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

[Quentin Monnet]

2017-12-04 12:34 UTC+0000 ~ Roman Gushchin <guro@xxxxxx>
> 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@xxxxxx>
>>>> 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@xxxxxx>
>>>> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
>>>> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
>>>> Cc: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
>>>> ---
>>>>  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/"
>>> [â]
>>>
>>> #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.

Quentin