[PATCH - v3] mount.nfs: Fix fallback from tcp to udp

Protocol negotiation in mount.nfs does not correctly negotiate with a
server which only supports NFSv3 and UDP.

When mount.nfs attempts an NFSv4 mount and fails with ECONNREFUSED
it does not fall back to NFSv3, as this is not recognised as a
"does not support NFSv4" error.
However ECONNREFUSED is a clear indication that the server doesn't
support TCP, and ipso facto does not support NFSv4.
So ECONNREFUSED should trigger a fallback from v4 to v2/3.

However ECONNREFUSED may simply indicate that NFSv4 isn't supported
*yet*.  i.e. the server is still booting and isn't responding to NFS
requests yet.  So if we subsequently find that NFSv3 is supported, we
need to check with the server to confirm that NFSv4 really isn't
supported.

If server reports that v4 is not supported after reporting that v3
is, we can safely use v4.  If it reports that v4 is supported, we need
to retry v4.

Signed-off-by: Steve Dickson <steved@redhat.com>
Reported-by: Carsten Ziepke <kieltux@gmail.com>

1 files changed, 23 insertions, 9 deletions

diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
index a642394..2d72d5b 100644
--- a/utils/mount/stropts.c
+++ b/utils/mount/stropts.c
@@ -484,7 +484,7 @@ static int nfs_construct_new_options(struct mount_options *options,
  * FALSE is returned if some failure occurred.
  */
 static int
-nfs_rewrite_pmap_mount_options(struct mount_options *options)
+nfs_rewrite_pmap_mount_options(struct mount_options *options, int checkv4)
 {
 	union nfs_sockaddr nfs_address;
 	struct sockaddr *nfs_saddr = &nfs_address.sa;
@@ -534,7 +534,7 @@ nfs_rewrite_pmap_mount_options(struct mount_options *options)
 	 * negotiate.  Bail now if we can't contact it.
 	 */
 	if (!nfs_probe_bothports(mnt_saddr, mnt_salen, &mnt_pmap,
-				 nfs_saddr, nfs_salen, &nfs_pmap)) {
+				 nfs_saddr, nfs_salen, &nfs_pmap, checkv4)) {
 		errno = ESPIPE;
 		if (rpc_createerr.cf_stat == RPC_PROGNOTREGISTERED)
 			errno = EOPNOTSUPP;
@@ -595,7 +595,8 @@ static int nfs_sys_mount(struct nfsmount_info *mi, struct mount_options *opts)
 }
 
 static int nfs_do_mount_v3v2(struct nfsmount_info *mi,
-		struct sockaddr *sap, socklen_t salen)
+			     struct sockaddr *sap, socklen_t salen,
+			     int checkv4)
 {
 	struct mount_options *options = po_dup(mi->options);
 	int result = 0;
@@ -637,7 +638,7 @@ static int nfs_do_mount_v3v2(struct nfsmount_info *mi,
 		printf(_("%s: trying text-based options '%s'\n"),
 			progname, *mi->extra_opts);
 
-	if (!nfs_rewrite_pmap_mount_options(options))
+	if (!nfs_rewrite_pmap_mount_options(options, checkv4))
 		goto out_fail;
 
 	result = nfs_sys_mount(mi, options);
@@ -653,13 +654,13 @@ out_fail:
  * Returns TRUE if successful, otherwise FALSE.
  * "errno" is set to reflect the individual error.
  */
-static int nfs_try_mount_v3v2(struct nfsmount_info *mi)
+static int nfs_try_mount_v3v2(struct nfsmount_info *mi, int checkv4)
 {
 	struct addrinfo *ai;
 	int ret = 0;
 
 	for (ai = mi->address; ai != NULL; ai = ai->ai_next) {
-		ret = nfs_do_mount_v3v2(mi, ai->ai_addr, ai->ai_addrlen);
+		ret = nfs_do_mount_v3v2(mi, ai->ai_addr, ai->ai_addrlen, checkv4);
 		if (ret != 0)
 			return ret;
 
@@ -793,7 +794,8 @@ static int nfs_autonegotiate(struct nfsmount_info *mi)
 	result = nfs_try_mount_v4(mi);
 	if (result)
 		return result;
-		
+
+check_errno:
 	switch (errno) {
 	case EPROTONOSUPPORT:
 		/* A clear indication that the server or our
@@ -807,12 +809,24 @@ static int nfs_autonegotiate(struct nfsmount_info *mi)
 		/* Linux servers prior to 2.6.25 may return
 		 * EPERM when NFS version 4 is not supported. */
 		goto fall_back;
+	case ECONNREFUSED:
+		/* UDP-Only servers won't support v4, but maybe it
+		 * just isn't ready yet.  So try v3, but double-check
+		 * with rpcbind for v4. */
+		result = nfs_try_mount_v3v2(mi, TRUE);
+		if (result == 0 && errno == EAGAIN) {
+			/* v4 server seems to be registered now. */
+			result = nfs_try_mount_v4(mi);
+			if (result == 0 && errno != ECONNREFUSED)
+				goto check_errno;
+		}
+		return result;
 	default:
 		return result;
 	}
 
 fall_back:
-	return nfs_try_mount_v3v2(mi);
+	return nfs_try_mount_v3v2(mi, FALSE);
 }
 
 /*
@@ -831,7 +845,7 @@ static int nfs_try_mount(struct nfsmount_info *mi)
 		break;
 	case 2:
 	case 3:
-		result = nfs_try_mount_v3v2(mi);
+		result = nfs_try_mount_v3v2(mi, FALSE);
 		break;
 	case 4:
 		result = nfs_try_mount_v4(mi);