#include <sys/mman.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <limits.h>
#include <pthread.h>

char* __strchrnul(const char*, int);

char* __shm_mapname(const char* name, char* buf) {
  char* p;
  while (*name == '/')
    name++;
  if (*(p = __strchrnul(name, '/')) || p == name ||
      (p - name <= 2 && name[0] == '.' && p[-1] == '.')) {
    errno = EINVAL;
    return 0;
  }
  if (p - name > NAME_MAX) {
    errno = ENAMETOOLONG;
    return 0;
  }
  memcpy(buf, "/dev/shm/", 9);
  memcpy(buf + 9, name, p - name + 1);
  return buf;
}

int shm_open(const char* name, int flag, mode_t mode) {
  int cs;
  char buf[NAME_MAX + 10];
  if (!(name = __shm_mapname(name, buf)))
    return -1;
  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
  int fd = open(name, flag | O_NOFOLLOW | O_CLOEXEC | O_NONBLOCK, mode);
  pthread_setcancelstate(cs, 0);
  return fd;
}

int shm_unlink(const char* name) {
  char buf[NAME_MAX + 10];
  if (!(name = __shm_mapname(name, buf)))
    return -1;
  return unlink(name);
}