Add automerge property back after conflict.

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377879 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/uuid.c

@@ -0,0 +1,206 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2012, Digium, Inc.
+ *
+ * Mark Michelson <mmmichelson@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file
+ * \brief Universally unique identifier support
+ */
+
+#include "asterisk.h"
+#include <uuid/uuid.h>
+#include <fcntl.h>
+
+#include "asterisk/uuid.h"
+#include "asterisk/utils.h"
+#include "asterisk/strings.h"
+#include "asterisk/logger.h"
+#include "asterisk/lock.h"
+
+AST_MUTEX_DEFINE_STATIC(uuid_lock);
+
+static int has_dev_urandom;
+
+struct ast_uuid {
+	uuid_t uu;
+};
+
+struct ast_uuid *ast_uuid_generate(void)
+{
+	struct ast_uuid *uuid = ast_malloc(sizeof(*uuid));
+
+	if (!uuid) {
+		return NULL;
+	}
+	/* libuuid provides three methods of generating uuids,
+	 * uuid_generate(), uuid_generate_random(), and uuid_generate_time().
+	 *
+	 * uuid_generate_random() creates a UUID based on random numbers. The method
+	 * attempts to use either /dev/urandom or /dev/random to generate random values.
+	 * If these resources are unavailable, then random numbers will be generated
+	 * using C library calls to generate pseudorandom numbers.
+	 * This method of generating UUIDs corresponds to section 4.4 of RFC 4122.
+	 *
+	 * uuid_generate_time() creates a UUID based on the current time plus
+	 * a system identifier (MAC address of the ethernet interface). This
+	 * method of generating UUIDs corresponds to section 4.2 of RFC 4122.
+	 *
+	 * uuid_generate() will check if /dev/urandom or /dev/random is available to
+	 * use. If so, it will use uuid_generate_random(). Otherwise, it will use
+	 * uuid_generate_time(). The idea is that it avoids using pseudorandom
+	 * numbers if necessary.
+	 *
+	 * For our purposes, we do not use the time-based UUID at all. There are
+	 * several reasons for this:
+	 *
+	 * 1) The time-based algorithm makes use of a daemon process (uuidd) in order
+	 * to ensure that any concurrent requests for UUIDs result in unique results.
+	 * Use of this daemon is a bit dodgy for a few reasons
+	 *
+	 *     a) libuuid assumes a hardcoded location for the .pid file of the daemon.
+	 *     However, the daemon could already be running on the system in a different
+	 *     location than expected. If this is the case, then attempting to connect
+	 *     to the daemon will fail, and attempting to launch another instance in
+	 *     the expected location will also fail.
+	 *
+	 *     b) If the daemon is not running, then the first attempt to create a
+	 *     time-based UUID will result in launching the daemon. Because of the hard-
+	 *     coded locations that libuuid assumes for the daemon, Asterisk must be
+	 *     run with permissions that will allow for the daemon to be launched in
+	 *     the expected directories.
+	 *
+	 *     c) Once the daemon is running, concurrent requests for UUIDs are thread-safe.
+	 *     However, the actual launching of the daemon is not thread-safe since libuuid
+	 *     uses no synchronization primitives to ensure that only one thread (or process)
+	 *     launches the daemon.
+	 *
+	 *     d) When libuuid launches the daemon, it sets an inactivity timer.
+	 *     If no UUID generation requests are issued in that time period,
+	 *     then the daemon will exit. If a new request should occur after the daemon
+	 *     exits, then the daemon will be relaunched. Given point c), we cannot
+	 *     necessarily guarantee the thread-safety of time-based UUID generation since
+	 *     we cannot necessarily guarantee the daemon is running as we expect.
+	 *     We could set up a watchdog thread to generate UUIDs at regular intervals to
+	 *     prevent the daemon from exiting, but frankly, that sucks.
+	 *
+	 * 2) Since the MAC address of the Ethernet interface is part of the UUID when
+	 * using the time-based method, there is information leaked.
+	 *
+	 * Given these drawbacks, we stick to only using random UUIDs. The chance of /dev/random
+	 * or /dev/urandom not existing on systems in this age is next to none.
+	 */
+
+	/* XXX Currently, we only protect this call if the user has no /dev/urandon on their system.
+	 * If it turns out that there are issues with UUID generation despite the presence of
+	 * /dev/urandom, then we may need to make the locking/unlocking unconditional.
+	 */
+	if (!has_dev_urandom) {
+		ast_mutex_lock(&uuid_lock);
+	}
+	uuid_generate_random(uuid->uu);
+	if (!has_dev_urandom) {
+		ast_mutex_unlock(&uuid_lock);
+	}
+	return uuid;
+}
+
+char *ast_uuid_to_str(const struct ast_uuid *uuid, char *buf, size_t size)
+{
+	ast_assert(size >= AST_UUID_STR_LEN);
+	uuid_unparse_lower(uuid->uu, buf);
+	return buf;
+}
+
+struct ast_uuid *ast_str_to_uuid(const char *str)
+{
+	struct ast_uuid *uuid = ast_malloc(sizeof(*uuid));
+	int res;
+	if (!uuid) {
+		return NULL;
+	}
+	res = uuid_parse(str, uuid->uu);
+	if (res) {
+		ast_log(LOG_WARNING, "Unable to convert string %s into a UUID\n", str);
+		ast_free(uuid);
+		return NULL;
+	}
+	return uuid;
+}
+
+struct ast_uuid *ast_uuid_copy(const struct ast_uuid *src)
+{
+	struct ast_uuid *dst = ast_malloc(sizeof(*dst));
+	if (!dst) {
+		return NULL;
+	}
+	uuid_copy(dst->uu, src->uu);
+	return dst;
+}
+
+int ast_uuid_compare(const struct ast_uuid *left, const struct ast_uuid *right)
+{
+	return uuid_compare(left->uu, right->uu);
+}
+
+void ast_uuid_clear(struct ast_uuid *uuid)
+{
+	uuid_clear(uuid->uu);
+}
+
+int ast_uuid_is_nil(const struct ast_uuid *uuid)
+{
+	return uuid_is_null(uuid->uu);
+}
+
+void ast_uuid_init(void)
+{
+	/* This requires some explanation.
+	 *
+	 * libuuid generates UUIDs based on random number generation. This involves
+	 * opening a handle to /dev/urandom or /dev/random in order to get random
+	 * data for the UUIDs.
+	 *
+	 * This is thread-safe, to a point. The problem is that the first attempt
+	 * to generate a UUID will result in opening the random number handle. Once
+	 * the handle is opened, all further generation is thread safe. This
+	 * first generation can be potentially risky if multiple threads attempt
+	 * to generate a UUID at the same time, though, since there is no thread
+	 * synchronization used within libuuid. To get around this potential
+	 * issue, we go ahead and generate a UUID up front so that the underlying
+	 * work is done before we start requesting UUIDs for real.
+	 *
+	 * Think of this along the same lines as initializing a singleton.
+	 */
+	uuid_t uu;
+	int dev_urandom_fd;
+
+	dev_urandom_fd = open("/dev/urandom", O_RDONLY);
+	if (dev_urandom_fd < 0) {
+		ast_log(LOG_WARNING, "It appears your system does not have /dev/urandom on it. This\n"
+				"means that UUID generation will use a pseudorandom number generator. Since\n"
+				"the thread-safety of your system's random number generator cannot\n"
+				"be guaranteed, we have to synchronize UUID generation. This may result\n"
+				"in decreased performance. It is highly recommended that you set up your\n"
+				"system to have /dev/urandom\n");
+	} else {
+		has_dev_urandom = 1;
+		close(dev_urandom_fd);
+	}
+	uuid_generate_random(uu);
+
+	ast_debug(1, "UUID system initiated\n");
+	return;
+}