Date:   Mon, 24 May 2021 17:06:45 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 0/5] libbpf: error reporting changes for v1.0

On Mon, May 24, 2021 at 3:20 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
>
> > On Mon, May 24, 2021 at 2:34 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >>
> >> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
> >>
> >> > On Mon, May 24, 2021 at 1:53 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >> >>
> >> >> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
> >> >>
> >> >> > On Sun, May 23, 2021 at 11:36 PM John Fastabend
> >> >> > <john.fastabend@...il.com> wrote:
> >> >> >>
> >> >> >> Andrii Nakryiko wrote:
> >> >> >> > Implement error reporting changes discussed in "Libbpf: the road to v1.0"
> >> >> >> > ([0]) document.
> >> >> >> >
> >> >> >> > Libbpf gets a new API, libbpf_set_strict_mode() which accepts a set of flags
> >> >> >> > that turn on a set of libbpf 1.0 changes, that might be potentially breaking.
> >> >> >> > It's possible to opt-in into all current and future 1.0 features by specifying
> >> >> >> > LIBBPF_STRICT_ALL flag.
> >> >> >> >
> >> >> >> > When some of the 1.0 "features" are requested, libbpf APIs might behave
> >> >> >> > differently. In this patch set a first set of changes are implemented, all
> >> >> >> > related to the way libbpf returns errors. See individual patches for details.
> >> >> >> >
> >> >> >> > Patch #1 adds a no-op libbpf_set_strict_mode() functionality to enable
> >> >> >> > updating selftests.
> >> >> >> >
> >> >> >> > Patch #2 gets rid of all the bad code patterns that will break in libbpf 1.0
> >> >> >> > (exact -1 comparison for low-level APIs, direct IS_ERR() macro usage to check
> >> >> >> > pointer-returning APIs for error, etc). These changes make selftest work in
> >> >> >> > both legacy and 1.0 libbpf modes. Selftests also opt-in into 100% libbpf 1.0
> >> >> >> > mode to automatically gain all the subsequent changes, which will come in
> >> >> >> > follow up patches.
> >> >> >> >
> >> >> >> > Patch #3 streamlines error reporting for low-level APIs wrapping bpf() syscall.
> >> >> >> >
> >> >> >> > Patch #4 streamlines errors for all the rest APIs.
> >> >> >> >
> >> >> >> > Patch #5 ensures that BPF skeletons propagate errors properly as well, as
> >> >> >> > currently on error some APIs will return NULL with no way of checking exact
> >> >> >> > error code.
> >> >> >> >
> >> >> >> >   [0] https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY
> >> >> >> >
> >> >> >> > Andrii Nakryiko (5):
> >> >> >> >   libbpf: add libbpf_set_strict_mode() API to turn on libbpf 1.0
> >> >> >> >     behaviors
> >> >> >> >   selftests/bpf: turn on libbpf 1.0 mode and fix all IS_ERR checks
> >> >> >> >   libbpf: streamline error reporting for low-level APIs
> >> >> >> >   libbpf: streamline error reporting for high-level APIs
> >> >> >> >   bpftool: set errno on skeleton failures and propagate errors
> >> >> >> >
> >> >> >>
> >> >> >> LGTM for the series,
> >> >> >>
> >> >> >> Acked-by: John Fastabend <john.fastabend@...il.com>
> >> >> >
> >> >> > Thanks, John!
> >> >> >
> >> >> > Toke, Stanislav, you cared about these aspects of libbpf 1.0 (by
> >> >> > commenting on the doc itself), do you mind also taking a brief look
> >> >> > and letting me know if this works for your use cases? Thanks!
> >> >>
> >> >> Changes LGTM:
> >> >>
> >> >> Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
> >> >>
> >> >> As a side note, the series seems to have been chopped up into individual
> >> >> emails with no threading; was a bit weird that I had to go hunting for
> >> >> the individual patches in my mailbox...
> >> >>
> >> >
> >> > That's my bad, I messed up and sent them individually and probably
> >> > that's why they weren't threaded properly.
> >>
> >> Right, OK, I'll stop looking for bugs on my end, then :)
> >>
> >> BTW, one more thing that just came to mind: since that gdoc is not
> >> likely to be around forever, would it be useful to make the reference in
> >> the commit message(s) point to something more stable? IDK what that
> >> shoul be, really. Maybe just pasting (an abbreviated outline of?) the
> >> text in the document into the cover letter / merge commit could work?
> >
> > I was hoping Google won't deprecate Google Docs any time soon and I
> > had no intention to remove that document. But I was also thinking to
> > start wiki page at github.com/libbpf/libbpf with migration
> > instructions, so once that is up and running I can link that from
> > libbpf_set_strict_mode() doc comment.
>
> Right, that sounds reasonable :)
>
> > But I'd like to avoid blocking on that.
>
> Understandable; but just pasting an outline into the commit message (and
> keeping the link) could work in the meantime?

I'm not sure what are we trying to achieve by copy/pasting parts of
that doc here. Each patch succinctly explains how each feature
behaves, so it's completely self-describing. I put the link to the
document for anyone that wants to read the entire discussion or leave
some more comments, but it's not mandatory to understand this patch
set.

>
> -Toke
>

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