Subject: Re: [PATCH net-next 1/5] libbpf: add ability to guess program type
 based on section name
To: Roman Gushchin <guro@fb.com>, netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, ast@kernel.org,
        daniel@iogearbox.net, jakub.kicinski@netronome.com, kafai@fb.com
References: <20171130134302.2840-1-guro@fb.com>
 <20171130134302.2840-2-guro@fb.com>
From: Quentin Monnet <quentin.monnet@netronome.com>
Message-ID: <614dc433-9445-52df-a202-f7cb1cb79ca1@netronome.com>
Date: Fri, 1 Dec 2017 10:22:57 +0000
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Thanks Roman!
One comment in-line.

2017-11-30 13:42 UTC+0000 ~ Roman Gushchin <guro@fb.com>
> The bpf_prog_load() function will guess program type if it's not
> specified explicitly. This functionality will be used to implement
> loading of different programs without asking a user to specify
> the program type. In first order it will be used by bpftool.
> 
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
> ---
>  tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 5aa45f89da93..9f2410beaa18 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1721,6 +1721,41 @@ BPF_PROG_TYPE_FNS(tracepoint, BPF_PROG_TYPE_TRACEPOINT);
>  BPF_PROG_TYPE_FNS(xdp, BPF_PROG_TYPE_XDP);
>  BPF_PROG_TYPE_FNS(perf_event, BPF_PROG_TYPE_PERF_EVENT);
>  
> +static enum bpf_prog_type bpf_program__guess_type(struct bpf_program *prog)
> +{
> +	if (!prog->section_name)
> +		goto err;
> +
> +	if (strncmp(prog->section_name, "socket", 6) == 0)
> +		return BPF_PROG_TYPE_SOCKET_FILTER;
> +	if (strncmp(prog->section_name, "kprobe/", 7) == 0)
> +		return BPF_PROG_TYPE_KPROBE;
> +	if (strncmp(prog->section_name, "kretprobe/", 10) == 0)
> +		return BPF_PROG_TYPE_KPROBE;
> +	if (strncmp(prog->section_name, "tracepoint/", 11) == 0)
> +		return BPF_PROG_TYPE_TRACEPOINT;
> +	if (strncmp(prog->section_name, "xdp", 3) == 0)
> +		return BPF_PROG_TYPE_XDP;
> +	if (strncmp(prog->section_name, "perf_event", 10) == 0)
> +		return BPF_PROG_TYPE_PERF_EVENT;
> +	if (strncmp(prog->section_name, "cgroup/skb", 10) == 0)
> +		return BPF_PROG_TYPE_CGROUP_SKB;
> +	if (strncmp(prog->section_name, "cgroup/sock", 11) == 0)
> +		return BPF_PROG_TYPE_CGROUP_SOCK;
> +	if (strncmp(prog->section_name, "cgroup/dev", 10) == 0)
> +		return BPF_PROG_TYPE_CGROUP_DEVICE;
> +	if (strncmp(prog->section_name, "sockops", 7) == 0)
> +		return BPF_PROG_TYPE_SOCK_OPS;
> +	if (strncmp(prog->section_name, "sk_skb", 6) == 0)
> +		return BPF_PROG_TYPE_SK_SKB;

I do not really like these hard-coded lengths, maybe we could work out
something nicer with a bit of pre-processing work? Perhaps something like:

#define SOCKET_FILTER_SEC_PREFIX "socket"
#define KPROBE_SEC_PREFIX "kprobe/"
[…]

#define TRY_TYPE(string, __TYPE)				\
	do {							\
		if (!strncmp(string, __TYPE ## _SEC_PREFIX,	\
			     sizeof(__TYPE ## _SEC_PREFIX)))	\
			return BPF_PROG_TYPE_ ## __TYPE;	\
	} while(0);

static enum bpf_prog_type bpf_program__guess_type(struct bpf_program *prog)
{
	if (!prog->section_name)
		goto err;

	TRY_TYPE(prog->section_name, SOCKET_FILTER);
	TRY_TYPE(prog->section_name, KPROBE);
	[…]

err:
	pr_warning("…",
	           prog->section_name);

	return BPF_PROG_TYPE_UNSPEC;
}

> +
> +err:
> +	pr_warning("failed to guess program type based on section name %s\n",
> +		   prog->section_name);
> +
> +	return BPF_PROG_TYPE_UNSPEC;
> +}
> +
>  int bpf_map__fd(struct bpf_map *map)
>  {
>  	return map ? map->fd : -EINVAL;