netdev - Re: [PATCH bpf-next v4 20/27] libbpf: Add btf__find_by_glob

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Date:   Wed, 1 Sep 2021 13:33:35 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Daniel Xu <dxu@...uu.xyz>,
        Viktor Malik <vmalik@...hat.com>
Subject: Re: [PATCH bpf-next v4 20/27] libbpf: Add btf__find_by_glob_kind
 function

On Tue, Aug 31, 2021 at 05:10:52PM -0700, Andrii Nakryiko wrote:
> On Thu, Aug 26, 2021 at 12:41 PM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > Adding btf__find_by_glob_kind function that returns array of
> > BTF ids that match given kind and allow/deny patterns.
> >
> > int btf__find_by_glob_kind(const struct btf *btf, __u32 kind,
> >                            const char *allow_pattern,
> >                            const char *deny_pattern,
> >                            __u32 **__ids);
> >
> > The __ids array is allocated and needs to be manually freed.
> >
> > At the moment the supported pattern is '*' at the beginning or
> > the end of the pattern.
> >
> > Kindly borrowed from retsnoop.
> >
> > Suggested-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/lib/bpf/btf.c | 80 +++++++++++++++++++++++++++++++++++++++++++++
> >  tools/lib/bpf/btf.h |  3 ++
> >  2 files changed, 83 insertions(+)
> >
> > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> > index 77dc24d58302..5baaca6c3134 100644
> > --- a/tools/lib/bpf/btf.c
> > +++ b/tools/lib/bpf/btf.c
> > @@ -711,6 +711,86 @@ __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
> >         return libbpf_err(-ENOENT);
> >  }
> >
> > +/* 'borrowed' from retsnoop */
> > +static bool glob_matches(const char *glob, const char *s)
> > +{
> > +       int n = strlen(glob);
> > +
> > +       if (n == 1 && glob[0] == '*')
> > +               return true;
> > +
> > +       if (glob[0] == '*' && glob[n - 1] == '*') {
> > +               const char *subs;
> > +               /* substring match */
> > +
> > +               /* this is hacky, but we don't want to allocate for no good reason */
> > +               ((char *)glob)[n - 1] = '\0';
> > +               subs = strstr(s, glob + 1);
> > +               ((char *)glob)[n - 1] = '*';
> > +
> > +               return subs != NULL;
> > +       } else if (glob[0] == '*') {
> > +               size_t nn = strlen(s);
> > +               /* suffix match */
> > +
> > +               /* too short for a given suffix */
> > +               if (nn < n - 1)
> > +                       return false;
> > +
> > +               return strcmp(s + nn - (n - 1), glob + 1) == 0;
> > +       } else if (glob[n - 1] == '*') {
> > +               /* prefix match */
> > +               return strncmp(s, glob, n - 1) == 0;
> > +       } else {
> > +               /* exact match */
> > +               return strcmp(glob, s) == 0;
> > +       }
> > +}
> > +
> > +int btf__find_by_glob_kind(const struct btf *btf, __u32 kind,
> > +                          const char *allow_pattern, const char *deny_pattern,
> > +                          __u32 **__ids)
> > +{
> > +       __u32 i, nr_types = btf__get_nr_types(btf);
> > +       int cnt = 0, alloc = 0;
> > +       __u32 *ids = NULL;
> > +
> > +       for (i = 1; i <= nr_types; i++) {
> > +               const struct btf_type *t = btf__type_by_id(btf, i);
> > +               bool match = false;
> > +               const char *name;
> > +               __u32 *p;
> > +
> > +               if (btf_kind(t) != kind)
> > +                       continue;
> > +               name = btf__name_by_offset(btf, t->name_off);
> > +               if (!name)
> > +                       continue;
> > +
> > +               if (allow_pattern && glob_matches(allow_pattern, name))
> > +                       match = true;
> > +               if (deny_pattern && !glob_matches(deny_pattern, name))
> > +                       match = true;
> 
> this is wrong, if it matches both deny and allow patterns, you'll
> still pass it through. Drop the match flag, just check deny first and
> `continue` if matches.

true, ok

> 
> > +               if (!match)
> > +                       continue;
> > +
> > +               if (cnt == alloc) {
> > +                       alloc = max(100, alloc * 3 / 2);
> 
> nit: maybe start with something like 16?

ok

> 
> > +                       p = realloc(ids, alloc * sizeof(__u32));
> 
> we have libbpf_reallocarray, please use it

ok

> 
> > +                       if (!p) {
> > +                               free(ids);
> > +                               return -ENOMEM;
> > +                       }
> > +                       ids = p;
> > +               }
> > +               ids[cnt] = i;
> > +               cnt++;
> > +       }
> > +
> > +       *__ids = ids;
> > +       return cnt ?: -ENOENT;
> 
> cnt == 0 means -ENOENT, basically, no? It's up to the application to
> decide if that's an error, let's just return the number of matches,
> i.e., zero.

ok

thanks,
jirka