When writing to a tty would block, wall(1) attempts to fork a child process which will block for up to 5 minutes trying to deliver the message. This doesn't actually work because an incorrect usage of fnctl leaves non-blocking mode on. fcntl(fd, O_NONBLOCK, &off)? Not even close! fcntl is not setsockopt... FreeBSD fixed this bug 7 years ago. NetBSD picked up the fix 4 years ago. If we go next we can still beat OpenBSD. (But for them it actually worked before the fix, at least part of the time, because their O_NONBLOCK==F_SETFL). I've also enjoyed reading the parts of ttymsg.c that have been rewritten more clumsily than the BSD original because "Linux doesn't have snprintf". The FreeBSD commit diff: http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/wall/ttymsg.c.diff?r1=1.4;r2=1.5 applies, after removing the hunk containing the rcsid, to util-linux-ng/login-utils/ttymsg.c; here's a copy for your convenience: --- src/usr.bin/wall/ttymsg.c 1999/08/28 01:07:31 1.4 +++ src/usr.bin/wall/ttymsg.c 2000/06/09 19:38:28 1.5 @@ -120,7 +120,7 @@ ttymsg(iov, iovcnt, line, tmout) continue; } if (errno == EWOULDBLOCK) { - int cpid, off = 0; + int cpid; if (forked) { (void) close(fd); @@ -143,7 +143,7 @@ ttymsg(iov, iovcnt, line, tmout) (void) signal(SIGTERM, SIG_DFL); /* XXX */ (void) sigsetmask(0); (void) alarm((u_int)tmout); - (void) fcntl(fd, O_NONBLOCK, &off); + (void) fcntl(fd, F_SETFL, 0); /* clear O_NONBLOCK */ continue; } /* - To unsubscribe from this list: send the line "unsubscribe util-linux-ng" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
