When the SHARED function modifies a variable, it removes it from its list of variables and reinserts the new value at the head of the list of variables. Doing this inside a standard list traversal can be dangerous, as the standard list traversal does not account for the list being changed. While the code in question should not cause a use after free violation due to its breaking out of the loop after freeing the variable, it could lead to a maintenance issue if the loop was modified. This also fixes a violation reported by a static analysis tool, which also makes this code easier to maintain in the future. ........ Merged revisions 361657 from http://svn.asterisk.org/svn/asterisk/branches/1.8 ........ Merged revisions 361658 from http://svn.asterisk.org/svn/asterisk/branches/10 git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@361659 65c4cc65-6c06-0410-ace0-fbb531ad65f3
302 lines
7.9 KiB
C
302 lines
7.9 KiB
C
/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 2006, Tilghman Lesher
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*
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* Tilghman Lesher <func_global__200605@the-tilghman.com>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*! \file
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*
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* \brief Global variable dialplan functions
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*
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* \author Tilghman Lesher <func_global__200605@the-tilghman.com>
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*
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* \ingroup functions
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*/
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/*** MODULEINFO
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<support_level>core</support_level>
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***/
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#include "asterisk.h"
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ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
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#include <sys/stat.h>
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#include "asterisk/module.h"
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#include "asterisk/pbx.h"
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#include "asterisk/channel.h"
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#include "asterisk/app.h"
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#include "asterisk/manager.h"
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/*** DOCUMENTATION
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<function name="GLOBAL" language="en_US">
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<synopsis>
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Gets or sets the global variable specified.
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</synopsis>
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<syntax>
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<parameter name="varname" required="true">
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<para>Global variable name</para>
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</parameter>
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</syntax>
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<description>
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<para>Set or get the value of a global variable specified in <replaceable>varname</replaceable></para>
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</description>
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</function>
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<function name="SHARED" language="en_US">
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<synopsis>
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Gets or sets the shared variable specified.
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</synopsis>
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<syntax>
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<parameter name="varname" required="true">
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<para>Variable name</para>
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</parameter>
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<parameter name="channel">
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<para>If not specified will default to current channel. It is the complete
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channel name: <literal>SIP/12-abcd1234</literal> or the prefix only <literal>SIP/12</literal>.</para>
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</parameter>
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</syntax>
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<description>
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<para>Implements a shared variable area, in which you may share variables between
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channels.</para>
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<para>The variables used in this space are separate from the general namespace of
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the channel and thus <variable>SHARED(foo)</variable> and <variable>foo</variable>
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represent two completely different variables, despite sharing the same name.</para>
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<para>Finally, realize that there is an inherent race between channels operating
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at the same time, fiddling with each others' internal variables, which is why
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this special variable namespace exists; it is to remind you that variables in
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the SHARED namespace may change at any time, without warning. You should
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therefore take special care to ensure that when using the SHARED namespace,
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you retrieve the variable and store it in a regular channel variable before
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using it in a set of calculations (or you might be surprised by the result).</para>
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</description>
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</function>
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***/
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static void shared_variable_free(void *data);
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static struct ast_datastore_info shared_variable_info = {
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.type = "SHARED_VARIABLES",
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.destroy = shared_variable_free,
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};
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static void shared_variable_free(void *data)
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{
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struct varshead *varshead = data;
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struct ast_var_t *var;
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while ((var = AST_LIST_REMOVE_HEAD(varshead, entries))) {
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ast_var_delete(var);
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}
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ast_free(varshead);
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}
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static int global_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
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{
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const char *var = pbx_builtin_getvar_helper(NULL, data);
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*buf = '\0';
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if (var)
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ast_copy_string(buf, var, len);
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return 0;
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}
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static int global_write(struct ast_channel *chan, const char *cmd, char *data, const char *value)
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{
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pbx_builtin_setvar_helper(NULL, data, value);
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return 0;
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}
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static struct ast_custom_function global_function = {
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.name = "GLOBAL",
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.read = global_read,
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.write = global_write,
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};
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static int shared_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
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{
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struct ast_datastore *varstore;
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struct varshead *varshead;
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struct ast_var_t *var;
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AST_DECLARE_APP_ARGS(args,
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AST_APP_ARG(var);
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AST_APP_ARG(chan);
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);
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struct ast_channel *c_ref = NULL;
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if (ast_strlen_zero(data)) {
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ast_log(LOG_WARNING, "SHARED() requires an argument: SHARED(<var>[,<chan>])\n");
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return -1;
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}
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AST_STANDARD_APP_ARGS(args, data);
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if (!ast_strlen_zero(args.chan)) {
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char *prefix = alloca(strlen(args.chan) + 2);
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sprintf(prefix, "%s-", args.chan);
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if (!(c_ref = ast_channel_get_by_name(args.chan)) && !(c_ref = ast_channel_get_by_name_prefix(prefix, strlen(prefix)))) {
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ast_log(LOG_ERROR, "Channel '%s' not found! Variable '%s' will be blank.\n", args.chan, args.var);
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return -1;
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}
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chan = c_ref;
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}
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ast_channel_lock(chan);
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if (!(varstore = ast_channel_datastore_find(chan, &shared_variable_info, NULL))) {
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ast_channel_unlock(chan);
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if (c_ref) {
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c_ref = ast_channel_unref(c_ref);
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}
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return -1;
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}
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varshead = varstore->data;
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*buf = '\0';
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/* Protected by the channel lock */
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AST_LIST_TRAVERSE(varshead, var, entries) {
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if (!strcmp(args.var, ast_var_name(var))) {
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ast_copy_string(buf, ast_var_value(var), len);
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break;
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}
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}
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ast_channel_unlock(chan);
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if (c_ref) {
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c_ref = ast_channel_unref(c_ref);
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}
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return 0;
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}
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static int shared_write(struct ast_channel *chan, const char *cmd, char *data, const char *value)
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{
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struct ast_datastore *varstore;
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struct varshead *varshead;
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struct ast_var_t *var;
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AST_DECLARE_APP_ARGS(args,
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AST_APP_ARG(var);
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AST_APP_ARG(chan);
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);
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struct ast_channel *c_ref = NULL;
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if (ast_strlen_zero(data)) {
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ast_log(LOG_WARNING, "SHARED() requires an argument: SHARED(<var>[,<chan>])\n");
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return -1;
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}
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AST_STANDARD_APP_ARGS(args, data);
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if (!ast_strlen_zero(args.chan)) {
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char *prefix = alloca(strlen(args.chan) + 2);
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sprintf(prefix, "%s-", args.chan);
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if (!(c_ref = ast_channel_get_by_name(args.chan)) && !(c_ref = ast_channel_get_by_name_prefix(prefix, strlen(prefix)))) {
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ast_log(LOG_ERROR, "Channel '%s' not found! Variable '%s' not set to '%s'.\n", args.chan, args.var, value);
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return -1;
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}
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chan = c_ref;
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}
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ast_channel_lock(chan);
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if (!(varstore = ast_channel_datastore_find(chan, &shared_variable_info, NULL))) {
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if (!(varstore = ast_datastore_alloc(&shared_variable_info, NULL))) {
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ast_log(LOG_ERROR, "Unable to allocate new datastore. Shared variable not set.\n");
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ast_channel_unlock(chan);
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if (c_ref) {
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c_ref = ast_channel_unref(c_ref);
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}
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return -1;
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}
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if (!(varshead = ast_calloc(1, sizeof(*varshead)))) {
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ast_log(LOG_ERROR, "Unable to allocate variable structure. Shared variable not set.\n");
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ast_datastore_free(varstore);
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ast_channel_unlock(chan);
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if (c_ref) {
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c_ref = ast_channel_unref(c_ref);
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}
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return -1;
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}
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varstore->data = varshead;
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ast_channel_datastore_add(chan, varstore);
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}
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varshead = varstore->data;
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/* Protected by the channel lock */
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AST_LIST_TRAVERSE_SAFE_BEGIN(varshead, var, entries) {
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/* If there's a previous value, remove it */
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if (!strcmp(args.var, ast_var_name(var))) {
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AST_LIST_REMOVE_CURRENT(entries);
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ast_var_delete(var);
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break;
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}
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}
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AST_LIST_TRAVERSE_SAFE_END;
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var = ast_var_assign(args.var, S_OR(value, ""));
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AST_LIST_INSERT_HEAD(varshead, var, entries);
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manager_event(EVENT_FLAG_DIALPLAN, "VarSet",
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"Channel: %s\r\n"
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"Variable: SHARED(%s)\r\n"
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"Value: %s\r\n"
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"Uniqueid: %s\r\n",
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chan ? ast_channel_name(chan) : "none", args.var, value,
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chan ? ast_channel_uniqueid(chan) : "none");
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ast_channel_unlock(chan);
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if (c_ref) {
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c_ref = ast_channel_unref(c_ref);
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}
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return 0;
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}
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static struct ast_custom_function shared_function = {
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.name = "SHARED",
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.read = shared_read,
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.write = shared_write,
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};
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static int unload_module(void)
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{
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int res = 0;
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res |= ast_custom_function_unregister(&global_function);
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res |= ast_custom_function_unregister(&shared_function);
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return res;
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}
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static int load_module(void)
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{
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int res = 0;
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res |= ast_custom_function_register(&global_function);
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res |= ast_custom_function_register(&shared_function);
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return res;
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}
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AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Variable dialplan functions");
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