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.

AC_DEFUN([AX_HAVE_EPOLL], [dnl
  ax_have_epoll_cppflags="${CPPFLAGS}"
  AC_CHECK_HEADER([linux/version.h], [CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
  AC_MSG_CHECKING([for Linux epoll(7) interface])
  AC_CACHE_VAL([ax_cv_have_epoll], [dnl
    AC_LINK_IFELSE([dnl
      AC_LANG_PROGRAM([dnl
#include <sys/epoll.h>
#ifdef HAVE_LINUX_VERSION_H
#  include <linux/version.h>
#  if LINUX_VERSION_CODE < KERNEL_VERSION(2,5,45)
#    error linux kernel version is too old to have epoll
#  endif
#endif
], [dnl
int fd, rc;
struct epoll_event ev;
fd = epoll_create(128);
rc = epoll_wait(fd, &ev, 1, 0);])],
      [ax_cv_have_epoll=yes],
      [ax_cv_have_epoll=no])])
  CPPFLAGS="${ax_have_epoll_cppflags}"
  AS_IF([test "${ax_cv_have_epoll}" = "yes"],
    [AC_MSG_RESULT([yes])
$1],[AC_MSG_RESULT([no])
$2])
])dnl

AC_DEFUN([AX_HAVE_EPOLL_PWAIT], [dnl
  ax_have_epoll_cppflags="${CPPFLAGS}"
  AC_CHECK_HEADER([linux/version.h],
    [CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
  AC_MSG_CHECKING([for Linux epoll(7) interface with signals extension])
  AC_CACHE_VAL([ax_cv_have_epoll_pwait], [dnl
    AC_LINK_IFELSE([dnl
      AC_LANG_PROGRAM([dnl
#ifdef HAVE_LINUX_VERSION_H
#  include <linux/version.h>
#  if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,19)
#    error linux kernel version is too old to have epoll_pwait
#  endif
#endif
#include <sys/epoll.h>
#include <signal.h>
], [dnl
int fd, rc;
struct epoll_event ev;
fd = epoll_create(128);
rc = epoll_wait(fd, &ev, 1, 0);
rc = epoll_pwait(fd, &ev, 1, 0, (sigset_t const *)(0));])],
      [ax_cv_have_epoll_pwait=yes],
      [ax_cv_have_epoll_pwait=no])])
  CPPFLAGS="${ax_have_epoll_cppflags}"
  AS_IF([test "${ax_cv_have_epoll_pwait}" = "yes"],
    [AC_MSG_RESULT([yes])
$1],[AC_MSG_RESULT([no])
$2])
])dnl

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