[TAPDISK] add tapdisk support for image chaining

Enables tapdisk to chain an arbitrary number of VDIs, propagating reads of
holes in children to their parent images.  Introduces two new functions to the
tapdisk interface to facilitate this.  Modifies the QCoW plugin to take
advantage of these changes, thus providing support for arbitrarily long chains
of QCoW image types.

2 files changed, 14 insertions, 7 deletions

diff --git a/tools/blktap/lib/blktaplib.h b/tools/blktap/lib/blktaplib.h
index 12f4950133..0ba3c04ec8 100644
--- a/tools/blktap/lib/blktaplib.h
+++ b/tools/blktap/lib/blktaplib.h
@@ -91,8 +91,9 @@ struct blkif;
 
 typedef struct {
 	blkif_request_t  req;
-	struct blkif         *blkif;
-	int              count;
+	struct blkif    *blkif;
+	int              submitting;
+	int              secs_pending;
         int16_t          status;
 } pending_req_t;
 
@@ -116,7 +117,7 @@ typedef struct blkif {
 	
 	void *prv;  /* device-specific data */
 	void *info; /*Image parameter passing */
-	pending_req_t    pending_list[MAX_REQUESTS];
+	pending_req_t pending_list[MAX_REQUESTS];
 	int devnum;
 	int fds[2];
 	int be_id;
@@ -141,6 +142,11 @@ int blkif_init(blkif_t *blkif, long int handle, long int pdev,
 void free_blkif(blkif_t *blkif);
 void __init_blkif(void);
 
+typedef struct busy_state {
+	int seg_idx;
+	blkif_request_t *req;
+} busy_state_t;
+
 typedef struct tapdev_info {
 	int fd;
 	char *mem;
@@ -148,6 +154,7 @@ typedef struct tapdev_info {
 	blkif_back_ring_t  fe_ring;
 	unsigned long vstart;
 	blkif_t *blkif;
+	busy_state_t busy;
 } tapdev_info_t;
 
 typedef struct domid_translate {
diff --git a/tools/blktap/lib/xs_api.c b/tools/blktap/lib/xs_api.c
index eded38afdc..539d0e3c51 100644
--- a/tools/blktap/lib/xs_api.c
+++ b/tools/blktap/lib/xs_api.c
@@ -311,8 +311,8 @@ int unregister_xenbus_watch(struct xs_handle *h, struct xenbus_watch *watch)
 	}
 
 	if (!xs_unwatch(h, watch->node, token))
-		DPRINTF("XENBUS Failed to release watch %s: %i\n",
-			watch->node, er);
+		DPRINTF("XENBUS Failed to release watch %s\n",
+			watch->node);
 
 	list_del(&watch->list);
 	
@@ -351,9 +351,9 @@ int xs_fire_next_watch(struct xs_handle *h)
 	
 	node  = res[XS_WATCH_PATH];
 	token = res[XS_WATCH_TOKEN];
-	
+
 	w = find_watch(token);
-	if (w)
+	if (w) 
 		w->callback(h, w, node);
 
 	free(res);