[PATCH 0/2] compat/mingw: fix EACCESS when opening files with `O_CREAT | O_EXCL`

[Patrick Steinhardt <ps@pks.im>]

Hi,

I finally found some time to have a look at why t0610 is failing
regularly in MinGW. As it turns out the root cause is our emulation of
open(3p): when trying to open a file with `_wopen(..., O_CREAT|O_EXCL)`
the call fails in case another process has marked the same file for
deletion via `DeleteFileW()`. This gets triggered by t0610 because we
race around locking the reftable stack and thus causes the failure.

The fix is simple: we get `ERROR_ACCESS_DENIED` in this situation, so
instead of translating that error to `EACCESS` we translate it to
`EEXIST`. This fixes the flake on my machine, but as usual when it comes
to Windows I would very much like to ask those in the know to point out
any obvious mistakes I did.

The other patch is a while-at-it patch that I was wondering about while
debugging the issue. It's not needed and I'm happy to drop it if you
don't think we should include it.

Thanks!

Patrick

---
Patrick Steinhardt (2):
      compat/mingw: handle O_CLOEXEC in `mingw_open_existing()`
      compat/mingw: fix EACCESS when opening files with `O_CREAT | O_EXCL`

 compat/mingw.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)


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base-commit: 4b68faf6b93311254efad80e554780e372deb42f
change-id: 20250313-b4-pks-mingw-lockfile-flake-49dfcce8e7c2