linux-kernel - Re: [PATCH v2] moduleparam: Save information about built-in modules in separate file

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Message-ID: <CAK7LNATfo0K6kzwobkAZ_u2KnWL3XycJzbr3KPtPF=ePziCuDg@mail.gmail.com>
Date:   Thu, 18 Apr 2019 20:10:27 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Alexey Gladkov <gladkov.alexey@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-api@...r.kernel.org, linux-modules@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Jessica Yu <jeyu@...nel.org>,
        Lucas De Marchi <lucas.de.marchi@...il.com>
Subject: Re: [PATCH v2] moduleparam: Save information about built-in modules
 in separate file

On Sat, Apr 6, 2019 at 9:15 PM Alexey Gladkov <gladkov.alexey@...il.com> wrote:
>
> Problem:
>
> When a kernel module is compiled as a separate module, some important
> information about the kernel module is available via .modinfo section of
> the module.  In contrast, when the kernel module is compiled into the
> kernel, that information is not available.
>
> Information about built-in modules is necessary in the following cases:
>
> 1. When it is necessary to find out what additional parameters can be
> passed to the kernel at boot time.
>
> 2. When you need to know which module names and their aliases are in
> the kernel. This is very useful for creating an initrd image.
>
> Proposal:
>
> The proposed patch does not remove .modinfo section with module
> information from the vmlinux at the build time and saves it into a
> separate file after kernel linking. So, the kernel does not increase in
> size and no additional information remains in it. Information is stored
> in the same format as in the separate modules (null-terminated string
> array). Because the .modinfo section is already exported with a separate
> modules, we are not creating a new API.
>
> It can be easily read in the userspace:
>
> $ tr '\0' '\n' < kernel.builtin
> ext4.softdep=pre: crc32c
> ext4.license=GPL
> ext4.description=Fourth Extended Filesystem
> ext4.author=Remy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Theodore Ts'o and others
> ext4.alias=fs-ext4
> ext4.alias=ext3
> ext4.alias=fs-ext3
> ext4.alias=ext2
> ext4.alias=fs-ext2
> md_mod.alias=block-major-9-*
> md_mod.alias=md
> md_mod.description=MD RAID framework
> md_mod.license=GPL
> md_mod.parmtype=create_on_open:bool
> md_mod.parmtype=start_dirty_degraded:int
> ...
>
> v2:
>  * Extract modinfo from vmlinux.o as suggested by Masahiro Yamada;
>  * Rename output file to kernel.builtin;

Sorry, I do not get why you renamed
"kernel.builtin.modinfo" to "kernel.builtin".

If you drop "modinfo", we do not understand
what kind information is contained in it.

I think "kernel" and "builtin" have
a quite similar meaning here.

How about "builtin.modinfo" for example?


It is shorter, and it is clear enough
that it contains module_info.



>  * Add MODULE_VERSION to modinfo that is saved to the kernel.builtin;
>  * Fix build warnings on powerpc.
>
> Co-Developed-by: Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>
> Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>
> Signed-off-by: Alexey Gladkov <gladkov.alexey@...il.com>
> ---


> diff --git a/.gitignore b/.gitignore
> index a20ac26aa2f5..432332fd745e 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -45,6 +45,7 @@
>  *.xz
>  Module.symvers
>  modules.builtin
> +kernel.builtin

This file is generated only in the top of the tree.

Please add '/' prefix and move it to
the "# Top-level generic files" section.




> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index c8cf45362bd6..b914e026ef28 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -226,6 +226,10 @@ modpost_link vmlinux.o
>  # modpost vmlinux.o to check for section mismatches
>  ${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
>
> +info MODINFO kernel.builtin
> +"${OBJCOPY}" -j .modinfo -O binary vmlinux.o kernel.builtin
> +chmod 444 kernel.builtin


Could you explain why this "chmod" is necessary?


Thanks.




--
Best Regards
Masahiro Yamada