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