posix: sched: Implement get APIs for scheduling parameters

Implement `sched_getparam()` and `sched_getscheduler()` POSIX APIs
as a part of PSE53 `_POSIX_PRIORITY_SCHEDULING` option group.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>

arch/posix/include/posix_cheats.h

@@ -151,6 +151,8 @@ extern "C" int _posix_zephyr_main(void);
 #define sched_yield(...)		zap_sched_yield(__VA_ARGS__)
 #define sched_get_priority_min(...)	zap_sched_get_priority_min(__VA_ARGS__)
 #define sched_get_priority_max(...)	zap_sched_get_priority_max(__VA_ARGS__)
+#define sched_getparam(...)		zap_sched_getparam(__VA_ARGS__)
+#define sched_getscheduler(...)		zap_sched_getscheduler(__VA_ARGS__)
 
 /* Sleep */
 #define sleep(...)			zap_sleep(__VA_ARGS__)

doc/services/portability/posix/option_groups/index.rst

@@ -446,8 +446,8 @@ _POSIX_PRIORITY_SCHEDULING
 
     sched_get_priority_max(),yes
     sched_get_priority_min(),yes
-    sched_getparam(),
-    sched_getscheduler(),
+    sched_getparam(),yes
+    sched_getscheduler(),yes
     sched_rr_get_interval(),
     sched_setparam(),
     sched_setscheduler(),

include/zephyr/posix/sched.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 Intel Corporation
+ * Copyright (c) 2018-2023 Intel Corporation
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -8,6 +8,8 @@
 
 #include <zephyr/kernel.h>
 
+#include "posix_types.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -46,6 +48,9 @@ static inline int sched_yield(void)
 int sched_get_priority_min(int policy);
 int sched_get_priority_max(int policy);
 
+int sched_getparam(pid_t pid, struct sched_param *param);
+int sched_getscheduler(pid_t pid);
+
 #ifdef __cplusplus
 }
 #endif

lib/posix/sched.c

@@ -1,12 +1,14 @@
 /*
- * Copyright (c) 2018 Intel Corporation
+ * Copyright (c) 2018-2023 Intel Corporation
  *
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include "posix_internal.h"
 #include "pthread_sched.h"
 
 #include <zephyr/kernel.h>
+#include <zephyr/posix/pthread.h>
 #include <zephyr/posix/sched.h>
 
 /**
@@ -41,3 +43,57 @@ int sched_get_priority_max(int policy)
 	errno = EINVAL;
 	return -1;
 }
+
+/**
+ * @brief Get scheduling parameters
+ *
+ * See IEEE 1003.1
+ */
+int sched_getparam(pid_t pid, struct sched_param *param)
+{
+	/* TODO: Ensure the Zephyr POSIX process id (PID) value is assigned
+	 * with its first thread's id (TID).
+	 */
+	struct sched_param dummy_param = {0};
+	pthread_t tid = (pthread_t)pid;
+	int t_policy = -1;
+	int ret = -1;
+
+	if (param == NULL) {
+		param = &dummy_param;
+	}
+
+	if (tid == 0) {
+		tid = pthread_self();
+	}
+
+	ret = pthread_getschedparam(tid, &t_policy, param);
+	errno = ret;
+
+	return ((ret) ? -1 : 0);
+}
+
+/**
+ * @brief Get scheduling policy
+ *
+ * See IEEE 1003.1
+ */
+int sched_getscheduler(pid_t pid)
+{
+	/* TODO: Ensure the Zephyr POSIX process id (PID) value is assigned
+	 * with its first thread's id (TID).
+	 */
+	struct sched_param dummy_param = {0};
+	pthread_t tid = z_get_tid(pid);
+	int t_policy = -1;
+	int ret = -1;
+
+	if (tid == 0) {
+		tid = pthread_self();
+	}
+
+	ret = pthread_getschedparam(tid, &t_policy, &dummy_param);
+	errno = ret;
+
+	return (ret == 0) ? t_policy : -1;
+}

tests/posix/common/src/pthread.c

@@ -28,6 +28,7 @@
 
 K_THREAD_STACK_ARRAY_DEFINE(stack_e, N_THR_E, STACKS);
 K_THREAD_STACK_ARRAY_DEFINE(stack_t, N_THR_T, STACKS);
+K_THREAD_STACK_ARRAY_DEFINE(stack_s, 1, STACKS);
 K_THREAD_STACK_ARRAY_DEFINE(stack_1, 1, 32);
 
 void *thread_top_exec(void *p1);
@@ -644,6 +645,87 @@ ZTEST(posix_apis, test_pthread_descriptor_leak)
 	}
 }
 
+static void *create_thread_sched(void *p1)
+{
+	struct sched_param param = { .sched_priority = -1 };
+	int err = 0;
+	int rc = 0;
+
+	/* Get scheduling params of the current process. */
+	rc = sched_getparam(0, &param);
+	err = errno;
+	zassert_ok(rc, "unable to get scheduling parameters: rc=%d, errno=%d",
+		   rc, err);
+
+	rc = sched_getscheduler(0);
+	err = errno;
+	zassert_not_equal(rc, -1, "unable to get scheduling policy: errno=%d",
+			  err);
+	zassert_equal(rc, SCHED_RR, "unexpected scheduling policy: %d", rc);
+
+	if (p1) {
+		zassert_equal(param.sched_priority,
+			      ((struct sched_param *)p1)->sched_priority,
+			      "unexpected sched_priority=%d expects=%d",
+			      param.sched_priority,
+			      ((struct sched_param *)p1)->sched_priority);
+	}
+
+	return NULL;
+}
+
+ZTEST(posix_apis, test_sched_getparam)
+{
+	struct sched_param param = { .sched_priority = -1 };
+	int err = 0;
+	int rc = 0;
+
+	/* TODO: Assuming non-existent PID is -1 */
+	rc = sched_getparam(-1, &param);
+	err = errno;
+	zassert_true((rc == -1 && err == ESRCH),
+		     "failed parameter check: rc=%d, errno=%d", rc, err);
+
+	rc = sched_getscheduler(-1);
+	err = errno;
+	zassert_true((rc == -1 && err == ESRCH),
+		     "failed parameter check: rc=%d, errno=%d", rc, err);
+
+	/* .. and it is safe to call with NULL as praram. */
+	rc = sched_getparam(-1, NULL);
+	err = errno;
+	zassert_true((rc == -1 && err == ESRCH),
+		     "failed parameter check: rc=%d, errno=%d", rc, err);
+
+	/* Try with the current PID as ztest execution thread - it fails. */
+	rc = sched_getparam(0, &param);
+	err = errno;
+	zassert_true((rc == -1 && err == ESRCH),
+		     "Unexpected result : rc=%d, errno=%d", rc, err);
+
+	rc = sched_getscheduler(0);
+	err = errno;
+	zassert_true((rc == -1 && err == ESRCH),
+		     "Unexpected result : rc=%d, errno=%d", rc, err);
+
+	/* Check with a test thread. */
+	pthread_t pthread1;
+	pthread_attr_t attr1 = (pthread_attr_t){0};
+
+	param.sched_priority = sched_get_priority_min(SCHED_RR);
+	err = errno;
+	zassert_not_equal(-1, param.sched_priority,
+			  "sched_get_priority_min(SCHED_RR) failed: errno=%d", err);
+	zassert_ok(pthread_attr_init(&attr1));
+	zassert_ok(pthread_attr_setschedparam(&attr1, &param),
+			   "pthread_attr_setschedparam() failed");
+	zassert_ok(pthread_attr_setstack(&attr1, &stack_s[0][0], STACKS));
+	zassert_ok(pthread_create(&pthread1, &attr1, create_thread_sched, (void *)&param),
+			   "unable to create a test thread");
+	k_msleep(100);
+	zassert_ok(pthread_join(pthread1, NULL), "unable to join the test thread");
+}
+
 ZTEST(posix_apis, test_sched_policy)
 {
 	/*

tests/posix/headers/src/sched_h.c

@@ -30,8 +30,8 @@ ZTEST(posix_headers, test_sched_h)
 		zassert_not_null(sched_get_priority_max);
 		zassert_not_null(sched_get_priority_min);
 
-		/* zassert_not_null(sched_getparam); */ /* not implemented */
-		/* zassert_not_null(sched_getscheduler); */ /* not implemented */
+		zassert_not_null(sched_getparam);
+		zassert_not_null(sched_getscheduler);
 
 		/* zassert_not_null(sched_rr_get_interval); */ /* not implemented */