Re: [RFC PATCH] xen/design: Add design for EFI dom0less system start

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.09.2021 11:17, Julien Grall wrote:
> On 07/09/2021 09:33, Jan Beulich wrote:
>> I'd like to suggest a different scheme, not the least because I expect
>> the individual domains being independent of e.g. hypervisor command
>> line options or Dom0 kernel versions. Yet varying sets of these are,
>> for example, a reason to have multiple sections in the current scheme.
>> Every dom0less guest would then require spelling out in every such
>> section. Hence I think we'd be better off having a section per guest:
>>
>> [guest1]
>> kernel=Image-domu1.bin console=ttyAMA0 root=/dev/ram0 rw
>> property=cpus=1
>> property=memory=0xC0000
>> dtb=domu.dtb
> 
> I much prefer the idea of the section. This is going to be easier to 
> parse the configuration file as we would not have to look for "domuX_" 
> and then distinguishing X.
> 
>>
>> These sections would then be referenced by other sections, e.g. by a
>> new "guests" (or "domus", but this ends up looking a little odd for
>> its matching of an unrelated latin word) keyword:
>>
>> guests=guest1,guest2
>>
>> If it is deemed necessary to make sure such a section can't be
>> (mistakenly) used to create Dom0, such sections would need identifying
>> in some way. Presence of property= (or, as per below, properties=)
>> could be one means (allowing an empty setting would then be desirable).
> 
> I would expect dom0 to be described in the similar fashion at some 
> point. So maybe we should name the property "domains=...".

Not sure - the order above doesn't mandate domain IDs, yet Dom0 needs
creating with ID 0. IOW I was deliberately suggesting "guests=".

>> As to the properties, is there anything wrong with having them all on
>> one line:
>>
>> [guest1]
>> kernel=Image-domu1.bin console=ttyAMA0 root=/dev/ram0 rw
>> dtb=domu.dtb
>> properties=cpus=1 memory=0xC0000
> 
> It depends on the number of properties for the domain, this may become 
> quickly unreadable.
> 
> But... if we use sections, then I think it would be better to have:
> 
> kernel=..
> dtb=...
> cpu=1
> memory=0xC0000
> 
> This would also allow us to create more complex setup (such as for the 
> static memory allocation).

If that's feasible parsing-wise - sure. I was first thinking to suggest
separate keywords, but then decided there was a reason this wasn't done
in the original proposal (with respective dom#_ prefixes).

Jan