[GIT PULL] Add ftruncate

[tontinton]

To accompany the patches I sent for adding ftruncate, here are the changes for usermode.

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git request-pull output:

The following changes since commit 63342497bec87b72d4b415c8bed930c15ff83b0d:

  test/read-mshot: check that IORING_CQE_F_MORE isn't set on error (2024-01-22 14:56:08 -0700)

are available in the Git repository at:

  git@github.com:tontinton/liburing.git truncate

for you to fetch changes up to c023393f3a3b960e3df77e5bcfd1b2e93e3b5e0f:

  man/io_uring_prep_ftruncate: Add the new ftruncate command (2024-01-31 17:52:13 +0200)

----------------------------------------------------------------
Tony Solomonik (4):
      Add ftruncate helpers
      test/truncate: Add test for ftruncate
      test/truncate: Add test for failure on truncate path
      man/io_uring_prep_ftruncate: Add the new ftruncate command

 man/io_uring_prep_ftruncate.3   |  48 ++++++++++++++++++++++++++++++++
 src/include/liburing.h          |   6 ++++
 src/include/liburing/io_uring.h |   1 +
 src/liburing-ffi.map            |   1 +
 test/Makefile                   |   1 +
 test/truncate.c                 | 179 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 236 insertions(+)
 create mode 100644 man/io_uring_prep_ftruncate.3
 create mode 100644 test/truncate.c

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[axboe]

Two minor things:

1) The prep helper should go into the ffi as well, and the ffi map (in the 2.6 section). See src/liburing-ffi.map. 2) The test case tests functionality, which is great, but it should also the failure case. Since we're potentially adding truncate support later where we'll put the path in sqe->addr, add a test case that issues an sqe where addr is set to a filename and verify that it fails with EINVAL.

[axboe]

I think this looks fine, but one problem is that if you run this test case on an older kernel, then the test will fail. If you get -EINVAL for the first ftruncate you try, just assume the kernel doesn't support it and return T_EXIT_SKIP for that and skip the other tests. That way it'll just skip the test case on older kernels, but test it on newer kernels.

See other test cases that do this very thing, usually with a static int no_ftruncate global that can be set by the first test invocation, and then checked again for non-zero when that first test case returns. If true, then it should return T_EXIT_SKIP.

[tontinton]

It already runs goto out which returns 0, when ftruncate is not supported.

[axboe]

It already runs goto out which returns 0, when ftruncate is not supported.

It does, but it doesn't return T_EXIT_SKIPPED. I think you should also distinguish between "we got EBADF/EINVAL on the first test, it's probably not supported, T_EXIT_SKIPPED" rather than just have any of the test cases returning EINVAL leading to a skipped test where it probably should've been a failure.