On Tue, 2014-02-25 at 09:51 +0000, David Laight wrote:

Do you need the union here?
If you don't attempt to convert the value to a u64 then code
is less likely to process it incorrectly.

Check the second patch, it uses :

	first_ackt.v64 = 0;
...
	last_ackt = skb->skb_mstamp;
	if (!first_ackt.v64)
		first_ackt = last_ackt;

...

	skb_mstamp_get(&now);
	if (first_ackt.v64) {
        	seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
        	ca_seq_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
	}


Without the union, it would be more expensive on 64bit arches,
or relying on the compiler to be smart enough.

Most modern ABI pass/return short structures in registers,
so the actual code should be similar if you return the struct
by value.

I am well aware of this, but this is a matter of taste, and I prefer
this more traditional way.