Re: [PATCH kvmtool 0/3] Change what --nodefaults does and a revert

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 11/10/2023 15:56, Alexandru Elisei wrote:
> Hi Will,
> 
> Sorry for the late reply, was on holiday.
> 
> On Mon, Sep 18, 2023 at 12:05:14PM +0100, Will Deacon wrote:
>> On Thu, 7 Sep 2023 18:16:52 +0100, Alexandru Elisei wrote:
>>> The first two patches revert "virtio-net: Don't print the compat warning
>>> for the default device" because using --network mode=none disables the
>>> device and lets the user know that it can use that to disable the default
>>> virtio-net device. I don't think the changes are controversial.
>>>
>>> And the last patch is there to get the conversation going about changing
>>> what --nodefaults does. Details in the patch.
>>>
>>> [...]
>>
>> Applied first two to kvmtool (master), thanks!
>>
>> [1/3] Revert "virtio-net: Don't print the compat warning for the default device"
>>        https://git.kernel.org/will/kvmtool/c/4498eb7400c6
>> [2/3] builtin-run: Document mode=none for -n/--network
>>        https://git.kernel.org/will/kvmtool/c/c7b7a542cdcd
>>
>> I'm also not sure about the final RFC patch:
>>
>> [3/3] builtin-run: Have --nodefaults disable the default virtio-net device
>>
>> so it would be great to hear if anybody else has an opinion on that. IIRC,
>> we introduced this for some EFI work, so perhaps those folks might have
>> an opinion?
> 
> It was actually introduced to allow kvmtool to load a kvm-unit-tests test
> file using --kernel instead of --firmware [1].
> 
> The user can specify parameters for a test using two methods: using the
> kernel command line (for selecting a specific test from a test file with
> multiple tests, for example) and from an initrd (for environment variables,
> in a key=value format). --firmware cannot load an initrd, so the only
> option is to use --kernel. But kvmtool mangles the kernel command line by
> prepending several kernel options, which breaks kvm-unit-tests' command
> line parser. Until --defaults there was no way to disable this behaviour.
> 
> To the point of running kvm-unit-tests, it makes no functional difference
> if a test is run with --nodefaults --network mode=none or with --nodefaults
> only. It's just that I think that --nodefaults disabling the default
> configuration options is slightly more intuitive, but I'm not sure the
> effort of changing the semantics is worth it (need to inspect all the code
> that sets the default configuration options, then possibly adding new
> kvmtool command line parameters to bring back those options if there's no
> other way of changing them - I suspect this can get rather tedious).

I personally prefer "--nodefaults" doing what it says. i.e., kvmtool
not adding *anything* by default on its own.

Suzuki


> 
> [1] https://lore.kernel.org/all/20210923144505.60776-1-alexandru.elisei@arm.com/
> 
> Thanks,
> Alex
> 
>>
>> Cheers,
>> -- 
>> Will
>>
>> https://fixes.arm64.dev
>> https://next.arm64.dev
>> https://will.arm64.dev