[PATCH 0/3] fuse: atomic open

[jamz <jamz@amazon.com>]

From: Jimmy Zuber <jamz@amazon.com>

Add FUSE_OPEN_ATOMIC, allowing the kernel to skip LOOKUP to improve
performance. A server implementing FUSE_OPEN_ATOMIC will look up
the name, create it if O_CREAT is supplied, and open it in one request.

The reply says whether the file was created, as Miklos suggested in [1].
The overall pattern follows his sketch in [2]. For a cached
name, the kernel compares the returned nodeid with the cached one and
looks the name up again on a mismatch.

A server without FUSE_OPEN_ATOMIC replies -ENOSYS and keeps today's
behaviour.

Tested with a new selftest under UML and KVM.

[1] https://lore.kernel.org/all/CAJfpeguEK4JsFo60=yHkpLL6XkDGS7cQ5GOhiFL379KsYk0TsQ@mail.gmail.com/
[2] https://lore.kernel.org/all/CAJfpegvXtXY=Pbxv+dMGFR8mvWN0DUwhSo6NwaVexk6Y6sao+w@mail.gmail.com/


Jimmy Zuber (3):
  fuse: add FUSE_OPEN_ATOMIC
  fuse: open cached files with FUSE_OPEN_ATOMIC
  selftests/fuse: add test for FUSE_OPEN_ATOMIC

 fs/fuse/dir.c                                 | 359 +++++++++++--
 fs/fuse/file.c                                |   4 +-
 fs/fuse/fuse_i.h                              |   4 +
 include/uapi/linux/fuse.h                     |   8 +-
 .../selftests/filesystems/fuse/.gitignore     |   1 +
 .../selftests/filesystems/fuse/Makefile       |   3 +-
 .../filesystems/fuse/atomic_open_test.c       | 473 ++++++++++++++++++
 7 files changed, 797 insertions(+), 55 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/fuse/atomic_open_test.c


base-commit: b776cbe24cc1b79c7f5101762b0069b3f48b6a4b
-- 
2.50.1