block/blk-barrier.c

   1 /*
   2  * Functions related to barrier IO handling
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/bio.h>
   7 #include <linux/blkdev.h>
   8
   9 #include "blk.h"
  10
  11 /**
  12  * blk_queue_ordered - does this queue support ordered writes
  13  * @q:        the request queue
  14  * @ordered:  one of QUEUE_ORDERED_*
  15  * @prepare_flush_fn: rq setup helper for cache flush ordered writes
  16  *
  17  * Description:
  18  *   For journalled file systems, doing ordered writes on a commit
  19  *   block instead of explicitly doing wait_on_buffer (which is bad
  20  *   for performance) can be a big win. Block drivers supporting this
  21  *   feature should call this function and indicate so.
  22  *
  23  **/
  24 int blk_queue_ordered(struct request_queue *q, unsigned ordered,
  25                       prepare_flush_fn *prepare_flush_fn)
  26 {
  27         if (!prepare_flush_fn && (ordered & (QUEUE_ORDERED_DO_PREFLUSH |
  28                                              QUEUE_ORDERED_DO_POSTFLUSH))) {
  29                 printk(KERN_ERR "%s: prepare_flush_fn required\n", __func__);
  30                 return -EINVAL;
  31         }
  32
  33         if (ordered != QUEUE_ORDERED_NONE &&
  34             ordered != QUEUE_ORDERED_DRAIN &&
  35             ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
  36             ordered != QUEUE_ORDERED_DRAIN_FUA &&
  37             ordered != QUEUE_ORDERED_TAG &&
  38             ordered != QUEUE_ORDERED_TAG_FLUSH &&
  39             ordered != QUEUE_ORDERED_TAG_FUA) {
  40                 printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
  41                 return -EINVAL;
  42         }
  43
  44         q->ordered = ordered;
  45         q->next_ordered = ordered;
  46         q->prepare_flush_fn = prepare_flush_fn;
  47
  48         return 0;
  49 }
  50 EXPORT_SYMBOL(blk_queue_ordered);
  51
  52 /*
  53  * Cache flushing for ordered writes handling
  54  */
  55 unsigned blk_ordered_cur_seq(struct request_queue *q)
  56 {
  57         if (!q->ordseq)
  58                 return 0;
  59         return 1 << ffz(q->ordseq);
  60 }
  61
  62 unsigned blk_ordered_req_seq(struct request *rq)
  63 {
  64         struct request_queue *q = rq->q;
  65
  66         BUG_ON(q->ordseq == 0);
  67
  68         if (rq == &q->pre_flush_rq)
  69                 return QUEUE_ORDSEQ_PREFLUSH;
  70         if (rq == &q->bar_rq)
  71                 return QUEUE_ORDSEQ_BAR;
  72         if (rq == &q->post_flush_rq)
  73                 return QUEUE_ORDSEQ_POSTFLUSH;
  74
  75         /*
  76          * !fs requests don't need to follow barrier ordering.  Always
  77          * put them at the front.  This fixes the following deadlock.
  78          *
  79          * http://thread.gmane.org/gmane.linux.kernel/537473
  80          */
  81         if (!blk_fs_request(rq))
  82                 return QUEUE_ORDSEQ_DRAIN;
  83
  84         if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
  85             (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
  86                 return QUEUE_ORDSEQ_DRAIN;
  87         else
  88                 return QUEUE_ORDSEQ_DONE;
  89 }
  90
  91 bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
  92 {
  93         struct request *rq;
  94
  95         if (error && !q->orderr)
  96                 q->orderr = error;
  97
  98         BUG_ON(q->ordseq & seq);
  99         q->ordseq |= seq;
 100
 101         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
 102                 return false;
 103
 104         /*
 105          * Okay, sequence complete.
 106          */
 107         q->ordseq = 0;
 108         rq = q->orig_bar_rq;
 109
 110         if (__blk_end_request(rq, q->orderr, blk_rq_bytes(rq)))
 111                 BUG();
 112
 113         return true;
 114 }
 115
 116 static void pre_flush_end_io(struct request *rq, int error)
 117 {
 118         elv_completed_request(rq->q, rq);
 119         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
 120 }
 121
 122 static void bar_end_io(struct request *rq, int error)
 123 {
 124         elv_completed_request(rq->q, rq);
 125         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
 126 }
 127
 128 static void post_flush_end_io(struct request *rq, int error)
 129 {
 130         elv_completed_request(rq->q, rq);
 131         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
 132 }
 133
 134 static void queue_flush(struct request_queue *q, unsigned which)
 135 {
 136         struct request *rq;
 137         rq_end_io_fn *end_io;
 138
 139         if (which == QUEUE_ORDERED_DO_PREFLUSH) {
 140                 rq = &q->pre_flush_rq;
 141                 end_io = pre_flush_end_io;
 142         } else {
 143                 rq = &q->post_flush_rq;
 144                 end_io = post_flush_end_io;
 145         }
 146
 147         blk_rq_init(q, rq);
 148         rq->cmd_flags = REQ_HARDBARRIER;
 149         rq->rq_disk = q->bar_rq.rq_disk;
 150         rq->end_io = end_io;
 151         q->prepare_flush_fn(q, rq);
 152
 153         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 154 }
 155
 156 static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 157 {
 158         struct request *rq = *rqp;
 159         unsigned skip = 0;
 160
 161         q->orderr = 0;
 162         q->ordered = q->next_ordered;
 163         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 164
 165         /*
 166          * For an empty barrier, there's no actual BAR request, which
 167          * in turn makes POSTFLUSH unnecessary.  Mask them off.
 168          */
 169         if (!rq->hard_nr_sectors) {
 170                 q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
 171                                 QUEUE_ORDERED_DO_POSTFLUSH);
 172                 /*
 173                  * Empty barrier on a write-through device w/ ordered
 174                  * tag has no command to issue and without any command
 175                  * to issue, ordering by tag can't be used.  Drain
 176                  * instead.
 177                  */
 178                 if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
 179                     !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
 180                         q->ordered &= ~QUEUE_ORDERED_BY_TAG;
 181                         q->ordered |= QUEUE_ORDERED_BY_DRAIN;
 182                 }
 183         }
 184
 185         /* stash away the original request */
 186         elv_dequeue_request(q, rq);
 187         q->orig_bar_rq = rq;
 188         rq = NULL;
 189
 190         /*
 191          * Queue ordered sequence.  As we stack them at the head, we
 192          * need to queue in reverse order.  Note that we rely on that
 193          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
 194          * request gets inbetween ordered sequence.
 195          */
 196         if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
 197                 queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
 198                 rq = &q->post_flush_rq;
 199         } else
 200                 skip |= QUEUE_ORDSEQ_POSTFLUSH;
 201
 202         if (q->ordered & QUEUE_ORDERED_DO_BAR) {
 203                 rq = &q->bar_rq;
 204
 205                 /* initialize proxy request and queue it */
 206                 blk_rq_init(q, rq);
 207                 if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 208                         rq->cmd_flags |= REQ_RW;
 209                 if (q->ordered & QUEUE_ORDERED_DO_FUA)
 210                         rq->cmd_flags |= REQ_FUA;
 211                 init_request_from_bio(rq, q->orig_bar_rq->bio);
 212                 rq->end_io = bar_end_io;
 213
 214                 elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 215         } else
 216                 skip |= QUEUE_ORDSEQ_BAR;
 217
 218         if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
 219                 queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
 220                 rq = &q->pre_flush_rq;
 221         } else
 222                 skip |= QUEUE_ORDSEQ_PREFLUSH;
 223
 224         if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && q->in_flight)
 225                 rq = NULL;
 226         else
 227                 skip |= QUEUE_ORDSEQ_DRAIN;
 228
 229         *rqp = rq;
 230
 231         /*
 232          * Complete skipped sequences.  If whole sequence is complete,
 233          * return false to tell elevator that this request is gone.
 234          */
 235         return !blk_ordered_complete_seq(q, skip, 0);
 236 }
 237
 238 bool blk_do_ordered(struct request_queue *q, struct request **rqp)
 239 {
 240         struct request *rq = *rqp;
 241         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
 242
 243         if (!q->ordseq) {
 244                 if (!is_barrier)
 245                         return true;
 246
 247                 if (q->next_ordered != QUEUE_ORDERED_NONE)
 248                         return start_ordered(q, rqp);
 249                 else {
 250                         /*
 251                          * Queue ordering not supported.  Terminate
 252                          * with prejudice.
 253                          */
 254                         elv_dequeue_request(q, rq);
 255                         if (__blk_end_request(rq, -EOPNOTSUPP,
 256                                               blk_rq_bytes(rq)))
 257                                 BUG();
 258                         *rqp = NULL;
 259                         return false;
 260                 }
 261         }
 262
 263         /*
 264          * Ordered sequence in progress
 265          */
 266
 267         /* Special requests are not subject to ordering rules. */
 268         if (!blk_fs_request(rq) &&
 269             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
 270                 return true;
 271
 272         if (q->ordered & QUEUE_ORDERED_BY_TAG) {
 273                 /* Ordered by tag.  Blocking the next barrier is enough. */
 274                 if (is_barrier && rq != &q->bar_rq)
 275                         *rqp = NULL;
 276         } else {
 277                 /* Ordered by draining.  Wait for turn. */
 278                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 279                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
 280                         *rqp = NULL;
 281         }
 282
 283         return true;
 284 }
 285
 286 static void bio_end_empty_barrier(struct bio *bio, int err)
 287 {
 288         if (err) {
 289                 if (err == -EOPNOTSUPP)
 290                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 291                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 292         }
 293
 294         complete(bio->bi_private);
 295 }
 296
 297 /**
 298  * blkdev_issue_flush - queue a flush
 299  * @bdev:       blockdev to issue flush for
 300  * @error_sector:       error sector
 301  *
 302  * Description:
 303  *    Issue a flush for the block device in question. Caller can supply
 304  *    room for storing the error offset in case of a flush error, if they
 305  *    wish to.  Caller must run wait_for_completion() on its own.
 306  */
 307 int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
 308 {
 309         DECLARE_COMPLETION_ONSTACK(wait);
 310         struct request_queue *q;
 311         struct bio *bio;
 312         int ret;
 313
 314         if (bdev->bd_disk == NULL)
 315                 return -ENXIO;
 316
 317         q = bdev_get_queue(bdev);
 318         if (!q)
 319                 return -ENXIO;
 320
 321         bio = bio_alloc(GFP_KERNEL, 0);
 322         if (!bio)
 323                 return -ENOMEM;
 324
 325         bio->bi_end_io = bio_end_empty_barrier;
 326         bio->bi_private = &wait;
 327         bio->bi_bdev = bdev;
 328         submit_bio(WRITE_BARRIER, bio);
 329
 330         wait_for_completion(&wait);
 331
 332         /*
 333          * The driver must store the error location in ->bi_sector, if
 334          * it supports it. For non-stacked drivers, this should be copied
 335          * from rq->sector.
 336          */
 337         if (error_sector)
 338                 *error_sector = bio->bi_sector;
 339
 340         ret = 0;
 341         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 342                 ret = -EOPNOTSUPP;
 343         else if (!bio_flagged(bio, BIO_UPTODATE))
 344                 ret = -EIO;
 345
 346         bio_put(bio);
 347         return ret;
 348 }
 349 EXPORT_SYMBOL(blkdev_issue_flush);
 350
 351 static void blkdev_discard_end_io(struct bio *bio, int err)
 352 {
 353         if (err) {
 354                 if (err == -EOPNOTSUPP)
 355                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 356                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 357         }
 358
 359         bio_put(bio);
 360 }
 361
 362 /**
 363  * blkdev_issue_discard - queue a discard
 364  * @bdev:       blockdev to issue discard for
 365  * @sector:     start sector
 366  * @nr_sects:   number of sectors to discard
 367  * @gfp_mask:   memory allocation flags (for bio_alloc)
 368  *
 369  * Description:
 370  *    Issue a discard request for the sectors in question. Does not wait.
 371  */
 372 int blkdev_issue_discard(struct block_device *bdev,
 373                          sector_t sector, sector_t nr_sects, gfp_t gfp_mask)
 374 {
 375         struct request_queue *q;
 376         struct bio *bio;
 377         int ret = 0;
 378
 379         if (bdev->bd_disk == NULL)
 380                 return -ENXIO;
 381
 382         q = bdev_get_queue(bdev);
 383         if (!q)
 384                 return -ENXIO;
 385
 386         if (!q->prepare_discard_fn)
 387                 return -EOPNOTSUPP;
 388
 389         while (nr_sects && !ret) {
 390                 bio = bio_alloc(gfp_mask, 0);
 391                 if (!bio)
 392                         return -ENOMEM;
 393
 394                 bio->bi_end_io = blkdev_discard_end_io;
 395                 bio->bi_bdev = bdev;
 396
 397                 bio->bi_sector = sector;
 398
 399                 if (nr_sects > q->max_hw_sectors) {
 400                         bio->bi_size = q->max_hw_sectors << 9;
 401                         nr_sects -= q->max_hw_sectors;
 402                         sector += q->max_hw_sectors;
 403                 } else {
 404                         bio->bi_size = nr_sects << 9;
 405                         nr_sects = 0;
 406                 }
 407                 bio_get(bio);
 408                 submit_bio(DISCARD_BARRIER, bio);
 409
 410                 /* Check if it failed immediately */
 411                 if (bio_flagged(bio, BIO_EOPNOTSUPP))
 412                         ret = -EOPNOTSUPP;
 413                 else if (!bio_flagged(bio, BIO_UPTODATE))
 414                         ret = -EIO;
 415                 bio_put(bio);
 416         }
 417         return ret;
 418 }
 419 EXPORT_SYMBOL(blkdev_issue_discard);