tools/nolibc: allow limiting of printf destination size

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.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 5c893b4903a3040a366e11b600ccde30913d7db2..b17b473bd8751a6283309178b4848e61e1683305 100644 (file)
--- 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)))