Re: [PULL 06/14] ci: Add a migration compatibility test job

[Peter Xu]

On Mon, Feb 05, 2024 at 10:22:35AM +0000, Daniel P. Berrangé wrote:
> On Mon, Feb 05, 2024 at 11:25:13AM +0800, Peter Xu wrote:
> > On Fri, Feb 02, 2024 at 10:47:05AM -0300, Fabiano Rosas wrote:
> > > Peter Maydell <peter.maydell@linaro.org> writes:
> > > 
> > > > On Mon, 29 Jan 2024 at 03:04, <peterx@redhat.com> wrote:
> > > >>
> > > >> From: Fabiano Rosas <farosas@suse.de>
> > > >>
> > > >> The migration tests have support for being passed two QEMU binaries to
> > > >> test migration compatibility.
> > > >>
> > > >> Add a CI job that builds the lastest release of QEMU and another job
> > > >> that uses that version plus an already present build of the current
> > > >> version and run the migration tests with the two, both as source and
> > > >> destination. I.e.:
> > > >>
> > > >>  old QEMU (n-1) -> current QEMU (development tree)
> > > >>  current QEMU (development tree) -> old QEMU (n-1)
> > > >>
> > > >> The purpose of this CI job is to ensure the code we're about to merge
> > > >> will not cause a migration compatibility problem when migrating the
> > > >> next release (which will contain that code) to/from the previous
> > > >> release.
> > > >>
> > > >> The version of migration-test used will be the one matching the older
> > > >> QEMU. That way we can avoid special-casing new tests that wouldn't be
> > > >> compatible with the older QEMU.
> > > >>
> > > >> Note: for user forks, the version tags need to be pushed to gitlab
> > > >> otherwise it won't be able to checkout a different version.
> > > >>
> > > >> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> > > >> Link: https://lore.kernel.org/r/20240118164951.30350-3-farosas@suse.de
> > > >> Signed-off-by: Peter Xu <peterx@redhat.com>
> > > >> ---
> > > >>  .gitlab-ci.d/buildtest.yml | 60 ++++++++++++++++++++++++++++++++++++++
> > > >>  1 file changed, 60 insertions(+)
> > > >>
> > > >> diff --git a/.gitlab-ci.d/buildtest.yml b/.gitlab-ci.d/buildtest.yml
> > > >> index e1c7801598..f0b0edc634 100644
> > > >> --- a/.gitlab-ci.d/buildtest.yml
> > > >> +++ b/.gitlab-ci.d/buildtest.yml
> > > >> @@ -167,6 +167,66 @@ build-system-centos:
> > > >>        x86_64-softmmu rx-softmmu sh4-softmmu nios2-softmmu
> > > >>      MAKE_CHECK_ARGS: check-build
> > > >>
> > > >> +# Previous QEMU release. Used for cross-version migration tests.
> > > >> +build-previous-qemu:
> > > >> +  extends: .native_build_job_template
> > > >> +  artifacts:
> > > >> +    when: on_success
> > > >> +    expire_in: 2 days
> > > >> +    paths:
> > > >> +      - build-previous
> > > >> +    exclude:
> > > >> +      - build-previous/**/*.p
> > > >> +      - build-previous/**/*.a.p
> > > >> +      - build-previous/**/*.fa.p
> > > >> +      - build-previous/**/*.c.o
> > > >> +      - build-previous/**/*.c.o.d
> > > >> +      - build-previous/**/*.fa
> > > >> +  needs:
> > > >> +    job: amd64-opensuse-leap-container
> > > >> +  variables:
> > > >> +    IMAGE: opensuse-leap
> > > >> +    TARGETS: x86_64-softmmu aarch64-softmmu
> > > >> +  before_script:
> > > >> +    - export QEMU_PREV_VERSION="$(sed 's/\([0-9.]*\)\.[0-9]*/v\1.0/' 
> > > >> VERSION)"
> > > >> +    - git checkout $QEMU_PREV_VERSION
> > > >> +  after_script:
> > > >> +    - mv build build-previous
> > > >
> > > > There seems to be a problem with this new CI job. Running a CI
> > > > run in my local repository it fails:
> > > >
> > > > https://gitlab.com/pm215/qemu/-/jobs/6075873685
> > > >
> > > > $ export QEMU_PREV_VERSION="$(sed 's/\([0-9.]*\)\.[0-9]*/v .0/' 
> > > > VERSION)"
> > > > $ git checkout $QEMU_PREV_VERSION
> > > > error: pathspec 'v8.2.0' did not match any file(s) known to git
> > > > Running after_script
> > > > Running after script...
> > > > $ mv build build-previous
> > > > mv: cannot stat 'build': No such file or directory
> > > > WARNING: after_script failed, but job will continue unaffected: exit 
> > > > code 1
> > > > Saving cache for failed job
> > > >
> > > >
> > > > I don't think you can assume that private forks doing submaintainer CI
> > > > runs necessarily have the full set of tags that the main repo does.
> > > 
> > > Yes, I thought this would be rare enough not to be an issue, but it
> > > seems it's not. I don't know what could be done here, if there's no tag,
> > > then there's no way to resolve the actual commit hash I think.
> > > 
> > > > I suspect the sed run will also do the wrong thing when run on the
> > > > commit that updates the version, because then it will replace
> > > > "9.0.0" with "9.0.0".
> > > 
> > > I just ignored this completly because my initial idea was to leave this
> > > job disabled and only run it for migration patchsets and pull requests,
> > > so it wouldn't make sense to run at that commit.
> > > 
> > > This job is also not entirely fail proof by design because we could
> > > always be hitting bugs in the older QEMU version that were already fixed
> > > in the new version.
> > > 
> > > I think the simplest fix here is to leave the test disabled, possibly
> > > with an env variable to enable it.
> > 
> > However if so that'll be unfortunate.. because the goal of the "n-1" test
> > is to fail the exact commit that will break compatibility and make it
> > enforced, IMHO.
> > 
> > Failing for some migration guy pushing CI can be better than nothing
> > indeed, but it is just less ideal..  we want the developer / module
> > maintainer notice this issue, fix it instead of merging something wrong
> > already, then we try to find what is broken and ask for a fix (where there
> > will still be a window it's broken; and if unlucky across major releases).
> > 
> > Currently the coverage of n-1 test is indeed still more focused on
> > migration framework, but it'll also cover quite some default configs of the
> > system layout (even if only x86 is covered), and some default devices IIRC.
> > We can already attach a few more standard devices in the cmdline so more
> > things can get covered.
> > 
> > A pretty dumb (but might be working?) solution is we keep commit ID rather
> > than tags to avoid all kinds of tag hassles:
> > 
> >   PREVIOUS_VERSION_COMMIT_ID=1600b9f46b1bd08b00fe86c46ef6dbb48cbe10d6
> > 
> > Then we boost it after a release.  I think it'll also work for the release
> > commit then.
> 
> Please don't go for hardcoding stuff. AFAICS, the solution is very easy
> and only requires adding two git commands to the test job:
> 
>   export QEMU_PREV_VERSION="$(sed 's/\([0-9.]*\)\.[0-9]*/v\1.0/' VERSION)"
>   git remote add upstream https://gitlab.com/qemu-project/qemu
>   git fetch upstream $QEMU_PRRV_VERSION
>   git checkout $QEMU_PREV_VERSION

True...  I'm as stupid as I could have. :)  Thanks.

For the CI test when at exactly the commit to release QEMU: I assume it's
fine to simply run it with 9.0 <-> 9.0 for example, which is one more time
of current migration qtest. IIUC that shouldn't be a big deal.

-- 
Peter Xu