rbd: don't establish watch for read-only mappings

With exclusive lock out of the way, watch is the only thing left that
prevents a read-only mapping from being used with read-only OSD caps.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>

drivers/block/rbd.c

@@ -6961,6 +6961,24 @@ static int rbd_dev_header_name(struct rbd_device *rbd_dev)
 	return ret;
 }
 
+static void rbd_print_dne(struct rbd_device *rbd_dev, bool is_snap)
+{
+	if (!is_snap) {
+		pr_info("image %s/%s%s%s does not exist\n",
+			rbd_dev->spec->pool_name,
+			rbd_dev->spec->pool_ns ?: "",
+			rbd_dev->spec->pool_ns ? "/" : "",
+			rbd_dev->spec->image_name);
+	} else {
+		pr_info("snap %s/%s%s%s@%s does not exist\n",
+			rbd_dev->spec->pool_name,
+			rbd_dev->spec->pool_ns ?: "",
+			rbd_dev->spec->pool_ns ? "/" : "",
+			rbd_dev->spec->image_name,
+			rbd_dev->spec->snap_name);
+	}
+}
+
 static void rbd_dev_image_release(struct rbd_device *rbd_dev)
 {
 	rbd_dev_unprobe(rbd_dev);
@@ -6979,6 +6997,7 @@ static void rbd_dev_image_release(struct rbd_device *rbd_dev)
  */
 static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 {
+	bool need_watch = !rbd_is_ro(rbd_dev);
 	int ret;
 
 	/*
@@ -6995,22 +7014,21 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 	if (ret)
 		goto err_out_format;
 
-	if (!depth) {
+	if (need_watch) {
 		ret = rbd_register_watch(rbd_dev);
 		if (ret) {
 			if (ret == -ENOENT)
-				pr_info("image %s/%s%s%s does not exist\n",
-					rbd_dev->spec->pool_name,
-					rbd_dev->spec->pool_ns ?: "",
-					rbd_dev->spec->pool_ns ? "/" : "",
-					rbd_dev->spec->image_name);
+				rbd_print_dne(rbd_dev, false);
 			goto err_out_format;
 		}
 	}
 
 	ret = rbd_dev_header_info(rbd_dev);
-	if (ret)
+	if (ret) {
+		if (ret == -ENOENT && !need_watch)
+			rbd_print_dne(rbd_dev, false);
 		goto err_out_watch;
+	}
 
 	/*
 	 * If this image is the one being mapped, we have pool name and
@@ -7024,12 +7042,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 		ret = rbd_spec_fill_names(rbd_dev);
 	if (ret) {
 		if (ret == -ENOENT)
-			pr_info("snap %s/%s%s%s@%s does not exist\n",
-				rbd_dev->spec->pool_name,
-				rbd_dev->spec->pool_ns ?: "",
-				rbd_dev->spec->pool_ns ? "/" : "",
-				rbd_dev->spec->image_name,
-				rbd_dev->spec->snap_name);
+			rbd_print_dne(rbd_dev, true);
 		goto err_out_probe;
 	}
 
@@ -7061,7 +7074,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 err_out_probe:
 	rbd_dev_unprobe(rbd_dev);
 err_out_watch:
-	if (!depth)
+	if (need_watch)
 		rbd_unregister_watch(rbd_dev);
 err_out_format:
 	rbd_dev->image_format = 0;