1 files changed, 212 insertions, 0 deletions
diff --git a/samples/rust/rust_semaphore_c.c b/samples/rust/rust_semaphore_c.c
new file mode 100644
index 000000000000..7672b0b4c105
--- /dev/null
+++ b/samples/rust/rust_semaphore_c.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Rust semaphore sample (in C, for comparison)
+ *
+ * This is a C implementation of `rust_semaphore.rs`. Refer to the description
+ * in that file for details on the device.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/refcount.h>
+#include <linux/wait.h>
+
+#define IOCTL_GET_READ_COUNT _IOR('c', 1, u64)
+#define IOCTL_SET_READ_COUNT _IOW('c', 1, u64)
+
+struct semaphore_state {
+	struct kref ref;
+	struct miscdevice miscdev;
+	wait_queue_head_t changed;
+	struct mutex mutex;
+	size_t count;
+	size_t max_seen;
+};
+
+struct file_state {
+	atomic64_t read_count;
+	struct semaphore_state *shared;
+};
+
+static int semaphore_consume(struct semaphore_state *state)
+{
+	DEFINE_WAIT(wait);
+
+	mutex_lock(&state->mutex);
+	while (state->count == 0) {
+		prepare_to_wait(&state->changed, &wait, TASK_INTERRUPTIBLE);
+		mutex_unlock(&state->mutex);
+		schedule();
+		finish_wait(&state->changed, &wait);
+		if (signal_pending(current))
+			return -EINTR;
+		mutex_lock(&state->mutex);
+	}
+
+	state->count--;
+	mutex_unlock(&state->mutex);
+
+	return 0;
+}
+
+static int semaphore_open(struct inode *nodp, struct file *filp)
+{
+	struct semaphore_state *shared =
+		container_of(filp->private_data, struct semaphore_state, miscdev);
+	struct file_state *state;
+
+	state = kzalloc(sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	kref_get(&shared->ref);
+	state->shared = shared;
+	atomic64_set(&state->read_count, 0);
+
+	filp->private_data = state;
+
+	return 0;
+}
+
+static ssize_t semaphore_write(struct file *filp, const char __user *buffer, size_t count,
+			       loff_t *ppos)
+{
+	struct file_state *state = filp->private_data;
+	struct semaphore_state *shared = state->shared;
+
+	mutex_lock(&shared->mutex);
+
+	shared->count += count;
+	if (shared->count < count)
+		shared->count = SIZE_MAX;
+
+	if (shared->count > shared->max_seen)
+		shared->max_seen = shared->count;
+
+	mutex_unlock(&shared->mutex);
+
+	wake_up_all(&shared->changed);
+
+	return count;
+}
+
+static ssize_t semaphore_read(struct file *filp, char __user *buffer,
+			      size_t count, loff_t *ppos)
+{
+	struct file_state *state = filp->private_data;
+	char c = 0;
+	int ret;
+
+	if (count == 0 || *ppos > 0)
+		return 0;
+
+	ret = semaphore_consume(state->shared);
+	if (ret)
+		return ret;
+
+	if (copy_to_user(buffer, &c, sizeof(c)))
+		return -EFAULT;
+
+	atomic64_add(1, &state->read_count);
+	*ppos += 1;
+	return 1;
+}
+
+static long semaphore_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	struct file_state *state = filp->private_data;
+	void __user *buffer = (void __user *)arg;
+	u64 value;
+
+	switch (cmd) {
+	case IOCTL_GET_READ_COUNT:
+		value = atomic64_read(&state->read_count);
+		if (copy_to_user(buffer, &value, sizeof(value)))
+			return -EFAULT;
+		return 0;
+	case IOCTL_SET_READ_COUNT:
+		if (copy_from_user(&value, buffer, sizeof(value)))
+			return -EFAULT;
+		atomic64_set(&state->read_count, value);
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static void semaphore_free(struct kref *kref)
+{
+	struct semaphore_state *device;
+
+	device = container_of(kref, struct semaphore_state, ref);
+	kfree(device);
+}
+
+static int semaphore_release(struct inode *nodp, struct file *filp)
+{
+	struct file_state *state = filp->private_data;
+
+	kref_put(&state->shared->ref, semaphore_free);
+	kfree(state);
+	return 0;
+}
+
+static const struct file_operations semaphore_fops = {
+	.owner = THIS_MODULE,
+	.open = semaphore_open,
+	.read = semaphore_read,
+	.write = semaphore_write,
+	.compat_ioctl = semaphore_ioctl,
+	.release = semaphore_release,
+};
+
+static struct semaphore_state *device;
+
+static int __init semaphore_init(void)
+{
+	int ret;
+	struct semaphore_state *state;
+
+	pr_info("Rust semaphore sample (in C, for comparison) (init)\n");
+
+	state = kzalloc(sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	mutex_init(&state->mutex);
+	kref_init(&state->ref);
+	init_waitqueue_head(&state->changed);
+
+	state->miscdev.fops = &semaphore_fops;
+	state->miscdev.minor = MISC_DYNAMIC_MINOR;
+	state->miscdev.name = "semaphore";
+
+	ret = misc_register(&state->miscdev);
+	if (ret < 0) {
+		kfree(state);
+		return ret;
+	}
+
+	device = state;
+
+	return 0;
+}
+
+static void __exit semaphore_exit(void)
+{
+	pr_info("Rust semaphore sample (in C, for comparison) (exit)\n");
+
+	misc_deregister(&device->miscdev);
+	kref_put(&device->ref, semaphore_free);
+}
+
+module_init(semaphore_init);
+module_exit(semaphore_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Rust for Linux Contributors");
+MODULE_DESCRIPTION("Rust semaphore sample (in C, for comparison)");