[PATCH] mount.nfs: improve version negotiation when vers=4 is specified.

[NeilBrown <neilb@suse.com>]

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If NFSv4, in general, is requested (possibly by -t nfs4 or -o v4 or -o
vers=4 etc) then we need to negotiate the best minor version, but must
not fallback to v3 or v2.  Internally, this state is reflected in v_mode
== V_GENERAL.  This means that a major version was given, but the minor
version still needs to be negotiated.

This is handled by nfs_autonegotiate(). It currently does the right
thing for EPROTONOSUPPORT and EINVAL, but not for other errors.
In particular, ENOENT can cause problems as  NFSv4 might export
a different namespace than NFSv3 (e.g. by using fsid=0 in the Linux
NFS server).  Currently a mount request for NFSv4 and a particular path
can result if an NFSv3 mount if the path is available with v3 but
not v4.

So move the special handling of V_GENERAL into the common fall_back:
code, and add extra checking in the ENCONNREFUSED case, which does
not use fall_back:.

Tested-by: Steve Dickson <steved@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.com>
---
 utils/mount/stropts.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
index 0fbb37569ef9..b20ad1c8bf55 100644
--- a/utils/mount/stropts.c
+++ b/utils/mount/stropts.c
@@ -838,9 +838,6 @@ check_result:
 	case EINVAL:
 		/* A less clear indication that our client
 		 * does not support NFSv4 minor version. */
-		if (mi->version.v_mode == V_GENERAL &&
-			mi->version.minor == 0)
-				return result;
 		if (mi->version.v_mode != V_SPECIFIC) {
 			if (mi->version.minor > 0) {
 				mi->version.minor--;
@@ -862,6 +859,9 @@ check_result:
 		/* 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. */
+		if (mi->version.v_mode == V_GENERAL)
+			/* Mustn't try v2,v3 */
+			return result;
 		result = nfs_try_mount_v3v2(mi, TRUE);
 		if (result == 0 && errno == EAGAIN) {
 			/* v4 server seems to be registered now. */
@@ -878,6 +878,9 @@ check_result:
 	}
 
 fall_back:
+	if (mi->version.v_mode == V_GENERAL)
+		/* v2,3 fallback not allowed */
+		return result;
 	return nfs_try_mount_v3v2(mi, FALSE);
 }
 
-- 
2.12.2


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