Index: nfs_syscalls.c
===================================================================
RCS file: /cvsroot/src/sys/nfs/nfs_syscalls.c,v
retrieving revision 1.158
diff -p -u -r1.158 nfs_syscalls.c
--- nfs_syscalls.c	12 Feb 2017 18:24:31 -0000	1.158
+++ nfs_syscalls.c	24 Jan 2018 10:41:18 -0000
@@ -488,6 +488,7 @@ nfssvc_nfsd(struct nfssvc_copy_ops *ops,
 	int error = 0, cacherep, siz, sotype, writes_todo;
 	struct proc *p = l->l_proc;
 	bool doreinit;
+	size_t nfsd_idx;
 
 #ifndef nolint
 	cacherep = RC_DOIT;
@@ -505,8 +506,33 @@ nfssvc_nfsd(struct nfssvc_copy_ops *ops,
 		}
 		TAILQ_INSERT_TAIL(&nfsd_head, nfsd, nfsd_chain);
 		nfs_numnfsd++;
+		nfsd_idx = nfs_numnfsd;
 		mutex_exit(&nfsd_lock);
+	} else {
+		/*
+		 * idx == 0 => NULL above
+		 * idx == 1 -> first entry
+		 */
+		size_t count = 0;
+		struct nfsd *entry;
+
+		nfsd_idx = (uintptr)nfsd;
+
+		mutex_enter(&nfsd_lock);
+		if (idx > nfs_numnfsd) {
+			mutex_exit(&nfsd_lock);
+			return EINVAL;
+		}
+		TAILQ_FOREACH(&nfsd_head, entry, nfsd_chain) {
+			if (++count == idx)
+				break;
+		}
+		KASSERT(count <= nfs_numnfsd);
+		mutex_exit(&nfsd_lock);
+
+		nsd->nsd_nfsd = nfsd = entry;
 	}
+
 	/*
 	 * Loop getting rpc requests until SIGKILL.
 	 */
@@ -620,6 +646,10 @@ nfssvc_nfsd(struct nfssvc_copy_ops *ops,
 				    struct sockaddr_in *)->sin_addr.s_addr;
 				nsd->nsd_authlen = nfsd->nfsd_authlen;
 				nsd->nsd_verflen = nfsd->nfsd_verflen;
+				/*
+				 * Put the nfsd index in place for the copyout.
+				 */
+				nsd->nsd_nfsd = (uintptr_t)nfsd_idx;
 				if (!copyout(nfsd->nfsd_authstr,
 				    nsd->nsd_authstr, nfsd->nfsd_authlen) &&
 				    !copyout(nfsd->nfsd_verfstr,
@@ -627,6 +657,7 @@ nfssvc_nfsd(struct nfssvc_copy_ops *ops,
 				    !ops->nsd_out(argp, nsd)) {
 					return (ENEEDAUTH);
 				}
+				nsd->nsd_nfsd = nfsd;
 				cacherep = RC_DROPIT;
 			} else
 				cacherep = nfsrv_getcache(nd, slp, &mreq);