printk: Add APIs to print into strings instead of default output

These correspond to the libc snprintf and vsnprintf APIs.

Change-Id: If3944972ed95934a4967756593bb2932c3359b72
Signed-off-by: Johan Hedberg <[email protected]>

Author: Johan Hedberg

include/misc/printk.h

@@ -19,6 +19,8 @@
 #define _PRINTK_H_
 
 #include <toolchain.h>
+#include <stddef.h>
+#include <stdarg.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -50,12 +52,33 @@ extern "C" {
  */
 #ifdef CONFIG_PRINTK
 extern __printf_like(1, 2) int printk(const char *fmt, ...);
+extern __printf_like(3, 4) int snprintk(char *str, size_t size,
+					const char *fmt, ...);
+extern int vsnprintk(char *str, size_t size, const char *fmt, va_list ap);
 #else
 static inline __printf_like(1, 2) int printk(const char *fmt, ...)
 {
 	ARG_UNUSED(fmt);
 	return 0;
 }
+
+static inline __printf_like(3, 4) int snprintk(char *str, size_t size,
+					       const char *fmt, ...)
+{
+	ARG_UNUSED(str);
+	ARG_UNUSED(size);
+	ARG_UNUSED(fmt);
+	return 0;
+}
+
+static inline int vsnprintk(char *str, size_t size, const char *fmt,
+			    va_list ap)
+{
+	ARG_UNUSED(str);
+	ARG_UNUSED(size);
+	ARG_UNUSED(fmt);
+	return 0;
+}
 #endif
 
 #ifdef __cplusplus

misc/printk.c

@@ -287,3 +287,53 @@ static void _printk_dec_ulong(out_func_t out, void *ctx,
 	out((int)(remainder + 48), ctx);
 }
 
+struct str_context {
+	char *str;
+	int max;
+	int count;
+};
+
+static int str_out(int c, struct str_context *ctx)
+{
+	if (!ctx->str || ctx->count >= ctx->max) {
+		ctx->count++;
+		return c;
+	}
+
+	if (ctx->count == ctx->max - 1) {
+		ctx->str[ctx->count++] = '\0';
+	} else {
+		ctx->str[ctx->count++] = c;
+	}
+
+	return c;
+}
+
+int snprintk(char *str, size_t size, const char *fmt, ...)
+{
+	struct str_context ctx = { str, size, 0 };
+	va_list ap;
+
+	va_start(ap, fmt);
+	_vprintk((out_func_t)str_out, &ctx, fmt, ap);
+	va_end(ap);
+
+	if (ctx.count < ctx.max) {
+		str[ctx.count] = '\0';
+	}
+
+	return ctx.count;
+}
+
+int vsnprintk(char *str, size_t size, const char *fmt, va_list ap)
+{
+	struct str_context ctx = { str, size, 0 };
+
+	_vprintk((out_func_t)str_out, &ctx, fmt, ap);
+
+	if (ctx.count < ctx.max) {
+		str[ctx.count] = '\0';
+	}
+
+	return ctx.count;
+}

tests/kernel/test_common/src/printk.c

@@ -67,6 +67,8 @@ static int ram_console_out(int character)
 
 void printk_test(void)
 {
+	int count;
+
 	_old_char_out = _char_out;
 	_char_out = ram_console_out;
 
@@ -82,4 +84,30 @@ void printk_test(void)
 
 	ram_console[pos] = '\0';
 	assert_true((strcmp(ram_console, expected) == 0), "printk failed");
+
+	memset(ram_console, 0, sizeof(ram_console));
+	count = 0;
+
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			 "%zu %hhu %hu %u %lu %llu\n",
+			 stv, uc, usi, ui, ul, ull);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "%c %hhd %hd %d %ld %lld\n", c, c, ssi, si, sl, sll);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "0x%x %p\n", hex, ptr);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "0x%x 0x%02x 0x%04x 0x%08x\n", 1, 1, 1, 1);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "0x%x 0x%2x 0x%4x 0x%8x\n", 1, 1, 1, 1);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "%d %02d %04d %08d\n", 42, 42, 42, 42);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "%d %02d %04d %08d\n", -42, -42, -42, -42);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "%u %2u %4u %8u\n", 42, 42, 42, 42);
+	count += snprintk(ram_console + count, sizeof(ram_console) - count,
+			  "%u %02u %04u %08u\n", 42, 42, 42, 42);
+
+	ram_console[count] = '\0';
+	assert_true((strcmp(ram_console, expected) == 0), "snprintk failed");
 }