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Message-ID: <CAK7LNARfcVt9L=BBmB7N8GNBHHU_LZx7mjMF9zW0ozfW3WNfeg@mail.gmail.com>
Date: Thu, 31 Mar 2022 15:27:56 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Padmanabha Srinivasaiah <treasure4paddy@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
Jonathan Corbet <corbet@....net>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
Randy Dunlap <rdunlap@...radead.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel
On Thu, Mar 31, 2022 at 2:56 PM Masami Hiramatsu <mhiramat@...nel.org> 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@...nel.org>
> ---
> Changes in v6:
> - Split out the .incbin asm part as bootconfig-data.S according to
> Masahiro's comment.
> Changes in v5:
> - Fix .gitignore to be sorted alphabetically.
> - Make default.bconf is cleaned up correctly.
> - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> (Thanks Masahiro!)
> Changes in v4:
> - Avoid updating the default.bconf if the file is not changed.
> ---
> MAINTAINERS | 1 +
> include/linux/bootconfig.h | 10 ++++++++++
> init/Kconfig | 21 +++++++++++++++++++++
> init/main.c | 13 ++++++++-----
> lib/.gitignore | 1 +
> lib/Makefile | 8 ++++++++
> lib/bootconfig-data.S | 11 +++++++++++
> lib/bootconfig.c | 13 +++++++++++++
> 8 files changed, 73 insertions(+), 5 deletions(-)
> create mode 100644 lib/bootconfig-data.S
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b555a5e8704f..9b4910685412 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7350,6 +7350,7 @@ S: Maintained
> F: Documentation/admin-guide/bootconfig.rst
> F: fs/proc/bootconfig.c
> F: include/linux/bootconfig.h
> +F: lib/bootconfig-data.S
> F: lib/bootconfig.c
> F: tools/bootconfig/*
> F: tools/bootconfig/scripts/*
> 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 97463a33baa7..f5d14a78cfce 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1361,6 +1361,27 @@ 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 266d61bc67b0..a5db3e36b809 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;
> @@ -412,12 +412,15 @@ 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,
> @@ -436,8 +439,8 @@ 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 +453,7 @@ 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..54596b634ecb 100644
> --- a/lib/.gitignore
> +++ b/lib/.gitignore
> @@ -1,6 +1,7 @@
> # SPDX-License-Identifier: GPL-2.0-only
> /crc32table.h
> /crc64table.h
> +/default.bconf
> /gen_crc32table
> /gen_crc64table
> /oid_registry_data.c
> diff --git a/lib/Makefile b/lib/Makefile
> index 08053df16c7c..2a82cc324f91 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
> lib-$(CONFIG_LIBFDT) += $(libfdt_files)
>
> obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> +obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
> +
> +$(obj)/bootconfig-data.o: $(obj)/default.bconf
> +
> +targets += default.bconf
> +filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
> +$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
> + $(call filechk,defbconf)
>
> obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
> diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
> new file mode 100644
> index 000000000000..df674ea7d8be
> --- /dev/null
> +++ b/lib/bootconfig-data.S
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Embed default bootconfig in the kernel.
> + */
> + .pushsection .init.data, "aw"
> + .global embedded_bootconfig_data
> +embedded_bootconfig_data:
> + .incbin "lib/default.bconf"
> + .global embedded_bootconfig_data_end
> +embedded_bootconfig_data_end:
> + .popsection
You used .pushsection / .popsection because it was
previously located in bootconfig.c, where there are
functions, which should go to the ".text" section.
Now that you split this into a separate compilation unit,
there is only one ".init.data" section in the file.
.section .init.data, "aw"
should be enough.
BTW, is it reasonable/possible to make it explicitly read-only?
I have not tested this patch at all. Nor do I have enough insight.
.section .init.rodata, "a"
I am not sure whether this is possible or not.
Some more nits:
default n
default ""
are the redundant defaults in Kconfig.
Personally, I prefer seeing the common prefix
for options that belong to the same group,
for example,
CONFIG_BOOT_CONFIG
CONFIG_BOOT_CONFIG_EMBED
CONFIG_BOOT_CONFIG_EMBEDDED_FILE
But, this is something like "up to you" things.
> diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> index 74f3201ab8e5..6d30aee85ebe 100644
> --- a/lib/bootconfig.c
> +++ b/lib/bootconfig.c
> @@ -12,6 +12,19 @@
> #include <linux/kernel.h>
> #include <linux/memblock.h>
> #include <linux/string.h>
> +
> +#ifdef CONFIG_EMBED_BOOT_CONFIG
> +/* embedded_bootconfig_data is defined in bootconfig-data.S */
> +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
>
--
Best Regards
Masahiro Yamada
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