[PATCH liburing v2 0/3] Bring back `CONFIG_HAVE_MEMFD_CREATE` to fix Android build error

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

Hello,

This is the v2 revision of the patch series to address the Android
build error related to `memfd_create()`. The series consists of three
patches:

1) Bring back `CONFIG_HAVE_MEMFD_CREATE` to fix Android build error.

Partially reverts commit:

  732bf609b670 ("test/io_uring_register: kill old memfd test")

to bring back `CONFIG_HAVE_MEMFD_CREATE` 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 patch for a proper fix by ensuring
`memfd_create()` usage is guarded and portable. It's only a partial
revert because the test itself is not restored.

2) Move `memfd_create()` to helpers.c, make it accessible for all tests.

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) Also, add `memfd_create()` helper in the examples directory.

Changelog:
v1 -> v2:
  - Omit the old memfd test because it's not needed anymore (Jens Axboe)
    Link: https://lore.kernel.org/io-uring/4bc75566-9cb5-42ec-a6b7-16e04062e0c6@kernel.dk

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

Alviro Iskandar Setiawan (3):
  Bring back `CONFIG_HAVE_MEMFD_CREATE` to fix Android build errors
  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 +++++
 5 files changed, 45 insertions(+)


base-commit: 0272bfa96f02cc47c024ec510a764ef7e37b76bf
-- 
Alviro Iskandar Setiawan