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

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