posix: Add implementation of mq_notify() function

The function was the last missing piece of the `_POSIX_MESSAGE_PASSING`
option group. Due to lack of signal subsystem in the Zephyr RTOS
the `sigev_notify` member of the `sigevent` structure that describes
the notification cannot be set to `SIGEV_SIGNAL` - this notification
type is not implemented, the function will return -1 and set `errno`
to `ENOSYS`.

`mq_notify` documentation:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_notify.html

Fixes #66958

Signed-off-by: Adam Wojasinski <awojasinski@baylibre.com>

include/zephyr/posix/mqueue.h

@@ -10,6 +10,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/posix/time.h>
 #include <zephyr/posix/fcntl.h>
+#include <zephyr/posix/signal.h>
 #include <zephyr/posix/sys/stat.h>
 #include "posix_types.h"
 
@@ -40,6 +41,7 @@ int mq_timedreceive(mqd_t mqdes, char *msg_ptr, size_t msg_len,
 			unsigned int *msg_prio, const struct timespec *abstime);
 int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
 		 unsigned int msg_prio, const struct timespec *abstime);
+int mq_notify(mqd_t mqdes, const struct sigevent *notification);
 
 #ifdef __cplusplus
 }

lib/posix/mqueue.c

@@ -1,14 +1,17 @@
 /*
  * Copyright (c) 2018 Intel Corporation
+ * Copyright (c) 2024 BayLibre, SAS
  *
  * SPDX-License-Identifier: Apache-2.0
  */
 #include <zephyr/kernel.h>
 #include <errno.h>
 #include <string.h>
 #include <zephyr/sys/atomic.h>
-#include <zephyr/posix/time.h>
 #include <zephyr/posix/mqueue.h>
+#include <zephyr/posix/pthread.h>
+
+#define SIGEV_MASK (SIGEV_NONE | SIGEV_SIGNAL | SIGEV_THREAD)
 
 typedef struct mqueue_object {
 	sys_snode_t snode;
@@ -17,6 +20,7 @@ typedef struct mqueue_object {
 	struct k_msgq queue;
 	atomic_t ref_count;
 	char *name;
+	struct sigevent not;
 } mqueue_object;
 
 typedef struct mqueue_desc {
@@ -34,9 +38,11 @@ int64_t timespec_to_timeoutms(const struct timespec *abstime);
 static mqueue_object *find_in_list(const char *name);
 static int32_t send_message(mqueue_desc *mqd, const char *msg_ptr, size_t msg_len,
 			  k_timeout_t timeout);
-static int receive_message(mqueue_desc *mqd, char *msg_ptr, size_t msg_len,
+static int32_t receive_message(mqueue_desc *mqd, char *msg_ptr, size_t msg_len,
 			   k_timeout_t timeout);
+static void remove_notification(mqueue_object *msg_queue);
 static void remove_mq(mqueue_object *msg_queue);
+static void *mq_notify_thread(void *arg);
 
 /**
  * @brief Open a message queue.
@@ -341,6 +347,74 @@ int mq_setattr(mqd_t mqdes, const struct mq_attr *mqstat,
 	return 0;
 }
 
+/**
+ * @brief Notify process that a message is available.
+ *
+ * See IEEE 1003.1
+ */
+int mq_notify(mqd_t mqdes, const struct sigevent *notification)
+{
+	mqueue_desc *mqd = (mqueue_desc *)mqdes;
+
+	if (mqd == NULL) {
+		errno = EBADF;
+		return -1;
+	}
+
+	mqueue_object *msg_queue = mqd->mqueue;
+
+	if (notification == NULL) {
+		if ((msg_queue->not.sigev_notify & SIGEV_MASK) == 0) {
+			errno = EINVAL;
+			return -1;
+		}
+		remove_notification(msg_queue);
+		return 0;
+	}
+
+	if ((msg_queue->not.sigev_notify & SIGEV_MASK) != 0) {
+		errno = EBUSY;
+		return -1;
+	}
+	if (notification->sigev_notify == SIGEV_SIGNAL) {
+		errno = ENOSYS;
+		return -1;
+	}
+	if (notification->sigev_notify_attributes != NULL) {
+		int ret = pthread_attr_setdetachstate(notification->sigev_notify_attributes,
+						      PTHREAD_CREATE_DETACHED);
+		if (ret != 0) {
+			errno = ret;
+			return -1;
+		}
+	}
+
+	k_sem_take(&mq_sem, K_FOREVER);
+	memcpy(&msg_queue->not, notification, sizeof(struct sigevent));
+	k_sem_give(&mq_sem);
+
+	return 0;
+}
+
+static void *mq_notify_thread(void *arg)
+{
+	mqueue_object *mqueue = (mqueue_object *)arg;
+	struct sigevent *sevp = &mqueue->not;
+
+	pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
+
+	if (sevp->sigev_notify_attributes == NULL) {
+		pthread_detach(pthread_self());
+	}
+
+	sevp->sigev_notify_function(sevp->sigev_value);
+
+	remove_notification(mqueue);
+
+	pthread_exit(NULL);
+	return NULL;
+}
+
 /* Internal functions */
 static mqueue_object *find_in_list(const char *name)
 {
@@ -380,11 +454,28 @@ static int32_t send_message(mqueue_desc *mqd, const char *msg_ptr, size_t msg_le
 		return ret;
 	}
 
+	uint32_t msgq_num = k_msgq_num_used_get(&mqd->mqueue->queue);
+
 	if (k_msgq_put(&mqd->mqueue->queue, (void *)msg_ptr, timeout) != 0) {
 		errno = K_TIMEOUT_EQ(timeout, K_NO_WAIT) ? EAGAIN : ETIMEDOUT;
 		return ret;
 	}
 
+	if (k_msgq_num_used_get(&mqd->mqueue->queue) - msgq_num > 0) {
+		struct sigevent *sevp = &mqd->mqueue->not;
+
+		if (sevp->sigev_notify == SIGEV_NONE) {
+			sevp->sigev_notify_function(sevp->sigev_value);
+		} else if (sevp->sigev_notify == SIGEV_THREAD) {
+			pthread_t th;
+
+			ret = pthread_create(&th,
+					     sevp->sigev_notify_attributes,
+					     mq_notify_thread,
+					     mqd->mqueue);
+		}
+	}
+
 	return 0;
 }
 
@@ -428,3 +519,10 @@ static void remove_mq(mqueue_object *msg_queue)
 		k_free(msg_queue->mem_obj);
 	}
 }
+
+static void remove_notification(mqueue_object *msg_queue)
+{
+	k_sem_take(&mq_sem, K_FOREVER);
+	memset(&msg_queue->not, 0, sizeof(struct sigevent));
+	k_sem_give(&mq_sem);
+}