cvs commit: src/sys/net bpf.c

[Jung-uk Kim]

On Monday 24 July 2006 01:38 pm, David Malone wrote:
> > Thanks for taking care of this! It is not very desirable for the
> > same packet to have different timestamps associated with it
> > across different bpf peers. It certainly could cause a problem if
> > people are using timestamps to correlate events from different
> > programs on the same system.
>
> Indeed - calling microtime more than necessary and generating
> inconsistent timestamps just didn't seem good.
>
> I think jkim@ has interesting work related to this that might allow
> us to exploit hardware that does hardware timestamping of packets.
> It is some way down the road though.

Darn, I guess I have to finish the work now since you said it. ;-)  
The idea is simply to pass timeval to bpf_tap() from network drivers 
when it is available and bpf is attached.  (Something like 
bpf_*tap_ts()?)   Additionally we may add an ioctl for bpf to select 
timestamping method, e.g., microtime(9), getmicrotime(9), 
timestamping from lower layer, or no timestamping at all because we 
don't need (accurate) timestamps in many places.  For the 
hardware-based accurate timestamping, the big challenge is actually 
timecounter to timeval conversion, not the bpf API itself because we 
can only select one hardware timecounter at a given time if the 
controller does not give us timeval, bintime, or something similar.  
We have to come up with some API to register additional timecounter, 
which is not primary timecounter but synchronized with system uptime.  
On top of that, the timecounter in the given descriptor is not 
current timecounter.  So we need 'what time was it then', not 'what 
time is it now.'

Jung-uk Kim