Merge branch 'macb-add-pad-and-fcs-support'

Merge branch 'macb-add-pad-and-fcs-support'

Claudiu Beznea says:

====================
net: macb: add pad and fcs support

In [1] it was reported that UDP checksum is offloaded to hardware no mather
it was previously computed in software or not. The proposal on [1] was to
disable TX checksum offload.

This series (mostly patch 3/3) address the issue described at [1] by
setting NOCRC bit to TX buffer descriptor for SKBs that arrived from
networking stack with checksum computed. For these packets padding and FCS
need to be added (hardware doesn't compute them if NOCRC bit is set). The
minimum packet size that hardware expects is 64 bytes (including FCS).
This feature could not be used in case of GSO, so, it was used only for
no GSO SKBs.

For SKBs wich requires padding and FCS computation macb_pad_and_fcs()
checks if there is enough headroom and tailroom in SKB to avoid copying
SKB structure. Since macb_pad_and_fcs() may change SKB the
macb_pad_and_fcs() was places in macb_start_xmit() b/w macb_csum_clear()
and skb_headlen() calls.

This patch was tested with pktgen in kernel tool in a script like this:
(pktgen_sample01_simple.sh is at [2]):

minSize=1
maxSize=1500

for i in `seq $minSize $maxSize` ; do
	copy="$(shuf -i 1-2000 -n 1)"
	./pktgen_sample01_simple.sh -i eth0 \
		-m <dst-mac-addr> -d <dst-ip-addr> -x -s $i -c $copy
done

minStep=1
maxStep=200
for i in `seq $minStep $maxStep` ; do
	copy="$(shuf -i 1-2000 -n 1)"
	size="$(shuf -i 1-1500 -n 1)"
	./pktgen_sample01_simple.sh -i eth0 \
		-m <dst-mac-addr> -d <dst-ip-addr> -x -s $size -c $copy
done

Changes since RFC:
- in patch 3/3 order local variables by their lenght (reverse christmas tree
  format)

[1] https://www.spinics.net/lists/netdev/msg505065.html
[2] https://github.com/netoptimizer/network-testing/blob/master/pktgen/pktgen_sample01_simple.sh
====================

Signed-off-by: David S. Miller <davem@davemloft.net>