btrfs: update documentation for a block group's bg_list member

Currently we are only documenting two uses of the bg_list member of a
block group, but there two more:

1) To track deleted block groups for discard purposes, introduced in
   commit e33e17ee1098 ("btrfs: add missing discards when unpinning
   extents with -o discard");

2) To track block groups for automatic reclaim, introduced more recently
   by commit 18bb8bbf13c1 ("btrfs: zoned: automatically reclaim zones")

So document those two other use cases.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index cc0e4b3..f204add 100644 (file)
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -162,7 +162,14 @@ struct btrfs_block_group {
         */
        struct list_head cluster_list;
 
-       /* For delayed block group creation or deletion of empty block groups */
+       /*
+        * Used for several lists:
+        *
+        * 1) struct btrfs_fs_info::unused_bgs
+        * 2) struct btrfs_fs_info::reclaim_bgs
+        * 3) struct btrfs_transaction::deleted_bgs
+        * 4) struct btrfs_trans_handle::new_bgs
+        */
        struct list_head bg_list;
 
        /* For read-only block groups */