// SPDX-License-Identifier: GPL-2.0

  /*
   *  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/gfp.h>

  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/bio.h>
  #include <linux/swapops.h>

  #include <linux/buffer_head.h>

  #include <linux/writeback.h>

  #include <linux/frontswap.h>

  #include <linux/blkdev.h>

  #include <linux/uio.h>

  #include <linux/sched/task.h>

  #include <asm/pgtable.h>

  static struct bio *get_swap_bio(gfp_t gfp_flags,

  				struct page *page, bio_end_io_t end_io)
  {

  	int i, nr = hpage_nr_pages(page);

  	struct bio *bio;

  	bio = bio_alloc(gfp_flags, nr);

  	if (bio) {

  		struct block_device *bdev;
  
  		bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
  		bio_set_dev(bio, bdev);

  		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;

  		bio->bi_end_io = end_io;

  		for (i = 0; i < nr; i++)
  			bio_add_page(bio, page + i, PAGE_SIZE, 0);
  		VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);

  	}
  	return bio;
  }

  void end_swap_bio_write(struct bio *bio)

  {

  	struct page *page = bio->bi_io_vec[0].bv_page;

  	if (bio->bi_status) {

  		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);

  		pr_alert("Write-error on swap-device (%u:%u:%llu)
  ",

  			 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),

  			 (unsigned long long)bio->bi_iter.bi_sector);

  		ClearPageReclaim(page);
  	}

  	end_page_writeback(page);
  	bio_put(bio);

  }

  static void swap_slot_free_notify(struct page *page)
  {
  	struct swap_info_struct *sis;
  	struct gendisk *disk;
  
  	/*
  	 * There is no guarantee that the page is in swap cache - the software
  	 * suspend code (at least) uses end_swap_bio_read() against a non-
  	 * swapcache page.  So we must check PG_swapcache before proceeding with
  	 * this optimization.
  	 */
  	if (unlikely(!PageSwapCache(page)))
  		return;
  
  	sis = page_swap_info(page);
  	if (!(sis->flags & SWP_BLKDEV))
  		return;
  
  	/*
  	 * The swap subsystem performs lazy swap slot freeing,
  	 * expecting that the page will be swapped out again.
  	 * So we can avoid an unnecessary write if the page
  	 * isn't redirtied.
  	 * This is good for real swap storage because we can
  	 * reduce unnecessary I/O and enhance wear-leveling
  	 * if an SSD is used as the as swap device.
  	 * But if in-memory swap device (eg zram) is used,
  	 * this causes a duplicated copy between uncompressed
  	 * data in VM-owned memory and compressed data in
  	 * zram-owned memory.  So let's free zram-owned memory
  	 * and make the VM-owned decompressed page *dirty*,
  	 * so the page should be swapped out somewhere again if
  	 * we again wish to reclaim it.
  	 */
  	disk = sis->bdev->bd_disk;
  	if (disk->fops->swap_slot_free_notify) {
  		swp_entry_t entry;
  		unsigned long offset;
  
  		entry.val = page_private(page);
  		offset = swp_offset(entry);
  
  		SetPageDirty(page);
  		disk->fops->swap_slot_free_notify(sis->bdev,
  				offset);
  	}
  }

  static void end_swap_bio_read(struct bio *bio)

  {

  	struct page *page = bio->bi_io_vec[0].bv_page;

  	struct task_struct *waiter = bio->bi_private;

  	if (bio->bi_status) {

  		SetPageError(page);
  		ClearPageUptodate(page);

  		pr_alert("Read-error on swap-device (%u:%u:%llu)
  ",

  			 MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),

  			 (unsigned long long)bio->bi_iter.bi_sector);

  		goto out;

  	}

  
  	SetPageUptodate(page);

  	swap_slot_free_notify(page);

  out:

  	unlock_page(page);

  	WRITE_ONCE(bio->bi_private, NULL);

  	bio_put(bio);

  	wake_up_process(waiter);

  	put_task_struct(waiter);

  }

  int generic_swapfile_activate(struct swap_info_struct *sis,
  				struct file *swap_file,
  				sector_t *span)
  {
  	struct address_space *mapping = swap_file->f_mapping;
  	struct inode *inode = mapping->host;
  	unsigned blocks_per_page;
  	unsigned long page_no;
  	unsigned blkbits;
  	sector_t probe_block;
  	sector_t last_block;
  	sector_t lowest_block = -1;
  	sector_t highest_block = 0;
  	int nr_extents = 0;
  	int ret;
  
  	blkbits = inode->i_blkbits;
  	blocks_per_page = PAGE_SIZE >> blkbits;
  
  	/*
  	 * Map all the blocks into the extent list.  This code doesn't try
  	 * to be very smart.
  	 */
  	probe_block = 0;
  	page_no = 0;
  	last_block = i_size_read(inode) >> blkbits;
  	while ((probe_block + blocks_per_page) <= last_block &&
  			page_no < sis->max) {
  		unsigned block_in_page;
  		sector_t first_block;

  		cond_resched();

  		first_block = bmap(inode, probe_block);
  		if (first_block == 0)
  			goto bad_bmap;
  
  		/*
  		 * It must be PAGE_SIZE aligned on-disk
  		 */
  		if (first_block & (blocks_per_page - 1)) {
  			probe_block++;
  			goto reprobe;
  		}
  
  		for (block_in_page = 1; block_in_page < blocks_per_page;
  					block_in_page++) {
  			sector_t block;
  
  			block = bmap(inode, probe_block + block_in_page);
  			if (block == 0)
  				goto bad_bmap;
  			if (block != first_block + block_in_page) {
  				/* Discontiguity */
  				probe_block++;
  				goto reprobe;
  			}
  		}
  
  		first_block >>= (PAGE_SHIFT - blkbits);
  		if (page_no) {	/* exclude the header page */
  			if (first_block < lowest_block)
  				lowest_block = first_block;
  			if (first_block > highest_block)
  				highest_block = first_block;
  		}
  
  		/*
  		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
  		 */
  		ret = add_swap_extent(sis, page_no, 1, first_block);
  		if (ret < 0)
  			goto out;
  		nr_extents += ret;
  		page_no++;
  		probe_block += blocks_per_page;
  reprobe:
  		continue;
  	}
  	ret = nr_extents;
  	*span = 1 + highest_block - lowest_block;
  	if (page_no == 0)
  		page_no = 1;	/* force Empty message */
  	sis->max = page_no;
  	sis->pages = page_no - 1;
  	sis->highest_bit = page_no - 1;
  out:
  	return ret;
  bad_bmap:

  	pr_err("swapon: swapfile has holes
  ");

  	ret = -EINVAL;
  	goto out;
  }

  /*
   * 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)
  {

  	int ret = 0;

  	if (try_to_free_swap(page)) {

  		unlock_page(page);
  		goto out;
  	}

  	if (frontswap_store(page) == 0) {

  		set_page_writeback(page);
  		unlock_page(page);
  		end_page_writeback(page);
  		goto out;
  	}

  	ret = __swap_writepage(page, wbc, end_swap_bio_write);

  out:
  	return ret;
  }

  static sector_t swap_page_sector(struct page *page)
  {

  	return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);

  }

  static inline void count_swpout_vm_event(struct page *page)
  {
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  	if (unlikely(PageTransHuge(page)))
  		count_vm_event(THP_SWPOUT);
  #endif
  	count_vm_events(PSWPOUT, hpage_nr_pages(page));
  }

  int __swap_writepage(struct page *page, struct writeback_control *wbc,

  		bio_end_io_t end_write_func)

  {
  	struct bio *bio;

  	int ret;

  	struct swap_info_struct *sis = page_swap_info(page);

  	VM_BUG_ON_PAGE(!PageSwapCache(page), page);

  	if (sis->flags & SWP_FILE) {
  		struct kiocb kiocb;
  		struct file *swap_file = sis->swap_file;
  		struct address_space *mapping = swap_file->f_mapping;

  		struct bio_vec bv = {
  			.bv_page = page,
  			.bv_len  = PAGE_SIZE,
  			.bv_offset = 0
  		};

  		struct iov_iter from;

  		iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);

  		init_sync_kiocb(&kiocb, swap_file);
  		kiocb.ki_pos = page_file_offset(page);

  		set_page_writeback(page);

  		unlock_page(page);

  		ret = mapping->a_ops->direct_IO(&kiocb, &from);

  		if (ret == PAGE_SIZE) {
  			count_vm_event(PSWPOUT);
  			ret = 0;

  		} else {

  			/*
  			 * In the case of swap-over-nfs, this can be a
  			 * temporary failure if the system has limited
  			 * memory for allocating transmit buffers.
  			 * Mark the page dirty and avoid
  			 * rotate_reclaimable_page but rate-limit the
  			 * messages but do not flag PageError like
  			 * the normal direct-to-bio case as it could
  			 * be temporary.
  			 */

  			set_page_dirty(page);

  			ClearPageReclaim(page);

  			pr_err_ratelimited("Write error on dio swapfile (%llu)
  ",
  					   page_file_offset(page));

  		}

  		end_page_writeback(page);

  		return ret;
  	}

  	ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
  	if (!ret) {

  		count_swpout_vm_event(page);

  		return 0;
  	}
  
  	ret = 0;

  	bio = get_swap_bio(GFP_NOIO, page, end_write_func);

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

  	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);

  	count_swpout_vm_event(page);

  	set_page_writeback(page);
  	unlock_page(page);

  	submit_bio(bio);

  out:
  	return ret;
  }

  int swap_readpage(struct page *page, bool do_poll)

  {
  	struct bio *bio;
  	int ret = 0;

  	struct swap_info_struct *sis = page_swap_info(page);

  	blk_qc_t qc;

  	struct gendisk *disk;

  	VM_BUG_ON_PAGE(!PageSwapCache(page), page);

  	VM_BUG_ON_PAGE(!PageLocked(page), page);
  	VM_BUG_ON_PAGE(PageUptodate(page), page);

  	if (frontswap_load(page) == 0) {

  		SetPageUptodate(page);
  		unlock_page(page);
  		goto out;
  	}

  
  	if (sis->flags & SWP_FILE) {
  		struct file *swap_file = sis->swap_file;
  		struct address_space *mapping = swap_file->f_mapping;
  
  		ret = mapping->a_ops->readpage(swap_file, page);
  		if (!ret)
  			count_vm_event(PSWPIN);
  		return ret;
  	}

  	ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
  	if (!ret) {

  		if (trylock_page(page)) {
  			swap_slot_free_notify(page);
  			unlock_page(page);
  		}

  		count_vm_event(PSWPIN);
  		return 0;
  	}
  
  	ret = 0;

  	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);

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

  	disk = bio->bi_disk;

  	/*
  	 * Keep this task valid during swap readpage because the oom killer may
  	 * attempt to access it in the page fault retry time check.
  	 */
  	get_task_struct(current);

  	bio->bi_private = current;

  	bio_set_op_attrs(bio, REQ_OP_READ, 0);

  	count_vm_event(PSWPIN);

  	bio_get(bio);
  	qc = submit_bio(bio);
  	while (do_poll) {
  		set_current_state(TASK_UNINTERRUPTIBLE);
  		if (!READ_ONCE(bio->bi_private))
  			break;

  		if (!blk_poll(disk->queue, qc))

  			break;
  	}
  	__set_current_state(TASK_RUNNING);
  	bio_put(bio);

  out:
  	return ret;
  }

  
  int swap_set_page_dirty(struct page *page)
  {
  	struct swap_info_struct *sis = page_swap_info(page);
  
  	if (sis->flags & SWP_FILE) {
  		struct address_space *mapping = sis->swap_file->f_mapping;

  
  		VM_BUG_ON_PAGE(!PageSwapCache(page), page);

  		return mapping->a_ops->set_page_dirty(page);
  	} else {
  		return __set_page_dirty_no_writeback(page);
  	}
  }