[PATCH v2 26/32] tools/nolibc: allow limiting of printf destination size

[Thomas Weißschuh]

snprintf() allows limiting the output buffer, while still returning the
number of all bytes that would have been written.
Implement the limitation logic in preparation for snprintf().

Signed-off-by: Thomas Weißschuh <thomas.weisssc...@linutronix.de>
Acked-by: Willy Tarreau <w...@1wt.eu>
---
 tools/include/nolibc/stdio.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 
5c893b4903a3040a366e11b600ccde30913d7db2..b17b473bd8751a6283309178b4848e61e1683305
 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -215,13 +215,13 @@ char *fgets(char *s, int size, FILE *stream)
  */
 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)
+static __attribute__((unused, format(printf, 4, 0)))
+int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const 
char *fmt, va_list args)
 {
        char escape, lpref, c;
        unsigned long long v;
        unsigned int written;
-       size_t len, ofs;
+       size_t len, ofs, w;
        char tmpbuf[21];
        const char *outstr;
 
@@ -306,8 +306,12 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, 
const char *fmt, va_l
                        outstr = fmt;
                        len = ofs - 1;
                flush_str:
-                       if (cb(state, outstr, len) != 0)
-                               break;
+                       if (n) {
+                               w = len < n ? len : n;
+                               n -= w;
+                               if (cb(state, outstr, w) != 0)
+                                       break;
+                       }
 
                        written += len;
                do_escape:
@@ -331,7 +335,7 @@ static int __nolibc_fprintf_cb(intptr_t state, const char 
*buf, size_t size)
 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);
+       return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, SIZE_MAX, 
fmt, args);
 }
 
 static __attribute__((unused, format(printf, 1, 0)))

-- 
2.49.0