linux-kernel - [PATCH v2 25/32] tools/nolibc: allow different write callbacks in printf

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Message-Id: <20250407-nolibc-kselftest-harness-v2-25-f8812f76e930@linutronix.de>
Date: Mon, 07 Apr 2025 08:52:48 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Shuah Khan <shuah@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>, 
 Willy Tarreau <w@....eu>, 
 Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH v2 25/32] tools/nolibc: allow different write callbacks in
 printf

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>
Acked-by: Willy Tarreau <w@....eu>
---
 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..5c893b4903a3040a366e11b600ccde30913d7db2 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 (*__nolibc_printf_cb)(intptr_t state, const char *buf, size_t size);
+
+static __attribute__((unused, format(printf, 3, 0)))
+int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, const char *fmt, va_list args)
 {
 	char escape, lpref, c;
 	unsigned long long v;
@@ -304,7 +306,7 @@ int vfprintf(FILE *stream, const char *fmt, va_list args)
 			outstr = fmt;
 			len = ofs - 1;
 		flush_str:
-			if (_fwrite(outstr, len, stream) != 0)
+			if (cb(state, outstr, len) != 0)
 				break;
 
 			written += len;
@@ -321,6 +323,17 @@ int vfprintf(FILE *stream, const char *fmt, va_list args)
 	return written;
 }
 
+static int __nolibc_fprintf_cb(intptr_t state, const char *buf, size_t size)
+{
+	return _fwrite(buf, size, (FILE *)state);
+}
+
+static __attribute__((unused, format(printf, 2, 0)))
+int vfprintf(FILE *stream, const char *fmt, va_list args)
+{
+	return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, fmt, args);
+}
+
 static __attribute__((unused, format(printf, 1, 0)))
 int vprintf(const char *fmt, va_list args)
 {

-- 
2.49.0