/* One of many ways to emulate flock() on top of real (good) POSIX locks. */

#ident "$RH: flock.c,v 1.2 2000/08/23 17:07:00 nalin Exp $"

#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

int flock(int fd, int operation)
{
	int i, cmd;
	struct flock l = {0, 0, 0, 0, 0};
	if(operation & LOCK_NB) {
		cmd = F_SETLK;
	} else {
		cmd = F_SETLKW;
	}
	l.l_whence = SEEK_SET;
	switch(operation & (~LOCK_NB)) {
		case LOCK_EX:
			l.l_type = F_WRLCK;
			i = fcntl(fd, cmd, &l);
			if(i == -1) {
				if((errno == EAGAIN) || (errno == EACCES)) {
					errno = EWOULDBLOCK;
				}
			}
			break;
		case LOCK_SH:
			l.l_type = F_RDLCK;
			i = fcntl(fd, cmd, &l);
			if(i == -1) {
				if((errno == EAGAIN) || (errno == EACCES)) {
					errno = EWOULDBLOCK;
				}
			}
			break;
		case LOCK_UN:
			l.l_type = F_UNLCK;
			i = fcntl(fd, cmd, &l);
			if(i == -1) {
				if((errno == EAGAIN) || (errno == EACCES)) {
					errno = EWOULDBLOCK;
				}
			}
			break;
		default:
			i = -1;
			errno = EINVAL;
			break;
	}
	return i; 
}

#ifdef FLOCK_EMULATE_IS_MAIN
int main(int argc, char **argv)
{
	int fd = open(argv[1], O_WRONLY);
	flock(fd, LOCK_EX);
	return 0;
}
#endif