From 655307b88817f5e2445153c9bf0018e3eae5a034 Mon Sep 17 00:00:00 2001
From: rmacklem <rmacklem@FreeBSD.org>
Date: Sat, 19 Nov 2016 23:58:50 +0000
Subject: [PATCH] Modify umount so that it does not do an Unmount RPC for NFSv4
 mounts and uses TCP for the Unmount RPC if the mount is over TCP. Without
 this patch, umount does an Unmount RPC over UDP for all NFS mounts.

Suggested by:	cperciva
Reviewed by:	cperciva
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D8503
---
 sbin/umount/umount.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/sbin/umount/umount.c b/sbin/umount/umount.c
index 20b78043de14..e6ece316e82d 100644
--- a/sbin/umount/umount.c
+++ b/sbin/umount/umount.c
@@ -49,6 +49,7 @@ static const char rcsid[] =
 #include <netdb.h>
 #include <rpc/rpc.h>
 #include <rpcsvc/mount.h>
+#include <nfs/nfssvc.h>
 
 #include <ctype.h>
 #include <err.h>
@@ -323,6 +324,9 @@ umountfs(struct statfs *sfs)
 	CLIENT *clp;
 	char *nfsdirname, *orignfsdirname;
 	char *hostp, *delimp;
+	char buf[1024];
+	struct nfscl_dumpmntopts dumpmntopts;
+	const char *proto_ptr = NULL;
 
 	ai = NULL;
 	do_rpc = 0;
@@ -361,8 +365,24 @@ umountfs(struct statfs *sfs)
 		 * mount from mntfromname that is still mounted.
 		 */
 		if (getmntentry(sfs->f_mntfromname, NULL, NULL,
-		    CHECKUNIQUE) != NULL)
+		    CHECKUNIQUE) != NULL) {
 			do_rpc = 1;
+			proto_ptr = "udp";
+			/*
+			 * Try and find out whether this NFS mount is NFSv4 and
+			 * what protocol is being used. If this fails, the
+			 * default is NFSv2,3 and use UDP for the Unmount RPC.
+			 */
+			dumpmntopts.ndmnt_fname = sfs->f_mntonname;
+			dumpmntopts.ndmnt_buf = buf;
+			dumpmntopts.ndmnt_blen = sizeof(buf);
+			if (nfssvc(NFSSVC_DUMPMNTOPTS, &dumpmntopts) >= 0) {
+				if (strstr(buf, "nfsv4,") != NULL)
+					do_rpc = 0;
+				else if (strstr(buf, ",tcp,") != NULL)
+					proto_ptr = "tcp";
+			}
+		}
 	}
 
 	if (!namematch(ai)) {
@@ -400,7 +420,7 @@ umountfs(struct statfs *sfs)
 	 * has been unmounted.
 	 */
 	if (ai != NULL && !(fflag & MNT_FORCE) && do_rpc) {
-		clp = clnt_create(hostp, MOUNTPROG, MOUNTVERS3, "udp");
+		clp = clnt_create(hostp, MOUNTPROG, MOUNTVERS3, proto_ptr);
 		if (clp  == NULL) {
 			warnx("%s: %s", hostp,
 			    clnt_spcreateerror("MOUNTPROG"));