/*
 * linux/fs/ext4/readpage.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 * Copyright (C) 2015, Google, Inc.
 *
 * This was originally taken from fs/mpage.c
 *
 * The intent is the ext4_mpage_readpages() function here is intended
 * to replace mpage_readpages() in the general case, not just for
 * encrypted files.  It has some limitations (see below), where it
 * will fall back to read_block_full_page(), but these limitations
 * should only be hit when page_size != block_size.
 *
 * This will allow us to attach a callback function to support ext4
 * encryption.
 *
 * 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.
 *
 */

#include <linux/kernel.h>
#include <linux/export.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>
#include <linux/cleancache.h>

#include "ext4.h"

/*
 * Call ext4_decrypt on every single page, reusing the encryption
 * context.
 */
static void completion_pages(struct work_struct *work)
{
#ifdef CONFIG_EXT4_FS_ENCRYPTION
        struct ext4_crypto_ctx *ctx =
                container_of(work, struct ext4_crypto_ctx, work);
        struct bio      *bio    = ctx->bio;
        struct bio_vec  *bv;
        int             i;

        bio_for_each_segment_all(bv, bio, i) {
                struct page *page = bv->bv_page;

                int ret = ext4_decrypt(ctx, page);
                if (ret) {
                        WARN_ON_ONCE(1);
                        SetPageError(page);
                } else
                        SetPageUptodate(page);
                unlock_page(page);
        }
        ext4_release_crypto_ctx(ctx);
        bio_put(bio);
#else
        BUG();
#endif
}

static inline bool ext4_bio_encrypted(struct bio *bio)
{
#ifdef CONFIG_EXT4_FS_ENCRYPTION
        return unlikely(bio->bi_private != NULL);
#else
        return false;
#endif
}

/*
 * 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)
{
        struct bio_vec *bv;
        int i;

        if (ext4_bio_encrypted(bio)) {
                struct ext4_crypto_ctx *ctx = bio->bi_private;

                if (err) {
                        ext4_release_crypto_ctx(ctx);
                } else {
                        INIT_WORK(&ctx->work, completion_pages);
                        ctx->bio = bio;
                        queue_work(ext4_read_workqueue, &ctx->work);
                        return;
                }
        }
        bio_for_each_segment_all(bv, bio, i) {
                struct page *page = bv->bv_page;

                if (!err) {
                        SetPageUptodate(page);
                } else {
                        ClearPageUptodate(page);
                        SetPageError(page);
                }
                unlock_page(page);
        }

        bio_put(bio);
}

int ext4_mpage_readpages(struct address_space *mapping,
                         struct list_head *pages, struct page *page,
                         unsigned nr_pages)
{
        struct bio *bio = NULL;
        unsigned page_idx;
        sector_t last_block_in_bio = 0;

        struct inode *inode = 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;
        struct block_device *bdev = inode->i_sb->s_bdev;
        int length;
        unsigned relative_block = 0;
        struct ext4_map_blocks map;

        map.m_pblk = 0;
        map.m_lblk = 0;
        map.m_len = 0;
        map.m_flags = 0;

        for (page_idx = 0; nr_pages; page_idx++, nr_pages--) {
                int fully_mapped = 1;
                unsigned first_hole = blocks_per_page;

                prefetchw(&page->flags);
                if (pages) {
                        page = list_entry(pages->prev, struct page, lru);
                        list_del(&page->lru);
                        if (add_to_page_cache_lru(page, mapping,
                                                  page->index, GFP_KERNEL))
                                goto next_page;
                }

                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 previous result first.
                 */
                if ((map.m_flags & EXT4_MAP_MAPPED) &&
                    block_in_file > map.m_lblk &&
                    block_in_file < (map.m_lblk + map.m_len)) {
                        unsigned map_offset = block_in_file - map.m_lblk;
                        unsigned last = map.m_len - map_offset;

                        for (relative_block = 0; ; relative_block++) {
                                if (relative_block == last) {
                                        /* needed? */
                                        map.m_flags &= ~EXT4_MAP_MAPPED;
                                        break;
                                }
                                if (page_block == blocks_per_page)
                                        break;
                                blocks[page_block] = map.m_pblk + map_offset +
                                        relative_block;
                                page_block++;
                                block_in_file++;
                        }
                }

                /*
                 * Then do more ext4_map_blocks() calls until we are
                 * done with this page.
                 */
                while (page_block < blocks_per_page) {
                        if (block_in_file < last_block) {
                                map.m_lblk = block_in_file;
                                map.m_len = last_block - block_in_file;

                                if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
                                set_error_page:
                                        SetPageError(page);
                                        zero_user_segment(page, 0,
                                                          PAGE_CACHE_SIZE);
                                        unlock_page(page);
                                        goto next_page;
                                }
                        }
                        if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
                                fully_mapped = 0;
                                if (first_hole == blocks_per_page)
                                        first_hole = page_block;
                                page_block++;
                                block_in_file++;
                                continue;
                        }
                        if (first_hole != blocks_per_page)
                                goto confused;          /* hole -> non-hole */

                        /* Contiguous blocks? */
                        if (page_block && blocks[page_block-1] != map.m_pblk-1)
                                goto confused;
                        for (relative_block = 0; ; relative_block++) {
                                if (relative_block == map.m_len) {
                                        /* needed? */
                                        map.m_flags &= ~EXT4_MAP_MAPPED;
                                        break;
                                } else if (page_block == blocks_per_page)
                                        break;
                                blocks[page_block] = map.m_pblk+relative_block;
                                page_block++;
                                block_in_file++;
                        }
                }
                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 next_page;
                        }
                } else if (fully_mapped) {
                        SetPageMappedToDisk(page);
                }
                if (fully_mapped && blocks_per_page == 1 &&
                    !PageUptodate(page) && cleancache_get_page(page) == 0) {
                        SetPageUptodate(page);
                        goto confused;
                }

                /*
                 * This page will go to BIO.  Do we need to send this
                 * BIO off first?
                 */
                if (bio && (last_block_in_bio != blocks[0] - 1)) {
                submit_and_realloc:
                        submit_bio(READ, bio);
                        bio = NULL;
                }
                if (bio == NULL) {
                        struct ext4_crypto_ctx *ctx = NULL;

                        if (ext4_encrypted_inode(inode) &&
                            S_ISREG(inode->i_mode)) {
                                ctx = ext4_get_crypto_ctx(inode);
                                if (IS_ERR(ctx))
                                        goto set_error_page;
                        }
                        bio = bio_alloc(GFP_KERNEL,
                                min_t(int, nr_pages, bio_get_nr_vecs(bdev)));
                        if (!bio) {
                                if (ctx)
                                        ext4_release_crypto_ctx(ctx);
                                goto set_error_page;
                        }
                        bio->bi_bdev = bdev;
                        bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
                        bio->bi_end_io = mpage_end_io;
                        bio->bi_private = ctx;
                }

                length = first_hole << blkbits;
                if (bio_add_page(bio, page, length, 0) < length)
                        goto submit_and_realloc;

                if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
                     (relative_block == map.m_len)) ||
                    (first_hole != blocks_per_page)) {
                        submit_bio(READ, bio);
                        bio = NULL;
                } else
                        last_block_in_bio = blocks[blocks_per_page - 1];
                goto next_page;
        confused:
                if (bio) {
                        submit_bio(READ, bio);
                        bio = NULL;
                }
                if (!PageUptodate(page))
                        block_read_full_page(page, ext4_get_block);
                else
                        unlock_page(page);
        next_page:
                if (pages)
                        page_cache_release(page);
        }
        BUG_ON(pages && !list_empty(pages));
        if (bio)
                submit_bio(READ, bio);
        return 0;
}