lib: add ringbuf_peek()

Peek functionality for ring buffers and associated tests.

Also:
* Slight optimization to avoid 0-byte memcpy() by changing > to >=
* Add rv checks for some ringbuf_[put|get] calls that were missing them
  in the test

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/lib/ringbuf.c b/lib/ringbuf.c
index fee5b5d69..f8e9a9bd8 100644
--- a/lib/ringbuf.c
+++ b/lib/ringbuf.c
@@ -77,7 +77,7 @@ size_t ringbuf_get(struct ringbuf *buf, void *data, size_t size)
 	size_t remain = ringbuf_remain(buf);
 	size_t copysize = MIN(remain, size);
 	size_t tocopy = copysize;
-	if (tocopy > buf->size - buf->start) {
+	if (tocopy >= buf->size - buf->start) {
 		size_t ts = buf->size - buf->start;
 		memcpy(dp, buf->data + buf->start, ts);
 		buf->start = 0;
@@ -90,6 +90,26 @@ size_t ringbuf_get(struct ringbuf *buf, void *data, size_t size)
 	return copysize;
 }
 
+size_t ringbuf_peek(struct ringbuf *buf, size_t offset, void *data, size_t size)
+{
+	uint8_t *dp = data;
+	size_t remain = ringbuf_remain(buf);
+	if (offset >= remain)
+		return 0;
+	size_t copysize = MAX(MIN(remain - offset, size), (size_t) 0);
+	size_t tocopy = copysize;
+	size_t cstart = (buf->start + offset) % buf->size;
+	if (tocopy >= buf->size - cstart) {
+		size_t ts = buf->size - cstart;
+		memcpy(dp, buf->data + cstart, ts);
+		buf->start = cstart = 0;
+		tocopy -= ts;
+		dp += ts;
+	}
+	memcpy(dp, buf->data + cstart, tocopy);
+	return copysize;
+}
+
 void ringbuf_reset(struct ringbuf *buf)
 {
 	buf->start = buf->end = 0;