dm-delay.c

Go to the documentation of this file.

/*
 * Copyright (C) 2005-2007 Red Hat GmbH
 *
 * A target that delays reads and/or writes and can send
 * them to different devices.
 *
 * This file is released under the GPL.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/slab.h>

#include <linux/device-mapper.h>

#define DM_MSG_PREFIX "delay"

struct delay_c {
    struct timer_list delay_timer;
    struct mutex timer_lock;
    struct work_struct flush_expired_bios;
    struct list_head delayed_bios;
    atomic_t may_delay;
    mempool_t *delayed_pool;

    struct dm_dev *dev_read;
    sector_t start_read;
    unsigned read_delay;
    unsigned reads;

    struct dm_dev *dev_write;
    sector_t start_write;
    unsigned write_delay;
    unsigned writes;
};

struct dm_delay_info {
    struct delay_c *context;
    struct list_head list;
    struct bio *bio;
    unsigned long expires;
};

static DEFINE_MUTEX(delayed_bios_lock);

static struct workqueue_struct *kdelayd_wq;
static struct kmem_cache *delayed_cache;

static void handle_delayed_timer(unsigned long data)
{
    struct delay_c *dc = (struct delay_c *)data;

    queue_work(kdelayd_wq, &dc->flush_expired_bios);
}

static void queue_timeout(struct delay_c *dc, unsigned long expires)
{
    mutex_lock(&dc->timer_lock);

    if (!timer_pending(&dc->delay_timer) || expires < dc->delay_timer.expires)
        mod_timer(&dc->delay_timer, expires);

    mutex_unlock(&dc->timer_lock);
}

static void flush_bios(struct bio *bio)
{
    struct bio *n;

    while (bio) {
        n = bio->bi_next;
        bio->bi_next = NULL;
        generic_make_request(bio);
        bio = n;
    }
}

static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all)
{
    struct dm_delay_info *delayed, *next;
    unsigned long next_expires = 0;
    int start_timer = 0;
    struct bio_list flush_bios = { };

    mutex_lock(&delayed_bios_lock);
    list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) {
        if (flush_all || time_after_eq(jiffies, delayed->expires)) {
            list_del(&delayed->list);
            bio_list_add(&flush_bios, delayed->bio);
            if ((bio_data_dir(delayed->bio) == WRITE))
                delayed->context->writes--;
            else
                delayed->context->reads--;
            mempool_free(delayed, dc->delayed_pool);
            continue;
        }

        if (!start_timer) {
            start_timer = 1;
            next_expires = delayed->expires;
        } else
            next_expires = min(next_expires, delayed->expires);
    }

    mutex_unlock(&delayed_bios_lock);

    if (start_timer)
        queue_timeout(dc, next_expires);

    return bio_list_get(&flush_bios);
}

static void flush_expired_bios(struct work_struct *work)
{
    struct delay_c *dc;

    dc = container_of(work, struct delay_c, flush_expired_bios);
    flush_bios(flush_delayed_bios(dc, 0));
}

/*
 * Mapping parameters:
 *    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
 *
 * With separate write parameters, the first set is only used for reads.
 * Delays are specified in milliseconds.
 */
static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
    struct delay_c *dc;
    unsigned long long tmpll;
    char dummy;

    if (argc != 3 && argc != 6) {
        ti->error = "requires exactly 3 or 6 arguments";
        return -EINVAL;
    }

    dc = kmalloc(sizeof(*dc), GFP_KERNEL);
    if (!dc) {
        ti->error = "Cannot allocate context";
        return -ENOMEM;
    }

    dc->reads = dc->writes = 0;

    if (sscanf(argv[1], "%llu%c", &tmpll, &dummy) != 1) {
        ti->error = "Invalid device sector";
        goto bad;
    }
    dc->start_read = tmpll;

    if (sscanf(argv[2], "%u%c", &dc->read_delay, &dummy) != 1) {
        ti->error = "Invalid delay";
        goto bad;
    }

    if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
              &dc->dev_read)) {
        ti->error = "Device lookup failed";
        goto bad;
    }

    dc->dev_write = NULL;
    if (argc == 3)
        goto out;

    if (sscanf(argv[4], "%llu%c", &tmpll, &dummy) != 1) {
        ti->error = "Invalid write device sector";
        goto bad_dev_read;
    }
    dc->start_write = tmpll;

    if (sscanf(argv[5], "%u%c", &dc->write_delay, &dummy) != 1) {
        ti->error = "Invalid write delay";
        goto bad_dev_read;
    }

    if (dm_get_device(ti, argv[3], dm_table_get_mode(ti->table),
              &dc->dev_write)) {
        ti->error = "Write device lookup failed";
        goto bad_dev_read;
    }

out:
    dc->delayed_pool = mempool_create_slab_pool(128, delayed_cache);
    if (!dc->delayed_pool) {
        DMERR("Couldn't create delayed bio pool.");
        goto bad_dev_write;
    }

    setup_timer(&dc->delay_timer, handle_delayed_timer, (unsigned long)dc);

    INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
    INIT_LIST_HEAD(&dc->delayed_bios);
    mutex_init(&dc->timer_lock);
    atomic_set(&dc->may_delay, 1);

    ti->num_flush_requests = 1;
    ti->num_discard_requests = 1;
    ti->private = dc;
    return 0;

bad_dev_write:
    if (dc->dev_write)
        dm_put_device(ti, dc->dev_write);
bad_dev_read:
    dm_put_device(ti, dc->dev_read);
bad:
    kfree(dc);
    return -EINVAL;
}

static void delay_dtr(struct dm_target *ti)
{
    struct delay_c *dc = ti->private;

    flush_workqueue(kdelayd_wq);

    dm_put_device(ti, dc->dev_read);

    if (dc->dev_write)
        dm_put_device(ti, dc->dev_write);

    mempool_destroy(dc->delayed_pool);
    kfree(dc);
}

static int delay_bio(struct delay_c *dc, int delay, struct bio *bio)
{
    struct dm_delay_info *delayed;
    unsigned long expires = 0;

    if (!delay || !atomic_read(&dc->may_delay))
        return 1;

    delayed = mempool_alloc(dc->delayed_pool, GFP_NOIO);

    delayed->context = dc;
    delayed->bio = bio;
    delayed->expires = expires = jiffies + (delay * HZ / 1000);

    mutex_lock(&delayed_bios_lock);

    if (bio_data_dir(bio) == WRITE)
        dc->writes++;
    else
        dc->reads++;

    list_add_tail(&delayed->list, &dc->delayed_bios);

    mutex_unlock(&delayed_bios_lock);

    queue_timeout(dc, expires);

    return 0;
}

static void delay_presuspend(struct dm_target *ti)
{
    struct delay_c *dc = ti->private;

    atomic_set(&dc->may_delay, 0);
    del_timer_sync(&dc->delay_timer);
    flush_bios(flush_delayed_bios(dc, 1));
}

static void delay_resume(struct dm_target *ti)
{
    struct delay_c *dc = ti->private;

    atomic_set(&dc->may_delay, 1);
}

static int delay_map(struct dm_target *ti, struct bio *bio,
             union map_info *map_context)
{
    struct delay_c *dc = ti->private;

    if ((bio_data_dir(bio) == WRITE) && (dc->dev_write)) {
        bio->bi_bdev = dc->dev_write->bdev;
        if (bio_sectors(bio))
            bio->bi_sector = dc->start_write +
                     dm_target_offset(ti, bio->bi_sector);

        return delay_bio(dc, dc->write_delay, bio);
    }

    bio->bi_bdev = dc->dev_read->bdev;
    bio->bi_sector = dc->start_read + dm_target_offset(ti, bio->bi_sector);

    return delay_bio(dc, dc->read_delay, bio);
}

static int delay_status(struct dm_target *ti, status_type_t type,
            unsigned status_flags, char *result, unsigned maxlen)
{
    struct delay_c *dc = ti->private;
    int sz = 0;

    switch (type) {
    case STATUSTYPE_INFO:
        DMEMIT("%u %u", dc->reads, dc->writes);
        break;

    case STATUSTYPE_TABLE:
        DMEMIT("%s %llu %u", dc->dev_read->name,
               (unsigned long long) dc->start_read,
               dc->read_delay);
        if (dc->dev_write)
            DMEMIT(" %s %llu %u", dc->dev_write->name,
                   (unsigned long long) dc->start_write,
                   dc->write_delay);
        break;
    }

    return 0;
}

static int delay_iterate_devices(struct dm_target *ti,
                 iterate_devices_callout_fn fn, void *data)
{
    struct delay_c *dc = ti->private;
    int ret = 0;

    ret = fn(ti, dc->dev_read, dc->start_read, ti->len, data);
    if (ret)
        goto out;

    if (dc->dev_write)
        ret = fn(ti, dc->dev_write, dc->start_write, ti->len, data);

out:
    return ret;
}

static struct target_type delay_target = {
    .name        = "delay",
    .version     = {1, 1, 0},
    .module      = THIS_MODULE,
    .ctr         = delay_ctr,
    .dtr         = delay_dtr,
    .map         = delay_map,
    .presuspend  = delay_presuspend,
    .resume      = delay_resume,
    .status      = delay_status,
    .iterate_devices = delay_iterate_devices,
};

static int __init dm_delay_init(void)
{
    int r = -ENOMEM;

    kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0);
    if (!kdelayd_wq) {
        DMERR("Couldn't start kdelayd");
        goto bad_queue;
    }

    delayed_cache = KMEM_CACHE(dm_delay_info, 0);
    if (!delayed_cache) {
        DMERR("Couldn't create delayed bio cache.");
        goto bad_memcache;
    }

    r = dm_register_target(&delay_target);
    if (r < 0) {
        DMERR("register failed %d", r);
        goto bad_register;
    }

    return 0;

bad_register:
    kmem_cache_destroy(delayed_cache);
bad_memcache:
    destroy_workqueue(kdelayd_wq);
bad_queue:
    return r;
}

static void __exit dm_delay_exit(void)
{
    dm_unregister_target(&delay_target);
    kmem_cache_destroy(delayed_cache);
    destroy_workqueue(kdelayd_wq);
}

/* Module hooks */
module_init(dm_delay_init);
module_exit(dm_delay_exit);

MODULE_DESCRIPTION(DM_NAME " delay target");
MODULE_AUTHOR("Heinz Mauelshagen <[email protected]>");
MODULE_LICENSE("GPL");