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   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",
  30                                                                 __FUNCTION__);
  31                 return -EINVAL;
  32         }
  33
  34         if (ordered != QUEUE_ORDERED_NONE &&
  35             ordered != QUEUE_ORDERED_DRAIN &&
  36             ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
  37             ordered != QUEUE_ORDERED_DRAIN_FUA &&
  38             ordered != QUEUE_ORDERED_TAG &&
  39             ordered != QUEUE_ORDERED_TAG_FLUSH &&
  40             ordered != QUEUE_ORDERED_TAG_FUA) {
  41                 printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
  42                 return -EINVAL;
  43         }
  44
  45         q->ordered = ordered;
  46         q->next_ordered = ordered;
  47         q->prepare_flush_fn = prepare_flush_fn;
  48
  49         return 0;
  50 }
  51 EXPORT_SYMBOL(blk_queue_ordered);
  52
  53 /*
  54  * Cache flushing for ordered writes handling
  55  */
  56 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_init(q, rq);
 147         rq->cmd_flags = REQ_HARDBARRIER;
 148         rq->rq_disk = q->bar_rq.rq_disk;
 149         rq->end_io = end_io;
 150         q->prepare_flush_fn(q, rq);
 151
 152         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 153 }
 154
 155 static inline struct request *start_ordered(struct request_queue *q,
 156                                             struct request *rq)
 157 {
 158         q->orderr = 0;
 159         q->ordered = q->next_ordered;
 160         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 161
 162         /*
 163          * Prep proxy barrier request.
 164          */
 165         blkdev_dequeue_request(rq);
 166         q->orig_bar_rq = rq;
 167         rq = &q->bar_rq;
 168         rq_init(q, rq);
 169         if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
 170                 rq->cmd_flags |= REQ_RW;
 171         if (q->ordered & QUEUE_ORDERED_FUA)
 172                 rq->cmd_flags |= REQ_FUA;
 173         init_request_from_bio(rq, q->orig_bar_rq->bio);
 174         rq->end_io = bar_end_io;
 175
 176         /*
 177          * Queue ordered sequence.  As we stack them at the head, we
 178          * need to queue in reverse order.  Note that we rely on that
 179          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
 180          * request gets inbetween ordered sequence. If this request is
 181          * an empty barrier, we don't need to do a postflush ever since
 182          * there will be no data written between the pre and post flush.
 183          * Hence a single flush will suffice.
 184          */
 185         if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
 186                 queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
 187         else
 188                 q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
 189
 190         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 191
 192         if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
 193                 queue_flush(q, QUEUE_ORDERED_PREFLUSH);
 194                 rq = &q->pre_flush_rq;
 195         } else
 196                 q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
 197
 198         if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
 199                 q->ordseq |= QUEUE_ORDSEQ_DRAIN;
 200         else
 201                 rq = NULL;
 202
 203         return rq;
 204 }
 205
 206 int blk_do_ordered(struct request_queue *q, struct request **rqp)
 207 {
 208         struct request *rq = *rqp;
 209         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
 210
 211         if (!q->ordseq) {
 212                 if (!is_barrier)
 213                         return 1;
 214
 215                 if (q->next_ordered != QUEUE_ORDERED_NONE) {
 216                         *rqp = start_ordered(q, rq);
 217                         return 1;
 218                 } else {
 219                         /*
 220                          * This can happen when the queue switches to
 221                          * ORDERED_NONE while this request is on it.
 222                          */
 223                         blkdev_dequeue_request(rq);
 224                         if (__blk_end_request(rq, -EOPNOTSUPP,
 225                                               blk_rq_bytes(rq)))
 226                                 BUG();
 227                         *rqp = NULL;
 228                         return 0;
 229                 }
 230         }
 231
 232         /*
 233          * Ordered sequence in progress
 234          */
 235
 236         /* Special requests are not subject to ordering rules. */
 237         if (!blk_fs_request(rq) &&
 238             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
 239                 return 1;
 240
 241         if (q->ordered & QUEUE_ORDERED_TAG) {
 242                 /* Ordered by tag.  Blocking the next barrier is enough. */
 243                 if (is_barrier && rq != &q->bar_rq)
 244                         *rqp = NULL;
 245         } else {
 246                 /* Ordered by draining.  Wait for turn. */
 247                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 248                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
 249                         *rqp = NULL;
 250         }
 251
 252         return 1;
 253 }
 254
 255 static void bio_end_empty_barrier(struct bio *bio, int err)
 256 {
 257         if (err) {
 258                 if (err == -EOPNOTSUPP)
 259                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 260                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 261         }
 262
 263         complete(bio->bi_private);
 264 }
 265
 266 /**
 267  * blkdev_issue_flush - queue a flush
 268  * @bdev:       blockdev to issue flush for
 269  * @error_sector:       error sector
 270  *
 271  * Description:
 272  *    Issue a flush for the block device in question. Caller can supply
 273  *    room for storing the error offset in case of a flush error, if they
 274  *    wish to.  Caller must run wait_for_completion() on its own.
 275  */
 276 int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
 277 {
 278         DECLARE_COMPLETION_ONSTACK(wait);
 279         struct request_queue *q;
 280         struct bio *bio;
 281         int ret;
 282
 283         if (bdev->bd_disk == NULL)
 284                 return -ENXIO;
 285
 286         q = bdev_get_queue(bdev);
 287         if (!q)
 288                 return -ENXIO;
 289
 290         bio = bio_alloc(GFP_KERNEL, 0);
 291         if (!bio)
 292                 return -ENOMEM;
 293
 294         bio->bi_end_io = bio_end_empty_barrier;
 295         bio->bi_private = &wait;
 296         bio->bi_bdev = bdev;
 297         submit_bio(1 << BIO_RW_BARRIER, bio);
 298
 299         wait_for_completion(&wait);
 300
 301         /*
 302          * The driver must store the error location in ->bi_sector, if
 303          * it supports it. For non-stacked drivers, this should be copied
 304          * from rq->sector.
 305          */
 306         if (error_sector)
 307                 *error_sector = bio->bi_sector;
 308
 309         ret = 0;
 310         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 311                 ret = -EOPNOTSUPP;
 312         else if (!bio_flagged(bio, BIO_UPTODATE))
 313                 ret = -EIO;
 314
 315         bio_put(bio);
 316         return ret;
 317 }
 318 EXPORT_SYMBOL(blkdev_issue_flush);