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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /fs/direct-io.c
downloadlwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
lwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.zip
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'fs/direct-io.c')
-rw-r--r--fs/direct-io.c1258
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(&current->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(&current->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);