ax_have_epoll

This macro determines whether the system supports the epoll I/O event interface. A neat usage example would be:

  AX_HAVE_EPOLL(
    [AX_CONFIG_FEATURE_ENABLE(epoll)],
    [AX_CONFIG_FEATURE_DISABLE(epoll)])
  AX_CONFIG_FEATURE(
    [epoll], [This platform supports epoll(7)],
    [HAVE_EPOLL], [This platform supports epoll(7).])

The epoll interface was added to the Linux kernel in version 2.5.45, and the macro verifies that a kernel newer than this is installed. This check is somewhat unreliable if <linux/version.h> doesn't match the running kernel, but it is necessary regardless, because glibc comes with stubs for the epoll_create(), epoll_wait(), etc. that allow programs to compile and link even if the kernel is too old; the problem would then be detected only at runtime.

Linux kernel version 2.6.19 adds the epoll_pwait() call in addition to epoll_wait(). The availability of that function can be tested with the second macro. Generally speaking, it is safe to assume that AX_HAVE_EPOLL would succeed if AX_HAVE_EPOLL_PWAIT has, but not the other way round.