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 (ordered & (QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH) &&
  28             prepare_flush_fn == NULL) {
  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 void 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;
 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
 114 static void pre_flush_end_io(struct request *rq, int error)
 115 {
 116         elv_completed_request(rq->q, rq);
 117         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
 118 }
 119
 120 static void bar_end_io(struct request *rq, int error)
 121 {
 122         elv_completed_request(rq->q, rq);
 123         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
 124 }
 125
 126 static void post_flush_end_io(struct request *rq, int error)
 127 {
 128         elv_completed_request(rq->q, rq);
 129         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
 130 }
 131
 132 static void queue_flush(struct request_queue *q, unsigned which)
 133 {
 134         struct request *rq;
 135         rq_end_io_fn *end_io;
 136
 137         if (which == QUEUE_ORDERED_PREFLUSH) {
 138                 rq = &q->pre_flush_rq;
 139                 end_io = pre_flush_end_io;
 140         } else {
 141                 rq = &q->post_flush_rq;
 142                 end_io = post_flush_end_io;
 143         }
 144
 145         blk_rq_init(q, rq);
 146         rq->cmd_flags = REQ_HARDBARRIER;
 147         rq->rq_disk = q->bar_rq.rq_disk;
 148         rq->end_io = end_io;
 149         q->prepare_flush_fn(q, rq);
 150
 151         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 152 }
 153
 154 static inline struct request *start_ordered(struct request_queue *q,
 155                                             struct request *rq)
 156 {
 157         q->orderr = 0;
 158         q->ordered = q->next_ordered;
 159         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 160
 161         /*
 162          * Prep proxy barrier request.
 163          */
 164         blkdev_dequeue_request(rq);
 165         q->orig_bar_rq = rq;
 166         rq = &q->bar_rq;
 167         blk_rq_init(q, rq);
 168         if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 169                 rq->cmd_flags |= REQ_RW;
 170         if (q->ordered & QUEUE_ORDERED_FUA)
 171                 rq->cmd_flags |= REQ_FUA;
 172         init_request_from_bio(rq, q->orig_bar_rq->bio);
 173         rq->end_io = bar_end_io;
 174
 175         /*
 176          * Queue ordered sequence.  As we stack them at the head, we
 177          * need to queue in reverse order.  Note that we rely on that
 178          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
 179          * request gets inbetween ordered sequence. If this request is
 180          * an empty barrier, we don't need to do a postflush ever since
 181          * there will be no data written between the pre and post flush.
 182          * Hence a single flush will suffice.
 183          */
 184         if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
 185                 queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
 186         else
 187                 q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
 188
 189         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 190
 191         if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
 192                 queue_flush(q, QUEUE_ORDERED_PREFLUSH);
 193                 rq = &q->pre_flush_rq;
 194         } else
 195                 q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
 196
 197         if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
 198                 q->ordseq |= QUEUE_ORDSEQ_DRAIN;
 199         else
 200                 rq = NULL;
 201
 202         return rq;
 203 }
 204
 205 int blk_do_ordered(struct request_queue *q, struct request **rqp)
 206 {
 207         struct request *rq = *rqp;
 208         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
 209
 210         if (!q->ordseq) {
 211                 if (!is_barrier)
 212                         return 1;
 213
 214                 if (q->next_ordered != QUEUE_ORDERED_NONE) {
 215                         *rqp = start_ordered(q, rq);
 216                         return 1;
 217                 } else {
 218                         /*
 219                          * This can happen when the queue switches to
 220                          * ORDERED_NONE while this request is on it.
 221                          */
 222                         blkdev_dequeue_request(rq);
 223                         if (__blk_end_request(rq, -EOPNOTSUPP,
 224                                               blk_rq_bytes(rq)))
 225                                 BUG();
 226                         *rqp = NULL;
 227                         return 0;
 228                 }
 229         }
 230
 231         /*
 232          * Ordered sequence in progress
 233          */
 234
 235         /* Special requests are not subject to ordering rules. */
 236         if (!blk_fs_request(rq) &&
 237             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
 238                 return 1;
 239
 240         if (q->ordered & QUEUE_ORDERED_TAG) {
 241                 /* Ordered by tag.  Blocking the next barrier is enough. */
 242                 if (is_barrier && rq != &q->bar_rq)
 243                         *rqp = NULL;
 244         } else {
 245                 /* Ordered by draining.  Wait for turn. */
 246                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 247                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
 248                         *rqp = NULL;
 249         }
 250
 251         return 1;
 252 }
 253
 254 static void bio_end_empty_barrier(struct bio *bio, int err)
 255 {
 256         if (err) {
 257                 if (err == -EOPNOTSUPP)
 258                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 259                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 260         }
 261
 262         complete(bio->bi_private);
 263 }
 264
 265 /**
 266  * blkdev_issue_flush - queue a flush
 267  * @bdev:       blockdev to issue flush for
 268  * @error_sector:       error sector
 269  *
 270  * Description:
 271  *    Issue a flush for the block device in question. Caller can supply
 272  *    room for storing the error offset in case of a flush error, if they
 273  *    wish to.  Caller must run wait_for_completion() on its own.
 274  */
 275 int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
 276 {
 277         DECLARE_COMPLETION_ONSTACK(wait);
 278         struct request_queue *q;
 279         struct bio *bio;
 280         int ret;
 281
 282         if (bdev->bd_disk == NULL)
 283                 return -ENXIO;
 284
 285         q = bdev_get_queue(bdev);
 286         if (!q)
 287                 return -ENXIO;
 288
 289         bio = bio_alloc(GFP_KERNEL, 0);
 290         if (!bio)
 291                 return -ENOMEM;
 292
 293         bio->bi_end_io = bio_end_empty_barrier;
 294         bio->bi_private = &wait;
 295         bio->bi_bdev = bdev;
 296         submit_bio(1 << BIO_RW_BARRIER, bio);
 297
 298         wait_for_completion(&wait);
 299
 300         /*
 301          * The driver must store the error location in ->bi_sector, if
 302          * it supports it. For non-stacked drivers, this should be copied
 303          * from rq->sector.
 304          */
 305         if (error_sector)
 306                 *error_sector = bio->bi_sector;
 307
 308         ret = 0;
 309         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 310                 ret = -EOPNOTSUPP;
 311         else if (!bio_flagged(bio, BIO_UPTODATE))
 312                 ret = -EIO;
 313
 314         bio_put(bio);
 315         return ret;
 316 }
 317 EXPORT_SYMBOL(blkdev_issue_flush);