[smb3] improve error message when mount options conflict with posix

POSIX extensions require SMB3.1.1 (so improve the error
message when vers=3.0, 2.1 or 2.0 is specified on mount)
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -2340,10 +2340,19 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 		if (ses->server->posix_ext_supported) {
 			tcon->posix_extensions = true;
 			pr_warn_once("SMB3.11 POSIX Extensions are experimental\n");
-		} else {
+		} else if ((ses->server->vals->protocol_id == SMB311_PROT_ID) ||
+		    (strcmp(ses->server->vals->version_string,
+		     SMB3ANY_VERSION_STRING) == 0) ||
+		    (strcmp(ses->server->vals->version_string,
+		     SMBDEFAULT_VERSION_STRING) == 0)) {
 			cifs_dbg(VFS, "Server does not support mounting with posix SMB3.11 extensions\n");
 			rc = -EOPNOTSUPP;
 			goto out_fail;
+		} else {
+			cifs_dbg(VFS, "Check vers= mount option. SMB3.11 "
+				"disabled but required for POSIX extensions\n");
+			rc = -EOPNOTSUPP;
+			goto out_fail;
 		}
 	}