/*
   * Copyright (C) 2005-2007 Red Hat GmbH
   *
   * A target that delays reads and/or writes and can send
   * them to different devices.
   *
   * This file is released under the GPL.
   */
  
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/blkdev.h>
  #include <linux/bio.h>
  #include <linux/slab.h>
  
  #include <linux/device-mapper.h>
  
  #define DM_MSG_PREFIX "delay"
  
  struct delay_c {
  	struct timer_list delay_timer;
  	struct mutex timer_lock;
  	struct workqueue_struct *kdelayd_wq;
  	struct work_struct flush_expired_bios;
  	struct list_head delayed_bios;
  	atomic_t may_delay;
  
  	struct dm_dev *dev_read;
  	sector_t start_read;
  	unsigned read_delay;
  	unsigned reads;
  
  	struct dm_dev *dev_write;
  	sector_t start_write;
  	unsigned write_delay;
  	unsigned writes;
  };
  
  struct dm_delay_info {
  	struct delay_c *context;
  	struct list_head list;
  	unsigned long expires;
  };
  
  static DEFINE_MUTEX(delayed_bios_lock);
  
  static void handle_delayed_timer(unsigned long data)
  {
  	struct delay_c *dc = (struct delay_c *)data;
  
  	queue_work(dc->kdelayd_wq, &dc->flush_expired_bios);
  }
  
  static void queue_timeout(struct delay_c *dc, unsigned long expires)
  {
  	mutex_lock(&dc->timer_lock);
  
  	if (!timer_pending(&dc->delay_timer) || expires < dc->delay_timer.expires)
  		mod_timer(&dc->delay_timer, expires);
  
  	mutex_unlock(&dc->timer_lock);
  }
  
  static void flush_bios(struct bio *bio)
  {
  	struct bio *n;
  
  	while (bio) {
  		n = bio->bi_next;
  		bio->bi_next = NULL;
  		generic_make_request(bio);
  		bio = n;
  	}
  }
  
  static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all)
  {
  	struct dm_delay_info *delayed, *next;
  	unsigned long next_expires = 0;
  	int start_timer = 0;
  	struct bio_list flush_bios = { };
  
  	mutex_lock(&delayed_bios_lock);
  	list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) {
  		if (flush_all || time_after_eq(jiffies, delayed->expires)) {
  			struct bio *bio = dm_bio_from_per_bio_data(delayed,
  						sizeof(struct dm_delay_info));
  			list_del(&delayed->list);
  			bio_list_add(&flush_bios, bio);
  			if ((bio_data_dir(bio) == WRITE))
  				delayed->context->writes--;
  			else
  				delayed->context->reads--;
  			continue;
  		}
  
  		if (!start_timer) {
  			start_timer = 1;
  			next_expires = delayed->expires;
  		} else
  			next_expires = min(next_expires, delayed->expires);
  	}
  
  	mutex_unlock(&delayed_bios_lock);
  
  	if (start_timer)
  		queue_timeout(dc, next_expires);
  
  	return bio_list_get(&flush_bios);
  }
  
  static void flush_expired_bios(struct work_struct *work)
  {
  	struct delay_c *dc;
  
  	dc = container_of(work, struct delay_c, flush_expired_bios);
  	flush_bios(flush_delayed_bios(dc, 0));
  }
  
  /*
   * Mapping parameters:
   *    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
   *
   * With separate write parameters, the first set is only used for reads.
   * Delays are specified in milliseconds.
   */
  static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  {
  	struct delay_c *dc;
  	unsigned long long tmpll;
  	char dummy;
  
  	if (argc != 3 && argc != 6) {
  		ti->error = "requires exactly 3 or 6 arguments";
  		return -EINVAL;
  	}
  
  	dc = kmalloc(sizeof(*dc), GFP_KERNEL);
  	if (!dc) {
  		ti->error = "Cannot allocate context";
  		return -ENOMEM;
  	}
  
  	dc->reads = dc->writes = 0;
  
  	if (sscanf(argv[1], "%llu%c", &tmpll, &dummy) != 1) {
  		ti->error = "Invalid device sector";
  		goto bad;
  	}
  	dc->start_read = tmpll;
  
  	if (sscanf(argv[2], "%u%c", &dc->read_delay, &dummy) != 1) {
  		ti->error = "Invalid delay";
  		goto bad;
  	}
  
  	if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
  			  &dc->dev_read)) {
  		ti->error = "Device lookup failed";
  		goto bad;
  	}
  
  	dc->dev_write = NULL;
  	if (argc == 3)
  		goto out;
  
  	if (sscanf(argv[4], "%llu%c", &tmpll, &dummy) != 1) {
  		ti->error = "Invalid write device sector";
  		goto bad_dev_read;
  	}
  	dc->start_write = tmpll;
  
  	if (sscanf(argv[5], "%u%c", &dc->write_delay, &dummy) != 1) {
  		ti->error = "Invalid write delay";
  		goto bad_dev_read;
  	}
  
  	if (dm_get_device(ti, argv[3], dm_table_get_mode(ti->table),
  			  &dc->dev_write)) {
  		ti->error = "Write device lookup failed";
  		goto bad_dev_read;
  	}
  
  out:
  	dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0);
  	if (!dc->kdelayd_wq) {
  		DMERR("Couldn't start kdelayd");
  		goto bad_queue;
  	}
  
  	setup_timer(&dc->delay_timer, handle_delayed_timer, (unsigned long)dc);
  
  	INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
  	INIT_LIST_HEAD(&dc->delayed_bios);
  	mutex_init(&dc->timer_lock);
  	atomic_set(&dc->may_delay, 1);
  
  	ti->num_flush_bios = 1;
  	ti->num_discard_bios = 1;
  	ti->per_bio_data_size = sizeof(struct dm_delay_info);
  	ti->private = dc;
  	return 0;
  
  bad_queue:
  	if (dc->dev_write)
  		dm_put_device(ti, dc->dev_write);
  bad_dev_read:
  	dm_put_device(ti, dc->dev_read);
  bad:
  	kfree(dc);
  	return -EINVAL;
  }
  
  static void delay_dtr(struct dm_target *ti)
  {
  	struct delay_c *dc = ti->private;
  
  	destroy_workqueue(dc->kdelayd_wq);
  
  	dm_put_device(ti, dc->dev_read);
  
  	if (dc->dev_write)
  		dm_put_device(ti, dc->dev_write);
  
  	kfree(dc);
  }
  
  static int delay_bio(struct delay_c *dc, int delay, struct bio *bio)
  {
  	struct dm_delay_info *delayed;
  	unsigned long expires = 0;
  
  	if (!delay || !atomic_read(&dc->may_delay))
  		return 1;
  
  	delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));
  
  	delayed->context = dc;
  	delayed->expires = expires = jiffies + (delay * HZ / 1000);
  
  	mutex_lock(&delayed_bios_lock);
  
  	if (bio_data_dir(bio) == WRITE)
  		dc->writes++;
  	else
  		dc->reads++;
  
  	list_add_tail(&delayed->list, &dc->delayed_bios);
  
  	mutex_unlock(&delayed_bios_lock);
  
  	queue_timeout(dc, expires);
  
  	return 0;
  }
  
  static void delay_presuspend(struct dm_target *ti)
  {
  	struct delay_c *dc = ti->private;
  
  	atomic_set(&dc->may_delay, 0);
  	del_timer_sync(&dc->delay_timer);
  	flush_bios(flush_delayed_bios(dc, 1));
  }
  
  static void delay_resume(struct dm_target *ti)
  {
  	struct delay_c *dc = ti->private;
  
  	atomic_set(&dc->may_delay, 1);
  }
  
  static int delay_map(struct dm_target *ti, struct bio *bio)
  {
  	struct delay_c *dc = ti->private;
  
  	if ((bio_data_dir(bio) == WRITE) && (dc->dev_write)) {
  		bio->bi_bdev = dc->dev_write->bdev;
  		if (bio_sectors(bio))
  			bio->bi_iter.bi_sector = dc->start_write +
  				dm_target_offset(ti, bio->bi_iter.bi_sector);
  
  		return delay_bio(dc, dc->write_delay, bio);
  	}
  
  	bio->bi_bdev = dc->dev_read->bdev;
  	bio->bi_iter.bi_sector = dc->start_read +
  		dm_target_offset(ti, bio->bi_iter.bi_sector);
  
  	return delay_bio(dc, dc->read_delay, bio);
  }
  
  static void delay_status(struct dm_target *ti, status_type_t type,
  			 unsigned status_flags, char *result, unsigned maxlen)
  {
  	struct delay_c *dc = ti->private;
  	int sz = 0;
  
  	switch (type) {
  	case STATUSTYPE_INFO:
  		DMEMIT("%u %u", dc->reads, dc->writes);
  		break;
  
  	case STATUSTYPE_TABLE:
  		DMEMIT("%s %llu %u", dc->dev_read->name,
  		       (unsigned long long) dc->start_read,
  		       dc->read_delay);
  		if (dc->dev_write)
  			DMEMIT(" %s %llu %u", dc->dev_write->name,
  			       (unsigned long long) dc->start_write,
  			       dc->write_delay);
  		break;
  	}
  }
  
  static int delay_iterate_devices(struct dm_target *ti,
  				 iterate_devices_callout_fn fn, void *data)
  {
  	struct delay_c *dc = ti->private;
  	int ret = 0;
  
  	ret = fn(ti, dc->dev_read, dc->start_read, ti->len, data);
  	if (ret)
  		goto out;
  
  	if (dc->dev_write)
  		ret = fn(ti, dc->dev_write, dc->start_write, ti->len, data);
  
  out:
  	return ret;
  }
  
  static struct target_type delay_target = {
  	.name	     = "delay",
  	.version     = {1, 2, 1},
  	.module      = THIS_MODULE,
  	.ctr	     = delay_ctr,
  	.dtr	     = delay_dtr,
  	.map	     = delay_map,
  	.presuspend  = delay_presuspend,
  	.resume	     = delay_resume,
  	.status	     = delay_status,
  	.iterate_devices = delay_iterate_devices,
  };
  
  static int __init dm_delay_init(void)
  {
  	int r;
  
  	r = dm_register_target(&delay_target);
  	if (r < 0) {
  		DMERR("register failed %d", r);
  		goto bad_register;
  	}
  
  	return 0;
  
  bad_register:
  	return r;
  }
  
  static void __exit dm_delay_exit(void)
  {
  	dm_unregister_target(&delay_target);
  }
  
  /* Module hooks */
  module_init(dm_delay_init);
  module_exit(dm_delay_exit);
  
  MODULE_DESCRIPTION(DM_NAME " delay target");
  MODULE_AUTHOR("Heinz Mauelshagen <mauelshagen@redhat.com>");
  MODULE_LICENSE("GPL");