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 static struct request *queue_next_ordseq(struct request_queue *q);
  13
  14 /*
  15  * Cache flushing for ordered writes handling
  16  */
  17 unsigned blk_ordered_cur_seq(struct request_queue *q)
  18 {
  19         if (!q->ordseq)
  20                 return 0;
  21         return 1 << ffz(q->ordseq);
  22 }
  23
  24 static struct request *blk_ordered_complete_seq(struct request_queue *q,
  25                                                 unsigned seq, int error)
  26 {
  27         struct request *next_rq = NULL;
  28
  29         if (error && !q->orderr)
  30                 q->orderr = error;
  31
  32         BUG_ON(q->ordseq & seq);
  33         q->ordseq |= seq;
  34
  35         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE) {
  36                 /* not complete yet, queue the next ordered sequence */
  37                 next_rq = queue_next_ordseq(q);
  38         } else {
  39                 /* complete this barrier request */
  40                 __blk_end_request_all(q->orig_bar_rq, q->orderr);
  41                 q->orig_bar_rq = NULL;
  42                 q->ordseq = 0;
  43
  44                 /* dispatch the next barrier if there's one */
  45                 if (!list_empty(&q->pending_barriers)) {
  46                         next_rq = list_entry_rq(q->pending_barriers.next);
  47                         list_move(&next_rq->queuelist, &q->queue_head);
  48                 }
  49         }
  50         return next_rq;
  51 }
  52
  53 static void pre_flush_end_io(struct request *rq, int error)
  54 {
  55         elv_completed_request(rq->q, rq);
  56         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
  57 }
  58
  59 static void bar_end_io(struct request *rq, int error)
  60 {
  61         elv_completed_request(rq->q, rq);
  62         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
  63 }
  64
  65 static void post_flush_end_io(struct request *rq, int error)
  66 {
  67         elv_completed_request(rq->q, rq);
  68         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
  69 }
  70
  71 static void queue_flush(struct request_queue *q, struct request *rq,
  72                         rq_end_io_fn *end_io)
  73 {
  74         blk_rq_init(q, rq);
  75         rq->cmd_type = REQ_TYPE_FS;
  76         rq->cmd_flags = REQ_FLUSH;
  77         rq->rq_disk = q->orig_bar_rq->rq_disk;
  78         rq->end_io = end_io;
  79
  80         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
  81 }
  82
  83 static struct request *queue_next_ordseq(struct request_queue *q)
  84 {
  85         struct request *rq = &q->bar_rq;
  86
  87         switch (blk_ordered_cur_seq(q)) {
  88         case QUEUE_ORDSEQ_PREFLUSH:
  89                 queue_flush(q, rq, pre_flush_end_io);
  90                 break;
  91
  92         case QUEUE_ORDSEQ_BAR:
  93                 /* initialize proxy request and queue it */
  94                 blk_rq_init(q, rq);
  95                 init_request_from_bio(rq, q->orig_bar_rq->bio);
  96                 rq->cmd_flags &= ~REQ_HARDBARRIER;
  97                 if (q->ordered & QUEUE_ORDERED_DO_FUA)
  98                         rq->cmd_flags |= REQ_FUA;
  99                 rq->end_io = bar_end_io;
 100
 101                 elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 102                 break;
 103
 104         case QUEUE_ORDSEQ_POSTFLUSH:
 105                 queue_flush(q, rq, post_flush_end_io);
 106                 break;
 107
 108         default:
 109                 BUG();
 110         }
 111         return rq;
 112 }
 113
 114 struct request *blk_do_ordered(struct request_queue *q, struct request *rq)
 115 {
 116         unsigned skip = 0;
 117
 118         if (!(rq->cmd_flags & REQ_HARDBARRIER))
 119                 return rq;
 120
 121         if (q->ordseq) {
 122                 /*
 123                  * Barrier is already in progress and they can't be
 124                  * processed in parallel.  Queue for later processing.
 125                  */
 126                 list_move_tail(&rq->queuelist, &q->pending_barriers);
 127                 return NULL;
 128         }
 129
 130         if (unlikely(q->next_ordered == QUEUE_ORDERED_NONE)) {
 131                 /*
 132                  * Queue ordering not supported.  Terminate
 133                  * with prejudice.
 134                  */
 135                 blk_dequeue_request(rq);
 136                 __blk_end_request_all(rq, -EOPNOTSUPP);
 137                 return NULL;
 138         }
 139
 140         /*
 141          * Start a new ordered sequence
 142          */
 143         q->orderr = 0;
 144         q->ordered = q->next_ordered;
 145         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 146
 147         /*
 148          * For an empty barrier, there's no actual BAR request, which
 149          * in turn makes POSTFLUSH unnecessary.  Mask them off.
 150          */
 151         if (!blk_rq_sectors(rq))
 152                 q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
 153                                 QUEUE_ORDERED_DO_POSTFLUSH);
 154
 155         /* stash away the original request */
 156         blk_dequeue_request(rq);
 157         q->orig_bar_rq = rq;
 158
 159         if (!(q->ordered & QUEUE_ORDERED_DO_PREFLUSH))
 160                 skip |= QUEUE_ORDSEQ_PREFLUSH;
 161
 162         if (!(q->ordered & QUEUE_ORDERED_DO_BAR))
 163                 skip |= QUEUE_ORDSEQ_BAR;
 164
 165         if (!(q->ordered & QUEUE_ORDERED_DO_POSTFLUSH))
 166                 skip |= QUEUE_ORDSEQ_POSTFLUSH;
 167
 168         /* complete skipped sequences and return the first sequence */
 169         return blk_ordered_complete_seq(q, skip, 0);
 170 }
 171
 172 static void bio_end_empty_barrier(struct bio *bio, int err)
 173 {
 174         if (err) {
 175                 if (err == -EOPNOTSUPP)
 176                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 177                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 178         }
 179         if (bio->bi_private)
 180                 complete(bio->bi_private);
 181         bio_put(bio);
 182 }
 183
 184 /**
 185  * blkdev_issue_flush - queue a flush
 186  * @bdev:       blockdev to issue flush for
 187  * @gfp_mask:   memory allocation flags (for bio_alloc)
 188  * @error_sector:       error sector
 189  * @flags:      BLKDEV_IFL_* flags to control behaviour
 190  *
 191  * Description:
 192  *    Issue a flush for the block device in question. Caller can supply
 193  *    room for storing the error offset in case of a flush error, if they
 194  *    wish to. If WAIT flag is not passed then caller may check only what
 195  *    request was pushed in some internal queue for later handling.
 196  */
 197 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 198                 sector_t *error_sector, unsigned long flags)
 199 {
 200         DECLARE_COMPLETION_ONSTACK(wait);
 201         struct request_queue *q;
 202         struct bio *bio;
 203         int ret = 0;
 204
 205         if (bdev->bd_disk == NULL)
 206                 return -ENXIO;
 207
 208         q = bdev_get_queue(bdev);
 209         if (!q)
 210                 return -ENXIO;
 211
 212         /*
 213          * some block devices may not have their queue correctly set up here
 214          * (e.g. loop device without a backing file) and so issuing a flush
 215          * here will panic. Ensure there is a request function before issuing
 216          * the barrier.
 217          */
 218         if (!q->make_request_fn)
 219                 return -ENXIO;
 220
 221         bio = bio_alloc(gfp_mask, 0);
 222         bio->bi_end_io = bio_end_empty_barrier;
 223         bio->bi_bdev = bdev;
 224         if (test_bit(BLKDEV_WAIT, &flags))
 225                 bio->bi_private = &wait;
 226
 227         bio_get(bio);
 228         submit_bio(WRITE_BARRIER, bio);
 229         if (test_bit(BLKDEV_WAIT, &flags)) {
 230                 wait_for_completion(&wait);
 231                 /*
 232                  * The driver must store the error location in ->bi_sector, if
 233                  * it supports it. For non-stacked drivers, this should be
 234                  * copied from blk_rq_pos(rq).
 235                  */
 236                 if (error_sector)
 237                         *error_sector = bio->bi_sector;
 238         }
 239
 240         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 241                 ret = -EOPNOTSUPP;
 242         else if (!bio_flagged(bio, BIO_UPTODATE))
 243                 ret = -EIO;
 244
 245         bio_put(bio);
 246         return ret;
 247 }
 248 EXPORT_SYMBOL(blkdev_issue_flush);