block/blk-flush.c

   1 /*
   2  * Functions to sequence FLUSH and FUA writes.
   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 /* FLUSH/FUA sequences */
  13 enum {
  14         QUEUE_FSEQ_STARTED      = (1 << 0), /* flushing in progress */
  15         QUEUE_FSEQ_PREFLUSH     = (1 << 1), /* pre-flushing in progress */
  16         QUEUE_FSEQ_DATA         = (1 << 2), /* data write in progress */
  17         QUEUE_FSEQ_POSTFLUSH    = (1 << 3), /* post-flushing in progress */
  18         QUEUE_FSEQ_DONE         = (1 << 4),
  19 };
  20
  21 static struct request *queue_next_fseq(struct request_queue *q);
  22
  23 unsigned blk_flush_cur_seq(struct request_queue *q)
  24 {
  25         if (!q->flush_seq)
  26                 return 0;
  27         return 1 << ffz(q->flush_seq);
  28 }
  29
  30 static struct request *blk_flush_complete_seq(struct request_queue *q,
  31                                               unsigned seq, int error)
  32 {
  33         struct request *next_rq = NULL;
  34
  35         if (error && !q->flush_err)
  36                 q->flush_err = error;
  37
  38         BUG_ON(q->flush_seq & seq);
  39         q->flush_seq |= seq;
  40
  41         if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
  42                 /* not complete yet, queue the next flush sequence */
  43                 next_rq = queue_next_fseq(q);
  44         } else {
  45                 /* complete this flush request */
  46                 __blk_end_request_all(q->orig_flush_rq, q->flush_err);
  47                 q->orig_flush_rq = NULL;
  48                 q->flush_seq = 0;
  49
  50                 /* dispatch the next flush if there's one */
  51                 if (!list_empty(&q->pending_flushes)) {
  52                         next_rq = list_entry_rq(q->pending_flushes.next);
  53                         list_move(&next_rq->queuelist, &q->queue_head);
  54                 }
  55         }
  56         return next_rq;
  57 }
  58
  59 static void pre_flush_end_io(struct request *rq, int error)
  60 {
  61         elv_completed_request(rq->q, rq);
  62         blk_flush_complete_seq(rq->q, QUEUE_FSEQ_PREFLUSH, error);
  63 }
  64
  65 static void flush_data_end_io(struct request *rq, int error)
  66 {
  67         elv_completed_request(rq->q, rq);
  68         blk_flush_complete_seq(rq->q, QUEUE_FSEQ_DATA, error);
  69 }
  70
  71 static void post_flush_end_io(struct request *rq, int error)
  72 {
  73         elv_completed_request(rq->q, rq);
  74         blk_flush_complete_seq(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
  75 }
  76
  77 static void init_flush_request(struct request *rq, struct gendisk *disk)
  78 {
  79         rq->cmd_type = REQ_TYPE_FS;
  80         rq->cmd_flags = WRITE_FLUSH;
  81         rq->rq_disk = disk;
  82 }
  83
  84 static struct request *queue_next_fseq(struct request_queue *q)
  85 {
  86         struct request *orig_rq = q->orig_flush_rq;
  87         struct request *rq = &q->flush_rq;
  88
  89         blk_rq_init(q, rq);
  90
  91         switch (blk_flush_cur_seq(q)) {
  92         case QUEUE_FSEQ_PREFLUSH:
  93                 init_flush_request(rq, orig_rq->rq_disk);
  94                 rq->end_io = pre_flush_end_io;
  95                 break;
  96         case QUEUE_FSEQ_DATA:
  97                 init_request_from_bio(rq, orig_rq->bio);
  98                 rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
  99                 rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
 100                 rq->end_io = flush_data_end_io;
 101                 break;
 102         case QUEUE_FSEQ_POSTFLUSH:
 103                 init_flush_request(rq, orig_rq->rq_disk);
 104                 rq->end_io = post_flush_end_io;
 105                 break;
 106         default:
 107                 BUG();
 108         }
 109
 110         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 111         return rq;
 112 }
 113
 114 struct request *blk_do_flush(struct request_queue *q, struct request *rq)
 115 {
 116         unsigned int fflags = q->flush_flags; /* may change, cache it */
 117         bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
 118         bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
 119         bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
 120         unsigned skip = 0;
 121
 122         /*
 123          * Special case.  If there's data but flush is not necessary,
 124          * the request can be issued directly.
 125          *
 126          * Flush w/o data should be able to be issued directly too but
 127          * currently some drivers assume that rq->bio contains
 128          * non-zero data if it isn't NULL and empty FLUSH requests
 129          * getting here usually have bio's without data.
 130          */
 131         if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
 132                 rq->cmd_flags &= ~REQ_FLUSH;
 133                 if (!has_fua)
 134                         rq->cmd_flags &= ~REQ_FUA;
 135                 return rq;
 136         }
 137
 138         /*
 139          * Sequenced flushes can't be processed in parallel.  If
 140          * another one is already in progress, queue for later
 141          * processing.
 142          */
 143         if (q->flush_seq) {
 144                 list_move_tail(&rq->queuelist, &q->pending_flushes);
 145                 return NULL;
 146         }
 147
 148         /*
 149          * Start a new flush sequence
 150          */
 151         q->flush_err = 0;
 152         q->flush_seq |= QUEUE_FSEQ_STARTED;
 153
 154         /* adjust FLUSH/FUA of the original request and stash it away */
 155         rq->cmd_flags &= ~REQ_FLUSH;
 156         if (!has_fua)
 157                 rq->cmd_flags &= ~REQ_FUA;
 158         blk_dequeue_request(rq);
 159         q->orig_flush_rq = rq;
 160
 161         /* skip unneded sequences and return the first one */
 162         if (!do_preflush)
 163                 skip |= QUEUE_FSEQ_PREFLUSH;
 164         if (!blk_rq_sectors(rq))
 165                 skip |= QUEUE_FSEQ_DATA;
 166         if (!do_postflush)
 167                 skip |= QUEUE_FSEQ_POSTFLUSH;
 168         return blk_flush_complete_seq(q, skip, 0);
 169 }
 170
 171 static void bio_end_empty_barrier(struct bio *bio, int err)
 172 {
 173         if (err) {
 174                 if (err == -EOPNOTSUPP)
 175                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 176                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 177         }
 178         if (bio->bi_private)
 179                 complete(bio->bi_private);
 180         bio_put(bio);
 181 }
 182
 183 /**
 184  * blkdev_issue_flush - queue a flush
 185  * @bdev:       blockdev to issue flush for
 186  * @gfp_mask:   memory allocation flags (for bio_alloc)
 187  * @error_sector:       error sector
 188  * @flags:      BLKDEV_IFL_* flags to control behaviour
 189  *
 190  * Description:
 191  *    Issue a flush for the block device in question. Caller can supply
 192  *    room for storing the error offset in case of a flush error, if they
 193  *    wish to. If WAIT flag is not passed then caller may check only what
 194  *    request was pushed in some internal queue for later handling.
 195  */
 196 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 197                 sector_t *error_sector, unsigned long flags)
 198 {
 199         DECLARE_COMPLETION_ONSTACK(wait);
 200         struct request_queue *q;
 201         struct bio *bio;
 202         int ret = 0;
 203
 204         if (bdev->bd_disk == NULL)
 205                 return -ENXIO;
 206
 207         q = bdev_get_queue(bdev);
 208         if (!q)
 209                 return -ENXIO;
 210
 211         /*
 212          * some block devices may not have their queue correctly set up here
 213          * (e.g. loop device without a backing file) and so issuing a flush
 214          * here will panic. Ensure there is a request function before issuing
 215          * the barrier.
 216          */
 217         if (!q->make_request_fn)
 218                 return -ENXIO;
 219
 220         bio = bio_alloc(gfp_mask, 0);
 221         bio->bi_end_io = bio_end_empty_barrier;
 222         bio->bi_bdev = bdev;
 223         if (test_bit(BLKDEV_WAIT, &flags))
 224                 bio->bi_private = &wait;
 225
 226         bio_get(bio);
 227         submit_bio(WRITE_BARRIER, bio);
 228         if (test_bit(BLKDEV_WAIT, &flags)) {
 229                 wait_for_completion(&wait);
 230                 /*
 231                  * The driver must store the error location in ->bi_sector, if
 232                  * it supports it. For non-stacked drivers, this should be
 233                  * copied from blk_rq_pos(rq).
 234                  */
 235                 if (error_sector)
 236                         *error_sector = bio->bi_sector;
 237         }
 238
 239         if (bio_flagged(bio, BIO_EOPNOTSUPP))
 240                 ret = -EOPNOTSUPP;
 241         else if (!bio_flagged(bio, BIO_UPTODATE))
 242                 ret = -EIO;
 243
 244         bio_put(bio);
 245         return ret;
 246 }
 247 EXPORT_SYMBOL(blkdev_issue_flush);