[bug#28198] [PATCH 1/4] vm: Add disk-image-size to <virtual-machine>.

[Ludovic Courtès]

Hi Chris!

Christopher Baines <address@hidden> skribis:

> On Thu, 31 Aug 2017 14:29:56 +0200
> address@hidden (Ludovic Courtès) wrote:
>
>> Hi Chris,
>
> Thanks for reviewing these patches Ludo, unfortunately its taken me
> nearly a month to get around to replying.
>
> Thankfully, I've made some progress in that time.
>
>> Christopher Baines <address@hidden> skribis:
>> 
>> > * gnu/system/vm.scm (<virtual-machine>): Add
>> >   disk-image-size.
>> >   (port-forwardings->qemu-options): Use disk-image-size from
>> >   <virtual-machine>.  
>> 
>> In which case is it useful?  Perhaps if you want to create lots of
>> data on the root file system in the MongoDB test?
>> 
>> Currently <virtual-machine> builds a shared-store VM (like ‘guix
>> system vm’) in which the root file system has a fixed size that’s
>> usually good enough.
>
> The best answer I have at the moment is that I think MongoDB creates a
> rather large file, even if it has no data to store in it. I'll do some
> more investigation to confirm this though.

OK, that’s a good reason anyway.  :-)

>> > --- a/gnu/system/vm.scm
>> > +++ b/gnu/system/vm.scm
>> > @@ -653,6 +653,8 @@ it is mostly useful when FULL-BOOT?  is true."
>> >                      (default #f))
>> >    (memory-size      virtual-machine-memory-size   ;integer (MiB)
>> >                      (default 256))
>> > +  (disk-image-size  virtual-machine-disk-image-size   ;integer
>> > (bytes)
>> > +                    (default (* 70 (expt 2 20))))  
>> 
>> I think we can use 'guess here as the default value (and we should do
>> the same in places where #:disk-image-size has an arbitrary default.)
>
> I've been looking at this in the last few days. Making 'guess the
> default value here does mean something, and I think it's a good idea.
>
> As far as I can tell, for this specific test, these are the 3 functions
> that are called on the way to using the actual size, and the defaults
> they have:
>
> system-qemu-image/shared-store-script default:
>   (* (if full-boot? 500 70)
>      (expt 2 20)))
>
> system-qemu-image/shared-store default: 
>   (* (if full-boot? 500 30) 
>      (expt 2 20)))
>
> qemu-image default:
>   'guess
>
> From my tests, if the default in the <virtual-machine> is set to
> 'guess, then for the mongodb test the guess seems to be 0 MiB at the
> moment, which doesn't work. I've started looking at setting a sensible
> default in qemu-image, so that the root filesystem size isn't 0 MiB.

Indeed.  Maybe we can go with your patch as-is and investigate the
problem with 'guess separately.  Thoughts?

(I’ll comment on the other issue separately.)

Thanks,
Ludo’.