[RFC,0/3] fat: add support for the renameat2 RENAME_EXCHANGE flag

Message

Javier Martinez Canillas May 19, 2022, 9:23 a.m. UTC

Hello,

This series add support for the renameat2 system call RENAME_EXCHANGE flag
(which allows to atomically replace two paths) to the vfat filesystem code.

There are many use cases for this, but we are particularly interested in
making possible for vfat filesystems to be part of OSTree [0] deployments.

Currently OSTree relies on symbolic links to make the deployment updates
an atomic transactional operation. But RENAME_EXCHANGE could be used [1]
to achieve a similar level of robustness when using a vfat filesystem.

Patch #1 is just a preparatory patch to introduce the RENAME_EXCHANGE
support in patch #2 and finally patch #3 adds some kselftests to test it.

This is my first contribution to the fs/* subsystem, so I'm marking this
set as RFC, in case I got anything wrong with the patches. But they work
correctly on my local testing.

[0]: https://github.com/ostreedev/ostree
[1]: https://github.com/ostreedev/ostree/issues/1649


Javier Martinez Canillas (3):
  fat: add a vfat_rename2() and make existing .rename callback a helper
  fat: add renameat2 RENAME_EXCHANGE flag support
  selftests/filesystems: add a vfat RENAME_EXCHANGE test

 MAINTAINERS                                   |   1 +
 fs/fat/namei_vfat.c                           | 172 +++++++++++++++++-
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/filesystems/fat/Makefile        |   7 +
 .../testing/selftests/filesystems/fat/config  |   2 +
 .../filesystems/fat/rename_exchange.c         |  37 ++++
 .../filesystems/fat/run_fat_tests.sh          |  80 ++++++++
 7 files changed, 293 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/fat/Makefile
 create mode 100644 tools/testing/selftests/filesystems/fat/config
 create mode 100644 tools/testing/selftests/filesystems/fat/rename_exchange.c
 create mode 100755 tools/testing/selftests/filesystems/fat/run_fat_tests.sh