[TAPDISK] minor changes to tapdisk and plugins

* open all parent images read-only
* expose parent image names to tapdisk (needed for locking api)
Signed-off-by: Jake Wires <jwires@xensource.com>

9 files changed, 224 insertions, 143 deletions

diff --git a/tools/blktap/drivers/block-aio.c b/tools/blktap/drivers/block-aio.c
index bbcc4c785a..733407b8c6 100644
--- a/tools/blktap/drivers/block-aio.c
+++ b/tools/blktap/drivers/block-aio.c
@@ -152,9 +152,9 @@ static inline void init_fds(struct disk_driver *dd)
 }
 
 /* Open the disk file and initialize aio state. */
-int tdaio_open (struct disk_driver *dd, const char *name)
+int tdaio_open (struct disk_driver *dd, const char *name, td_flag_t flags)
 {
-	int i, fd, ret = 0;
+	int i, fd, ret = 0, o_flags;
 	struct td_state    *s   = dd->td_state;
 	struct tdaio_state *prv = (struct tdaio_state *)dd->private;
 
@@ -187,12 +187,15 @@ int tdaio_open (struct disk_driver *dd, const char *name)
 		prv->iocb_free[i] = &prv->iocb_list[i];
 
 	/* Open the file */
-        fd = open(name, O_RDWR | O_DIRECT | O_LARGEFILE);
+	o_flags = O_DIRECT | O_LARGEFILE | 
+		((flags == TD_RDONLY) ? O_RDONLY : O_RDWR);
+        fd = open(name, o_flags);
 
         if ( (fd == -1) && (errno == EINVAL) ) {
 
                 /* Maybe O_DIRECT isn't supported. */
-                fd = open(name, O_RDWR | O_LARGEFILE);
+		o_flags &= ~O_DIRECT;
+                fd = open(name, o_flags);
                 if (fd != -1) DPRINTF("WARNING: Accessing image without"
                                      "O_DIRECT! (%s)\n", name);
 
@@ -280,6 +283,9 @@ int tdaio_submit(struct disk_driver *dd)
 	int ret;
 	struct tdaio_state *prv = (struct tdaio_state *)dd->private;
 
+	if (!prv->iocb_queued)
+		return 0;
+
 	ret = io_submit(prv->aio_ctx, prv->iocb_queued, prv->iocb_queue);
 	
 	/* XXX: TODO: Handle error conditions here. */
@@ -324,12 +330,13 @@ int tdaio_do_callbacks(struct disk_driver *dd, int sid)
 	return rsp;
 }
 
-int tdaio_has_parent(struct disk_driver *dd)
+int tdaio_get_parent_id(struct disk_driver *dd, struct disk_id *id)
 {
-	return 0;
+	return TD_NO_PARENT;
 }
 
-int tdaio_get_parent(struct disk_driver *dd, struct disk_driver *parent)
+int tdaio_validate_parent(struct disk_driver *dd, 
+			  struct disk_driver *parent, td_flag_t flags)
 {
 	return -EINVAL;
 }
@@ -341,8 +348,8 @@ struct tap_disk tapdisk_aio = {
 	.td_queue_read      = tdaio_queue_read,
 	.td_queue_write     = tdaio_queue_write,
 	.td_submit          = tdaio_submit,
-	.td_has_parent      = tdaio_has_parent,
-	.td_get_parent      = tdaio_get_parent,
 	.td_close           = tdaio_close,
 	.td_do_callbacks    = tdaio_do_callbacks,
+	.td_get_parent_id   = tdaio_get_parent_id,
+	.td_validate_parent = tdaio_validate_parent
 };
diff --git a/tools/blktap/drivers/block-qcow.c b/tools/blktap/drivers/block-qcow.c
index 2859b08829..185c670111 100644
--- a/tools/blktap/drivers/block-qcow.c
+++ b/tools/blktap/drivers/block-qcow.c
@@ -209,23 +209,6 @@ static int init_aio_state(struct disk_driver *dd)
 	return -1;
 }
 
-/*
- *Test if block is zero. 
- * Return: 
- *       1 for TRUE
- *       0 for FALSE
- */
-static inline int IS_ZERO(char *buf, int len)
-{
-	int i;
-
-	for (i = 0; i < len; i++) {
-		/*if not zero, return false*/
-		if (ZERO_TEST(*(buf + i))) return 0; 
-	}
-	return 1;
-}
-
 static uint32_t gen_cksum(char *ptr, int len)
 {
 	unsigned char *md;
@@ -825,9 +808,9 @@ static inline void init_fds(struct disk_driver *dd)
 }
 
 /* Open the disk file and initialize qcow state. */
-int tdqcow_open (struct disk_driver *dd, const char *name)
+int tdqcow_open (struct disk_driver *dd, const char *name, td_flag_t flags)
 {
-	int fd, len, i, shift, ret, size, l1_table_size;
+	int fd, len, i, shift, ret, size, l1_table_size, o_flags;
 	struct td_state     *bs = dd->td_state;
 	struct tdqcow_state *s  = (struct tdqcow_state *)dd->private;
 	char *buf;
@@ -838,7 +821,9 @@ int tdqcow_open (struct disk_driver *dd, const char *name)
 
  	DPRINTF("QCOW: Opening %s\n",name);
 
-	fd = open(name, O_RDWR | O_DIRECT | O_LARGEFILE);
+	o_flags = O_DIRECT | O_LARGEFILE | 
+		((flags == TD_RDONLY) ? O_RDONLY : O_RDWR);
+	fd = open(name, o_flags);
 	if (fd < 0) {
 		DPRINTF("Unable to open %s (%d)\n",name,0 - errno);
 		return -1;
@@ -1016,7 +1001,8 @@ int tdqcow_queue_read(struct disk_driver *dd, uint64_t sector,
 				 * as busy and try again later */
 				return cb(dd, -EBUSY, sector + n,
 					  nb_sectors - n, id, private);
-			} else rsp += ret;
+			} else
+				rsp += ret;
 		} else if (cluster_offset & QCOW_OFLAG_COMPRESSED) {
 			aio_unlock(s, sector);
 			if (decompress_cluster(s, cluster_offset) < 0) {
@@ -1403,21 +1389,15 @@ int qcow_compress_cluster(struct tdqcow_state *s, int64_t sector_num,
 	return 0;
 }
 
-int tdqcow_has_parent(struct disk_driver *dd)
-{
-	struct tdqcow_state *s = (struct tdqcow_state *)dd->private;
-	return (s->backing_file_offset ? 1 : 0);
-}
-
-int tdqcow_get_parent(struct disk_driver *cdd, struct disk_driver *pdd)
+int tdqcow_get_parent_id(struct disk_driver *dd, struct disk_id *id)
 {
 	off_t off;
 	char *buf, *filename;
-	int len, secs, ret = -1;
-	struct tdqcow_state *child  = (struct tdqcow_state *)cdd->private;
+	int len, secs, err = -EINVAL;
+	struct tdqcow_state *child  = (struct tdqcow_state *)dd->private;
 
 	if (!child->backing_file_offset)
-		return -1;
+		return TD_NO_PARENT;
 
 	/* read the backing file name */
 	len  = child->backing_file_size;
@@ -1432,14 +1412,39 @@ int tdqcow_get_parent(struct disk_driver *cdd, struct disk_driver *pdd)
 
 	if (read(child->fd, buf, secs << 9) != secs << 9)
 		goto out;
-	filename      = buf + (child->backing_file_offset - off);
-	filename[len] = '\0';
+	filename       = buf + (child->backing_file_offset - off);
+	filename[len]  = '\0';
 
-	/*Open backing file*/
-	ret = tdqcow_open(pdd, filename);
+	id->name       = strdup(filename);
+	id->drivertype = DISK_TYPE_QCOW;
+	err            = 0;
  out:
 	free(buf);
-	return ret;
+	return err;
+}
+
+int tdqcow_validate_parent(struct disk_driver *child,
+			   struct disk_driver *parent, td_flag_t flags)
+{
+	struct stat stats;
+	uint64_t psize, csize;
+	struct tdqcow_state *c = (struct tdqcow_state *)child->private;
+	struct tdqcow_state *p = (struct tdqcow_state *)parent->private;
+	
+	if (stat(p->name, &stats))
+		return -EINVAL;
+	if (get_filesize(p->name, &psize, &stats))
+		return -EINVAL;
+
+	if (stat(c->name, &stats))
+		return -EINVAL;
+	if (get_filesize(c->name, &csize, &stats))
+		return -EINVAL;
+
+	if (csize != psize)
+		return -EINVAL;
+
+	return 0;
 }
 
 struct tap_disk tapdisk_qcow = {
@@ -1449,8 +1454,8 @@ struct tap_disk tapdisk_qcow = {
 	.td_queue_read       = tdqcow_queue_read,
 	.td_queue_write      = tdqcow_queue_write,
 	.td_submit           = tdqcow_submit,
-	.td_has_parent       = tdqcow_has_parent,
-	.td_get_parent       = tdqcow_get_parent,
 	.td_close            = tdqcow_close,
 	.td_do_callbacks     = tdqcow_do_callbacks,
+	.td_get_parent_id    = tdqcow_get_parent_id,
+	.td_validate_parent  = tdqcow_validate_parent
 };
diff --git a/tools/blktap/drivers/block-ram.c b/tools/blktap/drivers/block-ram.c
index c23dd6b27e..3b4ef7ceb5 100644
--- a/tools/blktap/drivers/block-ram.c
+++ b/tools/blktap/drivers/block-ram.c
@@ -135,11 +135,11 @@ static inline void init_fds(struct disk_driver *dd)
 }
 
 /* Open the disk file and initialize ram state. */
-int tdram_open (struct disk_driver *dd, const char *name)
+int tdram_open (struct disk_driver *dd, const char *name, td_flag_t flags)
 {
 	char *p;
 	uint64_t size;
-	int i, fd, ret = 0, count = 0;
+	int i, fd, ret = 0, count = 0, o_flags;
 	struct td_state    *s     = dd->td_state;
 	struct tdram_state *prv   = (struct tdram_state *)dd->private;
 
@@ -167,12 +167,15 @@ int tdram_open (struct disk_driver *dd, const char *name)
 	}
 
 	/* Open the file */
-        fd = open(name, O_RDWR | O_DIRECT | O_LARGEFILE);
+	o_flags = O_DIRECT | O_LARGEFILE | 
+		((flags == TD_RDONLY) ? O_RDONLY : O_RDWR);
+        fd = open(name, o_flags);
 
         if ((fd == -1) && (errno == EINVAL)) {
 
                 /* Maybe O_DIRECT isn't supported. */
-                fd = open(name, O_RDWR | O_LARGEFILE);
+		o_flags &= ~O_DIRECT;
+                fd = open(name, o_flags);
                 if (fd != -1) DPRINTF("WARNING: Accessing image without"
                                      "O_DIRECT! (%s)\n", name);
 
@@ -275,12 +278,13 @@ int tdram_do_callbacks(struct disk_driver *dd, int sid)
 	return 1;
 }
 
-int tdram_has_parent(struct disk_driver *dd)
+int tdram_get_parent_id(struct disk_driver *dd, struct disk_id *id)
 {
-	return 0;
+	return TD_NO_PARENT;
 }
 
-int tdram_get_parent(struct disk_driver *dd, struct disk_driver *parent)
+int tdram_validate_parent(struct disk_driver *dd, 
+			  struct disk_driver *parent, td_flag_t flags)
 {
 	return -EINVAL;
 }
@@ -292,8 +296,8 @@ struct tap_disk tapdisk_ram = {
 	.td_queue_read      = tdram_queue_read,
 	.td_queue_write     = tdram_queue_write,
 	.td_submit          = tdram_submit,
-	.td_has_parent      = tdram_has_parent,
-	.td_get_parent      = tdram_get_parent,
 	.td_close           = tdram_close,
 	.td_do_callbacks    = tdram_do_callbacks,
+	.td_get_parent_id   = tdram_get_parent_id,
+	.td_validate_parent = tdram_validate_parent
 };
diff --git a/tools/blktap/drivers/block-sync.c b/tools/blktap/drivers/block-sync.c
index 367eb70ab9..74f77d6f61 100644
--- a/tools/blktap/drivers/block-sync.c
+++ b/tools/blktap/drivers/block-sync.c
@@ -118,9 +118,9 @@ static inline void init_fds(struct disk_driver *dd)
 }
 
 /* Open the disk file and initialize aio state. */
-int tdsync_open (struct disk_driver *dd, const char *name)
+int tdsync_open (struct disk_driver *dd, const char *name, td_flag_t flags)
 {
-	int i, fd, ret = 0;
+	int i, fd, ret = 0, o_flags;
 	struct td_state     *s   = dd->td_state;
 	struct tdsync_state *prv = (struct tdsync_state *)dd->private;
 	
@@ -130,11 +130,14 @@ int tdsync_open (struct disk_driver *dd, const char *name)
 		return (0 - errno);
 	
 	/* Open the file */
-        fd = open(name, O_RDWR | O_DIRECT | O_LARGEFILE);
+	o_flags = O_DIRECT | O_LARGEFILE | 
+		((flags == TD_RDONLY) ? O_RDONLY : O_RDWR);
+        fd = open(name, o_flags);
 
         if ( (fd == -1) && (errno == EINVAL) ) {
 
                 /* Maybe O_DIRECT isn't supported. */
+		o_flags &= ~O_DIRECT;
                 fd = open(name, O_RDWR | O_LARGEFILE);
                 if (fd != -1) DPRINTF("WARNING: Accessing image without"
                                      "O_DIRECT! (%s)\n", name);
@@ -223,12 +226,13 @@ int tdsync_do_callbacks(struct disk_driver *dd, int sid)
 	return 1;
 }
 
-int tdsync_has_parent(struct disk_driver *dd)
+int tdsync_get_parent_id(struct disk_driver *dd, struct disk_id *id)
 {
-	return 0;
+	return TD_NO_PARENT;
 }
 
-int tdsync_get_parent(struct disk_driver *dd, struct disk_driver *parent)
+int tdsync_validate_parent(struct disk_driver *dd, 
+			   struct disk_driver *parent, td_flag_t flags)
 {
 	return -EINVAL;
 }
@@ -240,8 +244,8 @@ struct tap_disk tapdisk_sync = {
 	.td_queue_read       = tdsync_queue_read,
 	.td_queue_write      = tdsync_queue_write,
 	.td_submit           = tdsync_submit,
-	.td_has_parent       = tdsync_has_parent,
-	.td_get_parent       = tdsync_get_parent,
 	.td_close            = tdsync_close,
 	.td_do_callbacks     = tdsync_do_callbacks,
+	.td_get_parent_id    = tdsync_get_parent_id,
+	.td_validate_parent  = tdsync_validate_parent
 };
diff --git a/tools/blktap/drivers/block-vmdk.c b/tools/blktap/drivers/block-vmdk.c
index 5a6a5ca775..4ab88373ea 100644
--- a/tools/blktap/drivers/block-vmdk.c
+++ b/tools/blktap/drivers/block-vmdk.c
@@ -119,10 +119,11 @@ static inline void init_fds(struct disk_driver *dd)
 }
 
 /* Open the disk file and initialize aio state. */
-static int tdvmdk_open (struct disk_driver *dd, const char *name)
+static int tdvmdk_open (struct disk_driver *dd, 
+			const char *name, td_flag_t flags)
 {
 	int ret, fd;
-    	int l1_size, i;
+    	int l1_size, i, o_flags;
     	uint32_t magic;
 	struct td_state     *s   = dd->td_state;
 	struct tdvmdk_state *prv = (struct tdvmdk_state *)dd->private;
@@ -133,12 +134,15 @@ static int tdvmdk_open (struct disk_driver *dd, const char *name)
 		return -1;
 	
 	/* Open the file */
-        fd = open(name, O_RDWR | O_LARGEFILE); 
+	o_flags = O_DIRECT | O_LARGEFILE | 
+		((flags == TD_RDONLY) ? O_RDONLY : O_RDWR);
+        fd = open(name, o_flags); 
 
         if ( (fd == -1) && (errno == EINVAL) ) {
 
                 /* Maybe O_DIRECT isn't supported. */
-                fd = open(name, O_RDWR | O_LARGEFILE);
+		o_flags &= ~O_DIRECT;
+                fd = open(name, o_flags);
                 if (fd != -1) DPRINTF("WARNING: Accessing image without"
                                      "O_DIRECT! (%s)\n", name);
 
@@ -394,12 +398,13 @@ static int tdvmdk_do_callbacks(struct disk_driver *dd, int sid)
 	return 1;
 }
 
-static int tdvmdk_has_parent(struct disk_driver *dd)
+static int tdvmdk_get_parent_id(struct disk_driver *dd, struct disk_id *id)
 {
-	return 0;
+	return TD_NO_PARENT;
 }
 
-static int tdvmdk_get_parent(struct disk_driver *dd, struct disk_driver *parent)
+static int tdvmdk_validate_parent(struct disk_driver *dd, 
+				  struct disk_driver *parent, td_flag_t flags)
 {
 	return -EINVAL;
 }
@@ -411,8 +416,8 @@ struct tap_disk tapdisk_vmdk = {
 	.td_queue_read       = tdvmdk_queue_read,
 	.td_queue_write      = tdvmdk_queue_write,
 	.td_submit           = tdvmdk_submit,
-	.td_has_parent       = tdvmdk_has_parent,
-	.td_get_parent       = tdvmdk_get_parent,
 	.td_close            = tdvmdk_close,
 	.td_do_callbacks     = tdvmdk_do_callbacks,
+	.td_get_parent_id    = tdvmdk_get_parent_id,
+	.td_validate_parent  = tdvmdk_validate_parent
 };
diff --git a/tools/blktap/drivers/img2qcow.c b/tools/blktap/drivers/img2qcow.c
index 7baf28fb02..926cf2742e 100644
--- a/tools/blktap/drivers/img2qcow.c
+++ b/tools/blktap/drivers/img2qcow.c
@@ -201,7 +201,7 @@ int main(int argc, char *argv[])
 	dd.private  = malloc(dd.drv->private_data_size);
 
         /*Open qcow file*/
-        if (dd.drv->td_open(&dd, argv[1])!=0) {
+        if (dd.drv->td_open(&dd, argv[1], 0)!=0) {
 		DFPRINTF("Unable to open Qcow file [%s]\n",argv[1]);
 		exit(-1);
 	}
diff --git a/tools/blktap/drivers/qcow2raw.c b/tools/blktap/drivers/qcow2raw.c
index 8adf573309..55ae4ad108 100644
--- a/tools/blktap/drivers/qcow2raw.c
+++ b/tools/blktap/drivers/qcow2raw.c
@@ -169,7 +169,7 @@ int main(int argc, char *argv[])
 	ddqcow.drv = &tapdisk_qcow;
 	ddqcow.private = malloc(ddqcow.drv->private_data_size);
 
-        if (ddqcow.drv->td_open(&ddqcow, argv[2])!=0) {
+        if (ddqcow.drv->td_open(&ddqcow, argv[2], TD_RDONLY)!=0) {
 		DFPRINTF("Unable to open Qcow file [%s]\n",argv[2]);
 		exit(-1);
 	} else DFPRINTF("QCOW file opened, size %llu\n",
@@ -270,7 +270,7 @@ int main(int argc, char *argv[])
 	ddaio.drv = &tapdisk_aio;
 	ddaio.private = malloc(ddaio.drv->private_data_size);
 
-        if (ddaio.drv->td_open(&ddaio, argv[1])!=0) {
+        if (ddaio.drv->td_open(&ddaio, argv[1], 0)!=0) {
 		DFPRINTF("Unable to open Qcow file [%s]\n", argv[1]);
 		exit(-1);
 	}
diff --git a/tools/blktap/drivers/tapdisk.c b/tools/blktap/drivers/tapdisk.c
index 6215770d97..43a037a053 100644
--- a/tools/blktap/drivers/tapdisk.c
+++ b/tools/blktap/drivers/tapdisk.c
@@ -81,6 +81,15 @@ void daemonize(void)
 	return;
 }
 
+static void free_driver(struct disk_driver *d)
+{
+	if (d->name)
+		free(d->name);
+	if (d->private)
+		free(d->private);
+	free(d);
+}
+
 static void unmap_disk(struct td_state *s)
 {
 	tapdev_info_t *info = s->ring_info;
@@ -91,8 +100,7 @@ static void unmap_disk(struct td_state *s)
 	while (dd) {
 		tmp = dd->next;
 		dd->drv->td_close(dd);
-		free(dd->private);
-		free(dd);
+		free_driver(dd);
 		dd = tmp;
 	}
 
@@ -112,7 +120,6 @@ static void unmap_disk(struct td_state *s)
 	free(s);
 
 	return;
-
 }
 
 void sig_handler(int sig)
@@ -205,26 +212,6 @@ static struct td_state *state_init(void)
 	return s;
 }
 
-static struct disk_driver *disk_init(struct td_state *s, struct tap_disk *drv)
-{
-	struct disk_driver *dd;
-
-	dd = calloc(1, sizeof(struct disk_driver));
-	if (!dd)
-		return NULL;
-	
-	dd->private = malloc(drv->private_data_size);
-	if (!dd->private) {
-		free(dd);
-		return NULL;
-	}
-
-	dd->drv      = drv;
-	dd->td_state = s;
-
-	return dd;
-}
-
 static int map_new_dev(struct td_state *s, int minor)
 {
 	int tap_fd;
@@ -280,49 +267,94 @@ static int map_new_dev(struct td_state *s, int minor)
 	return -1;
 }
 
-static int open_disk(struct td_state *s, struct disk_driver *dd, char *path)
+static struct disk_driver *disk_init(struct td_state *s, 
+				     struct tap_disk *drv, char *name)
+{
+	struct disk_driver *dd;
+
+	dd = calloc(1, sizeof(struct disk_driver));
+	if (!dd)
+		return NULL;
+	
+	dd->private = malloc(drv->private_data_size);
+	if (!dd->private) {
+		free(dd);
+		return NULL;
+	}
+
+	dd->drv      = drv;
+	dd->td_state = s;
+	dd->name     = name;
+
+	return dd;
+}
+
+static int open_disk(struct td_state *s, struct tap_disk *drv, char *path)
 {
 	int err;
-	struct disk_driver *d = dd;
+	char *dup;
+	struct disk_id id;
+	struct disk_driver *d;
+
+	dup = strdup(path);
+	if (!dup)
+		return -ENOMEM;
 
-	err = dd->drv->td_open(dd, path);
+	memset(&id, 0, sizeof(struct disk_id));
+	s->disks = d = disk_init(s, drv, dup);
+	if (!d)
+		return -ENOMEM;
+
+	err = drv->td_open(d, path, 0);
 	if (err)
-		return err;
+		goto fail;
 
 	/* load backing files as necessary */
-	while (d->drv->td_has_parent(d)) {
+	while ((err = d->drv->td_get_parent_id(d, &id)) == 0) {
 		struct disk_driver *new;
 		
-		new = calloc(1, sizeof(struct disk_driver));
-		if (!new)
+		if (id.drivertype > MAX_DISK_TYPES || 
+		    !get_driver(id.drivertype) || !id.name)
 			goto fail;
-		new->drv      = d->drv;
-		new->td_state = s;
-		new->private  = malloc(new->drv->private_data_size);
-		if (!new->private) {
-			free(new);
+
+		dup = strdup(id.name);
+		if (!dup)
 			goto fail;
-		}
-		
-		err = d->drv->td_get_parent(d, new);
+
+		new = disk_init(s, get_driver(id.drivertype), dup);
+		if (!new)
+			goto fail;
+
+		err = new->drv->td_open(new, new->name, TD_RDONLY);
 		if (err)
 			goto fail;
 
+		err = d->drv->td_validate_parent(d, new, 0);
+		if (err) {
+			d->next = new;
+			goto fail;
+		}
+
 		d = d->next = new;
+		free(id.name);
 	}
 
-	return 0;
+	if (err >= 0)
+		return 0;
 
  fail:
 	DPRINTF("failed opening disk\n");
-	while (dd) {
-		d = dd->next;
-		dd->drv->td_close(dd);
-		free(dd->private);
-		free(dd);
-		dd = d;
+	if (id.name)
+		free(id.name);
+	d = s->disks;
+	while (d) {
+		struct disk_driver *tmp = d->next;
+		d->drv->td_close(d);
+		free_driver(d);
+		d = tmp;
 	}
-	return err;
+	s->disks = NULL;
+	return -1;
 }
 
 static int read_msg(char *buf)
@@ -334,7 +366,6 @@ static int read_msg(char *buf)
 	msg_newdev_t *msg_dev;
 	msg_pid_t *msg_pid;
 	struct tap_disk *drv;
-	struct disk_driver *dd;
 	int ret = -1;
 	struct td_state *s = NULL;
 	fd_list_entry_t *entry;
@@ -369,14 +400,8 @@ static int read_msg(char *buf)
 			if (s == NULL)
 				goto params_done;
 
-			s->disks = dd = disk_init(s, drv);
-			if (!dd) {
-				free(s);
-				goto params_done;
-			}
-
 			/*Open file*/
-			ret = open_disk(s, dd, path);
+			ret = open_disk(s, drv, path);
 			if (ret)
 				goto params_done;
 
@@ -785,6 +810,19 @@ int main(int argc, char *argv[])
 					}
 				}
 
+				/* completed io from above may have 
+				 * queued new requests on chained disks */
+				if (progress_made) {
+					td_for_each_disk(ptr->s, dd) {
+						dd->early += 
+							dd->drv->td_submit(dd);
+						if (dd->early > 0) {
+							io_done(dd, 10);
+							dd->early = 0;
+						}
+					}
+				}
+
 				if (FD_ISSET(ptr->tap_fd, &readfds) ||
 				    (info->busy.req && progress_made))
 					get_io_request(ptr->s);
diff --git a/tools/blktap/drivers/tapdisk.h b/tools/blktap/drivers/tapdisk.h
index 7b03fa0762..b76d46cce5 100644
--- a/tools/blktap/drivers/tapdisk.h
+++ b/tools/blktap/drivers/tapdisk.h
@@ -42,10 +42,15 @@
  * 
  *   - The fd used for poll is an otherwise unused pipe, which allows poll to 
  *     be safely called without ever returning anything.
- * 
+ *
  * NOTE: tapdisk uses the number of sectors submitted per request as a 
  * ref count.  Plugins must use the callback function to communicate the
  * completion--or error--of every sector submitted to them.
+ *
+ * td_get_parent_id returns:
+ *     0 if parent id successfully retrieved
+ *     TD_NO_PARENT if no parent exists
+ *     -errno on error
  */
 
 #ifndef TAPDISK_H_
@@ -71,12 +76,23 @@
 #define MAX_IOFD                 2
 
 #define BLK_NOT_ALLOCATED       99
+#define TD_NO_PARENT             1
+
+typedef uint32_t td_flag_t;
+
+#define TD_RDONLY                1
 
 struct td_state;
 struct tap_disk;
 
+struct disk_id {
+	char *name;
+	int drivertype;
+};
+
 struct disk_driver {
 	int early;
+	char *name;
 	void *private;
 	int io_fd[MAX_IOFD];
 	struct tap_disk *drv;
@@ -105,18 +121,20 @@ typedef int (*td_callback_t)(struct disk_driver *dd, int res, uint64_t sector,
 struct tap_disk {
 	const char *disk_type;
 	int private_data_size;
-	int (*td_open)        (struct disk_driver *dd, const char *name);
-	int (*td_queue_read)  (struct disk_driver *dd, uint64_t sector,
-			       int nb_sectors, char *buf, td_callback_t cb, 
-			       int id, void *prv);
-	int (*td_queue_write) (struct disk_driver *dd, uint64_t sector,
-			       int nb_sectors, char *buf, td_callback_t cb, 
-			       int id, void *prv);
-	int (*td_submit)      (struct disk_driver *dd);
-	int (*td_has_parent)  (struct disk_driver *dd);
-	int (*td_get_parent)  (struct disk_driver *dd, struct disk_driver *p);
-	int (*td_close)       (struct disk_driver *dd);
-	int (*td_do_callbacks)(struct disk_driver *dd, int sid);
+	int (*td_open)           (struct disk_driver *dd, 
+				  const char *name, td_flag_t flags);
+	int (*td_queue_read)     (struct disk_driver *dd, uint64_t sector,
+				  int nb_sectors, char *buf, td_callback_t cb,
+				  int id, void *prv);
+	int (*td_queue_write)    (struct disk_driver *dd, uint64_t sector,
+				  int nb_sectors, char *buf, td_callback_t cb, 
+				  int id, void *prv);
+	int (*td_submit)         (struct disk_driver *dd);
+	int (*td_close)          (struct disk_driver *dd);
+	int (*td_do_callbacks)   (struct disk_driver *dd, int sid);
+	int (*td_get_parent_id)  (struct disk_driver *dd, struct disk_id *id);
+	int (*td_validate_parent)(struct disk_driver *dd, 
+				  struct disk_driver *p, td_flag_t flags);
 };
 
 typedef struct disk_info {