Usage of sizeof in m_devget in 4.4BSD-Lite?

Question

In the line 605 to 608 of m_devget, there is a code segment look like this

if (off) {
     cp += off + 2 * sizeof(u_short);
     totlen -= 2 * sizeof(u_short);
 }

What is the 2 * sizeof(u_short) for?

Please add a reference or context to your question so that it is understood by future readers. As it stands, it is not a complete example. — Michael Foukarakis, Apr 03 '15 at 14:13

score 0 · Answer 1 · answered Apr 03 '15 at 14:03

The function in question copies data from device memory into an mbuf structure.

If off (initialised to the off0 parameter) is non-zero, it means that the packet being processed is trailer-encapsulated, so the code has to skip the type and length fields. Each of those fields are 16-bit wide. The code assumes u_short is 16-bit wide, as well.

Usage of sizeof in m_devget in 4.4BSD-Lite?

1 Answers1