Hi,
Here's a new patch that incorporates these comments. We now update
device->fs_devices->total_rw_bytes before the shrink, as Josef suggests,
and create a new field in btrfs_device to store an on-disk size that is
only updated on a successful shrink operation, as requested by Yan.
(Thanks, Yan and Josef, for the patient explanations.)
==
From: Chris Ball <c...@laptop.org>
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 <c...@laptop.org>
---
fs/btrfs/volumes.c | 35 ++++++++++++++++++++++++-----------
fs/btrfs/volumes.h | 3 +++
2 files changed, 27 insertions(+), 11 deletions(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 1316139..303b7d6 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1433,7 +1433,7 @@ 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);
@@ -1828,14 +1828,6 @@ 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);
@@ -1867,7 +1859,7 @@ 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);
@@ -1880,6 +1872,26 @@ 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;
@@ -2959,7 +2971,8 @@ 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 86c44e9..bf1ba75 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -52,6 +52,9 @@ struct btrfs_device {
/* size of the device */
u64 total_bytes;
+ /* size of the disk */
+ u64 disk_total_bytes;
+
/* bytes used */
u64 bytes_used;
--
1.6.1.3
- Chris.
--
Chris Ball <c...@laptop.org>
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