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Subject: Re: [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing
From:   Joe Perches <joe@perches.com>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Alan Maguire <alan.maguire@oracle.com>
Cc:     ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org,
        linux@rasmusvillemoes.dk, arnaldo.melo@gmail.com, yhs@fb.com,
        kafai@fb.com, songliubraving@fb.com, andriin@fb.com,
        john.fastabend@gmail.com, kpsingh@chromium.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Date:   Wed, 13 May 2020 15:48:17 -0700
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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

(ie: pointers do not use SPECIAL in lib/vsprintf.c)