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  *
  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 {
  26         if (ordered != QUEUE_ORDERED_NONE &&
  27             ordered != QUEUE_ORDERED_DRAIN &&
  28             ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
  29             ordered != QUEUE_ORDERED_DRAIN_FUA &&
  30             ordered != QUEUE_ORDERED_TAG &&
  31             ordered != QUEUE_ORDERED_TAG_FLUSH &&
  32             ordered != QUEUE_ORDERED_TAG_FUA) {
  33                 printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
  34                 return -EINVAL;
  35         }
  36
  37         q->ordered = ordered;
  38         q->next_ordered = ordered;
  39
  40         return 0;
  41 }
  42 EXPORT_SYMBOL(blk_queue_ordered);
  43
  44 /*
  45  * Cache flushing for ordered writes handling
  46  */
  47 unsigned blk_ordered_cur_seq(struct request_queue *q)
  48 {
  49         if (!q->ordseq)
  50                 return 0;
  51         return 1 << ffz(q->ordseq);
  52 }
  53
  54 unsigned blk_ordered_req_seq(struct request *rq)
  55 {
  56         struct request_queue *q = rq->q;
  57
  58         BUG_ON(q->ordseq == 0);
  59
  60         if (rq == &q->pre_flush_rq)
  61                 return QUEUE_ORDSEQ_PREFLUSH;
  62         if (rq == &q->bar_rq)
  63                 return QUEUE_ORDSEQ_BAR;
  64         if (rq == &q->post_flush_rq)
  65                 return QUEUE_ORDSEQ_POSTFLUSH;
  66
  67         /*
  68          * !fs requests don't need to follow barrier ordering.  Always
  69          * put them at the front.  This fixes the following deadlock.
  70          *
  71          * http://thread.gmane.org/gmane.linux.kernel/537473
  72          */
  73         if (rq->cmd_type != REQ_TYPE_FS)
  74                 return QUEUE_ORDSEQ_DRAIN;
  75
  76         if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
  77             (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
  78                 return QUEUE_ORDSEQ_DRAIN;
  79         else
  80                 return QUEUE_ORDSEQ_DONE;
  81 }
  82
  83 bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
  84 {
  85         struct request *rq;
  86
  87         if (error && !q->orderr)
  88                 q->orderr = error;
  89
  90         BUG_ON(q->ordseq & seq);
  91         q->ordseq |= seq;
  92
  93         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
  94                 return false;
  95
  96         /*
  97          * Okay, sequence complete.
  98          */
  99         q->ordseq = 0;
 100         rq = q->orig_bar_rq;
 101         __blk_end_request_all(rq, q->orderr);
 102         return true;
 103 }
 104
 105 static void pre_flush_end_io(struct request *rq, int error)
 106 {
 107         elv_completed_request(rq->q, rq);
 108         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
 109 }
 110
 111 static void bar_end_io(struct request *rq, int error)
 112 {
 113         elv_completed_request(rq->q, rq);
 114         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
 115 }
 116
 117 static void post_flush_end_io(struct request *rq, int error)
 118 {
 119         elv_completed_request(rq->q, rq);
 120         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
 121 }
 122
 123 static void queue_flush(struct request_queue *q, unsigned which)
 124 {
 125         struct request *rq;
 126         rq_end_io_fn *end_io;
 127
 128         if (which == QUEUE_ORDERED_DO_PREFLUSH) {
 129                 rq = &q->pre_flush_rq;
 130                 end_io = pre_flush_end_io;
 131         } else {
 132                 rq = &q->post_flush_rq;
 133                 end_io = post_flush_end_io;
 134         }
 135
 136         blk_rq_init(q, rq);
 137         rq->cmd_type = REQ_TYPE_FS;
 138         rq->cmd_flags = REQ_HARDBARRIER | REQ_FLUSH;
 139         rq->rq_disk = q->orig_bar_rq->rq_disk;
 140         rq->end_io = end_io;
 141
 142         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 143 }
 144
 145 static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 146 {
 147         struct request *rq = *rqp;
 148         unsigned skip = 0;
 149
 150         q->orderr = 0;
 151         q->ordered = q->next_ordered;
 152         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 153
 154         /*
 155          * For an empty barrier, there's no actual BAR request, which
 156          * in turn makes POSTFLUSH unnecessary.  Mask them off.
 157          */
 158         if (!blk_rq_sectors(rq)) {
 159                 q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
 160                                 QUEUE_ORDERED_DO_POSTFLUSH);
 161                 /*
 162                  * Empty barrier on a write-through device w/ ordered
 163                  * tag has no command to issue and without any command
 164                  * to issue, ordering by tag can't be used.  Drain
 165                  * instead.
 166                  */
 167                 if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
 168                     !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
 169                         q->ordered &= ~QUEUE_ORDERED_BY_TAG;
 170                         q->ordered |= QUEUE_ORDERED_BY_DRAIN;
 171                 }
 172         }
 173
 174         /* stash away the original request */
 175         blk_dequeue_request(rq);
 176         q->orig_bar_rq = rq;
 177         rq = NULL;
 178
 179         /*
 180          * Queue ordered sequence.  As we stack them at the head, we
 181          * need to queue in reverse order.  Note that we rely on that
 182          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
 183          * request gets inbetween ordered sequence.
 184          */
 185         if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
 186                 queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
 187                 rq = &q->post_flush_rq;
 188         } else
 189                 skip |= QUEUE_ORDSEQ_POSTFLUSH;
 190
 191         if (q->ordered & QUEUE_ORDERED_DO_BAR) {
 192                 rq = &q->bar_rq;
 193
 194                 /* initialize proxy request and queue it */
 195                 blk_rq_init(q, rq);
 196                 if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 197                         rq->cmd_flags |= REQ_WRITE;
 198                 if (q->ordered & QUEUE_ORDERED_DO_FUA)
 199                         rq->cmd_flags |= REQ_FUA;
 200                 init_request_from_bio(rq, q->orig_bar_rq->bio);
 201                 rq->end_io = bar_end_io;
 202
 203                 elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 204         } else
 205                 skip |= QUEUE_ORDSEQ_BAR;
 206
 207         if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
 208                 queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
 209                 rq = &q->pre_flush_rq;
 210         } else
 211                 skip |= QUEUE_ORDSEQ_PREFLUSH;
 212
 213         if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
 214                 rq = NULL;
 215         else
 216                 skip |= QUEUE_ORDSEQ_DRAIN;
 217
 218         *rqp = rq;
 219
 220         /*
 221          * Complete skipped sequences.  If whole sequence is complete,
 222          * return false to tell elevator that this request is gone.
 223          */
 224         return !blk_ordered_complete_seq(q, skip, 0);
 225 }
 226
 227 bool blk_do_ordered(struct request_queue *q, struct request **rqp)
 228 {
 229         struct request *rq = *rqp;
 230         const int is_barrier = rq->cmd_type == REQ_TYPE_FS &&
 231                                 (rq->cmd_flags & REQ_HARDBARRIER);
 232
 233         if (!q->ordseq) {
 234                 if (!is_barrier)
 235                         return true;
 236
 237                 if (q->next_ordered != QUEUE_ORDERED_NONE)
 238                         return start_ordered(q, rqp);
 239                 else {
 240                         /*
 241                          * Queue ordering not supported.  Terminate
 242                          * with prejudice.
 243                          */
 244                         blk_dequeue_request(rq);
 245                         __blk_end_request_all(rq, -EOPNOTSUPP);
 246                         *rqp = NULL;
 247                         return false;
 248                 }
 249         }
 250
 251         /*
 252          * Ordered sequence in progress
 253          */
 254
 255         /* Special requests are not subject to ordering rules. */
 256         if (rq->cmd_type != REQ_TYPE_FS &&
 257             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
 258                 return true;
 259
 260         if (q->ordered & QUEUE_ORDERED_BY_TAG) {
 261                 /* Ordered by tag.  Blocking the next barrier is enough. */
 262                 if (is_barrier && rq != &q->bar_rq)
 263                         *rqp = NULL;
 264         } else {
 265                 /* Ordered by draining.  Wait for turn. */
 266                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 267                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
 268                         *rqp = NULL;
 269         }
 270
 271         return true;
 272 }
 273
 274 static void bio_end_empty_barrier(struct bio *bio, int err)
 275 {
 276         if (err) {
 277                 if (err == -EOPNOTSUPP)
 278                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 279                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 280         }
 281         if (bio->bi_private)
 282                 complete(bio->bi_private);
 283         bio_put(bio);
 284 }
 285
 286 /**
 287  * blkdev_issue_flush - queue a flush
 288  * @bdev:       blockdev to issue flush for
 289  * @gfp_mask:   memory allocation flags (for bio_alloc)
 290  * @error_sector:       error sector
 291  * @flags:      BLKDEV_IFL_* flags to control behaviour
 292  *
 293  * Description:
 294  *    Issue a flush for the block device in question. Caller can supply
 295  *    room for storing the error offset in case of a flush error, if they
 296  *    wish to. If WAIT flag is not passed then caller may check only what
 297  *    request was pushed in some internal queue for later handling.
 298  */
 299 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 300                 sector_t *error_sector, unsigned long flags)
 301 {
 302         DECLARE_COMPLETION_ONSTACK(wait);
 303         struct request_queue *q;
 304         struct bio *bio;
 305         int ret = 0;
 306
 307         if (bdev->bd_disk == NULL)
 308                 return -ENXIO;
 309
 310         q = bdev_get_queue(bdev);
 311         if (!q)
 312                 return -ENXIO;
 313
 314         /*
 315          * some block devices may not have their queue correctly set up here
 316          * (e.g. loop device without a backing file) and so issuing a flush
 317          * here will panic. Ensure there is a request function before issuing
 318          * the barrier.
 319          */
 320         if (!q->make_request_fn)
 321                 return -ENXIO;
 322
 323         bio = bio_alloc(gfp_mask, 0);
 324         bio->bi_end_io = bio_end_empty_barrier;
 325         bio->bi_bdev = bdev;
 326         if (test_bit(BLKDEV_WAIT, &flags))
 327                 bio->bi_private = &wait;
 328
 329         bio_get(bio);
 330         submit_bio(WRITE_BARRIER, bio);
 331         if (test_bit(BLKDEV_WAIT, &flags)) {
 332                 wait_for_completion(&wait);
 333                 /*
 334                  * The driver must store the error location in ->bi_sector, if
 335                  * it supports it. For non-stacked drivers, this should be
 336                  * copied from blk_rq_pos(rq).
 337                  */
 338                 if (error_sector)
 339                         *error_sector = bio->bi_sector;
 340         }
 341
 342         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 343                 ret = -EOPNOTSUPP;
 344         else if (!bio_flagged(bio, BIO_UPTODATE))
 345                 ret = -EIO;
 346
 347         bio_put(bio);
 348         return ret;
 349 }
 350 EXPORT_SYMBOL(blkdev_issue_flush);