/*
   * fs/mpage.c
   *
   * Copyright (C) 2002, Linus Torvalds.
   *
   * Contains functions related to preparing and submitting BIOs which contain
   * multiple pagecache pages.
   *

   * 15May2002	Andrew Morton

   *		Initial version
   * 27Jun2002	axboe@suse.de
   *		use bio_add_page() to build bio's just the right size
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/mm.h>
  #include <linux/kdev_t.h>

  #include <linux/gfp.h>

  #include <linux/bio.h>
  #include <linux/fs.h>
  #include <linux/buffer_head.h>
  #include <linux/blkdev.h>
  #include <linux/highmem.h>
  #include <linux/prefetch.h>
  #include <linux/mpage.h>
  #include <linux/writeback.h>
  #include <linux/backing-dev.h>
  #include <linux/pagevec.h>
  
  /*
   * I/O completion handler for multipage BIOs.
   *
   * The mpage code never puts partial pages into a BIO (except for end-of-file).
   * If a page does not map to a contiguous run of blocks then it simply falls
   * back to block_read_full_page().
   *
   * Why is this?  If a page's completion depends on a number of different BIOs
   * which can complete in any order (or at the same time) then determining the
   * status of that page is hard.  See end_buffer_async_read() for the details.
   * There is no point in duplicating all that complexity.
   */

  static void mpage_end_io(struct bio *bio, int err)

  {
  	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;

  	do {
  		struct page *page = bvec->bv_page;
  
  		if (--bvec >= bio->bi_io_vec)
  			prefetchw(&bvec->bv_page->flags);

  		if (bio_data_dir(bio) == READ) {
  			if (uptodate) {
  				SetPageUptodate(page);
  			} else {
  				ClearPageUptodate(page);
  				SetPageError(page);
  			}
  			unlock_page(page);
  		} else { /* bio_data_dir(bio) == WRITE */
  			if (!uptodate) {
  				SetPageError(page);
  				if (page->mapping)
  					set_bit(AS_EIO, &page->mapping->flags);
  			}
  			end_page_writeback(page);

  		}

  	} while (bvec >= bio->bi_io_vec);
  	bio_put(bio);

  }

  static struct bio *mpage_bio_submit(int rw, struct bio *bio)

  {

  	bio->bi_end_io = mpage_end_io;

  	submit_bio(rw, bio);
  	return NULL;
  }
  
  static struct bio *
  mpage_alloc(struct block_device *bdev,
  		sector_t first_sector, int nr_vecs,

  		gfp_t gfp_flags)

  {
  	struct bio *bio;
  
  	bio = bio_alloc(gfp_flags, nr_vecs);
  
  	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
  		while (!bio && (nr_vecs /= 2))
  			bio = bio_alloc(gfp_flags, nr_vecs);
  	}
  
  	if (bio) {
  		bio->bi_bdev = bdev;
  		bio->bi_sector = first_sector;
  	}
  	return bio;
  }
  
  /*
   * support function for mpage_readpages.  The fs supplied get_block might
   * return an up to date buffer.  This is used to map that buffer into
   * the page, which allows readpage to avoid triggering a duplicate call
   * to get_block.
   *
   * The idea is to avoid adding buffers to pages that don't already have
   * them.  So when the buffer is up to date and the page size == block size,
   * this marks the page up to date instead of adding new buffers.
   */
  static void 
  map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
  {
  	struct inode *inode = page->mapping->host;
  	struct buffer_head *page_bh, *head;
  	int block = 0;
  
  	if (!page_has_buffers(page)) {
  		/*
  		 * don't make any buffers if there is only one buffer on
  		 * the page and the page just needs to be set up to date
  		 */
  		if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
  		    buffer_uptodate(bh)) {
  			SetPageUptodate(page);    
  			return;
  		}
  		create_empty_buffers(page, 1 << inode->i_blkbits, 0);
  	}
  	head = page_buffers(page);
  	page_bh = head;
  	do {
  		if (block == page_block) {
  			page_bh->b_state = bh->b_state;
  			page_bh->b_bdev = bh->b_bdev;
  			page_bh->b_blocknr = bh->b_blocknr;
  			break;
  		}
  		page_bh = page_bh->b_this_page;
  		block++;
  	} while (page_bh != head);
  }

  /*
   * This is the worker routine which does all the work of mapping the disk
   * blocks and constructs largest possible bios, submits them for IO if the
   * blocks are not contiguous on the disk.
   *
   * We pass a buffer_head back and forth and use its buffer_mapped() flag to
   * represent the validity of its disk mapping and to decide when to do the next
   * get_block() call.
   */

  static struct bio *
  do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,

  		sector_t *last_block_in_bio, struct buffer_head *map_bh,
  		unsigned long *first_logical_block, get_block_t get_block)

  {
  	struct inode *inode = page->mapping->host;
  	const unsigned blkbits = inode->i_blkbits;
  	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
  	const unsigned blocksize = 1 << blkbits;
  	sector_t block_in_file;
  	sector_t last_block;

  	sector_t last_block_in_file;

  	sector_t blocks[MAX_BUF_PER_PAGE];
  	unsigned page_block;
  	unsigned first_hole = blocks_per_page;
  	struct block_device *bdev = NULL;

  	int length;
  	int fully_mapped = 1;

  	unsigned nblocks;
  	unsigned relative_block;

  
  	if (page_has_buffers(page))
  		goto confused;

  	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);

  	last_block = block_in_file + nr_pages * blocks_per_page;
  	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
  	if (last_block > last_block_in_file)
  		last_block = last_block_in_file;
  	page_block = 0;
  
  	/*
  	 * Map blocks using the result from the previous get_blocks call first.
  	 */
  	nblocks = map_bh->b_size >> blkbits;
  	if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
  			block_in_file < (*first_logical_block + nblocks)) {
  		unsigned map_offset = block_in_file - *first_logical_block;
  		unsigned last = nblocks - map_offset;
  
  		for (relative_block = 0; ; relative_block++) {
  			if (relative_block == last) {
  				clear_buffer_mapped(map_bh);
  				break;
  			}
  			if (page_block == blocks_per_page)
  				break;
  			blocks[page_block] = map_bh->b_blocknr + map_offset +
  						relative_block;
  			page_block++;
  			block_in_file++;
  		}
  		bdev = map_bh->b_bdev;
  	}
  
  	/*
  	 * Then do more get_blocks calls until we are done with this page.
  	 */
  	map_bh->b_page = page;
  	while (page_block < blocks_per_page) {
  		map_bh->b_state = 0;
  		map_bh->b_size = 0;

  		if (block_in_file < last_block) {

  			map_bh->b_size = (last_block-block_in_file) << blkbits;
  			if (get_block(inode, block_in_file, map_bh, 0))

  				goto confused;

  			*first_logical_block = block_in_file;

  		}

  		if (!buffer_mapped(map_bh)) {

  			fully_mapped = 0;
  			if (first_hole == blocks_per_page)
  				first_hole = page_block;

  			page_block++;
  			block_in_file++;

  			continue;
  		}
  
  		/* some filesystems will copy data into the page during
  		 * the get_block call, in which case we don't want to
  		 * read it again.  map_buffer_to_page copies the data
  		 * we just collected from get_block into the page's buffers
  		 * so readpage doesn't have to repeat the get_block call
  		 */

  		if (buffer_uptodate(map_bh)) {
  			map_buffer_to_page(page, map_bh, page_block);

  			goto confused;
  		}
  	
  		if (first_hole != blocks_per_page)
  			goto confused;		/* hole -> non-hole */
  
  		/* Contiguous blocks? */

  		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)

  			goto confused;

  		nblocks = map_bh->b_size >> blkbits;
  		for (relative_block = 0; ; relative_block++) {
  			if (relative_block == nblocks) {
  				clear_buffer_mapped(map_bh);
  				break;
  			} else if (page_block == blocks_per_page)
  				break;
  			blocks[page_block] = map_bh->b_blocknr+relative_block;
  			page_block++;
  			block_in_file++;
  		}
  		bdev = map_bh->b_bdev;

  	}
  
  	if (first_hole != blocks_per_page) {

  		zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);

  		if (first_hole == 0) {
  			SetPageUptodate(page);
  			unlock_page(page);
  			goto out;
  		}
  	} else if (fully_mapped) {
  		SetPageMappedToDisk(page);
  	}
  
  	/*
  	 * This page will go to BIO.  Do we need to send this BIO off first?
  	 */
  	if (bio && (*last_block_in_bio != blocks[0] - 1))
  		bio = mpage_bio_submit(READ, bio);
  
  alloc_new:
  	if (bio == NULL) {
  		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
  			  	min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
  				GFP_KERNEL);
  		if (bio == NULL)
  			goto confused;
  	}
  
  	length = first_hole << blkbits;
  	if (bio_add_page(bio, page, length, 0) < length) {
  		bio = mpage_bio_submit(READ, bio);
  		goto alloc_new;
  	}

  	relative_block = block_in_file - *first_logical_block;
  	nblocks = map_bh->b_size >> blkbits;
  	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
  	    (first_hole != blocks_per_page))

  		bio = mpage_bio_submit(READ, bio);
  	else
  		*last_block_in_bio = blocks[blocks_per_page - 1];
  out:
  	return bio;
  
  confused:
  	if (bio)
  		bio = mpage_bio_submit(READ, bio);
  	if (!PageUptodate(page))
  	        block_read_full_page(page, get_block);
  	else
  		unlock_page(page);
  	goto out;
  }

  /**

   * mpage_readpages - populate an address space with some pages & start reads against them

   * @mapping: the address_space
   * @pages: The address of a list_head which contains the target pages.  These
   *   pages have their ->index populated and are otherwise uninitialised.

   *   The page at @pages->prev has the lowest file offset, and reads should be
   *   issued in @pages->prev to @pages->next order.

   * @nr_pages: The number of pages at *@pages
   * @get_block: The filesystem's block mapper function.
   *
   * This function walks the pages and the blocks within each page, building and
   * emitting large BIOs.
   *
   * If anything unusual happens, such as:
   *
   * - encountering a page which has buffers
   * - encountering a page which has a non-hole after a hole
   * - encountering a page with non-contiguous blocks
   *
   * then this code just gives up and calls the buffer_head-based read function.
   * It does handle a page which has holes at the end - that is a common case:
   * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
   *
   * BH_Boundary explanation:
   *
   * There is a problem.  The mpage read code assembles several pages, gets all
   * their disk mappings, and then submits them all.  That's fine, but obtaining
   * the disk mappings may require I/O.  Reads of indirect blocks, for example.
   *
   * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
   * submitted in the following order:
   * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16

   *

   * because the indirect block has to be read to get the mappings of blocks
   * 13,14,15,16.  Obviously, this impacts performance.
   *
   * So what we do it to allow the filesystem's get_block() function to set
   * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
   * after this one will require I/O against a block which is probably close to
   * this one.  So you should push what I/O you have currently accumulated.
   *
   * This all causes the disk requests to be issued in the correct order.
   */

  int
  mpage_readpages(struct address_space *mapping, struct list_head *pages,
  				unsigned nr_pages, get_block_t get_block)
  {
  	struct bio *bio = NULL;
  	unsigned page_idx;
  	sector_t last_block_in_bio = 0;

  	struct buffer_head map_bh;
  	unsigned long first_logical_block = 0;

  	struct blk_plug plug;
  
  	blk_start_plug(&plug);

  	map_bh.b_state = 0;
  	map_bh.b_size = 0;

  	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
  		struct page *page = list_entry(pages->prev, struct page, lru);
  
  		prefetchw(&page->flags);
  		list_del(&page->lru);

  		if (!add_to_page_cache_lru(page, mapping,

  					page->index, GFP_KERNEL)) {
  			bio = do_mpage_readpage(bio, page,
  					nr_pages - page_idx,

  					&last_block_in_bio, &map_bh,
  					&first_logical_block,
  					get_block);

  		}

  		page_cache_release(page);

  	}

  	BUG_ON(!list_empty(pages));
  	if (bio)
  		mpage_bio_submit(READ, bio);

  	blk_finish_plug(&plug);

  	return 0;
  }
  EXPORT_SYMBOL(mpage_readpages);
  
  /*
   * This isn't called much at all
   */
  int mpage_readpage(struct page *page, get_block_t get_block)
  {
  	struct bio *bio = NULL;
  	sector_t last_block_in_bio = 0;

  	struct buffer_head map_bh;
  	unsigned long first_logical_block = 0;

  	map_bh.b_state = 0;
  	map_bh.b_size = 0;

  	bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
  			&map_bh, &first_logical_block, get_block);

  	if (bio)
  		mpage_bio_submit(READ, bio);
  	return 0;
  }
  EXPORT_SYMBOL(mpage_readpage);
  
  /*
   * Writing is not so simple.
   *
   * If the page has buffers then they will be used for obtaining the disk
   * mapping.  We only support pages which are fully mapped-and-dirty, with a
   * special case for pages which are unmapped at the end: end-of-file.
   *
   * If the page has no buffers (preferred) then the page is mapped here.
   *
   * If all blocks are found to be contiguous then the page can go into the
   * BIO.  Otherwise fall back to the mapping's writepage().
   * 
   * FIXME: This code wants an estimate of how many pages are still to be
   * written, so it can intelligently allocate a suitably-sized BIO.  For now,
   * just allocate full-size (16-page) BIOs.
   */

  struct mpage_data {
  	struct bio *bio;
  	sector_t last_block_in_bio;
  	get_block_t *get_block;
  	unsigned use_writepage;
  };
  
  static int __mpage_writepage(struct page *page, struct writeback_control *wbc,

  		      void *data)

  {

  	struct mpage_data *mpd = data;
  	struct bio *bio = mpd->bio;

  	struct address_space *mapping = page->mapping;
  	struct inode *inode = page->mapping->host;
  	const unsigned blkbits = inode->i_blkbits;
  	unsigned long end_index;
  	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
  	sector_t last_block;
  	sector_t block_in_file;
  	sector_t blocks[MAX_BUF_PER_PAGE];
  	unsigned page_block;
  	unsigned first_unmapped = blocks_per_page;
  	struct block_device *bdev = NULL;
  	int boundary = 0;
  	sector_t boundary_block = 0;
  	struct block_device *boundary_bdev = NULL;
  	int length;
  	struct buffer_head map_bh;
  	loff_t i_size = i_size_read(inode);

  	int ret = 0;

  
  	if (page_has_buffers(page)) {
  		struct buffer_head *head = page_buffers(page);
  		struct buffer_head *bh = head;
  
  		/* If they're all mapped and dirty, do it */
  		page_block = 0;
  		do {
  			BUG_ON(buffer_locked(bh));
  			if (!buffer_mapped(bh)) {
  				/*
  				 * unmapped dirty buffers are created by
  				 * __set_page_dirty_buffers -> mmapped data
  				 */
  				if (buffer_dirty(bh))
  					goto confused;
  				if (first_unmapped == blocks_per_page)
  					first_unmapped = page_block;
  				continue;
  			}
  
  			if (first_unmapped != blocks_per_page)
  				goto confused;	/* hole -> non-hole */
  
  			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
  				goto confused;
  			if (page_block) {
  				if (bh->b_blocknr != blocks[page_block-1] + 1)
  					goto confused;
  			}
  			blocks[page_block++] = bh->b_blocknr;
  			boundary = buffer_boundary(bh);
  			if (boundary) {
  				boundary_block = bh->b_blocknr;
  				boundary_bdev = bh->b_bdev;
  			}
  			bdev = bh->b_bdev;
  		} while ((bh = bh->b_this_page) != head);
  
  		if (first_unmapped)
  			goto page_is_mapped;
  
  		/*
  		 * Page has buffers, but they are all unmapped. The page was
  		 * created by pagein or read over a hole which was handled by
  		 * block_read_full_page().  If this address_space is also
  		 * using mpage_readpages then this can rarely happen.
  		 */
  		goto confused;
  	}
  
  	/*
  	 * The page has no buffers: map it to disk
  	 */
  	BUG_ON(!PageUptodate(page));

  	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);

  	last_block = (i_size - 1) >> blkbits;
  	map_bh.b_page = page;
  	for (page_block = 0; page_block < blocks_per_page; ) {
  
  		map_bh.b_state = 0;

  		map_bh.b_size = 1 << blkbits;

  		if (mpd->get_block(inode, block_in_file, &map_bh, 1))

  			goto confused;
  		if (buffer_new(&map_bh))
  			unmap_underlying_metadata(map_bh.b_bdev,
  						map_bh.b_blocknr);
  		if (buffer_boundary(&map_bh)) {
  			boundary_block = map_bh.b_blocknr;
  			boundary_bdev = map_bh.b_bdev;
  		}
  		if (page_block) {
  			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
  				goto confused;
  		}
  		blocks[page_block++] = map_bh.b_blocknr;
  		boundary = buffer_boundary(&map_bh);
  		bdev = map_bh.b_bdev;
  		if (block_in_file == last_block)
  			break;
  		block_in_file++;
  	}
  	BUG_ON(page_block == 0);
  
  	first_unmapped = page_block;
  
  page_is_mapped:
  	end_index = i_size >> PAGE_CACHE_SHIFT;
  	if (page->index >= end_index) {
  		/*
  		 * The page straddles i_size.  It must be zeroed out on each

  		 * and every writepage invocation because it may be mmapped.

  		 * "A file is mapped in multiples of the page size.  For a file
  		 * that is not a multiple of the page size, the remaining memory
  		 * is zeroed when mapped, and writes to that region are not
  		 * written out to the file."
  		 */
  		unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);

  
  		if (page->index > end_index || !offset)
  			goto confused;

  		zero_user_segment(page, offset, PAGE_CACHE_SIZE);

  	}
  
  	/*
  	 * This page will go to BIO.  Do we need to send this BIO off first?
  	 */

  	if (bio && mpd->last_block_in_bio != blocks[0] - 1)

  		bio = mpage_bio_submit(WRITE, bio);
  
  alloc_new:
  	if (bio == NULL) {
  		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
  				bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
  		if (bio == NULL)
  			goto confused;
  	}
  
  	/*
  	 * Must try to add the page before marking the buffer clean or
  	 * the confused fail path above (OOM) will be very confused when
  	 * it finds all bh marked clean (i.e. it will not write anything)
  	 */
  	length = first_unmapped << blkbits;
  	if (bio_add_page(bio, page, length, 0) < length) {
  		bio = mpage_bio_submit(WRITE, bio);
  		goto alloc_new;
  	}
  
  	/*
  	 * OK, we have our BIO, so we can now mark the buffers clean.  Make
  	 * sure to only clean buffers which we know we'll be writing.
  	 */
  	if (page_has_buffers(page)) {
  		struct buffer_head *head = page_buffers(page);
  		struct buffer_head *bh = head;
  		unsigned buffer_counter = 0;
  
  		do {
  			if (buffer_counter++ == first_unmapped)
  				break;
  			clear_buffer_dirty(bh);
  			bh = bh->b_this_page;
  		} while (bh != head);
  
  		/*
  		 * we cannot drop the bh if the page is not uptodate
  		 * or a concurrent readpage would fail to serialize with the bh
  		 * and it would read from disk before we reach the platter.
  		 */
  		if (buffer_heads_over_limit && PageUptodate(page))
  			try_to_free_buffers(page);
  	}
  
  	BUG_ON(PageWriteback(page));
  	set_page_writeback(page);
  	unlock_page(page);
  	if (boundary || (first_unmapped != blocks_per_page)) {
  		bio = mpage_bio_submit(WRITE, bio);
  		if (boundary_block) {
  			write_boundary_block(boundary_bdev,
  					boundary_block, 1 << blkbits);
  		}
  	} else {

  		mpd->last_block_in_bio = blocks[blocks_per_page - 1];

  	}
  	goto out;
  
  confused:
  	if (bio)
  		bio = mpage_bio_submit(WRITE, bio);

  	if (mpd->use_writepage) {
  		ret = mapping->a_ops->writepage(page, wbc);

  	} else {

  		ret = -EAGAIN;

  		goto out;
  	}
  	/*
  	 * The caller has a ref on the inode, so *mapping is stable
  	 */

  	mapping_set_error(mapping, ret);

  out:

  	mpd->bio = bio;
  	return ret;

  }
  
  /**

   * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them

   * @mapping: address space structure to write
   * @wbc: subtract the number of written pages from *@wbc->nr_to_write
   * @get_block: the filesystem's block mapper function.
   *             If this is NULL then use a_ops->writepage.  Otherwise, go
   *             direct-to-BIO.
   *
   * This is a library function, which implements the writepages()
   * address_space_operation.
   *
   * If a page is already under I/O, generic_writepages() skips it, even
   * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
   * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
   * and msync() need to guarantee that all the data which was dirty at the time
   * the call was made get new I/O started against them.  If wbc->sync_mode is
   * WB_SYNC_ALL then we were called for data integrity and we must wait for
   * existing IO to complete.
   */
  int
  mpage_writepages(struct address_space *mapping,
  		struct writeback_control *wbc, get_block_t get_block)
  {

  	struct blk_plug plug;

  	int ret;

  	blk_start_plug(&plug);

  	if (!get_block)
  		ret = generic_writepages(mapping, wbc);
  	else {
  		struct mpage_data mpd = {
  			.bio = NULL,
  			.last_block_in_bio = 0,
  			.get_block = get_block,
  			.use_writepage = 1,
  		};
  
  		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
  		if (mpd.bio)
  			mpage_bio_submit(WRITE, mpd.bio);

  	}

  	blk_finish_plug(&plug);

  	return ret;
  }
  EXPORT_SYMBOL(mpage_writepages);

  
  int mpage_writepage(struct page *page, get_block_t get_block,
  	struct writeback_control *wbc)
  {

  	struct mpage_data mpd = {
  		.bio = NULL,
  		.last_block_in_bio = 0,
  		.get_block = get_block,
  		.use_writepage = 0,
  	};
  	int ret = __mpage_writepage(page, wbc, &mpd);
  	if (mpd.bio)
  		mpage_bio_submit(WRITE, mpd.bio);

  	return ret;
  }
  EXPORT_SYMBOL(mpage_writepage);