rbd: update remaining header fields for v2

There are three fields that are not yet updated for format 2 rbd
image headers:  the version of the header object; the encryption
type; and the compression type.  There is no interface defined for
fetching the latter two, so just initialize them explicitly to 0 for
now.

Change rbd_dev_v2_snap_context() so the caller can be supplied the
version for the header object.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -2241,7 +2241,7 @@ static int rbd_dev_v2_features(struct rbd_device *rbd_dev)
 						&rbd_dev->header.features);
 }
 
-static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev)
+static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev, u64 *ver)
 {
 	size_t size;
 	int ret;
@@ -2269,7 +2269,7 @@ static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev)
 				"rbd", "get_snapcontext",
 				NULL, 0,
 				reply_buf, size,
-				CEPH_OSD_FLAG_READ, NULL);
+				CEPH_OSD_FLAG_READ, ver);
 	dout("%s: rbd_req_sync_exec returned %d\n", __func__, ret);
 	if (ret < 0)
 		goto out;
@@ -2906,6 +2906,7 @@ static int rbd_dev_v2_probe(struct rbd_device *rbd_dev)
 {
 	size_t size;
 	int ret;
+	u64 ver = 0;
 
 	/*
 	 * Image id was filled in by the caller.  Record the header
@@ -2936,11 +2937,18 @@ static int rbd_dev_v2_probe(struct rbd_device *rbd_dev)
 	if (ret < 0)
 		goto out_err;
 
-	/* Get the snapshot context */
+	/* crypto and compression type aren't (yet) supported for v2 images */
+
+	rbd_dev->header.crypt_type = 0;
+	rbd_dev->header.comp_type = 0;
 
-	ret = rbd_dev_v2_snap_context(rbd_dev);
+	/* Get the snapshot context, plus the header version */
+
+	ret = rbd_dev_v2_snap_context(rbd_dev, &ver);
 	if (ret)
 		goto out_err;
+	rbd_dev->header.obj_version = ver;
+
 	rbd_dev->image_format = 2;
 
 	dout("discovered version 2 image, header name is %s\n",