#include <u.h>#include <libc.h> /* MAXHOSTNAMELEN is in sys/param.h */#define MAXHOSTNAMELEN	64 char lockstring[MAXHOSTNAMELEN+8]; voidmain(int argc, char *argv[]) {	char *lockfile;	int fd, ppid, ssize;	struct Dir *statbuf; 	if (argc != 4) {		fprint(2, "usage: LOCK lockfile hostname ppid\n");		exits("lock failed on usage");	}	lockfile = argv[1];	if ((fd=create(lockfile, ORDWR, DMEXCL|0666)) < 0) {		exits("lock failed on create");	}	ppid = atoi(argv[3]);	ssize = sprint(lockstring, "%s %s\n", argv[2], argv[3]);	if (write(fd, lockstring, ssize) != ssize) {		fprint(2, "LOCK:write(): %r\n");		exits("lock failed on write to lockfile");	} 	switch(fork()) {	default:		exits("");	case 0:		break;	case -1:		fprint(2, "LOCK:fork(): %r\n");		exits("lock failed on fork");	} 	for(;;) {		statbuf = dirfstat(fd);		if(statbuf == nil)			break;		if (statbuf->length == 0){			free(statbuf);			break;		}		free(statbuf);		if (write(fd, "", 0) < 0)			break;		sleep(3000);	} 	close(fd);	postnote(PNGROUP, ppid, "kill");	exits("");}