Move build-buildroot linux configs to build-linux.

Needs a lot of testing, and need to cleanup readme, but seems to work.

build-linux

@@ -7,6 +7,42 @@ import common
 
 class LinuxComponent(common.Component):
     def add_parser_arguments(self, parser):
+        parser.add_argument(
+            '--config', default=[], action='append',
+            help='''\
+Add a single kernel config configs to the current build.
+The `CONFIG_` prefix is added automatically. Sample values:
+'FORTIFY_SOURCE=y', `KGDB=n`. Can be used multiple times to add multiple
+configs. Takes precedence over any config files.
+'''
+        )
+        parser.add_argument(
+            '--config-fragment', default=[], action='append',
+            help='''\
+Also use the given kernel configuration fragment file.
+Pass multiple times to use multiple fragment files.
+'''
+        )
+        parser.add_argument(
+            '--custom-config-file',
+            help='''\
+Ignore all default kernel configurations and use this file instead.
+Still uses options explicitly passed with `--config` and
+`--config-fragment` on top of it.
+'''
+        )
+        parser.add_argument(
+            '--config-only', default=False, action='store_true',
+            help='''\
+Configure the kernel, but don't build it.
+'''
+        )
+        parser.add_argument(
+            '--initramfs', default=False, action='store_true',
+        )
+        parser.add_argument(
+            '--initrd', default=False, action='store_true',
+        )
         parser.add_argument(
             'extra_make_args',
             default=[],
@@ -16,11 +52,9 @@ class LinuxComponent(common.Component):
 
     def do_build(self, args):
         build_dir = self.get_build_dir(args)
+        if args.initrd or args.initramfs:
+            raise Exception('just trolling, --initrd and --initramfs are broken for now')
         os.makedirs(build_dir, exist_ok=True)
-        common.cp(
-            os.path.join(common.linux_config_dir, 'buildroot-{}'.format(args.arch)),
-            os.path.join(build_dir, '.config'),
-        )
         tool = 'gcc'
         gcc = common.get_toolchain_tool(tool)
         prefix = gcc[:-len(tool)]
@@ -33,6 +67,8 @@ class LinuxComponent(common.Component):
         else:
             cc = gcc
         common_make_args = [
+            'make',
+            '-j', str(args.nproc),
             'ARCH={}'.format(common.linux_arch),
             'CROSS_COMPILE={}'.format(prefix),
             'CC={}'.format(cc),
@@ -42,41 +78,51 @@ class LinuxComponent(common.Component):
             verbose = ['V=1']
         else:
             verbose = []
+        if args.custom_config_file is not None:
+            if not os.path.exists(args.custom_config_file):
+                raise Exception('config fragment file does not exist: {}'.format(args.custom_config_file))
+            base_config_file = args.custom_config_file
+            config_fragments = []
+        else:
+            base_config_file = os.path.join(common.linux_config_dir, 'buildroot-{}'.format(args.arch))
+            config_fragments = ['min', 'default']
+            for i, config_fragment in enumerate(config_fragments):
+                config_fragments[i] = os.path.join(common.linux_config_dir, config_fragment)
+        config_fragments.extend(args.config_fragment)
+        if args.config != []:
+            cli_config_fragment_path = os.path.join(build_dir, 'lkmc_cli_config_fragment')
+            cli_config_str = '\n'.join(map(lambda x: 'CONFIG_' + x, args.config))
+            with open(cli_config_fragment_path, 'w') as cli_config_fragment_cli:
+                cli_config_fragment_cli.write(cli_config_str)
+            config_fragments.append(cli_config_fragment_path)
+        common.cp(
+            base_config_file,
+            os.path.join(build_dir, '.config'),
+        )
         common.run_cmd(
             [
                 os.path.join(common.linux_src_dir, 'scripts', 'kconfig', 'merge_config.sh'),
                 '-m',
                 '-O', build_dir,
                 os.path.join(build_dir, '.config'),
-                os.path.join(common.linux_config_dir, 'min'),
-                os.path.join(common.linux_config_dir, 'default'),
-            ],
+            ] +
+            config_fragments
         )
         common.run_cmd(
             (
-                [
-                    'make',
-                    '-j', str(args.nproc),
-                ] +
                 common_make_args +
-                [
-                    'olddefconfig',
-                ]
+                ['olddefconfig']
             ),
-            **common_args,
-        )
-        common.run_cmd(
-            (
-                [
-                    'make',
-                    '-j', str(args.nproc),
-                ] +
-                common_make_args +
-                verbose +
-                args.extra_make_args
-            ),
-            **common_args,
+            **common_args
         )
+        if not args.config_only:
+            common.run_cmd(
+                (
+                    common_make_args +
+                    args.extra_make_args
+                ),
+                **common_args
+            )
 
     def get_argparse_args(self):
         return {