netdev - Re: [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program

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Date:	Mon, 04 Apr 2016 09:35:10 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Brenden Blanco <bblanco@...mgrid.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, tom@...bertland.com,
	alexei.starovoitov@...il.com, ogerlitz@...lanox.com,
	daniel@...earbox.net, john.fastabend@...il.com, brouer@...hat.com
Subject: Re: [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program

On Sat, 2016-04-02 at 23:38 -0700, Brenden Blanco wrote:
> 
> Having a common check makes sense. The tricky thing is that the type can
> only be checked after taking the reference, and I wanted to keep the
> scope of the prog brief in the case of errors. I would have to move the
> bpf_prog_get logic into dev_change_bpf_fd and pass a bpf_prog * into the
> ndo instead. Would that API look fine to you?

I can't really comment, I wasn't planning on using the API right now :)

However, what else is there that the driver could possibly do with the
FD, other than getting the bpf_prog?

> A possible extension of this is just to keep the bpf_prog * in the
> netdev itself and expose a feature flag from the driver rather than
> an ndo. But that would mean another 8 bytes in the netdev.

That also misses the signal to the driver when the program is
set/removed, so I don't think that works. I'd argue it's not really
desirable anyway though since I wouldn't expect a majority of drivers
to start supporting this.

johannes