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net-snmp/snmplib/callback.c

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/*
* callback.c: A generic callback mechanism
*/
/* Portions of this file are subject to the following copyright(s). See
* the Net-SNMP's COPYING file for more details and other copyrights
* that may apply:
*/
/*
* Portions of this file are copyrighted by:
* Copyright © 2003 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms specified in the COPYING file
* distributed with the Net-SNMP package.
*/
/** @defgroup callback A generic callback mechanism
* @ingroup library
*
* @{
*/
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-features.h>
#include <sys/types.h>
#include <stdio.h>
#if HAVE_STDLIB_H
#include <stdlib.h>
#endif
#if HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#if HAVE_STRING_H
#include <string.h>
#else
#include <strings.h>
#endif
#if HAVE_UNISTD_H
#include <unistd.h>
#endif
#if HAVE_DMALLOC_H
#include <dmalloc.h>
#endif
#if HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#if !defined(mingw32) && defined(HAVE_SYS_TIME_H)
#include <sys/time.h>
#endif
#include <net-snmp/types.h>
#include <net-snmp/output_api.h>
#include <net-snmp/utilities.h>
#include <net-snmp/library/callback.h>
#include <net-snmp/library/snmp_api.h>
netsnmp_feature_child_of(callbacks_all, libnetsnmp)
netsnmp_feature_child_of(callback_count, callbacks_all)
netsnmp_feature_child_of(callback_list, callbacks_all)
/*
* the inline callback methods use major/minor to index into arrays.
* all users in this function do range checking before calling these
* functions, so it is redundant for them to check again. But if you
* want to be paranoid, define this var, and additional range checks
* will be performed.
* #define NETSNMP_PARANOID_LEVEL_HIGH 1
*/
static int _callback_need_init = 1;
static struct snmp_gen_callback
*thecallbacks[MAX_CALLBACK_IDS][MAX_CALLBACK_SUBIDS];
#define CALLBACK_NAME_LOGGING 1
#ifdef CALLBACK_NAME_LOGGING
static const char *types[MAX_CALLBACK_IDS] = { "LIB", "APP" };
static const char *lib[MAX_CALLBACK_SUBIDS] = {
"POST_READ_CONFIG", /* 0 */
"STORE_DATA", /* 1 */
"SHUTDOWN", /* 2 */
"POST_PREMIB_READ_CONFIG", /* 3 */
"LOGGING", /* 4 */
"SESSION_INIT", /* 5 */
NULL, /* 6 */
NULL, /* 7 */
NULL, /* 8 */
NULL, /* 9 */
NULL, /* 10 */
NULL, /* 11 */
NULL, /* 12 */
NULL, /* 13 */
NULL, /* 14 */
NULL /* 15 */
};
#endif
/*
* extremely simplistic locking, just to find problems were the
* callback list is modified while being traversed. Not intended
* to do any real protection, or in any way imply that this code
* has been evaluated for use in a multi-threaded environment.
* In 5.2, it was a single lock. For 5.3, it has been updated to
* a lock per callback, since a particular callback may trigger
* registration/unregistration of other callbacks (eg AgentX
* subagents do this).
*/
#define LOCK_PER_CALLBACK_SUBID 1
#ifdef LOCK_PER_CALLBACK_SUBID
static int _locks[MAX_CALLBACK_IDS][MAX_CALLBACK_SUBIDS];
#define CALLBACK_LOCK(maj,min) ++_locks[maj][min]
#define CALLBACK_UNLOCK(maj,min) --_locks[maj][min]
#define CALLBACK_LOCK_COUNT(maj,min) _locks[maj][min]
#else
static int _lock;
#define CALLBACK_LOCK(maj,min) ++_lock
#define CALLBACK_UNLOCK(maj,min) --_lock
#define CALLBACK_LOCK_COUNT(maj,min) _lock
#endif
NETSNMP_STATIC_INLINE int
_callback_lock(int major, int minor, const char* warn, int do_assert)
{
int lock_holded=0;
struct timeval lock_time = { 0, 1000 };
#ifdef NETSNMP_PARANOID_LEVEL_HIGH
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
netsnmp_assert("bad callback id");
return 1;
}
#endif
#ifdef CALLBACK_NAME_LOGGING
DEBUGMSGTL(("9:callback:lock", "locked (%s,%s)\n",
types[major], (SNMP_CALLBACK_LIBRARY == major) ?
SNMP_STRORNULL(lib[minor]) : "null"));
#endif
while (CALLBACK_LOCK_COUNT(major,minor) >= 1 && ++lock_holded < 100)
select(0, NULL, NULL, NULL, &lock_time);
if(lock_holded >= 100) {
if (NULL != warn)
snmp_log(LOG_WARNING,
"lock in _callback_lock sleeps more than 100 milliseconds in %s\n", warn);
if (do_assert)
netsnmp_assert(lock_holded < 100);
return 1;
}
CALLBACK_LOCK(major,minor);
return 0;
}
NETSNMP_STATIC_INLINE void
_callback_unlock(int major, int minor)
{
#ifdef NETSNMP_PARANOID_LEVEL_HIGH
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
netsnmp_assert("bad callback id");
return;
}
#endif
CALLBACK_UNLOCK(major,minor);
#ifdef CALLBACK_NAME_LOGGING
DEBUGMSGTL(("9:callback:lock", "unlocked (%s,%s)\n",
types[major], (SNMP_CALLBACK_LIBRARY == major) ?
SNMP_STRORNULL(lib[minor]) : "null"));
#endif
}
/*
* the chicken. or the egg. You pick.
*/
void
init_callbacks(void)
{
/*
* (poses a problem if you put init_callbacks() inside of
* init_snmp() and then want the app to register a callback before
* init_snmp() is called in the first place. -- Wes
*/
if (0 == _callback_need_init)
return;
_callback_need_init = 0;
memset(thecallbacks, 0, sizeof(thecallbacks));
#ifdef LOCK_PER_CALLBACK_SUBID
memset(_locks, 0, sizeof(_locks));
#else
_lock = 0;
#endif
DEBUGMSGTL(("callback", "initialized\n"));
}
/**
* This function registers a generic callback function. The major and
* minor values are used to set the new_callback function into a global
* static multi-dimensional array of type struct snmp_gen_callback.
* The function makes sure to append this callback function at the end
* of the link list, snmp_gen_callback->next.
*
* @param major is the SNMP callback major type used
* - SNMP_CALLBACK_LIBRARY
* - SNMP_CALLBACK_APPLICATION
*
* @param minor is the SNMP callback minor type used
* - SNMP_CALLBACK_POST_READ_CONFIG
* - SNMP_CALLBACK_STORE_DATA
* - SNMP_CALLBACK_SHUTDOWN
* - SNMP_CALLBACK_POST_PREMIB_READ_CONFIG
* - SNMP_CALLBACK_LOGGING
* - SNMP_CALLBACK_SESSION_INIT
*
* @param new_callback is the callback function that is registered.
*
* @param arg when not NULL is a void pointer used whenever new_callback
* function is exercised. Ownership is transferred to the twodimensional
* thecallbacks[][] array. The function clear_callback() will deallocate
* the memory pointed at by calling free().
*
* @return
* Returns SNMPERR_GENERR if major is >= MAX_CALLBACK_IDS or minor is >=
* MAX_CALLBACK_SUBIDS or a snmp_gen_callback pointer could not be
* allocated, otherwise SNMPERR_SUCCESS is returned.
* - \#define MAX_CALLBACK_IDS 2
* - \#define MAX_CALLBACK_SUBIDS 16
*
* @see snmp_call_callbacks
* @see snmp_unregister_callback
*/
int
snmp_register_callback(int major, int minor, SNMPCallback * new_callback,
void *arg)
{
return netsnmp_register_callback( major, minor, new_callback, arg,
NETSNMP_CALLBACK_DEFAULT_PRIORITY);
}
/**
* Register a callback function.
*
* @param major Major callback event type.
* @param minor Minor callback event type.
* @param new_callback Callback function being registered.
* @param arg Argument that will be passed to the callback function.
* @param priority Handler invocation priority. When multiple handlers have
* been registered for the same (major, minor) callback event type, handlers
* with the numerically lowest priority will be invoked first. Handlers with
* identical priority are invoked in the order they have been registered.
*
* @see snmp_register_callback
*/
int
netsnmp_register_callback(int major, int minor, SNMPCallback * new_callback,
void *arg, int priority)
{
struct snmp_gen_callback *newscp = NULL, *scp = NULL;
struct snmp_gen_callback **prevNext = &(thecallbacks[major][minor]);
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
return SNMPERR_GENERR;
}
if (_callback_need_init)
init_callbacks();
_callback_lock(major,minor, "netsnmp_register_callback", 1);
if ((newscp = SNMP_MALLOC_STRUCT(snmp_gen_callback)) == NULL) {
_callback_unlock(major,minor);
return SNMPERR_GENERR;
} else {
newscp->priority = priority;
newscp->sc_client_arg = arg;
newscp->sc_callback = new_callback;
newscp->next = NULL;
for (scp = thecallbacks[major][minor]; scp != NULL;
scp = scp->next) {
if (newscp->priority < scp->priority) {
newscp->next = scp;
break;
}
prevNext = &(scp->next);
}
*prevNext = newscp;
DEBUGMSGTL(("callback", "registered (%d,%d) at %p with priority %d\n",
major, minor, newscp, priority));
_callback_unlock(major,minor);
return SNMPERR_SUCCESS;
}
}
/**
* This function calls the callback function for each registered callback of
* type major and minor.
*
* @param major is the SNMP callback major type used
*
* @param minor is the SNMP callback minor type used
*
* @param caller_arg is a void pointer which is sent in as the callback's
* serverarg parameter, if needed.
*
* @return Returns SNMPERR_GENERR if major is >= MAX_CALLBACK_IDS or
* minor is >= MAX_CALLBACK_SUBIDS, otherwise SNMPERR_SUCCESS is returned.
*
* @see snmp_register_callback
* @see snmp_unregister_callback
*/
int
snmp_call_callbacks(int major, int minor, void *caller_arg)
{
struct snmp_gen_callback *scp;
unsigned int count = 0;
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
return SNMPERR_GENERR;
}
if (_callback_need_init)
init_callbacks();
#ifdef LOCK_PER_CALLBACK_SUBID
_callback_lock(major,minor,"snmp_call_callbacks", 1);
#else
/*
* Notes:
* - this gets hit the first time a trap is sent after a new trap
* destination has been added (session init cb during send trap cb)
*/
_callback_lock(major,minor, NULL, 0);
#endif
DEBUGMSGTL(("callback", "START calling callbacks for maj=%d min=%d\n",
major, minor));
/*
* for each registered callback of type major and minor
*/
for (scp = thecallbacks[major][minor]; scp != NULL; scp = scp->next) {
/*
* skip unregistered callbacks
*/
if(NULL == scp->sc_callback)
continue;
DEBUGMSGTL(("callback", "calling a callback for maj=%d min=%d\n",
major, minor));
/*
* call them
*/
(*(scp->sc_callback)) (major, minor, caller_arg,
scp->sc_client_arg);
count++;
}
DEBUGMSGTL(("callback",
"END calling callbacks for maj=%d min=%d (%d called)\n",
major, minor, count));
_callback_unlock(major,minor);
return SNMPERR_SUCCESS;
}
#ifndef NETSNMP_FEATURE_REMOVE_CALLBACK_COUNT
int
snmp_count_callbacks(int major, int minor)
{
int count = 0;
struct snmp_gen_callback *scp;
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
return SNMPERR_GENERR;
}
if (_callback_need_init)
init_callbacks();
for (scp = thecallbacks[major][minor]; scp != NULL; scp = scp->next) {
count++;
}
return count;
}
#endif /* NETSNMP_FEATURE_REMOVE_CALLBACK_COUNT */
int
snmp_callback_available(int major, int minor)
{
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS) {
return SNMPERR_GENERR;
}
if (_callback_need_init)
init_callbacks();
if (thecallbacks[major][minor] != NULL) {
return SNMPERR_SUCCESS;
}
return SNMPERR_GENERR;
}
/**
* This function unregisters a specified callback function given a major
* and minor type.
*
* Note: no bound checking on major and minor.
*
* @param major is the SNMP callback major type used
*
* @param minor is the SNMP callback minor type used
*
* @param target is the callback function that will be unregistered.
*
* @param arg is a void pointer used for comparison against the registered
* callback's sc_client_arg variable.
*
* @param matchargs is an integer used to bypass the comparison of arg and the
* callback's sc_client_arg variable only when matchargs is set to 0.
*
*
* @return
* Returns the number of callbacks that were unregistered.
*
* @see snmp_register_callback
* @see snmp_call_callbacks
*/
int
snmp_unregister_callback(int major, int minor, SNMPCallback * target,
void *arg, int matchargs)
{
struct snmp_gen_callback *scp;
struct snmp_gen_callback **prevNext;
int count = 0;
if (major >= MAX_CALLBACK_IDS || minor >= MAX_CALLBACK_SUBIDS)
return SNMPERR_GENERR;
scp = thecallbacks[major][minor];
prevNext = &(thecallbacks[major][minor]);
if (_callback_need_init)
init_callbacks();
#ifdef LOCK_PER_CALLBACK_SUBID
_callback_lock(major,minor,"snmp_unregister_callback", 1);
#else
/*
* Notes;
* - this gets hit at shutdown, during cleanup. No easy fix.
*/
_callback_lock(major,minor,"snmp_unregister_callback", 0);
#endif
while (scp != NULL) {
if ((scp->sc_callback == target) &&
(!matchargs || (scp->sc_client_arg == arg))) {
DEBUGMSGTL(("callback", "unregistering (%d,%d) at %p\n", major,
minor, scp));
if(1 == CALLBACK_LOCK_COUNT(major,minor)) {
*prevNext = scp->next;
SNMP_FREE(scp);
scp = *prevNext;
}
else {
scp->sc_callback = NULL;
/** set cleanup flag? */
}
count++;
} else {
prevNext = &(scp->next);
scp = scp->next;
}
}
_callback_unlock(major,minor);
return count;
}
/**
* find and clear client args that match ptr
*
* @param ptr pointer to search for
* @param i callback id to start at
* @param j callback subid to start at
*/
int
netsnmp_callback_clear_client_arg(void *ptr, int i, int j)
{
struct snmp_gen_callback *scp = NULL;
int rc = 0;
/*
* don't init i and j before loop, since the caller specified
* the starting point explicitly. But *after* the i loop has
* finished executing once, init j to 0 for the next pass
* through the subids.
*/
for (; i < MAX_CALLBACK_IDS; i++,j=0) {
for (; j < MAX_CALLBACK_SUBIDS; j++) {
scp = thecallbacks[i][j];
while (scp != NULL) {
if ((NULL != scp->sc_callback) &&
(scp->sc_client_arg != NULL) &&
(scp->sc_client_arg == ptr)) {
DEBUGMSGTL(("9:callback", " clearing %p at [%d,%d]\n", ptr, i, j));
scp->sc_client_arg = NULL;
++rc;
}
scp = scp->next;
}
}
}
if (0 != rc) {
DEBUGMSGTL(("callback", "removed %d client args\n", rc));
}
return rc;
}
void
clear_callback(void)
{
unsigned int i = 0, j = 0;
struct snmp_gen_callback *scp = NULL;
if (_callback_need_init)
init_callbacks();
DEBUGMSGTL(("callback", "clear callback\n"));
for (i = 0; i < MAX_CALLBACK_IDS; i++) {
for (j = 0; j < MAX_CALLBACK_SUBIDS; j++) {
_callback_lock(i,j, "clear_callback", 1);
scp = thecallbacks[i][j];
while (scp != NULL) {
thecallbacks[i][j] = scp->next;
/*
* if there is a client arg, check for duplicates
* and then free it.
*/
if ((NULL != scp->sc_callback) &&
(scp->sc_client_arg != NULL)) {
void *tmp_arg;
/*
* save the client arg, then set it to null so that it
* won't look like a duplicate, then check for duplicates
* starting at the current i,j (earlier dups should have
* already been found) and free the pointer.
*/
tmp_arg = scp->sc_client_arg;
scp->sc_client_arg = NULL;
DEBUGMSGTL(("9:callback", " freeing %p at [%d,%d]\n", tmp_arg, i, j));
(void)netsnmp_callback_clear_client_arg(tmp_arg, i, j);
free(tmp_arg);
}
SNMP_FREE(scp);
scp = thecallbacks[i][j];
}
_callback_unlock(i,j);
}
}
}
#ifndef NETSNMP_FEATURE_REMOVE_CALLBACK_LIST
struct snmp_gen_callback *
snmp_callback_list(int major, int minor)
{
if (_callback_need_init)
init_callbacks();
return (thecallbacks[major][minor]);
}
#endif /* NETSNMP_FEATURE_REMOVE_CALLBACK_LIST */
/** @} */
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