[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>

2 files changed, 44 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 10c9439635ca..827b648fac50 100644
--- a/drivers/md/dm-table.c
+++ b/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;
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 010c8c5eeb37..61103d2bc244 100644
--- a/include/linux/device-mapper.h
+++ b/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 */