kfifo: add example files to the kernel sample directory

Add four examples to the kernel sample directory.

It shows how to handle:
- a byte stream fifo
- a integer type fifo
- a dynamic record sized fifo
- the fifo DMA functions

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

samples/kfifo/dma-example.c

@@ -0,0 +1,115 @@
+/*
+ * Sample fifo dma implementation
+ *
+ * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
+ *
+ * Released under the GPL version 2 only.
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kfifo.h>
+
+/*
+ * This module shows how to handle fifo dma operations.
+ */
+
+/* fifo size in elements (bytes) */
+#define FIFO_SIZE	32
+
+static struct kfifo fifo;
+
+static int __init example_init(void)
+{
+	int			i;
+	unsigned int		ret;
+	struct scatterlist	sg[10];
+
+	printk(KERN_INFO "DMA fifo test start\n");
+
+	if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
+		printk(KERN_ERR "error kfifo_alloc\n");
+		return 1;
+	}
+
+	printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
+
+	kfifo_in(&fifo, "test", 4);
+
+	for (i = 0; i != 9; i++)
+		kfifo_put(&fifo, &i);
+
+	/* kick away first byte */
+	ret = kfifo_get(&fifo, &i);
+
+	printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
+
+	ret = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
+	printk(KERN_INFO "DMA sgl entries: %d\n", ret);
+
+	/* if 0 was returned, fifo is full and no sgl was created */
+	if (ret) {
+		printk(KERN_INFO "scatterlist for receive:\n");
+		for (i = 0; i < ARRAY_SIZE(sg); i++) {
+			printk(KERN_INFO
+			"sg[%d] -> "
+			"page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
+				i, sg[i].page_link, sg[i].offset, sg[i].length);
+
+			if (sg_is_last(&sg[i]))
+				break;
+		}
+
+		/* but here your code to setup and exectute the dma operation */
+		/* ... */
+
+		/* example: zero bytes received */
+		ret = 0;
+
+		/* finish the dma operation and update the received data */
+		kfifo_dma_in_finish(&fifo, ret);
+	}
+
+	ret = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
+	printk(KERN_INFO "DMA sgl entries: %d\n", ret);
+
+	/* if 0 was returned, no data was available and no sgl was created */
+	if (ret) {
+		printk(KERN_INFO "scatterlist for transmit:\n");
+		for (i = 0; i < ARRAY_SIZE(sg); i++) {
+			printk(KERN_INFO
+			"sg[%d] -> "
+			"page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
+				i, sg[i].page_link, sg[i].offset, sg[i].length);
+
+			if (sg_is_last(&sg[i]))
+				break;
+		}
+
+		/* but here your code to setup and exectute the dma operation */
+		/* ... */
+
+		/* example: 5 bytes transmitted */
+		ret = 5;
+
+		/* finish the dma operation and update the transmitted data */
+		kfifo_dma_out_finish(&fifo, ret);
+	}
+
+	printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
+
+	return 0;
+}
+
+static void __exit example_exit(void)
+{
+#ifdef DYNAMIC
+	kfifo_free(&test);
+#endif
+}
+
+module_init(example_init);
+module_exit(example_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");