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Message-ID: <CAH0uvoge5QUsioZ-j8OS+VoxJAXuP9CyXOJbBkJPwUXWhEryMg@mail.gmail.com>
Date: Fri, 30 Aug 2024 08:16:38 +0800
From: Howard Chu <howardchu95@...il.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: adrian.hunter@...el.com, irogers@...gle.com, jolsa@...nel.org,
kan.liang@...ux.intel.com, namhyung@...nel.org,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v3 4/8] perf trace: Pretty print struct data
Hello Arnaldo,
On Thu, Aug 29, 2024 at 5:05 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> On Sun, Aug 25, 2024 at 12:33:18AM +0800, Howard Chu wrote:
> > Change the arg->augmented.args to arg->augmented.args->value to skip the
> > header for customized pretty printers, since we collect data in BPF
> > using the general augment_sys_enter(), which always adds the header.
> >
> > Use btf_dump API to pretty print augmented struct pointer.
> >
> > Prefer existed pretty-printer than btf general pretty-printer.
> >
> > set compact = true and skip_names = true, so that no newline character
> > and argument name are printed.
> >
> > Committer notes:
> >
> > Simplified the btf_dump_snprintf callback to avoid using multiple
> > buffers, as discussed in the thread accessible via the Link tag below.
> >
> > Signed-off-by: Howard Chu <howardchu95@...il.com>
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Ian Rogers <irogers@...gle.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Kan Liang <kan.liang@...ux.intel.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Link: https://lore.kernel.org/r/20240815013626.935097-7-howardchu95@gmail.com
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> > tools/perf/builtin-trace.c | 65 +++++++++++++++++++++--
> > tools/perf/trace/beauty/perf_event_open.c | 2 +-
> > tools/perf/trace/beauty/sockaddr.c | 2 +-
> > tools/perf/trace/beauty/timespec.c | 2 +-
> > 4 files changed, 63 insertions(+), 8 deletions(-)
> >
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index 43b1f63415b4..048bcb92624c 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -990,6 +990,54 @@ static size_t btf_enum_scnprintf(const struct btf_type *type, struct btf *btf, c
> > return 0;
> > }
> >
> > +struct trace_btf_dump_snprintf_ctx {
> > + char *bf;
> > + size_t printed, size;
> > +};
> > +
> > +static void trace__btf_dump_snprintf(void *vctx, const char *fmt, va_list args)
> > +{
> > + struct trace_btf_dump_snprintf_ctx *ctx = vctx;
> > +
> > + ctx->printed += vscnprintf(ctx->bf + ctx->printed, ctx->size - ctx->printed, fmt, args);
> > +}
> > +
> > +static size_t btf_struct_scnprintf(const struct btf_type *type, struct btf *btf, char *bf, size_t size, struct syscall_arg *arg)
> > +{
> > + struct trace_btf_dump_snprintf_ctx ctx = {
> > + .bf = bf,
> > + .size = size,
> > + };
> > + struct augmented_arg *augmented_arg = arg->augmented.args;
> > + int type_id = arg->fmt->type_id, consumed;
> > + struct btf_dump *btf_dump;
> > +
> > + LIBBPF_OPTS(btf_dump_opts, dump_opts);
> > + LIBBPF_OPTS(btf_dump_type_data_opts, dump_data_opts);
> > +
> > + if (arg == NULL || arg->augmented.args == NULL)
> > + return 0;
> > +
> > + dump_data_opts.compact = true;
> > + dump_data_opts.skip_names = true;
> > +
> > + btf_dump = btf_dump__new(btf, trace__btf_dump_snprintf, &ctx, &dump_opts);
> > + if (btf_dump == NULL)
> > + return 0;
> > +
> > + /* pretty print the struct data here */
> > + if (btf_dump__dump_type_data(btf_dump, type_id, arg->augmented.args->value, type->size, &dump_data_opts) == 0)
> > + return 0;
> > +
> > + consumed = sizeof(*augmented_arg) + augmented_arg->size;
> > + arg->augmented.args = ((void *)arg->augmented.args) + consumed;
> > + arg->augmented.size -= consumed;
> > +
> > + btf_dump__free(btf_dump);
> > +
> > + return ctx.printed;
> > +}
> > +
> > static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg *arg, char *bf,
> > size_t size, int val, char *type)
> > {
> > @@ -1009,6 +1057,8 @@ static size_t trace__btf_scnprintf(struct trace *trace, struct syscall_arg *arg,
> >
> > if (btf_is_enum(arg_fmt->type))
> > return btf_enum_scnprintf(arg_fmt->type, trace->btf, bf, size, val);
> > + else if (btf_is_struct(arg_fmt->type))
> > + return btf_struct_scnprintf(arg_fmt->type, trace->btf, bf, size, arg);
> >
> > return 0;
> > }
> > @@ -2222,6 +2272,7 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
> > .show_string_prefix = trace->show_string_prefix,
> > };
> > struct thread_trace *ttrace = thread__priv(thread);
> > + void *default_scnprintf;
> >
> > /*
> > * Things like fcntl will set this in its 'cmd' formatter to pick the
> > @@ -2263,11 +2314,15 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
> > if (trace->show_arg_names)
> > printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
> >
> > - btf_printed = trace__btf_scnprintf(trace, &arg, bf + printed,
> > - size - printed, val, field->type);
> > - if (btf_printed) {
> > - printed += btf_printed;
> > - continue;
> > + default_scnprintf = sc->arg_fmt[arg.idx].scnprintf;
> > +
> > + if (default_scnprintf == NULL || default_scnprintf == SCA_PTR) {
> > + btf_printed = trace__btf_scnprintf(trace, &arg, bf + printed,
> > + size - printed, val, field->type);
> > + if (btf_printed) {
> > + printed += btf_printed;
> > + continue;
> > + }
>
> Ok, we agreed on this one, and you noted that that in this cset comment,
> good.
>
> Next time make a note after the cset commit log message and before the
> actual patch, something like:
>
> vN: prefer pre-existing userspace scnprintf if explicitely specified,
> only fallbacking to the generic BTF one when none is specified.
>
> > }
> >
> > printed += syscall_arg_fmt__scnprintf_val(&sc->arg_fmt[arg.idx],
> > diff --git a/tools/perf/trace/beauty/perf_event_open.c b/tools/perf/trace/beauty/perf_event_open.c
> > index 01ee15fe9d0c..632237128640 100644
> > --- a/tools/perf/trace/beauty/perf_event_open.c
> > +++ b/tools/perf/trace/beauty/perf_event_open.c
> > @@ -76,7 +76,7 @@ static size_t perf_event_attr___scnprintf(struct perf_event_attr *attr, char *bf
>
> But this part will work if we use the old collectors in the BPF skel?
>
You are right, it won't. The one scenario is that when a vmlinux file
is presented, the general collector (the new one, based on BTF) will
fallback to the old collectors, and now we have new
consumers(ptr->value). This will break.
> I.e. isn't this a change in the protocol of the BPF colector with the
> userpace augmented snprintf routines?
>
> If I remember we discussed that first you make this change in the
> protocol, test it with the pre-existing BPF collector, it works. Ok, now
> we have a new protocol and we then use it in the generic BTF-based BPF
> collector. This way that option of using the BTF-based collector or the
> preexisting BPF collector works.
>
> I'll try to do this.
Thank you so much.
Thanks,
Howard
>
> - Arnaldo
>
> > static size_t syscall_arg__scnprintf_augmented_perf_event_attr(struct syscall_arg *arg, char *bf, size_t size)
> > {
> > - return perf_event_attr___scnprintf((void *)arg->augmented.args, bf, size, arg->trace->show_zeros);
> > + return perf_event_attr___scnprintf((void *)arg->augmented.args->value, bf, size, arg->trace->show_zeros);
> > }
> >
> > static size_t syscall_arg__scnprintf_perf_event_attr(char *bf, size_t size, struct syscall_arg *arg)
> > diff --git a/tools/perf/trace/beauty/sockaddr.c b/tools/perf/trace/beauty/sockaddr.c
> > index 2e0e867c0c1b..6ecebf776899 100644
> > --- a/tools/perf/trace/beauty/sockaddr.c
> > +++ b/tools/perf/trace/beauty/sockaddr.c
> > @@ -47,7 +47,7 @@ static size_t (*af_scnprintfs[])(struct sockaddr *sa, char *bf, size_t size) = {
> >
> > static size_t syscall_arg__scnprintf_augmented_sockaddr(struct syscall_arg *arg, char *bf, size_t size)
> > {
> > - struct sockaddr *sa = (struct sockaddr *)arg->augmented.args;
> > + struct sockaddr *sa = (struct sockaddr *)arg->augmented.args->value;
> > char family[32];
> > size_t printed;
> >
> > diff --git a/tools/perf/trace/beauty/timespec.c b/tools/perf/trace/beauty/timespec.c
> > index e1a61f092aad..b14ab72a2738 100644
> > --- a/tools/perf/trace/beauty/timespec.c
> > +++ b/tools/perf/trace/beauty/timespec.c
> > @@ -7,7 +7,7 @@
> >
> > static size_t syscall_arg__scnprintf_augmented_timespec(struct syscall_arg *arg, char *bf, size_t size)
> > {
> > - struct timespec *ts = (struct timespec *)arg->augmented.args;
> > + struct timespec *ts = (struct timespec *)arg->augmented.args->value;
> >
> > return scnprintf(bf, size, "{ .tv_sec: %" PRIu64 ", .tv_nsec: %" PRIu64 " }", ts->tv_sec, ts->tv_nsec);
> > }
> > --
> > 2.45.2
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