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

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