From 95a22b12174621aeba8ca3e0e61f7c66f03202bf Mon Sep 17 00:00:00 2001
From: Christopher Friedt <cfriedt@meta.com>
Date: Thu, 28 Dec 2023 01:43:52 -0500
Subject: [PATCH] posix: clock: clock_gettime() should not be a syscall

We try to implement Zephyr's POSIX API as regular library
functions, so remove the __syscall annotation from
clock_gettime() and implement the syscall portion of it under
the hood.

This also adds a bit of a micro-optimization in that
we can do a lot of processing outside of the system call.

In fact, processing CLOCK_MONOTONIC likely does not
require any syscall other than k_uptime_ticks().

Signed-off-by: Christopher Friedt <cfriedt@meta.com>
---
 include/zephyr/posix/time.h |  8 ------
 lib/posix/CMakeLists.txt    |  2 +-
 lib/posix/clock.c           | 50 ++++++++++++++++++++++++++-----------
 lib/posix/posix_clock.h     | 19 ++++++++++++++
 4 files changed, 56 insertions(+), 23 deletions(-)
 create mode 100644 lib/posix/posix_clock.h

diff --git a/include/zephyr/posix/time.h b/include/zephyr/posix/time.h
index 85cb7f8ae4226a..ea7e68cb079e97 100644
--- a/include/zephyr/posix/time.h
+++ b/include/zephyr/posix/time.h
@@ -82,11 +82,7 @@ static inline int32_t _ts_to_ms(const struct timespec *to)
 	return (to->tv_sec * MSEC_PER_SEC) + (to->tv_nsec / NSEC_PER_MSEC);
 }
 
-#if defined(CONFIG_ARCH_POSIX) && defined(CONFIG_EXTERNAL_LIBC)
 int clock_gettime(clockid_t clock_id, struct timespec *ts);
-#else
-__syscall int clock_gettime(clockid_t clock_id, struct timespec *ts);
-#endif /* CONFIG_ARCH_POSIX */
 int clock_settime(clockid_t clock_id, const struct timespec *ts);
 /* Timer APIs */
 int timer_create(clockid_t clockId, struct sigevent *evp, timer_t *timerid);
@@ -103,10 +99,6 @@ int clock_nanosleep(clockid_t clock_id, int flags,
 }
 #endif
 
-#if !(defined(CONFIG_ARCH_POSIX) && defined(CONFIG_EXTERNAL_LIBC))
-#include <syscalls/time.h>
-#endif /* CONFIG_ARCH_POSIX */
-
 #else /* ZEPHYR_INCLUDE_POSIX_TIME_H_ */
 /* Read the toolchain header when <posix/time.h> finds itself on the
  * first attempt.
diff --git a/lib/posix/CMakeLists.txt b/lib/posix/CMakeLists.txt
index c6b3a88aeab4a9..e73c78d40e4297 100644
--- a/lib/posix/CMakeLists.txt
+++ b/lib/posix/CMakeLists.txt
@@ -3,7 +3,7 @@
 set(GEN_DIR ${ZEPHYR_BINARY_DIR}/include/generated)
 
 zephyr_syscall_header(
-  ${ZEPHYR_BASE}/include/zephyr/posix/time.h
+  posix_clock.h
 )
 
 zephyr_interface_library_named(posix_subsys)
diff --git a/lib/posix/clock.c b/lib/posix/clock.c
index 9fef8586b4883d..0d085a6d0d00c9 100644
--- a/lib/posix/clock.c
+++ b/lib/posix/clock.c
@@ -3,6 +3,9 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
+
+#include "posix_clock.h"
+
 #include <zephyr/kernel.h>
 #include <errno.h>
 #include <zephyr/posix/time.h>
@@ -25,10 +28,40 @@ static struct k_spinlock rt_clock_base_lock;
  *
  * See IEEE 1003.1
  */
-int z_impl_clock_gettime(clockid_t clock_id, struct timespec *ts)
+int z_impl___posix_clock_get_base(clockid_t clock_id, struct timespec *base)
+{
+	switch (clock_id) {
+	case CLOCK_MONOTONIC:
+		base->tv_sec = 0;
+		base->tv_nsec = 0;
+		break;
+
+	case CLOCK_REALTIME:
+		K_SPINLOCK(&rt_clock_base_lock) {
+			*base = rt_clock_base;
+		}
+		break;
+
+	default:
+		errno = EINVAL;
+		return -1;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_USERSPACE
+int z_vrfy___posix_clock_get_base(clockid_t clock_id, struct timespec *ts)
+{
+	K_OOPS(K_SYSCALL_MEMORY_WRITE(ts, sizeof(*ts)));
+	return z_impl___posix_clock_get_base(clock_id, ts);
+}
+#include <syscalls/__posix_clock_get_base_mrsh.c>
+#endif
+
+int clock_gettime(clockid_t clock_id, struct timespec *ts)
 {
 	struct timespec base;
-	k_spinlock_key_t key;
 
 	switch (clock_id) {
 	case CLOCK_MONOTONIC:
@@ -37,9 +70,7 @@ int z_impl_clock_gettime(clockid_t clock_id, struct timespec *ts)
 		break;
 
 	case CLOCK_REALTIME:
-		key = k_spin_lock(&rt_clock_base_lock);
-		base = rt_clock_base;
-		k_spin_unlock(&rt_clock_base_lock, key);
+		(void)__posix_clock_get_base(clock_id, &base);
 		break;
 
 	default:
@@ -65,15 +96,6 @@ int z_impl_clock_gettime(clockid_t clock_id, struct timespec *ts)
 	return 0;
 }
 
-#ifdef CONFIG_USERSPACE
-int z_vrfy_clock_gettime(clockid_t clock_id, struct timespec *ts)
-{
-	K_OOPS(K_SYSCALL_MEMORY_WRITE(ts, sizeof(*ts)));
-	return z_impl_clock_gettime(clock_id, ts);
-}
-#include <syscalls/clock_gettime_mrsh.c>
-#endif
-
 /**
  * @brief Set the time of the specified clock.
  *
diff --git a/lib/posix/posix_clock.h b/lib/posix/posix_clock.h
new file mode 100644
index 00000000000000..a665f4ce06d90e
--- /dev/null
+++ b/lib/posix/posix_clock.h
@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2023, Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_LIB_POSIX_POSIX_CLOCK_H_
+#define ZEPHYR_LIB_POSIX_POSIX_CLOCK_H_
+
+#include <time.h>
+
+#include <zephyr/kernel.h>
+#include <zephyr/posix/posix_types.h>
+
+__syscall int __posix_clock_get_base(clockid_t clock_id, struct timespec *ts);
+
+#include <syscalls/posix_clock.h>
+
+#endif