github.com/afumu/libc@v0.0.6/musl/src/misc/lockf.c (about)

     1  #include <unistd.h>
     2  #include <fcntl.h>
     3  #include <errno.h>
     4  
     5  int lockf(int fd, int op, off_t size)
     6  {
     7  	struct flock l = {
     8  		.l_type = F_WRLCK,
     9  		.l_whence = SEEK_CUR,
    10  		.l_len = size,
    11  	};
    12  	switch (op) {
    13  	case F_TEST:
    14  		l.l_type = F_RDLCK;
    15  		if (fcntl(fd, F_GETLK, &l) < 0)
    16  			return -1;
    17  		if (l.l_type == F_UNLCK || l.l_pid == getpid())
    18  			return 0;
    19  		errno = EACCES;
    20  		return -1;
    21  	case F_ULOCK:
    22  		l.l_type = F_UNLCK;
    23  	case F_TLOCK:
    24  		return fcntl(fd, F_SETLK, &l);
    25  	case F_LOCK:
    26  		return fcntl(fd, F_SETLKW, &l);
    27  	}
    28  	errno = EINVAL;
    29  	return -1;
    30  }
    31  
    32  weak_alias(lockf, lockf64);