image: T9269: skip GRUB updates on container and diskless systems

Kernel cmdline and serial console updates rewrite the GRUB configuration on
the persistence partition. A container has no GRUB at all, and on a system
where the persistence partition is not mounted disk.find_persistence()
returns an empty string, so the code reads '//boot/grub/grub.cfg' and dies
with FileNotFoundError.

Extend is_running_as_container() to also honor /run/.containerenv (Podman)
and the container= variable systemd sets for PID 1, and add if_not_container()
plus if_persistence() decorators guarding all grub_util entry points.

2 files changed, 52 insertions, 1 deletions

diff --git a/python/vyos/system/grub_util.py b/python/vyos/system/grub_util.py
index edaea8ad3..98d3c1ddc 100644
--- a/python/vyos/system/grub_util.py
+++ b/python/vyos/system/grub_util.py
@@ -18,6 +18,8 @@ from vyos.system import grub
 from vyos.system import image
 from vyos.system import compat
 
+@image.if_not_container
+@image.if_persistence
 @compat.grub_cfg_update
 def set_serial_console(console_type: str, console_num: str,
                        console_speed: str, root_dir: str = '') -> None:
@@ -34,6 +36,8 @@ def set_serial_console(console_type: str, console_num: str,
     grub.set_serial_console(console_type, console_num, console_speed, root_dir)
 
 @image.if_not_live_boot
+@image.if_not_container
+@image.if_persistence
 def update_serial_console(console_type: str, console_num: str,
                           console_speed: str, root_dir: str = '') -> None:
     """Update console_speed if different from current value"""
@@ -53,6 +57,8 @@ def update_serial_console(console_type: str, console_num: str,
        console_speed != console_speed_current:
         set_serial_console(console_type, console_num, console_speed, root_dir)
 
+@image.if_not_container
+@image.if_persistence
 @compat.grub_cfg_update
 def set_kernel_cmdline_options(cmdline_options: str, version: str = '',
                                root_dir: str = '') -> None:
@@ -66,6 +72,8 @@ def set_kernel_cmdline_options(cmdline_options: str, version: str = '',
     grub.set_kernel_cmdline_options(cmdline_options, version, root_dir)
 
 @image.if_not_live_boot
+@image.if_not_container
+@image.if_persistence
 def update_kernel_cmdline_options(cmdline_options: str,
                                   root_dir: str = '',
                                   version = image.get_running_image()) -> None:
diff --git a/python/vyos/system/image.py b/python/vyos/system/image.py
index 02f2303b2..0b2eccf6d 100644
--- a/python/vyos/system/image.py
+++ b/python/vyos/system/image.py
@@ -283,6 +283,49 @@ def if_not_live_boot(func):
     return wrapper
 
 def is_running_as_container() -> bool:
-    if Path('/.dockerenv').exists():
+    """Detect if the system is running inside a container
+
+    Returns:
+        bool: True if running as container (Docker, Podman, LXC, ...)
+    """
+    # Docker and Podman drop a marker file into the container root
+    if Path('/.dockerenv').exists() or Path('/run/.containerenv').exists():
         return True
+    # systemd sets container= in the environment of PID 1 for all container
+    # types it knows about - this is only readable by root
+    try:
+        environ = Path('/proc/1/environ').read_bytes().decode(errors='ignore')
+        if 'container=' in environ:
+            return True
+    except (OSError, PermissionError):
+        pass
     return False
+
+def has_persistence() -> bool:
+    """Detect if a persistence storage partition is mounted
+
+    Returns:
+        bool: True if the persistence partition is available
+    """
+    return bool(disk.find_persistence())
+
+def if_persistence(func):
+    """Decorator to call function only if persistence storage is available.
+    Without it there is no writeable GRUB configuration to operate on"""
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        if has_persistence():
+            ret = func(*args, **kwargs)
+            return ret
+        return None
+    return wrapper
+
+def if_not_container(func):
+    """Decorator to call function only if not running inside a container"""
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        if not is_running_as_container():
+            ret = func(*args, **kwargs)
+            return ret
+        return None
+    return wrapper