[PATCH liburing 0/3] Bring back `CONFIG_HAVE_MEMFD_CREATE` to fix Android build error

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

Hello,

There are three patches in this series to address Android build
error related to `memfd_create()`. The changes are as follows:

1) Bring back `CONFIG_HAVE_MEMFD_CREATE` and the associated memfd test
to resolve Android build failures caused by:

  93d3a7a70b4a ("examples/zcrx: udmabuf backed areas")

It added a call to `memfd_create()`, which is unavailable on some
Android toolchains, leading to the following build error:
```
  zcrx.c:111:10: error: call to undeclared function 'memfd_create'; ISO C99 and \
  later do not support implicit function declarations \
  [-Wimplicit-function-declaration]
    111 |         memfd = memfd_create("udmabuf-test", MFD_ALLOW_SEALING);
        |                 ^
```
This reversion is a preparation step for a proper fix by ensuring
`memfd_create()` usage is guarded and portable. Issue #620 was
initially unclear, but we now suspect it stemmed from improper
compiler/linker flag combinations.

2) In test dir, relocate `memfd_create()` to helpers.c for broader
test access. Previously, the static definition of `memfd_create()` was
limited to io_uring_register.c. Now, promote it to a shared location
accessible to all test cases, ensuring that future tests using
`memfd_create()` do not trigger build failures on Android targets where
the syscall is undefined in the standard headers. It improves
portability and prevents regressions across test builds.

3) Last, in example dir, add `memfd_create()` helper to fix the
build error in zcrx example.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
---

Alviro Iskandar Setiawan (3):
  Revert "test/io_uring_register: kill old memfd test"
  test: Move `memfd_create()` to helpers.c, make it accessible for all tests
  examples: Add `memfd_create()` helper

 configure                |  19 +++++++
 examples/helpers.c       |   8 +++
 examples/helpers.h       |   5 ++
 test/helpers.c           |   8 +++
 test/helpers.h           |   5 ++
 test/io_uring_register.c | 108 +++++++++++++++++++++++++++++++++++++++
 6 files changed, 153 insertions(+)


base-commit: 0272bfa96f02cc47c024ec510a764ef7e37b76bf
-- 
Alviro Iskandar Setiawan