lib: os: add sys_sem data type

For systems with userspace, the sys_sem exist in user memory working
as counter semaphore for user mode thread. The implemention of sys_sem
is based on k_futex. And the majority of the synchronization operations
are performed in user mode to reduce the calling of system call.
And for systems without userspace enabled, sys_sem behaves like k_sem.

Fixes: #15139.

Signed-off-by: Wentong Wu <wentong.wu@intel.com>

include/sys/sem.h

@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2019 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ *
+ * @brief public sys_sem APIs.
+ */
+
+#ifndef ZEPHYR_INCLUDE_SYS_SEM_H_
+#define ZEPHYR_INCLUDE_SYS_SEM_H_
+
+/*
+ * sys_sem exists in user memory working as counter semaphore for
+ * user mode thread when user mode enabled. When user mode isn't
+ * enabled, sys_sem behaves like k_sem.
+ */
+
+#include <kernel.h>
+#include <atomic.h>
+#include <zephyr/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * sys_sem structure
+ */
+struct sys_sem {
+#ifdef CONFIG_USERSPACE
+	struct k_futex futex;
+	int limit;
+#else
+	struct k_sem kernel_sem;
+#endif
+};
+
+/**
+ * @brief Initialize a semaphore.
+ *
+ * This routine initializes a semaphore instance, prior to its first use.
+ *
+ * @param sem Address of the semaphore.
+ * @param initial_count Initial semaphore count.
+ * @param limit Maximum permitted semaphore count.
+ *
+ * @retval 0 Initial success.
+ * @retval -EINVAL Bad parameters, the value of limit should be located in
+ *         (0, INT_MAX] and initial_count shouldn't be greater than limit.
+ */
+int sys_sem_init(struct sys_sem *sem, unsigned int initial_count,
+		unsigned int limit);
+
+/**
+ * @brief Give a semaphore.
+ *
+ * This routine gives @a sem, unless the semaphore is already at its
+ * maximum permitted count.
+ *
+ * @param sem Address of the semaphore.
+ *
+ * @retval 0 Semaphore given.
+ * @retval -EINVAL Parameter address not recognized.
+ * @retval -EACCES Caller does not have enough access.
+ * @retval -EAGAIN Count reached Maximum permitted count and try again.
+ */
+int sys_sem_give(struct sys_sem *sem);
+
+/**
+ * @brief Take a sys_sem.
+ *
+ * This routine takes @a sem.
+ *
+ * @param sem Address of the sys_sem.
+ * @param timeout Waiting period to take the sys_sem (in milliseconds),
+ *                or one of the special values K_NO_WAIT and K_FOREVER.
+ *
+ * @retval 0 sys_sem taken.
+ * @retval -EINVAL Parameter address not recognized.
+ * @retval -ETIMEDOUT Waiting period timed out.
+ * @retval -EACCES Caller does not have enough access.
+ */
+int sys_sem_take(struct sys_sem *sem, s32_t timeout);
+
+/**
+ * @brief Get sys_sem's value
+ *
+ * This routine returns the current value of @a sem.
+ *
+ * @param sem Address of the sys_sem.
+ *
+ * @return Current value of sys_sem.
+ */
+unsigned int sys_sem_count_get(struct sys_sem *sem);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif