hammer_volume
struct hammer_volume *rootvol;
RB_HEAD(hammer_vol_rb_tree, hammer_volume);
RB_PROTOTYPE2(hammer_vol_rb_tree, hammer_volume, rb_node,
struct hammer_volume *volume;
RB_ENTRY(hammer_volume) rb_node;
struct hammer_volume;
RB_GENERATE2(hammer_vol_rb_tree, hammer_volume, rb_node,