Add resilienthandles mount parm

Since many servers (Windows clients, and non-clustered servers) do not
support persistent handles but do support resilient handles, allow
the user to specify a mount option "resilienthandles" in order
to get more reliable connections and less chance of data loss
(at least when SMB2.1 or later).  Default resilient handle
timeout (120 seconds to recent Windows server) is used.

Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <steve.french@primarydata.com>

fs/cifs/connect.c

@@ -88,6 +88,7 @@ enum {
 	Opt_fsc, Opt_mfsymlinks,
 	Opt_multiuser, Opt_sloppy, Opt_nosharesock,
 	Opt_persistent, Opt_nopersistent,
+	Opt_resilient, Opt_noresilient,
 
 	/* Mount options which take numeric value */
 	Opt_backupuid, Opt_backupgid, Opt_uid,
@@ -172,6 +173,8 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_nosharesock, "nosharesock" },
 	{ Opt_persistent, "persistenthandles"},
 	{ Opt_nopersistent, "nopersistenthandles"},
+	{ Opt_resilient, "resilienthandles"},
+	{ Opt_noresilient, "noresilienthandles"},
 
 	{ Opt_backupuid, "backupuid=%s" },
 	{ Opt_backupgid, "backupgid=%s" },
@@ -1510,12 +1513,23 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 			break;
 		case Opt_persistent:
 			vol->persistent = true;
-			if (vol->nopersistent) {
+			if ((vol->nopersistent) || (vol->resilient)) {
 				cifs_dbg(VFS,
 				  "persistenthandles mount options conflict\n");
 				goto cifs_parse_mount_err;
 			}
 			break;
+		case Opt_resilient:
+			vol->resilient = true;
+			if (vol->persistent) {
+				cifs_dbg(VFS,
+				  "persistenthandles mount options conflict\n");
+				goto cifs_parse_mount_err;
+			}
+			break;
+		case Opt_noresilient:
+			vol->resilient = false; /* already the default */
+			break;
 
 		/* Numeric Values */
 		case Opt_backupuid:
@@ -2681,6 +2695,7 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 			     "SMB3 or later required for persistent handles\n");
 			rc = -EOPNOTSUPP;
 			goto out_fail;
+#ifdef CONFIG_CIFS_SMB2
 		} else if (ses->server->capabilities &
 			   SMB2_GLOBAL_CAP_PERSISTENT_HANDLES)
 			tcon->use_persistent = true;
@@ -2689,12 +2704,23 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 				"Persistent handles not supported on share\n");
 			rc = -EOPNOTSUPP;
 			goto out_fail;
+#endif /* CONFIG_CIFS_SMB2 */
 		}
+#ifdef CONFIG_CIFS_SMB2
 	} else if ((tcon->capabilities & SMB2_SHARE_CAP_CONTINUOUS_AVAILABILITY)
 	     && (ses->server->capabilities & SMB2_GLOBAL_CAP_PERSISTENT_HANDLES)
 	     && (volume_info->nopersistent == false)) {
 		cifs_dbg(FYI, "enabling persistent handles\n");
 		tcon->use_persistent = true;
+#endif /* CONFIG_CIFS_SMB2 */
+	} else if (volume_info->resilient) {
+		if (ses->server->vals->protocol_id == 0) {
+			cifs_dbg(VFS,
+			     "SMB2.1 or later required for resilient handles\n");
+			rc = -EOPNOTSUPP;
+			goto out_fail;
+		}
+		tcon->use_resilient = true;
 	}
 
 	/*
@@ -3545,12 +3571,15 @@ try_mount_again:
 		goto mount_fail_check;
 	}
 
+#ifdef CONFIG_CIFS_SMB2
 	if ((volume_info->persistent == true) && ((ses->server->capabilities &
 		SMB2_GLOBAL_CAP_PERSISTENT_HANDLES) == 0)) {
 		cifs_dbg(VFS, "persistent handles not supported by server\n");
 		rc = -EOPNOTSUPP;
 		goto mount_fail_check;
 	}
+#endif /* CONFIG_CIFS_SMB2*/
+
 	/* search for existing tcon to this server share */
 	tcon = cifs_get_tcon(ses, volume_info);
 	if (IS_ERR(tcon)) {