file-lock 0.0.12

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

struct result {
  int fd;
  int error;
};

#define _LOCK(lock_type, cmd)                   \
struct result lock_type(const char* pathname) { \
  struct result my_result;                      \
                                                \
  int fd = open(                                \
    pathname,                                   \
    (O_WRONLY | O_CREAT),                       \
    (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)     \
  );                                            \
                                                \
  if (fd == -1) {                               \
    my_result.fd    = -1;                       \
    my_result.error = errno;                    \
    return my_result;                           \
  }                                             \
                                                \
  struct flock fl;                              \
  fl.l_type   = F_WRLCK;                        \
  fl.l_whence = SEEK_SET;                       \
  fl.l_start  = 0;                              \
  fl.l_len    = 0;                              \
                                                \
  if (fcntl(fd, cmd, &fl) == -1) {              \
    my_result.fd    = -1;                       \
    my_result.error = errno;                    \
    return my_result;                           \
  }                                             \
                                                \
  my_result.fd    = fd;                         \
  my_result.error = 0;                          \
  return my_result;                             \
}

_LOCK(c_lock,      F_SETLK);
_LOCK(c_lock_wait, F_SETLKW);

struct result c_unlock(int fd) {
  struct result my_result;

  if (close(fd) == -1) {
    my_result.fd    = -1;
    my_result.error = errno;
    return my_result;
  }

  my_result.fd    = 0;
  my_result.error = 0;
  return my_result;
}