Re: [PATCH v3 0/6] selftests/liveupdate: add memfd tests

[Pasha Tatashin]

On 04-29 15:20, Pratyush Yadav wrote:
> On Tue, Apr 28 2026, Pasha Tatashin wrote:
> 
> > On 04-04 10:24, Pratyush Yadav wrote:
> >> From: "Pratyush Yadav (Google)" <pratyush@xxxxxxxxxx>
> >> 
> >> Hi,
> >> 
> >> This series adds some tests for memfd preservation across a live update.
> >> Currently memfd is only tested indirectly via luo_kexec_simple or
> >> luo_multi_session. Add a dedicated test suite for it.
> >> 
> >> Patches 1 and 2 are preparatory, adding base framework and helpers, and
> >> the other patches each add a test. Some of the code is taken from the
> >> libluo patches [0] I sent a while ago.
> >> 
> >> [0] https://lore.kernel.org/linux-mm/20250723144649.1696299-33-pasha.tatashin@xxxxxxxxxx/
> >
> > Here are few observations that I noticed when I tried to run your tests:
> >
> > 1. The '-h' tells you nothing about --stage argument:
> >
> > root@liveupdate-vm:~/liveupdate# ./luo_memfd -h
> > Usage: ./luo_memfd [-h|-l|-d] [-t|-T|-v|-V|-f|-F|-r name]
> > 	-h       print help
> > 	-l       list all tests
> > 	-d       enable debug prints
> >
> > 	-t name  include test
> > 	-T name  exclude test
> > 	-v name  include variant
> > 	-V name  exclude variant
> > 	-f name  include fixture
> > 	-F name  exclude fixture
> > 	-r name  run specified test
> > 	...
> 
> Yeah, unfortunately that is a side effect of using test_harness_run(),
> which does not know anything about the options specific to our test.
> 
> >
> > 2. '-l' does not work after you run stage1, do you keep /dev/liveupdate 
> > open? That is not needed, we only need to keep session open.
> 
> Oh yeah, I keep forgetting that is no longer needed. The main process
> closes the FD but the forked daemons hold a reference. I can clean that
> up via a fixture.
> 
> >
> > root@liveupdate-vm:~/liveupdate# ./luo_memfd -l
> > 1..0 # SKIP Failed to open /dev/liveupdate (Device or resource busy) device. Is LUO enabled?
> >
> > 3. Stage 1 has proper [STAGE 1] prefix, but no [STAGE 2] prefix for 
> 
> Because stage 2 has no prints, all the prints are coming from the
> selftest harness. Those same lines are also not prefixed in stage 1. If
> you'd like, I can add a print beforehand that shows which stage is

Yes, please, add a least one [STAGE 2] print.

> running. Other than that, I don't see what else we can do. I don't want
> to modify the selftest harness.
> 
> > stage 2:
> > # Starting 4 tests from 1 test cases.
> > #  RUN           global.memfd_data ...
> > # [STAGE 1] Forking persistent child to hold sessions...
> > # [STAGE 1] Child PID: 245. Resources are pinned.
> > # [STAGE 1] You may now perform kexec reboot.
> > #            OK  global.memfd_data
> > ok 1 global.memfd_data
> > #  RUN           global.zero_memfd ...
> > # [STAGE 1] Forking persistent child to hold sessions...
> > # [STAGE 1] Child PID: 247. Resources are pinned.
> > # [STAGE 1] You may now perform kexec reboot.
> > #            OK  global.zero_memfd
> > ok 2 global.zero_memfd
> > #  RUN           global.preserved_ops ...
> > #            OK  global.preserved_ops
> > ok 3 global.preserved_ops
> > #  RUN           global.fallocate_memfd ...
> > # [STAGE 1] Forking persistent child to hold sessions...
> > # [STAGE 1] Child PID: 250. Resources are pinned.
> > # [STAGE 1] You may now perform kexec reboot.
> > #            OK  global.fallocate_memfd
> > ok 4 global.fallocate_memfd
> > # PASSED: 4 / 4 tests passed.
> > # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:0 error:0
> >
> > ./do_kexec
> >
> > root@liveupdate-vm:~/liveupdate# ./luo_memfd
> > TAP version 13
> > 1..4
> > # Starting 4 tests from 1 test cases.
> > #  RUN           global.memfd_data ...
> > #            OK  global.memfd_data
> > ok 1 global.memfd_data
> > #  RUN           global.zero_memfd ...
> > #            OK  global.zero_memfd
> > ok 2 global.zero_memfd
> > #  RUN           global.preserved_ops ...
> > #      SKIP      test only expected to run on stage 1
> > #            OK  global.preserved_ops
> > ok 3 global.preserved_ops # SKIP test only expected to run on stage 1
> > #  RUN           global.fallocate_memfd ...
> > #            OK  global.fallocate_memfd
> > ok 4 global.fallocate_memfd
> > # PASSED: 4 / 4 tests passed.
> > # 1 skipped test(s) detected. Consider enabling relevant config options to improve coverage.
> > # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:1 error:0
> >
> > 4. I also do not like that we now have duplicated stage parsing code in  
> > luo_test(), perhaps we should add our own  test_harness_run() variant 
> > that depends on stage, and use it in both current tests, and the new 
> > memfd tests.
> 
> Sounds good in principle, but unfortunately ends up duplicating a lot of
> logic in test_harness_run() that is not a good idea IMO. We should work
> with the harness not fork off into our own.
> 
> I suppose we can refactor some of the logic there to split into
> functions that we can then use in our luo_test_harness_run(), but
> keeping the option parsing logic in sync is going to be difficult.
> 
> And for the duplicated logic, I agree. I thought about cleaning it up
> but was feeling lazy... Well now that you have called it out let me see
> what I can do.

The main point is that the luo_sessions and luo_memfds tests should use 
a common framework, whether that's luo_test_harness_run() or the generic 
test_harness_run(). I don't have a definitive answer for this, so I 
recommend tinkering with it to see what works best.

Pasha

> 
> [...]
> 
> -- 
> Regards,
> Pratyush Yadav