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 "blk_queue_ordered: prepare_flush_fn required\n");
  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
  51 EXPORT_SYMBOL(blk_queue_ordered);
  52
  53 /*
  54  * Cache flushing for ordered writes handling
  55  */
  56 inline unsigned blk_ordered_cur_seq(struct request_queue *q)
  57 {
  58         if (!q->ordseq)
  59                 return 0;
  60         return 1 << ffz(q->ordseq);
  61 }
  62
  63 unsigned blk_ordered_req_seq(struct request *rq)
  64 {
  65         struct request_queue *q = rq->q;
  66
  67         BUG_ON(q->ordseq == 0);
  68
  69         if (rq == &q->pre_flush_rq)
  70                 return QUEUE_ORDSEQ_PREFLUSH;
  71         if (rq == &q->bar_rq)
  72                 return QUEUE_ORDSEQ_BAR;
  73         if (rq == &q->post_flush_rq)
  74                 return QUEUE_ORDSEQ_POSTFLUSH;
  75
  76         /*
  77          * !fs requests don't need to follow barrier ordering.  Always
  78          * put them at the front.  This fixes the following deadlock.
  79          *
  80          * http://thread.gmane.org/gmane.linux.kernel/537473
  81          */
  82         if (!blk_fs_request(rq))
  83                 return QUEUE_ORDSEQ_DRAIN;
  84
  85         if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
  86             (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
  87                 return QUEUE_ORDSEQ_DRAIN;
  88         else
  89                 return QUEUE_ORDSEQ_DONE;
  90 }
  91
  92 void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
  93 {
  94         struct request *rq;
  95
  96         if (error && !q->orderr)
  97                 q->orderr = error;
  98
  99         BUG_ON(q->ordseq & seq);
 100         q->ordseq |= seq;
 101
 102         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
 103                 return;
 104
 105         /*
 106          * Okay, sequence complete.
 107          */
 108         q->ordseq = 0;
 109         rq = q->orig_bar_rq;
 110
 111         if (__blk_end_request(rq, q->orderr, blk_rq_bytes(rq)))
 112                 BUG();
 113 }
 114
 115 static void pre_flush_end_io(struct request *rq, int error)
 116 {
 117         elv_completed_request(rq->q, rq);
 118         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
 119 }
 120
 121 static void bar_end_io(struct request *rq, int error)
 122 {
 123         elv_completed_request(rq->q, rq);
 124         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
 125 }
 126
 127 static void post_flush_end_io(struct request *rq, int error)
 128 {
 129         elv_completed_request(rq->q, rq);
 130         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
 131 }
 132
 133 static void queue_flush(struct request_queue *q, unsigned which)
 134 {
 135         struct request *rq;
 136         rq_end_io_fn *end_io;
 137
 138         if (which == QUEUE_ORDERED_PREFLUSH) {
 139                 rq = &q->pre_flush_rq;
 140                 end_io = pre_flush_end_io;
 141         } else {
 142                 rq = &q->post_flush_rq;
 143                 end_io = post_flush_end_io;
 144         }
 145
 146         rq->cmd_flags = REQ_HARDBARRIER;
 147         rq_init(q, rq);
 148         rq->elevator_private = NULL;
 149         rq->elevator_private2 = NULL;
 150         rq->rq_disk = q->bar_rq.rq_disk;
 151         rq->end_io = end_io;
 152         q->prepare_flush_fn(q, rq);
 153
 154         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 155 }
 156
 157 static inline struct request *start_ordered(struct request_queue *q,
 158                                             struct request *rq)
 159 {
 160         q->orderr = 0;
 161         q->ordered = q->next_ordered;
 162         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 163
 164         /*
 165          * Prep proxy barrier request.
 166          */
 167         blkdev_dequeue_request(rq);
 168         q->orig_bar_rq = rq;
 169         rq = &q->bar_rq;
 170         rq->cmd_flags = 0;
 171         rq_init(q, rq);
 172         if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 173                 rq->cmd_flags |= REQ_RW;
 174         if (q->ordered & QUEUE_ORDERED_FUA)
 175                 rq->cmd_flags |= REQ_FUA;
 176         rq->elevator_private = NULL;
 177         rq->elevator_private2 = NULL;
 178         init_request_from_bio(rq, q->orig_bar_rq->bio);
 179         rq->end_io = bar_end_io;
 180
 181         /*
 182          * Queue ordered sequence.  As we stack them at the head, we
 183          * need to queue in reverse order.  Note that we rely on that
 184          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
 185          * request gets inbetween ordered sequence. If this request is
 186          * an empty barrier, we don't need to do a postflush ever since
 187          * there will be no data written between the pre and post flush.
 188          * Hence a single flush will suffice.
 189          */
 190         if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
 191                 queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
 192         else
 193                 q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
 194
 195         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 196
 197         if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
 198                 queue_flush(q, QUEUE_ORDERED_PREFLUSH);
 199                 rq = &q->pre_flush_rq;
 200         } else
 201                 q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
 202
 203         if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
 204                 q->ordseq |= QUEUE_ORDSEQ_DRAIN;
 205         else
 206                 rq = NULL;
 207
 208         return rq;
 209 }
 210
 211 int blk_do_ordered(struct request_queue *q, struct request **rqp)
 212 {
 213         struct request *rq = *rqp;
 214         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
 215
 216         if (!q->ordseq) {
 217                 if (!is_barrier)
 218                         return 1;
 219
 220                 if (q->next_ordered != QUEUE_ORDERED_NONE) {
 221                         *rqp = start_ordered(q, rq);
 222                         return 1;
 223                 } else {
 224                         /*
 225                          * This can happen when the queue switches to
 226                          * ORDERED_NONE while this request is on it.
 227                          */
 228                         blkdev_dequeue_request(rq);
 229                         if (__blk_end_request(rq, -EOPNOTSUPP,
 230                                               blk_rq_bytes(rq)))
 231                                 BUG();
 232                         *rqp = NULL;
 233                         return 0;
 234                 }
 235         }
 236
 237         /*
 238          * Ordered sequence in progress
 239          */
 240
 241         /* Special requests are not subject to ordering rules. */
 242         if (!blk_fs_request(rq) &&
 243             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
 244                 return 1;
 245
 246         if (q->ordered & QUEUE_ORDERED_TAG) {
 247                 /* Ordered by tag.  Blocking the next barrier is enough. */
 248                 if (is_barrier && rq != &q->bar_rq)
 249                         *rqp = NULL;
 250         } else {
 251                 /* Ordered by draining.  Wait for turn. */
 252                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 253                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
 254                         *rqp = NULL;
 255         }
 256
 257         return 1;
 258 }
 259
 260 static void bio_end_empty_barrier(struct bio *bio, int err)
 261 {
 262         if (err)
 263                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 264
 265         complete(bio->bi_private);
 266 }
 267
 268 /**
 269  * blkdev_issue_flush - queue a flush
 270  * @bdev:       blockdev to issue flush for
 271  * @error_sector:       error sector
 272  *
 273  * Description:
 274  *    Issue a flush for the block device in question. Caller can supply
 275  *    room for storing the error offset in case of a flush error, if they
 276  *    wish to.  Caller must run wait_for_completion() on its own.
 277  */
 278 int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
 279 {
 280         DECLARE_COMPLETION_ONSTACK(wait);
 281         struct request_queue *q;
 282         struct bio *bio;
 283         int ret;
 284
 285         if (bdev->bd_disk == NULL)
 286                 return -ENXIO;
 287
 288         q = bdev_get_queue(bdev);
 289         if (!q)
 290                 return -ENXIO;
 291
 292         bio = bio_alloc(GFP_KERNEL, 0);
 293         if (!bio)
 294                 return -ENOMEM;
 295
 296         bio->bi_end_io = bio_end_empty_barrier;
 297         bio->bi_private = &wait;
 298         bio->bi_bdev = bdev;
 299         submit_bio(1 << BIO_RW_BARRIER, bio);
 300
 301         wait_for_completion(&wait);
 302
 303         /*
 304          * The driver must store the error location in ->bi_sector, if
 305          * it supports it. For non-stacked drivers, this should be copied
 306          * from rq->sector.
 307          */
 308         if (error_sector)
 309                 *error_sector = bio->bi_sector;
 310
 311         ret = 0;
 312         if (!bio_flagged(bio, BIO_UPTODATE))
 313                 ret = -EIO;
 314
 315         bio_put(bio);
 316         return ret;
 317 }
 318
 319 EXPORT_SYMBOL(blkdev_issue_flush);