missing file descriptors

[utzoo!decvax!duke!unc!smb]

If a process is interrupted while trying to open a file, the
file descriptor tentatively assigned is lost -- unless you
know what it should be and close it!  The following program
demonstrates this.  (This was run under 4bsd, but I believe
the same problem is present in V6 and V7.)  Note that this
implies that a device driver close routine can be called
for a file that was never successfully opened -- which might
cause problems for weird devices/drivers.



#include <signal.h>
#include <errno.h>

#define	CLOSEDTTY	"/dev/ttyia"	/* should wait forever */
#define	FLIM		25	/* maximum open files */

extern errno;

main()
{
	int i, j;
	int f;
	int tick();
	char lbuf[100];

	signal(SIGALRM, tick);

	for (j = 0; j<2; j++) {
		for (i = 3; i < FLIM; i++)
			close(i);
		for (i=0; i<FLIM; i++) {
			alarm(2);
			f = open(CLOSEDTTY, 1);
			if (f >= 0) {
				printf("Huh -- f=%d\n", f);
			}
			else if (errno != EINTR) {
				alarm(0);
				sprintf(lbuf, "i=%d j=%d", i, j);
				perror(lbuf);
				break;
			}
			if (j) {
				if (close(3) < 0) perror("close");
			}
		}
		printf("end inner loop, i=%d\n", i);
	}
}

tick()
{
	signal(SIGALRM, tick);
	return;
}