/*
 * 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");