rbd: record image-relative offset in object requests

For an image object request we will need to know what offset within
the rbd image the request covers.  Record that when the object
request gets created.

Update the I/O error warnings so they use this so what's reported
is more informative.

Rename a local variable to fit the convention used everywhere else.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -176,6 +176,7 @@ struct rbd_obj_request {
 	u64			length;		/* bytes from offset */
 
 	struct rbd_img_request	*img_request;
+	u64			img_offset;	/* image relative offset */
 	struct list_head	links;		/* img_request->obj_requests */
 	u32			which;		/* posn image request list */
 
@@ -1576,8 +1577,13 @@ static void rbd_img_obj_callback(struct rbd_obj_request *obj_request)
 		xferred = (unsigned int)obj_request->xferred;
 		result = obj_request->result;
 		if (result) {
-			rbd_warn(NULL, "obj_request %s result %d xferred %u\n",
+			struct rbd_device *rbd_dev = img_request->rbd_dev;
+
+			rbd_warn(rbd_dev, "%s %llx at %llx (%llx)\n",
 				img_request->write_request ? "write" : "read",
+				obj_request->length, obj_request->img_offset,
+				obj_request->offset);
+			rbd_warn(rbd_dev, "  result %d xferred %x\n",
 				result, xferred);
 			if (!img_request->result)
 				img_request->result = result;
@@ -1604,7 +1610,7 @@ static int rbd_img_request_fill_bio(struct rbd_img_request *img_request,
 	struct rbd_obj_request *next_obj_request;
 	bool write_request = img_request->write_request;
 	unsigned int bio_offset;
-	u64 image_offset;
+	u64 img_offset;
 	u64 resid;
 	u16 opcode;
 
@@ -1612,8 +1618,8 @@ static int rbd_img_request_fill_bio(struct rbd_img_request *img_request,
 
 	opcode = write_request ? CEPH_OSD_OP_WRITE : CEPH_OSD_OP_READ;
 	bio_offset = 0;
-	image_offset = img_request->offset;
-	rbd_assert(image_offset == bio_list->bi_sector << SECTOR_SHIFT);
+	img_offset = img_request->offset;
+	rbd_assert(img_offset == bio_list->bi_sector << SECTOR_SHIFT);
 	resid = img_request->length;
 	rbd_assert(resid > 0);
 	while (resid) {
@@ -1623,11 +1629,11 @@ static int rbd_img_request_fill_bio(struct rbd_img_request *img_request,
 		u64 offset;
 		u64 length;
 
-		object_name = rbd_segment_name(rbd_dev, image_offset);
+		object_name = rbd_segment_name(rbd_dev, img_offset);
 		if (!object_name)
 			goto out_unwind;
-		offset = rbd_segment_offset(rbd_dev, image_offset);
-		length = rbd_segment_length(rbd_dev, image_offset, resid);
+		offset = rbd_segment_offset(rbd_dev, img_offset);
+		length = rbd_segment_length(rbd_dev, img_offset, resid);
 		obj_request = rbd_obj_request_create(object_name,
 						offset, length,
 						OBJ_REQUEST_BIO);
@@ -1656,9 +1662,10 @@ static int rbd_img_request_fill_bio(struct rbd_img_request *img_request,
 				obj_request->bio_list, obj_request->length);
 		rbd_osd_req_format(obj_request, write_request);
 
+		obj_request->img_offset = img_offset;
 		rbd_img_obj_request_add(img_request, obj_request);
 
-		image_offset += length;
+		img_offset += length;
 		resid -= length;
 	}
 
@@ -1993,8 +2000,10 @@ static void rbd_request_fn(struct request_queue *q)
 end_request:
 		spin_lock_irq(q->queue_lock);
 		if (result < 0) {
-			rbd_warn(rbd_dev, "obj_request %s result %d\n",
-				write_request ? "write" : "read", result);
+			rbd_warn(rbd_dev, "%s %llx at %llx result %d\n",
+				write_request ? "write" : "read",
+				length, offset, result);
+
 			__blk_end_request_all(rq, result);
 		}
 	}