1 /* 2 * fs/direct-io.c 3 * 4 * Copyright (C) 2002, Linus Torvalds. 5 * 6 * O_DIRECT 7 * 8 * 04Jul2002 Andrew Morton 9 * Initial version 10 * 11Sep2002 janetinc@us.ibm.com 11 * added readv/writev support. 12 * 29Oct2002 Andrew Morton 13 * rewrote bio_add_page() support. 14 * 30Oct2002 pbadari@us.ibm.com 15 * added support for non-aligned IO. 16 * 06Nov2002 pbadari@us.ibm.com 17 * added asynchronous IO support. 18 * 21Jul2003 nathans@sgi.com 19 * added IO completion notifier. 20 */ 21 22 #include <linux/kernel.h> 23 #include <linux/module.h> 24 #include <linux/types.h> 25 #include <linux/fs.h> 26 #include <linux/mm.h> 27 #include <linux/slab.h> 28 #include <linux/highmem.h> 29 #include <linux/pagemap.h> 30 #include <linux/task_io_accounting_ops.h> 31 #include <linux/bio.h> 32 #include <linux/wait.h> 33 #include <linux/err.h> 34 #include <linux/blkdev.h> 35 #include <linux/buffer_head.h> 36 #include <linux/rwsem.h> 37 #include <linux/uio.h> 38 #include <asm/atomic.h> 39 40 /* 41 * How many user pages to map in one call to get_user_pages(). This determines 42 * the size of a structure on the stack. 43 */ 44 #define DIO_PAGES 64 45 46 /* 47 * This code generally works in units of "dio_blocks". A dio_block is 48 * somewhere between the hard sector size and the filesystem block size. it 49 * is determined on a per-invocation basis. When talking to the filesystem 50 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity 51 * down by dio->blkfactor. Similarly, fs-blocksize quantities are converted 52 * to bio_block quantities by shifting left by blkfactor. 53 * 54 * If blkfactor is zero then the user's request was aligned to the filesystem's 55 * blocksize. 56 */ 57 58 struct dio { 59 /* BIO submission state */ 60 struct bio *bio; /* bio under assembly */ 61 struct inode *inode; 62 int rw; 63 loff_t i_size; /* i_size when submitted */ 64 int flags; /* doesn't change */ 65 unsigned blkbits; /* doesn't change */ 66 unsigned blkfactor; /* When we're using an alignment which 67 is finer than the filesystem's soft 68 blocksize, this specifies how much 69 finer. blkfactor=2 means 1/4-block 70 alignment. Does not change */ 71 unsigned start_zero_done; /* flag: sub-blocksize zeroing has 72 been performed at the start of a 73 write */ 74 int pages_in_io; /* approximate total IO pages */ 75 size_t size; /* total request size (doesn't change)*/ 76 sector_t block_in_file; /* Current offset into the underlying 77 file in dio_block units. */ 78 unsigned blocks_available; /* At block_in_file. changes */ 79 sector_t final_block_in_request;/* doesn't change */ 80 unsigned first_block_in_page; /* doesn't change, Used only once */ 81 int boundary; /* prev block is at a boundary */ 82 int reap_counter; /* rate limit reaping */ 83 get_block_t *get_block; /* block mapping function */ 84 dio_iodone_t *end_io; /* IO completion function */ 85 sector_t final_block_in_bio; /* current final block in bio + 1 */ 86 sector_t next_block_for_io; /* next block to be put under IO, 87 in dio_blocks units */ 88 struct buffer_head map_bh; /* last get_block() result */ 89 90 /* 91 * Deferred addition of a page to the dio. These variables are 92 * private to dio_send_cur_page(), submit_page_section() and 93 * dio_bio_add_page(). 94 */ 95 struct page *cur_page; /* The page */ 96 unsigned cur_page_offset; /* Offset into it, in bytes */ 97 unsigned cur_page_len; /* Nr of bytes at cur_page_offset */ 98 sector_t cur_page_block; /* Where it starts */ 99 100 /* BIO completion state */ 101 spinlock_t bio_lock; /* protects BIO fields below */ 102 unsigned long refcount; /* direct_io_worker() and bios */ 103 struct bio *bio_list; /* singly linked via bi_private */ 104 struct task_struct *waiter; /* waiting task (NULL if none) */ 105 106 /* AIO related stuff */ 107 struct kiocb *iocb; /* kiocb */ 108 int is_async; /* is IO async ? */ 109 int io_error; /* IO error in completion path */ 110 ssize_t result; /* IO result */ 111 112 /* 113 * Page fetching state. These variables belong to dio_refill_pages(). 114 */ 115 int curr_page; /* changes */ 116 int total_pages; /* doesn't change */ 117 unsigned long curr_user_address;/* changes */ 118 119 /* 120 * Page queue. These variables belong to dio_refill_pages() and 121 * dio_get_page(). 122 */ 123 unsigned head; /* next page to process */ 124 unsigned tail; /* last valid page + 1 */ 125 int page_errors; /* errno from get_user_pages() */ 126 127 /* 128 * pages[] (and any fields placed after it) are not zeroed out at 129 * allocation time. Don't add new fields after pages[] unless you 130 * wish that they not be zeroed. 131 */ 132 struct page *pages[DIO_PAGES]; /* page buffer */ 133 }; 134 135 /* 136 * How many pages are in the queue? 137 */ 138 static inline unsigned dio_pages_present(struct dio *dio) 139 { 140 return dio->tail - dio->head; 141 } 142 143 /* 144 * Go grab and pin some userspace pages. Typically we'll get 64 at a time. 145 */ 146 static int dio_refill_pages(struct dio *dio) 147 { 148 int ret; 149 int nr_pages; 150 151 nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES); 152 ret = get_user_pages_fast( 153 dio->curr_user_address, /* Where from? */ 154 nr_pages, /* How many pages? */ 155 dio->rw == READ, /* Write to memory? */ 156 &dio->pages[0]); /* Put results here */ 157 158 if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) { 159 struct page *page = ZERO_PAGE(0); 160 /* 161 * A memory fault, but the filesystem has some outstanding 162 * mapped blocks. We need to use those blocks up to avoid 163 * leaking stale data in the file. 164 */ 165 if (dio->page_errors == 0) 166 dio->page_errors = ret; 167 page_cache_get(page); 168 dio->pages[0] = page; 169 dio->head = 0; 170 dio->tail = 1; 171 ret = 0; 172 goto out; 173 } 174 175 if (ret >= 0) { 176 dio->curr_user_address += ret * PAGE_SIZE; 177 dio->curr_page += ret; 178 dio->head = 0; 179 dio->tail = ret; 180 ret = 0; 181 } 182 out: 183 return ret; 184 } 185 186 /* 187 * Get another userspace page. Returns an ERR_PTR on error. Pages are 188 * buffered inside the dio so that we can call get_user_pages() against a 189 * decent number of pages, less frequently. To provide nicer use of the 190 * L1 cache. 191 */ 192 static struct page *dio_get_page(struct dio *dio) 193 { 194 if (dio_pages_present(dio) == 0) { 195 int ret; 196 197 ret = dio_refill_pages(dio); 198 if (ret) 199 return ERR_PTR(ret); 200 BUG_ON(dio_pages_present(dio) == 0); 201 } 202 return dio->pages[dio->head++]; 203 } 204 205 /** 206 * dio_complete() - called when all DIO BIO I/O has been completed 207 * @offset: the byte offset in the file of the completed operation 208 * 209 * This releases locks as dictated by the locking type, lets interested parties 210 * know that a DIO operation has completed, and calculates the resulting return 211 * code for the operation. 212 * 213 * It lets the filesystem know if it registered an interest earlier via 214 * get_block. Pass the private field of the map buffer_head so that 215 * filesystems can use it to hold additional state between get_block calls and 216 * dio_complete. 217 */ 218 static int dio_complete(struct dio *dio, loff_t offset, int ret) 219 { 220 ssize_t transferred = 0; 221 222 /* 223 * AIO submission can race with bio completion to get here while 224 * expecting to have the last io completed by bio completion. 225 * In that case -EIOCBQUEUED is in fact not an error we want 226 * to preserve through this call. 227 */ 228 if (ret == -EIOCBQUEUED) 229 ret = 0; 230 231 if (dio->result) { 232 transferred = dio->result; 233 234 /* Check for short read case */ 235 if ((dio->rw == READ) && ((offset + transferred) > dio->i_size)) 236 transferred = dio->i_size - offset; 237 } 238 239 if (dio->end_io && dio->result) 240 dio->end_io(dio->iocb, offset, transferred, 241 dio->map_bh.b_private); 242 243 if (dio->flags & DIO_LOCKING) 244 /* lockdep: non-owner release */ 245 up_read_non_owner(&dio->inode->i_alloc_sem); 246 247 if (ret == 0) 248 ret = dio->page_errors; 249 if (ret == 0) 250 ret = dio->io_error; 251 if (ret == 0) 252 ret = transferred; 253 254 return ret; 255 } 256 257 static int dio_bio_complete(struct dio *dio, struct bio *bio); 258 /* 259 * Asynchronous IO callback. 260 */ 261 static void dio_bio_end_aio(struct bio *bio, int error) 262 { 263 struct dio *dio = bio->bi_private; 264 unsigned long remaining; 265 unsigned long flags; 266 267 /* cleanup the bio */ 268 dio_bio_complete(dio, bio); 269 270 spin_lock_irqsave(&dio->bio_lock, flags); 271 remaining = --dio->refcount; 272 if (remaining == 1 && dio->waiter) 273 wake_up_process(dio->waiter); 274 spin_unlock_irqrestore(&dio->bio_lock, flags); 275 276 if (remaining == 0) { 277 int ret = dio_complete(dio, dio->iocb->ki_pos, 0); 278 aio_complete(dio->iocb, ret, 0); 279 kfree(dio); 280 } 281 } 282 283 /* 284 * The BIO completion handler simply queues the BIO up for the process-context 285 * handler. 286 * 287 * During I/O bi_private points at the dio. After I/O, bi_private is used to 288 * implement a singly-linked list of completed BIOs, at dio->bio_list. 289 */ 290 static void dio_bio_end_io(struct bio *bio, int error) 291 { 292 struct dio *dio = bio->bi_private; 293 unsigned long flags; 294 295 spin_lock_irqsave(&dio->bio_lock, flags); 296 bio->bi_private = dio->bio_list; 297 dio->bio_list = bio; 298 if (--dio->refcount == 1 && dio->waiter) 299 wake_up_process(dio->waiter); 300 spin_unlock_irqrestore(&dio->bio_lock, flags); 301 } 302 303 static int 304 dio_bio_alloc(struct dio *dio, struct block_device *bdev, 305 sector_t first_sector, int nr_vecs) 306 { 307 struct bio *bio; 308 309 bio = bio_alloc(GFP_KERNEL, nr_vecs); 310 311 bio->bi_bdev = bdev; 312 bio->bi_sector = first_sector; 313 if (dio->is_async) 314 bio->bi_end_io = dio_bio_end_aio; 315 else 316 bio->bi_end_io = dio_bio_end_io; 317 318 dio->bio = bio; 319 return 0; 320 } 321 322 /* 323 * In the AIO read case we speculatively dirty the pages before starting IO. 324 * During IO completion, any of these pages which happen to have been written 325 * back will be redirtied by bio_check_pages_dirty(). 326 * 327 * bios hold a dio reference between submit_bio and ->end_io. 328 */ 329 static void dio_bio_submit(struct dio *dio) 330 { 331 struct bio *bio = dio->bio; 332 unsigned long flags; 333 334 bio->bi_private = dio; 335 336 spin_lock_irqsave(&dio->bio_lock, flags); 337 dio->refcount++; 338 spin_unlock_irqrestore(&dio->bio_lock, flags); 339 340 if (dio->is_async && dio->rw == READ) 341 bio_set_pages_dirty(bio); 342 343 submit_bio(dio->rw, bio); 344 345 dio->bio = NULL; 346 dio->boundary = 0; 347 } 348 349 /* 350 * Release any resources in case of a failure 351 */ 352 static void dio_cleanup(struct dio *dio) 353 { 354 while (dio_pages_present(dio)) 355 page_cache_release(dio_get_page(dio)); 356 } 357 358 /* 359 * Wait for the next BIO to complete. Remove it and return it. NULL is 360 * returned once all BIOs have been completed. This must only be called once 361 * all bios have been issued so that dio->refcount can only decrease. This 362 * requires that that the caller hold a reference on the dio. 363 */ 364 static struct bio *dio_await_one(struct dio *dio) 365 { 366 unsigned long flags; 367 struct bio *bio = NULL; 368 369 spin_lock_irqsave(&dio->bio_lock, flags); 370 371 /* 372 * Wait as long as the list is empty and there are bios in flight. bio 373 * completion drops the count, maybe adds to the list, and wakes while 374 * holding the bio_lock so we don't need set_current_state()'s barrier 375 * and can call it after testing our condition. 376 */ 377 while (dio->refcount > 1 && dio->bio_list == NULL) { 378 __set_current_state(TASK_UNINTERRUPTIBLE); 379 dio->waiter = current; 380 spin_unlock_irqrestore(&dio->bio_lock, flags); 381 io_schedule(); 382 /* wake up sets us TASK_RUNNING */ 383 spin_lock_irqsave(&dio->bio_lock, flags); 384 dio->waiter = NULL; 385 } 386 if (dio->bio_list) { 387 bio = dio->bio_list; 388 dio->bio_list = bio->bi_private; 389 } 390 spin_unlock_irqrestore(&dio->bio_lock, flags); 391 return bio; 392 } 393 394 /* 395 * Process one completed BIO. No locks are held. 396 */ 397 static int dio_bio_complete(struct dio *dio, struct bio *bio) 398 { 399 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); 400 struct bio_vec *bvec = bio->bi_io_vec; 401 int page_no; 402 403 if (!uptodate) 404 dio->io_error = -EIO; 405 406 if (dio->is_async && dio->rw == READ) { 407 bio_check_pages_dirty(bio); /* transfers ownership */ 408 } else { 409 for (page_no = 0; page_no < bio->bi_vcnt; page_no++) { 410 struct page *page = bvec[page_no].bv_page; 411 412 if (dio->rw == READ && !PageCompound(page)) 413 set_page_dirty_lock(page); 414 page_cache_release(page); 415 } 416 bio_put(bio); 417 } 418 return uptodate ? 0 : -EIO; 419 } 420 421 /* 422 * Wait on and process all in-flight BIOs. This must only be called once 423 * all bios have been issued so that the refcount can only decrease. 424 * This just waits for all bios to make it through dio_bio_complete. IO 425 * errors are propagated through dio->io_error and should be propagated via 426 * dio_complete(). 427 */ 428 static void dio_await_completion(struct dio *dio) 429 { 430 struct bio *bio; 431 do { 432 bio = dio_await_one(dio); 433 if (bio) 434 dio_bio_complete(dio, bio); 435 } while (bio); 436 } 437 438 /* 439 * A really large O_DIRECT read or write can generate a lot of BIOs. So 440 * to keep the memory consumption sane we periodically reap any completed BIOs 441 * during the BIO generation phase. 442 * 443 * This also helps to limit the peak amount of pinned userspace memory. 444 */ 445 static int dio_bio_reap(struct dio *dio) 446 { 447 int ret = 0; 448 449 if (dio->reap_counter++ >= 64) { 450 while (dio->bio_list) { 451 unsigned long flags; 452 struct bio *bio; 453 int ret2; 454 455 spin_lock_irqsave(&dio->bio_lock, flags); 456 bio = dio->bio_list; 457 dio->bio_list = bio->bi_private; 458 spin_unlock_irqrestore(&dio->bio_lock, flags); 459 ret2 = dio_bio_complete(dio, bio); 460 if (ret == 0) 461 ret = ret2; 462 } 463 dio->reap_counter = 0; 464 } 465 return ret; 466 } 467 468 /* 469 * Call into the fs to map some more disk blocks. We record the current number 470 * of available blocks at dio->blocks_available. These are in units of the 471 * fs blocksize, (1 << inode->i_blkbits). 472 * 473 * The fs is allowed to map lots of blocks at once. If it wants to do that, 474 * it uses the passed inode-relative block number as the file offset, as usual. 475 * 476 * get_block() is passed the number of i_blkbits-sized blocks which direct_io 477 * has remaining to do. The fs should not map more than this number of blocks. 478 * 479 * If the fs has mapped a lot of blocks, it should populate bh->b_size to 480 * indicate how much contiguous disk space has been made available at 481 * bh->b_blocknr. 482 * 483 * If *any* of the mapped blocks are new, then the fs must set buffer_new(). 484 * This isn't very efficient... 485 * 486 * In the case of filesystem holes: the fs may return an arbitrarily-large 487 * hole by returning an appropriate value in b_size and by clearing 488 * buffer_mapped(). However the direct-io code will only process holes one 489 * block at a time - it will repeatedly call get_block() as it walks the hole. 490 */ 491 static int get_more_blocks(struct dio *dio) 492 { 493 int ret; 494 struct buffer_head *map_bh = &dio->map_bh; 495 sector_t fs_startblk; /* Into file, in filesystem-sized blocks */ 496 unsigned long fs_count; /* Number of filesystem-sized blocks */ 497 unsigned long dio_count;/* Number of dio_block-sized blocks */ 498 unsigned long blkmask; 499 int create; 500 501 /* 502 * If there was a memory error and we've overwritten all the 503 * mapped blocks then we can now return that memory error 504 */ 505 ret = dio->page_errors; 506 if (ret == 0) { 507 BUG_ON(dio->block_in_file >= dio->final_block_in_request); 508 fs_startblk = dio->block_in_file >> dio->blkfactor; 509 dio_count = dio->final_block_in_request - dio->block_in_file; 510 fs_count = dio_count >> dio->blkfactor; 511 blkmask = (1 << dio->blkfactor) - 1; 512 if (dio_count & blkmask) 513 fs_count++; 514 515 map_bh->b_state = 0; 516 map_bh->b_size = fs_count << dio->inode->i_blkbits; 517 518 /* 519 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we 520 * forbid block creations: only overwrites are permitted. 521 * We will return early to the caller once we see an 522 * unmapped buffer head returned, and the caller will fall 523 * back to buffered I/O. 524 * 525 * Otherwise the decision is left to the get_blocks method, 526 * which may decide to handle it or also return an unmapped 527 * buffer head. 528 */ 529 create = dio->rw & WRITE; 530 if (dio->flags & DIO_SKIP_HOLES) { 531 if (dio->block_in_file < (i_size_read(dio->inode) >> 532 dio->blkbits)) 533 create = 0; 534 } 535 536 ret = (*dio->get_block)(dio->inode, fs_startblk, 537 map_bh, create); 538 } 539 return ret; 540 } 541 542 /* 543 * There is no bio. Make one now. 544 */ 545 static int dio_new_bio(struct dio *dio, sector_t start_sector) 546 { 547 sector_t sector; 548 int ret, nr_pages; 549 550 ret = dio_bio_reap(dio); 551 if (ret) 552 goto out; 553 sector = start_sector << (dio->blkbits - 9); 554 nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev)); 555 BUG_ON(nr_pages <= 0); 556 ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages); 557 dio->boundary = 0; 558 out: 559 return ret; 560 } 561 562 /* 563 * Attempt to put the current chunk of 'cur_page' into the current BIO. If 564 * that was successful then update final_block_in_bio and take a ref against 565 * the just-added page. 566 * 567 * Return zero on success. Non-zero means the caller needs to start a new BIO. 568 */ 569 static int dio_bio_add_page(struct dio *dio) 570 { 571 int ret; 572 573 ret = bio_add_page(dio->bio, dio->cur_page, 574 dio->cur_page_len, dio->cur_page_offset); 575 if (ret == dio->cur_page_len) { 576 /* 577 * Decrement count only, if we are done with this page 578 */ 579 if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE) 580 dio->pages_in_io--; 581 page_cache_get(dio->cur_page); 582 dio->final_block_in_bio = dio->cur_page_block + 583 (dio->cur_page_len >> dio->blkbits); 584 ret = 0; 585 } else { 586 ret = 1; 587 } 588 return ret; 589 } 590 591 /* 592 * Put cur_page under IO. The section of cur_page which is described by 593 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page 594 * starts on-disk at cur_page_block. 595 * 596 * We take a ref against the page here (on behalf of its presence in the bio). 597 * 598 * The caller of this function is responsible for removing cur_page from the 599 * dio, and for dropping the refcount which came from that presence. 600 */ 601 static int dio_send_cur_page(struct dio *dio) 602 { 603 int ret = 0; 604 605 if (dio->bio) { 606 /* 607 * See whether this new request is contiguous with the old 608 */ 609 if (dio->final_block_in_bio != dio->cur_page_block) 610 dio_bio_submit(dio); 611 /* 612 * Submit now if the underlying fs is about to perform a 613 * metadata read 614 */ 615 if (dio->boundary) 616 dio_bio_submit(dio); 617 } 618 619 if (dio->bio == NULL) { 620 ret = dio_new_bio(dio, dio->cur_page_block); 621 if (ret) 622 goto out; 623 } 624 625 if (dio_bio_add_page(dio) != 0) { 626 dio_bio_submit(dio); 627 ret = dio_new_bio(dio, dio->cur_page_block); 628 if (ret == 0) { 629 ret = dio_bio_add_page(dio); 630 BUG_ON(ret != 0); 631 } 632 } 633 out: 634 return ret; 635 } 636 637 /* 638 * An autonomous function to put a chunk of a page under deferred IO. 639 * 640 * The caller doesn't actually know (or care) whether this piece of page is in 641 * a BIO, or is under IO or whatever. We just take care of all possible 642 * situations here. The separation between the logic of do_direct_IO() and 643 * that of submit_page_section() is important for clarity. Please don't break. 644 * 645 * The chunk of page starts on-disk at blocknr. 646 * 647 * We perform deferred IO, by recording the last-submitted page inside our 648 * private part of the dio structure. If possible, we just expand the IO 649 * across that page here. 650 * 651 * If that doesn't work out then we put the old page into the bio and add this 652 * page to the dio instead. 653 */ 654 static int 655 submit_page_section(struct dio *dio, struct page *page, 656 unsigned offset, unsigned len, sector_t blocknr) 657 { 658 int ret = 0; 659 660 if (dio->rw & WRITE) { 661 /* 662 * Read accounting is performed in submit_bio() 663 */ 664 task_io_account_write(len); 665 } 666 667 /* 668 * Can we just grow the current page's presence in the dio? 669 */ 670 if ( (dio->cur_page == page) && 671 (dio->cur_page_offset + dio->cur_page_len == offset) && 672 (dio->cur_page_block + 673 (dio->cur_page_len >> dio->blkbits) == blocknr)) { 674 dio->cur_page_len += len; 675 676 /* 677 * If dio->boundary then we want to schedule the IO now to 678 * avoid metadata seeks. 679 */ 680 if (dio->boundary) { 681 ret = dio_send_cur_page(dio); 682 page_cache_release(dio->cur_page); 683 dio->cur_page = NULL; 684 } 685 goto out; 686 } 687 688 /* 689 * If there's a deferred page already there then send it. 690 */ 691 if (dio->cur_page) { 692 ret = dio_send_cur_page(dio); 693 page_cache_release(dio->cur_page); 694 dio->cur_page = NULL; 695 if (ret) 696 goto out; 697 } 698 699 page_cache_get(page); /* It is in dio */ 700 dio->cur_page = page; 701 dio->cur_page_offset = offset; 702 dio->cur_page_len = len; 703 dio->cur_page_block = blocknr; 704 out: 705 return ret; 706 } 707 708 /* 709 * Clean any dirty buffers in the blockdev mapping which alias newly-created 710 * file blocks. Only called for S_ISREG files - blockdevs do not set 711 * buffer_new 712 */ 713 static void clean_blockdev_aliases(struct dio *dio) 714 { 715 unsigned i; 716 unsigned nblocks; 717 718 nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits; 719 720 for (i = 0; i < nblocks; i++) { 721 unmap_underlying_metadata(dio->map_bh.b_bdev, 722 dio->map_bh.b_blocknr + i); 723 } 724 } 725 726 /* 727 * If we are not writing the entire block and get_block() allocated 728 * the block for us, we need to fill-in the unused portion of the 729 * block with zeros. This happens only if user-buffer, fileoffset or 730 * io length is not filesystem block-size multiple. 731 * 732 * `end' is zero if we're doing the start of the IO, 1 at the end of the 733 * IO. 734 */ 735 static void dio_zero_block(struct dio *dio, int end) 736 { 737 unsigned dio_blocks_per_fs_block; 738 unsigned this_chunk_blocks; /* In dio_blocks */ 739 unsigned this_chunk_bytes; 740 struct page *page; 741 742 dio->start_zero_done = 1; 743 if (!dio->blkfactor || !buffer_new(&dio->map_bh)) 744 return; 745 746 dio_blocks_per_fs_block = 1 << dio->blkfactor; 747 this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1); 748 749 if (!this_chunk_blocks) 750 return; 751 752 /* 753 * We need to zero out part of an fs block. It is either at the 754 * beginning or the end of the fs block. 755 */ 756 if (end) 757 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks; 758 759 this_chunk_bytes = this_chunk_blocks << dio->blkbits; 760 761 page = ZERO_PAGE(0); 762 if (submit_page_section(dio, page, 0, this_chunk_bytes, 763 dio->next_block_for_io)) 764 return; 765 766 dio->next_block_for_io += this_chunk_blocks; 767 } 768 769 /* 770 * Walk the user pages, and the file, mapping blocks to disk and generating 771 * a sequence of (page,offset,len,block) mappings. These mappings are injected 772 * into submit_page_section(), which takes care of the next stage of submission 773 * 774 * Direct IO against a blockdev is different from a file. Because we can 775 * happily perform page-sized but 512-byte aligned IOs. It is important that 776 * blockdev IO be able to have fine alignment and large sizes. 777 * 778 * So what we do is to permit the ->get_block function to populate bh.b_size 779 * with the size of IO which is permitted at this offset and this i_blkbits. 780 * 781 * For best results, the blockdev should be set up with 512-byte i_blkbits and 782 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives 783 * fine alignment but still allows this function to work in PAGE_SIZE units. 784 */ 785 static int do_direct_IO(struct dio *dio) 786 { 787 const unsigned blkbits = dio->blkbits; 788 const unsigned blocks_per_page = PAGE_SIZE >> blkbits; 789 struct page *page; 790 unsigned block_in_page; 791 struct buffer_head *map_bh = &dio->map_bh; 792 int ret = 0; 793 794 /* The I/O can start at any block offset within the first page */ 795 block_in_page = dio->first_block_in_page; 796 797 while (dio->block_in_file < dio->final_block_in_request) { 798 page = dio_get_page(dio); 799 if (IS_ERR(page)) { 800 ret = PTR_ERR(page); 801 goto out; 802 } 803 804 while (block_in_page < blocks_per_page) { 805 unsigned offset_in_page = block_in_page << blkbits; 806 unsigned this_chunk_bytes; /* # of bytes mapped */ 807 unsigned this_chunk_blocks; /* # of blocks */ 808 unsigned u; 809 810 if (dio->blocks_available == 0) { 811 /* 812 * Need to go and map some more disk 813 */ 814 unsigned long blkmask; 815 unsigned long dio_remainder; 816 817 ret = get_more_blocks(dio); 818 if (ret) { 819 page_cache_release(page); 820 goto out; 821 } 822 if (!buffer_mapped(map_bh)) 823 goto do_holes; 824 825 dio->blocks_available = 826 map_bh->b_size >> dio->blkbits; 827 dio->next_block_for_io = 828 map_bh->b_blocknr << dio->blkfactor; 829 if (buffer_new(map_bh)) 830 clean_blockdev_aliases(dio); 831 832 if (!dio->blkfactor) 833 goto do_holes; 834 835 blkmask = (1 << dio->blkfactor) - 1; 836 dio_remainder = (dio->block_in_file & blkmask); 837 838 /* 839 * If we are at the start of IO and that IO 840 * starts partway into a fs-block, 841 * dio_remainder will be non-zero. If the IO 842 * is a read then we can simply advance the IO 843 * cursor to the first block which is to be 844 * read. But if the IO is a write and the 845 * block was newly allocated we cannot do that; 846 * the start of the fs block must be zeroed out 847 * on-disk 848 */ 849 if (!buffer_new(map_bh)) 850 dio->next_block_for_io += dio_remainder; 851 dio->blocks_available -= dio_remainder; 852 } 853 do_holes: 854 /* Handle holes */ 855 if (!buffer_mapped(map_bh)) { 856 loff_t i_size_aligned; 857 858 /* AKPM: eargh, -ENOTBLK is a hack */ 859 if (dio->rw & WRITE) { 860 page_cache_release(page); 861 return -ENOTBLK; 862 } 863 864 /* 865 * Be sure to account for a partial block as the 866 * last block in the file 867 */ 868 i_size_aligned = ALIGN(i_size_read(dio->inode), 869 1 << blkbits); 870 if (dio->block_in_file >= 871 i_size_aligned >> blkbits) { 872 /* We hit eof */ 873 page_cache_release(page); 874 goto out; 875 } 876 zero_user(page, block_in_page << blkbits, 877 1 << blkbits); 878 dio->block_in_file++; 879 block_in_page++; 880 goto next_block; 881 } 882 883 /* 884 * If we're performing IO which has an alignment which 885 * is finer than the underlying fs, go check to see if 886 * we must zero out the start of this block. 887 */ 888 if (unlikely(dio->blkfactor && !dio->start_zero_done)) 889 dio_zero_block(dio, 0); 890 891 /* 892 * Work out, in this_chunk_blocks, how much disk we 893 * can add to this page 894 */ 895 this_chunk_blocks = dio->blocks_available; 896 u = (PAGE_SIZE - offset_in_page) >> blkbits; 897 if (this_chunk_blocks > u) 898 this_chunk_blocks = u; 899 u = dio->final_block_in_request - dio->block_in_file; 900 if (this_chunk_blocks > u) 901 this_chunk_blocks = u; 902 this_chunk_bytes = this_chunk_blocks << blkbits; 903 BUG_ON(this_chunk_bytes == 0); 904 905 dio->boundary = buffer_boundary(map_bh); 906 ret = submit_page_section(dio, page, offset_in_page, 907 this_chunk_bytes, dio->next_block_for_io); 908 if (ret) { 909 page_cache_release(page); 910 goto out; 911 } 912 dio->next_block_for_io += this_chunk_blocks; 913 914 dio->block_in_file += this_chunk_blocks; 915 block_in_page += this_chunk_blocks; 916 dio->blocks_available -= this_chunk_blocks; 917 next_block: 918 BUG_ON(dio->block_in_file > dio->final_block_in_request); 919 if (dio->block_in_file == dio->final_block_in_request) 920 break; 921 } 922 923 /* Drop the ref which was taken in get_user_pages() */ 924 page_cache_release(page); 925 block_in_page = 0; 926 } 927 out: 928 return ret; 929 } 930 931 /* 932 * Releases both i_mutex and i_alloc_sem 933 */ 934 static ssize_t 935 direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode, 936 const struct iovec *iov, loff_t offset, unsigned long nr_segs, 937 unsigned blkbits, get_block_t get_block, dio_iodone_t end_io, 938 struct dio *dio) 939 { 940 unsigned long user_addr; 941 unsigned long flags; 942 int seg; 943 ssize_t ret = 0; 944 ssize_t ret2; 945 size_t bytes; 946 947 dio->inode = inode; 948 dio->rw = rw; 949 dio->blkbits = blkbits; 950 dio->blkfactor = inode->i_blkbits - blkbits; 951 dio->block_in_file = offset >> blkbits; 952 953 dio->get_block = get_block; 954 dio->end_io = end_io; 955 dio->final_block_in_bio = -1; 956 dio->next_block_for_io = -1; 957 958 dio->iocb = iocb; 959 dio->i_size = i_size_read(inode); 960 961 spin_lock_init(&dio->bio_lock); 962 dio->refcount = 1; 963 964 /* 965 * In case of non-aligned buffers, we may need 2 more 966 * pages since we need to zero out first and last block. 967 */ 968 if (unlikely(dio->blkfactor)) 969 dio->pages_in_io = 2; 970 971 for (seg = 0; seg < nr_segs; seg++) { 972 user_addr = (unsigned long)iov[seg].iov_base; 973 dio->pages_in_io += 974 ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE 975 - user_addr/PAGE_SIZE); 976 } 977 978 for (seg = 0; seg < nr_segs; seg++) { 979 user_addr = (unsigned long)iov[seg].iov_base; 980 dio->size += bytes = iov[seg].iov_len; 981 982 /* Index into the first page of the first block */ 983 dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits; 984 dio->final_block_in_request = dio->block_in_file + 985 (bytes >> blkbits); 986 /* Page fetching state */ 987 dio->head = 0; 988 dio->tail = 0; 989 dio->curr_page = 0; 990 991 dio->total_pages = 0; 992 if (user_addr & (PAGE_SIZE-1)) { 993 dio->total_pages++; 994 bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1)); 995 } 996 dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE; 997 dio->curr_user_address = user_addr; 998 999 ret = do_direct_IO(dio); 1000 1001 dio->result += iov[seg].iov_len - 1002 ((dio->final_block_in_request - dio->block_in_file) << 1003 blkbits); 1004 1005 if (ret) { 1006 dio_cleanup(dio); 1007 break; 1008 } 1009 } /* end iovec loop */ 1010 1011 if (ret == -ENOTBLK && (rw & WRITE)) { 1012 /* 1013 * The remaining part of the request will be 1014 * be handled by buffered I/O when we return 1015 */ 1016 ret = 0; 1017 } 1018 /* 1019 * There may be some unwritten disk at the end of a part-written 1020 * fs-block-sized block. Go zero that now. 1021 */ 1022 dio_zero_block(dio, 1); 1023 1024 if (dio->cur_page) { 1025 ret2 = dio_send_cur_page(dio); 1026 if (ret == 0) 1027 ret = ret2; 1028 page_cache_release(dio->cur_page); 1029 dio->cur_page = NULL; 1030 } 1031 if (dio->bio) 1032 dio_bio_submit(dio); 1033 1034 /* 1035 * It is possible that, we return short IO due to end of file. 1036 * In that case, we need to release all the pages we got hold on. 1037 */ 1038 dio_cleanup(dio); 1039 1040 /* 1041 * All block lookups have been performed. For READ requests 1042 * we can let i_mutex go now that its achieved its purpose 1043 * of protecting us from looking up uninitialized blocks. 1044 */ 1045 if (rw == READ && (dio->flags & DIO_LOCKING)) 1046 mutex_unlock(&dio->inode->i_mutex); 1047 1048 /* 1049 * The only time we want to leave bios in flight is when a successful 1050 * partial aio read or full aio write have been setup. In that case 1051 * bio completion will call aio_complete. The only time it's safe to 1052 * call aio_complete is when we return -EIOCBQUEUED, so we key on that. 1053 * This had *better* be the only place that raises -EIOCBQUEUED. 1054 */ 1055 BUG_ON(ret == -EIOCBQUEUED); 1056 if (dio->is_async && ret == 0 && dio->result && 1057 ((rw & READ) || (dio->result == dio->size))) 1058 ret = -EIOCBQUEUED; 1059 1060 if (ret != -EIOCBQUEUED) { 1061 /* All IO is now issued, send it on its way */ 1062 blk_run_address_space(inode->i_mapping); 1063 dio_await_completion(dio); 1064 } 1065 1066 /* 1067 * Sync will always be dropping the final ref and completing the 1068 * operation. AIO can if it was a broken operation described above or 1069 * in fact if all the bios race to complete before we get here. In 1070 * that case dio_complete() translates the EIOCBQUEUED into the proper 1071 * return code that the caller will hand to aio_complete(). 1072 * 1073 * This is managed by the bio_lock instead of being an atomic_t so that 1074 * completion paths can drop their ref and use the remaining count to 1075 * decide to wake the submission path atomically. 1076 */ 1077 spin_lock_irqsave(&dio->bio_lock, flags); 1078 ret2 = --dio->refcount; 1079 spin_unlock_irqrestore(&dio->bio_lock, flags); 1080 1081 if (ret2 == 0) { 1082 ret = dio_complete(dio, offset, ret); 1083 kfree(dio); 1084 } else 1085 BUG_ON(ret != -EIOCBQUEUED); 1086 1087 return ret; 1088 } 1089 1090 /* 1091 * This is a library function for use by filesystem drivers. 1092 * 1093 * The locking rules are governed by the flags parameter: 1094 * - if the flags value contains DIO_LOCKING we use a fancy locking 1095 * scheme for dumb filesystems. 1096 * For writes this function is called under i_mutex and returns with 1097 * i_mutex held, for reads, i_mutex is not held on entry, but it is 1098 * taken and dropped again before returning. 1099 * For reads and writes i_alloc_sem is taken in shared mode and released 1100 * on I/O completion (which may happen asynchronously after returning to 1101 * the caller). 1102 * 1103 * - if the flags value does NOT contain DIO_LOCKING we don't use any 1104 * internal locking but rather rely on the filesystem to synchronize 1105 * direct I/O reads/writes versus each other and truncate. 1106 * For reads and writes both i_mutex and i_alloc_sem are not held on 1107 * entry and are never taken. 1108 */ 1109 ssize_t 1110 __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode, 1111 struct block_device *bdev, const struct iovec *iov, loff_t offset, 1112 unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io, 1113 int flags) 1114 { 1115 int seg; 1116 size_t size; 1117 unsigned long addr; 1118 unsigned blkbits = inode->i_blkbits; 1119 unsigned bdev_blkbits = 0; 1120 unsigned blocksize_mask = (1 << blkbits) - 1; 1121 ssize_t retval = -EINVAL; 1122 loff_t end = offset; 1123 struct dio *dio; 1124 1125 if (rw & WRITE) 1126 rw = WRITE_ODIRECT_PLUG; 1127 1128 if (bdev) 1129 bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev)); 1130 1131 if (offset & blocksize_mask) { 1132 if (bdev) 1133 blkbits = bdev_blkbits; 1134 blocksize_mask = (1 << blkbits) - 1; 1135 if (offset & blocksize_mask) 1136 goto out; 1137 } 1138 1139 /* Check the memory alignment. Blocks cannot straddle pages */ 1140 for (seg = 0; seg < nr_segs; seg++) { 1141 addr = (unsigned long)iov[seg].iov_base; 1142 size = iov[seg].iov_len; 1143 end += size; 1144 if ((addr & blocksize_mask) || (size & blocksize_mask)) { 1145 if (bdev) 1146 blkbits = bdev_blkbits; 1147 blocksize_mask = (1 << blkbits) - 1; 1148 if ((addr & blocksize_mask) || (size & blocksize_mask)) 1149 goto out; 1150 } 1151 } 1152 1153 dio = kmalloc(sizeof(*dio), GFP_KERNEL); 1154 retval = -ENOMEM; 1155 if (!dio) 1156 goto out; 1157 /* 1158 * Believe it or not, zeroing out the page array caused a .5% 1159 * performance regression in a database benchmark. So, we take 1160 * care to only zero out what's needed. 1161 */ 1162 memset(dio, 0, offsetof(struct dio, pages)); 1163 1164 dio->flags = flags; 1165 if (dio->flags & DIO_LOCKING) { 1166 /* watch out for a 0 len io from a tricksy fs */ 1167 if (rw == READ && end > offset) { 1168 struct address_space *mapping = 1169 iocb->ki_filp->f_mapping; 1170 1171 /* will be released by direct_io_worker */ 1172 mutex_lock(&inode->i_mutex); 1173 1174 retval = filemap_write_and_wait_range(mapping, offset, 1175 end - 1); 1176 if (retval) { 1177 mutex_unlock(&inode->i_mutex); 1178 kfree(dio); 1179 goto out; 1180 } 1181 } 1182 1183 /* 1184 * Will be released at I/O completion, possibly in a 1185 * different thread. 1186 */ 1187 down_read_non_owner(&inode->i_alloc_sem); 1188 } 1189 1190 /* 1191 * For file extending writes updating i_size before data 1192 * writeouts complete can expose uninitialized blocks. So 1193 * even for AIO, we need to wait for i/o to complete before 1194 * returning in this case. 1195 */ 1196 dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) && 1197 (end > i_size_read(inode))); 1198 1199 retval = direct_io_worker(rw, iocb, inode, iov, offset, 1200 nr_segs, blkbits, get_block, end_io, dio); 1201 1202 /* 1203 * In case of error extending write may have instantiated a few 1204 * blocks outside i_size. Trim these off again for DIO_LOCKING. 1205 * 1206 * NOTE: filesystems with their own locking have to handle this 1207 * on their own. 1208 */ 1209 if (flags & DIO_LOCKING) { 1210 if (unlikely((rw & WRITE) && retval < 0)) { 1211 loff_t isize = i_size_read(inode); 1212 if (end > isize) 1213 vmtruncate(inode, isize); 1214 } 1215 } 1216 1217 out: 1218 return retval; 1219 } 1220 EXPORT_SYMBOL(__blockdev_direct_IO); 1221