// 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_first_page_all(bio);

        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)\n",
                         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_first_page_all(bio);
        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)\n",
                         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);
        if (waiter) {
                blk_wake_io_task(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\n");
        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, 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)\n",
                                           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 | REQ_SWAP | wbc_to_write_flags(wbc);
        bio_associate_blkg_from_page(bio, page);
        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 synchronous)
{
        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) && !synchronous, 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.
         */
        bio_set_op_attrs(bio, REQ_OP_READ, 0);
        if (synchronous) {
                bio->bi_opf |= REQ_HIPRI;
                get_task_struct(current);
                bio->bi_private = current;
        }
        count_vm_event(PSWPIN);
        bio_get(bio);
        qc = submit_bio(bio);
        while (synchronous) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (!READ_ONCE(bio->bi_private))
                        break;

                if (!blk_poll(disk->queue, qc, true))
                        io_schedule();
        }
        __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);
        }
}