netdev - Re: [PATCH bpf-next v2 2/2] samples/bpf: Add xdp_sample

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Date:   Wed, 06 Jun 2018 14:28:43 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     David Beckett <david.beckett@...ronome.com>, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/2] samples/bpf: Add xdp_sample_pkts example

David Beckett <david.beckett@...ronome.com> writes:

> On 04/06/18 17:33, Toke Høiland-Jørgensen wrote:
>> +
>> +#define SAMPLE_SIZE 64ul
>> +
> The program currently cannot sample minimum sized packets, as the 4 Byte 
> crc checksum isnt present in ctx,
> may be better to use 60ul sample size to allow for these packets to be 
> processed?

Right. However, this also reminds me that I wanted to make the sampling
size dynamic, so it is possible to dump packets that are smaller than
the configured SAMPLE_SIZE. Will fix :)

>> +	if (data + SAMPLE_SIZE < data_end) {
>> +		/* The XDP perf_event_output handler will use the upper 32 bits
>> +		 * of the flags argument as a number of bytes to include of the
> I may be wrong on this but should this also be <= to allow for packets 
> at SAMPLE_SIZE to be sampled?

Yes, you are right, but that goes away with the change I mentioned above.

-Toke