bootconfig: Support embedding a bootconfig file in kernel

This allows kernel developer to embed a default bootconfig file in
the kernel instead of embedding it in the initrd. This will be good
for who are using the kernel without initrd, or who needs a default
bootconfigs.
This needs to set two kconfigs: CONFIG_BOOT_CONFIG_EMBED=y and set
the file path to CONFIG_BOOT_CONFIG_EMBED_FILE.

Note that you still need 'bootconfig' command line option to load the
embedded bootconfig. Also if you boot using an initrd with a different
bootconfig, the kernel will use the bootconfig in the initrd, instead
of the default bootconfig.

Link: https://lkml.kernel.org/r/164921227943.1090670.14035119557571329218.stgit@devnote2

Cc: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

2 files changed, 32 insertions, 11 deletions

diff --git a/init/Kconfig b/init/Kconfig
index ddcbefe535e9..2462d4ae2dc8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1351,7 +1351,7 @@ endif
 
 config BOOT_CONFIG
 	bool "Boot config support"
-	select BLK_DEV_INITRD
+	select BLK_DEV_INITRD if !BOOT_CONFIG_EMBED
 	help
 	  Extra boot config allows system admin to pass a config file as
 	  complemental extension of kernel cmdline when booting.
@@ -1361,6 +1361,25 @@ config BOOT_CONFIG
 
 	  If unsure, say Y.
 
+config BOOT_CONFIG_EMBED
+	bool "Embed bootconfig file in the kernel"
+	depends on BOOT_CONFIG
+	help
+	  Embed a bootconfig file given by BOOT_CONFIG_EMBED_FILE in the
+	  kernel. Usually, the bootconfig file is loaded with the initrd
+	  image. But if the system doesn't support initrd, this option will
+	  help you by embedding a bootconfig file while building the kernel.
+
+	  If unsure, say N.
+
+config BOOT_CONFIG_EMBED_FILE
+	string "Embedded bootconfig file path"
+	depends on BOOT_CONFIG_EMBED
+	help
+	  Specify a bootconfig file which will be embedded to the kernel.
+	  This bootconfig will be used if there is no initrd or no other
+	  bootconfig in the initrd.
+
 choice
 	prompt "Compiler optimization level"
 	default CC_OPTIMIZE_FOR_PERFORMANCE
diff --git a/init/main.c b/init/main.c
index 266d61bc67b0..f7fe7cbb1df8 100644
--- a/init/main.c
+++ b/init/main.c
@@ -266,7 +266,7 @@ static int __init loglevel(char *str)
 early_param("loglevel", loglevel);
 
 #ifdef CONFIG_BLK_DEV_INITRD
-static void * __init get_boot_config_from_initrd(u32 *_size)
+static void * __init get_boot_config_from_initrd(size_t *_size)
 {
 	u32 size, csum;
 	char *data;
@@ -313,7 +313,7 @@ found:
 	return data;
 }
 #else
-static void * __init get_boot_config_from_initrd(u32 *_size)
+static void * __init get_boot_config_from_initrd(size_t *_size)
 {
 	return NULL;
 }
@@ -410,14 +410,16 @@ static int __init warn_bootconfig(char *str)
 static void __init setup_boot_config(void)
 {
 	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
-	const char *msg;
-	int pos;
-	u32 size;
-	char *data, *err;
-	int ret;
+	const char *msg, *data;
+	int pos, ret;
+	size_t size;
+	char *err;
 
 	/* Cut out the bootconfig data even if we have no bootconfig option */
 	data = get_boot_config_from_initrd(&size);
+	/* If there is no bootconfig in initrd, try embedded one. */
+	if (!data)
+		data = xbc_get_embedded_bootconfig(&size);
 
 	strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
@@ -436,8 +438,8 @@ static void __init setup_boot_config(void)
 	}
 
 	if (size >= XBC_DATA_MAX) {
-		pr_err("bootconfig size %d greater than max size %d\n",
-			size, XBC_DATA_MAX);
+		pr_err("bootconfig size %ld greater than max size %d\n",
+			(long)size, XBC_DATA_MAX);
 		return;
 	}
 
@@ -450,7 +452,7 @@ static void __init setup_boot_config(void)
 				msg, pos);
 	} else {
 		xbc_get_info(&ret, NULL);
-		pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
+		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
 		/* keys starting with "kernel." are passed via cmdline */
 		extra_command_line = xbc_make_cmdline("kernel");
 		/* Also, "init." keys are init arguments */