Re: [PATCH 11/19] vsprintf: add new `%pA` format specifier

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Dec 06, 2021 at 03:03:05PM +0100, 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>
> ---
>  lib/vsprintf.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 58d5e567f836..bc9c05427d9a 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2233,6 +2233,10 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
>  	return widen_string(buf, buf - buf_start, end, spec);
>  }
>  
> +#ifdef CONFIG_RUST
> +char *rust_fmt_argument(char* buf, char* end, void *ptr);
> +#endif

That should be in a .h file somewhere.  Remember, don't put #ifdef in .c
files please.

> +
>  /* Disable pointer hashing if requested */
>  bool no_hash_pointers __ro_after_init;
>  EXPORT_SYMBOL_GPL(no_hash_pointers);
> @@ -2388,6 +2392,10 @@ 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.
>   */
>  static noinline_for_stack
>  char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> @@ -2460,6 +2468,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  		return device_node_string(buf, end, ptr, spec, fmt + 1);
>  	case 'f':
>  		return fwnode_string(buf, end, ptr, spec, fmt + 1);
> +#ifdef CONFIG_RUST
> +	case 'A':
> +		return rust_fmt_argument(buf, end, ptr);
> +#endif

Same here, this should not be needed if you put it in a .h file
correctly.

thanks,

greg k-h