fix(image): select actual Gentoo distribution kernel image

hydra/image.py

@@ -129,16 +129,29 @@ def copy_overlay(root, overlay):
             destination.chmod(source.stat().st_mode & 0o777)
 
 
-def kernel_version(root):
+def _kernel_version(root):
     modules = root_path(root, 'lib/modules')
     versions = sorted(path.name for path in modules.iterdir() if path.is_dir()) if modules.is_dir() else []
     if len(versions) != 1 or not re.fullmatch(r'[A-Za-z0-9_.+-]+', versions[0]):
         raise ImageError('Exactly one installed payload kernel is required')
-    if not root_path(root, 'boot/vmlinuz-' + versions[0]).is_file():
-        raise ImageError('Installed modules have no matching /boot/vmlinuz-VERSION')
     return versions[0]
 
 
+def kernel_image(root):
+    version = _kernel_version(root)
+    candidates = [root_path(root, 'boot/' + prefix + version)
+                  for prefix in ('kernel-', 'vmlinuz-')]
+    images = [path for path in candidates if path.is_file()]
+    if len(images) != 1:
+        raise ImageError('Installed modules require exactly one matching boot kernel image')
+    return images[0]
+
+
+def kernel_version(root):
+    kernel_image(root)
+    return _kernel_version(root)
+
+
 def live_kernel_args():
     return [f'root=live:CDLABEL={LABEL}', 'rd.live.image', 'rd.live.overlay.overlayfs=1',
             'ro', 'console=tty0', 'console=ttyS0,115200n8']
@@ -356,7 +369,7 @@ def digest(path):
 
 def main(argv=None):
     parser = argparse.ArgumentParser(description=__doc__)
-    parser.add_argument('step', choices=('configure', 'kernel', 'network', 'audio'))
+    parser.add_argument('step', choices=('configure', 'kernel', 'kernel-image', 'network', 'audio'))
     parser.add_argument('root', nargs='?', type=Path)
     parser.add_argument('--source', type=Path)
     options = parser.parse_args(argv)
@@ -367,6 +380,8 @@ def main(argv=None):
             raise ImageError('An isolated rootfs directory is required')
         if options.step == 'kernel':
             print(kernel_version(options.root))
+        elif options.step == 'kernel-image':
+            print(kernel_image(options.root))
         elif options.step == 'audio':
             enable_user_audio(options.root)
         else: