/*
 * 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_iter.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_iter.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_iter.bi_sector = mp_bh->master_bio->bi_iter.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_iter.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_iter.bi_sector);
                        *bio = *(mp_bh->master_bio);
                        bio->bi_iter.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");