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+/*
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+ * Sample kfifo byte stream implementation
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+ *
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+ * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
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+ *
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+ * Released under the GPL version 2 only.
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+ *
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+ */
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+
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+#include <linux/init.h>
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+#include <linux/module.h>
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+#include <linux/proc_fs.h>
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+#include <linux/mutex.h>
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+#include <linux/kfifo.h>
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+
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+/*
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+ * This module shows how to create a byte stream fifo.
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+ */
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+
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+/* fifo size in elements (bytes) */
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+#define FIFO_SIZE 32
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+
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+/* name of the proc entry */
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+#define PROC_FIFO "bytestream-fifo"
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+
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+/* lock for procfs read access */
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+static DEFINE_MUTEX(read_lock);
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+
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+/* lock for procfs write access */
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+static DEFINE_MUTEX(write_lock);
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+
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+/*
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+ * define DYNAMIC in this example for a dynamically allocated fifo.
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+ *
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+ * Otherwise the fifo storage will be a part of the fifo structure.
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+ */
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+#if 0
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+#define DYNAMIC
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+#endif
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+
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+#ifdef DYNAMIC
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+static struct kfifo test;
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+#else
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+static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
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+#endif
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+
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+static int __init testfunc(void)
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+{
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+ unsigned char buf[6];
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+ unsigned char i;
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+ unsigned int ret;
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+
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+ printk(KERN_INFO "byte stream fifo test start\n");
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+
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+ /* put string into the fifo */
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+ kfifo_in(&test, "hello", 5);
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+
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+ /* put values into the fifo */
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+ for (i = 0; i != 10; i++)
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+ kfifo_put(&test, &i);
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+
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+ /* show the number of used elements */
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+ printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
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+
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+ /* get max of 5 bytes from the fifo */
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+ i = kfifo_out(&test, buf, 5);
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+ printk(KERN_INFO "buf: %.*s\n", i, buf);
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+
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+ /* get max of 2 elements from the fifo */
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+ ret = kfifo_out(&test, buf, 2);
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+ printk(KERN_INFO "ret: %d\n", ret);
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+ /* and put it back to the end of the fifo */
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+ ret = kfifo_in(&test, buf, ret);
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+ printk(KERN_INFO "ret: %d\n", ret);
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+
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+ /* put values into the fifo until is full */
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+ for (i = 20; kfifo_put(&test, &i); i++)
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+ ;
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+
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+ printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
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+
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+ /* print out all values in the fifo */
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+ while (kfifo_get(&test, &i))
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+ printk("%d ", i);
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+ printk("\n");
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+
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+ return 0;
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+}
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+
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+static ssize_t fifo_write(struct file *file, const char __user *buf,
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+ size_t count, loff_t *ppos)
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+{
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+ int ret;
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+ unsigned int copied;
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+
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+ if (mutex_lock_interruptible(&write_lock))
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+ return -ERESTARTSYS;
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+
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+ ret = kfifo_from_user(&test, buf, count, &copied);
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+
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+ mutex_unlock(&write_lock);
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+
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+ return ret ? ret : copied;
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+}
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+
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+static ssize_t fifo_read(struct file *file, char __user *buf,
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+ size_t count, loff_t *ppos)
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+{
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+ int ret;
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+ unsigned int copied;
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+
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+ if (mutex_lock_interruptible(&read_lock))
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+ return -ERESTARTSYS;
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+
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+ ret = kfifo_to_user(&test, buf, count, &copied);
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+
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+ mutex_unlock(&read_lock);
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+
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+ return ret ? ret : copied;
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+}
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+
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+static const struct file_operations fifo_fops = {
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+ .owner = THIS_MODULE,
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+ .read = fifo_read,
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+ .write = fifo_write,
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+};
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+
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+static int __init example_init(void)
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+{
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+#ifdef DYNAMIC
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+ int ret;
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+
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+ ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
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+ if (ret) {
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+ printk(KERN_ERR "error kfifo_alloc\n");
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+ return ret;
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+ }
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+#else
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+ INIT_KFIFO(test);
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+#endif
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+ testfunc();
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+
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+ if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
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+#ifdef DYNAMIC
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+ kfifo_free(&test);
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+#endif
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+ return -ENOMEM;
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+ }
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+ return 0;
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+}
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+
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+static void __exit example_exit(void)
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+{
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+ remove_proc_entry(PROC_FIFO, NULL);
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+#ifdef DYNAMIC
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+ kfifo_free(&test);
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+#endif
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+}
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+
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+module_init(example_init);
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+module_exit(example_exit);
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+MODULE_LICENSE("GPL");
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+MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
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