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>