text: /*
   * Copyright 2017 Facebook, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   * Work around the lack of <sys/eventfd.h> on glibc 2.5.1 which we still
   * need to support, sigh.
   */
  
  #pragma once
  
  #ifndef FOLLY_NO_CONFIG
  #include <folly/folly-config.h>
  #endif
  
  #ifdef FOLLY_HAVE_FEATURES_H
  # include <features.h>
  #endif
  
  #if defined(__GLIBC__) && !defined(__APPLE__)
  #if __GLIBC_PREREQ(2, 9)
  # define FOLLY_GLIBC_2_9
  #endif
  #endif
  
  // <sys/eventfd.h> doesn't exist on older glibc versions
  #ifdef FOLLY_GLIBC_2_9
  #include <sys/eventfd.h>
  #else /* !def FOLLY_GLIBC_2_9 */
  
  #include <sys/syscall.h>
  #include <unistd.h>
  #include <fcntl.h>
  
  // Use existing __NR_eventfd2 if already defined
  // Values from the Linux kernel source:
  // arch/x86/include/asm/unistd_{32,64}.h
  #ifndef __NR_eventfd2
  #if FOLLY_X64
  /* nolint */
  #define __NR_eventfd2  290
  #elif defined(__i386__)
  /* nolint */
  #define __NR_eventfd2  328
  #else
  #error "Can't define __NR_eventfd2 for your architecture."
  #endif
  #endif
  
  enum
    {
      EFD_SEMAPHORE = 1,
  #define EFD_SEMAPHORE EFD_SEMAPHORE
      EFD_CLOEXEC = 02000000,
  #define EFD_CLOEXEC EFD_CLOEXEC
      EFD_NONBLOCK = 04000
  #define EFD_NONBLOCK EFD_NONBLOCK
    };
  
  // http://www.kernel.org/doc/man-pages/online/pages/man2/eventfd.2.html
  // Use the eventfd2 system call, as in glibc 2.9+
  // (requires kernel 2.6.30+)
  #define eventfd(initval, flags) syscall(__NR_eventfd2,(initval),(flags))
  
  #endif /* !(defined(__GLIBC__) && __GLIBC_PREREQ(2, 9)) */
  