dm-flakey.c

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/*
 * 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
};

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 linear 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_requests = 1;
    ti->num_discard_requests = 1;
    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_sector = flakey_map_sector(ti, bio->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)\n",
            bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
            (bio_data_dir(bio) == WRITE) ? 'w' : 'r',
            bio->bi_rw, (unsigned long long)bio->bi_sector, bio_bytes);
    }
}

static int flakey_map(struct dm_target *ti, struct bio *bio,
              union map_info *map_context)
{
    struct flakey_c *fc = ti->private;
    unsigned elapsed;

    /* 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.
         */
        map_context->ll = 1;

        /*
         * 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, union map_info *map_context)
{
    struct flakey_c *fc = ti->private;
    unsigned bio_submitted_while_down = map_context->ll;

    /*
     * Corrupt successful READs while in down state.
     * If flags were specified, only corrupt those that match.
     */
    if (fc->corrupt_bio_byte && !error && bio_submitted_while_down &&
        (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 int 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;
    }
    return 0;
}

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, 2, 0},
    .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 <[email protected]>");
MODULE_LICENSE("GPL");