Initial import

1 files changed, 1332 insertions, 0 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
new file mode 100644
index 000000000..745d23426
--- /dev/null
+++ b/fs/direct-io.c
@@ -0,0 +1,1332 @@
+/*
+ * 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 <linux/atomic.h>
+#include <linux/prefetch.h>
+
+/*
+ * How many user pages to map in one call to get_user_pages().  This determines
+ * the size of a structure in the slab cache
+ */
+#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.
+ */
+
+/* dio_state only used in the submission path */
+
+struct dio_submit {
+	struct bio *bio;		/* bio under assembly */
+	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 */
+	sector_t block_in_file;		/* Current offset into the underlying
+					   file in dio_block units. */
+	unsigned blocks_available;	/* At block_in_file.  changes */
+	int reap_counter;		/* rate limit reaping */
+	sector_t final_block_in_request;/* doesn't change */
+	int boundary;			/* prev block is at a boundary */
+	get_block_t *get_block;		/* block mapping 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 */
+
+	/*
+	 * 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 */
+
+	struct iov_iter *iter;
+	/*
+	 * 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 */
+	size_t from, to;
+};
+
+/* dio_state communicated between submission path and end_io */
+struct dio {
+	int flags;			/* doesn't change */
+	int rw;
+	struct inode *inode;
+	loff_t i_size;			/* i_size when submitted */
+	dio_iodone_t *end_io;		/* IO completion function */
+
+	void *private;			/* copy from map_bh.b_private */
+
+	/* BIO completion state */
+	spinlock_t bio_lock;		/* protects BIO fields below */
+	int page_errors;		/* errno from get_user_pages() */
+	int is_async;			/* is IO async ? */
+	bool defer_completion;		/* defer AIO completion to workqueue? */
+	int io_error;			/* IO error in completion path */
+	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 */
+	ssize_t result;                 /* IO result */
+
+	/*
+	 * 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.
+	 */
+	union {
+		struct page *pages[DIO_PAGES];	/* page buffer */
+		struct work_struct complete_work;/* deferred AIO completion */
+	};
+} ____cacheline_aligned_in_smp;
+
+static struct kmem_cache *dio_cache __read_mostly;
+
+/*
+ * How many pages are in the queue?
+ */
+static inline unsigned dio_pages_present(struct dio_submit *sdio)
+{
+	return sdio->tail - sdio->head;
+}
+
+/*
+ * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
+ */
+static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
+{
+	ssize_t ret;
+
+	ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
+				&sdio->from);
+
+	if (ret < 0 && sdio->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;
+		sdio->head = 0;
+		sdio->tail = 1;
+		sdio->from = 0;
+		sdio->to = PAGE_SIZE;
+		return 0;
+	}
+
+	if (ret >= 0) {
+		iov_iter_advance(sdio->iter, ret);
+		ret += sdio->from;
+		sdio->head = 0;
+		sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
+		sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
+		return 0;
+	}
+	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 inline struct page *dio_get_page(struct dio *dio,
+					struct dio_submit *sdio)
+{
+	if (dio_pages_present(sdio) == 0) {
+		int ret;
+
+		ret = dio_refill_pages(dio, sdio);
+		if (ret)
+			return ERR_PTR(ret);
+		BUG_ON(dio_pages_present(sdio) == 0);
+	}
+	return dio->pages[sdio->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 drops i_dio_count, 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->private);
+
+	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+		inode_dio_end(dio->inode);
+
+	if (is_async) {
+		if (dio->rw & WRITE) {
+			int err;
+
+			err = generic_write_sync(dio->iocb->ki_filp, offset,
+						 transferred);
+			if (err < 0 && ret > 0)
+				ret = err;
+		}
+
+		dio->iocb->ki_complete(dio->iocb, ret, 0);
+	}
+
+	kmem_cache_free(dio_cache, dio);
+	return ret;
+}
+
+static void dio_aio_complete_work(struct work_struct *work)
+{
+	struct dio *dio = container_of(work, struct dio, complete_work);
+
+	dio_complete(dio, dio->iocb->ki_pos, 0, true);
+}
+
+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) {
+		if (dio->result && dio->defer_completion) {
+			INIT_WORK(&dio->complete_work, dio_aio_complete_work);
+			queue_work(dio->inode->i_sb->s_dio_done_wq,
+				   &dio->complete_work);
+		} else {
+			dio_complete(dio, dio->iocb->ki_pos, 0, true);
+		}
+	}
+}
+
+/*
+ * 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 inline void
+dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
+	      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_iter.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;
+
+	sdio->bio = bio;
+	sdio->logical_offset_in_bio = sdio->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 inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
+{
+	struct bio *bio = sdio->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 (sdio->submit_io)
+		sdio->submit_io(dio->rw, bio, dio->inode,
+			       sdio->logical_offset_in_bio);
+	else
+		submit_bio(dio->rw, bio);
+
+	sdio->bio = NULL;
+	sdio->boundary = 0;
+	sdio->logical_offset_in_bio = 0;
+}
+
+/*
+ * Release any resources in case of a failure
+ */
+static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
+{
+	while (sdio->head < sdio->tail)
+		page_cache_release(dio->pages[sdio->head++]);
+}
+
+/*
+ * 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;
+	unsigned i;
+
+	if (!uptodate)
+		dio->io_error = -EIO;
+
+	if (dio->is_async && dio->rw == READ) {
+		bio_check_pages_dirty(bio);	/* transfers ownership */
+	} else {
+		bio_for_each_segment_all(bvec, bio, i) {
+			struct page *page = bvec->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 inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
+{
+	int ret = 0;
+
+	if (sdio->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;
+		}
+		sdio->reap_counter = 0;
+	}
+	return ret;
+}
+
+/*
+ * Create workqueue for deferred direct IO completions. We allocate the
+ * workqueue when it's first needed. This avoids creating workqueue for
+ * filesystems that don't need it and also allows us to create the workqueue
+ * late enough so the we can include s_id in the name of the workqueue.
+ */
+static int sb_init_dio_done_wq(struct super_block *sb)
+{
+	struct workqueue_struct *old;
+	struct workqueue_struct *wq = alloc_workqueue("dio/%s",
+						      WQ_MEM_RECLAIM, 0,
+						      sb->s_id);
+	if (!wq)
+		return -ENOMEM;
+	/*
+	 * This has to be atomic as more DIOs can race to create the workqueue
+	 */
+	old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
+	/* Someone created workqueue before us? Free ours... */
+	if (old)
+		destroy_workqueue(wq);
+	return 0;
+}
+
+static int dio_set_defer_completion(struct dio *dio)
+{
+	struct super_block *sb = dio->inode->i_sb;
+
+	if (dio->defer_completion)
+		return 0;
+	dio->defer_completion = true;
+	if (!sb->s_dio_done_wq)
+		return sb_init_dio_done_wq(sb);
+	return 0;
+}
+
+/*
+ * Call into the fs to map some more disk blocks.  We record the current number
+ * of available blocks at sdio->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, struct dio_submit *sdio,
+			   struct buffer_head *map_bh)
+{
+	int ret;
+	sector_t fs_startblk;	/* Into file, in filesystem-sized blocks */
+	sector_t fs_endblk;	/* Into file, in filesystem-sized blocks */
+	unsigned long fs_count;	/* Number of filesystem-sized blocks */
+	int create;
+	unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
+
+	/*
+	 * 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(sdio->block_in_file >= sdio->final_block_in_request);
+		fs_startblk = sdio->block_in_file >> sdio->blkfactor;
+		fs_endblk = (sdio->final_block_in_request - 1) >>
+					sdio->blkfactor;
+		fs_count = fs_endblk - fs_startblk + 1;
+
+		map_bh->b_state = 0;
+		map_bh->b_size = fs_count << 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 (sdio->block_in_file < (i_size_read(dio->inode) >>
+							sdio->blkbits))
+				create = 0;
+		}
+
+		ret = (*sdio->get_block)(dio->inode, fs_startblk,
+						map_bh, create);
+
+		/* Store for completion */
+		dio->private = map_bh->b_private;
+
+		if (ret == 0 && buffer_defer_completion(map_bh))
+			ret = dio_set_defer_completion(dio);
+	}
+	return ret;
+}
+
+/*
+ * There is no bio.  Make one now.
+ */
+static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
+		sector_t start_sector, struct buffer_head *map_bh)
+{
+	sector_t sector;
+	int ret, nr_pages;
+
+	ret = dio_bio_reap(dio, sdio);
+	if (ret)
+		goto out;
+	sector = start_sector << (sdio->blkbits - 9);
+	nr_pages = min(sdio->pages_in_io, bio_get_nr_vecs(map_bh->b_bdev));
+	BUG_ON(nr_pages <= 0);
+	dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
+	sdio->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 inline int dio_bio_add_page(struct dio_submit *sdio)
+{
+	int ret;
+
+	ret = bio_add_page(sdio->bio, sdio->cur_page,
+			sdio->cur_page_len, sdio->cur_page_offset);
+	if (ret == sdio->cur_page_len) {
+		/*
+		 * Decrement count only, if we are done with this page
+		 */
+		if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
+			sdio->pages_in_io--;
+		page_cache_get(sdio->cur_page);
+		sdio->final_block_in_bio = sdio->cur_page_block +
+			(sdio->cur_page_len >> sdio->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 inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
+		struct buffer_head *map_bh)
+{
+	int ret = 0;
+
+	if (sdio->bio) {
+		loff_t cur_offset = sdio->cur_page_fs_offset;
+		loff_t bio_next_offset = sdio->logical_offset_in_bio +
+			sdio->bio->bi_iter.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 (sdio->final_block_in_bio != sdio->cur_page_block ||
+		    cur_offset != bio_next_offset)
+			dio_bio_submit(dio, sdio);
+	}
+
+	if (sdio->bio == NULL) {
+		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
+		if (ret)
+			goto out;
+	}
+
+	if (dio_bio_add_page(sdio) != 0) {
+		dio_bio_submit(dio, sdio);
+		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
+		if (ret == 0) {
+			ret = dio_bio_add_page(sdio);
+			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 inline int
+submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
+		    unsigned offset, unsigned len, sector_t blocknr,
+		    struct buffer_head *map_bh)
+{
+	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 (sdio->cur_page == page &&
+	    sdio->cur_page_offset + sdio->cur_page_len == offset &&
+	    sdio->cur_page_block +
+	    (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
+		sdio->cur_page_len += len;
+		goto out;
+	}
+
+	/*
+	 * If there's a deferred page already there then send it.
+	 */
+	if (sdio->cur_page) {
+		ret = dio_send_cur_page(dio, sdio, map_bh);
+		page_cache_release(sdio->cur_page);
+		sdio->cur_page = NULL;
+		if (ret)
+			return ret;
+	}
+
+	page_cache_get(page);		/* It is in dio */
+	sdio->cur_page = page;
+	sdio->cur_page_offset = offset;
+	sdio->cur_page_len = len;
+	sdio->cur_page_block = blocknr;
+	sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
+out:
+	/*
+	 * If sdio->boundary then we want to schedule the IO now to
+	 * avoid metadata seeks.
+	 */
+	if (sdio->boundary) {
+		ret = dio_send_cur_page(dio, sdio, map_bh);
+		dio_bio_submit(dio, sdio);
+		page_cache_release(sdio->cur_page);
+		sdio->cur_page = NULL;
+	}
+	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, struct buffer_head *map_bh)
+{
+	unsigned i;
+	unsigned nblocks;
+
+	nblocks = map_bh->b_size >> dio->inode->i_blkbits;
+
+	for (i = 0; i < nblocks; i++) {
+		unmap_underlying_metadata(map_bh->b_bdev,
+					  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 inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
+		int end, struct buffer_head *map_bh)
+{
+	unsigned dio_blocks_per_fs_block;
+	unsigned this_chunk_blocks;	/* In dio_blocks */
+	unsigned this_chunk_bytes;
+	struct page *page;
+
+	sdio->start_zero_done = 1;
+	if (!sdio->blkfactor || !buffer_new(map_bh))
+		return;
+
+	dio_blocks_per_fs_block = 1 << sdio->blkfactor;
+	this_chunk_blocks = sdio->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 << sdio->blkbits;
+
+	page = ZERO_PAGE(0);
+	if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
+				sdio->next_block_for_io, map_bh))
+		return;
+
+	sdio->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, struct dio_submit *sdio,
+			struct buffer_head *map_bh)
+{
+	const unsigned blkbits = sdio->blkbits;
+	int ret = 0;
+
+	while (sdio->block_in_file < sdio->final_block_in_request) {
+		struct page *page;
+		size_t from, to;
+
+		page = dio_get_page(dio, sdio);
+		if (IS_ERR(page)) {
+			ret = PTR_ERR(page);
+			goto out;
+		}
+		from = sdio->head ? 0 : sdio->from;
+		to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
+		sdio->head++;
+
+		while (from < to) {
+			unsigned this_chunk_bytes;	/* # of bytes mapped */
+			unsigned this_chunk_blocks;	/* # of blocks */
+			unsigned u;
+
+			if (sdio->blocks_available == 0) {
+				/*
+				 * Need to go and map some more disk
+				 */
+				unsigned long blkmask;
+				unsigned long dio_remainder;
+
+				ret = get_more_blocks(dio, sdio, map_bh);
+				if (ret) {
+					page_cache_release(page);
+					goto out;
+				}
+				if (!buffer_mapped(map_bh))
+					goto do_holes;
+
+				sdio->blocks_available =
+						map_bh->b_size >> sdio->blkbits;
+				sdio->next_block_for_io =
+					map_bh->b_blocknr << sdio->blkfactor;
+				if (buffer_new(map_bh))
+					clean_blockdev_aliases(dio, map_bh);
+
+				if (!sdio->blkfactor)
+					goto do_holes;
+
+				blkmask = (1 << sdio->blkfactor) - 1;
+				dio_remainder = (sdio->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))
+					sdio->next_block_for_io += dio_remainder;
+				sdio->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 (sdio->block_in_file >=
+						i_size_aligned >> blkbits) {
+					/* We hit eof */
+					page_cache_release(page);
+					goto out;
+				}
+				zero_user(page, from, 1 << blkbits);
+				sdio->block_in_file++;
+				from += 1 << blkbits;
+				dio->result += 1 << blkbits;
+				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(sdio->blkfactor && !sdio->start_zero_done))
+				dio_zero_block(dio, sdio, 0, map_bh);
+
+			/*
+			 * Work out, in this_chunk_blocks, how much disk we
+			 * can add to this page
+			 */
+			this_chunk_blocks = sdio->blocks_available;
+			u = (to - from) >> blkbits;
+			if (this_chunk_blocks > u)
+				this_chunk_blocks = u;
+			u = sdio->final_block_in_request - sdio->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);
+
+			if (this_chunk_blocks == sdio->blocks_available)
+				sdio->boundary = buffer_boundary(map_bh);
+			ret = submit_page_section(dio, sdio, page,
+						  from,
+						  this_chunk_bytes,
+						  sdio->next_block_for_io,
+						  map_bh);
+			if (ret) {
+				page_cache_release(page);
+				goto out;
+			}
+			sdio->next_block_for_io += this_chunk_blocks;
+
+			sdio->block_in_file += this_chunk_blocks;
+			from += this_chunk_bytes;
+			dio->result += this_chunk_bytes;
+			sdio->blocks_available -= this_chunk_blocks;
+next_block:
+			BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
+			if (sdio->block_in_file == sdio->final_block_in_request)
+				break;
+		}
+
+		/* Drop the ref which was taken in get_user_pages() */
+		page_cache_release(page);
+	}
+out:
+	return ret;
+}
+
+static inline int drop_refcount(struct dio *dio)
+{
+	int ret2;
+	unsigned long flags;
+
+	/*
+	 * 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 ->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);
+	return ret2;
+}
+
+/*
+ * 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.
+ *  - 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.
+ *
+ * To help with locking against truncate we incremented the i_dio_count
+ * counter before starting direct I/O, and decrement it once we are done.
+ * Truncate can wait for it to reach zero to provide exclusion.  It is
+ * expected that filesystem provide exclusion between new direct I/O
+ * and truncates.  For DIO_LOCKING filesystems this is done by i_mutex,
+ * but other filesystems need to take care of this on their own.
+ *
+ * NOTE: if you pass "sdio" to anything by pointer make sure that function
+ * is always inlined. Otherwise gcc is unable to split the structure into
+ * individual fields and will generate much worse code. This is important
+ * for the whole file.
+ */
+static inline ssize_t
+do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
+		      struct block_device *bdev, struct iov_iter *iter,
+		      loff_t offset, get_block_t get_block, dio_iodone_t end_io,
+		      dio_submit_t submit_io, int flags)
+{
+	unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
+	unsigned blkbits = i_blkbits;
+	unsigned blocksize_mask = (1 << blkbits) - 1;
+	ssize_t retval = -EINVAL;
+	size_t count = iov_iter_count(iter);
+	loff_t end = offset + count;
+	struct dio *dio;
+	struct dio_submit sdio = { 0, };
+	struct buffer_head map_bh = { 0, };
+	struct blk_plug plug;
+	unsigned long align = offset | iov_iter_alignment(iter);
+
+	/*
+	 * Avoid references to bdev if not absolutely needed to give
+	 * the early prefetch in the caller enough time.
+	 */
+
+	if (align & blocksize_mask) {
+		if (bdev)
+			blkbits = blksize_bits(bdev_logical_block_size(bdev));
+		blocksize_mask = (1 << blkbits) - 1;
+		if (align & blocksize_mask)
+			goto out;
+	}
+
+	/* watch out for a 0 len io from a tricksy fs */
+	if (iov_iter_rw(iter) == READ && !iov_iter_count(iter))
+		return 0;
+
+	dio = kmem_cache_alloc(dio_cache, 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) {
+		if (iov_iter_rw(iter) == READ) {
+			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);
+				kmem_cache_free(dio_cache, dio);
+				goto out;
+			}
+		}
+	}
+
+	/*
+	 * For file extending writes updating i_size before data writeouts
+	 * complete can expose uninitialized blocks in dumb filesystems.
+	 * In that case we need to wait for I/O completion even if asked
+	 * for an asynchronous write.
+	 */
+	if (is_sync_kiocb(iocb))
+		dio->is_async = false;
+	else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
+		 iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
+		dio->is_async = false;
+	else
+		dio->is_async = true;
+
+	dio->inode = inode;
+	dio->rw = iov_iter_rw(iter) == WRITE ? WRITE_ODIRECT : READ;
+
+	/*
+	 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
+	 * so that we can call ->fsync.
+	 */
+	if (dio->is_async && iov_iter_rw(iter) == WRITE &&
+	    ((iocb->ki_filp->f_flags & O_DSYNC) ||
+	     IS_SYNC(iocb->ki_filp->f_mapping->host))) {
+		retval = dio_set_defer_completion(dio);
+		if (retval) {
+			/*
+			 * We grab i_mutex only for reads so we don't have
+			 * to release it here
+			 */
+			kmem_cache_free(dio_cache, dio);
+			goto out;
+		}
+	}
+
+	/*
+	 * Will be decremented at I/O completion time.
+	 */
+	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+		inode_dio_begin(inode);
+
+	retval = 0;
+	sdio.blkbits = blkbits;
+	sdio.blkfactor = i_blkbits - blkbits;
+	sdio.block_in_file = offset >> blkbits;
+
+	sdio.get_block = get_block;
+	dio->end_io = end_io;
+	sdio.submit_io = submit_io;
+	sdio.final_block_in_bio = -1;
+	sdio.next_block_for_io = -1;
+
+	dio->iocb = iocb;
+	dio->i_size = i_size_read(inode);
+
+	spin_lock_init(&dio->bio_lock);
+	dio->refcount = 1;
+
+	sdio.iter = iter;
+	sdio.final_block_in_request =
+		(offset + iov_iter_count(iter)) >> blkbits;
+
+	/*
+	 * In case of non-aligned buffers, we may need 2 more
+	 * pages since we need to zero out first and last block.
+	 */
+	if (unlikely(sdio.blkfactor))
+		sdio.pages_in_io = 2;
+
+	sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
+
+	blk_start_plug(&plug);
+
+	retval = do_direct_IO(dio, &sdio, &map_bh);
+	if (retval)
+		dio_cleanup(dio, &sdio);
+
+	if (retval == -ENOTBLK) {
+		/*
+		 * The remaining part of the request will be
+		 * be handled by buffered I/O when we return
+		 */
+		retval = 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, &sdio, 1, &map_bh);
+
+	if (sdio.cur_page) {
+		ssize_t ret2;
+
+		ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
+		if (retval == 0)
+			retval = ret2;
+		page_cache_release(sdio.cur_page);
+		sdio.cur_page = NULL;
+	}
+	if (sdio.bio)
+		dio_bio_submit(dio, &sdio);
+
+	blk_finish_plug(&plug);
+
+	/*
+	 * 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, &sdio);
+
+	/*
+	 * 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 (iov_iter_rw(iter) == 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(retval == -EIOCBQUEUED);
+	if (dio->is_async && retval == 0 && dio->result &&
+	    (iov_iter_rw(iter) == READ || dio->result == count))
+		retval = -EIOCBQUEUED;
+	else
+		dio_await_completion(dio);
+
+	if (drop_refcount(dio) == 0) {
+		retval = dio_complete(dio, offset, retval, false);
+	} else
+		BUG_ON(retval != -EIOCBQUEUED);
+
+out:
+	return retval;
+}
+
+ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
+			     struct block_device *bdev, struct iov_iter *iter,
+			     loff_t offset, get_block_t get_block,
+			     dio_iodone_t end_io, dio_submit_t submit_io,
+			     int flags)
+{
+	/*
+	 * The block device state is needed in the end to finally
+	 * submit everything.  Since it's likely to be cache cold
+	 * prefetch it here as first thing to hide some of the
+	 * latency.
+	 *
+	 * Attempt to prefetch the pieces we likely need later.
+	 */
+	prefetch(&bdev->bd_disk->part_tbl);
+	prefetch(bdev->bd_queue);
+	prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
+
+	return do_blockdev_direct_IO(iocb, inode, bdev, iter, offset, get_block,
+				     end_io, submit_io, flags);
+}
+
+EXPORT_SYMBOL(__blockdev_direct_IO);
+
+static __init int dio_init(void)
+{
+	dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
+	return 0;
+}
+module_init(dio_init)