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Date:   Tue, 17 Mar 2020 14:03:00 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 2/4] bpftool: Print as a string for char array

On Tue, Mar 17, 2020 at 01:08:01PM -0700, Andrii Nakryiko wrote:
> On Sun, Mar 15, 2020 at 5:57 PM Martin KaFai Lau <kafai@...com> wrote:
> >
> > A char[] is currently printed as an integer array.
> > This patch will print it as a string when
> > 1) The array element type is an one byte int
> > 2) The array element type has a BTF_INT_CHAR encoding or
> >    the array element type's name is "char"
> > 3) All characters is between (0x1f, 0x7f) and it is terminated
> >    by a null character.
> >
> > Signed-off-by: Martin KaFai Lau <kafai@...com>
> > ---
> >  tools/bpf/bpftool/btf_dumper.c | 41 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> >
> > diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
> > index 57bd6c0fafc9..1d2d8d2cedea 100644
> > --- a/tools/bpf/bpftool/btf_dumper.c
> > +++ b/tools/bpf/bpftool/btf_dumper.c
> > @@ -77,6 +77,42 @@ static void btf_dumper_enum(const struct btf_dumper *d,
> >         jsonw_int(d->jw, value);
> >  }
> >
> > +static bool is_str_array(const struct btf *btf, const struct btf_array *arr,
> > +                        const char *s)
> > +{
> > +       const struct btf_type *elem_type;
> > +       const char *end_s;
> > +
> > +       if (!arr->nelems)
> > +               return false;
> > +
> > +       elem_type = btf__type_by_id(btf, arr->type);
> > +       /* Not skipping typedef.  typedef to char does not count as
> > +        * a string now.
> > +        */
> > +       while (elem_type && btf_is_mod(elem_type))
> > +               elem_type = btf__type_by_id(btf, elem_type->type);
> > +
> > +       if (!elem_type || !btf_is_int(elem_type) || elem_type->size != 1)
> > +               return false;
> > +
> > +       if (btf_int_encoding(elem_type) != BTF_INT_CHAR &&
> > +           strcmp("char", btf__name_by_offset(btf, elem_type->name_off)))
> > +               return false;
> > +
> > +       end_s = s + arr->nelems;
> > +       while (s < end_s) {
> > +               if (!*s)
> > +                       return true;
> > +               if (*s <= 0x1f || *s >= 0x7f)
> > +                       return false;
> > +               s++;
> > +       }
> > +
> > +       /* '\0' is not found */
> > +       return false;
> > +}
> > +
> >  static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,
> >                             const void *data)
> >  {
> > @@ -86,6 +122,11 @@ static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,
> >         int ret = 0;
> >         __u32 i;
> >
> > +       if (is_str_array(d->btf, arr, data)) {
> > +               jsonw_string(d->jw, data);
> > +               return 0;
> > +       }
> > +
> 
> Looks good, but curious how the string that contains ' or " will be
> output in json? Will it be escaped properly or will result in
> malformed JSON?
They will be escaped.

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