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.

3 files changed, 27 insertions, 4 deletions

diff --git a/python/vyos/flavor.py b/python/vyos/flavor.py
index 46c1775f5..a9dccf448 100644
--- a/python/vyos/flavor.py
+++ b/python/vyos/flavor.py
@@ -21,7 +21,8 @@ convenient interface to reading it.
 
 Example of the version data dict::
   {
-   'console_type': 'ttyS0',
+   'console_type': 'ttyS',
+   'console_num': '0',
    'console_speed': '115200'
   }
 """
diff --git a/python/vyos/system/grub.py b/python/vyos/system/grub.py
index 1bae0d5fb..9435d18d2 100644
--- a/python/vyos/system/grub.py
+++ b/python/vyos/system/grub.py
@@ -390,7 +390,7 @@ def set_console_type(console_type: str, root_dir: str = '') -> None:
     """Write default console type to GRUB configuration
 
     Args:
-        console_type (str): a default console type
+        console_type (str): GRUB default console type, e.g. tty, ttyS or ttyAMA
         root_dir (str, optional): an optional path to the root directory.
         Defaults to empty.
     """
diff --git a/python/vyos/utils/kernel.py b/python/vyos/utils/kernel.py
index 48a7e88ea..726025605 100644
--- a/python/vyos/utils/kernel.py
+++ b/python/vyos/utils/kernel.py
@@ -14,12 +14,13 @@
 # License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+from typing import Tuple
+from typing import Optional
 
 # A list of used Kernel constants
 # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/net/wireguard/messages.h?h=linux-6.6.y#n45
 WIREGUARD_REKEY_AFTER_TIME = 120
 
-
 def load_module(name: str, quiet: bool = True, dry_run: bool = False) -> int:
     """Load a kernel module via modprobe.
 
@@ -39,7 +40,6 @@ def load_module(name: str, quiet: bool = True, dry_run: bool = False) -> int:
     cmd.append(name)
     return run(cmd)
 
-
 def unload_module(name: str) -> int:
     """Unload a kernel module via rmmod.
 
@@ -150,3 +150,25 @@ def lsmod():
     for m in list_loaded_modules():
         mods_data.append(get_module_data(m))
     return mods_data
+
+def get_kernel_serial_console() -> Tuple[Optional[str], Optional[str], Optional[str]]:
+    """
+    Extract the serial console type, number, and speed setting from the kernel
+    command line which was used during system boot.
+    """
+    import re
+    from vyos.utils.file import read_file
+
+    cmdline_console_re = re.compile(
+        r'(?:^|\s)console=(?P<console_type>tty(?:S|AMA))(?P<console_num>\d+),(?P<console_speed>\d+)(?=\s|$)'
+    )
+
+    kernel_cmdline = read_file('/proc/cmdline')
+    if m := cmdline_console_re.search(kernel_cmdline):
+        return (
+            m.group('console_type'),
+            m.group('console_num'),
+            m.group('console_speed'),
+        )
+
+    return (None, None, None)