[PATCH] dm: create error table

Add a library function dm_create_error_table() to create a table that rejects
any I/O sent to a device with EIO.
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/dm-table.c

@@ -237,6 +237,44 @@ int dm_table_create(struct dm_table **result, int mode,
 	return 0;
 }
 
+int dm_create_error_table(struct dm_table **result, struct mapped_device *md)
+{
+	struct dm_table *t;
+	sector_t dev_size = 1;
+	int r;
+
+	/*
+	 * Find current size of device.
+	 * Default to 1 sector if inactive.
+	 */
+	t = dm_get_table(md);
+	if (t) {
+		dev_size = dm_table_get_size(t);
+		dm_table_put(t);
+	}
+
+	r = dm_table_create(&t, FMODE_READ, 1, md);
+	if (r)
+		return r;
+
+	r = dm_table_add_target(t, "error", 0, dev_size, NULL);
+	if (r)
+		goto out;
+
+	r = dm_table_complete(t);
+	if (r)
+		goto out;
+
+	*result = t;
+
+out:
+	if (r)
+		dm_table_put(t);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_create_error_table);
+
 static void free_devices(struct list_head *devices)
 {
 	struct list_head *tmp, *next;

include/linux/device-mapper.h

@@ -227,5 +227,11 @@ void dm_table_event(struct dm_table *t);
  */
 int dm_swap_table(struct mapped_device *md, struct dm_table *t);
 
+/*
+ * Prepare a table for a device that will error all I/O.
+ * To make it active, call dm_suspend(), dm_swap_table() then dm_resume().
+ */
+int dm_create_error_table(struct dm_table **result, struct mapped_device *md);
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_DEVICE_MAPPER_H */