Re: [PATCH v2 2/3] bootconfig: Support embedding a bootconfig file in kernel

[Padmanabha Srinivasaiah]

Hello Masami Hiramatsu,

On Mon, Mar 14, 2022 at 06:08:41PM +0900, Masami Hiramatsu wrote:
> 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_EMBED_BOOT_CONFIG=y and set
> the file path to CONFIG_EMBED_BOOT_CONFIG_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.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
>  include/linux/bootconfig.h |   10 ++++++++++
>  init/Kconfig               |   21 +++++++++++++++++++++
>  init/main.c                |   13 ++++++++-----
>  lib/.gitignore             |    1 +
>  lib/Makefile               |   12 ++++++++++++
>  lib/bootconfig.c           |   23 +++++++++++++++++++++++
>  6 files changed, 75 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> index a4665c7ab07c..5dbda5e3e9bb 100644
> --- a/include/linux/bootconfig.h
> +++ b/include/linux/bootconfig.h
> @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
>  /* XBC cleanup data structures */
>  void __init xbc_exit(void);
>  
> +/* XBC embedded bootconfig data in kernel */
> +#ifdef CONFIG_EMBED_BOOT_CONFIG
> +char * __init xbc_get_embedded_bootconfig(size_t *size);
> +#else
> +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> +{
> +	return NULL;
> +}
> +#endif
> +
>  #endif
> diff --git a/init/Kconfig b/init/Kconfig
> index e9119bf54b1f..70440804874d 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1357,6 +1357,27 @@ config BOOT_CONFIG
>  
>  	  If unsure, say Y.
>  
> +config EMBED_BOOT_CONFIG
> +	bool "Embed bootconfig file in the kernel"
> +	depends on BOOT_CONFIG
> +	default n
> +	help
> +	  Embed a bootconfig file given by EMBED_BOOT_CONFIG_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 EMBED_BOOT_CONFIG_FILE
> +	string "Embedded bootconfig file path"
> +	default ""
> +	depends on EMBED_BOOT_CONFIG
> +	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 421050be5039..3803bf2e22ea 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -265,7 +265,7 @@ 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;
> @@ -411,12 +411,15 @@ static void __init setup_boot_config(void)
>  	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
>  	const char *msg;
>  	int pos;
> -	u32 size;
> +	size_t size;
>  	char *data, *err;
>  	int ret;
>  
>  	/* 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,
> @@ -435,8 +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;
>  	}
>  
> @@ -449,7 +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 */
> diff --git a/lib/.gitignore b/lib/.gitignore
> index e5e217b8307b..30a2a5db7033 100644
> --- a/lib/.gitignore
> +++ b/lib/.gitignore
> @@ -6,3 +6,4 @@
>  /oid_registry_data.c
>  /test_fortify.log
>  /test_fortify/*.log
> +/default.bconf
> diff --git a/lib/Makefile b/lib/Makefile
> index 300f569c626b..8183785ee99d 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -279,6 +279,18 @@ $(foreach file, $(libfdt_files), \
>  	$(eval CFLAGS_$(file) = -I $(srctree)/scripts/dtc/libfdt))
>  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
>  
> +ifeq ($(CONFIG_EMBED_BOOT_CONFIG),y)
> +# Since the specified bootconfig file can be switched, we forcibly update the
> +# default.bconf file always.
> +$(obj)/default.bconf: FORCE
> +	$(call cmd,defbconf)
> +
> +quiet_cmd_defbconf = GEN     $@
> +      cmd_defbconf = cat < /dev/null $(CONFIG_EMBED_BOOT_CONFIG_FILE) > $@
> +clean-files	+= default.bconf
> +$(obj)/bootconfig.o: $(obj)/default.bconf
> +endif
> +
>  lib-$(CONFIG_BOOT_CONFIG) += bootconfig.o
>  
>  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> index 74f3201ab8e5..3a3bf3a208e3 100644
> --- a/lib/bootconfig.c
> +++ b/lib/bootconfig.c
> @@ -12,6 +12,29 @@
>  #include <linux/kernel.h>
>  #include <linux/memblock.h>
>  #include <linux/string.h>
> +
> +#ifdef CONFIG_EMBED_BOOT_CONFIG
> +asm (
> +"	.pushsection .init.data, \"aw\"			\n"
> +"	.global embedded_bootconfig_data		\n"
> +"embedded_bootconfig_data:				\n"
> +"	.incbin \"lib/default.bconf\"			\n"
> +"	.global embedded_bootconfig_data_end		\n"
> +"embedded_bootconfig_data_end:				\n"
> +"	.popsection					\n"
> +);
> +
> +extern __visible char embedded_bootconfig_data[];
> +extern __visible char embedded_bootconfig_data_end[];
> +
> +char * __init xbc_get_embedded_bootconfig(size_t *size)
> +{
> +	*size = embedded_bootconfig_data_end - embedded_bootconfig_data;
> +	return (*size) ? embedded_bootconfig_data : NULL;
> +}
> +
> +#endif
> +
>  #else /* !__KERNEL__ */
>  /*
>   * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
>

Thanks tested the implemation, it works as expected.

Also noted that a change in default.bconf requries a clean build, is it
expected behaviour?

Thanks and Regards,
Padmanabha.S