linux-kernel - Re: [PATCH v4 12/20] vsprintf: add new `%pA` format specifier

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Message-ID: <CANiq72=mNh415UG_nxDQc=9SCSVSPnqcAbgFZKzavnmsim_L0Q@mail.gmail.com>
Date:   Mon, 14 Feb 2022 13:12:24 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux <rust-for-linux@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Gary Guo <gary@...yguo.net>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v4 12/20] vsprintf: add new `%pA` format specifier

On Mon, Feb 14, 2022 at 11:52 AM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> I think the point is for vsnprintf() to call (back) into Rust code.

Indeed, this is the case.

> That said, I don't like the !CONFIG_RUST version to return NULL, that
> will surely crash moments later.
>
> So I prefer something like
>
> [rust.h]
> // no CONFIG_RUST conditional
> +char *rust_fmt_argument(char* buf, char* end, void *ptr);
>
> [vsprintf.c]
> +       case 'A':
> +               if (IS_ENABLED(CONFIG_RUST))
> +                   return rust_fmt_argument(buf, end, ptr);
> +               else
> +                   return string_nocheck(buf, end, "[%pA in non-Rust
> code?!]", default_str_spec);

Sounds good. Or perhaps simply `break` and let it print the pointer
(to be consistent with `g` case and non-error `e` case).

Cheers,
Miguel