Re: [PATCH net-next v4 10/10] tsnep: Support XDP BPF program setup

On Wed, 11 Jan 2023 20:11:44 +0100 Gerhard Engleder wrote:

I agree with you that this pattern is bad. Most XDP BPF program setup do
it like that, but this is of course no valid argument.

In the last review round I made the following suggestion (but got no
reply so far):

What about always using 'XDP_PACKET_HEADROOM' as offset in the RX
buffer? The offset 'NET_SKB_PAD + NET_IP_ALIGN' would not even be used
if XDP is not enabled. Changing this offset is the only task to be done
at the first XDP BFP prog setup call. By always using this offset
no

	close()
	change config
	open()

pattern is needed. As a result no handling for failed open() is needed
and __TSNEP_DOWN is not needed. Simpler code with less problems in my
opinion.

The only problem could be that NET_IP_ALIGN is not used, but
NET_IP_ALIGN is 0 anyway on the two platforms (x86, arm64) where this
driver is used.

You can add NET_IP_ALIGN as well, AFAIU XDP_PACKET_HEADROOM is more 
of a minimum headroom than an exact one.

The other thing off the top of my head is that you'll always need to
DMA map the Rx buffers BIDIR.

If those are acceptable for your platform / applications then indeed
seems like an easy way out of the problem!