wwan: T2529: migrate device from ttyUSB to usbXbY.YpZ.Z

During testing it was discovered that there is a well known problem (we had for
ethernet interfaces) also in the serial port world. They will be enumerated and
mapped to /dev/ttyUSBxxx differently from boot to boot. This is especially
painful on my development APU4 board which also has a Sierra Wireless MC7710
LTE module installed.

The serial port will toggle between ttyUSB2 and ttyUSB5 depending on the
amount of serial port extenders attached (FT4232H).

The shipped udev rule (/usr/lib/udev/rules.d/60-serial.rules) partly solves
this by enumerating the devices into /dev/serial/by-id folder with their name
and serial number - it's a very good idea but I've found that not all of the
FT4232H dongles have a serial number programmed - this leads to the situation
that when you plug in two cables with both having serial number 0 - only one
device symlink will appear - the previous one is always overwritten by the
latter one.

Derive /usr/lib/udev/rules.d/60-serial.rules and create a /dev/serial/by-bus
directory and group devices by attached USB root port.

  vyos@vyos:~$ find /dev/serial/by-bus/ -name usb* -exec basename {} \; | sort
  usb0b1.3p1.0
  usb0b1.3p1.2
  usb0b1.3p1.3
  usb0b2.4p1.0
  usb0b2.4p1.1
  usb0b2.4p1.2
  usb0b2.4p1.3

So we have USB root 0 with bus 1.3 and port 1.0. The enumeration is constant
accross reboots.

1 files changed, 26 insertions, 6 deletions

diff --git a/src/conf_mode/interfaces-wirelessmodem.py b/src/conf_mode/interfaces-wirelessmodem.py
index a13c70990..f16457a7f 100755
--- a/src/conf_mode/interfaces-wirelessmodem.py
+++ b/src/conf_mode/interfaces-wirelessmodem.py
@@ -16,9 +16,10 @@
 
 import os
 
-from sys import exit
 from copy import deepcopy
+from fnmatch import fnmatch
 from netifaces import interfaces
+from sys import exit
 
 from vyos.config import Config
 from vyos.ifconfig import BridgeIf, Section
@@ -36,7 +37,7 @@ default_config_data = {
     'chat_script': '',
     'deleted': False,
     'description': '',
-    'device': 'ttyUSB0',
+    'device': '',
     'disable': False,
     'disable_link_detect': 1,
     'on_demand': False,
@@ -56,6 +57,16 @@ def check_kmod():
             if call(f'modprobe {module}') != 0:
                 raise ConfigError(f'Loading Kernel module {module} failed')
 
+def find_device_file(device):
+    """ Recurively search /dev for the given device file and return its full path.
+        If no device file was found 'None' is returned """
+    for root, dirs, files in os.walk('/dev'):
+        for basename in files:
+            if fnmatch(basename, device):
+                return os.path.join(root, basename)
+
+    return None
+
 def get_config():
     wwan = deepcopy(default_config_data)
     conf = Config()
@@ -93,7 +104,13 @@ def get_config():
 
     # System device name
     if conf.exists(['device']):
-        wwan['device'] = conf.return_value(['device'])
+        tmp = conf.return_value(['device'])
+        wwan['device'] = find_device_file(tmp)
+        # If device file was not found in /dev we will just re-use
+        # the plain device name, thus we can trigger the exception
+        # in verify() as it's a non existent file
+        if wwan['device'] == None:
+            wwan['device'] = tmp
 
     # disable interface
     if conf.exists('disable'):
@@ -131,7 +148,10 @@ def verify(wwan):
         return None
 
     if not wwan['apn']:
-        raise ConfigError(f"APN for {wwan['intf']} not configured")
+        raise ConfigError('No APN configured for "{intf}"'.format(**wwan))
+
+    if not wwan['device']:
+        raise ConfigError('Physical "device" must be configured')
 
     # we can not use isfile() here as Linux device files are no regular files
     # thus the check will return False
@@ -169,7 +189,7 @@ def generate(wwan):
                     script_wwan_ip_up, script_wwan_ip_down]
 
     # Always hang-up WWAN connection prior generating new configuration file
-    cmd(f'systemctl stop ppp@{intf}.service')
+    call(f'systemctl stop ppp@{intf}.service')
 
     if wwan['deleted']:
         # Delete PPP configuration files
@@ -205,9 +225,9 @@ def apply(wwan):
     if not wwan['disable']:
         # "dial" WWAN connection
         intf = wwan['intf']
-        cmd(f'systemctl start ppp@{intf}.service')
         # make logfile owned by root / vyattacfg
         chown(wwan['logfile'], 'root', 'vyattacfg')
+        call(f'systemctl start ppp@{intf}.service')
 
         # re-add ourselves to any bridge we might have fallen out of
         # FIXME: wwan isn't under vyos.ifconfig so we can't call