That structure is our ultimate object for all __btrfs_map_block()
related functions. We have some hard to understand members, like
tgtdev_map, but without any comments.
This patch will improve the situation:
- Add extra comments for num_stripes, mirror_num, num_tgtdevs and
tgtdev_map[]
Especially for the last two members, add a dedicated (thus very long)
comments for them, with example to explain it.
- Shrink those int members to u16.
In fact our on-disk format is only using u16 for num_stripes, thus
no need to use int at all.
Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>