[PATCH v2 0/7] vmsplice: fix some problems in my previous vmsplice patchset

[Askar Safin <safinaskar@gmail.com>]

This patchset is for VFS. Of course, it depends on my previous vmsplice
patchset ( https://lore.kernel.org/all/20260531010107.1953702-1-safinaskar@gmail.com/ ).

I fix some problems in my previous patchset.

1. Fix problem with CLASS(fd, f)(fd). See first patch in this patchset
for details. This is probably not so important, but I fix it anyway.

2. Change "unsigned long" back to "int". See second patch for details.
Again, this is probably not important, but I want to fix this anyway.

3. Fix that LTP vmsplice01 bug.

4. libfuse relies on sharing vmsplice behavior. So we detect particular
combination of flags to pipe2(2) and vmsplice(2) and return -EINVAL.
This forces libfuse to fail back to non-vmsplice code path.
I. e. we fix libfuse-related regression [1].
I did debian code search for regex "vmsplice.*SPLICE_F_NONBLOCK" and
I found no other packages with this particular combination of flags
except for fuse itself. (Okay, other packages are fio and stress-ng,
but these are merely testers.) So, I think this is okay to return
EINVAL here, breakage will be minimal.

5. Set FMODE_NOWAIT for named FIFOs. CRIU relies on ability to do
vmsplice(SPLICE_F_NONBLOCK) on named FIFOs. So, I fix this CRIU-related
regression [2]. But there is another CRIU-related regression, which I do not
fix [3]: CRIU behavior in splice mode becomes so slow that splice mode
becomes useless. I personally still believe that removing vmsplice is
right thing to do. Other option is doing nothing. Yet another option
is to implement some deprecation period [3]. Let other developers
decide.

See patches for details.

Please, run that LTP vmsplice01 test again.

Notes:

- I want to repeat: I change behavior around SPLICE_F_NONBLOCK.
Previously, vmsplice ignored whether pipe itself was opened as
non-blocking file. Now it is not ignored. And in my opinion
new behavior is better.
- vmsplice(2) now is in fs/read_write.c . It is very similar to
preadv2 and pwritev2 now, so I think it belongs to fs/read_write.c now.

Please, review this patchset carefully. I'm still new contributor.
In particular, please, review that do-while loop, I'm not sure I did
everything right.

Tested in Qemu.

[1] https://lore.kernel.org/all/CAJnrk1Y9egYizkx1H9K0cqxSYuB+7vLvQbV7Tf4C5eHFqnnC-A@mail.gmail.com/
[2] https://lore.kernel.org/all/CANaxB-zK5q=Xw6UZTmeFtXsDZjUsPkFk=p485m-wtNTBnf4hgg@mail.gmail.com/
[3] https://lore.kernel.org/all/CANaxB-xUrLQYGiRJZc4Boi+KX=0TJSWymErNovANVko20fMDVA@mail.gmail.com/

v1: https://lore.kernel.org/lkml/20260606061031.3744880-1-safinaskar@gmail.com/

Changes since v1: fix fuse-related and CRIU-related regressions (see above).

Askar Safin (7):
  vmsplice: open-code do_writev and do_readv
  vmsplice: change argument type back to "int"
  splice: turn wait_for_space flags argument into bool
  pipe: move wait_for_space to fs/pipe.c and rename it
  vmsplice: make sure we don't wait after writing some data
  vmsplice: return -EINVAL for particular combination of flags
  pipe: set FMODE_NOWAIT for named FIFOs

 fs/pipe.c                 | 23 +++++++++++++
 fs/read_write.c           | 71 +++++++++++++++++++++++++++++++++++----
 fs/splice.c               | 19 +----------
 include/linux/pipe_fs_i.h |  2 ++
 include/linux/syscalls.h  |  2 +-
 5 files changed, 91 insertions(+), 26 deletions(-)


base-commit: 8d86fcfc2857d64af85f5c87c193c25655c970af
-- 
2.47.3