Subject: Re: [bug#41011] [PATCH] gnu: grub: Support for network boot via tftp/nfs.

From: Danny Milosavljevic <[email-masked]>
Date: Sun, 6 Sep 2020 16:35:59 +0200

Hi Stefan,

I think this looks good in general.

I'd like to do some nitpicking on the names--especially since the procedure is
exported and thus presumably can't have its signature modified later without
breaking backward compatibility.

In this case, the man page grub-mknetdir(8) mentions "netboot" ?
Do you think "net" or "netboot" is a better name for this functionality ?

On Sat, 5 Sep 2020 13:25:24 +0200
Stefan <[email-masked]> wrote:

> +            install-grub-net

I'm fine with whatever--but the man page says "netboot".  If that's the usual
name, let's use it.  If "net"'s the usual name, let's use that.

> +  (let* ((arch (car (string-split (or (%current-target-system)
> +                                      (%current-system))
> +                                  #\-)))

Let's not use arcane Scheme anachronisms like "car".  I know most Scheme
programmers probably know what it does--but still, better not to use
names of registers of a machine no one uses anymore.

Better something like this:

(let* ((system-parts (string-split (or (%current-target-system)
                                       (%current-system))
                            #\-)))

> +         (efi-bootloader-link (string-append "/boot"

> +                                             (match arch
> +                                               ("i686" "ia32")
> +                                               ("x86_64" "x64")
> +                                               ("arm" "arm")
> +                                               ("armhf" "arm")
> +                                               ("aarch64" "aa64")
> +                                               ("riscv" "riscv32")
> +                                               ("riscv64" "riscv64"))
> +                                             ".efi"))

Also, I have a slight preference for greppable file names even when it's a
little more redundant, so more like that:

(match system-parts
 (("i686" _ ...) "ia32.efi")
 (("x86_64" _ ...) "x64.efi")
 (("arm" _ ...) "arm.efi")
 (("armhf" _ ...) "arm.efi")
 (("aarch64" _ ...) "aa64.efi")
 (("riscv" _ ...) "riscv32.efi")
 (("riscv64" _ ...) "riscv64.efi"))

> +         (efi-bootloader (string-append (match arch
> +                                          ("i686" "i386")
> +                                          ("x86_64" "x86_64")
> +                                          ("arm" "arm")
> +                                          ("armhf" "arm")
> +                                          ("aarch64" "arm64")
> +                                          ("riscv" "riscv32")
> +                                          ("riscv64" "riscv64"))
> +                                        "-efi/core.efi")))

Likewise:

         (efi-bootloader (match system-parts
                          (("i686" _ ...) "i386-efi/core.efi")
                          (("x86_64" _ ...) "x86_64-efi/core.efi")
                          (("arm" _ ...) "arm-efi/core.efi")
                          (("armhf" _ ...) "arm-efi/core.efi")
                          (("aarch64" _ ...) "arm64-efi/core.efi")
                          (("riscv" _ ...) "riscv32-efi/core.efi")
                          (("riscv64" _ ...) "riscv64-efi/core.efi"))))

> +    #~(lambda (bootloader target mount-point)

> +        "Install GRUB as e.g. \"bootx64.efi\" or \"bootarm64.efi\" \"into
> +SUBDIR, which is usually \"efi/boot\" or \"efi/Guix\" below the directory TARGET
> +for the system whose root is mounted at MOUNT-POINT."

I think you mean:

> +        "Install GRUB as e.g. \"bootx64.efi\" or \"bootarm64.efi\" \"into
> +SUBDIR (which is usually \"efi/boot\" or \"efi/Guix\") below the directory TARGET
> +for the system whose root is mounted at MOUNT-POINT."

> +        (let* (;; Use target-depth and subdir-depth to construct links to
> +               ;; "../gnu" and "../../../boot/grub/grub.cfg" with the correct
> +               ;; number of "../". Note: This doesn't consider ".." or ".",
> +               ;; which may appear inside target or subdir.

Uhhhh... that could use some more explanationary comments in the source code
of why it is done in the first place.

Also, is TARGET itself assumed to be an absolute path or is it relative to
something else ?  According to the rest of the patch it's relative to
MOUNT-POINT--but please state this explicitly in the docstring.

> +               (target-depth (length (delete "" (string-split target #\/))))

> +               (subdir-depth (length (delete "" (string-split #$subdir #\/))))

> +               (up1 (string-join (make-list target-depth "..") "/" 'suffix))

Maybe better name: escape-target or something.

> +               (up2 (string-join (make-list subdir-depth "..") "/" 'suffix))

Maybe better name: escape-subdir or something.

So this is in order to get out of (string-append TARGET "/" SUBDIR), correct?
Does the (string-append TARGET "/" SUBDIR) have an official name ?
If not, fine.

> +               (net-dir (string-append mount-point target "/"))

So TARGET is relative to MOUNT-POINT ?
And MOUNT-POINT is assumed to have a slash at the end ?

> +               (store-name (car (delete "" (string-split bootloader #\/))))

Maybe use match.

Also isn't there an official way to find out how the store is called ?
(%store-prefix) ?

> +               (store (string-append up1 store-name))

(string-append escape-target store-name)

> +               (store-link (string-append net-dir store-name))

*mumbles to self* (string-append MOUNT-POINT TARGET) is net-dir.
So it tries to get to (string-append MOUNT-POINT "/gnu").

I vaguely remember our docker pack adding some serious plumbing to support
symlinks like that.

I'll try to find it.  I just wanted to send this E-Mail because of the following:

>  ;;;
>  ;;; Bootloader definitions.
>  ;;;
> +;;; For all these grub-bootloader variables the path to /boot/grub/grub.cfg
> +;;; is fixed.  Inheriting and overwriting the field 'configuration-file' will
> +;;; break 'guix system delete-generations', 'guix system switch-generation',
> +;;; and 'guix system roll-back'.

I've added that comment to the source code in an extra commit
3f2bd9df410e85795ec656052f44d2cddec2a060 in guix master.
Thank you very much for it.

> -(define* grub-minimal-bootloader
> +(define grub-minimal-bootloader
>    (bootloader

> -(define* grub-efi-bootloader
> +(define grub-efi-bootloader
>    (bootloader

> -(define* grub-mkrescue-bootloader
> +(define grub-mkrescue-bootloader

I've applied this hunk to guix master as commit
8664c35d6d7fd6e9ce1ca8adefa8070a8e556db4.

Thanks.