From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masahiro Yamada Subject: Re: [RESEND PATCH v1] moduleparam: Save information about built-in modules in separate file Date: Wed, 3 Apr 2019 20:30:55 +0900 Message-ID: References: <20190315101013.GN8455@Legion-PC.fortress> <20190326172411.GA15936@Legion-PC.fortress> <20190327154025.GB23293@linux-8ccs> <20190327160440.GE15936@Legion-PC.fortress> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20190327160440.GE15936@Legion-PC.fortress> Sender: linux-kernel-owner@vger.kernel.org To: Alexey Gladkov Cc: Jessica Yu , Michal Marek , Linux Kernel Mailing List , Linux Kbuild mailing list , linux-api@vger.kernel.org, "Kirill A . Shutemov" , Gleb Fotengauer-Malinovskiy , "Dmitry V. Levin" , Dmitry Torokhov , Rusty Russell , Lucas De Marchi List-Id: linux-api@vger.kernel.org On Thu, Mar 28, 2019 at 1:04 AM Alexey Gladkov w= rote: > > On Wed, Mar 27, 2019 at 04:40:25PM +0100, Jessica Yu wrote: > > +++ Alexey Gladkov [26/03/19 18:24 +0100]: > > >On Fri, Mar 22, 2019 at 02:34:12PM +0900, Masahiro Yamada wrote: > > >> Hi. > > >> > > >> (added some people to CC) > > > > (Thanks Masahiro for the CC!) > > > > >> > > >> On Fri, Mar 15, 2019 at 7:10 PM Alexey Gladkov wrote: > > >> > > > >> > Problem: > > >> > > > >> > When a kernel module is compiled as a separate module, some import= ant > > >> > information about the kernel module is available via .modinfo sect= ion of > > >> > the module. In contrast, when the kernel module is compiled into = the > > >> > kernel, that information is not available. > > >> > > >> > > >> I might be missing something, but > > >> vmlinux provides info of builtin modules > > >> in /sys/module/. > > > > > >No. There are definitely not all modules. I have a builtin sha256_gene= ric, > > >but I can't find him in the /sys/module. > > > > Yeah, you'll only find builtin modules under /sys/module/ if it has any= module > > parameters, otherwise you won't find it there. As Masahiro already ment= ioned, > > if a builtin module has any parameters, they would be accessible under = /sys/module/. > > > > >> (Looks like currently only module_param and MODULE_VERSION) > > >> > > >> This patch is not exactly the same, but I see a kind of overwrap. > > >> I'd like to be sure if we want this new scheme. > > > > > >The /sys/module is only for running kernel. One of my use cases is > > >to create an initrd for a new kernel. > > > > > >> > > >> > Information about built-in modules is necessary in the following c= ases: > > >> > > > >> > 1. When it is necessary to find out what additional parameters can= be > > >> > passed to the kernel at boot time. > > >> > > >> > > >> Actually, /sys/module//parameters/ > > >> exposes this information. > > >> > > >> Doesn't it work for your purpose? > > > > > >No, since creating an initrd needs to know all the modalias before > > >I get the sysfs for new kernel. Also there are no modalias at all. > > > > > >> > 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. > > >> > > > > > Hm, I do see one possible additional use-case for preserving module ali= as > > information for built-in modules - modprobe will currently error (I thi= nk, > > correct me if I'm wrong) if we try invoking modprobe with an alias of a > > built-in module, simply because this information is not in modules.buil= tin or > > modules.alias. > > Yes. Patch for modprobe in my todo list. The reason I didn=E2=80=99t do i= t was > because I wasn=E2=80=99t sure that the file format was final. > > > Since kbuild already outputs modules.builtin, I would suggest outputtin= g > > something like a modules.builtin.alias file (and I guess maybe a module= s.builtin.param > > file too if that's deemed useful), in a format that is consumable by km= od/modprobe, > > so that modprobing an alias of a built-in module doesn't produce an err= or. I > > think this should be easy to do if we keep and parse the resulting .mod= info for > > builtin modules. This is just an idea, opinions welcome. I've added Luc= as to CC > > in case he has any thoughts. > > You don't like kernel.builtin.modinfo ? Naming is often the most difficult thing. :) IMHO, 'kernel' and 'builtin' have a similar meaning here. Is 'kernel.builtin' unnecessarily too long? Perhaps, another idea is: 'builtin.alias' instead of 'modules.builtin.alias' if we want a separate file in the same format. In hindsight, 'modules.builtin' should have been 'builtin.order', I think. > It is much easier to create and it has almost the same format as the > modules. So I think it will be easier to parse in kmod. --=20 Best Regards Masahiro Yamada