From 3a809b9faadfd0a8d898aede15cabfd24ee1a13f Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Thu, 3 Jul 2025 18:20:22 -0400
Subject: kernel: synch: Add mutual exclusion locks

Add mutex locks, these differ from spinlocks as they are named and also
yield to the scheduler instead of just spinning if the lock is acquired.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/sys/mutex.h | 52 ++++++++++++++++++++++++++++++++++++++++++++
 sys/kern/kern_synch.c   | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 sys/include/sys/mutex.h

diff --git a/sys/include/sys/mutex.h b/sys/include/sys/mutex.h
new file mode 100644
index 0000000..8a4d50a
--- /dev/null
+++ b/sys/include/sys/mutex.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_MUTEX_H_
+#define _SYS_MUTEX_H_
+
+#include <sys/types.h>
+#include <vm/dynalloc.h>
+
+#define MUTEX_NAME_LEN 32
+
+#if defined(_KERNEL)
+
+struct mutex {
+    char name[MUTEX_NAME_LEN];
+    volatile uint8_t lock;
+};
+
+struct mutex *mutex_new(const char *name);
+void mutex_free(struct mutex *mtx);
+
+int mutex_acquire(struct mutex *mtx, int flags);
+void mutex_release(struct mutex *mtx);
+
+#endif  /* _KERNEL */
+#endif  /* !_SYS_MUTEX_H_ */
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 57b27d0..0d36d7f 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -28,12 +28,15 @@
  */
 
 #include <sys/types.h>
+#include <sys/mutex.h>
 #include <sys/systm.h>
 #include <sys/errno.h>
+#include <sys/sched.h>
 #include <sys/atomic.h>
 #include <sys/syslog.h>
 #include <sys/spinlock.h>
 #include <dev/timer.h>
+#include <string.h>
 
 #define pr_trace(fmt, ...) kprintf("synch: " fmt, ##__VA_ARGS__)
 #define pr_error(...) pr_trace(__VA_ARGS__)
@@ -136,3 +139,57 @@ sysrel(void)
 {
     spinlock_release(&__syslock);
 }
+
+/*
+ * Create a new mutex lock object
+ */
+struct mutex *
+mutex_new(const char *name)
+{
+    struct mutex *mtx;
+    size_t namelen;
+
+    mtx = dynalloc(sizeof(*mtx));
+    if (mtx == NULL) {
+        return NULL;
+    }
+
+    mtx->lock = 0;
+    namelen = strlen(name);
+
+    /* Don't overflow the name buffer */
+    if (namelen >= MUTEX_NAME_LEN) {
+        namelen = MUTEX_NAME_LEN - 1;
+    }
+
+    memcpy(mtx->name, name, namelen);
+    return mtx;
+}
+
+/*
+ * Acquire a mutex
+ *
+ * @mtx: Mutex to acquire
+ * @flags: Optional flags
+ */
+int
+mutex_acquire(struct mutex *mtx, int flags)
+{
+    while (__atomic_test_and_set(&mtx->lock, __ATOMIC_ACQUIRE)) {
+        sched_yield();
+    }
+
+    return 0;
+}
+
+void
+mutex_release(struct mutex *mtx)
+{
+    __atomic_clear(&mtx->lock, __ATOMIC_RELEASE);
+}
+
+void
+mutex_free(struct mutex *mtx)
+{
+    dynfree(mtx);
+}
-- 
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