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

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Date:   Thu, 18 Apr 2019 17:36:12 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Alexey Gladkov <gladkov.alexey@...il.com>,
        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>,
        Lucas De Marchi <lucas.de.marchi@...il.com>
Subject: Re: [PATCH v2] moduleparam: Save information about built-in modules
 in separate file

+++ Masahiro Yamada [19/04/19 00:26 +0900]:
>On Thu, Apr 18, 2019 at 10:52 PM Jessica Yu <jeyu@...nel.org> wrote:
>>
>> +++ Masahiro Yamada [18/04/19 20:10 +0900]:
>> >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.
>>
>> I agree that the name kernel.builtin is unclear in what kind of
>> information it contains. Apologies for not having clarified this in
>> the previous review.
>>
>> Since kbuild already produces "modules.order" and "modules.builtin"
>> files, why not just name it "modules.builtin.modinfo" to keep the
>> names consistent with what is already there?
>
>
>Is it consistent?
>
>If we had "modules.order" and "modules.builtin.order" there,
>I would agree with "modules.builtin.modinfo",
>and also "modules.alias" vs "modules.builtin.alias".
>
>
>We already have "modules.builtin", and probably impossible
>to rename it, so we cannot keep consistency in any way.
>
>
>"modules.builtin" is a weird name since
>it actually contains "order", but its extension
>does not express what kind of information is in it.
>Hence, I doubt "modules.builtin" is a good precedent.
>
>IMHO, "modules" and "builtin" are opposite
>to each other. "modules.builtin" sounds iffy to me.

I've always interpreted "modules.builtin" to mean "this is a list of
modules that have been built-in into the kernel", no? So I thought the
name made sense. But you are the maintainer, so I do not have a strong
opinion on this either way :-)

Thanks,

Jessica