[PATCH next 02/12] tools/nolibc/printf: Add buffering to vfprintf() callback.

[david.laight.linux@gmail.com]

From: David Laight <david.laight.linux@gmail.com>

Add per-call buffering to the vprintf() callback.
While this adds some extra code it will speed things up and
makes a massive difference to anyone looking at strace output.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 tools/include/nolibc/stdio.h | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 6c8fa41dbc01..985e10d747db 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -381,15 +381,41 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
 	return written;
 }
 
-static int __nolibc_fprintf_cb(void *stream, const char *buf, size_t size)
+struct __nolibc_fprintf_cb_state {
+	FILE *stream;
+	unsigned int buf_offset;
+	char buf[128];
+};
+
+static int __nolibc_fprintf_cb(void *v_state, const char *buf, size_t size)
 {
-	return size ? _fwrite(buf, size, stream) : 0;
+	struct __nolibc_fprintf_cb_state *state = v_state;
+	unsigned int off = state->buf_offset;
+
+	if (off + size > sizeof(state->buf) || buf == NULL) {
+		state->buf_offset = 0;
+		if (off && _fwrite(state->buf, off, state->stream))
+			return -1;
+		if (size > sizeof(state->buf))
+			return _fwrite(buf, size, state->stream);
+		off = 0;
+	}
+
+	if (size) {
+		state->buf_offset = off + size;
+		memcpy(state->buf + off, buf, size);
+	}
+	return 0;
 }
 
 static __attribute__((unused, format(printf, 2, 0)))
 int vfprintf(FILE *stream, const char *fmt, va_list args)
 {
-	return __nolibc_printf(__nolibc_fprintf_cb, stream, fmt, args);
+	struct __nolibc_fprintf_cb_state state;
+
+	state.stream = stream;
+	state.buf_offset = 0;
+	return __nolibc_printf(__nolibc_fprintf_cb, &state, fmt, args);
 }
 
 static __attribute__((unused, format(printf, 1, 0)))
-- 
2.39.5