fs/bio.c

   1 /*
   2  * Copyright (C) 2001 Jens Axboe <axboe@suse.de>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public Licens
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
  17  *
  18  */
  19 #include <linux/mm.h>
  20 #include <linux/bio.h>
  21 #include <linux/blk.h>
  22 #include <linux/slab.h>
  23 #include <linux/init.h>
  24 #include <linux/kernel.h>
  25 #include <linux/module.h>
  26 #include <linux/mempool.h>
  27
  28 #define BIO_POOL_SIZE 256
  29
  30 static mempool_t *bio_pool;
  31 static kmem_cache_t *bio_slab;
  32
  33 #define BIOVEC_NR_POOLS 6
  34
  35 struct biovec_pool {
  36         int nr_vecs;
  37         char *name;
  38         kmem_cache_t *slab;
  39         mempool_t *pool;
  40 };
  41
  42 /*
  43  * if you change this list, also change bvec_alloc or things will
  44  * break badly! cannot be bigger than what you can fit into an
  45  * unsigned short
  46  */
  47
  48 #define BV(x) { x, "biovec-" #x }
  49 static struct biovec_pool bvec_array[BIOVEC_NR_POOLS] = {
  50         BV(1), BV(4), BV(16), BV(64), BV(128), BV(BIO_MAX_PAGES),
  51 };
  52 #undef BV
  53
  54 static void *slab_pool_alloc(int gfp_mask, void *data)
  55 {
  56         return kmem_cache_alloc(data, gfp_mask);
  57 }
  58
  59 static void slab_pool_free(void *ptr, void *data)
  60 {
  61         kmem_cache_free(data, ptr);
  62 }
  63
  64 static inline struct bio_vec *bvec_alloc(int gfp_mask, int nr, unsigned long *idx)
  65 {
  66         struct biovec_pool *bp;
  67         struct bio_vec *bvl;
  68
  69         /*
  70          * see comment near bvec_array define!
  71          */
  72         switch (nr) {
  73                 case   1        : *idx = 0; break;
  74                 case   2 ...   4: *idx = 1; break;
  75                 case   5 ...  16: *idx = 2; break;
  76                 case  17 ...  64: *idx = 3; break;
  77                 case  65 ... 128: *idx = 4; break;
  78                 case 129 ... BIO_MAX_PAGES: *idx = 5; break;
  79                 default:
  80                         return NULL;
  81         }
  82         /*
  83          * idx now points to the pool we want to allocate from
  84          */
  85         bp = bvec_array + *idx;
  86
  87         bvl = mempool_alloc(bp->pool, gfp_mask);
  88         if (bvl)
  89                 memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));
  90         return bvl;
  91 }
  92
  93 /*
  94  * default destructor for a bio allocated with bio_alloc()
  95  */
  96 void bio_destructor(struct bio *bio)
  97 {
  98         const int pool_idx = BIO_POOL_IDX(bio);
  99         struct biovec_pool *bp = bvec_array + pool_idx;
 100
 101         BIO_BUG_ON(pool_idx >= BIOVEC_NR_POOLS);
 102
 103         /*
 104          * cloned bio doesn't own the veclist
 105          */
 106         if (!bio_flagged(bio, BIO_CLONED))
 107                 mempool_free(bio->bi_io_vec, bp->pool);
 108
 109         mempool_free(bio, bio_pool);
 110 }
 111
 112 inline void bio_init(struct bio *bio)
 113 {
 114         bio->bi_next = NULL;
 115         bio->bi_flags = 1 << BIO_UPTODATE;
 116         bio->bi_rw = 0;
 117         bio->bi_vcnt = 0;
 118         bio->bi_idx = 0;
 119         bio->bi_phys_segments = 0;
 120         bio->bi_hw_segments = 0;
 121         bio->bi_size = 0;
 122         bio->bi_max_vecs = 0;
 123         bio->bi_end_io = NULL;
 124         atomic_set(&bio->bi_cnt, 1);
 125         bio->bi_private = NULL;
 126 }
 127
 128 /**
 129  * bio_alloc - allocate a bio for I/O
 130  * @gfp_mask:   the GFP_ mask given to the slab allocator
 131  * @nr_iovecs:  number of iovecs to pre-allocate
 132  *
 133  * Description:
 134  *   bio_alloc will first try it's on mempool to satisfy the allocation.
 135  *   If %__GFP_WAIT is set then we will block on the internal pool waiting
 136  *   for a &struct bio to become free.
 137  **/
 138 struct bio *bio_alloc(int gfp_mask, int nr_iovecs)
 139 {
 140         int pf_flags = current->flags;
 141         struct bio_vec *bvl = NULL;
 142         unsigned long idx;
 143         struct bio *bio;
 144
 145         current->flags |= PF_NOWARN;
 146         bio = mempool_alloc(bio_pool, gfp_mask);
 147         if (unlikely(!bio))
 148                 goto out;
 149
 150         bio_init(bio);
 151
 152         if (unlikely(!nr_iovecs))
 153                 goto noiovec;
 154
 155         bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx);
 156         if (bvl) {
 157                 bio->bi_flags |= idx << BIO_POOL_OFFSET;
 158                 bio->bi_max_vecs = bvec_array[idx].nr_vecs;
 159 noiovec:
 160                 bio->bi_io_vec = bvl;
 161                 bio->bi_destructor = bio_destructor;
 162 out:
 163                 current->flags = pf_flags;
 164                 return bio;
 165         }
 166
 167         mempool_free(bio, bio_pool);
 168         bio = NULL;
 169         goto out;
 170 }
 171
 172 /**
 173  * bio_put - release a reference to a bio
 174  * @bio:   bio to release reference to
 175  *
 176  * Description:
 177  *   Put a reference to a &struct bio, either one you have gotten with
 178  *   bio_alloc or bio_get. The last put of a bio will free it.
 179  **/
 180 void bio_put(struct bio *bio)
 181 {
 182         BIO_BUG_ON(!atomic_read(&bio->bi_cnt));
 183
 184         /*
 185          * last put frees it
 186          */
 187         if (atomic_dec_and_test(&bio->bi_cnt)) {
 188                 bio->bi_next = NULL;
 189                 bio->bi_destructor(bio);
 190         }
 191 }
 192
 193 inline int bio_phys_segments(request_queue_t *q, struct bio *bio)
 194 {
 195         if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
 196                 blk_recount_segments(q, bio);
 197
 198         return bio->bi_phys_segments;
 199 }
 200
 201 inline int bio_hw_segments(request_queue_t *q, struct bio *bio)
 202 {
 203         if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
 204                 blk_recount_segments(q, bio);
 205
 206         return bio->bi_hw_segments;
 207 }
 208
 209 /**
 210  *      __bio_clone     -       clone a bio
 211  *      @bio: destination bio
 212  *      @bio_src: bio to clone
 213  *
 214  *      Clone a &bio. Caller will own the returned bio, but not
 215  *      the actual data it points to. Reference count of returned
 216  *      bio will be one.
 217  */
 218 inline void __bio_clone(struct bio *bio, struct bio *bio_src)
 219 {
 220         bio->bi_io_vec = bio_src->bi_io_vec;
 221
 222         bio->bi_sector = bio_src->bi_sector;
 223         bio->bi_bdev = bio_src->bi_bdev;
 224         bio->bi_flags |= 1 << BIO_CLONED;
 225         bio->bi_rw = bio_src->bi_rw;
 226
 227         /*
 228          * notes -- maybe just leave bi_idx alone. assume identical mapping
 229          * for the clone
 230          */
 231         bio->bi_vcnt = bio_src->bi_vcnt;
 232         bio->bi_idx = bio_src->bi_idx;
 233         if (bio_flagged(bio, BIO_SEG_VALID)) {
 234                 bio->bi_phys_segments = bio_src->bi_phys_segments;
 235                 bio->bi_hw_segments = bio_src->bi_hw_segments;
 236                 bio->bi_flags |= (1 << BIO_SEG_VALID);
 237         }
 238         bio->bi_size = bio_src->bi_size;
 239
 240         /*
 241          * cloned bio does not own the bio_vec, so users cannot fiddle with
 242          * it. clear bi_max_vecs and clear the BIO_POOL_BITS to make this
 243          * apparent
 244          */
 245         bio->bi_max_vecs = 0;
 246         bio->bi_flags &= (BIO_POOL_MASK - 1);
 247 }
 248
 249 /**
 250  *      bio_clone       -       clone a bio
 251  *      @bio: bio to clone
 252  *      @gfp_mask: allocation priority
 253  *
 254  *      Like __bio_clone, only also allocates the returned bio
 255  */
 256 struct bio *bio_clone(struct bio *bio, int gfp_mask)
 257 {
 258         struct bio *b = bio_alloc(gfp_mask, 0);
 259
 260         if (b)
 261                 __bio_clone(b, bio);
 262
 263         return b;
 264 }
 265
 266 /**
 267  *      bio_copy        -       create copy of a bio
 268  *      @bio: bio to copy
 269  *      @gfp_mask: allocation priority
 270  *      @copy: copy data to allocated bio
 271  *
 272  *      Create a copy of a &bio. Caller will own the returned bio and
 273  *      the actual data it points to. Reference count of returned
 274  *      bio will be one.
 275  */
 276 struct bio *bio_copy(struct bio *bio, int gfp_mask, int copy)
 277 {
 278         struct bio *b = bio_alloc(gfp_mask, bio->bi_vcnt);
 279         unsigned long flags = 0; /* gcc silly */
 280         struct bio_vec *bv;
 281         int i;
 282
 283         if (unlikely(!b))
 284                 return NULL;
 285
 286         /*
 287          * iterate iovec list and alloc pages + copy data
 288          */
 289         __bio_for_each_segment(bv, bio, i, 0) {
 290                 struct bio_vec *bbv = &b->bi_io_vec[i];
 291                 char *vfrom, *vto;
 292
 293                 bbv->bv_page = alloc_page(gfp_mask);
 294                 if (bbv->bv_page == NULL)
 295                         goto oom;
 296
 297                 bbv->bv_len = bv->bv_len;
 298                 bbv->bv_offset = bv->bv_offset;
 299
 300                 /*
 301                  * if doing a copy for a READ request, no need
 302                  * to memcpy page data
 303                  */
 304                 if (!copy)
 305                         continue;
 306
 307                 if (gfp_mask & __GFP_WAIT) {
 308                         vfrom = kmap(bv->bv_page);
 309                         vto = kmap(bbv->bv_page);
 310                 } else {
 311                         local_irq_save(flags);
 312                         vfrom = kmap_atomic(bv->bv_page, KM_BIO_SRC_IRQ);
 313                         vto = kmap_atomic(bbv->bv_page, KM_BIO_DST_IRQ);
 314                 }
 315
 316                 memcpy(vto + bbv->bv_offset, vfrom + bv->bv_offset, bv->bv_len);
 317                 if (gfp_mask & __GFP_WAIT) {
 318                         kunmap(bbv->bv_page);
 319                         kunmap(bv->bv_page);
 320                 } else {
 321                         kunmap_atomic(vto, KM_BIO_DST_IRQ);
 322                         kunmap_atomic(vfrom, KM_BIO_SRC_IRQ);
 323                         local_irq_restore(flags);
 324                 }
 325         }
 326
 327         b->bi_sector = bio->bi_sector;
 328         b->bi_bdev = bio->bi_bdev;
 329         b->bi_rw = bio->bi_rw;
 330
 331         b->bi_vcnt = bio->bi_vcnt;
 332         b->bi_size = bio->bi_size;
 333
 334         return b;
 335
 336 oom:
 337         while (--i >= 0)
 338                 __free_page(b->bi_io_vec[i].bv_page);
 339
 340         mempool_free(b, bio_pool);
 341         return NULL;
 342 }
 343
 344 /**
 345  *      bio_get_nr_vecs         - return approx number of vecs
 346  *      @bdev:  I/O target
 347  *
 348  *      Return the approximate number of pages we can send to this target.
 349  *      There's no guarentee that you will be able to fit this number of pages
 350  *      into a bio, it does not account for dynamic restrictions that vary
 351  *      on offset.
 352  */
 353 int bio_get_nr_vecs(struct block_device *bdev)
 354 {
 355         request_queue_t *q = bdev_get_queue(bdev);
 356         int nr_pages;
 357
 358         nr_pages = ((q->max_sectors << 9) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 359         if (nr_pages > q->max_phys_segments)
 360                 nr_pages = q->max_phys_segments;
 361         if (nr_pages > q->max_hw_segments)
 362                 nr_pages = q->max_hw_segments;
 363
 364         return nr_pages;
 365 }
 366
 367 /**
 368  *      bio_add_page    -       attempt to add page to bio
 369  *      @bio: destination bio
 370  *      @page: page to add
 371  *      @len: vec entry length
 372  *      @offset: vec entry offset
 373  *
 374  *      Attempt to add a page to the bio_vec maplist. This can fail for a
 375  *      number of reasons, such as the bio being full or target block
 376  *      device limitations.
 377  */
 378 int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
 379                  unsigned int offset)
 380 {
 381         request_queue_t *q = bdev_get_queue(bio->bi_bdev);
 382         int fail_segments = 0, retried_segments = 0;
 383         struct bio_vec *bvec;
 384
 385         /*
 386          * cloned bio must not modify vec list
 387          */
 388         if (unlikely(bio_flagged(bio, BIO_CLONED)))
 389                 return 0;
 390
 391         if (bio->bi_vcnt >= bio->bi_max_vecs)
 392                 return 0;
 393
 394         if (((bio->bi_size + len) >> 9) > q->max_sectors)
 395                 return 0;
 396
 397         /*
 398          * we might loose a segment or two here, but rather that than
 399          * make this too complex.
 400          */
 401 retry_segments:
 402         if (bio_phys_segments(q, bio) >= q->max_phys_segments
 403             || bio_hw_segments(q, bio) >= q->max_hw_segments)
 404                 fail_segments = 1;
 405
 406         if (fail_segments) {
 407                 if (retried_segments)
 408                         return 0;
 409
 410                 bio->bi_flags &= ~(1 << BIO_SEG_VALID);
 411                 retried_segments = 1;
 412                 goto retry_segments;
 413         }
 414
 415         /*
 416          * setup the new entry, we might clear it again later if we
 417          * cannot add the page
 418          */
 419         bvec = &bio->bi_io_vec[bio->bi_vcnt];
 420         bvec->bv_page = page;
 421         bvec->bv_len = len;
 422         bvec->bv_offset = offset;
 423
 424         /*
 425          * if queue has other restrictions (eg varying max sector size
 426          * depending on offset), it can specify a merge_bvec_fn in the
 427          * queue to get further control
 428          */
 429         if (q->merge_bvec_fn) {
 430                 /*
 431                  * merge_bvec_fn() returns number of bytes it can accept
 432                  * at this offset
 433                  */
 434                 if (q->merge_bvec_fn(q, bio, bvec) < len) {
 435                         bvec->bv_page = NULL;
 436                         bvec->bv_len = 0;
 437                         bvec->bv_offset = 0;
 438                         return 0;
 439                 }
 440         }
 441
 442         bio->bi_vcnt++;
 443         bio->bi_phys_segments++;
 444         bio->bi_hw_segments++;
 445         bio->bi_size += len;
 446         return len;
 447 }
 448
 449 /**
 450  *      bio_map_user    -       map user address into bio
 451  *      @bdev: destination block device
 452  *      @uaddr: start of user address
 453  *      @len: length in bytes
 454  *      @write_to_vm: bool indicating writing to pages or not
 455  *
 456  *      Map the user space address into a bio suitable for io to a block
 457  *      device. Caller should check the size of the returned bio, we might
 458  *      not have mapped the entire range specified.
 459  */
 460 struct bio *bio_map_user(struct block_device *bdev, unsigned long uaddr,
 461                          unsigned int len, int write_to_vm)
 462 {
 463         unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 464         unsigned long start = uaddr >> PAGE_SHIFT;
 465         const int nr_pages = end - start;
 466         request_queue_t *q = bdev_get_queue(bdev);
 467         int ret, offset, i;
 468         struct page **pages;
 469         struct bio *bio;
 470
 471         /*
 472          * transfer and buffer must be aligned to at least hardsector
 473          * size for now, in the future we can relax this restriction
 474          */
 475         if ((uaddr & queue_dma_alignment(q)) || (len & queue_dma_alignment(q)))
 476                 return NULL;
 477
 478         bio = bio_alloc(GFP_KERNEL, nr_pages);
 479         if (!bio)
 480                 return NULL;
 481
 482         pages = kmalloc(nr_pages * sizeof(struct page *), GFP_KERNEL);
 483         if (!pages)
 484                 goto out;
 485
 486         down_read(&current->mm->mmap_sem);
 487         ret = get_user_pages(current, current->mm, uaddr, nr_pages,
 488                                                 write_to_vm, 0, pages, NULL);
 489         up_read(&current->mm->mmap_sem);
 490
 491         if (ret < nr_pages)
 492                 goto out;
 493
 494         bio->bi_bdev = bdev;
 495
 496         offset = uaddr & ~PAGE_MASK;
 497         for (i = 0; i < nr_pages; i++) {
 498                 unsigned int bytes = PAGE_SIZE - offset;
 499
 500                 if (len <= 0)
 501                         break;
 502
 503                 if (bytes > len)
 504                         bytes = len;
 505
 506                 /*
 507                  * sorry...
 508                  */
 509                 if (bio_add_page(bio, pages[i], bytes, offset) < bytes)
 510                         break;
 511
 512                 len -= bytes;
 513                 offset = 0;
 514         }
 515
 516         /*
 517          * release the pages we didn't map into the bio, if any
 518          */
 519         while (i < nr_pages)
 520                 page_cache_release(pages[i++]);
 521
 522         kfree(pages);
 523
 524         /*
 525          * check if the mapped pages need bouncing for an isa host.
 526          */
 527         blk_queue_bounce(q, &bio);
 528         return bio;
 529 out:
 530         kfree(pages);
 531         bio_put(bio);
 532         return NULL;
 533 }
 534
 535 /**
 536  *      bio_unmap_user  -       unmap a bio
 537  *      @bio:           the bio being unmapped
 538  *      @write_to_vm:   bool indicating whether pages were written to
 539  *
 540  *      Unmap a bio previously mapped by bio_map_user(). The @write_to_vm
 541  *      must be the same as passed into bio_map_user(). Must be called with
 542  *      a process context.
 543  */
 544 void bio_unmap_user(struct bio *bio, int write_to_vm)
 545 {
 546         struct bio_vec *bvec;
 547         int i;
 548
 549         /*
 550          * find original bio if it was bounced
 551          */
 552         if (bio->bi_private) {
 553                 /*
 554                  * someone stole our bio, must not happen
 555                  */
 556                 BUG_ON(!bio_flagged(bio, BIO_BOUNCED));
 557
 558                 bio = bio->bi_private;
 559         }
 560
 561         /*
 562          * make sure we dirty pages we wrote to
 563          */
 564         __bio_for_each_segment(bvec, bio, i, 0) {
 565                 if (write_to_vm)
 566                         set_page_dirty(bvec->bv_page);
 567
 568                 page_cache_release(bvec->bv_page);
 569         }
 570
 571         bio_put(bio);
 572  }
 573
 574 /**
 575  * bio_endio - end I/O on a bio
 576  * @bio:        bio
 577  * @bytes_done: number of bytes completed
 578  * @error:      error, if any
 579  *
 580  * Description:
 581  *   bio_endio() will end I/O on @bytes_done number of bytes. This may be
 582  *   just a partial part of the bio, or it may be the whole bio. bio_endio()
 583  *   is the preferred way to end I/O on a bio, it takes care of decrementing
 584  *   bi_size and clearing BIO_UPTODATE on error. @error is 0 on success, and
 585  *   and one of the established -Exxxx (-EIO, for instance) error values in
 586  *   case something went wrong. Noone should call bi_end_io() directly on
 587  *   a bio unless they own it and thus know that it has an end_io function.
 588  **/
 589 void bio_endio(struct bio *bio, unsigned int bytes_done, int error)
 590 {
 591         if (error)
 592                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
 593
 594         if (unlikely(bytes_done > bio->bi_size)) {
 595                 printk("%s: want %u bytes done, only %u left\n", __FUNCTION__,
 596                                                 bytes_done, bio->bi_size);
 597                 bytes_done = bio->bi_size;
 598         }
 599
 600         bio->bi_size -= bytes_done;
 601
 602         if (bio->bi_end_io)
 603                 bio->bi_end_io(bio, bytes_done, error);
 604 }
 605
 606 static void __init biovec_init_pools(void)
 607 {
 608         int i, size, megabytes, pool_entries = BIO_POOL_SIZE;
 609         int scale = BIOVEC_NR_POOLS;
 610
 611         megabytes = nr_free_pages() >> (20 - PAGE_SHIFT);
 612
 613         /*
 614          * find out where to start scaling
 615          */
 616         if (megabytes <= 16)
 617                 scale = 0;
 618         else if (megabytes <= 32)
 619                 scale = 1;
 620         else if (megabytes <= 64)
 621                 scale = 2;
 622         else if (megabytes <= 96)
 623                 scale = 3;
 624         else if (megabytes <= 128)
 625                 scale = 4;
 626
 627         /*
 628          * scale number of entries
 629          */
 630         pool_entries = megabytes * 2;
 631         if (pool_entries > 256)
 632                 pool_entries = 256;
 633
 634         for (i = 0; i < BIOVEC_NR_POOLS; i++) {
 635                 struct biovec_pool *bp = bvec_array + i;
 636
 637                 size = bp->nr_vecs * sizeof(struct bio_vec);
 638
 639                 bp->slab = kmem_cache_create(bp->name, size, 0,
 640                                                 SLAB_HWCACHE_ALIGN, NULL, NULL);
 641                 if (!bp->slab)
 642                         panic("biovec: can't init slab cache\n");
 643
 644                 if (i >= scale)
 645                         pool_entries >>= 1;
 646
 647                 bp->pool = mempool_create(pool_entries, slab_pool_alloc,
 648                                         slab_pool_free, bp->slab);
 649                 if (!bp->pool)
 650                         panic("biovec: can't init mempool\n");
 651
 652                 printk("biovec pool[%d]: %3d bvecs: %3d entries (%d bytes)\n",
 653                                                 i, bp->nr_vecs, pool_entries,
 654                                                 size);
 655         }
 656 }
 657
 658 static int __init init_bio(void)
 659 {
 660         bio_slab = kmem_cache_create("bio", sizeof(struct bio), 0,
 661                                         SLAB_HWCACHE_ALIGN, NULL, NULL);
 662         if (!bio_slab)
 663                 panic("bio: can't create slab cache\n");
 664         bio_pool = mempool_create(BIO_POOL_SIZE, slab_pool_alloc, slab_pool_free, bio_slab);
 665         if (!bio_pool)
 666                 panic("bio: can't create mempool\n");
 667
 668         printk("BIO: pool of %d setup, %ZuKb (%Zd bytes/bio)\n", BIO_POOL_SIZE, BIO_POOL_SIZE * sizeof(struct bio) >> 10, sizeof(struct bio));
 669
 670         biovec_init_pools();
 671
 672         return 0;
 673 }
 674
 675 subsys_initcall(init_bio);
 676
 677 EXPORT_SYMBOL(bio_alloc);
 678 EXPORT_SYMBOL(bio_put);
 679 EXPORT_SYMBOL(bio_endio);
 680 EXPORT_SYMBOL(bio_init);
 681 EXPORT_SYMBOL(bio_copy);
 682 EXPORT_SYMBOL(__bio_clone);
 683 EXPORT_SYMBOL(bio_clone);
 684 EXPORT_SYMBOL(bio_phys_segments);
 685 EXPORT_SYMBOL(bio_hw_segments);
 686 EXPORT_SYMBOL(bio_add_page);
 687 EXPORT_SYMBOL(bio_get_nr_vecs);
 688 EXPORT_SYMBOL(bio_map_user);
 689 EXPORT_SYMBOL(bio_unmap_user);