linux/drivers/md/multipath.c
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   1/*
   2 * multipath.c : Multiple Devices driver for Linux
   3 *
   4 * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
   5 *
   6 * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
   7 *
   8 * MULTIPATH management functions.
   9 *
  10 * derived from raid1.c.
  11 *
  12 * This program is free software; you can redistribute it and/or modify
  13 * it under the terms of the GNU General Public License as published by
  14 * the Free Software Foundation; either version 2, or (at your option)
  15 * any later version.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * (for example /usr/src/linux/COPYING); if not, write to the Free
  19 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22#include <linux/blkdev.h>
  23#include <linux/module.h>
  24#include <linux/raid/md_u.h>
  25#include <linux/seq_file.h>
  26#include <linux/slab.h>
  27#include "md.h"
  28#include "multipath.h"
  29
  30#define MAX_WORK_PER_DISK 128
  31
  32#define NR_RESERVED_BUFS        32
  33
  34
  35static int multipath_map (struct mpconf *conf)
  36{
  37        int i, disks = conf->raid_disks;
  38
  39        /*
  40         * Later we do read balancing on the read side 
  41         * now we use the first available disk.
  42         */
  43
  44        rcu_read_lock();
  45        for (i = 0; i < disks; i++) {
  46                struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
  47                if (rdev && test_bit(In_sync, &rdev->flags)) {
  48                        atomic_inc(&rdev->nr_pending);
  49                        rcu_read_unlock();
  50                        return i;
  51                }
  52        }
  53        rcu_read_unlock();
  54
  55        printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
  56        return (-1);
  57}
  58
  59static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
  60{
  61        unsigned long flags;
  62        struct mddev *mddev = mp_bh->mddev;
  63        struct mpconf *conf = mddev->private;
  64
  65        spin_lock_irqsave(&conf->device_lock, flags);
  66        list_add(&mp_bh->retry_list, &conf->retry_list);
  67        spin_unlock_irqrestore(&conf->device_lock, flags);
  68        md_wakeup_thread(mddev->thread);
  69}
  70
  71
  72/*
  73 * multipath_end_bh_io() is called when we have finished servicing a multipathed
  74 * operation and are ready to return a success/failure code to the buffer
  75 * cache layer.
  76 */
  77static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
  78{
  79        struct bio *bio = mp_bh->master_bio;
  80        struct mpconf *conf = mp_bh->mddev->private;
  81
  82        bio_endio(bio, err);
  83        mempool_free(mp_bh, conf->pool);
  84}
  85
  86static void multipath_end_request(struct bio *bio, int error)
  87{
  88        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  89        struct multipath_bh *mp_bh = bio->bi_private;
  90        struct mpconf *conf = mp_bh->mddev->private;
  91        struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;
  92
  93        if (uptodate)
  94                multipath_end_bh_io(mp_bh, 0);
  95        else if (!(bio->bi_rw & REQ_RAHEAD)) {
  96                /*
  97                 * oops, IO error:
  98                 */
  99                char b[BDEVNAME_SIZE];
 100                md_error (mp_bh->mddev, rdev);
 101                printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n", 
 102                       bdevname(rdev->bdev,b), 
 103                       (unsigned long long)bio->bi_sector);
 104                multipath_reschedule_retry(mp_bh);
 105        } else
 106                multipath_end_bh_io(mp_bh, error);
 107        rdev_dec_pending(rdev, conf->mddev);
 108}
 109
 110static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 111{
 112        struct mpconf *conf = mddev->private;
 113        struct multipath_bh * mp_bh;
 114        struct multipath_info *multipath;
 115
 116        if (unlikely(bio->bi_rw & REQ_FLUSH)) {
 117                md_flush_request(mddev, bio);
 118                return;
 119        }
 120
 121        mp_bh = mempool_alloc(conf->pool, GFP_NOIO);
 122
 123        mp_bh->master_bio = bio;
 124        mp_bh->mddev = mddev;
 125
 126        mp_bh->path = multipath_map(conf);
 127        if (mp_bh->path < 0) {
 128                bio_endio(bio, -EIO);
 129                mempool_free(mp_bh, conf->pool);
 130                return;
 131        }
 132        multipath = conf->multipaths + mp_bh->path;
 133
 134        mp_bh->bio = *bio;
 135        mp_bh->bio.bi_sector += multipath->rdev->data_offset;
 136        mp_bh->bio.bi_bdev = multipath->rdev->bdev;
 137        mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
 138        mp_bh->bio.bi_end_io = multipath_end_request;
 139        mp_bh->bio.bi_private = mp_bh;
 140        generic_make_request(&mp_bh->bio);
 141        return;
 142}
 143
 144static void multipath_status (struct seq_file *seq, struct mddev *mddev)
 145{
 146        struct mpconf *conf = mddev->private;
 147        int i;
 148        
 149        seq_printf (seq, " [%d/%d] [", conf->raid_disks,
 150                    conf->raid_disks - mddev->degraded);
 151        for (i = 0; i < conf->raid_disks; i++)
 152                seq_printf (seq, "%s",
 153                               conf->multipaths[i].rdev && 
 154                               test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
 155        seq_printf (seq, "]");
 156}
 157
 158static int multipath_congested(void *data, int bits)
 159{
 160        struct mddev *mddev = data;
 161        struct mpconf *conf = mddev->private;
 162        int i, ret = 0;
 163
 164        if (mddev_congested(mddev, bits))
 165                return 1;
 166
 167        rcu_read_lock();
 168        for (i = 0; i < mddev->raid_disks ; i++) {
 169                struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
 170                if (rdev && !test_bit(Faulty, &rdev->flags)) {
 171                        struct request_queue *q = bdev_get_queue(rdev->bdev);
 172
 173                        ret |= bdi_congested(&q->backing_dev_info, bits);
 174                        /* Just like multipath_map, we just check the
 175                         * first available device
 176                         */
 177                        break;
 178                }
 179        }
 180        rcu_read_unlock();
 181        return ret;
 182}
 183
 184/*
 185 * Careful, this can execute in IRQ contexts as well!
 186 */
 187static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
 188{
 189        struct mpconf *conf = mddev->private;
 190        char b[BDEVNAME_SIZE];
 191
 192        if (conf->raid_disks - mddev->degraded <= 1) {
 193                /*
 194                 * Uh oh, we can do nothing if this is our last path, but
 195                 * first check if this is a queued request for a device
 196                 * which has just failed.
 197                 */
 198                printk(KERN_ALERT 
 199                       "multipath: only one IO path left and IO error.\n");
 200                /* leave it active... it's all we have */
 201                return;
 202        }
 203        /*
 204         * Mark disk as unusable
 205         */
 206        if (test_and_clear_bit(In_sync, &rdev->flags)) {
 207                unsigned long flags;
 208                spin_lock_irqsave(&conf->device_lock, flags);
 209                mddev->degraded++;
 210                spin_unlock_irqrestore(&conf->device_lock, flags);
 211        }
 212        set_bit(Faulty, &rdev->flags);
 213        set_bit(MD_CHANGE_DEVS, &mddev->flags);
 214        printk(KERN_ALERT "multipath: IO failure on %s,"
 215               " disabling IO path.\n"
 216               "multipath: Operation continuing"
 217               " on %d IO paths.\n",
 218               bdevname(rdev->bdev, b),
 219               conf->raid_disks - mddev->degraded);
 220}
 221
 222static void print_multipath_conf (struct mpconf *conf)
 223{
 224        int i;
 225        struct multipath_info *tmp;
 226
 227        printk("MULTIPATH conf printout:\n");
 228        if (!conf) {
 229                printk("(conf==NULL)\n");
 230                return;
 231        }
 232        printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
 233                         conf->raid_disks);
 234
 235        for (i = 0; i < conf->raid_disks; i++) {
 236                char b[BDEVNAME_SIZE];
 237                tmp = conf->multipaths + i;
 238                if (tmp->rdev)
 239                        printk(" disk%d, o:%d, dev:%s\n",
 240                                i,!test_bit(Faulty, &tmp->rdev->flags),
 241                               bdevname(tmp->rdev->bdev,b));
 242        }
 243}
 244
 245
 246static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 247{
 248        struct mpconf *conf = mddev->private;
 249        struct request_queue *q;
 250        int err = -EEXIST;
 251        int path;
 252        struct multipath_info *p;
 253        int first = 0;
 254        int last = mddev->raid_disks - 1;
 255
 256        if (rdev->raid_disk >= 0)
 257                first = last = rdev->raid_disk;
 258
 259        print_multipath_conf(conf);
 260
 261        for (path = first; path <= last; path++)
 262                if ((p=conf->multipaths+path)->rdev == NULL) {
 263                        q = rdev->bdev->bd_disk->queue;
 264                        disk_stack_limits(mddev->gendisk, rdev->bdev,
 265                                          rdev->data_offset << 9);
 266
 267                /* as we don't honour merge_bvec_fn, we must never risk
 268                 * violating it, so limit ->max_segments to one, lying
 269                 * within a single page.
 270                 * (Note: it is very unlikely that a device with
 271                 * merge_bvec_fn will be involved in multipath.)
 272                 */
 273                        if (q->merge_bvec_fn) {
 274                                blk_queue_max_segments(mddev->queue, 1);
 275                                blk_queue_segment_boundary(mddev->queue,
 276                                                           PAGE_CACHE_SIZE - 1);
 277                        }
 278
 279                        spin_lock_irq(&conf->device_lock);
 280                        mddev->degraded--;
 281                        rdev->raid_disk = path;
 282                        set_bit(In_sync, &rdev->flags);
 283                        spin_unlock_irq(&conf->device_lock);
 284                        rcu_assign_pointer(p->rdev, rdev);
 285                        err = 0;
 286                        md_integrity_add_rdev(rdev, mddev);
 287                        break;
 288                }
 289
 290        print_multipath_conf(conf);
 291
 292        return err;
 293}
 294
 295static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 296{
 297        struct mpconf *conf = mddev->private;
 298        int err = 0;
 299        int number = rdev->raid_disk;
 300        struct multipath_info *p = conf->multipaths + number;
 301
 302        print_multipath_conf(conf);
 303
 304        if (rdev == p->rdev) {
 305                if (test_bit(In_sync, &rdev->flags) ||
 306                    atomic_read(&rdev->nr_pending)) {
 307                        printk(KERN_ERR "hot-remove-disk, slot %d is identified"
 308                               " but is still operational!\n", number);
 309                        err = -EBUSY;
 310                        goto abort;
 311                }
 312                p->rdev = NULL;
 313                synchronize_rcu();
 314                if (atomic_read(&rdev->nr_pending)) {
 315                        /* lost the race, try later */
 316                        err = -EBUSY;
 317                        p->rdev = rdev;
 318                        goto abort;
 319                }
 320                err = md_integrity_register(mddev);
 321        }
 322abort:
 323
 324        print_multipath_conf(conf);
 325        return err;
 326}
 327
 328
 329
 330/*
 331 * This is a kernel thread which:
 332 *
 333 *      1.      Retries failed read operations on working multipaths.
 334 *      2.      Updates the raid superblock when problems encounter.
 335 *      3.      Performs writes following reads for array syncronising.
 336 */
 337
 338static void multipathd (struct mddev *mddev)
 339{
 340        struct multipath_bh *mp_bh;
 341        struct bio *bio;
 342        unsigned long flags;
 343        struct mpconf *conf = mddev->private;
 344        struct list_head *head = &conf->retry_list;
 345
 346        md_check_recovery(mddev);
 347        for (;;) {
 348                char b[BDEVNAME_SIZE];
 349                spin_lock_irqsave(&conf->device_lock, flags);
 350                if (list_empty(head))
 351                        break;
 352                mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
 353                list_del(head->prev);
 354                spin_unlock_irqrestore(&conf->device_lock, flags);
 355
 356                bio = &mp_bh->bio;
 357                bio->bi_sector = mp_bh->master_bio->bi_sector;
 358                
 359                if ((mp_bh->path = multipath_map (conf))<0) {
 360                        printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
 361                                " error for block %llu\n",
 362                                bdevname(bio->bi_bdev,b),
 363                                (unsigned long long)bio->bi_sector);
 364                        multipath_end_bh_io(mp_bh, -EIO);
 365                } else {
 366                        printk(KERN_ERR "multipath: %s: redirecting sector %llu"
 367                                " to another IO path\n",
 368                                bdevname(bio->bi_bdev,b),
 369                                (unsigned long long)bio->bi_sector);
 370                        *bio = *(mp_bh->master_bio);
 371                        bio->bi_sector += conf->multipaths[mp_bh->path].rdev->data_offset;
 372                        bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
 373                        bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
 374                        bio->bi_end_io = multipath_end_request;
 375                        bio->bi_private = mp_bh;
 376                        generic_make_request(bio);
 377                }
 378        }
 379        spin_unlock_irqrestore(&conf->device_lock, flags);
 380}
 381
 382static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 383{
 384        WARN_ONCE(sectors || raid_disks,
 385                  "%s does not support generic reshape\n", __func__);
 386
 387        return mddev->dev_sectors;
 388}
 389
 390static int multipath_run (struct mddev *mddev)
 391{
 392        struct mpconf *conf;
 393        int disk_idx;
 394        struct multipath_info *disk;
 395        struct md_rdev *rdev;
 396        int working_disks;
 397
 398        if (md_check_no_bitmap(mddev))
 399                return -EINVAL;
 400
 401        if (mddev->level != LEVEL_MULTIPATH) {
 402                printk("multipath: %s: raid level not set to multipath IO (%d)\n",
 403                       mdname(mddev), mddev->level);
 404                goto out;
 405        }
 406        /*
 407         * copy the already verified devices into our private MULTIPATH
 408         * bookkeeping area. [whatever we allocate in multipath_run(),
 409         * should be freed in multipath_stop()]
 410         */
 411
 412        conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
 413        mddev->private = conf;
 414        if (!conf) {
 415                printk(KERN_ERR 
 416                        "multipath: couldn't allocate memory for %s\n",
 417                        mdname(mddev));
 418                goto out;
 419        }
 420
 421        conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
 422                                   GFP_KERNEL);
 423        if (!conf->multipaths) {
 424                printk(KERN_ERR 
 425                        "multipath: couldn't allocate memory for %s\n",
 426                        mdname(mddev));
 427                goto out_free_conf;
 428        }
 429
 430        working_disks = 0;
 431        rdev_for_each(rdev, mddev) {
 432                disk_idx = rdev->raid_disk;
 433                if (disk_idx < 0 ||
 434                    disk_idx >= mddev->raid_disks)
 435                        continue;
 436
 437                disk = conf->multipaths + disk_idx;
 438                disk->rdev = rdev;
 439                disk_stack_limits(mddev->gendisk, rdev->bdev,
 440                                  rdev->data_offset << 9);
 441
 442                /* as we don't honour merge_bvec_fn, we must never risk
 443                 * violating it, not that we ever expect a device with
 444                 * a merge_bvec_fn to be involved in multipath */
 445                if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
 446                        blk_queue_max_segments(mddev->queue, 1);
 447                        blk_queue_segment_boundary(mddev->queue,
 448                                                   PAGE_CACHE_SIZE - 1);
 449                }
 450
 451                if (!test_bit(Faulty, &rdev->flags))
 452                        working_disks++;
 453        }
 454
 455        conf->raid_disks = mddev->raid_disks;
 456        conf->mddev = mddev;
 457        spin_lock_init(&conf->device_lock);
 458        INIT_LIST_HEAD(&conf->retry_list);
 459
 460        if (!working_disks) {
 461                printk(KERN_ERR "multipath: no operational IO paths for %s\n",
 462                        mdname(mddev));
 463                goto out_free_conf;
 464        }
 465        mddev->degraded = conf->raid_disks - working_disks;
 466
 467        conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
 468                                                 sizeof(struct multipath_bh));
 469        if (conf->pool == NULL) {
 470                printk(KERN_ERR 
 471                        "multipath: couldn't allocate memory for %s\n",
 472                        mdname(mddev));
 473                goto out_free_conf;
 474        }
 475
 476        {
 477                mddev->thread = md_register_thread(multipathd, mddev,
 478                                                   "multipath");
 479                if (!mddev->thread) {
 480                        printk(KERN_ERR "multipath: couldn't allocate thread"
 481                                " for %s\n", mdname(mddev));
 482                        goto out_free_conf;
 483                }
 484        }
 485
 486        printk(KERN_INFO 
 487                "multipath: array %s active with %d out of %d IO paths\n",
 488                mdname(mddev), conf->raid_disks - mddev->degraded,
 489               mddev->raid_disks);
 490        /*
 491         * Ok, everything is just fine now
 492         */
 493        md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));
 494
 495        mddev->queue->backing_dev_info.congested_fn = multipath_congested;
 496        mddev->queue->backing_dev_info.congested_data = mddev;
 497
 498        if (md_integrity_register(mddev))
 499                goto out_free_conf;
 500
 501        return 0;
 502
 503out_free_conf:
 504        if (conf->pool)
 505                mempool_destroy(conf->pool);
 506        kfree(conf->multipaths);
 507        kfree(conf);
 508        mddev->private = NULL;
 509out:
 510        return -EIO;
 511}
 512
 513
 514static int multipath_stop (struct mddev *mddev)
 515{
 516        struct mpconf *conf = mddev->private;
 517
 518        md_unregister_thread(&mddev->thread);
 519        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
 520        mempool_destroy(conf->pool);
 521        kfree(conf->multipaths);
 522        kfree(conf);
 523        mddev->private = NULL;
 524        return 0;
 525}
 526
 527static struct md_personality multipath_personality =
 528{
 529        .name           = "multipath",
 530        .level          = LEVEL_MULTIPATH,
 531        .owner          = THIS_MODULE,
 532        .make_request   = multipath_make_request,
 533        .run            = multipath_run,
 534        .stop           = multipath_stop,
 535        .status         = multipath_status,
 536        .error_handler  = multipath_error,
 537        .hot_add_disk   = multipath_add_disk,
 538        .hot_remove_disk= multipath_remove_disk,
 539        .size           = multipath_size,
 540};
 541
 542static int __init multipath_init (void)
 543{
 544        return register_md_personality (&multipath_personality);
 545}
 546
 547static void __exit multipath_exit (void)
 548{
 549        unregister_md_personality (&multipath_personality);
 550}
 551
 552module_init(multipath_init);
 553module_exit(multipath_exit);
 554MODULE_LICENSE("GPL");
 555MODULE_DESCRIPTION("simple multi-path personality for MD");
 556MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
 557MODULE_ALIAS("md-multipath");
 558MODULE_ALIAS("md-level--4");
 559
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