Ringbuffer using memory mapping

main.c

#include "ringbuffer.h"

#include <stdio.h>
#include <string.h>

int main(){
  char* buf = ringbuffer_create("Hello World ringbuffer");
  strcpy(buf+ring_buffer_size-6, "Hello ");
  strcpy(buf, "World!");
  printf("%s\n", buf+ring_buffer_size-6);
  ringbuffer_destroy(buf);
}

makefile

all:
	gcc -std=c11 -Wall -Wextra -Werror -pedantic main.c ringbuffer.c -o hello

ringbuffer.c

#define _GNU_SOURCE
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>

#include "ringbuffer.h"

intptr_t ring_buffer_size;
intptr_t ring_buffer_mask;

__attribute__((constructor(200),used))
static void init_ringbuffers(){
  ring_buffer_size = sysconf(_SC_PAGESIZE);
  ring_buffer_mask = ring_buffer_size - 1;
}

void* ringbuffer_create(const char* name){
  const int fd = memfd_create(name, MFD_CLOEXEC);
  if(fd == -1){
    perror("memfd_create");
    return 0;
  }
  if(ftruncate(fd, ring_buffer_size) == -1){
    perror("ftruncate");
    close(fd);
    return 0;
  }
  // Allocate any 2 free pages  |A|B|
  char*const mem = mmap(0, ring_buffer_size*2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
  if(mem == MAP_FAILED){
    perror("mmap 1");
    close(fd);
    return 0;
  }
  // Replace them with the same one  |C|B|
  if(mmap(mem, ring_buffer_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, 0) == MAP_FAILED){
    perror("mmap 2");
    munmap(mem, ring_buffer_size*2);
    close(fd);
    return 0;
  }
  // Replace them with the same one  |C|C|
  if(mmap(mem+ring_buffer_size, ring_buffer_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, 0) == MAP_FAILED){
    perror("mmap 3");
    munmap(mem, ring_buffer_size*2);
    close(fd);
    return 0;
  }
  close(fd);
  return mem;
}

void ringbuffer_destroy(void* ringbuffer){
  munmap(ringbuffer, ring_buffer_size*2);
}

ringbuffer.h

#ifndef KITSU_RINGBUFFER_H
#define KITSU_RINGBUFFER_H

#include <stdint.h>

extern intptr_t ring_buffer_size;
extern intptr_t ring_buffer_mask;

void* ringbuffer_create(const char* name);
void ringbuffer_destroy(void* ringbuffer);

#endif