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.
diff --git a/tests/strrb/strrb_test.c b/tests/strrb/strrb_test.c
new file mode 100644
index 0000000..abe649f
--- /dev/null
+++ b/tests/strrb/strrb_test.c
@@ -0,0 +1,225 @@
+/* (C) 2012-2013 by Katerina Barone-Adesi <kat.obsc@gmail.com>
+ * All Rights Reserved
+ *
+ * This program is iree 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.
+ *
+ */
+
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+
+#include <osmocom/core/strrb.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/core/logging.h>
+
+struct osmo_strrb *rb0, *rb1, *rb2, *rb3, *rb4, *rb5;
+
+#define STR0 "hello"
+#define STR1 "a"
+#define STR2 "world"
+#define STR3 "sky"
+#define STR4 "moon"
+
+#define TESTSIZE 3
+
+void init_rbs(void)
+{
+	rb0 = osmo_strrb_create(NULL, TESTSIZE);
+
+	rb1 = osmo_strrb_create(NULL, TESTSIZE);
+	osmo_strrb_add(rb1, STR0);
+
+	rb2 = osmo_strrb_create(NULL, TESTSIZE);
+	osmo_strrb_add(rb2, STR0);
+	osmo_strrb_add(rb2, STR1);
+
+	rb3 = osmo_strrb_create(NULL, TESTSIZE);
+	osmo_strrb_add(rb3, STR0);
+	osmo_strrb_add(rb3, STR1);
+	osmo_strrb_add(rb3, STR2);
+
+	rb4 = osmo_strrb_create(NULL, TESTSIZE);
+	osmo_strrb_add(rb4, STR0);
+	osmo_strrb_add(rb4, STR1);
+	osmo_strrb_add(rb4, STR2);
+	osmo_strrb_add(rb4, STR3);
+
+	rb5 = osmo_strrb_create(NULL, TESTSIZE);
+	osmo_strrb_add(rb5, STR0);
+	osmo_strrb_add(rb5, STR1);
+	osmo_strrb_add(rb5, STR2);
+	osmo_strrb_add(rb5, STR3);
+	osmo_strrb_add(rb5, STR4);
+}
+
+void free_rbs(void)
+{
+	talloc_free(rb0);
+	talloc_free(rb1);
+	talloc_free(rb2);
+	talloc_free(rb3);
+	talloc_free(rb4);
+	talloc_free(rb5);
+}
+
+void test_offset_valid(void)
+{
+	assert(_osmo_strrb_is_bufindex_valid(rb1, 0));
+	assert(!_osmo_strrb_is_bufindex_valid(rb1, 1));
+	assert(!_osmo_strrb_is_bufindex_valid(rb1, 2));
+
+	assert(!_osmo_strrb_is_bufindex_valid(rb3, 0));
+	assert(_osmo_strrb_is_bufindex_valid(rb3, 1));
+	assert(_osmo_strrb_is_bufindex_valid(rb3, 2));
+
+	assert(_osmo_strrb_is_bufindex_valid(rb4, 0));
+	assert(!_osmo_strrb_is_bufindex_valid(rb4, 1));
+	assert(_osmo_strrb_is_bufindex_valid(rb4, 2));
+
+	assert(_osmo_strrb_is_bufindex_valid(rb5, 0));
+	assert(_osmo_strrb_is_bufindex_valid(rb5, 1));
+	assert(!_osmo_strrb_is_bufindex_valid(rb5, 2));
+}
+
+void test_elems(void)
+{
+	assert(osmo_strrb_elements(rb0) == 0);
+	assert(osmo_strrb_elements(rb1) == 1);
+	assert(osmo_strrb_elements(rb2) == 2);
+	assert(osmo_strrb_elements(rb3) == 2);
+}
+
+void test_getn(void)
+{
+	assert(!osmo_strrb_get_nth(rb0, 0));
+	assert(!strcmp(STR0, osmo_strrb_get_nth(rb2, 0)));
+	assert(!strcmp(STR1, osmo_strrb_get_nth(rb2, 1)));
+	assert(!strcmp(STR1, osmo_strrb_get_nth(rb3, 0)));
+	assert(!strcmp(STR2, osmo_strrb_get_nth(rb3, 1)));
+	assert(!osmo_strrb_get_nth(rb3, 2));
+}
+
+void test_getn_wrap(void)
+{
+	assert(!strcmp(STR2, osmo_strrb_get_nth(rb4, 0)));
+	assert(!strcmp(STR3, osmo_strrb_get_nth(rb4, 1)));
+
+	assert(!strcmp(STR3, osmo_strrb_get_nth(rb5, 0)));
+	assert(!strcmp(STR4, osmo_strrb_get_nth(rb5, 1)));
+}
+
+void test_add(void)
+{
+	struct osmo_strrb *rb = osmo_strrb_create(NULL, 4);
+	assert(rb->start == 0);
+	assert(rb->end == 0);
+
+	osmo_strrb_add(rb, "a");
+	osmo_strrb_add(rb, "b");
+	osmo_strrb_add(rb, "c");
+	assert(rb->start == 0);
+	assert(rb->end == 3);
+	assert(osmo_strrb_elements(rb) == 3);
+
+	osmo_strrb_add(rb, "d");
+	assert(rb->start == 1);
+	assert(rb->end == 0);
+	assert(osmo_strrb_elements(rb) == 3);
+	assert(!strcmp("b", osmo_strrb_get_nth(rb, 0)));
+	assert(!strcmp("c", osmo_strrb_get_nth(rb, 1)));
+	assert(!strcmp("d", osmo_strrb_get_nth(rb, 2)));
+
+	osmo_strrb_add(rb, "e");
+	assert(rb->start == 2);
+	assert(rb->end == 1);
+	assert(!strcmp("c", osmo_strrb_get_nth(rb, 0)));
+	assert(!strcmp("d", osmo_strrb_get_nth(rb, 1)));
+	assert(!strcmp("e", osmo_strrb_get_nth(rb, 2)));
+
+	osmo_strrb_add(rb, "f");
+	assert(rb->start == 3);
+	assert(rb->end == 2);
+	assert(!strcmp("d", osmo_strrb_get_nth(rb, 0)));
+	assert(!strcmp("e", osmo_strrb_get_nth(rb, 1)));
+	assert(!strcmp("f", osmo_strrb_get_nth(rb, 2)));
+
+	osmo_strrb_add(rb, "g");
+	assert(rb->start == 0);
+	assert(rb->end == 3);
+	assert(!strcmp("e", osmo_strrb_get_nth(rb, 0)));
+	assert(!strcmp("f", osmo_strrb_get_nth(rb, 1)));
+	assert(!strcmp("g", osmo_strrb_get_nth(rb, 2)));
+
+	osmo_strrb_add(rb, "h");
+	assert(rb->start == 1);
+	assert(rb->end == 0);
+	assert(!strcmp("f", osmo_strrb_get_nth(rb, 0)));
+	assert(!strcmp("g", osmo_strrb_get_nth(rb, 1)));
+	assert(!strcmp("h", osmo_strrb_get_nth(rb, 2)));
+
+	talloc_free(rb);
+}
+
+void test_long_msg(void)
+{
+	struct osmo_strrb *rb = osmo_strrb_create(NULL, 2);
+	int test_size = RB_MAX_MESSAGE_SIZE + 7;
+	char *tests1, *tests2;
+	const char *rb_content;
+	int i;
+
+	tests1 = malloc(test_size);
+	tests2 = malloc(test_size);
+	/* Be certain allocating memory worked before continuing */
+	assert(tests1);
+	assert(tests2);
+
+	for (i = 0; i < RB_MAX_MESSAGE_SIZE; i += 2) {
+		tests1[i] = 'a';
+		tests1[i + 1] = 'b';
+	}
+	tests1[i] = '\0';
+
+	osmo_strrb_add(rb, tests1);
+	strcpy(tests2, tests1);
+
+	/* Verify that no stale data from test1 is lingering... */
+	bzero(tests1, test_size);
+	free(tests1);
+
+	rb_content = osmo_strrb_get_nth(rb, 0);
+	assert(!strncmp(tests2, rb_content, RB_MAX_MESSAGE_SIZE - 1));
+	assert(!rb_content[RB_MAX_MESSAGE_SIZE - 1]);
+	assert(strlen(rb_content) == RB_MAX_MESSAGE_SIZE - 1);
+
+	free(tests2);
+	talloc_free(rb);
+}
+
+int main(int argc, char **argv)
+{
+	init_rbs();
+	test_offset_valid();
+	test_elems();
+	test_getn();
+	test_getn_wrap();
+	test_add();
+	test_long_msg();
+	printf("All tests passed\n");
+
+	free_rbs();
+	return 0;
+}