GNU bug report logs - #32167
Kernel 'build' directory in the store is a broken symbolic link

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: <pkill9 <at> runbox.com>
To: "bug-guix" <bug-guix <at> gnu.org>
Subject: Kernel 'build' directory in the store is a broken symbolic link
Date: Sun, 15 Jul 2018 21:07:57 +0100 (BST)

/run/booted-system/kernel/lib/modules/<kernel version>/build is a broken symbolic link.

Message #8 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: Nils Gillmann <ng0 <at> n0.is>
To: pkill9 <at> runbox.com
Cc: Mark H Weaver <mhw <at> netris.org>, 32167 <at> debbugs.gnu.org
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Sun, 15 Jul 2018 21:32:53 +0000

pkill9 <at> runbox.com transcribed 94 bytes:
> /run/booted-system/kernel/lib/modules/<kernel version>/build is a broken symbolic link.

Yep. This is not a bug until it comes to what you are possibly trying to attempt,
build a software which relies on your *current* kernel sources.

For a solution I can point to the Nix package for linux, where they deal with this
within the kernel package, for firmware and more. Because I'm short on time these
days I haven't sent a patch yet but I can confirm the issues you probably ran into
as I had them many months back already.

Mark, you are mostly responsible for the linux module in Guix.

Besides my own notes, this was relevant:
https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/linux/kernel/manual-config.nix#L161

Message #11 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: <pkill9 <at> runbox.com>
To: "32167" <32167 <at> debbugs.gnu.org>
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Mon, 16 Jul 2018 18:55:11 +0100 (BST)

It would be good to keep the build directory though, since it's expected to exist, and it's easier to just download a module's source and compile it and test it.

Message #14 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: Danny Milosavljevic <dannym <at> scratchpost.org>
To: <pkill9 <at> runbox.com>
Cc: Mark H Weaver <mhw <at> netris.org>, 32167 <32167 <at> debbugs.gnu.org>
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Mon, 16 Jul 2018 20:15:00 +0200

[Message part 1 (text/plain, inline)]

On Mon, 16 Jul 2018 18:55:11 +0100 (BST)
<pkill9 <at> runbox.com> wrote:

> It would be good to keep the build directory though, since it's expected to exist, and it's easier to just download a module's source and compile it and test it.

I agree.

/run/booted-system/kernel/lib/modules/4.17.3-gnu is in the store anyway so it will be seen by the GC.

The fix would be in linux-libre.

[Message part 2 (application/pgp-signature, inline)]

Message #17 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: Mark H Weaver <mhw <at> netris.org>
To: Danny Milosavljevic <dannym <at> scratchpost.org>
Cc: 32167 <at> debbugs.gnu.org, pkill9 <at> runbox.com
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Mon, 16 Jul 2018 18:03:58 -0400

Danny Milosavljevic <dannym <at> scratchpost.org> writes:

> On Mon, 16 Jul 2018 18:55:11 +0100 (BST)
> <pkill9 <at> runbox.com> wrote:
>
>> It would be good to keep the build directory though, since it's
>> expected to exist, and it's easier to just download a module's
>> source and compile it and test it.
>
> I agree.
>
> /run/booted-system/kernel/lib/modules/4.17.3-gnu is in the store
> anyway so it will be seen by the GC.
>
> The fix would be in linux-libre.

If we were to preserve the kernel build directory as a store item, and
keep a link from the modules directory to the build directory, that
would greatly increase the size of the most minimal system that users
could build.

The unpacked linux-libre-4.17 source directory is 929 megabytes, and
that's before building it.  So, keeping the build directory would surely
increase the closure size of the most minimal system by more than a
gigabyte.  I don't think it's okay to force all Guix users to pay that
price.  Some users will need to build minimal systems.

I'd like to hear more specifics about what the original poster is trying
to accomplish here.  It's possible that they simply noticed the broken
links and wanted to let us know.  In that case, it's probably best to
simply delete those broken symlinks.

If the intent here is to allow support for out-of-tree kernel modules,
then fixing these symlinks would not solve the problem, and it's not
clear to me that fixing them would be part of a proper solution on
GuixSD.  GuixSD is not a system where you can simply compile a kernel
module manually and install it, because our module directory is
immutable.  If the goal is to support building out-of-tree kernel
modules, that's a separate discussion that deserves its own "wishlist"
bug report, I think.

Thoughts?

       Mark

Message #20 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: <pkill9 <at> runbox.com>
To: "Mark H Weaver" <mhw <at> netris.org>
Cc: Danny Milosavljevic <dannym <at> scratchpost.org>, 32167 <32167 <at> debbugs.gnu.org>,
 pkill9 <pkill9 <at> runbox.com>
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Tue, 17 Jul 2018 00:10:13 +0100 (BST)

Yes I agree with you, since it is a lot of space then it's probably best to just delete the symlink.

The reasoning behind my suggestion of keeping it is mostly for convenience in compiling/testing an external kernel module, i.e. just downloading the source and then compiling it with the currently running kernel, and then loading it to test it.

Come to think of it, could the build directory be put in another output of the linux-libre package?

On Mon, 16 Jul 2018 18:03:58 -0400, Mark H Weaver <mhw <at> netris.org> wrote:

> Danny Milosavljevic <dannym <at> scratchpost.org> writes:
> 
> > On Mon, 16 Jul 2018 18:55:11 +0100 (BST)
> > <pkill9 <at> runbox.com> wrote:
> >
> >> It would be good to keep the build directory though, since it's
> >> expected to exist, and it's easier to just download a module's
> >> source and compile it and test it.
> >
> > I agree.
> >
> > /run/booted-system/kernel/lib/modules/4.17.3-gnu is in the store
> > anyway so it will be seen by the GC.
> >
> > The fix would be in linux-libre.
> 
> If we were to preserve the kernel build directory as a store item, and
> keep a link from the modules directory to the build directory, that
> would greatly increase the size of the most minimal system that users
> could build.
> 
> The unpacked linux-libre-4.17 source directory is 929 megabytes, and
> that's before building it.  So, keeping the build directory would surely
> increase the closure size of the most minimal system by more than a
> gigabyte.  I don't think it's okay to force all Guix users to pay that
> price.  Some users will need to build minimal systems.
> 
> I'd like to hear more specifics about what the original poster is trying
> to accomplish here.  It's possible that they simply noticed the broken
> links and wanted to let us know.  In that case, it's probably best to
> simply delete those broken symlinks.
> 
> If the intent here is to allow support for out-of-tree kernel modules,
> then fixing these symlinks would not solve the problem, and it's not
> clear to me that fixing them would be part of a proper solution on
> GuixSD.  GuixSD is not a system where you can simply compile a kernel
> module manually and install it, because our module directory is
> immutable.  If the goal is to support building out-of-tree kernel
> modules, that's a separate discussion that deserves its own "wishlist"
> bug report, I think.
> 
> Thoughts?
> 
>        Mark

Message #23 received at 32167 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Mark H Weaver <mhw <at> netris.org>
Cc: Danny Milosavljevic <dannym <at> scratchpost.org>, 32167 <at> debbugs.gnu.org,
 pkill9 <at> runbox.com
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Mon, 23 Jul 2018 15:00:57 +0200

Hi,

Mark H Weaver <mhw <at> netris.org> skribis:

> Danny Milosavljevic <dannym <at> scratchpost.org> writes:
>
>> On Mon, 16 Jul 2018 18:55:11 +0100 (BST)
>> <pkill9 <at> runbox.com> wrote:
>>
>>> It would be good to keep the build directory though, since it's
>>> expected to exist, and it's easier to just download a module's
>>> source and compile it and test it.
>>
>> I agree.
>>
>> /run/booted-system/kernel/lib/modules/4.17.3-gnu is in the store
>> anyway so it will be seen by the GC.
>>
>> The fix would be in linux-libre.
>
> If we were to preserve the kernel build directory as a store item, and
> keep a link from the modules directory to the build directory, that
> would greatly increase the size of the most minimal system that users
> could build.

Yeah, we shouldn’t do that IMO.

> If the intent here is to allow support for out-of-tree kernel modules,
> then fixing these symlinks would not solve the problem, and it's not
> clear to me that fixing them would be part of a proper solution on
> GuixSD.  GuixSD is not a system where you can simply compile a kernel
> module manually and install it, because our module directory is
> immutable.  If the goal is to support building out-of-tree kernel
> modules, that's a separate discussion that deserves its own "wishlist"
> bug report, I think.

I agree.

Ludo’.

Message #28 received at 32167-done <at> debbugs.gnu.org (full text, mbox):

From: Sarah Morgensen <iskarian <at> mgsn.dev>
To: ludo <at> gnu.org (Ludovic Courtès)
Cc: Mark H Weaver <mhw <at> netris.org>, 32167-done <at> debbugs.gnu.org,
 pkill9 <at> runbox.com, Danny Milosavljevic <dannym <at> scratchpost.org>
Subject: Re: bug#32167: Kernel 'build' directory in the store is a broken
 symbolic link
Date: Fri, 24 Sep 2021 17:51:39 -0700

Hi all,

ludo <at> gnu.org (Ludovic Courtès) writes:

> Hi,
>
> Mark H Weaver <mhw <at> netris.org> skribis:
>
>> Danny Milosavljevic <dannym <at> scratchpost.org> writes:
>>
>>> On Mon, 16 Jul 2018 18:55:11 +0100 (BST)
>>> <pkill9 <at> runbox.com> wrote:
>>>
>>>> It would be good to keep the build directory though, since it's
>>>> expected to exist, and it's easier to just download a module's
>>>> source and compile it and test it.
>>>
>>> I agree.
>>>
>>> /run/booted-system/kernel/lib/modules/4.17.3-gnu is in the store
>>> anyway so it will be seen by the GC.
>>>
>>> The fix would be in linux-libre.
>>
>> If we were to preserve the kernel build directory as a store item, and
>> keep a link from the modules directory to the build directory, that
>> would greatly increase the size of the most minimal system that users
>> could build.
>
> Yeah, we shouldn’t do that IMO.
>
>> If the intent here is to allow support for out-of-tree kernel modules,
>> then fixing these symlinks would not solve the problem, and it's not
>> clear to me that fixing them would be part of a proper solution on
>> GuixSD.  GuixSD is not a system where you can simply compile a kernel
>> module manually and install it, because our module directory is
>> immutable.  If the goal is to support building out-of-tree kernel
>> modules, that's a separate discussion that deserves its own "wishlist"
>> bug report, I think.
>
> I agree.
>
> Ludo’.

I am closing this old bug since the broken 'build' symlink no longer
exists (nor do any other broken symlinks, as far as I can tell).

As for building out-of-tree kernel modules, we now have
linux-module-build-system, which uses `make-linux-module-builder', which
builds the 'build' directory straight from the linux source with `make
modules_prepare'.  There are some improvements to be had there, for
sure, but like mentioned above, that deserves its own wishlist item.

--
Sarah

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