[PATCH v4 04/10] kunit: string-stream: Add option to make all lines end with newline

[Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>]

Add an optional feature to string_stream that will append a newline to
any added string that does not already end with a newline. The purpose
of this is so that string_stream can be used to collect log lines.

This is enabled/disabled by calling string_stream_set_append_newlines().

Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
---
 lib/kunit/string-stream.c | 28 +++++++++++++++++++++-------
 lib/kunit/string-stream.h |  7 +++++++
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/lib/kunit/string-stream.c b/lib/kunit/string-stream.c
index ed24d86af9f5..1dcf6513b692 100644
--- a/lib/kunit/string-stream.c
+++ b/lib/kunit/string-stream.c
@@ -44,32 +44,46 @@ int string_stream_vadd(struct string_stream *stream,
 		       va_list args)
 {
 	struct string_stream_fragment *frag_container;
-	int len;
+	int buf_len, result_len;
 	va_list args_for_counting;
 
 	/* Make a copy because `vsnprintf` could change it */
 	va_copy(args_for_counting, args);
 
 	/* Evaluate length of formatted string */
-	len = vsnprintf(NULL, 0, fmt, args_for_counting);
+	buf_len = vsnprintf(NULL, 0, fmt, args_for_counting);
 
 	va_end(args_for_counting);
 
-	if (len == 0)
+	if (buf_len == 0)
 		return 0;
 
+	/* Reserve one extra for possible appended newline. */
+	if (stream->append_newlines)
+		buf_len++;
+
 	/* Need space for null byte. */
-	len++;
+	buf_len++;
 
 	frag_container = alloc_string_stream_fragment(stream->test,
-						      len,
+						      buf_len,
 						      stream->gfp);
 	if (IS_ERR(frag_container))
 		return PTR_ERR(frag_container);
 
-	len = vsnprintf(frag_container->fragment, len, fmt, args);
+	if (stream->append_newlines) {
+		/* Don't include reserved newline byte in writeable length. */
+		result_len = vsnprintf(frag_container->fragment, buf_len - 1, fmt, args);
+
+		/* Append newline if necessary. */
+		if (frag_container->fragment[result_len - 1] != '\n')
+			result_len = strlcat(frag_container->fragment, "\n", buf_len);
+	} else {
+		result_len = vsnprintf(frag_container->fragment, buf_len, fmt, args);
+	}
+
 	spin_lock(&stream->lock);
-	stream->length += len;
+	stream->length += result_len;
 	list_add_tail(&frag_container->node, &stream->fragments);
 	spin_unlock(&stream->lock);
 
diff --git a/lib/kunit/string-stream.h b/lib/kunit/string-stream.h
index b669f9a75a94..048930bf97f0 100644
--- a/lib/kunit/string-stream.h
+++ b/lib/kunit/string-stream.h
@@ -25,6 +25,7 @@ struct string_stream {
 	spinlock_t lock;
 	struct kunit *test;
 	gfp_t gfp;
+	bool append_newlines;
 };
 
 struct kunit;
@@ -47,4 +48,10 @@ bool string_stream_is_empty(struct string_stream *stream);
 
 void string_stream_destroy(struct string_stream *stream);
 
+static inline void string_stream_set_append_newlines(struct string_stream *stream,
+						     bool append_newlines)
+{
+	stream->append_newlines = append_newlines;
+}
+
 #endif /* _KUNIT_STRING_STREAM_H */
-- 
2.30.2