[bug#41961,1/1] services: childhurd: Support more than one instance.

* gnu/services/virtualization.scm (<hurd-vm-configuration>)[id,net-options]:
New fields.
(hurd-vm-net-options): New prodecure.  Parameterize port forwarding with ID.
* gnu/services/virtualization.scm (hurd-vm-shepherd-service): Use them.
Parameterize provision with ID, if set.
* doc/guix.texi (Virtualization Services): Document new fields.
---
 doc/guix.texi                   | 35 ++++++++++++++++++++--------
 gnu/services/virtualization.scm | 41 +++++++++++++++++++++++++--------
 2 files changed, 58 insertions(+), 18 deletions(-)

Hey janneke!

> * gnu/services/virtualization.scm (<hurd-vm-configuration>)[id,net-options]:
> New fields.
> (hurd-vm-net-options): New prodecure.  Parameterize port forwarding with ID.
                               ^
                               typo

> +@item @code{options} (default: @code{'("--snapshot" "--hda")})
>  The extra options for running QEMU.

Does it really make sense to have "--hda" standalone here, without a
specific image argument?

> +  (net-options hurd-vm-configuration-net-options        ;list of string
> +               (thunked)
> +               (default (hurd-vm-net-options this-record))))

Why does it need to be thunked?

Otherwise this looks nice!

Thanks,

Mathieu

Mathieu Othacehe writes:

Hey Mathieu,

>> * gnu/services/virtualization.scm (<hurd-vm-configuration>)[id,net-options]:
>> New fields.
>> (hurd-vm-net-options): New prodecure.  Parameterize port forwarding with ID.
>                                ^
>                                typo

Oops, thanks.

>> +@item @code{options} (default: @code{'("--snapshot" "--hda")})
>>  The extra options for running QEMU.
>
> Does it really make sense to have "--hda" standalone here, without a
> specific image argument?

Hmm...yes, this looked a bit awkward to me too.  It's being used like
this:

o--8<---------------cut here---------------start------------->8---
  (let ((image       (hurd-vm-configuration-image config))
     ...)
    (define vm-command
      #~(list
         (string-append #$qemu "/bin/qemu-system-i386")
         #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
         "-m" (number->string #$memory-size)
         #$@net-options
         #$@options
         #+image))
--8<---------------cut here---------------end--------------->8---

so that you can play with options and image; have the
"hurd-vm-configuration-image" procedure to return anything, something
that may require something else than --hda <image>...but it's quite
implicit.  Ideas?

>> +  (net-options hurd-vm-configuration-net-options        ;list of string
>> +               (thunked)
>> +               (default (hurd-vm-net-options this-record))))
>
> Why does it need to be thunked?

It uses ID from the configuration like so

--8<---------------cut here---------------start------------->8---
(define (hurd-vm-net-options config)
  (let ((id (or (hurd-vm-configuration-id config) 0)))
    (define (qemu-vm-port base)
      (number->string (+ base (* 1000 id))))
    [...]
     ",hostfwd=tcp:127.0.0.1:" (qemu-vm-port 10022) "-:2222"
    [...]))
--8<---------------cut here---------------end--------------->8---

to fix parameterize the ports for QEMU.  Is there a better way to do
that?

> Otherwise this looks nice!

Great, thanks!

Greetigs,
Janneke

> Hmm...yes, this looked a bit awkward to me too.  It's being used like
> this:
>
> o--8<---------------cut here---------------start------------->8---
>   (let ((image       (hurd-vm-configuration-image config))
>      ...)
>     (define vm-command
>       #~(list
>          (string-append #$qemu "/bin/qemu-system-i386")
>          #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
>          "-m" (number->string #$memory-size)
>          #$@net-options
>          #$@options
>          #+image))

What about having something like:

--8<---------------cut here---------------start------------->8---
(define vm-command
  #~(list
     (string-append #$qemu "/bin/qemu-system-i386")
     #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
     "-m" (number->string #$memory-size)
     #$@options
     #+@(list "--hda" image)))
--8<---------------cut here---------------end--------------->8---

instead?

> to fix parameterize the ports for QEMU.  Is there a better way to do
> that?

Oh I see, then it's fine I guess.

Thanks,

Mathieu

Mathieu Othacehe writes:

>> Hmm...yes, this looked a bit awkward to me too.  It's being used like
>> this:
>>
>> o--8<---------------cut here---------------start------------->8---
>>   (let ((image       (hurd-vm-configuration-image config))
>>      ...)
>>     (define vm-command
>>       #~(list
>>          (string-append #$qemu "/bin/qemu-system-i386")
>>          #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
>>          "-m" (number->string #$memory-size)
>>          #$@net-options
>>          #$@options
>>          #+image))
>
> What about having something like:
>
> (define vm-command
>   #~(list
>      (string-append #$qemu "/bin/qemu-system-i386")
>      #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
>      "-m" (number->string #$memory-size)
>      #$@options
>      #+@(list "--hda" image)))
>
> instead?

So we hardcode it.  Simply changed to

--8<---------------cut here---------------start------------->8---
    (define vm-command
      #~(list
         (string-append #$qemu "/bin/qemu-system-i386")
         #$@(if (file-exists? "/dev/kvm") '("--enable-kvm") '())
         "-m" (number->string #$memory-size)
         #$@net-options
         #$@options
         "--hda" #+image))
--8<---------------cut here---------------end--------------->8---

I guess that's better than the original fragile softcoding, because it's
more robust and we have no usecase for changing '--hda' yet.  Maybe I'm
a bit too inclined to always enable the user to override stuff, even if
I cannot imagine its use case yet :-)

Pushed to master as, b7249aa4726193653e05e694ec4bb311aa4ec6c2.

Thanks,
Janneke