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faulty.c

/*
 * faulty.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 2004 Neil Brown
 *
 * fautly-device-simulator personality for md
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */


/*
 * The "faulty" personality causes some requests to fail.
 *
 * Possible failure modes are:
 *   reads fail "randomly" but succeed on retry
 *   writes fail "randomly" but succeed on retry
 *   reads for some address fail and then persist until a write
 *   reads for some address fail and then persist irrespective of write
 *   writes for some address fail and persist
 *   all writes fail
 *
 * Different modes can be active at a time, but only
 * one can be set at array creation.  Others can be added later.
 * A mode can be one-shot or recurrent with the recurrance being
 * once in every N requests.
 * The bottom 5 bits of the "layout" indicate the mode.  The
 * remainder indicate a period, or 0 for one-shot.
 *
 * There is an implementation limit on the number of concurrently
 * persisting-faulty blocks. When a new fault is requested that would
 * exceed the limit, it is ignored.
 * All current faults can be clear using a layout of "0".
 *
 * Requests are always sent to the device.  If they are to fail,
 * we clone the bio and insert a new b_end_io into the chain.
 */

#define     WriteTransient    0
#define     ReadTransient     1
#define     WritePersistent   2
#define     ReadPersistent    3
#define     WriteAll    4 /* doesn't go to device */
#define     ReadFixable 5
#define     Modes 6

#define     ClearErrors 31
#define     ClearFaults 30

#define AllPersist      100 /* internal use only */
#define     NoPersist   101

#define     ModeMask    0x1f
#define     ModeShift   5

#define MaxFault  50
#include <linux/raid/md.h>


static void faulty_fail(struct bio *bio, int error)
{
      struct bio *b = bio->bi_private;

      b->bi_size = bio->bi_size;
      b->bi_sector = bio->bi_sector;

      bio_put(bio);

      bio_io_error(b);
}

typedef struct faulty_conf {
      int period[Modes];
      atomic_t counters[Modes];
      sector_t faults[MaxFault];
      int   modes[MaxFault];
      int nfaults;
      mdk_rdev_t *rdev;
} conf_t;

static int check_mode(conf_t *conf, int mode)
{
      if (conf->period[mode] == 0 &&
          atomic_read(&conf->counters[mode]) <= 0)
            return 0; /* no failure, no decrement */


      if (atomic_dec_and_test(&conf->counters[mode])) {
            if (conf->period[mode])
                  atomic_set(&conf->counters[mode], conf->period[mode]);
            return 1;
      }
      return 0;
}

static int check_sector(conf_t *conf, sector_t start, sector_t end, int dir)
{
      /* If we find a ReadFixable sector, we fix it ... */
      int i;
      for (i=0; i<conf->nfaults; i++)
            if (conf->faults[i] >= start &&
                conf->faults[i] < end) {
                  /* found it ... */
                  switch (conf->modes[i] * 2 + dir) {
                  case WritePersistent*2+WRITE: return 1;
                  case ReadPersistent*2+READ: return 1;
                  case ReadFixable*2+READ: return 1;
                  case ReadFixable*2+WRITE:
                        conf->modes[i] = NoPersist;
                        return 0;
                  case AllPersist*2+READ:
                  case AllPersist*2+WRITE: return 1;
                  default:
                        return 0;
                  }
            }
      return 0;
}

static void add_sector(conf_t *conf, sector_t start, int mode)
{
      int i;
      int n = conf->nfaults;
      for (i=0; i<conf->nfaults; i++)
            if (conf->faults[i] == start) {
                  switch(mode) {
                  case NoPersist: conf->modes[i] = mode; return;
                  case WritePersistent:
                        if (conf->modes[i] == ReadPersistent ||
                            conf->modes[i] == ReadFixable)
                              conf->modes[i] = AllPersist;
                        else
                              conf->modes[i] = WritePersistent;
                        return;
                  case ReadPersistent:
                        if (conf->modes[i] == WritePersistent)
                              conf->modes[i] = AllPersist;
                        else
                              conf->modes[i] = ReadPersistent;
                        return;
                  case ReadFixable:
                        if (conf->modes[i] == WritePersistent ||
                            conf->modes[i] == ReadPersistent)
                              conf->modes[i] = AllPersist;
                        else
                              conf->modes[i] = ReadFixable;
                        return;
                  }
            } else if (conf->modes[i] == NoPersist)
                  n = i;

      if (n >= MaxFault)
            return;
      conf->faults[n] = start;
      conf->modes[n] = mode;
      if (conf->nfaults == n)
            conf->nfaults = n+1;
}

static int make_request(struct request_queue *q, struct bio *bio)
{
      mddev_t *mddev = q->queuedata;
      conf_t *conf = (conf_t*)mddev->private;
      int failit = 0;

      if (bio_data_dir(bio) == WRITE) {
            /* write request */
            if (atomic_read(&conf->counters[WriteAll])) {
                  /* special case - don't decrement, don't generic_make_request,
                   * just fail immediately
                   */
                  bio_endio(bio, -EIO);
                  return 0;
            }

            if (check_sector(conf, bio->bi_sector, bio->bi_sector+(bio->bi_size>>9),
                         WRITE))
                  failit = 1;
            if (check_mode(conf, WritePersistent)) {
                  add_sector(conf, bio->bi_sector, WritePersistent);
                  failit = 1;
            }
            if (check_mode(conf, WriteTransient))
                  failit = 1;
      } else {
            /* read request */
            if (check_sector(conf, bio->bi_sector, bio->bi_sector + (bio->bi_size>>9),
                         READ))
                  failit = 1;
            if (check_mode(conf, ReadTransient))
                  failit = 1;
            if (check_mode(conf, ReadPersistent)) {
                  add_sector(conf, bio->bi_sector, ReadPersistent);
                  failit = 1;
            }
            if (check_mode(conf, ReadFixable)) {
                  add_sector(conf, bio->bi_sector, ReadFixable);
                  failit = 1;
            }
      }
      if (failit) {
            struct bio *b = bio_clone(bio, GFP_NOIO);
            b->bi_bdev = conf->rdev->bdev;
            b->bi_private = bio;
            b->bi_end_io = faulty_fail;
            generic_make_request(b);
            return 0;
      } else {
            bio->bi_bdev = conf->rdev->bdev;
            return 1;
      }
}

static void status(struct seq_file *seq, mddev_t *mddev)
{
      conf_t *conf = (conf_t*)mddev->private;
      int n;

      if ((n=atomic_read(&conf->counters[WriteTransient])) != 0)
            seq_printf(seq, " WriteTransient=%d(%d)",
                     n, conf->period[WriteTransient]);

      if ((n=atomic_read(&conf->counters[ReadTransient])) != 0)
            seq_printf(seq, " ReadTransient=%d(%d)",
                     n, conf->period[ReadTransient]);

      if ((n=atomic_read(&conf->counters[WritePersistent])) != 0)
            seq_printf(seq, " WritePersistent=%d(%d)",
                     n, conf->period[WritePersistent]);

      if ((n=atomic_read(&conf->counters[ReadPersistent])) != 0)
            seq_printf(seq, " ReadPersistent=%d(%d)",
                     n, conf->period[ReadPersistent]);


      if ((n=atomic_read(&conf->counters[ReadFixable])) != 0)
            seq_printf(seq, " ReadFixable=%d(%d)",
                     n, conf->period[ReadFixable]);

      if ((n=atomic_read(&conf->counters[WriteAll])) != 0)
            seq_printf(seq, " WriteAll");

      seq_printf(seq, " nfaults=%d", conf->nfaults);
}


static int reconfig(mddev_t *mddev, int layout, int chunk_size)
{
      int mode = layout & ModeMask;
      int count = layout >> ModeShift;
      conf_t *conf = mddev->private;

      if (chunk_size != -1)
            return -EINVAL;

      /* new layout */
      if (mode == ClearFaults)
            conf->nfaults = 0;
      else if (mode == ClearErrors) {
            int i;
            for (i=0 ; i < Modes ; i++) {
                  conf->period[i] = 0;
                  atomic_set(&conf->counters[i], 0);
            }
      } else if (mode < Modes) {
            conf->period[mode] = count;
            if (!count) count++;
            atomic_set(&conf->counters[mode], count);
      } else
            return -EINVAL;
      mddev->layout = -1; /* makes sure further changes come through */
      return 0;
}

static int run(mddev_t *mddev)
{
      mdk_rdev_t *rdev;
      struct list_head *tmp;
      int i;

      conf_t *conf = kmalloc(sizeof(*conf), GFP_KERNEL);

      for (i=0; i<Modes; i++) {
            atomic_set(&conf->counters[i], 0);
            conf->period[i] = 0;
      }
      conf->nfaults = 0;

      ITERATE_RDEV(mddev, rdev, tmp)
            conf->rdev = rdev;

      mddev->array_size = mddev->size;
      mddev->private = conf;

      reconfig(mddev, mddev->layout, -1);

      return 0;
}

static int stop(mddev_t *mddev)
{
      conf_t *conf = (conf_t *)mddev->private;

      kfree(conf);
      mddev->private = NULL;
      return 0;
}

static struct mdk_personality faulty_personality =
{
      .name       = "faulty",
      .level            = LEVEL_FAULTY,
      .owner            = THIS_MODULE,
      .make_request     = make_request,
      .run        = run,
      .stop       = stop,
      .status           = status,
      .reconfig   = reconfig,
};

static int __init raid_init(void)
{
      return register_md_personality(&faulty_personality);
}

static void raid_exit(void)
{
      unregister_md_personality(&faulty_personality);
}

module_init(raid_init);
module_exit(raid_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-10"); /* faulty */
MODULE_ALIAS("md-faulty");
MODULE_ALIAS("md-level--5");

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