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

[Luca Fancellu <luca.fancellu@arm.com>]

> On 7 Sep 2021, at 10:24, Jan Beulich <jbeulich@suse.com> wrote:
> 
> 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=".

Hi Jan, Julien,

Thanks for your feedbacks, really appreciated, I agree with you that sections
are easier to read.
I stand with the “guests=“ or “domus=“ or “domu_guests=“ keywords where
the references to “guest sections” can be listed, separated by commas. 

> 
>>> 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).

Yes I think it is feasible and easy to read, so given your feedback we can agree on
something like that:

[global]
default=xen

[xen]
options=[xen command line]
kernel=[dom0 kernel file] [domain 0 command line options]
ramdisk=[dom0 ramdisk]
xsm=[xsm filename]
dtb=[xen device tree blob]
domu_guests=guest1,...

[guest1]
address-cells=2
size-cells=2
kernel=[domU kernel file] [domU command line options]
cpus=1
memory=0xC0000
dtb=[domU passthrough dtb]

This won’t break the compatibility because on older version the domu_guests keyword
Is ignored, the user needs just to check that a guest section is not specified as default=
argument because in this case it will be loaded as dom0 kernel (and probably won’t work),
but I think we can just update the documentation to highlight this thing.

Finally this example should load a dom0less system:

[global]
default=xen

[xen]
# Xen boot arguments
options=noreboot console=dtuart dtuart=serial0 bootscrub=0
# Xen device tree
dtb=devtree.dtb
# domus to be started
domu_guests=guest1,guest2

[guest1]
address-cells=2
size-cells=2
kernel=Image-domu1.bin console=ttyAMA0 root=/dev/ram0 rw
cpus=1
memory=0xC0000
dtb=domu.dtb

[guest2]
kernel=Image-domu2.bin console=ttyAMA0 root=/dev/ram0 rw
cpus=2
memory=0x100000
vpl011


> 
> Jan
>