dm-stripe.c

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/*
 * Copyright (C) 2001-2003 Sistina Software (UK) Limited.
 *
 * 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>
#include <linux/log2.h>

#define DM_MSG_PREFIX "striped"
#define DM_IO_ERROR_THRESHOLD 15

struct stripe {
    struct dm_dev *dev;
    sector_t physical_start;

    atomic_t error_count;
};

struct stripe_c {
    uint32_t stripes;
    int stripes_shift;

    /* The size of this target / num. stripes */
    sector_t stripe_width;

    uint32_t chunk_size;
    int chunk_size_shift;

    /* Needed for handling events */
    struct dm_target *ti;

    /* Work struct used for triggering events*/
    struct work_struct trigger_event;

    struct stripe stripe[0];
};

/*
 * An event is triggered whenever a drive
 * drops out of a stripe volume.
 */
static void trigger_event(struct work_struct *work)
{
    struct stripe_c *sc = container_of(work, struct stripe_c,
                       trigger_event);
    dm_table_event(sc->ti->table);
}

static inline struct stripe_c *alloc_context(unsigned int stripes)
{
    size_t len;

    if (dm_array_too_big(sizeof(struct stripe_c), sizeof(struct stripe),
                 stripes))
        return NULL;

    len = sizeof(struct stripe_c) + (sizeof(struct stripe) * stripes);

    return kmalloc(len, GFP_KERNEL);
}

/*
 * Parse a single <dev> <sector> pair
 */
static int get_stripe(struct dm_target *ti, struct stripe_c *sc,
              unsigned int stripe, char **argv)
{
    unsigned long long start;
    char dummy;

    if (sscanf(argv[1], "%llu%c", &start, &dummy) != 1)
        return -EINVAL;

    if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
              &sc->stripe[stripe].dev))
        return -ENXIO;

    sc->stripe[stripe].physical_start = start;

    return 0;
}

/*
 * Construct a striped mapping.
 * <number of stripes> <chunk size> [<dev_path> <offset>]+
 */
static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
    struct stripe_c *sc;
    sector_t width;
    uint32_t stripes;
    uint32_t chunk_size;
    int r;
    unsigned int i;

    if (argc < 2) {
        ti->error = "Not enough arguments";
        return -EINVAL;
    }

    if (kstrtouint(argv[0], 10, &stripes) || !stripes) {
        ti->error = "Invalid stripe count";
        return -EINVAL;
    }

    if (kstrtouint(argv[1], 10, &chunk_size) || !chunk_size) {
        ti->error = "Invalid chunk_size";
        return -EINVAL;
    }

    width = ti->len;
    if (sector_div(width, chunk_size)) {
        ti->error = "Target length not divisible by "
            "chunk size";
        return -EINVAL;
    }

    if (sector_div(width, stripes)) {
        ti->error = "Target length not divisible by "
            "number of stripes";
        return -EINVAL;
    }

    /*
     * Do we have enough arguments for that many stripes ?
     */
    if (argc != (2 + 2 * stripes)) {
        ti->error = "Not enough destinations "
            "specified";
        return -EINVAL;
    }

    sc = alloc_context(stripes);
    if (!sc) {
        ti->error = "Memory allocation for striped context "
            "failed";
        return -ENOMEM;
    }

    INIT_WORK(&sc->trigger_event, trigger_event);

    /* Set pointer to dm target; used in trigger_event */
    sc->ti = ti;
    sc->stripes = stripes;
    sc->stripe_width = width;

    if (stripes & (stripes - 1))
        sc->stripes_shift = -1;
    else
        sc->stripes_shift = __ffs(stripes);

    r = dm_set_target_max_io_len(ti, chunk_size);
    if (r)
        return r;

    ti->num_flush_requests = stripes;
    ti->num_discard_requests = stripes;

    sc->chunk_size = chunk_size;
    if (chunk_size & (chunk_size - 1))
        sc->chunk_size_shift = -1;
    else
        sc->chunk_size_shift = __ffs(chunk_size);

    /*
     * Get the stripe destinations.
     */
    for (i = 0; i < stripes; i++) {
        argv += 2;

        r = get_stripe(ti, sc, i, argv);
        if (r < 0) {
            ti->error = "Couldn't parse stripe destination";
            while (i--)
                dm_put_device(ti, sc->stripe[i].dev);
            kfree(sc);
            return r;
        }
        atomic_set(&(sc->stripe[i].error_count), 0);
    }

    ti->private = sc;

    return 0;
}

static void stripe_dtr(struct dm_target *ti)
{
    unsigned int i;
    struct stripe_c *sc = (struct stripe_c *) ti->private;

    for (i = 0; i < sc->stripes; i++)
        dm_put_device(ti, sc->stripe[i].dev);

    flush_work(&sc->trigger_event);
    kfree(sc);
}

static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
                  uint32_t *stripe, sector_t *result)
{
    sector_t chunk = dm_target_offset(sc->ti, sector);
    sector_t chunk_offset;

    if (sc->chunk_size_shift < 0)
        chunk_offset = sector_div(chunk, sc->chunk_size);
    else {
        chunk_offset = chunk & (sc->chunk_size - 1);
        chunk >>= sc->chunk_size_shift;
    }

    if (sc->stripes_shift < 0)
        *stripe = sector_div(chunk, sc->stripes);
    else {
        *stripe = chunk & (sc->stripes - 1);
        chunk >>= sc->stripes_shift;
    }

    if (sc->chunk_size_shift < 0)
        chunk *= sc->chunk_size;
    else
        chunk <<= sc->chunk_size_shift;

    *result = chunk + chunk_offset;
}

static void stripe_map_range_sector(struct stripe_c *sc, sector_t sector,
                    uint32_t target_stripe, sector_t *result)
{
    uint32_t stripe;

    stripe_map_sector(sc, sector, &stripe, result);
    if (stripe == target_stripe)
        return;

    /* round down */
    sector = *result;
    if (sc->chunk_size_shift < 0)
        *result -= sector_div(sector, sc->chunk_size);
    else
        *result = sector & ~(sector_t)(sc->chunk_size - 1);

    if (target_stripe < stripe)
        *result += sc->chunk_size;      /* next chunk */
}

static int stripe_map_discard(struct stripe_c *sc, struct bio *bio,
                  uint32_t target_stripe)
{
    sector_t begin, end;

    stripe_map_range_sector(sc, bio->bi_sector, target_stripe, &begin);
    stripe_map_range_sector(sc, bio->bi_sector + bio_sectors(bio),
                target_stripe, &end);
    if (begin < end) {
        bio->bi_bdev = sc->stripe[target_stripe].dev->bdev;
        bio->bi_sector = begin + sc->stripe[target_stripe].physical_start;
        bio->bi_size = to_bytes(end - begin);
        return DM_MAPIO_REMAPPED;
    } else {
        /* The range doesn't map to the target stripe */
        bio_endio(bio, 0);
        return DM_MAPIO_SUBMITTED;
    }
}

static int stripe_map(struct dm_target *ti, struct bio *bio,
              union map_info *map_context)
{
    struct stripe_c *sc = ti->private;
    uint32_t stripe;
    unsigned target_request_nr;

    if (bio->bi_rw & REQ_FLUSH) {
        target_request_nr = map_context->target_request_nr;
        BUG_ON(target_request_nr >= sc->stripes);
        bio->bi_bdev = sc->stripe[target_request_nr].dev->bdev;
        return DM_MAPIO_REMAPPED;
    }
    if (unlikely(bio->bi_rw & REQ_DISCARD)) {
        target_request_nr = map_context->target_request_nr;
        BUG_ON(target_request_nr >= sc->stripes);
        return stripe_map_discard(sc, bio, target_request_nr);
    }

    stripe_map_sector(sc, bio->bi_sector, &stripe, &bio->bi_sector);

    bio->bi_sector += sc->stripe[stripe].physical_start;
    bio->bi_bdev = sc->stripe[stripe].dev->bdev;

    return DM_MAPIO_REMAPPED;
}

/*
 * Stripe status:
 *
 * INFO
 * #stripes [stripe_name <stripe_name>] [group word count]
 * [error count 'A|D' <error count 'A|D'>]
 *
 * TABLE
 * #stripes [stripe chunk size]
 * [stripe_name physical_start <stripe_name physical_start>]
 *
 */

static int stripe_status(struct dm_target *ti, status_type_t type,
             unsigned status_flags, char *result, unsigned maxlen)
{
    struct stripe_c *sc = (struct stripe_c *) ti->private;
    char buffer[sc->stripes + 1];
    unsigned int sz = 0;
    unsigned int i;

    switch (type) {
    case STATUSTYPE_INFO:
        DMEMIT("%d ", sc->stripes);
        for (i = 0; i < sc->stripes; i++)  {
            DMEMIT("%s ", sc->stripe[i].dev->name);
            buffer[i] = atomic_read(&(sc->stripe[i].error_count)) ?
                'D' : 'A';
        }
        buffer[i] = '\0';
        DMEMIT("1 %s", buffer);
        break;

    case STATUSTYPE_TABLE:
        DMEMIT("%d %llu", sc->stripes,
            (unsigned long long)sc->chunk_size);
        for (i = 0; i < sc->stripes; i++)
            DMEMIT(" %s %llu", sc->stripe[i].dev->name,
                (unsigned long long)sc->stripe[i].physical_start);
        break;
    }
    return 0;
}

static int stripe_end_io(struct dm_target *ti, struct bio *bio,
             int error, union map_info *map_context)
{
    unsigned i;
    char major_minor[16];
    struct stripe_c *sc = ti->private;

    if (!error)
        return 0; /* I/O complete */

    if ((error == -EWOULDBLOCK) && (bio->bi_rw & REQ_RAHEAD))
        return error;

    if (error == -EOPNOTSUPP)
        return error;

    memset(major_minor, 0, sizeof(major_minor));
    sprintf(major_minor, "%d:%d",
        MAJOR(disk_devt(bio->bi_bdev->bd_disk)),
        MINOR(disk_devt(bio->bi_bdev->bd_disk)));

    /*
     * Test to see which stripe drive triggered the event
     * and increment error count for all stripes on that device.
     * If the error count for a given device exceeds the threshold
     * value we will no longer trigger any further events.
     */
    for (i = 0; i < sc->stripes; i++)
        if (!strcmp(sc->stripe[i].dev->name, major_minor)) {
            atomic_inc(&(sc->stripe[i].error_count));
            if (atomic_read(&(sc->stripe[i].error_count)) <
                DM_IO_ERROR_THRESHOLD)
                schedule_work(&sc->trigger_event);
        }

    return error;
}

static int stripe_iterate_devices(struct dm_target *ti,
                  iterate_devices_callout_fn fn, void *data)
{
    struct stripe_c *sc = ti->private;
    int ret = 0;
    unsigned i = 0;

    do {
        ret = fn(ti, sc->stripe[i].dev,
             sc->stripe[i].physical_start,
             sc->stripe_width, data);
    } while (!ret && ++i < sc->stripes);

    return ret;
}

static void stripe_io_hints(struct dm_target *ti,
                struct queue_limits *limits)
{
    struct stripe_c *sc = ti->private;
    unsigned chunk_size = sc->chunk_size << SECTOR_SHIFT;

    blk_limits_io_min(limits, chunk_size);
    blk_limits_io_opt(limits, chunk_size * sc->stripes);
}

static int stripe_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
            struct bio_vec *biovec, int max_size)
{
    struct stripe_c *sc = ti->private;
    sector_t bvm_sector = bvm->bi_sector;
    uint32_t stripe;
    struct request_queue *q;

    stripe_map_sector(sc, bvm_sector, &stripe, &bvm_sector);

    q = bdev_get_queue(sc->stripe[stripe].dev->bdev);
    if (!q->merge_bvec_fn)
        return max_size;

    bvm->bi_bdev = sc->stripe[stripe].dev->bdev;
    bvm->bi_sector = sc->stripe[stripe].physical_start + bvm_sector;

    return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
}

static struct target_type stripe_target = {
    .name   = "striped",
    .version = {1, 5, 0},
    .module = THIS_MODULE,
    .ctr    = stripe_ctr,
    .dtr    = stripe_dtr,
    .map    = stripe_map,
    .end_io = stripe_end_io,
    .status = stripe_status,
    .iterate_devices = stripe_iterate_devices,
    .io_hints = stripe_io_hints,
    .merge  = stripe_merge,
};

int __init dm_stripe_init(void)
{
    int r;

    r = dm_register_target(&stripe_target);
    if (r < 0) {
        DMWARN("target registration failed");
        return r;
    }

    return r;
}

void dm_stripe_exit(void)
{
    dm_unregister_target(&stripe_target);
}