Date:   Thu, 31 Mar 2022 15:49:18 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masahiro Yamada <masahiroy@...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, 31 Mar 2022 15:27:56 +0900
Masahiro Yamada <masahiroy@...nel.org> wrote:

> 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.

Oops, yes. I have made a dumb copy from the inline asm...

> 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.

OK.

> 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.

Yes, it can be. The data is passed via 'const char *'.

> 
> 
> 
> Some more nits:
> 
>     default n
> 
>     default ""
> 
> are the redundant defaults in Kconfig.

Thanks for that information. Let me remove those lines. :)

> 
> 
> 
> 
> 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.

Good comment. OK, I'll change it next version.

Thank you!

> 
> 
> 
> 
> 
> 
> 
> > 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


-- 
Masami Hiramatsu <mhiramat@...nel.org>

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