posix: Implement set and get inheritsched APIs for pthread attr

Implement `pthread_attr_setinheritsched()` and
`pthread_attr_getinheritsched()`are required
as part of _POSIX_THREAD_PRIORITY_SCHEDULING Option Group.

signed-off-by: Gaetan Perrot <gaetanperrotpro@gmail.com>

include/zephyr/posix/pthread.h

@@ -39,6 +39,12 @@ extern "C" {
 #define PTHREAD_CANCEL_DEFERRED     0
 #define PTHREAD_CANCEL_ASYNCHRONOUS 1
 
+/* Pthread inherit scheduler */
+#undef PTHREAD_INHERIT_SCHED
+#define PTHREAD_INHERIT_SCHED  0
+#undef PTHREAD_EXPLICIT_SCHED
+#define PTHREAD_EXPLICIT_SCHED 1
+
 /* Passed to pthread_once */
 #define PTHREAD_ONCE_INIT {0}
 
@@ -429,6 +435,8 @@ int pthread_attr_getstack(const pthread_attr_t *attr,
 			  void **stackaddr, size_t *stacksize);
 int pthread_attr_setstack(pthread_attr_t *attr, void *stackaddr,
 			  size_t stacksize);
+int pthread_attr_getinheritsched(const pthread_attr_t *attr, int *inheritsched);
+int pthread_attr_setinheritsched(pthread_attr_t *attr, int inheritsched);
 #ifdef CONFIG_PTHREAD_IPC
 int pthread_once(pthread_once_t *once, void (*initFunc)(void));
 #endif

lib/posix/options/posix_internal.h

@@ -29,6 +29,7 @@ struct posix_thread_attr {
 	uint16_t guardsize : CONFIG_POSIX_PTHREAD_ATTR_GUARDSIZE_BITS;
 	int8_t priority;
 	uint8_t schedpolicy: 2;
+	bool inheritsched: 1;
 	union {
 		bool caller_destroys: 1;
 		bool initialized: 1;

lib/posix/options/pthread.c

@@ -384,6 +384,45 @@ int pthread_attr_setstack(pthread_attr_t *_attr, void *stackaddr, size_t stacksi
 	return 0;
 }
 
+/**
+ * @brief Get inherit scheduler attributes in thread attributes object.
+ *
+ * See IEEE 1003.1
+ */
+int pthread_attr_getinheritsched(const pthread_attr_t *_attr, int *inheritsched)
+{
+struct posix_thread_attr *attr = (struct posix_thread_attr *)_attr;
+
+	if (!__attr_is_initialized(attr) || inheritsched == NULL) {
+		return EINVAL;
+	}
+	*inheritsched = attr->inheritsched;
+	return 0;
+}
+
+/**
+ * @brief Set inherit scheduler attributes in thread attributes object.
+ *
+ * See IEEE 1003.1
+ */
+int pthread_attr_setinheritsched(pthread_attr_t *_attr, int inheritsched)
+{
+	struct posix_thread_attr *attr = (struct posix_thread_attr *)_attr;
+
+	if (!__attr_is_initialized(attr)) {
+		LOG_DBG("attr %p is not initialized", attr);
+		return EINVAL;
+	}
+
+	if (inheritsched != PTHREAD_INHERIT_SCHED && inheritsched != PTHREAD_EXPLICIT_SCHED) {
+		LOG_DBG("Invalid inheritsched %d", inheritsched);
+		return EINVAL;
+	}
+
+	attr->inheritsched = inheritsched;
+	return 0;
+}
+
 static void posix_thread_recycle_work_handler(struct k_work *work)
 {
 	ARG_UNUSED(work);
@@ -556,6 +595,20 @@ int pthread_create(pthread_t *th, const pthread_attr_t *_attr, void *(*threadrou
 		t->attr = *(struct posix_thread_attr *)_attr;
 	}
 
+	struct posix_thread *self = NULL;
+
+	K_SPINLOCK(&pthread_pool_lock) {
+		self = to_posix_thread(pthread_self());
+		if (self == NULL) {
+			K_SPINLOCK_BREAK;
+		}
+		if (self_attr.inheritsched == PTHREAD_INHERIT_SCHED) {
+			t->attr.priority = self->attr.priority;
+			t->attr.schedpolicy = self->attr.schedpolicy;
+			t->attr.inheritsched = self->attr.inheritsched;
+		}
+	}
+
 	/* spawn the thread */
 	k_thread_create(
 		&t->thread, t->attr.stack, __get_attr_stacksize(&t->attr) + t->attr.guardsize,
@@ -797,6 +850,7 @@ int pthread_attr_init(pthread_attr_t *_attr)
 
 	*attr = (struct posix_thread_attr){0};
 	attr->guardsize = CONFIG_POSIX_PTHREAD_ATTR_GUARDSIZE_DEFAULT;
+	attr->inheritsched = PTHREAD_INHERIT_SCHED;
 
 	if (DYNAMIC_STACK_SIZE > 0) {
 		attr->stack = k_thread_stack_alloc(DYNAMIC_STACK_SIZE + attr->guardsize,