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

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Date:   Wed, 28 Nov 2018 16:52:30 +0000
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        linux-api@...r.kernel.org, Y Song <ys114321@...il.com>
Subject: Re: [PATCH v3 3/4] libbpf: add bpf_prog_test_run_xattr

On Wed, 28 Nov 2018 at 05:05, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> 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?

Basically, you can only change the input part without having to reset
data_size_out to sizeof(buffer). Not a big deal, I'll change it.

>
> > 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.

Yeah, I wasn't thinking too hard on this one, sorry. User space needs to check
where the end of the buffer is.

-- 
Lorenz Bauer  |  Systems Engineer
25 Lavington St., London SE1 0NZ

www.cloudflare.com