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Date: Thu, 31 Mar 2022 16:20:56 +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 15:54:40 +0900
Masahiro Yamada <masahiroy@...nel.org> wrote:
> On Thu, Mar 31, 2022 at 3:49 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> > 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 *'.
>
> But, you didn't add "const" in the C code:
>
> extern __visible char embedded_bootconfig_data[];
> extern __visible char embedded_bootconfig_data_end[];
>
>
> Is it possible to use "const char" ?
Yes, I need to update C part too, and that is not a problem. :)
Thank you!
>
>
>
> --
> Best Regards
> Masahiro Yamada
--
Masami Hiramatsu <mhiramat@...nel.org>
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