btrfs: add cancellable chunk relocation support

Add support code that will allow canceling relocation on the chunk
granularity. This is different and independent of balance, that also
uses relocation but is a higher level operation and manages it's own
state and pause/cancellation requests.

Relocation is used for resize (shrink) and device deletion so this will
be a common point to implement cancellation for both. The context is
entirely in btrfs_relocate_block_group and btrfs_recover_relocation,
enclosing one chunk relocation. The status bit is set and unset between
the chunks. As relocation can take long, the effects may not be
immediate and the request and actual action can slightly race.

The fs_info::reloc_cancel_req is only supposed to be increased and does
not pair with decrement like fs_info::balance_cancel_req.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4049f533e35e..b7c36aad45ef 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -565,6 +565,12 @@ enum {
 	 */
 	BTRFS_FS_BALANCE_RUNNING,
 
+	/*
+	 * Indicate that relocation of a chunk has started, it's set per chunk
+	 * and is toggled between chunks.
+	 */
+	BTRFS_FS_RELOC_RUNNING,
+
 	/* Indicate that the cleaner thread is awake and doing something. */
 	BTRFS_FS_CLEANER_RUNNING,
 
@@ -871,6 +877,9 @@ struct btrfs_fs_info {
 	struct btrfs_balance_control *balance_ctl;
 	wait_queue_head_t balance_wait_q;
 
+	/* Cancellation requests for chunk relocation */
+	atomic_t reloc_cancel_req;
+
 	u32 data_chunk_allocations;
 	u32 metadata_ratio;