netdev - Re: [PATCH bpf-next 2/2] bpftool: show flow

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Date:   Tue, 23 Apr 2019 17:13:07 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net, quentin.monnet@...ronome.com
Subject: Re: [PATCH bpf-next 2/2] bpftool: show flow_dissector attachment
 status

On 04/23, Jakub Kicinski wrote:
> On Tue, 23 Apr 2019 16:22:00 -0700, Stanislav Fomichev wrote:
> > +static int query_flow_dissector(struct bpf_attach_info *attach_info)
> > +{
> > +	__u32 prog_ids[1] = {0};
> > +	__u32 prog_cnt = ARRAY_SIZE(prog_ids);
> > +	__u32 attach_flags;
> > +	int fd;
> > +	int err;
> 
> reverse christmas tree, please :)
> 
> Move the init into the code if necessary.
Ack, initialization didn't let me do that. But I think I can drop it, I
don't look prog_cnt in the syscall, maybe I should :-/

> > +	fd = open("/proc/self/ns/net", O_RDONLY);
> > +	if (fd < 0) {
> > +		p_err("can't open /proc/self/ns/net: %d",
> > +		      strerror(errno));
> > +		return -1;
> > +	}
> > +	err = bpf_prog_query(fd, BPF_FLOW_DISSECTOR, 0,
> > +			     &attach_flags, prog_ids, &prog_cnt);
> > +	close(fd);
> > +	if (err) {
> > +		if (errno == EINVAL) {
> > +			/* Older kernel's don't support querying
> > +			 * flow dissector programs.
> > +			 */
> > +			return 0;
> > +		}
> > +		p_err("can't query prog: %s", strerror(errno));
> > +		return -1;
> > +	}
> > +
> > +	if (prog_cnt == 1)
> > +		attach_info->flow_dissector_id = prog_ids[0];
> 
> So the count can only be 0 or 1?  Hm.
Yes, its either attached or not; there is nothing like prog_array.

> > +	return 0;
> > +}