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, 55 insertions, 0 deletions

diff --git a/src/migration-scripts/interfaces/10-to-11 b/src/migration-scripts/interfaces/10-to-11
new file mode 100755
index 000000000..6b8e49ed9
--- /dev/null
+++ b/src/migration-scripts/interfaces/10-to-11
@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2020 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# rename WWAN (wirelessmodem) serial interface from non persistent ttyUSB2 to
+# a bus like name, e.g. "usb0b1.3p1.3"
+
+import os
+
+from sys import exit, argv
+from vyos.configtree import ConfigTree
+
+if __name__ == '__main__':
+    if (len(argv) < 1):
+        print("Must specify file name!")
+        exit(1)
+
+    file_name = argv[1]
+    with open(file_name, 'r') as f:
+        config_file = f.read()
+
+    config = ConfigTree(config_file)
+    base = ['interfaces', 'wirelessmodem']
+    if not config.exists(base):
+        # Nothing to do
+        exit(0)
+
+    for wwan in config.list_nodes(base):
+        if config.exists(base + [wwan, 'device']):
+            device = config.return_value(base + [wwan, 'device'])
+
+            for root, dirs, files in os.walk('/dev/serial/by-bus'):
+                for file in files:
+                    device_file = os.path.realpath(os.path.join(root, file))
+                    if os.path.basename(device_file) == device:
+                        config.set(base + [wwan, 'device'], value=file, replace=True)
+
+    try:
+        with open(file_name, 'w') as f:
+            f.write(config.to_string())
+    except OSError as e:
+        print("Failed to save the modified config: {}".format(e))
+        exit(1)