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>

2 files changed, 27 insertions, 11 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e53835b88594..5f01dad4b696 100644
--- 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 5836327ba5dd..5c3ff6d02fd7 100644
--- 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;