/* uprobe_example.c, modified to try to register the same probe 3 times */
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/uprobes.h>

/*
 * Usage: insmod wenji3x.ko pid=<pid> vaddr=<address> [verbose=0]
 * where <pid> identifies the probed process and <address> is the virtual
 * address of the probed instruction.
 *
 * insmod should report success (0) for the first registration attempt
 * and failure (-16 = EBUSY) for the second and third attempts.  The
 * probe should work.
 */

static int pid = 0;
module_param(pid, int, 0);
MODULE_PARM_DESC(pid, "pid");

static int verbose = 1;
module_param(verbose, int, 0);
MODULE_PARM_DESC(verbose, "verbose");

static long vaddr = 0;
module_param(vaddr, long, 0);
MODULE_PARM_DESC(vaddr, "vaddr");

static int nhits;
static struct uprobe usp;

static void uprobe_handler(struct uprobe *u, struct pt_regs *regs)
{
	nhits++;
	if (verbose)
		printk(KERN_INFO "Hit #%d on probepoint at %#lx\n",
			nhits, u->vaddr);
}

int __init init_module(void)
{
	int ret, try, success = 0;
	usp.pid = pid;
	usp.vaddr = vaddr;
	usp.handler = uprobe_handler;
	printk(KERN_INFO "Registering uprobe on pid %d, vaddr %#lx\n",
		usp.pid, usp.vaddr);
	for (try = 1; try <= 3; try++) {
		ret = register_uprobe(&usp);
		printk(KERN_ERR "Try #%d: register_uprobe() returned %d\n",
			try, ret);
		if (ret == 0)
			success++;
	}
	return (success ? 0 : ret);
}

void __exit cleanup_module(void)
{
	printk(KERN_INFO "Unregistering uprobe on pid %d, vaddr %#lx\n",
		usp.pid, usp.vaddr);
	printk(KERN_INFO "Probepoint was hit %d times\n", nhits);
	unregister_uprobe(&usp);
}
MODULE_LICENSE("GPL");