lklfuse: support exclusive locks to avoid duplicate mounts

[ddiss]

Duplicate mounts are a risk when running multiple lklfuse instances, as we don't have a single arbitrator to manage access. This patchset adds a new lock parameter, which can provide host-side flock() based exclusion.

The following changes since commit 46f599b0575197f5756d2d171c294e1242e25a9d:

  Merge pull request #610 from ddiss/minor_test_changes (2025-07-03 14:53:53 -0700)

are available in the Git repository at:

  https://github.com/ddiss/linux lklfuse_flock

for you to fetch changes up to 656eccf1fe59c61d980bc8f3a97cb705699e0d8a:

  lkl: tests: fix net setup_backend return status (2025-07-04 14:51:32 +1000)

----------------------------------------------------------------
David Disseldorp (5):
      lklfuse: add lock parameter to avoid duplicate mounts
      lkl: systemd: use lklfuse lock parameter
      lkl: tests: add lklfuse_lock_conflict test
      lkl: tests: drop sleep before lklfuse unmount
      lkl: tests: fix net setup_backend return status

 Documentation/lkl/lklfuse.rst            |  4 +++-
 tools/lkl/lklfuse.c                      | 27 ++++++++++++++++++++++++---
 tools/lkl/systemd/lklfuse-mount@.service |  8 ++++++--
 tools/lkl/tests/lklfuse.sh               | 29 ++++++++++++++++++++++-------
 tools/lkl/tests/net.sh                   |  2 +-
 5 files changed, 56 insertions(+), 14 deletions(-)

[ddiss]

The windows build failure here appears to be the same gcc -std=gnu23 issue fixed in #610 , so I'll rebase atop that for a clean build. The checkpatch warning is also legit so will fix.

[ddiss]

v2:

• rebase atop lkl: tests: minor fn parameter and kasan parsing changes #610 to fix windows build failure
• fix typo found by checkpatch
• minor commit msg changes

[ddiss]

checkpatch still complains but I think it can be ignored:

Run tools/lkl/scripts/checkpatch.sh
grep: write error: Broken pipe
WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
#13: 
  176 |                 return host_setsockopt(fd, level, optname, optval, optlen);

/tmp/tmp.mYV5y8POUm/0001-lkl-hijack-explicitly-build-with-std-gnu11.patch total: 0 errors, 1 warnings, 6 lines checked
WARNING: Missing commit description - Add an appropriate one

/tmp/tmp.mYV5y8POUm/0001-lkl-tests-fix-net-setup_backend-return-status.patch total: 0 errors, 1 warnings, 8 lines checked
Error: Process completed with exit code 1.

[tavip]

LGTM, left a couple minor comments. Thanks @ddiss!

[ddiss]

@tavip : thanks for the review!
v3:

• drop 1s sleep in lklfuse.sh test cleanup
• use block-device instead of file for lklfuse -ro help text
• minor commit msg changes