#include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/random.h>
  #include <linux/sched.h>
  #include <linux/stat.h>
  #include <linux/types.h>
  #include <linux/fs.h>
  #include <linux/export.h>
  #include <linux/interrupt.h>
  #include <linux/stacktrace.h>
  #include <linux/fault-inject.h>
  
  /*
   * setup_fault_attr() is a helper function for various __setup handlers, so it
   * returns 0 on error, because that is what __setup handlers do.
   */
  int setup_fault_attr(struct fault_attr *attr, char *str)
  {
  	unsigned long probability;
  	unsigned long interval;
  	int times;
  	int space;
  
  	/* "<interval>,<probability>,<space>,<times>" */
  	if (sscanf(str, "%lu,%lu,%d,%d",
  			&interval, &probability, &space, &times) < 4) {
  		printk(KERN_WARNING
  			"FAULT_INJECTION: failed to parse arguments
  ");
  		return 0;
  	}
  
  	attr->probability = probability;
  	attr->interval = interval;
  	atomic_set(&attr->times, times);
  	atomic_set(&attr->space, space);
  
  	return 1;
  }
  EXPORT_SYMBOL_GPL(setup_fault_attr);
  
  static void fail_dump(struct fault_attr *attr)
  {
  	if (attr->verbose > 0)
  		printk(KERN_NOTICE "FAULT_INJECTION: forcing a failure
  ");
  	if (attr->verbose > 1)
  		dump_stack();
  }
  
  #define atomic_dec_not_zero(v)		atomic_add_unless((v), -1, 0)
  
  static bool fail_task(struct fault_attr *attr, struct task_struct *task)
  {
  	return !in_interrupt() && task->make_it_fail;
  }
  
  #define MAX_STACK_TRACE_DEPTH 32
  
  #ifdef CONFIG_FAULT_INJECTION_STACKTRACE_FILTER
  
  static bool fail_stacktrace(struct fault_attr *attr)
  {
  	struct stack_trace trace;
  	int depth = attr->stacktrace_depth;
  	unsigned long entries[MAX_STACK_TRACE_DEPTH];
  	int n;
  	bool found = (attr->require_start == 0 && attr->require_end == ULONG_MAX);
  
  	if (depth == 0)
  		return found;
  
  	trace.nr_entries = 0;
  	trace.entries = entries;
  	trace.max_entries = depth;
  	trace.skip = 1;
  
  	save_stack_trace(&trace);
  	for (n = 0; n < trace.nr_entries; n++) {
  		if (attr->reject_start <= entries[n] &&
  			       entries[n] < attr->reject_end)
  			return false;
  		if (attr->require_start <= entries[n] &&
  			       entries[n] < attr->require_end)
  			found = true;
  	}
  	return found;
  }
  
  #else
  
  static inline bool fail_stacktrace(struct fault_attr *attr)
  {
  	return true;
  }
  
  #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
  
  /*
   * This code is stolen from failmalloc-1.0
   * http://www.nongnu.org/failmalloc/
   */
  
  bool should_fail(struct fault_attr *attr, ssize_t size)
  {
  	/* No need to check any other properties if the probability is 0 */
  	if (attr->probability == 0)
  		return false;
  
  	if (attr->task_filter && !fail_task(attr, current))
  		return false;
  
  	if (atomic_read(&attr->times) == 0)
  		return false;
  
  	if (atomic_read(&attr->space) > size) {
  		atomic_sub(size, &attr->space);
  		return false;
  	}
  
  	if (attr->interval > 1) {
  		attr->count++;
  		if (attr->count % attr->interval)
  			return false;
  	}
  
  	if (attr->probability <= prandom_u32() % 100)
  		return false;
  
  	if (!fail_stacktrace(attr))
  		return false;
  
  	fail_dump(attr);
  
  	if (atomic_read(&attr->times) != -1)
  		atomic_dec_not_zero(&attr->times);
  
  	return true;
  }
  EXPORT_SYMBOL_GPL(should_fail);
  
  #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
  
  static int debugfs_ul_set(void *data, u64 val)
  {
  	*(unsigned long *)data = val;
  	return 0;
  }
  
  static int debugfs_ul_get(void *data, u64 *val)
  {
  	*val = *(unsigned long *)data;
  	return 0;
  }
  
  DEFINE_SIMPLE_ATTRIBUTE(fops_ul, debugfs_ul_get, debugfs_ul_set, "%llu
  ");
  
  static struct dentry *debugfs_create_ul(const char *name, umode_t mode,
  				struct dentry *parent, unsigned long *value)
  {
  	return debugfs_create_file(name, mode, parent, value, &fops_ul);
  }
  
  #ifdef CONFIG_FAULT_INJECTION_STACKTRACE_FILTER
  
  static int debugfs_stacktrace_depth_set(void *data, u64 val)
  {
  	*(unsigned long *)data =
  		min_t(unsigned long, val, MAX_STACK_TRACE_DEPTH);
  
  	return 0;
  }
  
  DEFINE_SIMPLE_ATTRIBUTE(fops_stacktrace_depth, debugfs_ul_get,
  			debugfs_stacktrace_depth_set, "%llu
  ");
  
  static struct dentry *debugfs_create_stacktrace_depth(
  	const char *name, umode_t mode,
  	struct dentry *parent, unsigned long *value)
  {
  	return debugfs_create_file(name, mode, parent, value,
  				   &fops_stacktrace_depth);
  }
  
  #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
  
  struct dentry *fault_create_debugfs_attr(const char *name,
  			struct dentry *parent, struct fault_attr *attr)
  {
  	umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
  	struct dentry *dir;
  
  	dir = debugfs_create_dir(name, parent);
  	if (!dir)
  		return ERR_PTR(-ENOMEM);
  
  	if (!debugfs_create_ul("probability", mode, dir, &attr->probability))
  		goto fail;
  	if (!debugfs_create_ul("interval", mode, dir, &attr->interval))
  		goto fail;
  	if (!debugfs_create_atomic_t("times", mode, dir, &attr->times))
  		goto fail;
  	if (!debugfs_create_atomic_t("space", mode, dir, &attr->space))
  		goto fail;
  	if (!debugfs_create_ul("verbose", mode, dir, &attr->verbose))
  		goto fail;
  	if (!debugfs_create_bool("task-filter", mode, dir, &attr->task_filter))
  		goto fail;
  
  #ifdef CONFIG_FAULT_INJECTION_STACKTRACE_FILTER
  
  	if (!debugfs_create_stacktrace_depth("stacktrace-depth", mode, dir,
  				&attr->stacktrace_depth))
  		goto fail;
  	if (!debugfs_create_ul("require-start", mode, dir,
  				&attr->require_start))
  		goto fail;
  	if (!debugfs_create_ul("require-end", mode, dir, &attr->require_end))
  		goto fail;
  	if (!debugfs_create_ul("reject-start", mode, dir, &attr->reject_start))
  		goto fail;
  	if (!debugfs_create_ul("reject-end", mode, dir, &attr->reject_end))
  		goto fail;
  
  #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
  
  	return dir;
  fail:
  	debugfs_remove_recursive(dir);
  
  	return ERR_PTR(-ENOMEM);
  }
  EXPORT_SYMBOL_GPL(fault_create_debugfs_attr);
  
  #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */