changeset 1098:f38d77f9cfd3

Initial implementation of the hook mechanism
author Sebastien Decugis <sdecugis@freediameter.net>
date Thu, 09 May 2013 11:59:34 +0800
parents 4d2dcb54d9a6
children 40b48a3997a2
files include/freeDiameter/freeDiameter-host.h.in include/freeDiameter/libfdcore.h include/freeDiameter/libfdproto.h libfdcore/cnxctx.c libfdcore/core.c libfdcore/fdcore-internal.h libfdcore/hooks.c libfdproto/messages.c
diffstat 8 files changed, 267 insertions(+), 43 deletions(-) [+]
line wrap: on
line diff
--- a/include/freeDiameter/freeDiameter-host.h.in	Mon May 06 18:49:59 2013 +0800
+++ b/include/freeDiameter/freeDiameter-host.h.in	Thu May 09 11:59:34 2013 +0800
@@ -94,6 +94,9 @@
 #define FD_DEFAULT_CONF_FILENAME "freeDiameter.conf"
 #endif /* FD_DEFAULT_CONF_FILENAME */
 
+/* Maximum number of hooks handlers that can be registered. Make this compilation option if needed */
+#define FD_HOOK_HANDLE_LIMIT	5
+
 #ifdef __cplusplus
 }
 #endif
--- a/include/freeDiameter/libfdcore.h	Mon May 06 18:49:59 2013 +0800
+++ b/include/freeDiameter/libfdcore.h	Thu May 09 11:59:34 2013 +0800
@@ -878,7 +878,7 @@
 
 /* These functions allow an extension to collect state information about the
  * framework, as well as being hooked at some key checkpoints in the processing
- * for logging / statistics purpose.
+ * for logging or statistics purpose.
  */
  
 
@@ -886,11 +886,11 @@
  *
  * PARAMETERS:
  *  type	: The type of hook that triggered this call, in case same cb is registered for several hooks.
- *  msg 	: If relevant, the pointer to the message trigging the call. NULL otherwise.
+ *  msg 	: If relevant, the pointer to the message triggering the call. NULL otherwise.
  *  peer        : If relevant, the pointer to the peer associated with the call. NULL otherwise.
  *  other	: For some callbacks, the remaining information is passed in this parameter. See each hook detail.
  *  permsgdata  : Structure associated with a given message, across several hooks. 
- *                 Same structure is associated with requests and corresponding answers. 
+ *                 A different structure is associated with requests and corresponding answers. 
  *                 See fd_hook_data_hdl below for details.
  *                 If no fd_hook_data_hdl is registered with this callback, this parameter is always NULL
  *  regdata     : Data pointer stored at registration, opaque for the framework.
@@ -915,10 +915,8 @@
 		/* Hook called as soon as a message has been received from the network, after TLS & boundary processing.
 		 - {msg} is NULL.
 		 - {peer} is NULL.
-		 - {*other} is NULL, {other} points to a valid location where you can store a pointer. 
-		    This same pointer will then passed to the next hook, once message is processed.
-		    IMPORTANT: free() will be called on this pointer if any problem, so this pointer must be malloc'd.
-		 - {permsgdata} is NULL.
+		 - {other} is a pointer to a structure { size_t len; uint8_t * buf; } containing the received buffer.
+		 - {permsgdata} points to either a new empty structure allocated for this message (cf. fd_hook_data_hdl), or NULL if no hdl is registered.
 		 */
 		 
 	HOOK_MESSAGE_RECEIVED,
@@ -927,8 +925,8 @@
 		   try to call fd_msg_parse_dict, it will slow down the operation of a relay agent.
 		 - {peer} is set if the message is received from a peer's connection, and NULL if the message is from a new client
 		   connected and not yet identified
-		 - {*other} contains the pointer stored with the HOOK_DATA_RECEIVED hook if any, NULL otherwise. After this hook returns, free(*other) is called if not NULL.
-		 - {permsgdata} points to either a new empty structure allocated for this request (cf. fd_hook_data_hdl), or the request's existing structure if the message is an answer.
+		 - {other} is NULL.
+		 - {permsgdata} points to either a new empty structure allocated for this message or the one passed to HOOK_DATA_RECEIVED if used.
 		 */
 	
 	HOOK_MESSAGE_LOCAL,
@@ -945,10 +943,9 @@
 		 - {msg} points to the sent message. Again, the objects may not have been dictionary resolved. If you
 		   try to call fd_msg_parse_dict, it will slow down the operation of a relay agent.
 		 - {peer} is set if the message is sent to a peer's connection, and NULL if the message is sent to a new client
-		   connected and not yet identified / being rejected
+		   connected and not yet identified, or being rejected
 		 - {other} is NULL.
 		 - {permsgdata} points to existing structure if any, or a new structure otherwise. 
-		    If the message is an answer, the structure is shared with the corresponding request.
 		 */
 	
 	HOOK_MESSAGE_FAILOVER,
@@ -958,7 +955,7 @@
 		   try to call fd_msg_parse_dict, it might slow down the operation of a relay agent, although this hook is not on the normal execution path.
 		 - {peer} is the peer this message was previously sent to.
 		 - {other} is NULL.
-		 - {permsgdata} points to existing structure associated with this request. 
+		 - {permsgdata} points to existing structure if any, or a new structure otherwise. 
 		 */
 	
 	HOOK_MESSAGE_ROUTING_ERROR,
@@ -993,8 +990,8 @@
 		 */
 	
 	HOOK_MESSAGE_DROPPED,
-		/* Hook called when a message is being discarded by the framework because of some error.
-		   It is probably a good idea to log this for analysis.
+		/* Hook called when a message is being discarded by the framework because of some error condition (normal or abnormal).
+		   It is probably a good idea to log this for analysis / backup.
 		 - {msg} points to the message, which will be freed as soon as the hook returns.
 		 - {peer} is NULL.
 		 - {other} is a char * pointer to the error message (human-readable).
@@ -1021,7 +1018,7 @@
 };
 
 
-/* Type if the {permsgdata} ointer. It is up to each extension to define its own structure. This is opaque for the framework. */
+/* Type if the {permsgdata}. It is up to each extension to define its own structure. This is opaque for the framework. */
 struct fd_hook_permsgdata;
 
 /* A handle that will be associated with the extension, and with the permsgdata structures. */
@@ -1034,14 +1031,17 @@
  * FUNCTION:	fd_hook_data_register
  *
  * PARAMETERS:
- *  permsgdata_new_cb     : function called to initialize a new empty fd_hook_permsgdata structure, when a hook will be called for a message with not structure yet. If the function returns NULL, it will be called again for the next hook.
- *  permsgdata_destroy_cb : function called when a message is being disposed. It should free the resources associated with the fd_hook_permsgdata.
- *  new_handle            : On success, a handler to the registered callback is stored here. 
+ *  permsgdata_size     : the size of the fd_hook_permsgdata structure. 
+ *  permsgdata_init_cb  : function called to initialize a new fd_hook_permsgdata structure, when a hook will be called for a message that does not have such structure yet. 
+ *                           The memory is already allocated and blanked, so you can pass NULL if no further handling is required.
+ *  permsgdata_fini_cb  : function called when a message is being disposed. It should free the resources associated with the fd_hook_permsgdata. 
+ *                           You can pass NULL if no special handling is required. The memory of the permsgdata structure itself will be freed by the framework.
+ *  new_handle          : On success, a handler to the registered callback is stored here. 
  *		             This handler will be used to unregister the cb.
  *
  * DESCRIPTION: 
  *   Register a new fd_hook_data_hdl. This handle is used during hooks registration (see below) in order to associate data with the messages, to allow keeping tracking of the message easily.
- *  Note that these handlers are statically allocated and cannot be unregistered.
+ *  Note that these handlers are statically allocated and cannot be unregistered. FD_HOOK_HANDLE_LIMIT handlers can be registered at maximum (recompile libfdproto if you change this value)
  *
  * RETURN VALUE:
  *  0      	: The callback is registered.
@@ -1049,12 +1049,12 @@
  *  ENOSPC	: Too many handles already registered. You may need to increase the limit in the code.
  */
 int fd_hook_data_register(
-	struct fd_hook_permsgdata * (*permsgdata_new_cb)     (void),
-        void (*permsgdata_destroy_cb) (struct fd_hook_permsgdata *),
-        struct fd_hook_data_hdl **    new_handle
+	size_t permsgdata_size,
+	void (*permsgdata_init_cb) (struct fd_hook_permsgdata *),
+        void (*permsgdata_fini_cb) (struct fd_hook_permsgdata *),
+        struct fd_hook_data_hdl **new_handle
 );
 
-
 /* A handler associated with a registered hook callback (for cleanup) */
 struct fd_hook_hdl; 
 
@@ -1062,7 +1062,7 @@
  * FUNCTION:	fd_hook_register
  *
  * PARAMETERS:
- *  type	  : The fd_hook_type for which this cb is registered. Call several times if you want to register for several hooks.
+ *  type_mask	  : A bitmask of fd_hook_type bits for which this cb is registered, e.g. ((1 << HOOK_MESSAGE_RECEIVED) || (1 << HOOK_MESSAGE_SENT))
  *  fd_hook_cb	  : The callback function to register (see prototype above).
  *  regdata	  : Pointer to pass to the callback when it is called. The data is opaque to the daemon.
  *  data_hdl      : If permsgdata is requested for the hooks, a handler registered with fd_hook_data_register. NULL otherwise.
@@ -1078,9 +1078,9 @@
  *  EINVAL 	: A parameter is invalid.
  *  ENOMEM	: Not enough memory to complete the operation
  */
-int fd_hook_register (  enum fd_hook_type type, 
-			void (*fd_hook_cb)(enum fd_hook_type type, struct msg * msg, struct peer_hdr * peer, void * other, void * regdata), 
-			void * regdata, 
+int fd_hook_register (  uint32_t type_mask, 
+			void (*fd_hook_cb)(enum fd_hook_type type, struct msg * msg, struct peer_hdr * peer, void * other, struct fd_hook_permsgdata *pmd, void * regdata), 
+			void  *regdata, 
 			struct fd_hook_data_hdl *data_hdl,
 			struct fd_hook_hdl ** handler );
 
--- a/include/freeDiameter/libfdproto.h	Mon May 06 18:49:59 2013 +0800
+++ b/include/freeDiameter/libfdproto.h	Thu May 09 11:59:34 2013 +0800
@@ -2549,6 +2549,14 @@
 int fd_msg_sess_set(struct msg * msg, struct session * session);
 
 
+/* Helper for the hooks mechanism, for use from libfdcore */
+struct fd_msg_pmdl {
+	struct fd_list sentinel; /* if the sentinel.o field is NULL, the structure is not initialized. Otherwise it points to the cleanup function in libfdcore. */
+	pthread_mutex_t lock;
+};
+#define FD_MSG_PMDL_INITIALIZER(pmdl_ptr)        { FD_LIST_INITIALIZER(  (pmdl_ptr)->sentinel       ), PTHREAD_MUTEX_INITIALIZER }
+struct fd_msg_pmdl * fd_msg_pmdl_get(struct msg * msg);
+
 /***************************************/
 /*   Manage AVP values                 */
 /***************************************/
--- a/libfdcore/cnxctx.c	Mon May 06 18:49:59 2013 +0800
+++ b/libfdcore/cnxctx.c	Thu May 09 11:59:34 2013 +0800
@@ -735,6 +735,8 @@
 			received += ret;
 		}
 		
+		// fd_msg_log(....)
+		
 		/* We have received a complete message, pass it to the daemon */
 		CHECK_FCT_DO( fd_event_send( fd_cnx_target_queue(conn), FDEVP_CNX_MSG_RECV, length, newmsg), /* continue or destroy everything? */);
 		
--- a/libfdcore/core.c	Mon May 06 18:49:59 2013 +0800
+++ b/libfdcore/core.c	Thu May 09 11:59:34 2013 +0800
@@ -186,6 +186,7 @@
 	CHECK_FCT( fd_dict_base_protocol(fd_g_config->cnf_dict) );
 	
 	/* Initialize some modules */
+	CHECK_FCT( fd_hooks_init()  );
 	CHECK_FCT( fd_queues_init() );
 	CHECK_FCT( fd_msg_init()    );
 	CHECK_FCT( fd_sess_start()  );
--- a/libfdcore/fdcore-internal.h	Mon May 06 18:49:59 2013 +0800
+++ b/libfdcore/fdcore-internal.h	Thu May 09 11:59:34 2013 +0800
@@ -362,4 +362,8 @@
 /* Flags for the fd_cnx_send function : */
 #define FD_CNX_ORDERED		(1 << 0)	/* All messages sent with this flag set will be delivered in the same order. No guarantee on other messages */
 
+/* Internal calls of the hook mechanism */
+void   fd_hook_call(enum fd_hook_type type, struct msg * msg, struct fd_peer * peer, void * other, struct fd_msg_pmdl * pmdl);
+void   fd_hook_associate(struct msg * msg, struct fd_msg_pmdl * pmdl);
+int    fd_hooks_init(void);
 #endif /* _FDCORE_INTERNAL_H */
--- a/libfdcore/hooks.c	Mon May 06 18:49:59 2013 +0800
+++ b/libfdcore/hooks.c	Thu May 09 11:59:34 2013 +0800
@@ -35,30 +35,225 @@
 
 #include "fdcore-internal.h"
 
-struct fd_hook_hdl; 
-struct fd_hook_data_hdl;
+/* Structures for the fd_hook_data_hdl management */
+static struct fd_hook_data_hdl {
+	size_t	pmd_size;
+	void  (*pmd_init_cb)(struct fd_hook_permsgdata *);
+	void  (*pmd_fini_cb)(struct fd_hook_permsgdata *);
+} HDH_array[FD_HOOK_HANDLE_LIMIT];
+static int max_index = 0;
+static pthread_mutex_t HDH_lock = PTHREAD_MUTEX_INITIALIZER;
+
+/* The structure linked from the msg structure list */
+struct pmd_list_item {
+	struct fd_list	chain;		/* this list is ordered by hdl */
+	struct fd_hook_data_hdl * hdl; 
+	struct fd_hook_permsgdata { } pmd; /* this data belongs to the extension; we only know the size of it */
+};
+
+#define sizeof_pmd(hdl)	(((size_t)&((struct pmd_list_item *)0)->pmd) + hdl->pmd_size)
 
-int fd_hook_data_register(
-	struct fd_hook_permsgdata * (*permsgdata_new_cb)     (void),
-        void (*permsgdata_destroy_cb) (struct fd_hook_permsgdata *),
-        struct fd_hook_data_hdl **    new_handle
-)
+/* Now a hook registered by an extension */
+struct fd_hook_hdl {
+	struct fd_list chain[HOOK_PEER_LAST+1];
+	void (*fd_hook_cb)(enum fd_hook_type type, struct msg * msg, struct peer_hdr * peer, void * other, struct fd_hook_permsgdata *pmd, void * regdata);
+	void  *regdata;
+	struct fd_hook_data_hdl *data_hdl;
+};
+
+/* Array of those hooks */
+struct {
+	struct fd_list sentinel;
+	pthread_rwlock_t rwlock;
+} HS_array[HOOK_PEER_LAST+1];
+
+/* Initialize the array of sentinels for the hooks */
+int fd_hooks_init(void)
 {
-	return ENOTSUP;
+	int i;
+	for (i=0; i <= HOOK_PEER_LAST; i++) {
+		fd_list_init(&HS_array[i].sentinel, NULL);
+		CHECK_POSIX( pthread_rwlock_init(&HS_array[i].rwlock, NULL) );
+	}
+	return 0;
 }
 
-int fd_hook_register (  enum fd_hook_type type, 
-			void (*fd_hook_cb)(enum fd_hook_type type, struct msg * msg, struct peer_hdr * peer, void * other, void * regdata), 
-			void * regdata, 
+/* Get a slot in the array */
+int fd_hook_data_register(
+	size_t permsgdata_size,
+	void (*permsgdata_init_cb) (struct fd_hook_permsgdata *),
+        void (*permsgdata_fini_cb) (struct fd_hook_permsgdata *),
+        struct fd_hook_data_hdl **new_handle)
+{
+	int ret = ENOSPC, idx;
+	TRACE_ENTRY("%zd %p %p %p", permsgdata_size, permsgdata_init_cb, permsgdata_fini_cb, new_handle);
+	
+	CHECK_PARAMS( permsgdata_size && new_handle );
+	
+	CHECK_POSIX( pthread_mutex_lock(&HDH_lock) );
+	if (max_index < FD_HOOK_HANDLE_LIMIT) {
+		idx = max_index++;
+		ret = 0;
+	}
+	CHECK_POSIX( pthread_mutex_unlock(&HDH_lock) );
+	
+	if (ret == 0) {
+		HDH_array[idx].pmd_size = permsgdata_size;
+		HDH_array[idx].pmd_init_cb = permsgdata_init_cb;
+		HDH_array[idx].pmd_fini_cb = permsgdata_fini_cb;
+		*new_handle = &HDH_array[idx];
+	}
+	
+	return ret;
+}
+
+/* Register a new hook callback */
+int fd_hook_register (  uint32_t type_mask, 
+			void (*fd_hook_cb)(enum fd_hook_type type, struct msg * msg, struct peer_hdr * peer, void * other, struct fd_hook_permsgdata *pmd, void * regdata), 
+			void  *regdata, 
 			struct fd_hook_data_hdl *data_hdl,
 			struct fd_hook_hdl ** handler )
 {
-	return ENOTSUP;
+	struct fd_hook_hdl * newhdl = NULL;
+	int i;
+	
+	TRACE_ENTRY("%x %p %p %p %p", type_mask, fd_hook_cb, regdata, data_hdl, handler);
+	
+	CHECK_PARAMS( fd_hook_cb && handler );
+	
+	CHECK_MALLOC( newhdl = malloc(sizeof(struct fd_hook_hdl)) );
+	memset(newhdl, 0, sizeof(struct fd_hook_hdl));
+	
+	newhdl->fd_hook_cb = fd_hook_cb;
+	newhdl->regdata = regdata;
+	newhdl->data_hdl = data_hdl;
+	
+	for (i=0; i <= HOOK_PEER_LAST; i++) {
+		fd_list_init(&newhdl->chain[i], newhdl);
+		if (type_mask & (1<<i)) {
+			CHECK_POSIX( pthread_rwlock_wrlock(&HS_array[i].rwlock) );
+			fd_list_insert_before( &HS_array[i].sentinel, &newhdl->chain[i]);
+			CHECK_POSIX( pthread_rwlock_unlock(&HS_array[i].rwlock) );
+		}
+	}
+	
+	*handler = newhdl;
+	return 0;
+}
+
+/* free this hook callback */
+int fd_hook_unregister( struct fd_hook_hdl * handler )
+{
+	int i;
+	TRACE_ENTRY("%p", handler);
+	CHECK_PARAMS( handler );
+	
+	for (i=0; i <= HOOK_PEER_LAST; i++) {
+		if ( ! FD_IS_LIST_EMPTY(&handler->chain[i])) {
+			CHECK_POSIX( pthread_rwlock_wrlock(&HS_array[i].rwlock) );
+			fd_list_unlink(&handler->chain[i]);
+			CHECK_POSIX( pthread_rwlock_unlock(&HS_array[i].rwlock) );
+		}
+	}
+	
+	free(handler);
+	
+	return 0;
+}
+
+/* callback for the libfdproto to free the data associated with a message */
+static void pmdl_free(struct fd_msg_pmdl *pmdl)
+{
+	/* destroy all the items in the list */
+	while (!FD_IS_LIST_EMPTY(&pmdl->sentinel)) {
+		struct pmd_list_item * li = (struct pmd_list_item *)(pmdl->sentinel.next);
+		if (li->hdl->pmd_fini_cb) {
+			(*li->hdl->pmd_fini_cb)(&li->pmd);
+		}
+		fd_list_unlink(&li->chain);
+		free(li);
+	}
+	CHECK_POSIX_DO( pthread_mutex_destroy(&pmdl->lock), );
+	pmdl->sentinel.o = NULL;
+}
+
+/* Save the list of pmd into the message structure, as well as the callback to free this list */
+void   fd_hook_associate(struct msg * msg, struct fd_msg_pmdl * pmdl)
+{
+	struct fd_msg_pmdl * in_msg;
+	
+	CHECK_PARAMS_DO( msg && pmdl, return );
+	in_msg = fd_msg_pmdl_get(msg);
+	ASSERT(in_msg && (in_msg->sentinel.o == NULL)); /* error / already initialized ??? */
+	fd_list_init(&in_msg->sentinel, pmdl_free);
+	CHECK_POSIX_DO( pthread_mutex_init(&in_msg->lock, NULL), );
+	/* Now move all items from the pmdl pointer into the initialized list */
+	CHECK_POSIX_DO( pthread_mutex_lock(&pmdl->lock), );
+	fd_list_move_end(&in_msg->sentinel, &pmdl->sentinel);
+	CHECK_POSIX_DO( pthread_mutex_unlock(&pmdl->lock), );
+	pmdl_free(pmdl);
+	/* We're done */
+}
+
+/* Return the location of the permsgdata area corresponding to this handle, after eventually having created it. Return NULL in case of failure */
+static struct fd_hook_permsgdata * get_or_create_pmd(struct fd_msg_pmdl *pmdl, struct fd_hook_hdl * h) 
+{
+	struct fd_hook_permsgdata * ret = NULL;
+	struct fd_list * li;
+	CHECK_POSIX_DO( pthread_mutex_lock(&pmdl->lock), );
+	
+	/* Search in the list for an item with the same handle. The list is ordered by this handle */
+	for (li=pmdl->sentinel.next; li != &pmdl->sentinel; li = li->next) {
+		struct pmd_list_item * pli = (struct pmd_list_item *) li;
+		if (pli->hdl == h->data_hdl)
+			ret = &pli->pmd;
+		if (pli->hdl >= h->data_hdl)
+			break;
+	}
+	if (!ret) {
+		/* we need to create a new one and insert before li */
+		struct pmd_list_item * pli;
+		CHECK_MALLOC_DO( pli = malloc(sizeof_pmd(h->data_hdl)), );
+		if (pli) {
+			memset(pli, 0, sizeof_pmd(h->data_hdl));
+			fd_list_init(&pli->chain, pli);
+			pli->hdl = h->data_hdl;
+			ret = &pli->pmd;
+			if (h->data_hdl->pmd_init_cb) {
+				(*h->data_hdl->pmd_init_cb)(ret);
+			}
+			fd_list_insert_before(li, &pli->chain);
+		}
+	}
+	
+	CHECK_POSIX_DO( pthread_mutex_unlock(&pmdl->lock), );
+	return ret;
 }
 
 
-int fd_hook_unregister( struct fd_hook_hdl * handler )
+/* The function that does the work of calling the extension's callbacks and also managing the permessagedata structures */
+void   fd_hook_call(enum fd_hook_type type, struct msg * msg, struct fd_peer * peer, void * other, struct fd_msg_pmdl * pmdl)
 {
-	return ENOTSUP;
+	struct fd_list * li;
+	ASSERT(type <= HOOK_PEER_LAST);
+	
+	/* lock the list of hooks for this type */
+	CHECK_POSIX_DO( pthread_rwlock_rdlock(&HS_array[type].rwlock), );
+	
+	/* for each registered hook */
+	for (li = HS_array[type].sentinel.next; li != &HS_array[type].sentinel; li = li->next) {
+		struct fd_hook_hdl * h = (struct fd_hook_hdl *)li->o;
+		struct fd_hook_permsgdata * pmd = NULL;
+		
+		/* do we need to handle pmd ? */
+		if (h->data_hdl && pmdl) {
+			pmd = get_or_create_pmd(pmdl, h);
+		}
+		
+		/* Now, call this callback */
+		(*h->fd_hook_cb)(type, msg, &peer->p_hdr, other, pmd, h->regdata);
+	}
+	
+	/* done */
+	CHECK_POSIX_DO( pthread_rwlock_unlock(&HS_array[type].rwlock), );
 }
-
--- a/libfdproto/messages.c	Mon May 06 18:49:59 2013 +0800
+++ b/libfdproto/messages.c	Thu May 09 11:59:34 2013 +0800
@@ -136,7 +136,7 @@
 		}		 msg_cb;		/* Callback to be called when an answer is received, or timeout expires, if not NULL */
 	DiamId_t		 msg_src_id;		/* Diameter Id of the peer this message was received from. This string is malloc'd and must be freed */
 	size_t			 msg_src_id_len;	/* cached length of this string */
-	
+	struct fd_msg_pmdl	 msg_pmdl;		/* list of permessagedata structures. */
 };
 
 /* Macro to compute the message header size */
@@ -673,6 +673,10 @@
 		CHECK_FCT_DO( fd_sess_reclaim_msg ( &_M(obj)->msg_sess ), /* continue */);
 	}
 	
+	if ((obj->type == MSG_MSG) && (_M(obj)->msg_pmdl.sentinel.o != NULL)) {
+		((void (*)(struct fd_msg_pmdl *))_M(obj)->msg_pmdl.sentinel.o)(&_M(obj)->msg_pmdl);
+	}
+	
 	/* free the object */
 	free(obj);
 	
@@ -1497,6 +1501,13 @@
 	return 0;
 }
 
+/* Retrieve the location of the pmd list for the message; return NULL if failed */
+struct fd_msg_pmdl * fd_msg_pmdl_get(struct msg * msg)
+{
+	CHECK_PARAMS_DO( CHECK_MSG(msg), return NULL );
+	return &msg->msg_pmdl;
+}
+
 
 /******************* End-to-end counter *********************/
 static uint32_t fd_eteid;
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