hfsplus_min_io_size
buf = kmalloc(hfsplus_min_io_size(sb), GFP_KERNEL);
int buf_size = hfsplus_min_io_size(sb);
sbi->s_vhdr_buf = kmalloc(hfsplus_min_io_size(sb), GFP_KERNEL);
sbi->s_backup_vhdr_buf = kmalloc(hfsplus_min_io_size(sb), GFP_KERNEL);
u64 io_size = hfsplus_min_io_size(sb);