlinkd.
+
+Both dial the very same modem with the very same parameters - conf_mode when
+the CLI config is applied, vyos-netlinkd when a session has to be re-
+established after it was lost. Keeping the option string and the mmcli
+invocations in one place means a re-dial can never drift from what conf_mode
+would have done.
+"""
+
+from time import sleep
+
+from vyos.utils.dict import dict_search
+from vyos.utils.process import call
+from vyos.utils.process import cmdl
+from vyos.utils.process import DEVNULL
+from vyos.utils.process import is_systemd_service_active
+
+service_name = 'ModemManager.service'
+
+# Bounded wait for a modem to appear after ModemManager has been started. The
+# service being up is not enough - the modem is only dialable once it has been
+# probed and exported on the bus, which takes a moment longer.
+modem_wait_timeout = 25
+modem_wait_poll = 0.250
+
+def modem_index(ifname: str) -> str:
+    """ Return the ModemManager modem index backing an interface, wwan0 -> 0 """
+    if not ifname.startswith('wwan'):
+        raise ValueError(f'Specified interface "{ifname}" is not a WWAN interface')
+    return ifname[len('wwan'):]
+
+def start_modem_manager() -> None:
+    """ ModemManager is required to dial WWAN connections - a single instance
+    serves all modems. Start it if it is not running yet and wait until a modem
+    has been detected, so a dial that follows does not race the probing. """
+    if is_systemd_service_active(service_name):
+        return None
+
+    cmdl(['systemctl', 'start', service_name])
+
+    counter = int(modem_wait_timeout / modem_wait_poll)
+    while counter > 0:
+        counter -= 1
+        try:
+            tmp = cmdl(['mmcli', '-L'])
+        except OSError:
+            # ModemManager is up but not yet answering on the bus - keep
+            # polling, this is expected for the first moments after start.
+            tmp = ''
+        if tmp and tmp != 'No modems were found':
+            break
+        sleep(modem_wait_poll)
+
+    return None
+
+def connect_options(config: dict) -> str:
+    """ Build the mmcli --simple-connect option string for a WWAN interface.
+
+    config is an interface configuration dict as returned by
+    get_interface_dict() in conf_mode or op_mode_config_dict() in an op-mode
+    context - both are key-mangled the same way, so both are accepted here.
+    """
+    ip_type = 'ipv4'
+    slaac = dict_search('ipv6.address.autoconf', config) != None
+    if 'address' in config:
+        if 'dhcp' in config['address'] and ('dhcpv6' in config['address'] or slaac):
+            ip_type = 'ipv4v6'
+        elif 'dhcpv6' in config['address'] or slaac:
+            ip_type = 'ipv6'
+        elif 'dhcp' in config['address']:
+            ip_type = 'ipv4'
+
+    options = f'ip-type={ip_type},apn=' + config['apn']
+    if 'authentication' in config:
+        options += ',user={username},password={password}'.format(**config['authentication'])
+
+    return options
+
+def modem_disconnect(ifname: str) -> None:
+    """ Disconnect every bearer of the modem backing ifname. The number of
+    bearers a modem can hold is limited, so we always disconnect before we
+    dial again. """
+    call(f'mmcli --modem {modem_index(ifname)} --simple-disconnect')
+
+def modem_connect(ifname: str, options: str) -> bool:
+    """ Dial the modem backing ifname, returns True if the modem connected """
+    modem = modem_index(ifname)
+
+    # Some networks only ever admit a single combined IPv4+IPv6 PDN context per
+    # APN and reject a standalone IPv6 "Start Network" request outright (QMI
+    # CallEndReason ip-version-mismatch) once an IPv4 session already exists for
+    # that APN. ModemManager's --simple-connect with ip-type=ipv4v6 opens two
+    # separate WDS sessions (one per family) rather than negotiating both
+    # together, which is what a normal handset attach does and why this is
+    # invisible on most other devices.
+    #
+    # Pre-negotiating the attach-time PDN type upfront avoids the rejection; the
+    # resulting bearer only sets up what the *next* --simple-connect is allowed
+    # to request and can't be connected directly, so a failure here isn't fatal
+    # - unsupported modems simply proceed to --simple-connect exactly as before.
+    if options.partition('ip-type=')[2].partition(',')[0] in ('ipv6', 'ipv4v6'):
+        # best effort by definition, so do not report the rejection a modem
+        # without attach configuration support answers with on every dial
+        call(f'mmcli --modem {modem} --3gpp-set-initial-eps-bearer-settings="{options}"',
+             stdout=DEVNULL, stderr=DEVNULL)
+
+    command = f'mmcli --modem {modem} --simple-connect="{options}"'
+    return call(command, stdout=DEVNULL) == 0