serial: T8375: add CLI option to explicitly set kernel console

Previously, VyOS hardcoded the kernel boot log console to either ttyS0 or
tty0, with no post-install CLI method to change it (manual GRUB edits
were required).

This commit adds a new CLI node:
  system console device <name> kernel

When set, the selected serial console is used as the kernel boot console.
When removed, the kernel boot console falls back to tty0.

1 files changed, 19 insertions, 33 deletions

diff --git a/src/activation-scripts/05-serial_console.py b/src/activation-scripts/05-serial_console.py
index 93e381d17..ccda2ac4e 100755
--- a/src/activation-scripts/05-serial_console.py
+++ b/src/activation-scripts/05-serial_console.py
@@ -13,45 +13,31 @@
 # 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/>.
 
-import re
-
-from typing import Optional
-from typing import Tuple
-
 from vyos.configtree import ConfigTree
-from vyos.utils.file import read_file
 from vyos.system.image import is_live_boot
+from vyos.utils.kernel import get_kernel_serial_console
+from vyos.utils.serial import is_tty
 
 base = ['system', 'console', 'device']
 
-def get_kernel_serial_console() -> Tuple[Optional[str], Optional[str]]:
-    """
-    Extract the serial console device and speed setting from the kernel
-    command line.
-    """
-    device = speed = None
-    CMDLINE_CONSOLE_RE = re.compile(
-        r'(?:^|\s)console=(?P<device>tty(?:S|AMA)\d+),(?P<speed>\d+)(?=\s|$)'
-    )
-    kernel_cmdline = read_file('/proc/cmdline')
-    if m := CMDLINE_CONSOLE_RE.search(kernel_cmdline):
-        device = m.group("device") # "ttyS0"
-        speed = m.group("speed")   # Baud rate/speed, e.g. "115200"
-
-    return (device, speed)
-
 def activate(config: ConfigTree):
-    # Configure the kernel serial console only once during live boot.
-    # During installation, the user can define the console. If this is not
-    # limited to live boot, the serial interface will always be re-added during
-    # system boot, even if it was removed from config.boot.
+    # Configure the kernel serial console only once during live boot. During
+    # installation, the user can define the console type (VT TTY or serial
+    # TTY). If this is not limited to live boot, the serial interface will
+    # always be re-added during system boot, even if it was removed from
+    # config.boot.
     if not is_live_boot():
         return
 
-    (device, speed) = get_kernel_serial_console()
-    if device and speed:
-        # The kernel was booted with a configured serial console, but no
-        # console is configured in the CLI; align/fix the CLI configuration.
-        if not config.exists(base + [device]):
-            config.set(base + [device, 'speed'], value=speed)
-            config.set_tag(base)
+    # Parse current kernel cmdline and continue only for valid serial console
+    # data. Prevent writing incomplete/invalid console settings to config.boot.
+    console_type, console_num, console_speed = get_kernel_serial_console()
+    device = f'{console_type}{console_num}'
+    if not is_tty(device) or not console_speed:
+        return
+
+    # The kernel was booted with a configured serial console, but no console
+    # is configured via CLI; align/fix the CLI configuration.
+    if not config.exists(base + [device]):
+        config.set(base + [device, 'speed'], value=console_speed)
+        config.set_tag(base)