diff options
Diffstat (limited to 'fs/direct-io.c')
| -rw-r--r-- | fs/direct-io.c | 1258 |
1 files changed, 1258 insertions, 0 deletions
diff --git a/fs/direct-io.c b/fs/direct-io.c new file mode 100644 index 000000000000..5a674a0c7146 --- /dev/null +++ b/fs/direct-io.c @@ -0,0 +1,1258 @@ +/* + * fs/direct-io.c + * + * Copyright (C) 2002, Linus Torvalds. + * + * O_DIRECT + * + * 04Jul2002 akpm@zip.com.au + * Initial version + * 11Sep2002 janetinc@us.ibm.com + * added readv/writev support. + * 29Oct2002 akpm@zip.com.au + * 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/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. + * + * lock_type is DIO_LOCKING for regular files on direct-IO-naive filesystems. + * This determines whether we need to do the fancy locking which prevents + * direct-IO from being able to read uninitialised disk blocks. If its zero + * (blockdev) this locking is not done, and if it is DIO_OWN_LOCKING i_sem is + * not held for the entire direct write (taken briefly, initially, during a + * direct read though, but its never held for the duration of a direct-IO). + */ + +struct dio { + /* BIO submission state */ + struct bio *bio; /* bio under assembly */ + struct inode *inode; + int rw; + int lock_type; /* 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_blocks_t *get_blocks; /* block mapping function */ + dio_iodone_t *end_io; /* IO completion function */ + 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_blocks() 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 */ + + /* + * 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(). + */ + struct page *pages[DIO_PAGES]; /* page buffer */ + unsigned head; /* next page to process */ + unsigned tail; /* last valid page + 1 */ + int page_errors; /* errno from get_user_pages() */ + + /* BIO completion state */ + spinlock_t bio_lock; /* protects BIO fields below */ + int bio_count; /* nr bios to be completed */ + int bios_in_flight; /* nr bios in flight */ + 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 ? */ + ssize_t result; /* IO result */ +}; + +/* + * 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); + down_read(¤t->mm->mmap_sem); + ret = get_user_pages( + current, /* Task for fault acounting */ + current->mm, /* whose pages? */ + dio->curr_user_address, /* Where from? */ + nr_pages, /* How many pages? */ + dio->rw == READ, /* Write to memory? */ + 0, /* force (?) */ + &dio->pages[0], + NULL); /* vmas */ + up_read(¤t->mm->mmap_sem); + + if (ret < 0 && dio->blocks_available && (dio->rw == WRITE)) { + /* + * 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; + dio->pages[0] = ZERO_PAGE(dio->curr_user_address); + 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++]; +} + +/* + * Called when all DIO BIO I/O has been completed - let the filesystem + * know, if it registered an interest earlier via get_blocks. Pass the + * private field of the map buffer_head so that filesystems can use it + * to hold additional state between get_blocks calls and dio_complete. + */ +static void dio_complete(struct dio *dio, loff_t offset, ssize_t bytes) +{ + if (dio->end_io && dio->result) + dio->end_io(dio->inode, offset, bytes, dio->map_bh.b_private); + if (dio->lock_type == DIO_LOCKING) + up_read(&dio->inode->i_alloc_sem); +} + +/* + * Called when a BIO has been processed. If the count goes to zero then IO is + * complete and we can signal this to the AIO layer. + */ +static void finished_one_bio(struct dio *dio) +{ + unsigned long flags; + + spin_lock_irqsave(&dio->bio_lock, flags); + if (dio->bio_count == 1) { + if (dio->is_async) { + /* + * Last reference to the dio is going away. + * Drop spinlock and complete the DIO. + */ + spin_unlock_irqrestore(&dio->bio_lock, flags); + dio_complete(dio, dio->block_in_file << dio->blkbits, + dio->result); + /* Complete AIO later if falling back to buffered i/o */ + if (dio->result == dio->size || + ((dio->rw == READ) && dio->result)) { + aio_complete(dio->iocb, dio->result, 0); + kfree(dio); + return; + } else { + /* + * Falling back to buffered + */ + spin_lock_irqsave(&dio->bio_lock, flags); + dio->bio_count--; + if (dio->waiter) + wake_up_process(dio->waiter); + spin_unlock_irqrestore(&dio->bio_lock, flags); + return; + } + } + } + dio->bio_count--; + spin_unlock_irqrestore(&dio->bio_lock, flags); +} + +static int dio_bio_complete(struct dio *dio, struct bio *bio); +/* + * Asynchronous IO callback. + */ +static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error) +{ + struct dio *dio = bio->bi_private; + + if (bio->bi_size) + return 1; + + /* cleanup the bio */ + dio_bio_complete(dio, bio); + return 0; +} + +/* + * 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 int dio_bio_end_io(struct bio *bio, unsigned int bytes_done, int error) +{ + struct dio *dio = bio->bi_private; + unsigned long flags; + + if (bio->bi_size) + return 1; + + spin_lock_irqsave(&dio->bio_lock, flags); + bio->bi_private = dio->bio_list; + dio->bio_list = bio; + dio->bios_in_flight--; + if (dio->waiter && dio->bios_in_flight == 0) + wake_up_process(dio->waiter); + spin_unlock_irqrestore(&dio->bio_lock, flags); + return 0; +} + +static int +dio_bio_alloc(struct dio *dio, struct block_device *bdev, + sector_t first_sector, int nr_vecs) +{ + struct bio *bio; + + bio = bio_alloc(GFP_KERNEL, nr_vecs); + if (bio == NULL) + return -ENOMEM; + + 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; + return 0; +} + +/* + * 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(). + */ +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->bio_count++; + dio->bios_in_flight++; + spin_unlock_irqrestore(&dio->bio_lock, flags); + if (dio->is_async && dio->rw == READ) + bio_set_pages_dirty(bio); + submit_bio(dio->rw, bio); + + dio->bio = NULL; + dio->boundary = 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. + */ +static struct bio *dio_await_one(struct dio *dio) +{ + unsigned long flags; + struct bio *bio; + + spin_lock_irqsave(&dio->bio_lock, flags); + while (dio->bio_list == NULL) { + set_current_state(TASK_UNINTERRUPTIBLE); + if (dio->bio_list == NULL) { + dio->waiter = current; + spin_unlock_irqrestore(&dio->bio_lock, flags); + blk_run_address_space(dio->inode->i_mapping); + io_schedule(); + spin_lock_irqsave(&dio->bio_lock, flags); + dio->waiter = NULL; + } + set_current_state(TASK_RUNNING); + } + 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->result = -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); + } + finished_one_bio(dio); + return uptodate ? 0 : -EIO; +} + +/* + * Wait on and process all in-flight BIOs. + */ +static int dio_await_completion(struct dio *dio) +{ + int ret = 0; + + if (dio->bio) + dio_bio_submit(dio); + + /* + * The bio_lock is not held for the read of bio_count. + * This is ok since it is the dio_bio_complete() that changes + * bio_count. + */ + while (dio->bio_count) { + struct bio *bio = dio_await_one(dio); + int ret2; + + ret2 = dio_bio_complete(dio, bio); + if (ret == 0) + ret = ret2; + } + return ret; +} + +/* + * 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_blocks() 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_blocks() 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) { + map_bh->b_state = 0; + map_bh->b_size = 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++; + + create = dio->rw == WRITE; + if (dio->lock_type == DIO_LOCKING) { + if (dio->block_in_file < (i_size_read(dio->inode) >> + dio->blkbits)) + create = 0; + } else if (dio->lock_type == DIO_NO_LOCKING) { + create = 0; + } + /* + * For writes inside i_size we forbid block creations: only + * overwrites are permitted. We fall back to buffered writes + * at a higher level for inside-i_size block-instantiating + * writes. + */ + ret = (*dio->get_blocks)(dio->inode, fs_startblk, fs_count, + 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)); + BUG_ON(nr_pages <= 0); + ret = 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) { + /* + * See whether this new request is contiguous with the old + */ + if (dio->final_block_in_bio != dio->cur_page_block) + dio_bio_submit(dio); + /* + * Submit now if the underlying fs is about to perform a + * metadata read + */ + 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; + + /* + * 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; +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(dio->curr_user_address); + 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_blocks 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_blocks(). 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)) { + char *kaddr; + + /* AKPM: eargh, -ENOTBLK is a hack */ + if (dio->rw == WRITE) { + page_cache_release(page); + return -ENOTBLK; + } + + if (dio->block_in_file >= + i_size_read(dio->inode)>>blkbits) { + /* We hit eof */ + page_cache_release(page); + goto out; + } + kaddr = kmap_atomic(page, KM_USER0); + memset(kaddr + (block_in_page << blkbits), + 0, 1 << blkbits); + flush_dcache_page(page); + kunmap_atomic(kaddr, KM_USER0); + 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: + if (dio->block_in_file > dio->final_block_in_request) + BUG(); + 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_sem 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_blocks_t get_blocks, dio_iodone_t end_io, + struct dio *dio) +{ + unsigned long user_addr; + int seg; + ssize_t ret = 0; + ssize_t ret2; + size_t bytes; + + dio->bio = NULL; + dio->inode = inode; + dio->rw = rw; + dio->blkbits = blkbits; + dio->blkfactor = inode->i_blkbits - blkbits; + dio->start_zero_done = 0; + dio->size = 0; + dio->block_in_file = offset >> blkbits; + dio->blocks_available = 0; + dio->cur_page = NULL; + + dio->boundary = 0; + dio->reap_counter = 0; + dio->get_blocks = get_blocks; + dio->end_io = end_io; + dio->map_bh.b_private = NULL; + dio->final_block_in_bio = -1; + dio->next_block_for_io = -1; + + dio->page_errors = 0; + dio->result = 0; + dio->iocb = iocb; + + /* + * BIO completion state. + * + * ->bio_count starts out at one, and we decrement it to zero after all + * BIOs are submitted. This to avoid the situation where a really fast + * (or synchronous) device could take the count to zero while we're + * still submitting BIOs. + */ + dio->bio_count = 1; + dio->bios_in_flight = 0; + spin_lock_init(&dio->bio_lock); + dio->bio_list = NULL; + dio->waiter = NULL; + + /* + * 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; + else + dio->pages_in_io = 0; + + 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 && rw == WRITE) { + /* + * 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_sem go now that its achieved its purpose + * of protecting us from looking up uninitialized blocks. + */ + if ((rw == READ) && (dio->lock_type == DIO_LOCKING)) + up(&dio->inode->i_sem); + + /* + * OK, all BIOs are submitted, so we can decrement bio_count to truly + * reflect the number of to-be-processed BIOs. + */ + if (dio->is_async) { + int should_wait = 0; + + if (dio->result < dio->size && rw == WRITE) { + dio->waiter = current; + should_wait = 1; + } + if (ret == 0) + ret = dio->result; + finished_one_bio(dio); /* This can free the dio */ + blk_run_address_space(inode->i_mapping); + if (should_wait) { + unsigned long flags; + /* + * Wait for already issued I/O to drain out and + * release its references to user-space pages + * before returning to fallback on buffered I/O + */ + + spin_lock_irqsave(&dio->bio_lock, flags); + set_current_state(TASK_UNINTERRUPTIBLE); + while (dio->bio_count) { + spin_unlock_irqrestore(&dio->bio_lock, flags); + io_schedule(); + spin_lock_irqsave(&dio->bio_lock, flags); + set_current_state(TASK_UNINTERRUPTIBLE); + } + spin_unlock_irqrestore(&dio->bio_lock, flags); + set_current_state(TASK_RUNNING); + kfree(dio); + } + } else { + ssize_t transferred = 0; + + finished_one_bio(dio); + ret2 = dio_await_completion(dio); + if (ret == 0) + ret = ret2; + if (ret == 0) + ret = dio->page_errors; + if (dio->result) { + loff_t i_size = i_size_read(inode); + + transferred = dio->result; + /* + * Adjust the return value if the read crossed a + * non-block-aligned EOF. + */ + if (rw == READ && (offset + transferred > i_size)) + transferred = i_size - offset; + } + dio_complete(dio, offset, transferred); + if (ret == 0) + ret = transferred; + + /* We could have also come here on an AIO file extend */ + if (!is_sync_kiocb(iocb) && rw == WRITE && + ret >= 0 && dio->result == dio->size) + /* + * For AIO writes where we have completed the + * i/o, we have to mark the the aio complete. + */ + aio_complete(iocb, ret, 0); + kfree(dio); + } + return ret; +} + +/* + * This is a library function for use by filesystem drivers. + * The locking rules are governed by the dio_lock_type parameter. + * + * DIO_NO_LOCKING (no locking, for raw block device access) + * For writes, i_sem is not held on entry; it is never taken. + * + * DIO_LOCKING (simple locking for regular files) + * For writes we are called under i_sem and return with i_sem held, even though + * it is internally dropped. + * For reads, i_sem is not held on entry, but it is taken and dropped before + * returning. + * + * DIO_OWN_LOCKING (filesystem provides synchronisation and handling of + * uninitialised data, allowing parallel direct readers and writers) + * For writes we are called without i_sem, return without it, never touch it. + * For reads, i_sem is held on entry and will be released before returning. + * + * Additional i_alloc_sem locking requirements described inline below. + */ +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_blocks_t get_blocks, dio_iodone_t end_io, + int dio_lock_type) +{ + 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; + int reader_with_isem = (rw == READ && dio_lock_type == DIO_OWN_LOCKING); + + if (rw & WRITE) + current->flags |= PF_SYNCWRITE; + + if (bdev) + bdev_blkbits = blksize_bits(bdev_hardsect_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; + + /* + * For block device access DIO_NO_LOCKING is used, + * neither readers nor writers do any locking at all + * For regular files using DIO_LOCKING, + * readers need to grab i_sem and i_alloc_sem + * writers need to grab i_alloc_sem only (i_sem is already held) + * For regular files using DIO_OWN_LOCKING, + * neither readers nor writers take any locks here + * (i_sem is already held and release for writers here) + */ + dio->lock_type = dio_lock_type; + if (dio_lock_type != DIO_NO_LOCKING) { + /* watch out for a 0 len io from a tricksy fs */ + if (rw == READ && end > offset) { + struct address_space *mapping; + + mapping = iocb->ki_filp->f_mapping; + if (dio_lock_type != DIO_OWN_LOCKING) { + down(&inode->i_sem); + reader_with_isem = 1; + } + + retval = filemap_write_and_wait_range(mapping, offset, + end - 1); + if (retval) { + kfree(dio); + goto out; + } + + if (dio_lock_type == DIO_OWN_LOCKING) { + up(&inode->i_sem); + reader_with_isem = 0; + } + } + + if (dio_lock_type == DIO_LOCKING) + down_read(&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_blocks, end_io, dio); + + if (rw == READ && dio_lock_type == DIO_LOCKING) + reader_with_isem = 0; + +out: + if (reader_with_isem) + up(&inode->i_sem); + if (rw & WRITE) + current->flags &= ~PF_SYNCWRITE; + return retval; +} +EXPORT_SYMBOL(__blockdev_direct_IO); |
