Added ring_buffer_get_vecs() that returns iovecs describing the contents of

the buffer.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@35880 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/util/ring_buffer.h

@@ -9,6 +9,9 @@
 #include <OS.h>
 
 
+struct iovec;
+
+
 struct ring_buffer {
 	int32		first;
 	int32		in;
@@ -40,6 +43,7 @@ ssize_t ring_buffer_user_read(struct ring_buffer *buffer, uint8 *data, ssize_t l
 ssize_t ring_buffer_user_write(struct ring_buffer *buffer, const uint8 *data, ssize_t length);
 size_t ring_buffer_peek(struct ring_buffer *buffer, size_t offset, void *data,
 			size_t length);
+int32 ring_buffer_get_vecs(struct ring_buffer *buffer, struct iovec *vecs);
 
 #ifdef __cplusplus
 }

src/system/kernel/util/ring_buffer.cpp

@@ -13,6 +13,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <sys/uio.h>
 
 #ifndef HAIKU_TARGET_PLATFORM_HAIKU
 #define user_memcpy(x...) (memcpy(x), B_OK)
@@ -267,6 +268,40 @@ ring_buffer_peek(struct ring_buffer* buffer, size_t offset, void* data,
 }
 
 
+/*!	Returns iovecs describing the contents of the ring buffer.
+
+	\param buffer The ring buffer.
+	\param vecs Pointer to an iovec array with at least 2 elements to be filled
+		in by the function.
+	\return The number of iovecs the function has filled in to describe the
+		contents of the ring buffer. \c 0, if empty, \c 2 at maximum.
+*/
+int32
+ring_buffer_get_vecs(struct ring_buffer* buffer, struct iovec* vecs)
+{
+	if (buffer->in == 0)
+		return 0;
+
+	if (buffer->first + buffer->in <= buffer->size) {
+		// one element
+		vecs[0].iov_base = buffer->buffer + buffer->first;
+		vecs[0].iov_len = buffer->in;
+		return 1;
+	}
+
+	// two elements
+	size_t upper = buffer->size - buffer->first;
+	size_t lower = buffer->in - upper;
+
+	vecs[0].iov_base = buffer->buffer + buffer->first;
+	vecs[0].iov_len = upper;
+	vecs[1].iov_base = buffer->buffer;
+	vecs[1].iov_len = lower;
+
+	return 2;
+}
+
+
 #if 0
 /**	Sends the contents of the ring buffer to a port.
  *	The buffer will be empty afterwards only if sending the data actually works.