10216 xargs does not properly detect when -P is negative

Reviewed by: Patrick Mooney <patrick.mooney@joyent.com>
Reviewed by: Jason King <jason.brian.king@gmail.com>
Reviewed by: Andy Fiddaman <af@citrus-it.net>
Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Reviewed by: Peter Tribble <peter.tribble@gmail.com>
Approved by: Dan McDonald <danmcd@joyent.com>

usr/src/cmd/xargs/xargs.c

@@ -21,7 +21,7 @@
 /*
  * Copyright 2014 Garrett D'Amore <garrett@damore.org>
  * Copyright 2012 DEY Storage Systems, Inc.
- * Copyright (c) 2017, Joyent, Inc.
+ * Copyright (c) 2018, Joyent, Inc.
  *
  * Portions of this file developed by DEY Storage Systems, Inc. are licensed
  * under the terms of the Common Development and Distribution License (CDDL)
@@ -163,7 +163,7 @@ int
 main(int argc, char **argv)
 {
 	int	j;
-	unsigned long	l;
+	long	l;
 	struct inserts *psave;
 	int c;
 	int	initsize;
@@ -316,13 +316,19 @@ main(int argc, char **argv)
 
 		case 'P':	/* -P maxprocs: # of child processses	*/
 			errno = 0;
-			l = strtoul(optarg, &eptr, 10);
+			l = strtol(optarg, &eptr, 10);
 			if (*eptr != '\0' || errno != 0) {
 				ermsg(_("failed to parse maxprocs (-P): %s\n"),
 				    optarg);
 				break;
 			}
 
+			if (l < 0) {
+				ermsg(_("maximum number of processes (-P) "
+				    "cannot be negative\n"));
+				break;
+			}
+
 			/*
 			 * Come up with an upper bound that'll probably fit in
 			 * memory.

usr/src/man/man1/xargs.1

@@ -43,8 +43,9 @@
 .\" Copyright 1989 AT&T
 .\" Copyright (c) 1992, X/Open Company Limited.  All Rights Reserved.
 .\" Portions Copyright (c) 2007, Sun Microsystems, Inc. All Rights Reserved.
+.\" Copyright (c) 2018, Joyent, Inc.
 .\"
-.TH XARGS 1 "May 28, 2017"
+.TH XARGS 1 "September 13, 2018"
 .SH NAME
 xargs \- construct argument lists and invoke utility
 .SH SYNOPSIS
@@ -211,7 +212,9 @@ otherwise, that particular invocation of \fIutility\fR is skipped.
 .ad
 .RS 15n
 Invokes \fIutility\fR using at most \fImaxprocs\fR (a positive decimal integer)
-parallel child processes.
+parallel child processes. If \fImaxprocs\fR is zero, then the system
+will set a large upper bound to try and run as many processes as
+possible.
 .RE
 
 .sp