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Message-ID: <CAEf4BzbH700V1TcvcVufKD8v9PBZRoDDgZXs7JWbWccSDaGtZg@mail.gmail.com>
Date: Thu, 23 May 2019 10:26:57 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc: Andrii Nakryiko <andriin@...com>, Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Networking <netdev@...r.kernel.org>, bpf@...r.kernel.org,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 10/12] bpftool: add C output format option to btf
dump subcommand
On Thu, May 23, 2019 at 9:27 AM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Wed, 22 May 2019 21:43:43 -0700, Andrii Nakryiko wrote:
> > On Wed, May 22, 2019 at 6:23 PM Jakub Kicinski wrote:
> > > On Wed, 22 May 2019 17:58:23 -0700, Andrii Nakryiko wrote:
> > > > On Wed, May 22, 2019 at 5:25 PM Jakub Kicinski wrote:
> > > > > On Wed, 22 May 2019 12:50:51 -0700, Andrii Nakryiko wrote:
> > > > > > + * Copyright (C) 2019 Facebook
> > > > > > + */
> > > > > >
> > > > > > #include <errno.h>
> > > > > > #include <fcntl.h>
> > > > > > @@ -340,11 +347,48 @@ static int dump_btf_raw(const struct btf *btf,
> > > > > > return 0;
> > > > > > }
> > > > > >
> > > > > > +static void btf_dump_printf(void *ctx, const char *fmt, va_list args)
> > > > > > +{
> > > > > > + vfprintf(stdout, fmt, args);
> > > > > > +}
> > > > > > +
> > > > > > +static int dump_btf_c(const struct btf *btf,
> > > > > > + __u32 *root_type_ids, int root_type_cnt)
> > > > >
> > > > > Please break the line after static int.
> > > >
> > > > I don't mind, but it seems that prevalent formatting for such cases
> > > > (at least in bpftool code base) is aligning arguments and not break
> > > > static <return type> into separate line:
> > > >
> > > > // multi-line function definitions with static on the same line
> > > > $ rg '^static \w+.*\([^\)]*$' | wc -l
> > > > 45
> > > > // multi-line function definitions with static on separate line
> > > > $ rg '^static \w+[^\(\{;]*$' | wc -l
> > > > 12
> > > >
> > > > So I don't mind changing, but which one is canonical way of formatting?
> > >
> > > Not really, just my preference :)
> >
> > I'll stick to majority :) I feel like it's also a preferred style in
> > libbpf, so I'd rather converge to that.
>
> Majority is often wrong or at least lazy. But yeah, this is a waste of
> time. Do whatever. You also use inline keyword in C files in your
> libbpf patches.. I think kernel style rules should apply.
I'll remove inlines.
>
> > > In my experience having the return type on a separate line if its
> > > longer than a few chars is the simplest rule for consistent and good
> > > looking code.
> > >
> > > > > > + d = btf_dump__new(btf, NULL, NULL, btf_dump_printf);
> > > > > > + if (IS_ERR(d))
> > > > > > + return PTR_ERR(d);
> > > > > > +
> > > > > > + if (root_type_cnt) {
> > > > > > + for (i = 0; i < root_type_cnt; i++) {
> > > > > > + err = btf_dump__dump_type(d, root_type_ids[i]);
> > > > > > + if (err)
> > > > > > + goto done;
> > > > > > + }
> > > > > > + } else {
> > > > > > + int cnt = btf__get_nr_types(btf);
> > > > > > +
> > > > > > + for (id = 1; id <= cnt; id++) {
> > > > > > + err = btf_dump__dump_type(d, id);
> > > > > > + if (err)
> > > > > > + goto done;
> > > > > > + }
> > > > > > + }
> > > > > > +
> > > > > > +done:
> > > > > > + btf_dump__free(d);
> > > > > > + return err;
> > > > >
> > > > > What do we do for JSON output?
> > > >
> > > > Still dump C syntax. What do you propose? Error out if json enabled?
> > >
> > > I wonder. Letting it just print C is going to confuse anything that
> > > just feeds the output into a JSON parser. I'd err on the side of
> > > returning an error, we can always relax that later if we find a use
> > > case of returning C syntax via JSON.
> >
> > Ok, I'll emit error (seems like pr_err automatically handles JSON
> > output, which is very nice).
>
> Thanks
>
> > > > > > if (!btf) {
> > > > > > err = btf__get_from_id(btf_id, &btf);
> > > > > > if (err) {
> > > > > > @@ -444,7 +498,10 @@ static int do_dump(int argc, char **argv)
> > > > > > }
> > > > > > }
> > > > > >
> > > > > > - dump_btf_raw(btf, root_type_ids, root_type_cnt);
> > > > > > + if (dump_c)
> > > > > > + dump_btf_c(btf, root_type_ids, root_type_cnt);
> > > > > > + else
> > > > > > + dump_btf_raw(btf, root_type_ids, root_type_cnt);
> > > > > >
> > > > > > done:
> > > > > > close(fd);
> > > > > > @@ -460,7 +517,7 @@ static int do_help(int argc, char **argv)
> > > > > > }
> > > > > >
> > > > > > fprintf(stderr,
> > > > > > - "Usage: %s btf dump BTF_SRC\n"
> > > > > > + "Usage: %s btf dump BTF_SRC [c]\n"
> > > > >
> > > > > bpftool generally uses <key value> formats. So perhaps we could do
> > > > > something like "[format raw|c]" here for consistency, defaulting to raw?
> > > >
> > > > That's not true for options, though. I see that at cgroup, prog, and
> > > > some map subcommands (haven't checked all other) just accept a list of
> > > > options without extra identifying key.
> > >
> > > Yeah, we weren't 100% enforcing this rule and it's a bit messy now :/
> >
> > Unless you feel very strongly about this, it seems ok to me to allow
> > "boolean options" (similarly to boolean --flag args) as a stand-alone
> > set of tags. bpftool invocations are already very verbose, no need to
> > add to that. Plus it also makes bash-completion simpler, it's always
> > good not to complicate bash script unnecessarily :)
>
> It's more of a question if we're going to have more formats. If not
> then c as keyword is probably fine (although its worryingly short).
> If we start adding more then a key value would be better. Let's take a
> gamble and if we add 2 more output types I'll say "I told you so"? :)
Ok, that's fair :) There were talks about emitting Go, so it's not
unimaginable that we'll have another format. I'll switch that to
`format [c|raw]`.
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