/*
 * 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_opf & (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);

        r = -EINVAL;
        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;

        r = dm_get_device(ti, devname, dm_table_get_mode(ti->table), &fc->dev);
        if (r) {
                ti->error = "Device lookup failed";
                goto bad;
        }

        ti->num_flush_bios = 1;
        ti->num_discard_bios = 1;
        ti->per_io_data_size = sizeof(struct per_bio_data);
        ti->private = fc;
        return 0;

bad:
        kfree(fc);
        return r;
}

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_opf=%u bi_sector=%llu cur_bytes=%u)\n",
                        bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
                        (bio_data_dir(bio) == WRITE) ? 'w' : 'r', bio->bi_opf,
                        (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;

                /*
                 * Error reads if neither corrupt_bio_byte or drop_writes are set.
                 * Otherwise, flakey_end_io() will decide if the reads should be modified.
                 */
                if (bio_data_dir(bio) == READ) {
                        if (!fc->corrupt_bio_byte && !test_bit(DROP_WRITES, &fc->flags))
                                return -EIO;
                        goto map_bio;
                }

                /*
                 * Drop writes?
                 */
                if (test_bit(DROP_WRITES, &fc->flags)) {
                        bio_endio(bio);
                        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));

        if (!error && pb->bio_submitted && (bio_data_dir(bio) == READ)) {
                if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == READ) &&
                    all_corrupt_bio_flags_match(bio, fc)) {
                        /*
                         * Corrupt successful matching READs while in down state.
                         */
                        corrupt_bio_data(bio, fc);

                } else if (!test_bit(DROP_WRITES, &fc->flags)) {
                        /*
                         * Error read during the down_interval if drop_writes
                         * wasn't configured.
                         */
                        return -EIO;
                }
        }

        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_prepare_ioctl(struct dm_target *ti,
                struct block_device **bdev, fmode_t *mode)
{
        struct flakey_c *fc = ti->private;

        *bdev = fc->dev->bdev;

        /*
         * Only pass ioctls through if the device sizes match exactly.
         */
        if (fc->start ||
            ti->len != i_size_read((*bdev)->bd_inode) >> SECTOR_SHIFT)
                return 1;
        return 0;
}

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,
        .prepare_ioctl = flakey_prepare_ioctl,
        .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");