netdev - Re: [PATCH v2 net-next 8/9] bpf: nfp: Report bpf_prog ID during XDP_QUERY

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Date:   Tue, 13 Jun 2017 19:19:50 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>
Subject: Re: [PATCH v2 net-next 8/9] bpf: nfp: Report bpf_prog ID during
 XDP_QUERY_PROG

On Tue, 13 Jun 2017 17:37:50 -0700, Martin KaFai Lau wrote:
> On Tue, Jun 13, 2017 at 04:52:32PM -0700, Jakub Kicinski wrote:
> > On Tue, 13 Jun 2017 14:08:40 -0700, Martin KaFai Lau wrote:  
> > > -	case XDP_QUERY_PROG:
> > > -		xdp->prog_attached = !!nn->dp.xdp_prog;
> > > +	case XDP_QUERY_PROG: {
> > > +		const struct bpf_prog *xdp_prog;
> > > +
> > > +		xdp_prog = nn->dp.xdp_prog;
> > > +		if (xdp_prog) {
> > > +			xdp->prog_id = xdp_prog->aux->id;
> > > +			xdp->prog_attached = true;
> > > +		} else {
> > > +			xdp->prog_id = 0;
> > > +			xdp->prog_attached = false;
> > > +		}
> > >  		return 0;
> > > +	}  
> >
> > I'm sorry to nit pick but it could be done on a single line:
> >
> > 	case XDP_QUERY_PROG:
> > 		xdp->prog_attached = !!nn->dp.xdp_prog;
> > +		xdp->prog_id = nn->dp.xdp_prog ? nn->dp.xdp_prog->aux->id : 0;
> >  		return 0;
> >  	default:
> >  		return -EINVAL;  
> OK...
> 
> >
> >
> > What would be even cooler is a helper like this:
> >
> > static inline u32 bpf_prog_id(struct bpf_prog *prog)
> > {
> > 	if (!prog)
> > 		return 0;
> > 	return prog->aux->id;
> > }
> >
> > in linux/bpf.h.
> Good idea.

You may actually have to add that into a source file, because bpf.h
does not know the definition of struct bpf_prog :(

> I had been thinking I may not need to change all the
> drivers now.  I did that in v1 because I wanted to remove
> prog_attached which is redundant.  With prog_attached reserved,
> prog_id is optional.
> 
> Considering I don't have all the hardwares to test it,  I think
> it may make more sense for me to only change the HW that I have?

Coccinelle to the rescue?

@@
expression ex;
@@
		xdp->prog_attached = !!(ex);
+		xdp->prog_id = bpf_prog_id(ex);

> > In patch 1 I would be tempted to add a new command for getting the prog
> > id, instead of muxing through query to avoid the output parameter?  But
> > I'm OK with the code as is, its just a preference rather than an objection :)  
> Have one command to query a new field?  I think it is overkilled.

Perhaps.  I was just trying to come up with a way of avoiding the
output parameter.  It seems hard to do unless we stop using
__dev_xdp_attached() for filling in the netlink attributes.  I'm OK
with leaving the code as is..