file-lock 0.0.17

File locking via POSIX advisory record locks
Documentation 
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#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

int c_lock(int fd, int should_block, int is_write_lock) {
  if (fd < 0) {
    return EBADF;
  }

  struct flock fl;

  fl.l_type   = is_write_lock ? F_WRLCK : F_RDLCK;
  fl.l_whence = SEEK_SET;
  fl.l_start  = 0;
  fl.l_len    = 0;

  if (fcntl(fd, should_block ? F_SETLKW : F_SETLK, &fl) == -1) {
    return errno;
  }

  return 0;
}

int c_unlock(int fd) {
  struct flock fl;

  if (fd < 0) {
    return EBADF;
  }

  fl.l_type   = F_UNLCK;
  fl.l_whence = SEEK_SET;
  fl.l_start  = 0;
  fl.l_len    = 0;

  if (fcntl(fd, F_SETLK, &fl) == -1) {
    return errno;
  }

  return 0;
}