Re: [PATCH net-next 1/5] libbpf: add ability to guess program type based on section name

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Fri, 1 Dec 2017 10:22:57 +0000, Quentin Monnet wrote:
> 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);

I like the suggestion, but I think return and goto statements hiding
inside macros are slightly frowned upon in the netdev.  Perhaps just 
a macro that wraps the strncmp() with sizeof would be enough?  Without
the return inside?

> 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;
> }