Re: [PATCH v21 bpf-next 18/23] libbpf: Add SEC name for xdp_mb programs

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 12/01/2022 23.04, Toke Høiland-Jørgensen wrote:
> Lorenzo Bianconi <lorenzo.bianconi@redhat.com> writes:
> 
>>> On Wed, Jan 12, 2022 at 11:47 AM Alexei Starovoitov
>>> <alexei.starovoitov@gmail.com> wrote:
>>>>
>>>> On Wed, Jan 12, 2022 at 11:21 AM Andrii Nakryiko
>>>> <andrii.nakryiko@gmail.com> wrote:
>>>>>
>>>>> On Wed, Jan 12, 2022 at 11:17 AM Alexei Starovoitov
>>>>> <alexei.starovoitov@gmail.com> wrote:
>>>>>>
>>>>>> On Wed, Jan 12, 2022 at 10:24 AM Andrii Nakryiko
>>>>>> <andrii.nakryiko@gmail.com> wrote:
>>>>>>>
>>>>>>> On Wed, Jan 12, 2022 at 10:18 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
>>>>>>>>
>>>>>>>>> On Sun, Jan 9, 2022 at 7:05 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
>>>>>>>>>>
>>>>>>>>>> Introduce support for the following SEC entries for XDP multi-buff
>>>>>>>>>> property:
>>>>>>>>>> - SEC("xdp_mb/")
>>>>>>>>>> - SEC("xdp_devmap_mb/")
>>>>>>>>>> - SEC("xdp_cpumap_mb/")
>>>>>>>>>
>>>>>>>>> Libbpf seemed to went with .<suffix> rule (e.g., fentry.s for
>>>>>>>>> sleepable, seems like we'll have kprobe.multi or  something along
>>>>>>>>> those lines as well), so let's stay consistent and call this "xdp_mb",
>>>>>>>>> "xdp_devmap.mb", "xdp_cpumap.mb" (btw, is "mb" really all that
>>>>>>>>> recognizable? would ".multibuf" be too verbose?). Also, why the "/"
>>>>>>>>> part? Also it shouldn't be "sloppy" either. Neither expected attach
>>>>>>>>> type should be optional.  Also not sure SEC_ATTACHABLE is needed. So
>>>>>>>>> at most it should be SEC_XDP_MB, probably.
>>>>>>>>
>>>>>>>> ack, I fine with it. Something like:
>>>>>>>>
>>>>>>>>          SEC_DEF("lsm.s/",               LSM, BPF_LSM_MAC, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_lsm),
>>>>>>>>          SEC_DEF("iter/",                TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF, attach_iter),
>>>>>>>>          SEC_DEF("syscall",              SYSCALL, 0, SEC_SLEEPABLE),
>>>>>>>> +       SEC_DEF("xdp_devmap.multibuf",  XDP, BPF_XDP_DEVMAP, 0),
>>>>>>>>          SEC_DEF("xdp_devmap/",          XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE),
>>>>>>>> +       SEC_DEF("xdp_cpumap.multibuf",  XDP, BPF_XDP_CPUMAP, 0),
>>>>>>>>          SEC_DEF("xdp_cpumap/",          XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE),
>>>>>>>> +       SEC_DEF("xdp.multibuf",         XDP, BPF_XDP, 0),
>>>>>>>
>>>>>>> yep, but please use SEC_NONE instead of zero
>>>>>>>
>>>>>>>>          SEC_DEF("xdp",                  XDP, BPF_XDP, SEC_ATTACHABLE_OPT | SEC_SLOPPY_PFX),
>>>>>>>>          SEC_DEF("perf_event",           PERF_EVENT, 0, SEC_NONE | SEC_SLOPPY_PFX),
>>>>>>>>          SEC_DEF("lwt_in",               LWT_IN, 0, SEC_NONE | SEC_SLOPPY_PFX),
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Acked-by: Toke Hoiland-Jorgensen <toke@redhat.com>
>>>>>>>>>> Acked-by: John Fastabend <john.fastabend@gmail.com>
>>>>>>>>>> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
>>>>>>>>>> ---
>>>>>>>>>>   tools/lib/bpf/libbpf.c | 8 ++++++++
>>>>>>>>>>   1 file changed, 8 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>>>>>>>>>> index 7f10dd501a52..c93f6afef96c 100644
>>>>>>>>>> --- a/tools/lib/bpf/libbpf.c
>>>>>>>>>> +++ b/tools/lib/bpf/libbpf.c
>>>>>>>>>> @@ -235,6 +235,8 @@ enum sec_def_flags {
>>>>>>>>>>          SEC_SLEEPABLE = 8,
>>>>>>>>>>          /* allow non-strict prefix matching */
>>>>>>>>>>          SEC_SLOPPY_PFX = 16,
>>>>>>>>>> +       /* BPF program support XDP multi-buff */
>>>>>>>>>> +       SEC_XDP_MB = 32,
>>>>>>>>>>   };
>>>>>>>>>>
>>>>>>>>>>   struct bpf_sec_def {
>>>>>>>>>> @@ -6562,6 +6564,9 @@ static int libbpf_preload_prog(struct bpf_program *prog,
>>>>>>>>>>          if (def & SEC_SLEEPABLE)
>>>>>>>>>>                  opts->prog_flags |= BPF_F_SLEEPABLE;
>>>>>>>>>>
>>>>>>>>>> +       if (prog->type == BPF_PROG_TYPE_XDP && (def & SEC_XDP_MB))
>>>>>>>>>> +               opts->prog_flags |= BPF_F_XDP_MB;
>>>>>>>>>
>>>>>>>>> I'd say you don't even need SEC_XDP_MB flag at all, you can just check
>>>>>>>>> that prog->sec_name is one of "xdp.mb", "xdp_devmap.mb" or
>>>>>>>>> "xdp_cpumap.mb" and add the flag. SEC_XDP_MB doesn't seem generic
>>>>>>>>> enough to warrant a flag.
>>>>>>>>
>>>>>>>> ack, something like:
>>>>>>>>
>>>>>>>> +       if (prog->type == BPF_PROG_TYPE_XDP &&
>>>>>>>> +           (!strcmp(prog->sec_name, "xdp_devmap.multibuf") ||
>>>>>>>> +            !strcmp(prog->sec_name, "xdp_cpumap.multibuf") ||
>>>>>>>> +            !strcmp(prog->sec_name, "xdp.multibuf")))
>>>>>>>> +               opts->prog_flags |= BPF_F_XDP_MB;
>>>>>>>
>>>>>>> yep, can also simplify it a bit with strstr(prog->sec_name,
>>>>>>> ".multibuf") instead of three strcmp
>>>>>>
>>>>>> Maybe ".mb" ?
>>>>>> ".multibuf" is too verbose.
>>>>>> We're fine with ".s" for sleepable :)
>>>>>
>>>>>
>>>>> I had reservations about "mb" because the first and strong association
>>>>> is "megabyte", not "multibuf". And it's not like anyone would have
>>>>> tens of those programs in a single file so that ".multibuf" becomes
>>>>> way too verbose. But I don't feel too strongly about this, if the
>>>>> consensus is on ".mb".
>>>>
>>>> The rest of the patches are using _mb everywhere.
>>>> I would keep libbpf consistent.
>>>
>>> Should the rest of the patches maybe use "multibuf" instead of "mb"? I've been
>>> following this patch series closely and excitedly, and I keep having to remind
>>> myself that "mb" is "multibuff" and not "megabyte". If I'm having to correct
>>> myself while following the patch series, I'm wondering if future confusion is
>>> inevitable?
>>>
>>> But, is it enough confusion to be worth updating many other patches? I'm not
>>> sure.
>>>
>>> I agree consistency is more important than the specific term we're consistent
>>> on.
>>
>> I would prefer to keep the "_mb" postfix, but naming is hard and I am
>> polarized :)
> 
> I would lean towards keeping _mb as well, but if it does have to be
> changed why not _mbuf? At least that's not quite as verbose :)

I dislike the "mb" abbreviation as I forget it stands for multi-buffer.
I like the "mbuf" suggestion, even-though it conflicts with (Free)BSD 
mbufs (which is their SKB).

I prefer/support the .<suffix> idea from Andrii.
Which would then be ".mbuf" for my taste.

--Jesper
p.s. I like the bikeshed red, meaning I don't feel too strongly about this.