multipath.c

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/*
 * multipath.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
 *
 * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *
 * MULTIPATH management functions.
 *
 * derived from raid1.c.
 *
 * 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.
 */

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/raid/md_u.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include "md.h"
#include "multipath.h"

#define MAX_WORK_PER_DISK 128

#define NR_RESERVED_BUFS    32


static int multipath_map (struct mpconf *conf)
{
    int i, disks = conf->raid_disks;

    /*
     * Later we do read balancing on the read side 
     * now we use the first available disk.
     */

    rcu_read_lock();
    for (i = 0; i < disks; i++) {
        struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
        if (rdev && test_bit(In_sync, &rdev->flags)) {
            atomic_inc(&rdev->nr_pending);
            rcu_read_unlock();
            return i;
        }
    }
    rcu_read_unlock();

    printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
    return (-1);
}

static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
{
    unsigned long flags;
    struct mddev *mddev = mp_bh->mddev;
    struct mpconf *conf = mddev->private;

    spin_lock_irqsave(&conf->device_lock, flags);
    list_add(&mp_bh->retry_list, &conf->retry_list);
    spin_unlock_irqrestore(&conf->device_lock, flags);
    md_wakeup_thread(mddev->thread);
}


/*
 * multipath_end_bh_io() is called when we have finished servicing a multipathed
 * operation and are ready to return a success/failure code to the buffer
 * cache layer.
 */
static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
{
    struct bio *bio = mp_bh->master_bio;
    struct mpconf *conf = mp_bh->mddev->private;

    bio_endio(bio, err);
    mempool_free(mp_bh, conf->pool);
}

static void multipath_end_request(struct bio *bio, int error)
{
    int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
    struct multipath_bh *mp_bh = bio->bi_private;
    struct mpconf *conf = mp_bh->mddev->private;
    struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;

    if (uptodate)
        multipath_end_bh_io(mp_bh, 0);
    else if (!(bio->bi_rw & REQ_RAHEAD)) {
        /*
         * oops, IO error:
         */
        char b[BDEVNAME_SIZE];
        md_error (mp_bh->mddev, rdev);
        printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n", 
               bdevname(rdev->bdev,b), 
               (unsigned long long)bio->bi_sector);
        multipath_reschedule_retry(mp_bh);
    } else
        multipath_end_bh_io(mp_bh, error);
    rdev_dec_pending(rdev, conf->mddev);
}

static void multipath_make_request(struct mddev *mddev, struct bio * bio)
{
    struct mpconf *conf = mddev->private;
    struct multipath_bh * mp_bh;
    struct multipath_info *multipath;

    if (unlikely(bio->bi_rw & REQ_FLUSH)) {
        md_flush_request(mddev, bio);
        return;
    }

    mp_bh = mempool_alloc(conf->pool, GFP_NOIO);

    mp_bh->master_bio = bio;
    mp_bh->mddev = mddev;

    mp_bh->path = multipath_map(conf);
    if (mp_bh->path < 0) {
        bio_endio(bio, -EIO);
        mempool_free(mp_bh, conf->pool);
        return;
    }
    multipath = conf->multipaths + mp_bh->path;

    mp_bh->bio = *bio;
    mp_bh->bio.bi_sector += multipath->rdev->data_offset;
    mp_bh->bio.bi_bdev = multipath->rdev->bdev;
    mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
    mp_bh->bio.bi_end_io = multipath_end_request;
    mp_bh->bio.bi_private = mp_bh;
    generic_make_request(&mp_bh->bio);
    return;
}

static void multipath_status (struct seq_file *seq, struct mddev *mddev)
{
    struct mpconf *conf = mddev->private;
    int i;
    
    seq_printf (seq, " [%d/%d] [", conf->raid_disks,
            conf->raid_disks - mddev->degraded);
    for (i = 0; i < conf->raid_disks; i++)
        seq_printf (seq, "%s",
                   conf->multipaths[i].rdev && 
                   test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
    seq_printf (seq, "]");
}

static int multipath_congested(void *data, int bits)
{
    struct mddev *mddev = data;
    struct mpconf *conf = mddev->private;
    int i, ret = 0;

    if (mddev_congested(mddev, bits))
        return 1;

    rcu_read_lock();
    for (i = 0; i < mddev->raid_disks ; i++) {
        struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
        if (rdev && !test_bit(Faulty, &rdev->flags)) {
            struct request_queue *q = bdev_get_queue(rdev->bdev);

            ret |= bdi_congested(&q->backing_dev_info, bits);
            /* Just like multipath_map, we just check the
             * first available device
             */
            break;
        }
    }
    rcu_read_unlock();
    return ret;
}

/*
 * Careful, this can execute in IRQ contexts as well!
 */
static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
{
    struct mpconf *conf = mddev->private;
    char b[BDEVNAME_SIZE];

    if (conf->raid_disks - mddev->degraded <= 1) {
        /*
         * Uh oh, we can do nothing if this is our last path, but
         * first check if this is a queued request for a device
         * which has just failed.
         */
        printk(KERN_ALERT 
               "multipath: only one IO path left and IO error.\n");
        /* leave it active... it's all we have */
        return;
    }
    /*
     * Mark disk as unusable
     */
    if (test_and_clear_bit(In_sync, &rdev->flags)) {
        unsigned long flags;
        spin_lock_irqsave(&conf->device_lock, flags);
        mddev->degraded++;
        spin_unlock_irqrestore(&conf->device_lock, flags);
    }
    set_bit(Faulty, &rdev->flags);
    set_bit(MD_CHANGE_DEVS, &mddev->flags);
    printk(KERN_ALERT "multipath: IO failure on %s,"
           " disabling IO path.\n"
           "multipath: Operation continuing"
           " on %d IO paths.\n",
           bdevname(rdev->bdev, b),
           conf->raid_disks - mddev->degraded);
}

static void print_multipath_conf (struct mpconf *conf)
{
    int i;
    struct multipath_info *tmp;

    printk("MULTIPATH conf printout:\n");
    if (!conf) {
        printk("(conf==NULL)\n");
        return;
    }
    printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
             conf->raid_disks);

    for (i = 0; i < conf->raid_disks; i++) {
        char b[BDEVNAME_SIZE];
        tmp = conf->multipaths + i;
        if (tmp->rdev)
            printk(" disk%d, o:%d, dev:%s\n",
                i,!test_bit(Faulty, &tmp->rdev->flags),
                   bdevname(tmp->rdev->bdev,b));
    }
}


static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
{
    struct mpconf *conf = mddev->private;
    struct request_queue *q;
    int err = -EEXIST;
    int path;
    struct multipath_info *p;
    int first = 0;
    int last = mddev->raid_disks - 1;

    if (rdev->raid_disk >= 0)
        first = last = rdev->raid_disk;

    print_multipath_conf(conf);

    for (path = first; path <= last; path++)
        if ((p=conf->multipaths+path)->rdev == NULL) {
            q = rdev->bdev->bd_disk->queue;
            disk_stack_limits(mddev->gendisk, rdev->bdev,
                      rdev->data_offset << 9);

        /* as we don't honour merge_bvec_fn, we must never risk
         * violating it, so limit ->max_segments to one, lying
         * within a single page.
         * (Note: it is very unlikely that a device with
         * merge_bvec_fn will be involved in multipath.)
         */
            if (q->merge_bvec_fn) {
                blk_queue_max_segments(mddev->queue, 1);
                blk_queue_segment_boundary(mddev->queue,
                               PAGE_CACHE_SIZE - 1);
            }

            spin_lock_irq(&conf->device_lock);
            mddev->degraded--;
            rdev->raid_disk = path;
            set_bit(In_sync, &rdev->flags);
            spin_unlock_irq(&conf->device_lock);
            rcu_assign_pointer(p->rdev, rdev);
            err = 0;
            md_integrity_add_rdev(rdev, mddev);
            break;
        }

    print_multipath_conf(conf);

    return err;
}

static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
{
    struct mpconf *conf = mddev->private;
    int err = 0;
    int number = rdev->raid_disk;
    struct multipath_info *p = conf->multipaths + number;

    print_multipath_conf(conf);

    if (rdev == p->rdev) {
        if (test_bit(In_sync, &rdev->flags) ||
            atomic_read(&rdev->nr_pending)) {
            printk(KERN_ERR "hot-remove-disk, slot %d is identified"
                   " but is still operational!\n", number);
            err = -EBUSY;
            goto abort;
        }
        p->rdev = NULL;
        synchronize_rcu();
        if (atomic_read(&rdev->nr_pending)) {
            /* lost the race, try later */
            err = -EBUSY;
            p->rdev = rdev;
            goto abort;
        }
        err = md_integrity_register(mddev);
    }
abort:

    print_multipath_conf(conf);
    return err;
}



/*
 * This is a kernel thread which:
 *
 *  1.  Retries failed read operations on working multipaths.
 *  2.  Updates the raid superblock when problems encounter.
 *  3.  Performs writes following reads for array syncronising.
 */

static void multipathd(struct md_thread *thread)
{
    struct mddev *mddev = thread->mddev;
    struct multipath_bh *mp_bh;
    struct bio *bio;
    unsigned long flags;
    struct mpconf *conf = mddev->private;
    struct list_head *head = &conf->retry_list;

    md_check_recovery(mddev);
    for (;;) {
        char b[BDEVNAME_SIZE];
        spin_lock_irqsave(&conf->device_lock, flags);
        if (list_empty(head))
            break;
        mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
        list_del(head->prev);
        spin_unlock_irqrestore(&conf->device_lock, flags);

        bio = &mp_bh->bio;
        bio->bi_sector = mp_bh->master_bio->bi_sector;
        
        if ((mp_bh->path = multipath_map (conf))<0) {
            printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
                " error for block %llu\n",
                bdevname(bio->bi_bdev,b),
                (unsigned long long)bio->bi_sector);
            multipath_end_bh_io(mp_bh, -EIO);
        } else {
            printk(KERN_ERR "multipath: %s: redirecting sector %llu"
                " to another IO path\n",
                bdevname(bio->bi_bdev,b),
                (unsigned long long)bio->bi_sector);
            *bio = *(mp_bh->master_bio);
            bio->bi_sector += conf->multipaths[mp_bh->path].rdev->data_offset;
            bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
            bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
            bio->bi_end_io = multipath_end_request;
            bio->bi_private = mp_bh;
            generic_make_request(bio);
        }
    }
    spin_unlock_irqrestore(&conf->device_lock, flags);
}

static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
{
    WARN_ONCE(sectors || raid_disks,
          "%s does not support generic reshape\n", __func__);

    return mddev->dev_sectors;
}

static int multipath_run (struct mddev *mddev)
{
    struct mpconf *conf;
    int disk_idx;
    struct multipath_info *disk;
    struct md_rdev *rdev;
    int working_disks;

    if (md_check_no_bitmap(mddev))
        return -EINVAL;

    if (mddev->level != LEVEL_MULTIPATH) {
        printk("multipath: %s: raid level not set to multipath IO (%d)\n",
               mdname(mddev), mddev->level);
        goto out;
    }
    /*
     * copy the already verified devices into our private MULTIPATH
     * bookkeeping area. [whatever we allocate in multipath_run(),
     * should be freed in multipath_stop()]
     */

    conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
    mddev->private = conf;
    if (!conf) {
        printk(KERN_ERR 
            "multipath: couldn't allocate memory for %s\n",
            mdname(mddev));
        goto out;
    }

    conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
                   GFP_KERNEL);
    if (!conf->multipaths) {
        printk(KERN_ERR 
            "multipath: couldn't allocate memory for %s\n",
            mdname(mddev));
        goto out_free_conf;
    }

    working_disks = 0;
    rdev_for_each(rdev, mddev) {
        disk_idx = rdev->raid_disk;
        if (disk_idx < 0 ||
            disk_idx >= mddev->raid_disks)
            continue;

        disk = conf->multipaths + disk_idx;
        disk->rdev = rdev;
        disk_stack_limits(mddev->gendisk, rdev->bdev,
                  rdev->data_offset << 9);

        /* as we don't honour merge_bvec_fn, we must never risk
         * violating it, not that we ever expect a device with
         * a merge_bvec_fn to be involved in multipath */
        if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
            blk_queue_max_segments(mddev->queue, 1);
            blk_queue_segment_boundary(mddev->queue,
                           PAGE_CACHE_SIZE - 1);
        }

        if (!test_bit(Faulty, &rdev->flags))
            working_disks++;
    }

    conf->raid_disks = mddev->raid_disks;
    conf->mddev = mddev;
    spin_lock_init(&conf->device_lock);
    INIT_LIST_HEAD(&conf->retry_list);

    if (!working_disks) {
        printk(KERN_ERR "multipath: no operational IO paths for %s\n",
            mdname(mddev));
        goto out_free_conf;
    }
    mddev->degraded = conf->raid_disks - working_disks;

    conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
                         sizeof(struct multipath_bh));
    if (conf->pool == NULL) {
        printk(KERN_ERR 
            "multipath: couldn't allocate memory for %s\n",
            mdname(mddev));
        goto out_free_conf;
    }

    {
        mddev->thread = md_register_thread(multipathd, mddev,
                           "multipath");
        if (!mddev->thread) {
            printk(KERN_ERR "multipath: couldn't allocate thread"
                " for %s\n", mdname(mddev));
            goto out_free_conf;
        }
    }

    printk(KERN_INFO 
        "multipath: array %s active with %d out of %d IO paths\n",
        mdname(mddev), conf->raid_disks - mddev->degraded,
           mddev->raid_disks);
    /*
     * Ok, everything is just fine now
     */
    md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));

    mddev->queue->backing_dev_info.congested_fn = multipath_congested;
    mddev->queue->backing_dev_info.congested_data = mddev;

    if (md_integrity_register(mddev))
        goto out_free_conf;

    return 0;

out_free_conf:
    if (conf->pool)
        mempool_destroy(conf->pool);
    kfree(conf->multipaths);
    kfree(conf);
    mddev->private = NULL;
out:
    return -EIO;
}


static int multipath_stop (struct mddev *mddev)
{
    struct mpconf *conf = mddev->private;

    md_unregister_thread(&mddev->thread);
    blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
    mempool_destroy(conf->pool);
    kfree(conf->multipaths);
    kfree(conf);
    mddev->private = NULL;
    return 0;
}

static struct md_personality multipath_personality =
{
    .name       = "multipath",
    .level      = LEVEL_MULTIPATH,
    .owner      = THIS_MODULE,
    .make_request   = multipath_make_request,
    .run        = multipath_run,
    .stop       = multipath_stop,
    .status     = multipath_status,
    .error_handler  = multipath_error,
    .hot_add_disk   = multipath_add_disk,
    .hot_remove_disk= multipath_remove_disk,
    .size       = multipath_size,
};

static int __init multipath_init (void)
{
    return register_md_personality (&multipath_personality);
}

static void __exit multipath_exit (void)
{
    unregister_md_personality (&multipath_personality);
}

module_init(multipath_init);
module_exit(multipath_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("simple multi-path personality for MD");
MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
MODULE_ALIAS("md-multipath");
MODULE_ALIAS("md-level--4");