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

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Message-ID: <20171204132155.GA8165@castle.DHCP.thefacebook.com>
Date:   Mon, 4 Dec 2017 13:22:03 +0000
From:   Roman Gushchin <guro@...com>
To:     Quentin Monnet <quentin.monnet@...ronome.com>
CC:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>, <ast@...nel.org>, <daniel@...earbox.net>,
        <kafai@...com>
Subject: Re: [PATCH net-next 1/5] libbpf: add ability to guess program type
 based on section name

On Mon, Dec 04, 2017 at 01:12:33PM +0000, Quentin Monnet wrote:
> 2017-12-04 12:34 UTC+0000 ~ Roman Gushchin <guro@...com>
> > On Fri, Dec 01, 2017 at 02:46:06PM -0800, Jakub Kicinski wrote:
> >> 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@...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@...com>
> >>>> Cc: Alexei Starovoitov <ast@...nel.org>
> >>>> Cc: Daniel Borkmann <daniel@...earbox.net>
> >>>> Cc: Jakub Kicinski <jakub.kicinski@...ronome.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?
> > 
> > Hm, I'm not sure that using macroses here makes the code much easier to read.
> > Maybe we can use just strcmp() instead?
> > As we compare with hardcoded strings, there is no real difference.
> > Something like this:
> > 
> > if (!strcmp("socket", prog->section_name))
> > 	return BPF_PROG_TYPE_SOCKET_FILTER;
> > if (!strcmp("kprobe/", prog->section_name))
> > 	return BPF_PROG_TYPE_KPROBE;
> > if (!strcmp("kretprobe/", prog->section_name))
> > 	return BPF_PROG_TYPE_KPROBE;
> > if (!strcmp("tracepoint/", prog->section_name))
> > 	return BPF_PROG_TYPE_TRACEPOINT;
> > if (!strcmp("xdp", prog->section_name))
> > 	return BPF_PROG_TYPE_XDP;
> > if (!strcmp("perf_event", prog->section_name))
> > 	return BPF_PROG_TYPE_PERF_EVENT;
> > if (!strcmp("cgroup/skb", prog->section_name))
> > 	return BPF_PROG_TYPE_CGROUP_SKB;
> > if (!strcmp("cgroup/sock", prog->section_name))
> > 	return BPF_PROG_TYPE_CGROUP_SOCK;
> > if (!strcmp("cgroup/dev", prog->section_name))
> > 	return BPF_PROG_TYPE_CGROUP_DEVICE;
> > if (!strcmp("sockops", prog->section_name))
> > 	return BPF_PROG_TYPE_SOCK_OPS;
> > if (!strcmp("sk_skb", prog->section_name))
> > 	return BPF_PROG_TYPE_SK_SKB;
> > 
> > Thanks!
> > 
> 
> I do not believe this works. For kprobes for example, the idea was to
> compare "kprobe/" with only the beginning of prog->section_name, right?
> The string prog->section_name is supposed to be longer than this (e.g.
> "kprobe/sys_write"), and strcmp() will not detect a match in this case.

Ah, true, I've missed this part.
Ok, I'll try to master something with macroses.

Thanks!