shared: add ring buffer

New "struct ring" object that implements a basic ring buffer for arbitrary
byte-streams. A new basic runtime test is also added.

This will be needed for our pty helpers for systemd-console and friends.

1 files changed, 59 insertions, 0 deletions

diff --git a/src/shared/ring.h b/src/shared/ring.h
new file mode 100644
index 0000000000..6b12530e31
--- /dev/null
+++ b/src/shared/ring.h
@@ -0,0 +1,59 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/uio.h>
+
+struct ring {
+        uint8_t *buf;           /* buffer or NULL */
+        size_t size;            /* actual size of @buf */
+        size_t start;           /* start position of ring */
+        size_t used;            /* number of actually used bytes */
+};
+
+/* flush buffer so it is empty again */
+void ring_flush(struct ring *r);
+
+/* flush buffer, free allocated data and reset to initial state */
+void ring_clear(struct ring *r);
+
+/* get pointers to buffer data and their length */
+size_t ring_peek(struct ring *r, struct iovec *vec);
+
+/* copy data into external linear buffer */
+size_t ring_copy(struct ring *r, void *buf, size_t size);
+
+/* push data to the end of the buffer */
+int ring_push(struct ring *r, const void *u8, size_t size);
+
+/* pull data from the front of the buffer */
+void ring_pull(struct ring *r, size_t size);
+
+/* return size of occupied buffer in bytes */
+static inline size_t ring_get_size(struct ring *r)
+{
+        return r->used;
+}