/*
   *  linux/mm/page_io.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *
   *  Swap reorganised 29.12.95, 
   *  Asynchronous swapping added 30.12.95. Stephen Tweedie
   *  Removed race in async swapping. 14.4.1996. Bruno Haible
   *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
   *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
   */
  
  #include <linux/mm.h>
  #include <linux/kernel_stat.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/bio.h>
  #include <linux/swapops.h>
  #include <linux/writeback.h>
  #include <asm/pgtable.h>

  static struct bio *get_swap_bio(gfp_t gfp_flags,

  				struct page *page, bio_end_io_t end_io)
  {
  	struct bio *bio;
  
  	bio = bio_alloc(gfp_flags, 1);
  	if (bio) {

  		bio->bi_sector = map_swap_page(page, &bio->bi_bdev);

  		bio->bi_sector <<= PAGE_SHIFT - 9;

  		bio->bi_io_vec[0].bv_page = page;
  		bio->bi_io_vec[0].bv_len = PAGE_SIZE;
  		bio->bi_io_vec[0].bv_offset = 0;
  		bio->bi_vcnt = 1;
  		bio->bi_idx = 0;
  		bio->bi_size = PAGE_SIZE;
  		bio->bi_end_io = end_io;
  	}
  	return bio;
  }

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

  {
  	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  	struct page *page = bio->bi_io_vec[0].bv_page;

  	if (!uptodate) {

  		SetPageError(page);

  		/*
  		 * We failed to write the page out to swap-space.
  		 * Re-dirty the page in order to avoid it being reclaimed.
  		 * Also print a dire warning that things will go BAD (tm)
  		 * very quickly.
  		 *
  		 * Also clear PG_reclaim to avoid rotate_reclaimable_page()
  		 */
  		set_page_dirty(page);
  		printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)
  ",
  				imajor(bio->bi_bdev->bd_inode),
  				iminor(bio->bi_bdev->bd_inode),
  				(unsigned long long)bio->bi_sector);
  		ClearPageReclaim(page);
  	}

  	end_page_writeback(page);
  	bio_put(bio);

  }

  void end_swap_bio_read(struct bio *bio, int err)

  {
  	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  	struct page *page = bio->bi_io_vec[0].bv_page;

  	if (!uptodate) {
  		SetPageError(page);
  		ClearPageUptodate(page);

  		printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)
  ",
  				imajor(bio->bi_bdev->bd_inode),
  				iminor(bio->bi_bdev->bd_inode),
  				(unsigned long long)bio->bi_sector);

  	} else {
  		SetPageUptodate(page);
  	}
  	unlock_page(page);
  	bio_put(bio);

  }
  
  /*
   * We may have stale swap cache pages in memory: notice
   * them here and get rid of the unnecessary final write.
   */
  int swap_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct bio *bio;
  	int ret = 0, rw = WRITE;

  	if (try_to_free_swap(page)) {

  		unlock_page(page);
  		goto out;
  	}

  	bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);

  	if (bio == NULL) {
  		set_page_dirty(page);
  		unlock_page(page);
  		ret = -ENOMEM;
  		goto out;
  	}
  	if (wbc->sync_mode == WB_SYNC_ALL)

  		rw |= (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG);

  	count_vm_event(PSWPOUT);

  	set_page_writeback(page);
  	unlock_page(page);
  	submit_bio(rw, bio);
  out:
  	return ret;
  }

  int swap_readpage(struct page *page)

  {
  	struct bio *bio;
  	int ret = 0;

  	VM_BUG_ON(!PageLocked(page));
  	VM_BUG_ON(PageUptodate(page));

  	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);

  	if (bio == NULL) {
  		unlock_page(page);
  		ret = -ENOMEM;
  		goto out;
  	}

  	count_vm_event(PSWPIN);

  	submit_bio(READ, bio);
  out:
  	return ret;
  }