rbd: add read_only rbd map option

Add the ability to map an rbd image read-only, by specifying either
"read_only" or "ro" as an option on the rbd "command line."  Also
allow the inverse to be explicitly specified using "read_write" or
"rw".
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>

drivers/block/rbd.c

@@ -70,6 +70,7 @@
 #define MAX_INT_FORMAT_WIDTH	((5 * sizeof (int)) / 2 + 1)
 
 #define RBD_NOTIFY_TIMEOUT_DEFAULT	10
+#define RBD_READ_ONLY_DEFAULT		false
 
 /*
  * block device image metadata (in-memory version)
@@ -91,6 +92,7 @@ struct rbd_image_header {
 
 struct rbd_options {
 	int	notify_timeout;
+	bool	read_only;
 };
 
 /*
@@ -176,7 +178,7 @@ struct rbd_device {
 	u64                     snap_id;	/* current snapshot id */
 	/* whether the snap_id this device reads from still exists */
 	bool                    snap_exists;
-	int                     read_only;
+	bool			read_only;
 
 	struct list_head	node;
 
@@ -351,12 +353,21 @@ enum {
 	/* int args above */
 	Opt_last_string,
 	/* string args above */
+	Opt_read_only,
+	Opt_read_write,
+	/* Boolean args above */
+	Opt_last_bool,
 };
 
 static match_table_t rbd_opts_tokens = {
 	{Opt_notify_timeout, "notify_timeout=%d"},
 	/* int args above */
 	/* string args above */
+	{Opt_read_only, "read_only"},
+	{Opt_read_only, "ro"},		/* Alternate spelling */
+	{Opt_read_write, "read_write"},
+	{Opt_read_write, "rw"},		/* Alternate spelling */
+	/* Boolean args above */
 	{-1, NULL}
 };
 
@@ -381,6 +392,8 @@ static int parse_rbd_opts_token(char *c, void *private)
 	} else if (token > Opt_last_int && token < Opt_last_string) {
 		dout("got string token %d val %s\n", token,
 		     argstr[0].from);
+	} else if (token > Opt_last_string && token < Opt_last_bool) {
+		dout("got Boolean token %d\n", token);
 	} else {
 		dout("got token %d\n", token);
 	}
@@ -389,6 +402,12 @@ static int parse_rbd_opts_token(char *c, void *private)
 	case Opt_notify_timeout:
 		rbd_opts->notify_timeout = intval;
 		break;
+	case Opt_read_only:
+		rbd_opts->read_only = true;
+		break;
+	case Opt_read_write:
+		rbd_opts->read_only = false;
+		break;
 	default:
 		BUG_ON(token);
 	}
@@ -407,6 +426,7 @@ static int rbd_get_client(struct rbd_device *rbd_dev, const char *mon_addr,
 	struct rbd_client *rbdc;
 
 	rbd_opts->notify_timeout = RBD_NOTIFY_TIMEOUT_DEFAULT;
+	rbd_opts->read_only = RBD_READ_ONLY_DEFAULT;
 
 	ceph_opts = ceph_parse_options(options, mon_addr,
 					mon_addr + mon_addr_len,
@@ -620,7 +640,7 @@ static int rbd_header_set_snap(struct rbd_device *rbd_dev, u64 *size)
 		    sizeof (RBD_SNAP_HEAD_NAME))) {
 		rbd_dev->snap_id = CEPH_NOSNAP;
 		rbd_dev->snap_exists = false;
-		rbd_dev->read_only = 0;
+		rbd_dev->read_only = rbd_dev->rbd_opts.read_only;
 		if (size)
 			*size = rbd_dev->header.image_size;
 	} else {
@@ -632,7 +652,7 @@ static int rbd_header_set_snap(struct rbd_device *rbd_dev, u64 *size)
 			goto done;
 		rbd_dev->snap_id = snap_id;
 		rbd_dev->snap_exists = true;
-		rbd_dev->read_only = 1;
+		rbd_dev->read_only = true;	/* No choice for snapshots */
 	}
 
 	ret = 0;