prashants · October 5, 2012 11:48 · Oct 5, 2012
diff --git a/filter.c b/filter.c
@@ -0,0 +1,127 @@
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/cdev.h>
+#include <linux/kthread.h>
+#include <linux/interrupt.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/types.h>
+#include <linux/major.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+#include <linux/kdev_t.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <asm/uaccess.h>
+#include <linux/types.h>
+#include <linux/buffer_head.h>
+#include <linux/delay.h>
+#include <linux/workqueue.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+
+#define PARTITION_NAME "/dev/sda1"
+
+#define DELAY(); \
+	printk(KERN_INFO "filter: FUNCTION=%s LINE=%d\n", __FUNCTION__, __LINE__); \
+        set_current_state(TASK_UNINTERRUPTIBLE); \
+        schedule_timeout(HZ * 5);
+
+struct block_device *bd;
+
+make_request_fn *orig_mrqfn;
+
+static void filter_mrqfn(struct request_queue *rq, struct bio *b)
+{
+	orig_mrqfn(rq, b); /* calling the original make_request_fn() */
+}
+
+/*
+ * set_mrqfn() - Change the original make_request_fn() to our
+ * modules request function
+ */
+static void set_mrqfn(void)
+{
+	int ret;
+	struct super_block *sb =  bd->bd_super;
+	printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
+
+	DELAY();
+	/* lock filesystem to prevent any further changes */
+	sb = freeze_bdev(bd);
+	if (sb)
+		printk(KERN_INFO "filter: freez block device\n");
+	DELAY();
+
+	if (bd->bd_disk->queue->make_request_fn == filter_mrqfn) {
+		printk(KERN_INFO "filter: modules request function is already active\n");
+	} else {
+		/* save the pointer to the original make_request_fn() */
+		orig_mrqfn = bd->bd_disk->queue->make_request_fn;
+		/* replace the original with our modules request function */
+		bd->bd_disk->queue->make_request_fn = filter_mrqfn;
+	}
+
+	/* unlock filesystem */
+	thaw_bdev(bd, sb);
+}
+
+/*
+ * restore_mrqfn() - Restore the original make_request_fn()
+ */
+static void restore_mrqfn(void)
+{
+	struct super_block *sb =  bd->bd_super;
+	printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
+
+	if (orig_mrqfn) {
+		/* lock filesystem to prevent any further changes */
+		freeze_super(sb);
+
+		/* restore the original request function */
+		bd->bd_disk->queue->make_request_fn = orig_mrqfn;
+
+		/* unlock filesystem */
+		thaw_super(sb);
+	}
+	orig_mrqfn = NULL;
+}
+
+static int __init filter_init(void)
+{
+	printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
+
+	orig_mrqfn = NULL;
+
+	// Read block device from path
+	bd = blkdev_get_by_path(PARTITION_NAME, FMODE_READ, NULL);
+
+	if (IS_ERR(bd)) {
+		printk(KERN_ERR "filter: failed to get block device\n");
+		return 0;
+	}
+
+	set_mrqfn();
+
+	return 0;
+}
+
+static void __exit filter_exit(void)
+{
+	printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
+
+	restore_mrqfn();
+
+	if (!IS_ERR(bd)) {
+		blkdev_put(bd, FMODE_READ);
+	}
+}
+
+module_init(filter_init);
+module_exit(filter_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Me");