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