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

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Message-ID: <20160403063834.GE21980@gmail.com>
Date:	Sat, 2 Apr 2016 23:38:35 -0700
From:	Brenden Blanco <bblanco@...mgrid.com>
To:	Johannes Berg <johannes@...solutions.net>
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, Apr 02, 2016 at 08:40:55PM +0200, Johannes Berg wrote:
> On Fri, 2016-04-01 at 18:21 -0700, Brenden Blanco wrote:
> 
> > +static int mlx4_bpf_set(struct net_device *dev, int fd)
> > +{
> [...]
> > +		if (prog->type != BPF_PROG_TYPE_PHYS_DEV) {
> > +			bpf_prog_put(prog);
> > +			return -EINVAL;
> > +		}
> > +	}
> 
> Why wouldn't this check be done in the generic code that calls
> ndo_bpf_set()?
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?

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.
> 
> johannes