o added reference counting to the destination devices, make sure that the

destructor for any targets you write call dm_table_remove_device.

driver/device-mapper/device-mapper.h

@@ -39,12 +39,13 @@ struct dm_table;
 typedef unsigned int offset_t;
 
 /* constructor, destructor and map fn types */
-typedef int (*dm_ctr_fn)(offset_t b, offset_t e, struct dm_table *t,
+typedef int (*dm_ctr_fn)(struct dm_table *t,
+			 offset_t b, offset_t e,
 			 const char *cb, const char *ce, void **result);
-typedef void (*dm_dtr_fn)(void *c);
+typedef void (*dm_dtr_fn)(struct dm_table *t, void *c);
 typedef int (*dm_map_fn)(struct buffer_head *bh, void *context);
 
-int register_map_target(const char *name, dm_ctr_fn ctr, dm_dtr_fn dtr,
+int dm_register_target(const char *name, dm_ctr_fn ctr, dm_dtr_fn dtr,
 		       dm_map_fn map);
 
 
@@ -53,6 +54,7 @@ int register_map_target(const char *name, dm_ctr_fn ctr, dm_dtr_fn dtr,
  * (ie. opened/closed).
  */
 int dm_table_add_device(struct dm_table *t, kdev_t dev);
+void dm_table_remove_device(struct dm_table *t, kdev_t dev);
 
 #endif
 #endif

driver/device-mapper/dm-fs.c

@@ -277,12 +277,14 @@ static int process_table(const char *b, const char *e, int minor,
 		}
 
 		high = start + (size - 1);
-		if ((r = t->ctr(start, high, table, we, e, &context)))
+		if ((r = t->ctr(table, start, high, we, e, &context)))
 			return r;
 
-		if ((r = dm_table_add_entry(table, high, t->map, context)))
+		if ((r = dm_table_add_entry(table, high, t->map, context))) {
+			t->dtr(table, context);
 			return r;
 		}
+	}
 
 	return 0;
 }

driver/device-mapper/dm-table.c

@@ -147,7 +147,6 @@ struct dm_table *dm_table_create(void)
 
 void dm_table_destroy(struct dm_table *t)
 {
-	struct dev_list *d, *n;
 	int i;
 
 	if (!t)
@@ -164,10 +163,17 @@ void dm_table_destroy(struct dm_table *t)
 	kfree(t);
 
 	/* free the device list */
+	if (t->devices) {
+		struct dev_list *d, *n;
+
+		WARN("there are still devices present, someone isn't "
+		     "calling dm_table_remove_device");
+
 		for (d = t->devices; d; d = n) {
 			n = d->next;
 			kfree(d);
 		}
+	}
 }
 
 /*
@@ -200,20 +206,62 @@ int dm_table_add_entry(struct dm_table *t, offset_t high,
 	return 0;
 }
 
+/*
+ * see if we've already got a device in the list.
+ */
+static struct dev_list *find_device(struct dev_list *d, kdev_t dev)
+{
+	while(d) {
+		if (d->dev == dev)
+			break;
+
+		d = d->next;
+	}
+
+	return d;
+}
+
+/*
+ * add a device to the list, or just increment the
+ * usage count if it's already present.
+ */
 int dm_table_add_device(struct dm_table *t, kdev_t dev)
 {
-	struct dev_list *d = kmalloc(sizeof(*d), GFP_KERNEL);
+	struct dev_list *d;
 
+	d = find_device(t->devices, dev);
+	if (!d) {
+		d = kmalloc(sizeof(*d), GFP_KERNEL);
 		if (!d)
 			return -ENOMEM;
 
 		d->dev = dev;
+		atomic_set(&d->count, 0);
 		d->next = t->devices;
 		t->devices = d;
+	}
+	atomic_inc(&d->count);
 
 	return 0;
 }
 
+/*
+ * decrement a devices use count and remove it if
+ * neccessary.
+ */
+void dm_table_remove_device(struct dm_table *t, kdev_t dev)
+{
+	struct dev_list *d = find_device(t->devices, dev);
+
+	if (!d) {
+		WARN("asked to remove a device that isn't present");
+		return;
+	}
+
+	if (atomic_dec_and_test(&d->count))
+		kfree(d);
+}
+
 /*
  * builds the btree to index the map
  */

driver/device-mapper/dm-target.c

@@ -50,7 +50,7 @@ struct target_type *dm_get_target(const char *name)
 /*
  * register a new target_type.
  */
-int register_map_target(const char *name, dm_ctr_fn ctr,
+int dm_register_target(const char *name, dm_ctr_fn ctr,
 		       dm_dtr_fn dtr, dm_map_fn map)
 {
 	struct target_type *t =
@@ -85,7 +85,8 @@ int register_map_target(const char *name, dm_ctr_fn ctr,
  * io-err: always fails an io, useful for bringing
  * up LV's that have holes in them.
  */
-static int io_err_ctr(offset_t b, offset_t e, struct dm_table *t,
+static int io_err_ctr(struct dm_table *t,
+		      offset_t b, offset_t e,
 		      const char *cb, const char *ce, void **result)
 {
 	/* this takes no arguments */
@@ -93,7 +94,7 @@ static int io_err_ctr(offset_t b, offset_t e, struct dm_table *t,
 	return 0;
 }
 
-static void io_err_dtr(void *c)
+static void io_err_dtr(struct dm_table *t, void *c)
 {
 	/* empty */
 }
@@ -116,7 +117,8 @@ struct linear_c {
  * construct a linear mapping.
  * <major> <minor> <offset>
  */
-static int linear_ctr(offset_t low, offset_t high, struct dm_table *t,
+static int linear_ctr(struct dm_table *t,
+		      offset_t low, offset_t high,
 		      const char *cb, const char *ce, void **result)
 {
 	struct linear_c *lc;
@@ -149,8 +151,10 @@ static int linear_ctr(offset_t low, offset_t high, struct dm_table *t,
 	return 0;
 }
 
-static void linear_dtr(void *c)
+static void linear_dtr(struct dm_table *t, void *c)
 {
+	struct linear_c *lc = (struct linear_c *) c;
+	dm_table_remove_device(t, lc->dev);
 	kfree(c);
 }
 
@@ -171,7 +175,7 @@ int dm_target_init(void)
 	int ret;
 
 #define xx(n, fn) \
-	if ((ret = register_map_target(n, \
+	if ((ret = dm_register_target(n, \
              fn ## _ctr, fn ## _dtr, fn ## _map) < 0)) return ret
 
 	xx("io-err", io_err);
@@ -180,3 +184,5 @@ int dm_target_init(void)
 
 	return 0;
 }
+
+EXPORT_SYMBOL(dm_register_target);

driver/device-mapper/dm.c

@@ -216,12 +216,12 @@ static int blk_ioctl(struct inode *inode, struct file *file,
 	return 0;
 }
 
-inline static struct io_hook *alloc_io_hook(void)
+static inline struct io_hook *alloc_io_hook(void)
 {
 	return kmem_cache_alloc(_io_hook_cache, GFP_NOIO);
 }
 
-inline static void free_io_hook(struct io_hook *ih)
+static inline void free_io_hook(struct io_hook *ih)
 {
 	kmem_cache_free(_io_hook_cache, ih);
 }
@@ -231,12 +231,12 @@ inline static void free_io_hook(struct io_hook *ih)
  * their own slab, I say no for now since they are
  * only used when the device is suspended.
  */
-inline static struct deferred_io *alloc_deferred(void)
+static inline struct deferred_io *alloc_deferred(void)
 {
 	return kmalloc(sizeof(struct deferred_io), GFP_NOIO);
 }
 
-inline static void free_deferred(struct deferred_io *di)
+static inline void free_deferred(struct deferred_io *di)
 {
 	kfree(di);
 }
@@ -289,7 +289,7 @@ static int queue_io(struct mapped_device *md, struct buffer_head *bh, int rw)
 /*
  * do the bh mapping for a given leaf
  */
-inline static int __map_buffer(struct mapped_device *md,
+static inline int __map_buffer(struct mapped_device *md,
 			       struct buffer_head *bh, int leaf)
 {
 	dm_map_fn fn;
@@ -336,7 +336,7 @@ inline static int __map_buffer(struct mapped_device *md,
 /*
  * search the btree for the correct target.
  */
-inline static int __find_node(struct dm_table *t, struct buffer_head *bh)
+static inline int __find_node(struct dm_table *t, struct buffer_head *bh)
 {
 	int i = 0, l, r = 0;
 	offset_t *node;

driver/device-mapper/dm.h

@@ -147,6 +147,8 @@ enum {
  */
 struct dev_list {
 	kdev_t dev;
+	atomic_t count;
+
 	struct block_device *bd;
 	struct dev_list *next;
 };
@@ -260,12 +262,12 @@ int dm_fs_remove(struct mapped_device *md);
 
 #define WARN(f, x...) printk(KERN_WARNING "device-mapper: " f "\n" , ## x)
 
-inline static int is_active(struct mapped_device *md)
+static inline int is_active(struct mapped_device *md)
 {
 	return test_bit(DM_ACTIVE, &md->state);
 }
 
-inline static const char *eat_space(const char *b, const char *e)
+static inline const char *eat_space(const char *b, const char *e)
 {
 	while(b != e && isspace((int) *b))
 		b++;
@@ -273,7 +275,7 @@ inline static const char *eat_space(const char *b, const char *e)
 	return b;
 }
 
-inline static int get_number(const char **b, const char *e, unsigned int *n)
+static inline int get_number(const char **b, const char *e, unsigned int *n)
 {
 	char *ptr;
 	*b = eat_space(*b, e);