new method to identify system packages on gentoo

System packages are now:
* Anything in sys-boot/ category
* sys-libs/glibc and sys-libs/musl
* any ebuild that uses one of these eclasses:
    - dist-kernel-utils
    - linux-mod-r1
    - kernel-install

sau/gentoo.py

@@ -109,6 +109,45 @@ def _sync_portage():
         for line in err.splitlines():
             log.warning("stderr: {}".format(line))
 
+def is_system_package(atom):
+    name=re.sub(r'^[<=>]*(.*?)(?:-\d)?(?:::\w+)?$', r'\1', atom)
+
+    # sys-boot/ category should probably always be considered
+    # system-packages
+    if name.split('/')[0] == 'sys-boot':
+        return True
+
+    # libc-packages should be considered system-packages as they generally
+    # requires the system to be restarted. Not sure if there is a better way
+    # then just checking for specific packages here, but as far as I know there
+    # are not many of them anyway...
+    if re.search(r'^sys-libs/(glibc|musl)', name):
+        return True
+
+    # anything that requires boot-partition to be mounted should be considered
+    # system packages. So far I've identified these eclasses that touches
+    # boot/kernel:
+    # * dist-kernel-utils
+    # * linux-mod-r1
+    # * kernel-install
+    test_re = re.compile(r'^\s*inherit\s+(dist-kernel-utils|linux-mod|kernel-install)')
+    cmd=[ EQUERY_PATH, 'w', name ]
+    ret, out, err = sau.helpers.exec_cmd(cmd)
+    if not ret == 0:
+        log.warning(f'Unable to locate ebuild for {atom}')
+        # better safe than sorry; if we don't know, let's pretend it's a system
+        # package
+        return True
+    path = out.strip()
+    if not os.path.isfile(path):
+        log.warning(f"This path doesn't look lika a path to the ebuild for {name}: {path}")
+        return True
+    with open(path, 'r', encoding='utf-8') as f:
+        for line in f.readline():
+            if re.search(test_re, line):
+                return True
+
+    return False
 
 
 
@@ -161,11 +200,12 @@ def pkg_upgrade():
         else:
             log.error('{} -- {} -> {} configured level {} > pkg level {}'.format(name, old, new, sens, common))
             do_rebuild = False
-        if name.startswith('sys-kernel/'):
+
+        if is_system_package(f'{name}-{new}'):
             if do_system_upgrade:
                 do_grub = True
             else:
-                raise sau.errors.UpgradeError(f"Kernel package {name} has an update, but system upgrade is disabled")
+                raise sau.errors.UpgradeError(f"System package {name} has an update, but system upgrade is disabled")
 
     if not do_rebuild:
         raise sau.errors.UpgradeError('Some packages require manual attention, did not upgrade')