commit e7d1bd38b1d1de6b1bec603eeff915ebb57f3c37
Author: zoulasc <christos@zoulas.com>
Date:   Thu Mar 10 17:50:34 2016 -0500

    - There is really no ti-rpc nfsv4, so don't send one; instead send a v3 for now.

diff --git a/amd/srvr_nfs.c b/amd/srvr_nfs.c
index b7c852c..1418a1a 100644
--- a/amd/srvr_nfs.c
+++ b/amd/srvr_nfs.c
@@ -140,6 +140,7 @@ create_ping_payload(u_long nfs_version)
 {
   XDR ping_xdr;
   struct rpc_msg ping_msg;
+  int rpc_version;
 
   /*
    * Non nfs mounts like /afs/glue.umd.edu have ended up here.
@@ -150,7 +151,17 @@ create_ping_payload(u_long nfs_version)
   } else
     plog(XLOG_INFO, "%s: nfs_version: %d", __func__, (int) nfs_version);
 
-  rpc_msg_init(&ping_msg, NFS_PROGRAM, nfs_version, NFSPROC_NULL);
+  /*
+   * There is really no ti-rpc version for NFSv4; most servers respond
+   * with "program unavailable", which is ok since we don't check the
+   * payload, we just care about the pings. Some servers though are
+   * antisocial (Isilon) and don't respond (which is their right to do).
+   * Eventually we should make a new mechanism to do server pings for
+   * NFSv4, but for now it is easiest to downgrade the RPC version to 3.
+   */
+  rpc_version = nfs_version == 4 ? 3 : nfs_version;
+
+  rpc_msg_init(&ping_msg, NFS_PROGRAM, rpc_version, NFSPROC_NULL);
 
   /*
    * Create an XDR endpoint
@@ -600,6 +611,7 @@ nfs_keepalive(voidp v)
   case ENETUNREACH:
   case EHOSTDOWN:
   case EHOSTUNREACH:
+    dlog("Failed to NFS ping to %s (%d)", fs->fs_host, error);
     np->np_ping = MAX_ALLOWED_PINGS;	/* immediately down */
     np->np_ttl = (time_t) 0;
     /*