How to get serial device output buffer size ?

How to get serial device (rs-232, /dev/ser1)
input & output buffer size in qnx 4.25 ?

In qnx 6 the code to get these buffs size is:

int in_size, out_size;
devctl(dev_fd, DCMD_CHR_ISSIZE, &in_size, sizeof in_size, NULL);
devctl(dev_fd, DCMD_CHR_OSSIZE, &out_size, sizeof out_size, NULL);