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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 13 May 2020 15:50:17 -0700
Message-ID: <CAADnVQLPSvRCO-xxW+Rcz4bzLM-DXjSzm8AwhyogrNTufBdoNw@mail.gmail.com>
Subject: Re: [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing
To:     Joe Perches <joe@perches.com>
Cc:     Alan Maguire <alan.maguire@oracle.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        bpf <bpf@vger.kernel.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
        Yonghong Song <yhs@fb.com>, Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>
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On Wed, May 13, 2020 at 3:48 PM Joe Perches <joe@perches.com> wrote:
>
> On Wed, 2020-05-13 at 15:24 -0700, Alexei Starovoitov wrote:
> > On Tue, May 12, 2020 at 06:56:38AM +0100, Alan Maguire wrote:
> > > The printk family of functions support printing specific pointer types
> > > using %p format specifiers (MAC addresses, IP addresses, etc).  For
> > > full details see Documentation/core-api/printk-formats.rst.
> > >
> > > This patchset proposes introducing a "print typed pointer" format
> > > specifier "%pT"; the argument associated with the specifier is of
> > > form "struct btf_ptr *" which consists of a .ptr value and a .type
> > > value specifying a stringified type (e.g. "struct sk_buff") or
> > > an .id value specifying a BPF Type Format (BTF) id identifying
> > > the appropriate type it points to.
> > >
> > >   pr_info("%pT", BTF_PTR_TYPE(skb, "struct sk_buff"));
> > >
> > > ...gives us:
> > >
> > > (struct sk_buff){
> > >  .transport_header = (__u16)65535,
> > >  .mac_header = (__u16)65535,
> > >  .end = (sk_buff_data_t)192,
> > >  .head = (unsigned char *)000000007524fd8b,
> > >  .data = (unsigned char *)000000007524fd8b,
> >
> > could you add "0x" prefix here to make it even more C like
> > and unambiguous ?
>
> linux pointers are not emitted with an 0x prefix

So? This is not at all comparable to %p