Re: [PATCH] tests/qtest: optimize qtest_get_machines

[Steven Sistare <steven.sistare@oracle.com>]

On 9/20/2025 3:12 AM, Markus Armbruster wrote:
> Steve Sistare <steven.sistare@oracle.com> writes:
> 
>> qtest_get_machines returns the machines supported by the QEMU binary
>> described by an environment variable and caches the result.  If the
>> next call to qtest_get_machines passes the same variable name, the cached
>> result is returned, but if the name changes, the caching is defeated.
>> To make caching more effective, remember the path of the QEMU binary
>> instead.  Different env vars, eg QTEST_QEMU_BINARY_SRC and
>> QTEST_QEMU_BINARY_DST, usually resolve to the same path.
>>
>> Before the optimization, the test /x86_64/migration/precopy/unix/plain
>> exec's QEMU and calls query-machines 3 times.  After optimization, that
>> only happens once.  This does not significantly speed up the tests, but
>> it reduces QTEST_LOG output, and launches fewer QEMU instances, making
>> it easier to debug problems.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> 
> I guess this is a followup to an observation I made during review of my
> [PATCH 1/5] qtest/qom-test: Plug memory leak with -p:
> 
>      Message-ID: <87h5ymdzrf.fsf@pond.sub.org>
>      https://lore.kernel.org/qemu-devel/87h5ymdzrf.fsf@pond.sub.org/
> 
> Appreciated!

In truth, this new patch is not intended to reduce leaks.  If it does,
that is a bonus :)

- Steve