Index: kern_descrip_test.c
===================================================================
--- kern_descrip_test.c	(revision 262781)
+++ kern_descrip_test.c	(working copy)
@@ -29,14 +29,22 @@ __FBSDID("$FreeBSD$");
 
 #include <errno.h>
 #include <fcntl.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <strings.h>
 #include <sys/limits.h>
 #include <sys/stat.h>
+#include <sys/sysctl.h>
 #include <unistd.h>
 #include <atf-c.h>
 
+static int done;
+static int oldmaxfiles;
+
+#define PARALLEL 4 
+#define RENDEZVOUS "rendezvous"
+
 ATF_TC_WITHOUT_HEAD(dup2__simple);
 ATF_TC_BODY(dup2__simple, tc)
 {
@@ -68,11 +76,115 @@ ATF_TC_BODY(dup2__ebadf_when_2nd_arg_out_of_range,
 	ATF_CHECK_EQ(EBADF, errno);
 }
 
+static void
+handler(int s __unused)
+{
+	done++;
+}
+
+static void
+openfiles2(size_t n, int ignore)
+{
+	int i, r;
+
+	errno = 0;
+	for (i = 0; i < (int)n; i++) {
+		if (ignore == 1) {
+			if ((r = open("/etc/passwd", O_RDONLY)) == -1)
+				break;
+		} else
+			ATF_REQUIRE((r = open("/etc/passwd", O_RDONLY)) != -1);
+	}
+	kill(getppid(), SIGUSR1);
+
+	if (r != -1) {
+		for (;;) {
+			if (access(RENDEZVOUS, R_OK) != 0)
+				break;
+			usleep(1000);
+		}
+	}
+	_exit(0);
+}
+
+static void
+openfiles(size_t n, int ignore)
+{
+	int i, fd;
+
+	signal(SIGUSR1, handler);
+	ATF_REQUIRE((fd = open(RENDEZVOUS, O_CREAT, 0644)) != -1);
+	close(fd);
+	done = 0;
+	for (i = 0; i < PARALLEL; i++)
+		if (fork() == 0)
+			openfiles2(n / PARALLEL, ignore);
+	while (done != PARALLEL)
+		usleep(1000);
+	unlink(RENDEZVOUS);
+	usleep(40000);
+}
+
+static void
+cleanup(void)
+{
+	size_t oldlen;
+
+	if (oldmaxfiles > 0) {
+		oldlen = sizeof(oldmaxfiles);
+		if (sysctlbyname("kern.maxfiles", NULL, 0, &oldmaxfiles,
+		    oldlen) == -1)
+			atf_tc_fail("getsysctlbyname(%s): %s", "kern.maxfiles",
+			    strerror(errno));
+	}
+	unlink(RENDEZVOUS);
+}
+
+ATF_TC(kern.maxfiles__increase);
+ATF_TC_HEAD(kern.maxfiles__increase, tc)
+{
+        atf_tc_set_md_var(tc, "require.user", "root");
+	atf_tc_set_md_var(tc, "descr",
+	    "Check kern.maxfiles expansion");
+}
+
+ATF_TC_BODY(kern.maxfiles__increase, tc)
+{
+	int maxfiles;
+	size_t oldlen;
+
+	oldlen = sizeof(maxfiles);
+	if (sysctlbyname("kern.maxfiles", &maxfiles, &oldlen, NULL, 0) == -1)
+		atf_tc_fail("getsysctlbyname(%s): %s", "kern.maxfiles",
+		    strerror(errno));
+#ifdef TEST
+	/* The next line will cause:
+	   kern.maxfiles limit exceeded by uid 0, please see tuning(7).
+	 */
+	openfiles(maxfiles, 1);
+#endif
+
+	if (atexit(cleanup) == -1)
+		atf_tc_fail("atexit(): %s", strerror(errno));
+	oldmaxfiles = maxfiles;
+	maxfiles += 1000;
+	if (sysctlbyname("kern.maxfiles", NULL, 0, &maxfiles, oldlen) == -1)
+		atf_tc_fail("getsysctlbyname(%s): %s", "kern.maxfiles",
+		    strerror(errno));
+	openfiles(oldmaxfiles + 50, 0);
+	if (sysctlbyname("kern.maxfiles", NULL, 0, &oldmaxfiles,
+	    oldlen) == -1)
+		atf_tc_fail("getsysctlbyname(%s): %s", "kern.maxfiles",
+		    strerror(errno));
+	oldmaxfiles = 0;
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
         ATF_TP_ADD_TC(tp, dup2__simple);
         ATF_TP_ADD_TC(tp, dup2__ebadf_when_2nd_arg_out_of_range);
+        ATF_TP_ADD_TC(tp, kern.maxfiles__increase);
 
         return atf_no_error();
 }