[write_queue] Add a generic write queue class

The write queue can be a dropin replacement for the bsc_fd. It
is featuring two callbacks. One for ready read and one for ready
write. Whenever there is a message in the queue the write_queue
will set the BSC_FD_WRITE flag and then call the write callback.

It will make sure to delete the msgb after the write function
has been called. This class is intended to be be used in the
osmocom, layer2, bsc_msc_ip, bsc_hack and other applications.

include/osmocore/Makefile.am

@@ -1,6 +1,6 @@
 osmocore_HEADERS = signal.h linuxlist.h timer.h talloc.h msgb.h select.h \
 		   tlv.h bitvec.h comp128.h statistics.h gsm_utils.h utils.h \
-		   gsmtap.h
+		   gsmtap.h write_queue.h
 
 osmocoredir = $(includedir)/osmocore
 

include/osmocore/write_queue.h

@@ -0,0 +1,43 @@
+/* Generic write queue implementation */
+/*
+ * (C) 2010 by Holger Hans Peter Freyther
+ * (C) 2010 by On-Waves
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+#ifndef write_queue_h
+#define write_queue_h
+
+#include "select.h"
+#include "msgb.h"
+
+struct write_queue {
+	struct bsc_fd bfd;
+	unsigned int max_length;
+	unsigned int current_length;
+
+	struct llist_head msg_queue;
+
+	int (*read_cb)(struct bsc_fd *fd);
+	int (*write_cb)(struct bsc_fd *fd, struct msgb *msg);
+};
+
+void write_queue_init(struct write_queue *queue, int max_length);
+int write_queue_enqueue(struct write_queue *queue, struct msgb *data);
+
+#endif

src/Makefile.am

@@ -8,4 +8,5 @@ AM_CFLAGS = -fPIC -Wall
 lib_LTLIBRARIES = libosmocore.la
 
 libosmocore_la_SOURCES = msgb.c timer.c talloc.c select.c signal.c \
-			 tlv_parser.c bitvec.c comp128.c gsm_utils.c statistics.c
+			 tlv_parser.c bitvec.c comp128.c gsm_utils.c statistics.c \
+			 write_queue.c

src/write_queue.c

@@ -0,0 +1,74 @@
+/* Generic write queue implementation */
+/*
+ * (C) 2010 by Holger Hans Peter Freyther
+ * (C) 2010 by On-Waves
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <osmocore/write_queue.h>
+
+static int queue_cb(struct bsc_fd *fd, unsigned int what)
+{
+	struct write_queue *queue;
+
+	queue = container_of(fd, struct write_queue, bfd);
+
+	if (what & BSC_FD_READ)
+		queue->read_cb(fd);
+
+	if (what & BSC_FD_WRITE) {
+		struct msgb *msg;
+
+		fd->when &= ~BSC_FD_WRITE;
+		msg = msgb_dequeue(&queue->msg_queue);
+		if (!msg)
+			return -1;
+
+		--queue->current_length;
+		queue->write_cb(fd, msg);
+		msgb_free(msg);
+
+		if (!llist_empty(&queue->msg_queue))
+			fd->when |= BSC_FD_WRITE;
+	}
+
+	return 0;
+}
+
+void write_queue_init(struct write_queue *queue, int max_length)
+{
+	queue->max_length = max_length;
+	queue->current_length = 0;
+	queue->read_cb = NULL;
+	queue->write_cb = NULL;
+	queue->bfd.cb = queue_cb;
+	INIT_LLIST_HEAD(&queue->msg_queue);
+}
+
+int write_queue_enqueue(struct write_queue *queue, struct msgb *data)
+{
+//	if (queue->current_length + 1 >= queue->max_length)
+//		LOGP(DMSC, LOGL_ERROR, "The queue is full. Dropping not yet implemented.\n");
+
+	++queue->current_length;
+	msgb_enqueue(&queue->msg_queue, data);
+	queue->bfd.when |= BSC_FD_WRITE;
+
+	return 0;
+}