Re: [RFC PATCH bpf-next 0/6] bpf, printk: add BTF-based type printing

[Rasmus Villemoes <linux@rasmusvillemoes.dk>]

On 20/04/2020 18.32, Joe Perches wrote:
> On Mon, 2020-04-20 at 16:29 +0100, Alan Maguire wrote:

>>>>   struct sk_buff *skb = alloc_skb(64, GFP_KERNEL);
>>>>
>>>>   pr_info("%pTN<struct sk_buff>", skb);
>>>
>>> why follow "TN" convention?
>>> I think "%p<struct sk_buff>" is much more obvious, unambiguous, and
>>> equally easy to parse.
>>>
>>
>> That was my first choice, but the first character
>> after the 'p' in the '%p' specifier signifies the
>> pointer format specifier. If we use '<', and have
>> '%p<', where do we put the modifiers? '%p<xYz struct foo>'
>> seems clunky to me.

There's also the issue that %p followed by alnum has been understood to
be reserved/specially handled by the kernel's printf implementation for
a decade, while other characters have so far been treated as "OK, this
was just a normal %p". A quick grep for %p< only gives a hit in
drivers/scsi/dc395x.c, but there could be others (with field width
modifier between % and p), and in any case I think it's a bad idea to
extend the set of characters that cannot follow %p.

Rasmus