[lwip-devel] [task #6849] Test how checksum on copy could be integrated into the stack

[Bill Auerbach]

Follow-up Comment #31, task #6849 (project lwip):

I think on RX, should we assume that there is full checksum offloading? If
the MAC is going to do this, I would expect it to do everything (as it does on
the PC, or seems to).  If the Ethernet driver is going to receive the packet
and then do the hardware checksum, it will have to do some parsing to decide
what to do and fill in the checksum in the correct places.  If it's to be done
any higher up than that, then inet_chksum can use the hardware to checksum a
pbuf (or pbuf chain) just as easily.  I guess the question is, where is the
copy we're checksumming on copy?  The callbacks provide a pointer to the
payload and I used to hardware copy to concatenate the packets or I've never
had to copy incoming data - just look at it and do something locally with it. 
It's been outgoing where I could do the checksum as the data was being
streamed.

It is a tough thing.  The data is coming through the MAC and the driver
first.  On TX you originate with the data so it's easier to do it first or do
it as the data is formed into packets to send.

Do you implement this so it works for some platforms or methods and not
others?  Or insist it work for all cases or none at all?  And how do you test?
 Just fill in the checksum using a software call to simulate having the
checksum already?

    _______________________________________________________

Reply to this item at:

  <http://savannah.nongnu.org/task/?6849>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.nongnu.org/