enable LVM in Grub

Hello Guix,

Unless I missed something in the configuration process, the `grub.cfg`

generated by `guix system reconfigure` does not enable LVM, even if the store

is in an LVM volume. The immediate consequence is that Grub cannot load its

data files nor boot the system. The fix is as simple as adding `insmod lvm` in

`grub.cfg` before any `search` command, which I do by hand on each

`reconfigure`, but obviously Guix itself should do that.

I looked at `grub.scm` to see where things happen, and I see no mention of LVM

in this file. This surprises me because I am probably not the only one using

it. Actually, I use LVM on LUKS for full-system encryption, but this is

probably not rare either.

--

Emmanuel

Hello Emmanuel!

Thx for the report!

I think this is bug 44877, maybe we can/should merge it.

Here [1] is a patch (and testcase).

[1] https://issues.guix.gnu.org/60442

--

Man braucht zwei Jahre, um sprechen zu lernen,

und fünfzig, um schweigen zu lernen. E.Hemingway

De Michael Rohleder le 13/03/2023 à 14:56:

Indeed, it seems to be the same issue.

However, the patch sets the value of `GRUB_PRELOAD_MODULES`, which afaik is

used by `grub-mkconfig` to produce `grub.cfg`, but there seems to be code in

`grub.scm` that also produces `grub.cfg`, and no call to `grub-mkconfig`

there. I'm not sure I understand how all this works anyway…

--

Emmanuel

Hi,

Emmanuel Beffara <manu@beffara.org> writes:

Guix indeed takes care to generate the grub.cfg itself, via the

make-grub-configuration procedure from (gnu bootloader grub), and

grub-mkconfig is *not* used.

grub-install is used though, so perhaps GRUB_PRELOAD_MODULES could be

honored by it (although it's not documented so I doubt it). It seems to

me that since we produce grub.cfg ourselves if there's something to add

there for LVM support (which I'm not sure there is -- apparently it

already works for you ?), it should be explicitly coded in (gnu

bootloader grub).

info '(grub) Changes from GRUB Legacy' mentions that "* GRUB 2 can read

files directly from LVM and RAID devices.", so I would think there's

nothing special to do?

--

Thanks,

Maxim

Hello,

De Maxim Cournoyer le 23/03/2023 à 13:48:

It does not work for me, that is why I reported this! The system does not boot

unless I manually add `insmod lvm` in `grub.cfg` because Grub does not find

the partition that contains the store.

So I agree something has to be done there.

As I understand it, this just means that Grub 2 has a module for reading LVM

devices and a module for reading RAID devices. But it still has to load them

somehow (unless there is a way to include them statically so they are

available from the beginning).

--

Emmanuel

Hi,

Emmanuel Beffara <manu@beffara.org> writes:

OK, thanks for explaining. Could you please try

https://issues.guix.gnu.org/60442(by applying the patch to a local guix

checkout, building it, then 'sudo -E ./pre-inst-env sudo guix system

reconfigure /path/to/your/config.scm)? The test suite was broken it

seems (it passed without the fix), but perhaps the fix still does work?

--

Thanks,

Maxim

Hi,

De Maxim Cournoyer le 24/03/2023 à 13:24:

I did as you suggested, and unfortunately the patch has no observable effect

on my system.

I can't say it comes as a surprise. Indeed, what the patch does is set the

environment variable `GRUB_PRELOAD_MODULES` before calling `grub-install`,

which is expected to have no effect: this variable is used by `grub-mkconfig`

to generate a `grub.cfg`, but the code in Guix assembles a Grub configuration

file itself and never calls `grub-mkconfig`. The same applies to the variable

`GRUB_ENABLE_CRYPTODISK`, by the way. Maybe the way `grub.cfg` is produced has

changed at some point in history ?

The only hypothesis I can make is that it would influence `grub-install` by

preloading the given modules in the installed image, but that is not the case.

According to Grub's documentation, passing `--modules=...` to `grub-install`

would have this effect, but I'm not sure it is the right approach.

--

Emmanuel

Hi,

Emmanuel Beffara <manu@beffara.org> writes:

Thanks for testing it!

I'm not sure, but I agree it's confusing to have extraneous setenv

there if they serve no purpose (and my understanding is the same as

yours: I don't see how that'd work).

Since we already generate a custom grub.cfg, the right approach is

probably to add any needed directive directly to it.

--

Thanks,

Maxim

I could correctly implement lvm as root (I think), however there is any intention on support this on guix? Let me know and I will try to send a patch.