Added a ring buffer log target to store the last N log messages.

The log target can be used via log alarms and show alarms.
Why? This feature was proposed/requested at
http://openbsc.osmocom.org/trac/wiki/Tasks/ErrorLogTarget
All messages use the same amount of space, prioritizing simplicity.

1 files changed, 171 insertions, 0 deletions

diff --git a/src/strrb.c b/src/strrb.c
new file mode 100644
index 00000000..b137acb8
--- /dev/null
+++ b/src/strrb.c
@@ -0,0 +1,171 @@
+/* Ringbuffer implementation, tailored for logging.
+ * This is a lossy ringbuffer. It keeps up to N of the newest messages,
+ * overwriting the oldest as newer ones come in.
+ *
+ * (C) 2012-2013, Katerina Barone-Adesi <kat.obsc@gmail.com>
+ * 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 3 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.
+ *
+ */
+
+/*! \file strrb.c
+ *  \brief Lossy string ringbuffer for logging; keeps newest messages.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <strings.h>
+
+#include <osmocom/core/strrb.h>
+
+/* Ringbuffer assumptions, invarients, and notes:
+ * - start is the index of the first used index slot in the ring buffer.
+ * - end is the index of the next index slot in the ring buffer.
+ * - start == end => buffer is empty
+ * - Consequence: the buffer can hold at most size - 1 messages
+ * (if this were not the case, full and empty buffers would be indistinguishable
+ * given the conventions in this implementation).
+ * - Whenever the ringbuffer is full, start is advanced. The second oldest
+ * message becomes unreachable by valid indexes (end is not a valid index)
+ * and the oldest message is overwritten (if there was a message there, which
+ * is the case unless this is the first time the ringbuffer becomes full).
+*/
+
+/*! \brief Create an empty, initialized osmo_strrb.
+ *  \param[in] ctx The talloc memory context which should own this.
+ *  \param[in] rb_size The number of message slots the osmo_strrb can hold.
+ *  \returns A struct osmo_strrb* on success, NULL in case of error.
+ *
+ * This function creates and initializes a ringbuffer.
+ * Note that the ringbuffer stores at most rb_size - 1 messages.
+ */
+
+struct osmo_strrb *osmo_strrb_create(TALLOC_CTX * ctx, size_t rb_size)
+{
+	struct osmo_strrb *rb = NULL;
+	unsigned int i;
+
+	rb = talloc_zero(ctx, struct osmo_strrb);
+	if (!rb)
+		goto alloc_error;
+
+	/* start and end are zero already, which is correct */
+	rb->size = rb_size;
+
+	rb->buffer = talloc_array(rb, char *, rb->size);
+	if (!rb->buffer)
+		goto alloc_error;
+	for (i = 0; i < rb->size; i++) {
+		rb->buffer[i] =
+		    talloc_zero_size(rb->buffer, RB_MAX_MESSAGE_SIZE);
+		if (!rb->buffer[i])
+			goto alloc_error;
+	}
+
+	return rb;
+
+alloc_error:			/* talloc_free(NULL) is safe */
+	talloc_free(rb);
+	return NULL;
+}
+
+/*! \brief Check if an osmo_strrb is empty.
+ *  \param[in] rb The osmo_strrb to check.
+ *  \returns True if the osmo_strrb is empty, false otherwise.
+ */
+bool osmo_strrb_is_empty(const struct osmo_strrb *rb)
+{
+	return rb->end == rb->start;
+}
+
+/*! \brief Return a pointer to the Nth string in the osmo_strrb.
+ * \param[in] rb The osmo_strrb to search.
+ * \param[in] string_index The index sought (N), zero-indexed.
+ *
+ * Return a pointer to the Nth string in the osmo_strrb.
+ * Return NULL if there is no Nth string.
+ * Note that N is zero-indexed.
+ * \returns A pointer to the target string on success, NULL in case of error.
+ */
+const char *osmo_strrb_get_nth(const struct osmo_strrb *rb,
+			       unsigned int string_index)
+{
+	unsigned int offset = string_index + rb->start;
+
+	if ((offset >= rb->size) && (rb->start > rb->end))
+		offset -= rb->size;
+	if (_osmo_strrb_is_bufindex_valid(rb, offset))
+		return rb->buffer[offset];
+
+	return NULL;
+}
+
+bool _osmo_strrb_is_bufindex_valid(const struct osmo_strrb *rb,
+				   unsigned int bufi)
+{
+	if (osmo_strrb_is_empty(rb))
+		return 0;
+	if ((bufi >= rb->size) || (bufi < 0))
+		return 0;
+	if (rb->start < rb->end)
+		return (bufi >= rb->start) && (bufi < rb->end);
+	return (bufi < rb->end) || (bufi >= rb->start);
+}
+
+/*! \brief Count the number of log messages in an osmo_strrb.
+ *  \param[in] rb The osmo_strrb to count the elements of.
+ *
+ *  \returns The number of log messages in the osmo_strrb.
+ */
+size_t osmo_strrb_elements(const struct osmo_strrb *rb)
+{
+	if (rb->end < rb->start)
+		return rb->end + (rb->size - rb->start);
+
+	return rb->end - rb->start;
+}
+
+/*! \brief Add a string to the osmo_strrb.
+ * \param[in] rb The osmo_strrb to add to.
+ * \param[in] data The string to add.
+ *
+ * Add a message to the osmo_strrb.
+ * Older messages will be overwritten as necessary.
+ * \returns 0 normally, 1 as a warning (ie, if data was truncated).
+ */
+int osmo_strrb_add(struct osmo_strrb *rb, const char *data)
+{
+	size_t len = strlen(data);
+	int ret = 0;
+
+	if (len >= RB_MAX_MESSAGE_SIZE) {
+		len = RB_MAX_MESSAGE_SIZE - 1;
+		ret = 1;
+	}
+
+	memcpy(rb->buffer[rb->end], data, len);
+	rb->buffer[rb->end][len] = '\0';
+
+	rb->end += 1;
+	rb->end %= rb->size;
+
+	/* The buffer is full; oldest message is forgotten - see notes above */
+	if (rb->end == rb->start) {
+		rb->start += 1;
+		rb->start %= rb->size;
+	}
+	return ret;
+}