Btrfs: When shrinking, only update disk size on success

Previously, we updated a device's size prior to attempting a shrink
operation.  This patch moves the device resizing logic to only happen if
the shrink completes successfully.  In the process, it introduces a new
field to btrfs_device -- disk_total_bytes -- to track the on-disk size.

Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e53835b..5f01dad 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1543,7 +1543,7 @@ static noinline int btrfs_update_device(struct btrfs_trans_handle *trans,
        btrfs_set_device_io_align(leaf, dev_item, device->io_align);
        btrfs_set_device_io_width(leaf, dev_item, device->io_width);
        btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
-       btrfs_set_device_total_bytes(leaf, dev_item, device->total_bytes);
+       btrfs_set_device_total_bytes(leaf, dev_item, device->disk_total_bytes);
        btrfs_set_device_bytes_used(leaf, dev_item, device->bytes_used);
        btrfs_mark_buffer_dirty(leaf);
 
@@ -1940,14 +1940,6 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
        device->total_bytes = new_size;
        if (device->writeable)
                device->fs_devices->total_rw_bytes -= diff;
-       ret = btrfs_update_device(trans, device);
-       if (ret) {
-               unlock_chunks(root);
-               btrfs_end_transaction(trans, root);
-               goto done;
-       }
-       WARN_ON(diff > old_total);
-       btrfs_set_super_total_bytes(super_copy, old_total - diff);
        unlock_chunks(root);
        btrfs_end_transaction(trans, root);
 
@@ -1979,7 +1971,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
                length = btrfs_dev_extent_length(l, dev_extent);
 
                if (key.offset + length <= new_size)
-                       goto done;
+                       break;
 
                chunk_tree = btrfs_dev_extent_chunk_tree(l, dev_extent);
                chunk_objectid = btrfs_dev_extent_chunk_objectid(l, dev_extent);
@@ -1992,6 +1984,26 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
                        goto done;
        }
 
+       /* Shrinking succeeded, else we would be at "done". */
+       trans = btrfs_start_transaction(root, 1);
+       if (!trans) {
+               ret = -ENOMEM;
+               goto done;
+       }
+       lock_chunks(root);
+
+       device->disk_total_bytes = new_size;
+       /* Now btrfs_update_device() will change the on-disk size. */
+       ret = btrfs_update_device(trans, device);
+       if (ret) {
+               unlock_chunks(root);
+               btrfs_end_transaction(trans, root);
+               goto done;
+       }
+       WARN_ON(diff > old_total);
+       btrfs_set_super_total_bytes(super_copy, old_total - diff);
+       unlock_chunks(root);
+       btrfs_end_transaction(trans, root);
 done:
        btrfs_free_path(path);
        return ret;
@@ -3076,7 +3088,8 @@ static int fill_device_from_item(struct extent_buffer *leaf,
        unsigned long ptr;
 
        device->devid = btrfs_device_id(leaf, dev_item);
-       device->total_bytes = btrfs_device_total_bytes(leaf, dev_item);
+       device->disk_total_bytes = btrfs_device_total_bytes(leaf, dev_item);
+       device->total_bytes = device->disk_total_bytes;
        device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
        device->type = btrfs_device_type(leaf, dev_item);
        device->io_align = btrfs_device_io_align(leaf, dev_item);

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 5836327..5c3ff6d 100644 (file)
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -61,6 +61,9 @@ struct btrfs_device {
        /* size of the device */
        u64 total_bytes;
 
+       /* size of the disk */
+       u64 disk_total_bytes;
+
        /* bytes used */
        u64 bytes_used;