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Message-ID: <5f26a827-0220-da23-f2fb-08f35ee7412e@isovalent.com>
Date:   Mon, 10 Oct 2022 09:40:02 +0100
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Subject: Re: [bpf-next v7 1/3] bpftool: Add auto_attach for bpf prog
 load|loadall
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To:     wangyufen <wangyufen@huawei.com>, ast@kernel.org,
        daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev,
        song@kernel.org, yhs@fb.com, john.fastabend@gmail.com,
        kpsingh@kernel.org, sdf@google.com, haoluo@google.com,
        jolsa@kernel.org, davem@davemloft.net, kuba@kernel.org,
        hawk@kernel.org, nathan@kernel.org, ndesaulniers@google.com,
        trix@redhat.com
Cc:     bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, llvm@lists.linux.dev
References: <1664277676-2228-1-git-send-email-wangyufen@huawei.com>
 <83307f48-bef0-bff8-e3b5-f8df7a592678@isovalent.com>
 <0242ccfe-53e5-5b9d-9fd9-73fa8bd0d7a4@huawei.com>
From:   Quentin Monnet <quentin@isovalent.com>
In-Reply-To: <0242ccfe-53e5-5b9d-9fd9-73fa8bd0d7a4@huawei.com>
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Sat Oct 08 2022 06:16:42 GMT+0100 ~ wangyufen <wangyufen@huawei.com>
> 
> 在 2022/10/1 0:26, Quentin Monnet 写道:
>> Tue Sep 27 2022 12:21:14 GMT+0100 ~ Wang Yufen <wangyufen@huawei.com>
>>> Add auto_attach optional to support one-step load-attach-pin_link.
>> Nit: Now "autoattach" instead of "auto_attach". Same in commit title.
> will change in v8, thanks.
>>
>>> For example,
>>>     $ bpftool prog loadall test.o /sys/fs/bpf/test autoattach
>>>
>>>     $ bpftool link
>>>     26: tracing  name test1  tag f0da7d0058c00236  gpl
>>>         loaded_at 2022-09-09T21:39:49+0800  uid 0
>>>         xlated 88B  jited 55B  memlock 4096B  map_ids 3
>>>         btf_id 55
>>>     28: kprobe  name test3  tag 002ef1bef0723833  gpl
>>>         loaded_at 2022-09-09T21:39:49+0800  uid 0
>>>         xlated 88B  jited 56B  memlock 4096B  map_ids 3
>>>         btf_id 55
>>>     57: tracepoint  name oncpu  tag 7aa55dfbdcb78941  gpl
>>>         loaded_at 2022-09-09T21:41:32+0800  uid 0
>>>         xlated 456B  jited 265B  memlock 4096B  map_ids 17,13,14,15
>>>         btf_id 82
>>>
>>>     $ bpftool link
>>>     1: tracing  prog 26
>>>         prog_type tracing  attach_type trace_fentry
>>>     3: perf_event  prog 28
>>>     10: perf_event  prog 57
>>>
>>> The autoattach optional can support tracepoints, k(ret)probes,
>>> u(ret)probes.
>>>
>>> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
>>> Signed-off-by: Wang Yufen <wangyufen@huawei.com>
>>> ---
>>> v6 -> v7: add info msg print and update doc for the skip program
>>> v5 -> v6: skip the programs not supporting auto-attach,
>>>       and change optional name from "auto_attach" to "autoattach"
>>> v4 -> v5: some formatting nits of doc
>>> v3 -> v4: rename functions, update doc, bash and do_help()
>>> v2 -> v3: switch to extend prog load command instead of extend perf
>>> v2:
>>> https://patchwork.kernel.org/project/netdevbpf/patch/20220824033837.458197-1-weiyongjun1@huawei.com/
>>> v1:
>>> https://patchwork.kernel.org/project/netdevbpf/patch/20220816151725.153343-1-weiyongjun1@huawei.com/
>>>   tools/bpf/bpftool/prog.c | 81
>>> ++++++++++++++++++++++++++++++++++++++++++++++--
>>>   1 file changed, 79 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
>>> index c81362a..84eced8 100644
>>> --- a/tools/bpf/bpftool/prog.c
>>> +++ b/tools/bpf/bpftool/prog.c
>>> @@ -1453,6 +1453,72 @@ static int do_run(int argc, char **argv)
>>>       return ret;
>>>   }
>>>   +static int
>>> +auto_attach_program(struct bpf_program *prog, const char *path)
>>> +{
>>> +    struct bpf_link *link;
>>> +    int err;
>>> +
>>> +    link = bpf_program__attach(prog);
>>> +    if (!link)
>>> +        return -1;
>>> +
>>> +    err = bpf_link__pin(link, path);
>>> +    if (err) {
>>> +        bpf_link__destroy(link);
>>> +        return err;
>>> +    }
>>> +    return 0;
>>> +}
>>> +
>>> +static int pathname_concat(const char *path, const char *name, char
>>> *buf)
>>> +{
>>> +    int len;
>>> +
>>> +    len = snprintf(buf, PATH_MAX, "%s/%s", path, name);
>>> +    if (len < 0)
>>> +        return -EINVAL;
>>> +    if (len >= PATH_MAX)
>>> +        return -ENAMETOOLONG;
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int
>>> +auto_attach_programs(struct bpf_object *obj, const char *path)
>>> +{
>>> +    struct bpf_program *prog;
>>> +    char buf[PATH_MAX];
>>> +    int err;
>>> +
>>> +    bpf_object__for_each_program(prog, obj) {
>>> +        err = pathname_concat(path, bpf_program__name(prog), buf);
>>> +        if (err)
>>> +            goto err_unpin_programs;
>>> +
>>> +        err = auto_attach_program(prog, buf);
>>> +        if (!err)
>>> +            continue;
>>> +        if (errno == EOPNOTSUPP)
>>> +            p_info("Program %s does not support autoattach",
>>> +                   bpf_program__name(prog));
>>> +        else
>>> +            goto err_unpin_programs
>> With this code, if auto-attach fails, then we skip this program and move
>> on to the next. That's an improvement, but in that case the program
>> won't remain loaded in the kernel after bpftool exits. My suggestion in
>> my previous message (sorry if it was not clear) was to fall back to
>> regular pinning in that case (bpf_obj_pin()), along with the p_info()
>> message, so we can have the program pinned but not attached and let the
>> user know. If regular pinning fails as well, then we should unpin all
>> and error out, for consistency with bpf_object__pin_programs().
>>
>> And in that case, the (errno == EOPNOTSUPP) with fallback to regular
>> pinning could maybe be moved into auto_attach_program(), so that
>> auto-attaching single programs can use the fallback too?
>>
>> Thanks,
>> Quentin
> 
> If I understand correctly, can we just check link?  as following:

Yes, this is exactly what I meant

> 
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1460,9 +1460,10 @@ static int do_run(int argc, char **argv)
>         int err;
>  
>         link = bpf_program__attach(prog);
> -       if (!link)
> -               return -1;
> -
> +       if (!link) {
> +               p_info("Program %s attach failed",
> bpf_program__name(prog));
> +               return bpf_obj_pin(bpf_program__fd(prog), path);
> +       }
>         err = bpf_link__pin(link, path);
>         if (err) {
>                 bpf_link__destroy(link);
> @@ -1499,9 +1500,6 @@ static int pathname_concat(const char *path, const
> char *name, char *buf)
>                 err = auto_attach_program(prog, buf);
>                 if (!err)
>                         continue;
> -               if (errno == EOPNOTSUPP)
> -                       p_info("Program %s does not support autoattach",

p_info("Program %s does not support autoattach, falling back to pinning"

> -                              bpf_program__name(prog));
>                 else
>                         goto err_unpin_programs;
>         }
> 
> 
> and the doc is modified as follows:
> 
> If the program does not support autoattach, will do regular pin along
> with an
> info message such as "Program %s attach failed". If the *OBJ* contains
> multiple
> programs and **loadall** is used, if the program A in these programs
> does not
> support autoattach, the program A will do regular pin along with an info
> message,
> and continue to autoattach the next program.

Not sure the "program A" designation helps too much, I'd simply write this:

"If a program does not support autoattach, bpftool falls back to regular
pinning for that program instead."

Which should be enough for both the "load" and "loadall" behaviours? I
wouldn't mention the help message in the docs (the p_info() won't show
up in the JSON output for example).

Looks good otherwise, thanks!