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Date:   Sat, 26 Mar 2022 21:40:40 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Masahiro Yamada <masahiroy@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>
Subject: Re: [PATCH v2 2/3] bootconfig: Support embedding a bootconfig file
 in kernel
Message-Id: <20220326214040.07d4c8b99d7b83229509340d@kernel.org>
In-Reply-To: <CAK7LNAQKrybg7iAzPowqG5SuT6r5Y0v++96CKppM1=Ob4FG+bg@mail.gmail.com>
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        <20220316191649.GA11547@pswork>
        <20220318101445.fdb151efe58c6c3a1c572500@kernel.org>
        <CAK7LNAQKrybg7iAzPowqG5SuT6r5Y0v++96CKppM1=Ob4FG+bg@mail.gmail.com>
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On Sat, 26 Mar 2022 11:34:45 +0900
Masahiro Yamada <masahiroy@kernel.org> wrote:

> 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.

OK, thanks for the information! Let me check to learn how I can avoid
rebuilding it. I also found the Documentation/kbuild/makefile.rst,
which is very helpful! I'll update the patch.

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

Yes, it is the bootconfig version of the CONFIG_CMDLINE.
Since some boot-time tracing feature depends on the bootconfig (those can
not be set via kernel cmdline), we need this feature for those features
on non-initrd boot system.

Thank you!


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


-- 
Masami Hiramatsu <mhiramat@kernel.org>