From a18f34fe7787ddda9447ae4be28d68c2f57a7031 Mon Sep 17 00:00:00 2001
From: Andrew Gallatin <gallatin@FreeBSD.org>
Date: Mon, 31 Jul 2017 14:56:35 +0000
Subject: [PATCH] Don't request CTLTYPE_OPAQUE if we can't print them.

The intent is to skip expensive opaque sysctls like tcp_pcblist unless
they are explicitly requested. Sysctl nodes like this don't show up in
sysctl -a, but they do generate output that winds up being dropped,
unless the user specifically requested  binary/hex output or opaques.

This reduces the runtime of sysctl in many circumstances on a loaded
system.  It also reduces the likelihood that simply gathering
diagnostics on a sick machine (stuck lock, etc) via sysctl -a might
push it over the edge into a total lockup.

Reviewed by:	jtl
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D11461
---
 sbin/sysctl/sysctl.c | 44 ++++++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 18 deletions(-)

diff --git a/sbin/sysctl/sysctl.c b/sbin/sysctl/sysctl.c
index 97ab6ad2060..51ae95809a1 100644
--- a/sbin/sysctl/sysctl.c
+++ b/sbin/sysctl/sysctl.c
@@ -925,6 +925,32 @@ show_var(int *oid, int nlen)
 		printf("%s", buf);
 		return (0);
 	}
+
+	/* don't fetch opaques that we don't know how to print */
+	if (ctltype == CTLTYPE_OPAQUE) {
+		if (strcmp(fmt, "S,clockinfo") == 0)
+			func = S_clockinfo;
+		else if (strcmp(fmt, "S,timeval") == 0)
+			func = S_timeval;
+		else if (strcmp(fmt, "S,loadavg") == 0)
+			func = S_loadavg;
+		else if (strcmp(fmt, "S,vmtotal") == 0)
+			func = S_vmtotal;
+#ifdef __amd64__
+		else if (strcmp(fmt, "S,efi_map_header") == 0)
+			func = S_efi_map;
+#endif
+#if defined(__amd64__) || defined(__i386__)
+		else if (strcmp(fmt, "S,bios_smap_xattr") == 0)
+			func = S_bios_smap_xattr;
+#endif
+		else {
+			func = NULL;
+			if (!bflag && !oflag && !xflag)
+				return (1);
+		}
+	}
+
 	/* find an estimate of how much we need for this var */
 	if (Bflag)
 		j = Bflag;
@@ -1045,24 +1071,6 @@ show_var(int *oid, int nlen)
 
 	case CTLTYPE_OPAQUE:
 		i = 0;
-		if (strcmp(fmt, "S,clockinfo") == 0)
-			func = S_clockinfo;
-		else if (strcmp(fmt, "S,timeval") == 0)
-			func = S_timeval;
-		else if (strcmp(fmt, "S,loadavg") == 0)
-			func = S_loadavg;
-		else if (strcmp(fmt, "S,vmtotal") == 0)
-			func = S_vmtotal;
-#ifdef __amd64__
-		else if (strcmp(fmt, "S,efi_map_header") == 0)
-			func = S_efi_map;
-#endif
-#if defined(__amd64__) || defined(__i386__)
-		else if (strcmp(fmt, "S,bios_smap_xattr") == 0)
-			func = S_bios_smap_xattr;
-#endif
-		else
-			func = NULL;
 		if (func) {
 			if (!nflag)
 				printf("%s%s", name, sep);