netdev - Re: [PATCH v3 3/4] libbpf: add bpf_prog_test_run

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Date:   Tue, 27 Nov 2018 21:05:13 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Y Song <ys114321@...il.com>
Subject: Re: [PATCH v3 3/4] libbpf: add bpf_prog_test_run_xattr

On Mon, Nov 26, 2018 at 4:45 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> That's what I had initially, but that makes re-using test_attr really
> awkward. Either
> you need to reset data_out_size before every call because it is used
> to return the
> buffer size,

I think that is exactly what the user of the interface would want to do.
Why would anyone keep reusing the same test_attr on multiple calls
into the kernel without changing the fields?

> It also means
> we can't take a const struct attr, which is contrary to the other
> xattr functions which
> already exist.

I don't see an issue with that.

> I think actually inspecting the required size of the output buffer
> will be a rare
> occurrence, so making the user jump through the hoop of a pointer doesn't seem
> too onerous.

I think the opposite is the case.
If the output buffer is provided the test will be comparing it
to expected value.