/* * fs/direct-io.c * * Copyright (C) 2002, Linus Torvalds. * * O_DIRECT * * 04Jul2002 Andrew Morton * Initial version * 11Sep2002 janetinc@us.ibm.com * added readv/writev support. * 29Oct2002 Andrew Morton * rewrote bio_add_page() support. * 30Oct2002 pbadari@us.ibm.com * added support for non-aligned IO. * 06Nov2002 pbadari@us.ibm.com * added asynchronous IO support. * 21Jul2003 nathans@sgi.com * added IO completion notifier. */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/types.h> #include <linux/fs.h> #include <linux/mm.h> #include <linux/slab.h> #include <linux/highmem.h> #include <linux/pagemap.h> #include <linux/task_io_accounting_ops.h> #include <linux/bio.h> #include <linux/wait.h> #include <linux/err.h> #include <linux/blkdev.h> #include <linux/buffer_head.h> #include <linux/rwsem.h> #include <linux/uio.h> #include <asm/atomic.h> /* * How many user pages to map in one call to get_user_pages(). This determines * the size of a structure on the stack. */ #define DIO_PAGES 64 /* * This code generally works in units of "dio_blocks". A dio_block is * somewhere between the hard sector size and the filesystem block size. it * is determined on a per-invocation basis. When talking to the filesystem * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity * down by dio->blkfactor. Similarly, fs-blocksize quantities are converted * to bio_block quantities by shifting left by blkfactor. * * If blkfactor is zero then the user's request was aligned to the filesystem's * blocksize. */ struct dio { /* BIO submission state */ struct bio *bio; /* bio under assembly */ struct inode *inode; int rw; loff_t i_size; /* i_size when submitted */ int flags; /* doesn't change */ unsigned blkbits; /* doesn't change */ unsigned blkfactor; /* When we're using an alignment which is finer than the filesystem's soft blocksize, this specifies how much finer. blkfactor=2 means 1/4-block alignment. Does not change */ unsigned start_zero_done; /* flag: sub-blocksize zeroing has been performed at the start of a write */ int pages_in_io; /* approximate total IO pages */ size_t size; /* total request size (doesn't change)*/ sector_t block_in_file; /* Current offset into the underlying file in dio_block units. */ unsigned blocks_available; /* At block_in_file. changes */ sector_t final_block_in_request;/* doesn't change */ unsigned first_block_in_page; /* doesn't change, Used only once */ int boundary; /* prev block is at a boundary */ int reap_counter; /* rate limit reaping */ get_block_t *get_block; /* block mapping function */ dio_iodone_t *end_io; /* IO completion function */ dio_submit_t *submit_io; /* IO submition function */ loff_t logical_offset_in_bio; /* current first logical block in bio */ sector_t final_block_in_bio; /* current final block in bio + 1 */ sector_t next_block_for_io; /* next block to be put under IO, in dio_blocks units */ struct buffer_head map_bh; /* last get_block() result */ /* * Deferred addition of a page to the dio. These variables are * private to dio_send_cur_page(), submit_page_section() and * dio_bio_add_page(). */ struct page *cur_page; /* The page */ unsigned cur_page_offset; /* Offset into it, in bytes */ unsigned cur_page_len; /* Nr of bytes at cur_page_offset */ sector_t cur_page_block; /* Where it starts */ loff_t cur_page_fs_offset; /* Offset in file */ /* BIO completion state */ spinlock_t bio_lock; /* protects BIO fields below */ unsigned long refcount; /* direct_io_worker() and bios */ struct bio *bio_list; /* singly linked via bi_private */ struct task_struct *waiter; /* waiting task (NULL if none) */ /* AIO related stuff */ struct kiocb *iocb; /* kiocb */ int is_async; /* is IO async ? */ int io_error; /* IO error in completion path */ ssize_t result; /* IO result */ /* * Page fetching state. These variables belong to dio_refill_pages(). */ int curr_page; /* changes */ int total_pages; /* doesn't change */ unsigned long curr_user_address;/* changes */ /* * Page queue. These variables belong to dio_refill_pages() and * dio_get_page(). */ unsigned head; /* next page to process */ unsigned tail; /* last valid page + 1 */ int page_errors; /* errno from get_user_pages() */ /* * pages[] (and any fields placed after it) are not zeroed out at * allocation time. Don't add new fields after pages[] unless you * wish that they not be zeroed. */ struct page *pages[DIO_PAGES]; /* page buffer */ }; /* * How many pages are in the queue? */ static inline unsigned dio_pages_present(struct dio *dio) { return dio->tail - dio->head; } /* * Go grab and pin some userspace pages. Typically we'll get 64 at a time. */ static int dio_refill_pages(struct dio *dio) { int ret; int nr_pages; nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES); ret = get_user_pages_fast( dio->curr_user_address, /* Where from? */ nr_pages, /* How many pages? */ dio->rw == READ, /* Write to memory? */ &dio->pages[0]); /* Put results here */ if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) { struct page *page = ZERO_PAGE(0); /* * A memory fault, but the filesystem has some outstanding * mapped blocks. We need to use those blocks up to avoid * leaking stale data in the file. */ if (dio->page_errors == 0) dio->page_errors = ret; page_cache_get(page); dio->pages[0] = page; dio->head = 0; dio->tail = 1; ret = 0; goto out; } if (ret >= 0) { dio->curr_user_address += ret * PAGE_SIZE; dio->curr_page += ret; dio->head = 0; dio->tail = ret; ret = 0; } out: return ret; } /* * Get another userspace page. Returns an ERR_PTR on error. Pages are * buffered inside the dio so that we can call get_user_pages() against a * decent number of pages, less frequently. To provide nicer use of the * L1 cache. */ static struct page *dio_get_page(struct dio *dio) { if (dio_pages_present(dio) == 0) { int ret; ret = dio_refill_pages(dio); if (ret) return ERR_PTR(ret); BUG_ON(dio_pages_present(dio) == 0); } return dio->pages[dio->head++]; } /** * dio_complete() - called when all DIO BIO I/O has been completed * @offset: the byte offset in the file of the completed operation * * This releases locks as dictated by the locking type, lets interested parties * know that a DIO operation has completed, and calculates the resulting return * code for the operation. * * It lets the filesystem know if it registered an interest earlier via * get_block. Pass the private field of the map buffer_head so that * filesystems can use it to hold additional state between get_block calls and * dio_complete. */ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async) { ssize_t transferred = 0; /* * AIO submission can race with bio completion to get here while * expecting to have the last io completed by bio completion. * In that case -EIOCBQUEUED is in fact not an error we want * to preserve through this call. */ if (ret == -EIOCBQUEUED) ret = 0; if (dio->result) { transferred = dio->result; /* Check for short read case */ if ((dio->rw == READ) && ((offset + transferred) > dio->i_size)) transferred = dio->i_size - offset; } if (ret == 0) ret = dio->page_errors; if (ret == 0) ret = dio->io_error; if (ret == 0) ret = transferred; if (dio->end_io && dio->result) { dio->end_io(dio->iocb, offset, transferred, dio->map_bh.b_private, ret, is_async); } else if (is_async) { aio_complete(dio->iocb, ret, 0); } if (dio->flags & DIO_LOCKING) /* lockdep: non-owner release */ up_read_non_owner(&dio->inode->i_alloc_sem); return ret; } static int dio_bio_complete(struct dio *dio, struct bio *bio); /* * Asynchronous IO callback. */ static void dio_bio_end_aio(struct bio *bio, int error) { struct dio *dio = bio->bi_private; unsigned long remaining; unsigned long flags; /* cleanup the bio */ dio_bio_complete(dio, bio); spin_lock_irqsave(&dio->bio_lock, flags); remaining = --dio->refcount; if (remaining == 1 && dio->waiter) wake_up_process(dio->waiter); spin_unlock_irqrestore(&dio->bio_lock, flags); if (remaining == 0) { dio_complete(dio, dio->iocb->ki_pos, 0, true); kfree(dio); } } /* * The BIO completion handler simply queues the BIO up for the process-context * handler. * * During I/O bi_private points at the dio. After I/O, bi_private is used to * implement a singly-linked list of completed BIOs, at dio->bio_list. */ static void dio_bio_end_io(struct bio *bio, int error) { struct dio *dio = bio->bi_private; unsigned long flags; spin_lock_irqsave(&dio->bio_lock, flags); bio->bi_private = dio->bio_list; dio->bio_list = bio; if (--dio->refcount == 1 && dio->waiter) wake_up_process(dio->waiter); spin_unlock_irqrestore(&dio->bio_lock, flags); } /** * dio_end_io - handle the end io action for the given bio * @bio: The direct io bio thats being completed * @error: Error if there was one * * This is meant to be called by any filesystem that uses their own dio_submit_t * so that the DIO specific endio actions are dealt with after the filesystem * has done it's completion work. */ void dio_end_io(struct bio *bio, int error) { struct dio *dio = bio->bi_private; if (dio->is_async) dio_bio_end_aio(bio, error); else dio_bio_end_io(bio, error); } EXPORT_SYMBOL_GPL(dio_end_io); static void dio_bio_alloc(struct dio *dio, struct block_device *bdev, sector_t first_sector, int nr_vecs) { struct bio *bio; /* * bio_alloc() is guaranteed to return a bio when called with * __GFP_WAIT and we request a valid number of vectors. */ bio = bio_alloc(GFP_KERNEL, nr_vecs); bio->bi_bdev = bdev; bio->bi_sector = first_sector; if (dio->is_async) bio->bi_end_io = dio_bio_end_aio; else bio->bi_end_io = dio_bio_end_io; dio->bio = bio; dio->logical_offset_in_bio = dio->cur_page_fs_offset; } /* * In the AIO read case we speculatively dirty the pages before starting IO. * During IO completion, any of these pages which happen to have been written * back will be redirtied by bio_check_pages_dirty(). * * bios hold a dio reference between submit_bio and ->end_io. */ static void dio_bio_submit(struct dio *dio) { struct bio *bio = dio->bio; unsigned long flags; bio->bi_private = dio; spin_lock_irqsave(&dio->bio_lock, flags); dio->refcount++; spin_unlock_irqrestore(&dio->bio_lock, flags); if (dio->is_async && dio->rw == READ) bio_set_pages_dirty(bio); if (dio->submit_io) dio->submit_io(dio->rw, bio, dio->inode, dio->logical_offset_in_bio); else submit_bio(dio->rw, bio); dio->bio = NULL; dio->boundary = 0; dio->logical_offset_in_bio = 0; } /* * Release any resources in case of a failure */ static void dio_cleanup(struct dio *dio) { while (dio_pages_present(dio)) page_cache_release(dio_get_page(dio)); } /* * Wait for the next BIO to complete. Remove it and return it. NULL is * returned once all BIOs have been completed. This must only be called once * all bios have been issued so that dio->refcount can only decrease. This * requires that that the caller hold a reference on the dio. */ static struct bio *dio_await_one(struct dio *dio) { unsigned long flags; struct bio *bio = NULL; spin_lock_irqsave(&dio->bio_lock, flags); /* * Wait as long as the list is empty and there are bios in flight. bio * completion drops the count, maybe adds to the list, and wakes while * holding the bio_lock so we don't need set_current_state()'s barrier * and can call it after testing our condition. */ while (dio->refcount > 1 && dio->bio_list == NULL) { __set_current_state(TASK_UNINTERRUPTIBLE); dio->waiter = current; spin_unlock_irqrestore(&dio->bio_lock, flags); io_schedule(); /* wake up sets us TASK_RUNNING */ spin_lock_irqsave(&dio->bio_lock, flags); dio->waiter = NULL; } if (dio->bio_list) { bio = dio->bio_list; dio->bio_list = bio->bi_private; } spin_unlock_irqrestore(&dio->bio_lock, flags); return bio; } /* * Process one completed BIO. No locks are held. */ static int dio_bio_complete(struct dio *dio, struct bio *bio) { const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags); struct bio_vec *bvec = bio->bi_io_vec; int page_no; if (!uptodate) dio->io_error = -EIO; if (dio->is_async && dio->rw == READ) { bio_check_pages_dirty(bio); /* transfers ownership */ } else { for (page_no = 0; page_no < bio->bi_vcnt; page_no++) { struct page *page = bvec[page_no].bv_page; if (dio->rw == READ && !PageCompound(page)) set_page_dirty_lock(page); page_cache_release(page); } bio_put(bio); } return uptodate ? 0 : -EIO; } /* * Wait on and process all in-flight BIOs. This must only be called once * all bios have been issued so that the refcount can only decrease. * This just waits for all bios to make it through dio_bio_complete. IO * errors are propagated through dio->io_error and should be propagated via * dio_complete(). */ static void dio_await_completion(struct dio *dio) { struct bio *bio; do { bio = dio_await_one(dio); if (bio) dio_bio_complete(dio, bio); } while (bio); } /* * A really large O_DIRECT read or write can generate a lot of BIOs. So * to keep the memory consumption sane we periodically reap any completed BIOs * during the BIO generation phase. * * This also helps to limit the peak amount of pinned userspace memory. */ static int dio_bio_reap(struct dio *dio) { int ret = 0; if (dio->reap_counter++ >= 64) { while (dio->bio_list) { unsigned long flags; struct bio *bio; int ret2; spin_lock_irqsave(&dio->bio_lock, flags); bio = dio->bio_list; dio->bio_list = bio->bi_private; spin_unlock_irqrestore(&dio->bio_lock, flags); ret2 = dio_bio_complete(dio, bio); if (ret == 0) ret = ret2; } dio->reap_counter = 0; } return ret; } /* * Call into the fs to map some more disk blocks. We record the current number * of available blocks at dio->blocks_available. These are in units of the * fs blocksize, (1 << inode->i_blkbits). * * The fs is allowed to map lots of blocks at once. If it wants to do that, * it uses the passed inode-relative block number as the file offset, as usual. * * get_block() is passed the number of i_blkbits-sized blocks which direct_io * has remaining to do. The fs should not map more than this number of blocks. * * If the fs has mapped a lot of blocks, it should populate bh->b_size to * indicate how much contiguous disk space has been made available at * bh->b_blocknr. * * If *any* of the mapped blocks are new, then the fs must set buffer_new(). * This isn't very efficient... * * In the case of filesystem holes: the fs may return an arbitrarily-large * hole by returning an appropriate value in b_size and by clearing * buffer_mapped(). However the direct-io code will only process holes one * block at a time - it will repeatedly call get_block() as it walks the hole. */ static int get_more_blocks(struct dio *dio) { int ret; struct buffer_head *map_bh = &dio->map_bh; sector_t fs_startblk; /* Into file, in filesystem-sized blocks */ unsigned long fs_count; /* Number of filesystem-sized blocks */ unsigned long dio_count;/* Number of dio_block-sized blocks */ unsigned long blkmask; int create; /* * If there was a memory error and we've overwritten all the * mapped blocks then we can now return that memory error */ ret = dio->page_errors; if (ret == 0) { BUG_ON(dio->block_in_file >= dio->final_block_in_request); fs_startblk = dio->block_in_file >> dio->blkfactor; dio_count = dio->final_block_in_request - dio->block_in_file; fs_count = dio_count >> dio->blkfactor; blkmask = (1 << dio->blkfactor) - 1; if (dio_count & blkmask) fs_count++; map_bh->b_state = 0; map_bh->b_size = fs_count << dio->inode->i_blkbits; /* * For writes inside i_size on a DIO_SKIP_HOLES filesystem we * forbid block creations: only overwrites are permitted. * We will return early to the caller once we see an * unmapped buffer head returned, and the caller will fall * back to buffered I/O. * * Otherwise the decision is left to the get_blocks method, * which may decide to handle it or also return an unmapped * buffer head. */ create = dio->rw & WRITE; if (dio->flags & DIO_SKIP_HOLES) { if (dio->block_in_file < (i_size_read(dio->inode) >> dio->blkbits)) create = 0; } ret = (*dio->get_block)(dio->inode, fs_startblk, map_bh, create); } return ret; } /* * There is no bio. Make one now. */ static int dio_new_bio(struct dio *dio, sector_t start_sector) { sector_t sector; int ret, nr_pages; ret = dio_bio_reap(dio); if (ret) goto out; sector = start_sector << (dio->blkbits - 9); nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev)); nr_pages = min(nr_pages, BIO_MAX_PAGES); BUG_ON(nr_pages <= 0); dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages); dio->boundary = 0; out: return ret; } /* * Attempt to put the current chunk of 'cur_page' into the current BIO. If * that was successful then update final_block_in_bio and take a ref against * the just-added page. * * Return zero on success. Non-zero means the caller needs to start a new BIO. */ static int dio_bio_add_page(struct dio *dio) { int ret; ret = bio_add_page(dio->bio, dio->cur_page, dio->cur_page_len, dio->cur_page_offset); if (ret == dio->cur_page_len) { /* * Decrement count only, if we are done with this page */ if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE) dio->pages_in_io--; page_cache_get(dio->cur_page); dio->final_block_in_bio = dio->cur_page_block + (dio->cur_page_len >> dio->blkbits); ret = 0; } else { ret = 1; } return ret; } /* * Put cur_page under IO. The section of cur_page which is described by * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page * starts on-disk at cur_page_block. * * We take a ref against the page here (on behalf of its presence in the bio). * * The caller of this function is responsible for removing cur_page from the * dio, and for dropping the refcount which came from that presence. */ static int dio_send_cur_page(struct dio *dio) { int ret = 0; if (dio->bio) { loff_t cur_offset = dio->cur_page_fs_offset; loff_t bio_next_offset = dio->logical_offset_in_bio + dio->bio->bi_size; /* * See whether this new request is contiguous with the old. * * Btrfs cannot handle having logically non-contiguous requests * submitted. For example if you have * * Logical: [0-4095][HOLE][8192-12287] * Physical: [0-4095] [4096-8191] * * We cannot submit those pages together as one BIO. So if our * current logical offset in the file does not equal what would * be the next logical offset in the bio, submit the bio we * have. */ if (dio->final_block_in_bio != dio->cur_page_block || cur_offset != bio_next_offset) dio_bio_submit(dio); /* * Submit now if the underlying fs is about to perform a * metadata read */ else if (dio->boundary) dio_bio_submit(dio); } if (dio->bio == NULL) { ret = dio_new_bio(dio, dio->cur_page_block); if (ret) goto out; } if (dio_bio_add_page(dio) != 0) { dio_bio_submit(dio); ret = dio_new_bio(dio, dio->cur_page_block); if (ret == 0) { ret = dio_bio_add_page(dio); BUG_ON(ret != 0); } } out: return ret; } /* * An autonomous function to put a chunk of a page under deferred IO. * * The caller doesn't actually know (or care) whether this piece of page is in * a BIO, or is under IO or whatever. We just take care of all possible * situations here. The separation between the logic of do_direct_IO() and * that of submit_page_section() is important for clarity. Please don't break. * * The chunk of page starts on-disk at blocknr. * * We perform deferred IO, by recording the last-submitted page inside our * private part of the dio structure. If possible, we just expand the IO * across that page here. * * If that doesn't work out then we put the old page into the bio and add this * page to the dio instead. */ static int submit_page_section(struct dio *dio, struct page *page, unsigned offset, unsigned len, sector_t blocknr) { int ret = 0; if (dio->rw & WRITE) { /* * Read accounting is performed in submit_bio() */ task_io_account_write(len); } /* * Can we just grow the current page's presence in the dio? */ if ( (dio->cur_page == page) && (dio->cur_page_offset + dio->cur_page_len == offset) && (dio->cur_page_block + (dio->cur_page_len >> dio->blkbits) == blocknr)) { dio->cur_page_len += len; /* * If dio->boundary then we want to schedule the IO now to * avoid metadata seeks. */ if (dio->boundary) { ret = dio_send_cur_page(dio); page_cache_release(dio->cur_page); dio->cur_page = NULL; } goto out; } /* * If there's a deferred page already there then send it. */ if (dio->cur_page) { ret = dio_send_cur_page(dio); page_cache_release(dio->cur_page); dio->cur_page = NULL; if (ret) goto out; } page_cache_get(page); /* It is in dio */ dio->cur_page = page; dio->cur_page_offset = offset; dio->cur_page_len = len; dio->cur_page_block = blocknr; dio->cur_page_fs_offset = dio->block_in_file << dio->blkbits; out: return ret; } /* * Clean any dirty buffers in the blockdev mapping which alias newly-created * file blocks. Only called for S_ISREG files - blockdevs do not set * buffer_new */ static void clean_blockdev_aliases(struct dio *dio) { unsigned i; unsigned nblocks; nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits; for (i = 0; i < nblocks; i++) { unmap_underlying_metadata(dio->map_bh.b_bdev, dio->map_bh.b_blocknr + i); } } /* * If we are not writing the entire block and get_block() allocated * the block for us, we need to fill-in the unused portion of the * block with zeros. This happens only if user-buffer, fileoffset or * io length is not filesystem block-size multiple. * * `end' is zero if we're doing the start of the IO, 1 at the end of the * IO. */ static void dio_zero_block(struct dio *dio, int end) { unsigned dio_blocks_per_fs_block; unsigned this_chunk_blocks; /* In dio_blocks */ unsigned this_chunk_bytes; struct page *page; dio->start_zero_done = 1; if (!dio->blkfactor || !buffer_new(&dio->map_bh)) return; dio_blocks_per_fs_block = 1 << dio->blkfactor; this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1); if (!this_chunk_blocks) return; /* * We need to zero out part of an fs block. It is either at the * beginning or the end of the fs block. */ if (end) this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks; this_chunk_bytes = this_chunk_blocks << dio->blkbits; page = ZERO_PAGE(0); if (submit_page_section(dio, page, 0, this_chunk_bytes, dio->next_block_for_io)) return; dio->next_block_for_io += this_chunk_blocks; } /* * Walk the user pages, and the file, mapping blocks to disk and generating * a sequence of (page,offset,len,block) mappings. These mappings are injected * into submit_page_section(), which takes care of the next stage of submission * * Direct IO against a blockdev is different from a file. Because we can * happily perform page-sized but 512-byte aligned IOs. It is important that * blockdev IO be able to have fine alignment and large sizes. * * So what we do is to permit the ->get_block function to populate bh.b_size * with the size of IO which is permitted at this offset and this i_blkbits. * * For best results, the blockdev should be set up with 512-byte i_blkbits and * it should set b_size to PAGE_SIZE or more inside get_block(). This gives * fine alignment but still allows this function to work in PAGE_SIZE units. */ static int do_direct_IO(struct dio *dio) { const unsigned blkbits = dio->blkbits; const unsigned blocks_per_page = PAGE_SIZE >> blkbits; struct page *page; unsigned block_in_page; struct buffer_head *map_bh = &dio->map_bh; int ret = 0; /* The I/O can start at any block offset within the first page */ block_in_page = dio->first_block_in_page; while (dio->block_in_file < dio->final_block_in_request) { page = dio_get_page(dio); if (IS_ERR(page)) { ret = PTR_ERR(page); goto out; } while (block_in_page < blocks_per_page) { unsigned offset_in_page = block_in_page << blkbits; unsigned this_chunk_bytes; /* # of bytes mapped */ unsigned this_chunk_blocks; /* # of blocks */ unsigned u; if (dio->blocks_available == 0) { /* * Need to go and map some more disk */ unsigned long blkmask; unsigned long dio_remainder; ret = get_more_blocks(dio); if (ret) { page_cache_release(page); goto out; } if (!buffer_mapped(map_bh)) goto do_holes; dio->blocks_available = map_bh->b_size >> dio->blkbits; dio->next_block_for_io = map_bh->b_blocknr << dio->blkfactor; if (buffer_new(map_bh)) clean_blockdev_aliases(dio); if (!dio->blkfactor) goto do_holes; blkmask = (1 << dio->blkfactor) - 1; dio_remainder = (dio->block_in_file & blkmask); /* * If we are at the start of IO and that IO * starts partway into a fs-block, * dio_remainder will be non-zero. If the IO * is a read then we can simply advance the IO * cursor to the first block which is to be * read. But if the IO is a write and the * block was newly allocated we cannot do that; * the start of the fs block must be zeroed out * on-disk */ if (!buffer_new(map_bh)) dio->next_block_for_io += dio_remainder; dio->blocks_available -= dio_remainder; } do_holes: /* Handle holes */ if (!buffer_mapped(map_bh)) { loff_t i_size_aligned; /* AKPM: eargh, -ENOTBLK is a hack */ if (dio->rw & WRITE) { page_cache_release(page); return -ENOTBLK; } /* * Be sure to account for a partial block as the * last block in the file */ i_size_aligned = ALIGN(i_size_read(dio->inode), 1 << blkbits); if (dio->block_in_file >= i_size_aligned >> blkbits) { /* We hit eof */ page_cache_release(page); goto out; } zero_user(page, block_in_page << blkbits, 1 << blkbits); dio->block_in_file++; block_in_page++; goto next_block; } /* * If we're performing IO which has an alignment which * is finer than the underlying fs, go check to see if * we must zero out the start of this block. */ if (unlikely(dio->blkfactor && !dio->start_zero_done)) dio_zero_block(dio, 0); /* * Work out, in this_chunk_blocks, how much disk we * can add to this page */ this_chunk_blocks = dio->blocks_available; u = (PAGE_SIZE - offset_in_page) >> blkbits; if (this_chunk_blocks > u) this_chunk_blocks = u; u = dio->final_block_in_request - dio->block_in_file; if (this_chunk_blocks > u) this_chunk_blocks = u; this_chunk_bytes = this_chunk_blocks << blkbits; BUG_ON(this_chunk_bytes == 0); dio->boundary = buffer_boundary(map_bh); ret = submit_page_section(dio, page, offset_in_page, this_chunk_bytes, dio->next_block_for_io); if (ret) { page_cache_release(page); goto out; } dio->next_block_for_io += this_chunk_blocks; dio->block_in_file += this_chunk_blocks; block_in_page += this_chunk_blocks; dio->blocks_available -= this_chunk_blocks; next_block: BUG_ON(dio->block_in_file > dio->final_block_in_request); if (dio->block_in_file == dio->final_block_in_request) break; } /* Drop the ref which was taken in get_user_pages() */ page_cache_release(page); block_in_page = 0; } out: return ret; } /* * Releases both i_mutex and i_alloc_sem */ static ssize_t direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode, const struct iovec *iov, loff_t offset, unsigned long nr_segs, unsigned blkbits, get_block_t get_block, dio_iodone_t end_io, dio_submit_t submit_io, struct dio *dio) { unsigned long user_addr; unsigned long flags; int seg; ssize_t ret = 0; ssize_t ret2; size_t bytes; dio->inode = inode; dio->rw = rw; dio->blkbits = blkbits; dio->blkfactor = inode->i_blkbits - blkbits; dio->block_in_file = offset >> blkbits; dio->get_block = get_block; dio->end_io = end_io; dio->submit_io = submit_io; dio->final_block_in_bio = -1; dio->next_block_for_io = -1; dio->iocb = iocb; dio->i_size = i_size_read(inode); spin_lock_init(&dio->bio_lock); dio->refcount = 1; /* * In case of non-aligned buffers, we may need 2 more * pages since we need to zero out first and last block. */ if (unlikely(dio->blkfactor)) dio->pages_in_io = 2; for (seg = 0; seg < nr_segs; seg++) { user_addr = (unsigned long)iov[seg].iov_base; dio->pages_in_io += ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE - user_addr/PAGE_SIZE); } for (seg = 0; seg < nr_segs; seg++) { user_addr = (unsigned long)iov[seg].iov_base; dio->size += bytes = iov[seg].iov_len; /* Index into the first page of the first block */ dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits; dio->final_block_in_request = dio->block_in_file + (bytes >> blkbits); /* Page fetching state */ dio->head = 0; dio->tail = 0; dio->curr_page = 0; dio->total_pages = 0; if (user_addr & (PAGE_SIZE-1)) { dio->total_pages++; bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1)); } dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE; dio->curr_user_address = user_addr; ret = do_direct_IO(dio); dio->result += iov[seg].iov_len - ((dio->final_block_in_request - dio->block_in_file) << blkbits); if (ret) { dio_cleanup(dio); break; } } /* end iovec loop */ if (ret == -ENOTBLK) { /* * The remaining part of the request will be * be handled by buffered I/O when we return */ ret = 0; } /* * There may be some unwritten disk at the end of a part-written * fs-block-sized block. Go zero that now. */ dio_zero_block(dio, 1); if (dio->cur_page) { ret2 = dio_send_cur_page(dio); if (ret == 0) ret = ret2; page_cache_release(dio->cur_page); dio->cur_page = NULL; } if (dio->bio) dio_bio_submit(dio); /* * It is possible that, we return short IO due to end of file. * In that case, we need to release all the pages we got hold on. */ dio_cleanup(dio); /* * All block lookups have been performed. For READ requests * we can let i_mutex go now that its achieved its purpose * of protecting us from looking up uninitialized blocks. */ if (rw == READ && (dio->flags & DIO_LOCKING)) mutex_unlock(&dio->inode->i_mutex); /* * The only time we want to leave bios in flight is when a successful * partial aio read or full aio write have been setup. In that case * bio completion will call aio_complete. The only time it's safe to * call aio_complete is when we return -EIOCBQUEUED, so we key on that. * This had *better* be the only place that raises -EIOCBQUEUED. */ BUG_ON(ret == -EIOCBQUEUED); if (dio->is_async && ret == 0 && dio->result && ((rw & READ) || (dio->result == dio->size))) ret = -EIOCBQUEUED; if (ret != -EIOCBQUEUED) { /* All IO is now issued, send it on its way */ blk_run_address_space(inode->i_mapping); dio_await_completion(dio); } /* * Sync will always be dropping the final ref and completing the * operation. AIO can if it was a broken operation described above or * in fact if all the bios race to complete before we get here. In * that case dio_complete() translates the EIOCBQUEUED into the proper * return code that the caller will hand to aio_complete(). * * This is managed by the bio_lock instead of being an atomic_t so that * completion paths can drop their ref and use the remaining count to * decide to wake the submission path atomically. */ spin_lock_irqsave(&dio->bio_lock, flags); ret2 = --dio->refcount; spin_unlock_irqrestore(&dio->bio_lock, flags); if (ret2 == 0) { ret = dio_complete(dio, offset, ret, false); kfree(dio); } else BUG_ON(ret != -EIOCBQUEUED); return ret; } /* * This is a library function for use by filesystem drivers. * * The locking rules are governed by the flags parameter: * - if the flags value contains DIO_LOCKING we use a fancy locking * scheme for dumb filesystems. * For writes this function is called under i_mutex and returns with * i_mutex held, for reads, i_mutex is not held on entry, but it is * taken and dropped again before returning. * For reads and writes i_alloc_sem is taken in shared mode and released * on I/O completion (which may happen asynchronously after returning to * the caller). * * - if the flags value does NOT contain DIO_LOCKING we don't use any * internal locking but rather rely on the filesystem to synchronize * direct I/O reads/writes versus each other and truncate. * For reads and writes both i_mutex and i_alloc_sem are not held on * entry and are never taken. */ ssize_t __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode, struct block_device *bdev, const struct iovec *iov, loff_t offset, unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io, dio_submit_t submit_io, int flags) { int seg; size_t size; unsigned long addr; unsigned blkbits = inode->i_blkbits; unsigned bdev_blkbits = 0; unsigned blocksize_mask = (1 << blkbits) - 1; ssize_t retval = -EINVAL; loff_t end = offset; struct dio *dio; if (rw & WRITE) rw = WRITE_ODIRECT_PLUG; if (bdev) bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev)); if (offset & blocksize_mask) { if (bdev) blkbits = bdev_blkbits; blocksize_mask = (1 << blkbits) - 1; if (offset & blocksize_mask) goto out; } /* Check the memory alignment. Blocks cannot straddle pages */ for (seg = 0; seg < nr_segs; seg++) { addr = (unsigned long)iov[seg].iov_base; size = iov[seg].iov_len; end += size; if ((addr & blocksize_mask) || (size & blocksize_mask)) { if (bdev) blkbits = bdev_blkbits; blocksize_mask = (1 << blkbits) - 1; if ((addr & blocksize_mask) || (size & blocksize_mask)) goto out; } } dio = kmalloc(sizeof(*dio), GFP_KERNEL); retval = -ENOMEM; if (!dio) goto out; /* * Believe it or not, zeroing out the page array caused a .5% * performance regression in a database benchmark. So, we take * care to only zero out what's needed. */ memset(dio, 0, offsetof(struct dio, pages)); dio->flags = flags; if (dio->flags & DIO_LOCKING) { /* watch out for a 0 len io from a tricksy fs */ if (rw == READ && end > offset) { struct address_space *mapping = iocb->ki_filp->f_mapping; /* will be released by direct_io_worker */ mutex_lock(&inode->i_mutex); retval = filemap_write_and_wait_range(mapping, offset, end - 1); if (retval) { mutex_unlock(&inode->i_mutex); kfree(dio); goto out; } } /* * Will be released at I/O completion, possibly in a * different thread. */ down_read_non_owner(&inode->i_alloc_sem); } /* * For file extending writes updating i_size before data * writeouts complete can expose uninitialized blocks. So * even for AIO, we need to wait for i/o to complete before * returning in this case. */ dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) && (end > i_size_read(inode))); retval = direct_io_worker(rw, iocb, inode, iov, offset, nr_segs, blkbits, get_block, end_io, submit_io, dio); out: return retval; } EXPORT_SYMBOL(__blockdev_direct_IO);