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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * 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>
 
 #include "internal.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
 
 /*
  * Flags for dio_complete()
  */
 #define DIO_COMPLETE_ASYNC      0x01    /* This is async IO */
 #define DIO_COMPLETE_INVALIDATE     0x02    /* Can invalidate pages */
 
 /*
  * 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 */
     blk_opf_t opf;          /* request operation type and flags */
     struct gendisk *bio_disk;
     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? */
     bool should_dirty;      /* if pages should be dirtied */
     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)
 {
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     ssize_t ret;
 
     ret = iov_iter_get_pages2(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
                 &sdio->from);
 
     if (ret < 0 && sdio->blocks_available && dio_op == REQ_OP_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;
         get_page(page);
         dio->pages[0] = page;
         sdio->head = 0;
         sdio->tail = 1;
         sdio->from = 0;
         sdio->to = PAGE_SIZE;
         return 0;
     }
 
     if (ret >= 0) {
         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
  *
  * 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, ssize_t ret, unsigned int flags)
 {
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     loff_t offset = dio->iocb->ki_pos;
     ssize_t transferred = 0;
     int err;
 
     /*
      * 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_op == REQ_OP_READ &&
             ((offset + transferred) > dio->i_size))
             transferred = dio->i_size - offset;
         /* ignore EFAULT if some IO has been done */
         if (unlikely(ret == -EFAULT) && transferred)
             ret = 0;
     }
 
     if (ret == 0)
         ret = dio->page_errors;
     if (ret == 0)
         ret = dio->io_error;
     if (ret == 0)
         ret = transferred;
 
     if (dio->end_io) {
         // XXX: ki_pos??
         err = dio->end_io(dio->iocb, offset, ret, dio->private);
         if (err)
             ret = err;
     }
 
     /*
      * Try again to invalidate clean pages which might have been cached by
      * non-direct readahead, or faulted in by get_user_pages() if the source
      * of the write was an mmap'ed region of the file we're writing.  Either
      * one is a pretty crazy thing to do, so we don't support it 100%.  If
      * this invalidation fails, tough, the write still worked...
      *
      * And this page cache invalidation has to be after dio->end_io(), as
      * some filesystems convert unwritten extents to real allocations in
      * end_io() when necessary, otherwise a racing buffer read would cache
      * zeros from unwritten extents.
      */
     if (flags & DIO_COMPLETE_INVALIDATE &&
         ret > 0 && dio_op == REQ_OP_WRITE &&
         dio->inode->i_mapping->nrpages) {
         err = invalidate_inode_pages2_range(dio->inode->i_mapping,
                     offset >> PAGE_SHIFT,
                     (offset + ret - 1) >> PAGE_SHIFT);
         if (err)
             dio_warn_stale_pagecache(dio->iocb->ki_filp);
     }
 
     inode_dio_end(dio->inode);
 
     if (flags & DIO_COMPLETE_ASYNC) {
         /*
          * generic_write_sync expects ki_pos to have been updated
          * already, but the submission path only does this for
          * synchronous I/O.
          */
         dio->iocb->ki_pos += transferred;
 
         if (ret > 0 && dio_op == REQ_OP_WRITE)
             ret = generic_write_sync(dio->iocb, ret);
         dio->iocb->ki_complete(dio->iocb, ret);
     }
 
     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, 0, DIO_COMPLETE_ASYNC | DIO_COMPLETE_INVALIDATE);
 }
 
 static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio);
 
 /*
  * Asynchronous IO callback. 
  */
 static void dio_bio_end_aio(struct bio *bio)
 {
     struct dio *dio = bio->bi_private;
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     unsigned long remaining;
     unsigned long flags;
     bool defer_completion = false;
 
     /* 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) {
         /*
          * Defer completion when defer_completion is set or
          * when the inode has pages mapped and this is AIO write.
          * We need to invalidate those pages because there is a
          * chance they contain stale data in the case buffered IO
          * went in between AIO submission and completion into the
          * same region.
          */
         if (dio->result)
             defer_completion = dio->defer_completion ||
                        (dio_op == REQ_OP_WRITE &&
                         dio->inode->i_mapping->nrpages);
         if (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, 0, DIO_COMPLETE_ASYNC);
         }
     }
 }
 
 /*
  * 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)
 {
     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 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 allowed to sleep and
      * we request a valid number of vectors.
      */
     bio = bio_alloc(bdev, nr_vecs, dio->opf, GFP_KERNEL);
     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)
 {
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     struct bio *bio = sdio->bio;
     unsigned long flags;
 
     bio->bi_private = dio;
     /* don't account direct I/O as memory stall */
     bio_clear_flag(bio, BIO_WORKINGSET);
 
     spin_lock_irqsave(&dio->bio_lock, flags);
     dio->refcount++;
     spin_unlock_irqrestore(&dio->bio_lock, flags);
 
     if (dio->is_async && dio_op == REQ_OP_READ && dio->should_dirty)
         bio_set_pages_dirty(bio);
 
     dio->bio_disk = bio->bi_bdev->bd_disk;
 
     if (sdio->submit_io)
         sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
     else
         submit_bio(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)
         put_page(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 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);
         blk_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 blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
 {
     blk_status_t err = bio->bi_status;
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     bool should_dirty = dio_op == REQ_OP_READ && dio->should_dirty;
 
     if (err) {
         if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT))
             dio->io_error = -EAGAIN;
         else
             dio->io_error = -EIO;
     }
 
     if (dio->is_async && should_dirty) {
         bio_check_pages_dirty(bio); /* transfers ownership */
     } else {
         bio_release_pages(bio, should_dirty);
         bio_put(bio);
     }
     return err;
 }
 
 /*
  * 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 = blk_status_to_errno(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.
  */
 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, i_blocksize(inode).
  *
  * 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)
 {
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     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;
     loff_t i_size;
 
     /*
      * 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 that could fill holes 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_op == REQ_OP_WRITE;
         if (dio->flags & DIO_SKIP_HOLES) {
             i_size = i_size_read(dio->inode);
             if (i_size && fs_startblk <= (i_size - 1) >> i_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 = bio_max_segs(sdio->pages_in_io);
     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--;
         get_page(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)
 {
     const enum req_op dio_op = dio->opf & REQ_OP_MASK;
     int ret = 0;
     int boundary = sdio->boundary;  /* dio_send_cur_page may clear it */
 
     if (dio_op == REQ_OP_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);
         put_page(sdio->cur_page);
         sdio->cur_page = NULL;
         if (ret)
             return ret;
     }
 
     get_page(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 boundary then we want to schedule the IO now to
      * avoid metadata seeks.
      */
     if (boundary) {
         ret = dio_send_cur_page(dio, sdio, map_bh);
         if (sdio->bio)
             dio_bio_submit(dio, sdio);
         put_page(sdio->cur_page);
         sdio->cur_page = NULL;
     }
     return ret;
 }
 
 /*
  * 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 enum req_op dio_op = dio->opf & REQ_OP_MASK;
     const unsigned blkbits = sdio->blkbits;
     const unsigned i_blkbits = blkbits + sdio->blkfactor;
     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) {
                     put_page(page);
                     goto out;
                 }
                 if (!buffer_mapped(map_bh))
                     goto do_holes;
 
                 sdio->blocks_available =
                         map_bh->b_size >> blkbits;
                 sdio->next_block_for_io =
                     map_bh->b_blocknr << sdio->blkfactor;
                 if (buffer_new(map_bh)) {
                     clean_bdev_aliases(
                         map_bh->b_bdev,
                         map_bh->b_blocknr,
                         map_bh->b_size >> i_blkbits);
                 }
 
                 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_op == REQ_OP_WRITE) {
                     put_page(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 */
                     put_page(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) {
                 put_page(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() */
         put_page(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.
  */
 ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
         struct block_device *bdev, struct iov_iter *iter,
         get_block_t get_block, dio_iodone_t end_io,
         dio_submit_t submit_io, int flags)
 {
     unsigned i_blkbits = READ_ONCE(inode->i_blkbits);
     unsigned blkbits = i_blkbits;
     unsigned blocksize_mask = (1 << blkbits) - 1;
     ssize_t retval = -EINVAL;
     const size_t count = iov_iter_count(iter);
     loff_t offset = iocb->ki_pos;
     const 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.
      */
 
     /* watch out for a 0 len io from a tricksy fs */
     if (iov_iter_rw(iter) == READ && !count)
         return 0;
 
     dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
     if (!dio)
         return -ENOMEM;
     /*
      * 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 && iov_iter_rw(iter) == READ) {
         /* will be released by direct_io_worker */
         inode_lock(inode);
     }
 
     /* Once we sampled i_size check for reads beyond EOF */
     dio->i_size = i_size_read(inode);
     if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
         retval = 0;
         goto fail_dio;
     }
 
     if (align & blocksize_mask) {
         if (bdev)
             blkbits = blksize_bits(bdev_logical_block_size(bdev));
         blocksize_mask = (1 << blkbits) - 1;
         if (align & blocksize_mask)
             goto fail_dio;
     }
 
     if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
 
         retval = filemap_write_and_wait_range(mapping, offset, end - 1);
         if (retval)
             goto fail_dio;
     }
 
     /*
      * 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 (iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
         dio->is_async = false;
     else
         dio->is_async = true;
 
     dio->inode = inode;
     if (iov_iter_rw(iter) == WRITE) {
         dio->opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
         if (iocb->ki_flags & IOCB_NOWAIT)
             dio->opf |= REQ_NOWAIT;
     } else {
         dio->opf = REQ_OP_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) {
         retval = 0;
         if (iocb_is_dsync(iocb))
             retval = dio_set_defer_completion(dio);
         else if (!dio->inode->i_sb->s_dio_done_wq) {
             /*
              * In case of AIO write racing with buffered read we
              * need to defer completion. We can't decide this now,
              * however the workqueue needs to be initialized here.
              */
             retval = sb_init_dio_done_wq(dio->inode->i_sb);
         }
         if (retval)
             goto fail_dio;
     }
 
     /*
      * Will be decremented at I/O completion time.
      */
     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;
 
     spin_lock_init(&dio->bio_lock);
     dio->refcount = 1;
 
     dio->should_dirty = user_backed_iter(iter) && iov_iter_rw(iter) == READ;
     sdio.iter = iter;
     sdio.final_block_in_request = end >> 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
          * 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;
         put_page(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))
         inode_unlock(dio->inode);
 
     /*
      * 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, retval, DIO_COMPLETE_INVALIDATE);
     } else
         BUG_ON(retval != -EIOCBQUEUED);
 
     return retval;
 
 fail_dio:
     if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ)
         inode_unlock(inode);
 
     kmem_cache_free(dio_cache, dio);
     return retval;
 }
 EXPORT_SYMBOL(__blockdev_direct_IO);
 
 static __init int dio_init(void)
 {
     dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
     return 0;
 }
 module_init(dio_init)

This page was automatically generated by the 2.1.0 LXR engine. The LXR team