ClabureDB: Classified Bug-Reports Database

   /*
    * fs/direct-io.c
    *
    * Copyright (C) 2002, Linus Torvalds.
    *
    * O_DIRECT
    *
    * 04Jul2002        Andrew Morton
    *                Initial version
   * 11Sep2002        janetinc@us.ibm.com
   *                 added readv/writev support.
   * 29Oct2002        Andrew Morton
   *                rewrote bio_add_page() support.
   * 30Oct2002        pbadari@us.ibm.com
   *                added support for non-aligned IO.
   * 06Nov2002        pbadari@us.ibm.com
   *                added asynchronous IO support.
   * 21Jul2003        nathans@sgi.com
   *                added IO completion notifier.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/highmem.h>
  #include <linux/pagemap.h>
  #include <linux/task_io_accounting_ops.h>
  #include <linux/bio.h>
  #include <linux/wait.h>
  #include <linux/err.h>
  #include <linux/blkdev.h>
  #include <linux/buffer_head.h>
  #include <linux/rwsem.h>
  #include <linux/uio.h>
  #include <asm/atomic.h>
  
  /*
   * How many user pages to map in one call to get_user_pages().  This determines
   * the size of a structure on the stack.
   */
  #define DIO_PAGES        64
  
  /*
   * This code generally works in units of "dio_blocks".  A dio_block is
   * somewhere between the hard sector size and the filesystem block size.  it
   * is determined on a per-invocation basis.   When talking to the filesystem
   * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
   * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
   * to bio_block quantities by shifting left by blkfactor.
   *
   * If blkfactor is zero then the user's request was aligned to the filesystem's
   * blocksize.
   *
   * 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_mutex 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;
          loff_t i_size;                        /* i_size when submitted */
          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_block_t *get_block;                /* 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_block() result */
  
          /*
           * Deferred addition of a page to the dio.  These variables are
           * private to dio_send_cur_page(), submit_page_section() and
          * dio_bio_add_page().
          */
         struct page *cur_page;                /* The page */
         unsigned cur_page_offset;        /* Offset into it, in bytes */
         unsigned cur_page_len;                /* Nr of bytes at cur_page_offset */
         sector_t cur_page_block;        /* Where it starts */
 
         /*
          * 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 */
         unsigned long refcount;                /* direct_io_worker() and bios */
         struct bio *bio_list;                /* singly linked via bi_private */
         struct task_struct *waiter;        /* waiting task (NULL if none) */
 
         /* AIO related stuff */
         struct kiocb *iocb;                /* kiocb */
         int is_async;                        /* is IO async ? */
         int io_error;                        /* IO error in completion path */
         ssize_t result;                 /* IO result */
 };
 
 /*
  * How many pages are in the queue?
  */
 static inline unsigned dio_pages_present(struct dio *dio)
 {
         return dio->tail - dio->head;
 }
 
 /*
  * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
  */
 static int dio_refill_pages(struct dio *dio)
 {
         int ret;
         int nr_pages;
 
         nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
         ret = get_user_pages_fast(
                 dio->curr_user_address,                /* Where from? */
                 nr_pages,                        /* How many pages? */
                 dio->rw == READ,                /* Write to memory? */
                 &dio->pages[0]);                /* Put results here */
 
         if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
                 struct page *page = ZERO_PAGE(0);
                 /*
                  * A memory fault, but the filesystem has some outstanding
                  * mapped blocks.  We need to use those blocks up to avoid
                  * leaking stale data in the file.
                  */
                 if (dio->page_errors == 0)
                         dio->page_errors = ret;
                 page_cache_get(page);
                 dio->pages[0] = page;
                 dio->head = 0;
                 dio->tail = 1;
                 ret = 0;
                 goto out;
         }
 
         if (ret >= 0) {
                 dio->curr_user_address += ret * PAGE_SIZE;
                 dio->curr_page += ret;
                 dio->head = 0;
                 dio->tail = ret;
                 ret = 0;
         }
 out:
         return ret;        
 }
 
 /*
  * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
  * buffered inside the dio so that we can call get_user_pages() against a
  * decent number of pages, less frequently.  To provide nicer use of the
  * L1 cache.
  */
 static struct page *dio_get_page(struct dio *dio)
 {
         if (dio_pages_present(dio) == 0) {
                 int ret;
 
                 ret = dio_refill_pages(dio);
                 if (ret)
                         return ERR_PTR(ret);
                 BUG_ON(dio_pages_present(dio) == 0);
         }
         return dio->pages[dio->head++];
 }
 
 /**
  * dio_complete() - called when all DIO BIO I/O has been completed
  * @offset: the byte offset in the file of the completed operation
  *
  * This releases locks as dictated by the locking type, lets interested parties
  * know that a DIO operation has completed, and calculates the resulting return
  * code for the operation.
  *
  * It lets the filesystem know if it registered an interest earlier via
  * get_block.  Pass the private field of the map buffer_head so that
  * filesystems can use it to hold additional state between get_block calls and
  * dio_complete.
  */
 static int dio_complete(struct dio *dio, loff_t offset, int ret)
 {
         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 (dio->end_io && dio->result)
                 dio->end_io(dio->iocb, offset, transferred,
                             dio->map_bh.b_private);
         if (dio->lock_type == DIO_LOCKING)
                 /* lockdep: non-owner release */
                 up_read_non_owner(&dio->inode->i_alloc_sem);
 
         if (ret == 0)
                 ret = dio->page_errors;
         if (ret == 0)
                 ret = dio->io_error;
         if (ret == 0)
                 ret = transferred;
 
         return ret;
 }
 
 static int dio_bio_complete(struct dio *dio, struct bio *bio);
 /*
  * Asynchronous IO callback. 
  */
 static void dio_bio_end_aio(struct bio *bio, int error)
 {
         struct dio *dio = bio->bi_private;
         unsigned long remaining;
         unsigned long flags;
 
         /* cleanup the bio */
         dio_bio_complete(dio, bio);
 
         spin_lock_irqsave(&dio->bio_lock, flags);
         remaining = --dio->refcount;
         if (remaining == 1 && dio->waiter)
                 wake_up_process(dio->waiter);
         spin_unlock_irqrestore(&dio->bio_lock, flags);
 
         if (remaining == 0) {
                 int ret = dio_complete(dio, dio->iocb->ki_pos, 0);
                 aio_complete(dio->iocb, ret, 0);
                 kfree(dio);
         }
 }
 
 /*
  * The BIO completion handler simply queues the BIO up for the process-context
  * handler.
  *
  * During I/O bi_private points at the dio.  After I/O, bi_private is used to
  * implement a singly-linked list of completed BIOs, at dio->bio_list.
  */
 static void dio_bio_end_io(struct bio *bio, int error)
 {
         struct dio *dio = bio->bi_private;
         unsigned long flags;
 
         spin_lock_irqsave(&dio->bio_lock, flags);
         bio->bi_private = dio->bio_list;
         dio->bio_list = bio;
         if (--dio->refcount == 1 && dio->waiter)
                 wake_up_process(dio->waiter);
         spin_unlock_irqrestore(&dio->bio_lock, flags);
 }
 
 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().
  *
  * bios hold a dio reference between submit_bio and ->end_io.
  */
 static void dio_bio_submit(struct dio *dio)
 {
         struct bio *bio = dio->bio;
         unsigned long flags;
 
         bio->bi_private = dio;
 
         spin_lock_irqsave(&dio->bio_lock, flags);
         dio->refcount++;
         spin_unlock_irqrestore(&dio->bio_lock, flags);
 
         if (dio->is_async && dio->rw == READ)
                 bio_set_pages_dirty(bio);
 
         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.  NULL is
  * returned once all BIOs have been completed.  This must only be called once
  * all bios have been issued so that dio->refcount can only decrease.  This
  * requires that that the caller hold a reference on the dio.
  */
 static struct bio *dio_await_one(struct dio *dio)
 {
         unsigned long flags;
         struct bio *bio = NULL;
 
         spin_lock_irqsave(&dio->bio_lock, flags);
 
         /*
          * Wait as long as the list is empty and there are bios in flight.  bio
          * completion drops the count, maybe adds to the list, and wakes while
          * holding the bio_lock so we don't need set_current_state()'s barrier
          * and can call it after testing our condition.
          */
         while (dio->refcount > 1 && dio->bio_list == NULL) {
                 __set_current_state(TASK_UNINTERRUPTIBLE);
                 dio->waiter = current;
                 spin_unlock_irqrestore(&dio->bio_lock, flags);
                 io_schedule();
                 /* wake up sets us TASK_RUNNING */
                 spin_lock_irqsave(&dio->bio_lock, flags);
                 dio->waiter = NULL;
         }
         if (dio->bio_list) {
                 bio = dio->bio_list;
                 dio->bio_list = bio->bi_private;
         }
         spin_unlock_irqrestore(&dio->bio_lock, flags);
         return bio;
 }
 
 /*
  * Process one completed BIO.  No locks are held.
  */
 static int dio_bio_complete(struct dio *dio, struct bio *bio)
 {
         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
         struct bio_vec *bvec = bio->bi_io_vec;
         int page_no;
 
         if (!uptodate)
                 dio->io_error = -EIO;
 
         if (dio->is_async && dio->rw == READ) {
                 bio_check_pages_dirty(bio);        /* transfers ownership */
         } else {
                 for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
                         struct page *page = bvec[page_no].bv_page;
 
                         if (dio->rw == READ && !PageCompound(page))
                                 set_page_dirty_lock(page);
                         page_cache_release(page);
                 }
                 bio_put(bio);
         }
         return uptodate ? 0 : -EIO;
 }
 
 /*
  * Wait on and process all in-flight BIOs.  This must only be called once
  * all bios have been issued so that the refcount can only decrease.
  * This just waits for all bios to make it through dio_bio_complete.  IO
  * errors are propagated through dio->io_error and should be propagated via
  * dio_complete().
  */
 static void dio_await_completion(struct dio *dio)
 {
         struct bio *bio;
         do {
                 bio = dio_await_one(dio);
                 if (bio)
                         dio_bio_complete(dio, bio);
         } while (bio);
 }
 
 /*
  * A really large O_DIRECT read or write can generate a lot of BIOs.  So
  * to keep the memory consumption sane we periodically reap any completed BIOs
  * during the BIO generation phase.
  *
  * This also helps to limit the peak amount of pinned userspace memory.
  */
 static int dio_bio_reap(struct dio *dio)
 {
         int ret = 0;
 
         if (dio->reap_counter++ >= 64) {
                 while (dio->bio_list) {
                         unsigned long flags;
                         struct bio *bio;
                         int ret2;
 
                         spin_lock_irqsave(&dio->bio_lock, flags);
                         bio = dio->bio_list;
                         dio->bio_list = bio->bi_private;
                         spin_unlock_irqrestore(&dio->bio_lock, flags);
                         ret2 = dio_bio_complete(dio, bio);
                         if (ret == 0)
                                 ret = ret2;
                 }
                 dio->reap_counter = 0;
         }
         return ret;
 }
 
 /*
  * Call into the fs to map some more disk blocks.  We record the current number
  * of available blocks at dio->blocks_available.  These are in units of the
  * fs blocksize, (1 << inode->i_blkbits).
  *
  * The fs is allowed to map lots of blocks at once.  If it wants to do that,
  * it uses the passed inode-relative block number as the file offset, as usual.
  *
  * get_block() is passed the number of i_blkbits-sized blocks which direct_io
  * has remaining to do.  The fs should not map more than this number of blocks.
  *
  * If the fs has mapped a lot of blocks, it should populate bh->b_size to
  * indicate how much contiguous disk space has been made available at
  * bh->b_blocknr.
  *
  * If *any* of the mapped blocks are new, then the fs must set buffer_new().
  * This isn't very efficient...
  *
  * In the case of filesystem holes: the fs may return an arbitrarily-large
  * hole by returning an appropriate value in b_size and by clearing
  * buffer_mapped().  However the direct-io code will only process holes one
  * block at a time - it will repeatedly call get_block() as it walks the hole.
  */
 static int get_more_blocks(struct dio *dio)
 {
         int ret;
         struct buffer_head *map_bh = &dio->map_bh;
         sector_t fs_startblk;        /* Into file, in filesystem-sized blocks */
         unsigned long fs_count;        /* Number of filesystem-sized blocks */
         unsigned long dio_count;/* Number of dio_block-sized blocks */
         unsigned long blkmask;
         int create;
 
         /*
          * If there was a memory error and we've overwritten all the
          * mapped blocks then we can now return that memory error
          */
         ret = dio->page_errors;
         if (ret == 0) {
                 BUG_ON(dio->block_in_file >= dio->final_block_in_request);
                 fs_startblk = dio->block_in_file >> dio->blkfactor;
                 dio_count = dio->final_block_in_request - dio->block_in_file;
                 fs_count = dio_count >> dio->blkfactor;
                 blkmask = (1 << dio->blkfactor) - 1;
                 if (dio_count & blkmask)        
                         fs_count++;
 
                 map_bh->b_state = 0;
                 map_bh->b_size = fs_count << dio->inode->i_blkbits;
 
                 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_block)(dio->inode, fs_startblk,
                                                 map_bh, create);
         }
         return ret;
 }
 
 /*
  * There is no bio.  Make one now.
  */
 static int dio_new_bio(struct dio *dio, sector_t start_sector)
 {
         sector_t sector;
         int ret, nr_pages;
 
         ret = dio_bio_reap(dio);
         if (ret)
                 goto out;
         sector = start_sector << (dio->blkbits - 9);
         nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
         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;
 
         if (dio->rw & WRITE) {
                 /*
                  * Read accounting is performed in submit_bio()
                  */
                 task_io_account_write(len);
         }
 
         /*
          * Can we just grow the current page's presence in the dio?
          */
         if (        (dio->cur_page == page) &&
                 (dio->cur_page_offset + dio->cur_page_len == offset) &&
                 (dio->cur_page_block +
                         (dio->cur_page_len >> dio->blkbits) == blocknr)) {
                 dio->cur_page_len += len;
 
                 /*
                  * If dio->boundary then we want to schedule the IO now to
                  * avoid metadata seeks.
                  */
                 if (dio->boundary) {
                         ret = dio_send_cur_page(dio);
                         page_cache_release(dio->cur_page);
                         dio->cur_page = NULL;
                 }
                 goto out;
         }
 
         /*
          * If there's a deferred page already there then send it.
          */
         if (dio->cur_page) {
                 ret = dio_send_cur_page(dio);
                 page_cache_release(dio->cur_page);
                 dio->cur_page = NULL;
                 if (ret)
                         goto out;
         }
 
         page_cache_get(page);                /* It is in dio */
         dio->cur_page = page;
         dio->cur_page_offset = offset;
         dio->cur_page_len = len;
         dio->cur_page_block = blocknr;
 out:
         return ret;
 }
 
 /*
  * Clean any dirty buffers in the blockdev mapping which alias newly-created
  * file blocks.  Only called for S_ISREG files - blockdevs do not set
  * buffer_new
  */
 static void clean_blockdev_aliases(struct dio *dio)
 {
         unsigned i;
         unsigned nblocks;
 
         nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;
 
         for (i = 0; i < nblocks; i++) {
                 unmap_underlying_metadata(dio->map_bh.b_bdev,
                                         dio->map_bh.b_blocknr + i);
         }
 }
 
 /*
  * If we are not writing the entire block and get_block() allocated
  * the block for us, we need to fill-in the unused portion of the
  * block with zeros. This happens only if user-buffer, fileoffset or
  * io length is not filesystem block-size multiple.
  *
  * `end' is zero if we're doing the start of the IO, 1 at the end of the
  * IO.
  */
 static void dio_zero_block(struct dio *dio, int end)
 {
         unsigned dio_blocks_per_fs_block;
         unsigned this_chunk_blocks;        /* In dio_blocks */
         unsigned this_chunk_bytes;
         struct page *page;
 
         dio->start_zero_done = 1;
         if (!dio->blkfactor || !buffer_new(&dio->map_bh))
                 return;
 
         dio_blocks_per_fs_block = 1 << dio->blkfactor;
         this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);
 
         if (!this_chunk_blocks)
                 return;
 
         /*
          * We need to zero out part of an fs block.  It is either at the
          * beginning or the end of the fs block.
          */
         if (end) 
                 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
 
         this_chunk_bytes = this_chunk_blocks << dio->blkbits;
 
         page = ZERO_PAGE(0);
         if (submit_page_section(dio, page, 0, this_chunk_bytes, 
                                 dio->next_block_for_io))
                 return;
 
         dio->next_block_for_io += this_chunk_blocks;
 }
 
 /*
  * Walk the user pages, and the file, mapping blocks to disk and generating
  * a sequence of (page,offset,len,block) mappings.  These mappings are injected
  * into submit_page_section(), which takes care of the next stage of submission
  *
  * Direct IO against a blockdev is different from a file.  Because we can
  * happily perform page-sized but 512-byte aligned IOs.  It is important that
  * blockdev IO be able to have fine alignment and large sizes.
  *
  * So what we do is to permit the ->get_block function to populate bh.b_size
  * with the size of IO which is permitted at this offset and this i_blkbits.
  *
  * For best results, the blockdev should be set up with 512-byte i_blkbits and
  * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
  * fine alignment but still allows this function to work in PAGE_SIZE units.
  */
 static int do_direct_IO(struct dio *dio)
 {
         const unsigned blkbits = dio->blkbits;
         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
         struct page *page;
         unsigned block_in_page;
         struct buffer_head *map_bh = &dio->map_bh;
         int ret = 0;
 
         /* The I/O can start at any block offset within the first page */
         block_in_page = dio->first_block_in_page;
 
         while (dio->block_in_file < dio->final_block_in_request) {
                 page = dio_get_page(dio);
                 if (IS_ERR(page)) {
                         ret = PTR_ERR(page);
                         goto out;
                 }
 
                 while (block_in_page < blocks_per_page) {
                         unsigned offset_in_page = block_in_page << blkbits;
                         unsigned this_chunk_bytes;        /* # of bytes mapped */
                         unsigned this_chunk_blocks;        /* # of blocks */
                         unsigned u;
 
                         if (dio->blocks_available == 0) {
                                 /*
                                  * Need to go and map some more disk
                                  */
                                 unsigned long blkmask;
                                 unsigned long dio_remainder;
 
                                 ret = get_more_blocks(dio);
                                 if (ret) {
                                         page_cache_release(page);
                                         goto out;
                                 }
                                 if (!buffer_mapped(map_bh))
                                         goto do_holes;
 
                                 dio->blocks_available =
                                                 map_bh->b_size >> dio->blkbits;
                                 dio->next_block_for_io =
                                         map_bh->b_blocknr << dio->blkfactor;
                                 if (buffer_new(map_bh))
                                         clean_blockdev_aliases(dio);
 
                                 if (!dio->blkfactor)
                                         goto do_holes;
 
                                 blkmask = (1 << dio->blkfactor) - 1;
                                 dio_remainder = (dio->block_in_file & blkmask);
 
                                 /*
                                  * If we are at the start of IO and that IO
                                  * starts partway into a fs-block,
                                  * dio_remainder will be non-zero.  If the IO
                                  * is a read then we can simply advance the IO
                                  * cursor to the first block which is to be
                                  * read.  But if the IO is a write and the
                                  * block was newly allocated we cannot do that;
                                  * the start of the fs block must be zeroed out
                                  * on-disk
                                  */
                                 if (!buffer_new(map_bh))
                                         dio->next_block_for_io += dio_remainder;
                                 dio->blocks_available -= dio_remainder;
                         }
 do_holes:
                         /* Handle holes */
                         if (!buffer_mapped(map_bh)) {
                                 loff_t i_size_aligned;
 
                                 /* AKPM: eargh, -ENOTBLK is a hack */
                                 if (dio->rw & WRITE) {
                                         page_cache_release(page);
                                         return -ENOTBLK;
                                 }
 
                                 /*
                                  * Be sure to account for a partial block as the
                                  * last block in the file
                                  */
                                 i_size_aligned = ALIGN(i_size_read(dio->inode),
                                                         1 << blkbits);
                                 if (dio->block_in_file >=
                                                 i_size_aligned >> blkbits) {
                                         /* We hit eof */
                                         page_cache_release(page);
                                         goto out;
                                 }
                                 zero_user(page, block_in_page << blkbits,
                                                 1 << blkbits);
                                 dio->block_in_file++;
                                 block_in_page++;
                                 goto next_block;
                         }
 
                         /*
                          * If we're performing IO which has an alignment which
                          * is finer than the underlying fs, go check to see if
                          * we must zero out the start of this block.
                          */
                         if (unlikely(dio->blkfactor && !dio->start_zero_done))
                                 dio_zero_block(dio, 0);
 
                         /*
                          * Work out, in this_chunk_blocks, how much disk we
                          * can add to this page
                          */
                         this_chunk_blocks = dio->blocks_available;
                         u = (PAGE_SIZE - offset_in_page) >> blkbits;
                         if (this_chunk_blocks > u)
                                 this_chunk_blocks = u;
                         u = dio->final_block_in_request - dio->block_in_file;
                         if (this_chunk_blocks > u)
                                 this_chunk_blocks = u;
                         this_chunk_bytes = this_chunk_blocks << blkbits;
                         BUG_ON(this_chunk_bytes == 0);
 
                         dio->boundary = buffer_boundary(map_bh);
                         ret = submit_page_section(dio, page, offset_in_page,
                                 this_chunk_bytes, dio->next_block_for_io);
                         if (ret) {
                                 page_cache_release(page);
                                 goto out;
                         }
                         dio->next_block_for_io += this_chunk_blocks;
 
                         dio->block_in_file += this_chunk_blocks;
                         block_in_page += this_chunk_blocks;
                         dio->blocks_available -= this_chunk_blocks;
 next_block:
                         BUG_ON(dio->block_in_file > dio->final_block_in_request);
                         if (dio->block_in_file == dio->final_block_in_request)
                                 break;
                 }
 
                 /* Drop the ref which was taken in get_user_pages() */
                 page_cache_release(page);
                 block_in_page = 0;
         }
 out:
         return ret;
 }
 
 /*
  * Releases both i_mutex and i_alloc_sem
  */
 static ssize_t
 direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode, 
         const struct iovec *iov, loff_t offset, unsigned long nr_segs, 
         unsigned blkbits, get_block_t get_block, dio_iodone_t end_io,
         struct dio *dio)
 {
         unsigned long user_addr; 
         unsigned long flags;
         int seg;
         ssize_t ret = 0;
         ssize_t ret2;
         size_t bytes;
 
         dio->inode = inode;
         dio->rw = rw;
         dio->blkbits = blkbits;
         dio->blkfactor = inode->i_blkbits - blkbits;
         dio->block_in_file = offset >> blkbits;
 
         dio->get_block = get_block;
         dio->end_io = end_io;
         dio->final_block_in_bio = -1;
         dio->next_block_for_io = -1;
 
         dio->iocb = iocb;
         dio->i_size = i_size_read(inode);
 
         spin_lock_init(&dio->bio_lock);
         dio->refcount = 1;
 
         /*
          * In case of non-aligned buffers, we may need 2 more
          * pages since we need to zero out first and last block.
          */
         if (unlikely(dio->blkfactor))
                 dio->pages_in_io = 2;
 
         for (seg = 0; seg < nr_segs; seg++) {
                 user_addr = (unsigned long)iov[seg].iov_base;
                 dio->pages_in_io +=
                         ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
                                 - user_addr/PAGE_SIZE);
         }
 
         for (seg = 0; seg < nr_segs; seg++) {
                 user_addr = (unsigned long)iov[seg].iov_base;
                 dio->size += bytes = iov[seg].iov_len;
 
                 /* Index into the first page of the first block */
                 dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
                 dio->final_block_in_request = dio->block_in_file +
                                                 (bytes >> blkbits);
                 /* Page fetching state */
                 dio->head = 0;
                 dio->tail = 0;
                 dio->curr_page = 0;
 
                 dio->total_pages = 0;
                 if (user_addr & (PAGE_SIZE-1)) {
                         dio->total_pages++;
                         bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
                 }
                 dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
                 dio->curr_user_address = user_addr;
         
                 ret = do_direct_IO(dio);
 
                dio->result += iov[seg].iov_len -
                        ((dio->final_block_in_request - dio->block_in_file) <<
                                        blkbits);

                if (ret) {
                        dio_cleanup(dio);
                        break;
                }
        } /* end iovec loop */

        if (ret == -ENOTBLK && (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);

        /* All IO is now issued, send it on its way */
        blk_run_address_space(inode->i_mapping);

        /*
         * It is possible that, we return short IO due to end of file.
         * In that case, we need to release all the pages we got hold on.
         */
        dio_cleanup(dio);

        /*
         * All block lookups have been performed. For READ requests
         * we can let i_mutex go now that its achieved its purpose
         * of protecting us from looking up uninitialized blocks.
         */
        if ((rw == READ) && (dio->lock_type == DIO_LOCKING))
                mutex_unlock(&dio->inode->i_mutex);

        /*
         * The only time we want to leave bios in flight is when a successful
         * partial aio read or full aio write have been setup.  In that case
         * bio completion will call aio_complete.  The only time it's safe to
         * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
         * This had *better* be the only place that raises -EIOCBQUEUED.
         */
        BUG_ON(ret == -EIOCBQUEUED);
        if (dio->is_async && ret == 0 && dio->result &&
            ((rw & READ) || (dio->result == dio->size)))
                ret = -EIOCBQUEUED;

        if (ret != -EIOCBQUEUED)
                dio_await_completion(dio);

        /*
         * Sync will always be dropping the final ref and completing the
         * operation.  AIO can if it was a broken operation described above or
         * in fact if all the bios race to complete before we get here.  In
         * that case dio_complete() translates the EIOCBQUEUED into the proper
         * return code that the caller will hand to aio_complete().
         *
         * This is managed by the bio_lock instead of being an atomic_t so that
         * completion paths can drop their ref and use the remaining count to
         * decide to wake the submission path atomically.
         */
        spin_lock_irqsave(&dio->bio_lock, flags);
        ret2 = --dio->refcount;
        spin_unlock_irqrestore(&dio->bio_lock, flags);

        if (ret2 == 0) {
                ret = dio_complete(dio, offset, ret);
                kfree(dio);
        } else
                BUG_ON(ret != -EIOCBQUEUED);

        return ret;
}

/*
 * This is a library function for use by filesystem drivers.
 * The locking rules are governed by the dio_lock_type parameter.
 *
 * DIO_NO_LOCKING (no locking, for raw block device access)
 * For writes, i_mutex is not held on entry; it is never taken.
 *
 * DIO_LOCKING (simple locking for regular files)
 * For writes we are called under i_mutex and return with i_mutex held, even
 * though it is internally dropped.
 * For reads, i_mutex 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_mutex, return without it, never touch it.
 * For reads we are called under i_mutex and return with i_mutex held, even
 * though it may be internally dropped.
 *
 * 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_block_t get_block, 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 release_i_mutex = 0;
        int acquire_i_mutex = 0;

        if (rw & WRITE)
                rw = WRITE_SYNC;

        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 = kzalloc(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_mutex and i_alloc_sem
         *        writers need to grab i_alloc_sem only (i_mutex is already held)
         * For regular files using DIO_OWN_LOCKING,
         *        neither readers nor writers take any locks 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) {
                                mutex_lock(&inode->i_mutex);
                                release_i_mutex = 1;
                        }

                        retval = filemap_write_and_wait_range(mapping, offset,
                                                              end - 1);
                        if (retval) {
                                kfree(dio);
                                goto out;
                        }

                        if (dio_lock_type == DIO_OWN_LOCKING) {
                                mutex_unlock(&inode->i_mutex);
                                acquire_i_mutex = 1;
                        }
                }

                if (dio_lock_type == DIO_LOCKING)
                        /* lockdep: not the owner will release it */
                        down_read_non_owner(&inode->i_alloc_sem);
        }

        /*
         * For file extending writes updating i_size before data
         * writeouts complete can expose uninitialized blocks. So
         * even for AIO, we need to wait for i/o to complete before
         * returning in this case.
         */
        dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
                (end > i_size_read(inode)));

        retval = direct_io_worker(rw, iocb, inode, iov, offset,
                                nr_segs, blkbits, get_block, end_io, dio);

        if (rw == READ && dio_lock_type == DIO_LOCKING)
                release_i_mutex = 0;

out:
        if (release_i_mutex)
                mutex_unlock(&inode->i_mutex);
        else if (acquire_i_mutex)
                mutex_lock(&inode->i_mutex);
        return retval;
}
EXPORT_SYMBOL(__blockdev_direct_IO);