Date:   Mon, 29 Apr 2019 12:28:41 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Alexey Gladkov <gladkov.alexey@...il.com>
Cc:     Jessica Yu <jeyu@...nel.org>,
        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

On Sat, Apr 27, 2019 at 12:29 AM Alexey Gladkov
<gladkov.alexey@...il.com> wrote:
>
> On Fri, Apr 19, 2019 at 12:03:50PM +0900, Masahiro Yamada wrote:
> > On Fri, Apr 19, 2019 at 12:36 AM Jessica Yu <jeyu@...nel.org> wrote:
> > >
> > > +++ 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.
> >
> > OK, I see.
> >
> > > But you are the maintainer, so I do not have a strong
> > > opinion on this either way :-)
> >
> > My idea was to use
> > 'modules.<file-type>'  vs  'builtin.<file-type>'
> > instead of
> > 'modules.<file-type>'  vs  'modules.builtin.<file-type>'
> >
> > I am slightly in favor of the former
> > since it is shorter and
> > (I hope) still clear enough.
> >
> > If this naming is not nice for external projects such as kmod,
> > please speak up.
> >
> >
> > (BTW, I am thinking of renaming 'modules.builtin' into 'builtin.order'
> > for kbuild internal. We cannot change that for the installation area, though.)
>
> Since there were no other suggestions, how can I better name the file ?
> modules.builtin.modinfo or just builtin.modinfo ? I personally like the
> first one more.


Either is fine.

Please put it in Documentation/dontdiff too.

Thanks.



-- 
Best Regards
Masahiro Yamada

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