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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