/*
   * Copyright (C) 2003 Sistina Software (UK) Limited.
   * Copyright (C) 2004, 2010-2011 Red Hat, Inc. All rights reserved.
   *
   * This file is released under the GPL.
   */
  
  #include <linux/device-mapper.h>
  
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/blkdev.h>
  #include <linux/bio.h>
  #include <linux/slab.h>
  
  #define DM_MSG_PREFIX "flakey"
  
  #define all_corrupt_bio_flags_match(bio, fc)	\
  	(((bio)->bi_rw & (fc)->corrupt_bio_flags) == (fc)->corrupt_bio_flags)
  
  /*
   * Flakey: Used for testing only, simulates intermittent,
   * catastrophic device failure.
   */
  struct flakey_c {
  	struct dm_dev *dev;
  	unsigned long start_time;
  	sector_t start;
  	unsigned up_interval;
  	unsigned down_interval;
  	unsigned long flags;
  	unsigned corrupt_bio_byte;
  	unsigned corrupt_bio_rw;
  	unsigned corrupt_bio_value;
  	unsigned corrupt_bio_flags;
  };
  
  enum feature_flag_bits {
  	DROP_WRITES
  };
  
  struct per_bio_data {
  	bool bio_submitted;
  };
  
  static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
  			  struct dm_target *ti)
  {
  	int r;
  	unsigned argc;
  	const char *arg_name;
  
  	static struct dm_arg _args[] = {
  		{0, 6, "Invalid number of feature args"},
  		{1, UINT_MAX, "Invalid corrupt bio byte"},
  		{0, 255, "Invalid corrupt value to write into bio byte (0-255)"},
  		{0, UINT_MAX, "Invalid corrupt bio flags mask"},
  	};
  
  	/* No feature arguments supplied. */
  	if (!as->argc)
  		return 0;
  
  	r = dm_read_arg_group(_args, as, &argc, &ti->error);
  	if (r)
  		return r;
  
  	while (argc) {
  		arg_name = dm_shift_arg(as);
  		argc--;
  
  		/*
  		 * drop_writes
  		 */
  		if (!strcasecmp(arg_name, "drop_writes")) {
  			if (test_and_set_bit(DROP_WRITES, &fc->flags)) {
  				ti->error = "Feature drop_writes duplicated";
  				return -EINVAL;
  			}
  
  			continue;
  		}
  
  		/*
  		 * corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>
  		 */
  		if (!strcasecmp(arg_name, "corrupt_bio_byte")) {
  			if (!argc) {
  				ti->error = "Feature corrupt_bio_byte requires parameters";
  				return -EINVAL;
  			}
  
  			r = dm_read_arg(_args + 1, as, &fc->corrupt_bio_byte, &ti->error);
  			if (r)
  				return r;
  			argc--;
  
  			/*
  			 * Direction r or w?
  			 */
  			arg_name = dm_shift_arg(as);
  			if (!strcasecmp(arg_name, "w"))
  				fc->corrupt_bio_rw = WRITE;
  			else if (!strcasecmp(arg_name, "r"))
  				fc->corrupt_bio_rw = READ;
  			else {
  				ti->error = "Invalid corrupt bio direction (r or w)";
  				return -EINVAL;
  			}
  			argc--;
  
  			/*
  			 * Value of byte (0-255) to write in place of correct one.
  			 */
  			r = dm_read_arg(_args + 2, as, &fc->corrupt_bio_value, &ti->error);
  			if (r)
  				return r;
  			argc--;
  
  			/*
  			 * Only corrupt bios with these flags set.
  			 */
  			r = dm_read_arg(_args + 3, as, &fc->corrupt_bio_flags, &ti->error);
  			if (r)
  				return r;
  			argc--;
  
  			continue;
  		}
  
  		ti->error = "Unrecognised flakey feature requested";
  		return -EINVAL;
  	}
  
  	if (test_bit(DROP_WRITES, &fc->flags) && (fc->corrupt_bio_rw == WRITE)) {
  		ti->error = "drop_writes is incompatible with corrupt_bio_byte with the WRITE flag set";
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  /*
   * Construct a flakey mapping:
   * <dev_path> <offset> <up interval> <down interval> [<#feature args> [<arg>]*]
   *
   *   Feature args:
   *     [drop_writes]
   *     [corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>]
   *
   *   Nth_byte starts from 1 for the first byte.
   *   Direction is r for READ or w for WRITE.
   *   bio_flags is ignored if 0.
   */
  static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  {
  	static struct dm_arg _args[] = {
  		{0, UINT_MAX, "Invalid up interval"},
  		{0, UINT_MAX, "Invalid down interval"},
  	};
  
  	int r;
  	struct flakey_c *fc;
  	unsigned long long tmpll;
  	struct dm_arg_set as;
  	const char *devname;
  	char dummy;
  
  	as.argc = argc;
  	as.argv = argv;
  
  	if (argc < 4) {
  		ti->error = "Invalid argument count";
  		return -EINVAL;
  	}
  
  	fc = kzalloc(sizeof(*fc), GFP_KERNEL);
  	if (!fc) {
  		ti->error = "Cannot allocate context";
  		return -ENOMEM;
  	}
  	fc->start_time = jiffies;
  
  	devname = dm_shift_arg(&as);
  
  	if (sscanf(dm_shift_arg(&as), "%llu%c", &tmpll, &dummy) != 1) {
  		ti->error = "Invalid device sector";
  		goto bad;
  	}
  	fc->start = tmpll;
  
  	r = dm_read_arg(_args, &as, &fc->up_interval, &ti->error);
  	if (r)
  		goto bad;
  
  	r = dm_read_arg(_args, &as, &fc->down_interval, &ti->error);
  	if (r)
  		goto bad;
  
  	if (!(fc->up_interval + fc->down_interval)) {
  		ti->error = "Total (up + down) interval is zero";
  		goto bad;
  	}
  
  	if (fc->up_interval + fc->down_interval < fc->up_interval) {
  		ti->error = "Interval overflow";
  		goto bad;
  	}
  
  	r = parse_features(&as, fc, ti);
  	if (r)
  		goto bad;
  
  	if (dm_get_device(ti, devname, dm_table_get_mode(ti->table), &fc->dev)) {
  		ti->error = "Device lookup failed";
  		goto bad;
  	}
  
  	ti->num_flush_bios = 1;
  	ti->num_discard_bios = 1;
  	ti->per_bio_data_size = sizeof(struct per_bio_data);
  	ti->private = fc;
  	return 0;
  
  bad:
  	kfree(fc);
  	return -EINVAL;
  }
  
  static void flakey_dtr(struct dm_target *ti)
  {
  	struct flakey_c *fc = ti->private;
  
  	dm_put_device(ti, fc->dev);
  	kfree(fc);
  }
  
  static sector_t flakey_map_sector(struct dm_target *ti, sector_t bi_sector)
  {
  	struct flakey_c *fc = ti->private;
  
  	return fc->start + dm_target_offset(ti, bi_sector);
  }
  
  static void flakey_map_bio(struct dm_target *ti, struct bio *bio)
  {
  	struct flakey_c *fc = ti->private;
  
  	bio->bi_bdev = fc->dev->bdev;
  	if (bio_sectors(bio))
  		bio->bi_iter.bi_sector =
  			flakey_map_sector(ti, bio->bi_iter.bi_sector);
  }
  
  static void corrupt_bio_data(struct bio *bio, struct flakey_c *fc)
  {
  	unsigned bio_bytes = bio_cur_bytes(bio);
  	char *data = bio_data(bio);
  
  	/*
  	 * Overwrite the Nth byte of the data returned.
  	 */
  	if (data && bio_bytes >= fc->corrupt_bio_byte) {
  		data[fc->corrupt_bio_byte - 1] = fc->corrupt_bio_value;
  
  		DMDEBUG("Corrupting data bio=%p by writing %u to byte %u "
  			"(rw=%c bi_rw=%lu bi_sector=%llu cur_bytes=%u)
  ",
  			bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
  			(bio_data_dir(bio) == WRITE) ? 'w' : 'r', bio->bi_rw,
  			(unsigned long long)bio->bi_iter.bi_sector, bio_bytes);
  	}
  }
  
  static int flakey_map(struct dm_target *ti, struct bio *bio)
  {
  	struct flakey_c *fc = ti->private;
  	unsigned elapsed;
  	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
  	pb->bio_submitted = false;
  
  	/* Are we alive ? */
  	elapsed = (jiffies - fc->start_time) / HZ;
  	if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval) {
  		/*
  		 * Flag this bio as submitted while down.
  		 */
  		pb->bio_submitted = true;
  
  		/*
  		 * Map reads as normal.
  		 */
  		if (bio_data_dir(bio) == READ)
  			goto map_bio;
  
  		/*
  		 * Drop writes?
  		 */
  		if (test_bit(DROP_WRITES, &fc->flags)) {
  			bio_endio(bio, 0);
  			return DM_MAPIO_SUBMITTED;
  		}
  
  		/*
  		 * Corrupt matching writes.
  		 */
  		if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == WRITE)) {
  			if (all_corrupt_bio_flags_match(bio, fc))
  				corrupt_bio_data(bio, fc);
  			goto map_bio;
  		}
  
  		/*
  		 * By default, error all I/O.
  		 */
  		return -EIO;
  	}
  
  map_bio:
  	flakey_map_bio(ti, bio);
  
  	return DM_MAPIO_REMAPPED;
  }
  
  static int flakey_end_io(struct dm_target *ti, struct bio *bio, int error)
  {
  	struct flakey_c *fc = ti->private;
  	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
  
  	/*
  	 * Corrupt successful READs while in down state.
  	 * If flags were specified, only corrupt those that match.
  	 */
  	if (fc->corrupt_bio_byte && !error && pb->bio_submitted &&
  	    (bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw == READ) &&
  	    all_corrupt_bio_flags_match(bio, fc))
  		corrupt_bio_data(bio, fc);
  
  	return error;
  }
  
  static void flakey_status(struct dm_target *ti, status_type_t type,
  			  unsigned status_flags, char *result, unsigned maxlen)
  {
  	unsigned sz = 0;
  	struct flakey_c *fc = ti->private;
  	unsigned drop_writes;
  
  	switch (type) {
  	case STATUSTYPE_INFO:
  		result[0] = '\0';
  		break;
  
  	case STATUSTYPE_TABLE:
  		DMEMIT("%s %llu %u %u ", fc->dev->name,
  		       (unsigned long long)fc->start, fc->up_interval,
  		       fc->down_interval);
  
  		drop_writes = test_bit(DROP_WRITES, &fc->flags);
  		DMEMIT("%u ", drop_writes + (fc->corrupt_bio_byte > 0) * 5);
  
  		if (drop_writes)
  			DMEMIT("drop_writes ");
  
  		if (fc->corrupt_bio_byte)
  			DMEMIT("corrupt_bio_byte %u %c %u %u ",
  			       fc->corrupt_bio_byte,
  			       (fc->corrupt_bio_rw == WRITE) ? 'w' : 'r',
  			       fc->corrupt_bio_value, fc->corrupt_bio_flags);
  
  		break;
  	}
  }
  
  static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
  {
  	struct flakey_c *fc = ti->private;
  	struct dm_dev *dev = fc->dev;
  	int r = 0;
  
  	/*
  	 * Only pass ioctls through if the device sizes match exactly.
  	 */
  	if (fc->start ||
  	    ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
  		r = scsi_verify_blk_ioctl(NULL, cmd);
  
  	return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
  }
  
  static int flakey_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
  			struct bio_vec *biovec, int max_size)
  {
  	struct flakey_c *fc = ti->private;
  	struct request_queue *q = bdev_get_queue(fc->dev->bdev);
  
  	if (!q->merge_bvec_fn)
  		return max_size;
  
  	bvm->bi_bdev = fc->dev->bdev;
  	bvm->bi_sector = flakey_map_sector(ti, bvm->bi_sector);
  
  	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
  }
  
  static int flakey_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
  {
  	struct flakey_c *fc = ti->private;
  
  	return fn(ti, fc->dev, fc->start, ti->len, data);
  }
  
  static struct target_type flakey_target = {
  	.name   = "flakey",
  	.version = {1, 3, 1},
  	.module = THIS_MODULE,
  	.ctr    = flakey_ctr,
  	.dtr    = flakey_dtr,
  	.map    = flakey_map,
  	.end_io = flakey_end_io,
  	.status = flakey_status,
  	.ioctl	= flakey_ioctl,
  	.merge	= flakey_merge,
  	.iterate_devices = flakey_iterate_devices,
  };
  
  static int __init dm_flakey_init(void)
  {
  	int r = dm_register_target(&flakey_target);
  
  	if (r < 0)
  		DMERR("register failed %d", r);
  
  	return r;
  }
  
  static void __exit dm_flakey_exit(void)
  {
  	dm_unregister_target(&flakey_target);
  }
  
  /* Module hooks */
  module_init(dm_flakey_init);
  module_exit(dm_flakey_exit);
  
  MODULE_DESCRIPTION(DM_NAME " flakey target");
  MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
  MODULE_LICENSE("GPL");