Re: [PATCH v8 08/11] tests/qtest: Fix tests when no KVM or TCG are present

[Fabiano Rosas]

Thomas Huth <thuth@redhat.com> writes:

> On 10/03/2023 16.37, Fabiano Rosas wrote:
>> Thomas Huth <thuth@redhat.com> writes:
>> 
>>> On 10/03/2023 14.06, Fabiano Rosas wrote:
>>>> "Michael S. Tsirkin" <mst@redhat.com> writes:
>>>>
>>>>> On Thu, Mar 09, 2023 at 05:14:31PM -0300, Fabiano Rosas wrote:
>>>>>> It is possible to have a build with both TCG and KVM disabled due to
>>>>>> Xen requiring the i386 and x86_64 binaries to be present in an aarch64
>>>>>> host.
>>>>>>
>>>>>> If we build with --disable-tcg on the aarch64 host, we will end-up
>>>>>> with a QEMU binary (x86) that does not support TCG nor KVM.
>>>>>>
>>>>>> Fix tests that crash or hang in the above scenario. Do not include any
>>>>>> test cases if TCG and KVM are missing.
>>>>>>
>>>>>> Make sure that calls to qtest_has_accel are placed after g_test_init
>>>>>> in similar fashion to commit ae4b01b349 ("tests: Ensure TAP version is
>>>>>> printed before other messages") to avoid TAP parsing errors.
>>>>>>
>>>>>> Signed-off-by: Fabiano Rosas <farosas@suse.de>
>>>>>> Reviewed-by: Juan Quintela <quintela@redhat.com>
>>>>>
>>>>> I don't like it that we are hard-coding the list of accelerators
>>>>> like this. Make a wrapper?
>>>>>
>>>>
>>>> Are you thinking of some sort of "has_any_accel" wrapper?
>>>
>>> I think in the long run, we want something like what I described here:
>>>
>>> https://lore.kernel.org/qemu-devel/ee0cad00-a6f3-f0c1-adf0-ba32329354f3@redhat.com/
>>>
>> 
>> Wont't that function be too generic? The choice of accelerator is quite
>> specific to each individual test, some might not work with TCG, some
>> might not work with HVF and so on. There is no link between build-time
>> configuration and runtime test execution after all. We could always have
>> a build without an accelerator and then try to run a test that uses that
>> accelerator. And also have an accelerator present that the test does not
>> support at all.
>> 
>> 
>> For this particularly bizarre case of not having TCG nor KVM in the
>> build I'm inclined to go with Michael's suggestion of checking it at
>> build time and skipping all the hassle. This is what I'm preparing:
>> 
>> diff --git a/tests/qtest/meson.build b/tests/qtest/meson.build
>> index 29a4efb4c2..e698cdcb60 100644
>> --- a/tests/qtest/meson.build
>> +++ b/tests/qtest/meson.build
>> @@ -27,6 +27,12 @@ if config_host.has_key('CONFIG_MODULES')
>>     qtests_generic += [ 'modules-test' ]
>>   endif
>>   
>> +# For x86_64, i386 and aarch64 it is possible to have only Xen as an
>> +# accelerator. Some tests require either TCG or KVM, so make sure they
>> +# are present before building those tests.
>> +tcg_or_kvm_available = (config_all.has_key('CONFIG_TCG') or
>> +                        config_all.has_key('CONFIG_KVM'))

Ouch, this doesn't work because one of the binaries could still have KVM
support and we build the tests only once.

On an aarch64 host:
---disable-tcg --enable-kvm --enable-xen =>
qemu-system-aarch64 w/ Xen, KVM, no TCG
qemu-system-x86_64  w/ Xen, no KVM, no TCG