Subject: Re: [PATCHv2 bpf-next 4/4] selftests/bpf: Add attach bench test

From: Jiri Olsa <[email-masked]>
Date: Thu, 21 Apr 2022 08:56:26 +0200

On Wed, Apr 20, 2022 at 02:56:53PM -0700, Andrii Nakryiko wrote:

SNIP

> > +#define DEBUGFS "/sys/kernel/debug/tracing/"
> > +
> > +static int get_syms(char ***symsp, size_t *cntp)
> > +{
> > +       size_t cap = 0, cnt = 0, i;
> > +       char *name, **syms = NULL;
> > +       struct hashmap *map;
> > +       char buf[256];
> > +       FILE *f;
> > +       int err;
> > +
> > +       /*
> > +        * The available_filter_functions contains many duplicates,
> > +        * but other than that all symbols are usable in kprobe multi
> > +        * interface.
> > +        * Filtering out duplicates by using hashmap__add, which won't
> > +        * add existing entry.
> > +        */
> > +       f = fopen(DEBUGFS "available_filter_functions", "r");
> 
> nit: DEBUGFS "constant" just makes it harder to follow the code and
> doesn't add anything, please just use the full path here directly

there's another one DEBUGFS in trace_helpers.c,
we could put it in trace_helpers.h

> 
> > +       if (!f)
> > +               return -EINVAL;
> > +
> > +       map = hashmap__new(symbol_hash, symbol_equal, NULL);
> > +       err = libbpf_get_error(map);
> 
> hashmap__new() is an internal API, so please use IS_ERR() directly
> here. libbpf_get_error() should be used for public libbpf APIs, and
> preferably not in libbpf 1.0 mode

ok

> 
> > +       if (err)
> > +               goto error;
> > +
> > +       while (fgets(buf, sizeof(buf), f)) {
> > +               /* skip modules */
> > +               if (strchr(buf, '['))
> > +                       continue;
> 
> [...]
> 
> > +       attach_delta = (attach_end_ns - attach_start_ns) / 1000000000.0;
> > +       detach_delta = (detach_end_ns - detach_start_ns) / 1000000000.0;
> > +
> > +       fprintf(stderr, "%s: found %lu functions\n", __func__, cnt);
> > +       fprintf(stderr, "%s: attached in %7.3lfs\n", __func__, attach_delta);
> > +       fprintf(stderr, "%s: detached in %7.3lfs\n", __func__, detach_delta);
> 
> 
> why stderr? just do printf() and let test_progs handle output

ok

> 
> 
> > +
> > +cleanup:
> > +       kprobe_multi_empty__destroy(skel);
> > +       if (syms) {
> > +               for (i = 0; i < cnt; i++)
> > +                       free(syms[i]);
> > +               free(syms);
> > +       }
> > +}
> > +
> >  void test_kprobe_multi_test(void)
> >  {
> >         if (!ASSERT_OK(load_kallsyms(), "load_kallsyms"))
> > @@ -320,4 +454,6 @@ void test_kprobe_multi_test(void)
> >                 test_attach_api_syms();
> >         if (test__start_subtest("attach_api_fails"))
> >                 test_attach_api_fails();
> > +       if (test__start_subtest("bench_attach"))
> > +               test_bench_attach();
> >  }
> > diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_empty.c b/tools/testing/selftests/bpf/progs/kprobe_multi_empty.c
> > new file mode 100644
> > index 000000000000..be9e3d891d46
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/kprobe_multi_empty.c
> > @@ -0,0 +1,12 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +SEC("kprobe.multi/*")
> 
> use SEC("kprobe.multi") to make it clear that we are attaching it "manually"?

yep, will do

thanks,
jirka