CMDR_OFF
cdb_off = CMDR_OFF + cmd_head + base_command_size;
mb = vzalloc(udev->cmdr_size + CMDR_OFF);
udev->cmdr = (void *)mb + CMDR_OFF;
udev->data_off = udev->cmdr_size + CMDR_OFF;
udev->mmap_pages = (data_size + udev->cmdr_size + CMDR_OFF) >> PAGE_SHIFT;
mb->cmdr_off = CMDR_OFF;
info->mem[0].size = data_size + udev->cmdr_size + CMDR_OFF;
udev->cmdr_size = (val << 20) - CMDR_OFF;
(udev->cmdr_size + CMDR_OFF) >> 20);
(udev->cmdr_size + CMDR_OFF) >> 20);
#define CMDR_SIZE_DEF (MB_CMDR_SIZE_DEF - CMDR_OFF)