extent_logical_end
size = extent_logical_end(sbi, &ac->ac_o_ex);
loff_t orig_goal_end = extent_logical_end(sbi, &ex);
loff_t o_ex_end = extent_logical_end(sbi, &ac->ac_o_ex);
if (o_ex_end <= extent_logical_end(sbi, &ex))
BUG_ON(extent_logical_end(sbi, &ex) > orig_goal_end);
size = extent_logical_end(sbi, &ac->ac_o_ex);