linux-kernel - Re: [PATCH 25/32] tools/nolibc: allow different write callbacks in printf

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Message-ID: <20250304120932-827df661-9aa6-488e-8935-70915caaab15@linutronix.de>
Date: Tue, 4 Mar 2025 12:10:32 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Willy Tarreau <w@....eu>
Cc: Shuah Khan <shuah@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>, 
	Thomas Weißschuh <linux@...ssschuh.net>, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 25/32] tools/nolibc: allow different write callbacks in
 printf

On Tue, Mar 04, 2025 at 08:59:23AM +0100, Willy Tarreau wrote:
> On Tue, Mar 04, 2025 at 08:10:55AM +0100, Thomas Weißschuh wrote:
> > Decouple the formatting logic from the writing logic to later enable
> > writing straight to a buffer in sprintf().
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > ---
> >  tools/include/nolibc/stdio.h | 21 +++++++++++++++++----
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> > 
> > diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
> > index 262d0da4da9062e0c83b55661b2509f36548cf88..434fbaddae7a216159fecf618da85889d631dff7 100644
> > --- a/tools/include/nolibc/stdio.h
> > +++ b/tools/include/nolibc/stdio.h
> > @@ -208,13 +208,15 @@ char *fgets(char *s, int size, FILE *stream)
> >  }
> >  
> >  
> > -/* minimal vfprintf(). It supports the following formats:
> > +/* minimal printf(). It supports the following formats:
> >   *  - %[l*]{d,u,c,x,p}
> >   *  - %s
> >   *  - unknown modifiers are ignored.
> >   */
> > -static __attribute__((unused, format(printf, 2, 0)))
> > -int vfprintf(FILE *stream, const char *fmt, va_list args)
> > +typedef int (*_printf_cb)(intptr_t state, const char *buf, size_t size);
> 
> Keep in mind these ones will appear in the application, so you'd rather
> appropriate the type name by prefixing it with "nolibc" as we've done in
> a few macros and internal structs.

Ack. Technically it should be fine as names with leading underscores are
reserved for the implementation, but let's make it clearer.

> > +static __attribute__((unused, format(printf, 3, 0)))
> > +int _printf(_printf_cb cb, intptr_t state, const char *fmt, va_list args)
>        ^^^^^^^
> Here as well, since it's not meant to be exposed to the application.

Ack.

> > +static int _fprintf_cb(intptr_t state, const char *buf, size_t size)
> 
> Likewise here I think.

Ack, also to the same remarks in the other patches.