--- /dev/null
+/*
+ * 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)
Code Review / kvmfornfv.git / blobdiff