Re: [PATCH v6 14/23] vsprintf: add new `%pA` format specifier

Petr Mladek
2022-05-10T08:38:42Z

On Sat 2022-05-07 07:24:12, Miguel Ojeda wrote:
> From: Gary Guo <gary@garyguo.net>
>
> This patch adds a format specifier `%pA` to `vsprintf` which formats
> a pointer as `core::fmt::Arguments`. Doing so allows us to directly
> format to the internal buffer of `printf`, so we do not have to use
> a temporary buffer on the stack to pre-assemble the message on
> the Rust side.
>
> This specifier is intended only to be used from Rust and not for C, so
> `checkpatch.pl` is intentionally unchanged to catch any misuse.
>
> Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
> Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
> Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Feel free to use:

Acked-by: Petr Mladek <pmladek@suse.com>

See a comment below.

> ---
> lib/vsprintf.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 40d26a07a133..00f71f91d991 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2270,6 +2270,9 @@ int __init no_hash_pointers_enable(char *str)
> }
> early_param("no_hash_pointers", no_hash_pointers_enable);
>
> +/* Used for Rust formatting ('%pA'). */
> +char *rust_fmt_argument(char *buf, char *end, void *ptr);
> +
> /*
> * Show a '%p' thing. A kernel extension is that the '%p' is followed
> * by an extra set of alphanumeric characters that are extended format
> @@ -2396,6 +2399,10 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
> *
> * Note: The default behaviour (unadorned %p) is to hash the address,
> * rendering it useful as a unique identifier.
> + *
> + * There is also a '%pA' format specifier, but it is only intended to be used
> + * from Rust code to format core::fmt::Arguments. Do *not* use it from C.
> + * See rust/kernel/print.rs for details.
> */

It would be great to document it also in
Documentation/core-api/printk-formats.rst
I am sorry that I did not mentioned it earlier.

Also the check in checkpatch.pl, mentioned in another reply, sounds
like a good idea.

Best Regards,
Petr