posix: sched: add support for SCHED_OTHER

The `SCHED_OTHER` scheduling priority is mandatory as part of
POSIX. It must be numerically distinct from `SCHED_FIFO`,
`SCHED_RR`, and `SCHED_SPORADIC`, but is implementation-
defined and may behave identically to `SCHED_FIFO` or
`SCHED_RR`.

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

include/zephyr/posix/sched.h

@@ -6,10 +6,19 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_SCHED_H_
 #define ZEPHYR_INCLUDE_POSIX_SCHED_H_
 
+#include <zephyr/kernel.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/*
+ * Other mandatory scheduling policy. Must be numerically distinct. May
+ * execute identically to SCHED_RR or SCHED_FIFO. For Zephyr this is a
+ * pseudonym for SCHED_RR.
+ */
+#define SCHED_OTHER 0
+
 /* Cooperative scheduling policy */
 #define SCHED_FIFO 1
 

lib/posix/posix_internal.h

@@ -7,6 +7,8 @@
 #ifndef ZEPHYR_LIB_POSIX_POSIX_INTERNAL_H_
 #define ZEPHYR_LIB_POSIX_POSIX_INTERNAL_H_
 
+#include <zephyr/kernel.h>
+
 /*
  * Bit used to mark a pthread object as initialized. Initialization status is
  * verified (against internal status) in lock / unlock / destroy functions.

lib/posix/pthread.c

@@ -14,6 +14,7 @@
 #include <zephyr/sys/slist.h>
 
 #include "posix_internal.h"
+#include "pthread_sched.h"
 
 #define PTHREAD_INIT_FLAGS	PTHREAD_CANCEL_ENABLE
 #define PTHREAD_CANCELED	((void *) -1)
@@ -54,7 +55,7 @@ struct posix_thread *to_posix_thread(pthread_t pthread)
 	return &posix_thread_pool[pthread];
 }
 
-static bool is_posix_prio_valid(uint32_t priority, int policy)
+static bool is_posix_policy_prio_valid(uint32_t priority, int policy)
 {
 	if (priority >= sched_get_priority_min(policy) &&
 	    priority <= sched_get_priority_max(policy)) {
@@ -108,7 +109,7 @@ int pthread_attr_setschedparam(pthread_attr_t *_attr, const struct sched_param *
 	int priority = schedparam->sched_priority;
 
 	if ((attr == NULL) || (attr->initialized == 0U) ||
-	    (is_posix_prio_valid(priority, attr->schedpolicy) == false)) {
+	    (is_posix_policy_prio_valid(priority, attr->schedpolicy) == false)) {
 		return EINVAL;
 	}
 
@@ -298,11 +299,11 @@ int pthread_setschedparam(pthread_t pthread, int policy,
 		return ESRCH;
 	}
 
-	if (policy != SCHED_RR && policy != SCHED_FIFO) {
+	if (!valid_posix_policy(policy)) {
 		return EINVAL;
 	}
 
-	if (is_posix_prio_valid(param->sched_priority, policy) == false) {
+	if (is_posix_policy_prio_valid(param->sched_priority, policy) == false) {
 		return EINVAL;
 	}
 
@@ -565,8 +566,7 @@ int pthread_attr_setschedpolicy(pthread_attr_t *_attr, int policy)
 {
 	struct pthread_attr *attr = (struct pthread_attr *)_attr;
 
-	if ((attr == NULL) || (attr->initialized == 0U) ||
-	    (policy != SCHED_RR && policy != SCHED_FIFO)) {
+	if ((attr == NULL) || (attr->initialized == 0U) || !valid_posix_policy(policy)) {
 		return EINVAL;
 	}
 

lib/posix/pthread_sched.c

@@ -4,14 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include "pthread_sched.h"
+
 #include <zephyr/kernel.h>
 #include <zephyr/posix/sched.h>
 
-static inline bool valid_posix_policy(int policy)
-{
-	return policy == SCHED_FIFO || policy == SCHED_RR;
-}
-
 /**
  * @brief Get minimum priority value for a given policy
  *
@@ -36,7 +33,8 @@ int sched_get_priority_max(int policy)
 {
 	if (IS_ENABLED(CONFIG_COOP_ENABLED) && policy == SCHED_FIFO) {
 		return CONFIG_NUM_COOP_PRIORITIES - 1;
-	} else if (IS_ENABLED(CONFIG_PREEMPT_ENABLED) && policy == SCHED_RR) {
+	} else if (IS_ENABLED(CONFIG_PREEMPT_ENABLED) &&
+		   (policy == SCHED_RR || policy == SCHED_OTHER)) {
 		return CONFIG_NUM_PREEMPT_PRIORITIES - 1;
 	}
 

lib/posix/pthread_sched.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2023 Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_LIB_POSIX_POSIX_PTHREAD_SCHED_H_
+#define ZEPHYR_LIB_POSIX_POSIX_PTHREAD_SCHED_H_
+
+#include <stdbool.h>
+
+#include <zephyr/posix/sched.h>
+
+static inline bool valid_posix_policy(int policy)
+{
+	return policy == SCHED_FIFO || policy == SCHED_RR || policy == SCHED_OTHER;
+}
+
+#endif