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In-Reply-To: <20220318101445.fdb151efe58c6c3a1c572500@kernel.org>
From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Sat, 26 Mar 2022 11:34:45 +0900
Message-ID: <CAK7LNAQKrybg7iAzPowqG5SuT6r5Y0v++96CKppM1=Ob4FG+bg@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] bootconfig: Support embedding a bootconfig file in kernel
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Padmanabha Srinivasaiah <treasure4paddy@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>
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On Fri, Mar 18, 2022 at 10:14 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Wed, 16 Mar 2022 20:16:49 +0100
> Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:
>
> > 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@kernel.org>
> > > ---
> > >  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.
>
> Great!
>
> >
> > Also noted that a change in default.bconf requries a clean build, is it
> > expected behaviour?
>
> default.bconf will be always updated if CONFIG_EMBED_BOOT_CONFIG=y. So you can
> do incremental build. (I tested it with the incremental build environment)


So, default.bconf is always re-generated,
causing bootconfig.o to be always rebuilt,
causing vmlinux to be always rebuilt.

This is absolutely unacceptable.

If you do not change the source tree at all,
the incremental build must be really quick,
simply doing nothing.

You can check how $(obj)/config_data
avoids the unneeded timestamp update.


BTW, it is already possible to embed kernel parameters
into the kernel.
Is this another implementation of CONFIG_CMDLINE?


> Thank you,
>
> >
> > Thanks and Regards,
> > Padmanabha.S
>
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>


-- 
Best Regards
Masahiro Yamada