// SPDX-License-Identifier: GPL-2.0-only
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 */

/*
 * This file implements VFS file and inode operations for regular files, device
 * nodes and symlinks as well as address space operations.
 *
 * UBIFS uses 2 page flags: @PG_private and @PG_checked. @PG_private is set if
 * the page is dirty and is used for optimization purposes - dirty pages are
 * not budgeted so the flag shows that 'ubifs_write_end()' should not release
 * the budget for this page. The @PG_checked flag is set if full budgeting is
 * required for the page e.g., when it corresponds to a file hole or it is
 * beyond the file size. The budgeting is done in 'ubifs_write_begin()', because
 * it is OK to fail in this function, and the budget is released in
 * 'ubifs_write_end()'. So the @PG_private and @PG_checked flags carry
 * information about how the page was budgeted, to make it possible to release
 * the budget properly.
 *
 * A thing to keep in mind: inode @i_mutex is locked in most VFS operations we
 * implement. However, this is not true for 'ubifs_writepage()', which may be
 * called with @i_mutex unlocked. For example, when flusher thread is doing
 * background write-back, it calls 'ubifs_writepage()' with unlocked @i_mutex.
 * At "normal" work-paths the @i_mutex is locked in 'ubifs_writepage()', e.g.
 * in the "sys_write -> alloc_pages -> direct reclaim path". So, in
 * 'ubifs_writepage()' we are only guaranteed that the page is locked.
 *
 * Similarly, @i_mutex is not always locked in 'ubifs_readpage()', e.g., the
 * read-ahead path does not lock it ("sys_read -> generic_file_aio_read ->
 * ondemand_readahead -> readpage"). In case of readahead, @I_SYNC flag is not
 * set as well. However, UBIFS disables readahead.
 */

#include "ubifs.h"
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/migrate.h>

static int read_block(struct inode *inode, void *addr, unsigned int block,
                      struct ubifs_data_node *dn)
{
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        int err, len, out_len;
        union ubifs_key key;
        unsigned int dlen;

        data_key_init(c, &key, inode->i_ino, block);
        err = ubifs_tnc_lookup(c, &key, dn);
        if (err) {
                if (err == -ENOENT)
                        /* Not found, so it must be a hole */
                        memset(addr, 0, UBIFS_BLOCK_SIZE);
                return err;
        }

        ubifs_assert(c, le64_to_cpu(dn->ch.sqnum) >
                     ubifs_inode(inode)->creat_sqnum);
        len = le32_to_cpu(dn->size);
        if (len <= 0 || len > UBIFS_BLOCK_SIZE)
                goto dump;

        dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;

        if (IS_ENCRYPTED(inode)) {
                err = ubifs_decrypt(inode, dn, &dlen, block);
                if (err)
                        goto dump;
        }

        out_len = UBIFS_BLOCK_SIZE;
        err = ubifs_decompress(c, &dn->data, dlen, addr, &out_len,
                               le16_to_cpu(dn->compr_type));
        if (err || len != out_len)
                goto dump;

        /*
         * Data length can be less than a full block, even for blocks that are
         * not the last in the file (e.g., as a result of making a hole and
         * appending data). Ensure that the remainder is zeroed out.
         */
        if (len < UBIFS_BLOCK_SIZE)
                memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);

        return 0;

dump:
        ubifs_err(c, "bad data node (block %u, inode %lu)",
                  block, inode->i_ino);
        ubifs_dump_node(c, dn, UBIFS_MAX_DATA_NODE_SZ);
        return -EINVAL;
}

static int do_readpage(struct page *page)
{
        void *addr;
        int err = 0, i;
        unsigned int block, beyond;
        struct ubifs_data_node *dn;
        struct inode *inode = page->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        loff_t i_size = i_size_read(inode);

        dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
                inode->i_ino, page->index, i_size, page->flags);
        ubifs_assert(c, !PageChecked(page));
        ubifs_assert(c, !PagePrivate(page));

        addr = kmap(page);

        block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
        beyond = (i_size + UBIFS_BLOCK_SIZE - 1) >> UBIFS_BLOCK_SHIFT;
        if (block >= beyond) {
                /* Reading beyond inode */
                SetPageChecked(page);
                memset(addr, 0, PAGE_SIZE);
                goto out;
        }

        dn = kmalloc(UBIFS_MAX_DATA_NODE_SZ, GFP_NOFS);
        if (!dn) {
                err = -ENOMEM;
                goto error;
        }

        i = 0;
        while (1) {
                int ret;

                if (block >= beyond) {
                        /* Reading beyond inode */
                        err = -ENOENT;
                        memset(addr, 0, UBIFS_BLOCK_SIZE);
                } else {
                        ret = read_block(inode, addr, block, dn);
                        if (ret) {
                                err = ret;
                                if (err != -ENOENT)
                                        break;
                        } else if (block + 1 == beyond) {
                                int dlen = le32_to_cpu(dn->size);
                                int ilen = i_size & (UBIFS_BLOCK_SIZE - 1);

                                if (ilen && ilen < dlen)
                                        memset(addr + ilen, 0, dlen - ilen);
                        }
                }
                if (++i >= UBIFS_BLOCKS_PER_PAGE)
                        break;
                block += 1;
                addr += UBIFS_BLOCK_SIZE;
        }
        if (err) {
                struct ubifs_info *c = inode->i_sb->s_fs_info;
                if (err == -ENOENT) {
                        /* Not found, so it must be a hole */
                        SetPageChecked(page);
                        dbg_gen("hole");
                        goto out_free;
                }
                ubifs_err(c, "cannot read page %lu of inode %lu, error %d",
                          page->index, inode->i_ino, err);
                goto error;
        }

out_free:
        kfree(dn);
out:
        SetPageUptodate(page);
        ClearPageError(page);
        flush_dcache_page(page);
        kunmap(page);
        return 0;

error:
        kfree(dn);
        ClearPageUptodate(page);
        SetPageError(page);
        flush_dcache_page(page);
        kunmap(page);
        return err;
}

/**
 * release_new_page_budget - release budget of a new page.
 * @c: UBIFS file-system description object
 *
 * This is a helper function which releases budget corresponding to the budget
 * of one new page of data.
 */
static void release_new_page_budget(struct ubifs_info *c)
{
        struct ubifs_budget_req req = { .recalculate = 1, .new_page = 1 };

        ubifs_release_budget(c, &req);
}

/**
 * release_existing_page_budget - release budget of an existing page.
 * @c: UBIFS file-system description object
 *
 * This is a helper function which releases budget corresponding to the budget
 * of changing one page of data which already exists on the flash media.
 */
static void release_existing_page_budget(struct ubifs_info *c)
{
        struct ubifs_budget_req req = { .dd_growth = c->bi.page_budget};

        ubifs_release_budget(c, &req);
}

static int write_begin_slow(struct address_space *mapping,
                            loff_t pos, unsigned len, struct page **pagep,
                            unsigned flags)
{
        struct inode *inode = mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        pgoff_t index = pos >> PAGE_SHIFT;
        struct ubifs_budget_req req = { .new_page = 1 };
        int err, appending = !!(pos + len > inode->i_size);
        struct page *page;

        dbg_gen("ino %lu, pos %llu, len %u, i_size %lld",
                inode->i_ino, pos, len, inode->i_size);

        /*
         * At the slow path we have to budget before locking the page, because
         * budgeting may force write-back, which would wait on locked pages and
         * deadlock if we had the page locked. At this point we do not know
         * anything about the page, so assume that this is a new page which is
         * written to a hole. This corresponds to largest budget. Later the
         * budget will be amended if this is not true.
         */
        if (appending)
                /* We are appending data, budget for inode change */
                req.dirtied_ino = 1;

        err = ubifs_budget_space(c, &req);
        if (unlikely(err))
                return err;

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (unlikely(!page)) {
                ubifs_release_budget(c, &req);
                return -ENOMEM;
        }

        if (!PageUptodate(page)) {
                if (!(pos & ~PAGE_MASK) && len == PAGE_SIZE)
                        SetPageChecked(page);
                else {
                        err = do_readpage(page);
                        if (err) {
                                unlock_page(page);
                                put_page(page);
                                ubifs_release_budget(c, &req);
                                return err;
                        }
                }

                SetPageUptodate(page);
                ClearPageError(page);
        }

        if (PagePrivate(page))
                /*
                 * The page is dirty, which means it was budgeted twice:
                 *   o first time the budget was allocated by the task which
                 *     made the page dirty and set the PG_private flag;
                 *   o and then we budgeted for it for the second time at the
                 *     very beginning of this function.
                 *
                 * So what we have to do is to release the page budget we
                 * allocated.
                 */
                release_new_page_budget(c);
        else if (!PageChecked(page))
                /*
                 * We are changing a page which already exists on the media.
                 * This means that changing the page does not make the amount
                 * of indexing information larger, and this part of the budget
                 * which we have already acquired may be released.
                 */
                ubifs_convert_page_budget(c);

        if (appending) {
                struct ubifs_inode *ui = ubifs_inode(inode);

                /*
                 * 'ubifs_write_end()' is optimized from the fast-path part of
                 * 'ubifs_write_begin()' and expects the @ui_mutex to be locked
                 * if data is appended.
                 */
                mutex_lock(&ui->ui_mutex);
                if (ui->dirty)
                        /*
                         * The inode is dirty already, so we may free the
                         * budget we allocated.
                         */
                        ubifs_release_dirty_inode_budget(c, ui);
        }

        *pagep = page;
        return 0;
}

/**
 * allocate_budget - allocate budget for 'ubifs_write_begin()'.
 * @c: UBIFS file-system description object
 * @page: page to allocate budget for
 * @ui: UBIFS inode object the page belongs to
 * @appending: non-zero if the page is appended
 *
 * This is a helper function for 'ubifs_write_begin()' which allocates budget
 * for the operation. The budget is allocated differently depending on whether
 * this is appending, whether the page is dirty or not, and so on. This
 * function leaves the @ui->ui_mutex locked in case of appending. Returns zero
 * in case of success and %-ENOSPC in case of failure.
 */
static int allocate_budget(struct ubifs_info *c, struct page *page,
                           struct ubifs_inode *ui, int appending)
{
        struct ubifs_budget_req req = { .fast = 1 };

        if (PagePrivate(page)) {
                if (!appending)
                        /*
                         * The page is dirty and we are not appending, which
                         * means no budget is needed at all.
                         */
                        return 0;

                mutex_lock(&ui->ui_mutex);
                if (ui->dirty)
                        /*
                         * The page is dirty and we are appending, so the inode
                         * has to be marked as dirty. However, it is already
                         * dirty, so we do not need any budget. We may return,
                         * but @ui->ui_mutex hast to be left locked because we
                         * should prevent write-back from flushing the inode
                         * and freeing the budget. The lock will be released in
                         * 'ubifs_write_end()'.
                         */
                        return 0;

                /*
                 * The page is dirty, we are appending, the inode is clean, so
                 * we need to budget the inode change.
                 */
                req.dirtied_ino = 1;
        } else {
                if (PageChecked(page))
                        /*
                         * The page corresponds to a hole and does not
                         * exist on the media. So changing it makes
                         * make the amount of indexing information
                         * larger, and we have to budget for a new
                         * page.
                         */
                        req.new_page = 1;
                else
                        /*
                         * Not a hole, the change will not add any new
                         * indexing information, budget for page
                         * change.
                         */
                        req.dirtied_page = 1;

                if (appending) {
                        mutex_lock(&ui->ui_mutex);
                        if (!ui->dirty)
                                /*
                                 * The inode is clean but we will have to mark
                                 * it as dirty because we are appending. This
                                 * needs a budget.
                                 */
                                req.dirtied_ino = 1;
                }
        }

        return ubifs_budget_space(c, &req);
}

/*
 * This function is called when a page of data is going to be written. Since
 * the page of data will not necessarily go to the flash straight away, UBIFS
 * has to reserve space on the media for it, which is done by means of
 * budgeting.
 *
 * This is the hot-path of the file-system and we are trying to optimize it as
 * much as possible. For this reasons it is split on 2 parts - slow and fast.
 *
 * There many budgeting cases:
 *     o a new page is appended - we have to budget for a new page and for
 *       changing the inode; however, if the inode is already dirty, there is
 *       no need to budget for it;
 *     o an existing clean page is changed - we have budget for it; if the page
 *       does not exist on the media (a hole), we have to budget for a new
 *       page; otherwise, we may budget for changing an existing page; the
 *       difference between these cases is that changing an existing page does
 *       not introduce anything new to the FS indexing information, so it does
 *       not grow, and smaller budget is acquired in this case;
 *     o an existing dirty page is changed - no need to budget at all, because
 *       the page budget has been acquired by earlier, when the page has been
 *       marked dirty.
 *
 * UBIFS budgeting sub-system may force write-back if it thinks there is no
 * space to reserve. This imposes some locking restrictions and makes it
 * impossible to take into account the above cases, and makes it impossible to
 * optimize budgeting.
 *
 * The solution for this is that the fast path of 'ubifs_write_begin()' assumes
 * there is a plenty of flash space and the budget will be acquired quickly,
 * without forcing write-back. The slow path does not make this assumption.
 */
static int ubifs_write_begin(struct file *file, struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned flags,
                             struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        struct ubifs_inode *ui = ubifs_inode(inode);
        pgoff_t index = pos >> PAGE_SHIFT;
        int err, appending = !!(pos + len > inode->i_size);
        int skipped_read = 0;
        struct page *page;

        ubifs_assert(c, ubifs_inode(inode)->ui_size == inode->i_size);
        ubifs_assert(c, !c->ro_media && !c->ro_mount);

        if (unlikely(c->ro_error))
                return -EROFS;

        /* Try out the fast-path part first */
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (unlikely(!page))
                return -ENOMEM;

        if (!PageUptodate(page)) {
                /* The page is not loaded from the flash */
                if (!(pos & ~PAGE_MASK) && len == PAGE_SIZE) {
                        /*
                         * We change whole page so no need to load it. But we
                         * do not know whether this page exists on the media or
                         * not, so we assume the latter because it requires
                         * larger budget. The assumption is that it is better
                         * to budget a bit more than to read the page from the
                         * media. Thus, we are setting the @PG_checked flag
                         * here.
                         */
                        SetPageChecked(page);
                        skipped_read = 1;
                } else {
                        err = do_readpage(page);
                        if (err) {
                                unlock_page(page);
                                put_page(page);
                                return err;
                        }
                }

                SetPageUptodate(page);
                ClearPageError(page);
        }

        err = allocate_budget(c, page, ui, appending);
        if (unlikely(err)) {
                ubifs_assert(c, err == -ENOSPC);
                /*
                 * If we skipped reading the page because we were going to
                 * write all of it, then it is not up to date.
                 */
                if (skipped_read) {
                        ClearPageChecked(page);
                        ClearPageUptodate(page);
                }
                /*
                 * Budgeting failed which means it would have to force
                 * write-back but didn't, because we set the @fast flag in the
                 * request. Write-back cannot be done now, while we have the
                 * page locked, because it would deadlock. Unlock and free
                 * everything and fall-back to slow-path.
                 */
                if (appending) {
                        ubifs_assert(c, mutex_is_locked(&ui->ui_mutex));
                        mutex_unlock(&ui->ui_mutex);
                }
                unlock_page(page);
                put_page(page);

                return write_begin_slow(mapping, pos, len, pagep, flags);
        }

        /*
         * Whee, we acquired budgeting quickly - without involving
         * garbage-collection, committing or forcing write-back. We return
         * with @ui->ui_mutex locked if we are appending pages, and unlocked
         * otherwise. This is an optimization (slightly hacky though).
         */
        *pagep = page;
        return 0;

}

/**
 * cancel_budget - cancel budget.
 * @c: UBIFS file-system description object
 * @page: page to cancel budget for
 * @ui: UBIFS inode object the page belongs to
 * @appending: non-zero if the page is appended
 *
 * This is a helper function for a page write operation. It unlocks the
 * @ui->ui_mutex in case of appending.
 */
static void cancel_budget(struct ubifs_info *c, struct page *page,
                          struct ubifs_inode *ui, int appending)
{
        if (appending) {
                if (!ui->dirty)
                        ubifs_release_dirty_inode_budget(c, ui);
                mutex_unlock(&ui->ui_mutex);
        }
        if (!PagePrivate(page)) {
                if (PageChecked(page))
                        release_new_page_budget(c);
                else
                        release_existing_page_budget(c);
        }
}

static int ubifs_write_end(struct file *file, struct address_space *mapping,
                           loff_t pos, unsigned len, unsigned copied,
                           struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        struct ubifs_inode *ui = ubifs_inode(inode);
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        loff_t end_pos = pos + len;
        int appending = !!(end_pos > inode->i_size);

        dbg_gen("ino %lu, pos %llu, pg %lu, len %u, copied %d, i_size %lld",
                inode->i_ino, pos, page->index, len, copied, inode->i_size);

        if (unlikely(copied < len && len == PAGE_SIZE)) {
                /*
                 * VFS copied less data to the page that it intended and
                 * declared in its '->write_begin()' call via the @len
                 * argument. If the page was not up-to-date, and @len was
                 * @PAGE_SIZE, the 'ubifs_write_begin()' function did
                 * not load it from the media (for optimization reasons). This
                 * means that part of the page contains garbage. So read the
                 * page now.
                 */
                dbg_gen("copied %d instead of %d, read page and repeat",
                        copied, len);
                cancel_budget(c, page, ui, appending);
                ClearPageChecked(page);

                /*
                 * Return 0 to force VFS to repeat the whole operation, or the
                 * error code if 'do_readpage()' fails.
                 */
                copied = do_readpage(page);
                goto out;
        }

        if (!PagePrivate(page)) {
                attach_page_private(page, (void *)1);
                atomic_long_inc(&c->dirty_pg_cnt);
                __set_page_dirty_nobuffers(page);
        }

        if (appending) {
                i_size_write(inode, end_pos);
                ui->ui_size = end_pos;
                /*
                 * Note, we do not set @I_DIRTY_PAGES (which means that the
                 * inode has dirty pages), this has been done in
                 * '__set_page_dirty_nobuffers()'.
                 */
                __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
                ubifs_assert(c, mutex_is_locked(&ui->ui_mutex));
                mutex_unlock(&ui->ui_mutex);
        }

out:
        unlock_page(page);
        put_page(page);
        return copied;
}

/**
 * populate_page - copy data nodes into a page for bulk-read.
 * @c: UBIFS file-system description object
 * @page: page
 * @bu: bulk-read information
 * @n: next zbranch slot
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int populate_page(struct ubifs_info *c, struct page *page,
                         struct bu_info *bu, int *n)
{
        int i = 0, nn = *n, offs = bu->zbranch[0].offs, hole = 0, read = 0;
        struct inode *inode = page->mapping->host;
        loff_t i_size = i_size_read(inode);
        unsigned int page_block;
        void *addr, *zaddr;
        pgoff_t end_index;

        dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
                inode->i_ino, page->index, i_size, page->flags);

        addr = zaddr = kmap(page);

        end_index = (i_size - 1) >> PAGE_SHIFT;
        if (!i_size || page->index > end_index) {
                hole = 1;
                memset(addr, 0, PAGE_SIZE);
                goto out_hole;
        }

        page_block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
        while (1) {
                int err, len, out_len, dlen;

                if (nn >= bu->cnt) {
                        hole = 1;
                        memset(addr, 0, UBIFS_BLOCK_SIZE);
                } else if (key_block(c, &bu->zbranch[nn].key) == page_block) {
                        struct ubifs_data_node *dn;

                        dn = bu->buf + (bu->zbranch[nn].offs - offs);

                        ubifs_assert(c, le64_to_cpu(dn->ch.sqnum) >
                                     ubifs_inode(inode)->creat_sqnum);

                        len = le32_to_cpu(dn->size);
                        if (len <= 0 || len > UBIFS_BLOCK_SIZE)
                                goto out_err;

                        dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;
                        out_len = UBIFS_BLOCK_SIZE;

                        if (IS_ENCRYPTED(inode)) {
                                err = ubifs_decrypt(inode, dn, &dlen, page_block);
                                if (err)
                                        goto out_err;
                        }

                        err = ubifs_decompress(c, &dn->data, dlen, addr, &out_len,
                                               le16_to_cpu(dn->compr_type));
                        if (err || len != out_len)
                                goto out_err;

                        if (len < UBIFS_BLOCK_SIZE)
                                memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);

                        nn += 1;
                        read = (i << UBIFS_BLOCK_SHIFT) + len;
                } else if (key_block(c, &bu->zbranch[nn].key) < page_block) {
                        nn += 1;
                        continue;
                } else {
                        hole = 1;
                        memset(addr, 0, UBIFS_BLOCK_SIZE);
                }
                if (++i >= UBIFS_BLOCKS_PER_PAGE)
                        break;
                addr += UBIFS_BLOCK_SIZE;
                page_block += 1;
        }

        if (end_index == page->index) {
                int len = i_size & (PAGE_SIZE - 1);

                if (len && len < read)
                        memset(zaddr + len, 0, read - len);
        }

out_hole:
        if (hole) {
                SetPageChecked(page);
                dbg_gen("hole");
        }

        SetPageUptodate(page);
        ClearPageError(page);
        flush_dcache_page(page);
        kunmap(page);
        *n = nn;
        return 0;

out_err:
        ClearPageUptodate(page);
        SetPageError(page);
        flush_dcache_page(page);
        kunmap(page);
        ubifs_err(c, "bad data node (block %u, inode %lu)",
                  page_block, inode->i_ino);
        return -EINVAL;
}

/**
 * ubifs_do_bulk_read - do bulk-read.
 * @c: UBIFS file-system description object
 * @bu: bulk-read information
 * @page1: first page to read
 *
 * This function returns %1 if the bulk-read is done, otherwise %0 is returned.
 */
static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
                              struct page *page1)
{
        pgoff_t offset = page1->index, end_index;
        struct address_space *mapping = page1->mapping;
        struct inode *inode = mapping->host;
        struct ubifs_inode *ui = ubifs_inode(inode);
        int err, page_idx, page_cnt, ret = 0, n = 0;
        int allocate = bu->buf ? 0 : 1;
        loff_t isize;
        gfp_t ra_gfp_mask = readahead_gfp_mask(mapping) & ~__GFP_FS;

        err = ubifs_tnc_get_bu_keys(c, bu);
        if (err)
                goto out_warn;

        if (bu->eof) {
                /* Turn off bulk-read at the end of the file */
                ui->read_in_a_row = 1;
                ui->bulk_read = 0;
        }

        page_cnt = bu->blk_cnt >> UBIFS_BLOCKS_PER_PAGE_SHIFT;
        if (!page_cnt) {
                /*
                 * This happens when there are multiple blocks per page and the
                 * blocks for the first page we are looking for, are not
                 * together. If all the pages were like this, bulk-read would
                 * reduce performance, so we turn it off for a while.
                 */
                goto out_bu_off;
        }

        if (bu->cnt) {
                if (allocate) {
                        /*
                         * Allocate bulk-read buffer depending on how many data
                         * nodes we are going to read.
                         */
                        bu->buf_len = bu->zbranch[bu->cnt - 1].offs +
                                      bu->zbranch[bu->cnt - 1].len -
                                      bu->zbranch[0].offs;
                        ubifs_assert(c, bu->buf_len > 0);
                        ubifs_assert(c, bu->buf_len <= c->leb_size);
                        bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
                        if (!bu->buf)
                                goto out_bu_off;
                }

                err = ubifs_tnc_bulk_read(c, bu);
                if (err)
                        goto out_warn;
        }

        err = populate_page(c, page1, bu, &n);
        if (err)
                goto out_warn;

        unlock_page(page1);
        ret = 1;

        isize = i_size_read(inode);
        if (isize == 0)
                goto out_free;
        end_index = ((isize - 1) >> PAGE_SHIFT);

        for (page_idx = 1; page_idx < page_cnt; page_idx++) {
                pgoff_t page_offset = offset + page_idx;
                struct page *page;

                if (page_offset > end_index)
                        break;
                page = pagecache_get_page(mapping, page_offset,
                                 FGP_LOCK|FGP_ACCESSED|FGP_CREAT|FGP_NOWAIT,
                                 ra_gfp_mask);
                if (!page)
                        break;
                if (!PageUptodate(page))
                        err = populate_page(c, page, bu, &n);
                unlock_page(page);
                put_page(page);
                if (err)
                        break;
        }

        ui->last_page_read = offset + page_idx - 1;

out_free:
        if (allocate)
                kfree(bu->buf);
        return ret;

out_warn:
        ubifs_warn(c, "ignoring error %d and skipping bulk-read", err);
        goto out_free;

out_bu_off:
        ui->read_in_a_row = ui->bulk_read = 0;
        goto out_free;
}

/**
 * ubifs_bulk_read - determine whether to bulk-read and, if so, do it.
 * @page: page from which to start bulk-read.
 *
 * Some flash media are capable of reading sequentially at faster rates. UBIFS
 * bulk-read facility is designed to take advantage of that, by reading in one
 * go consecutive data nodes that are also located consecutively in the same
 * LEB. This function returns %1 if a bulk-read is done and %0 otherwise.
 */
static int ubifs_bulk_read(struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        struct ubifs_inode *ui = ubifs_inode(inode);
        pgoff_t index = page->index, last_page_read = ui->last_page_read;
        struct bu_info *bu;
        int err = 0, allocated = 0;

        ui->last_page_read = index;
        if (!c->bulk_read)
                return 0;

        /*
         * Bulk-read is protected by @ui->ui_mutex, but it is an optimization,
         * so don't bother if we cannot lock the mutex.
         */
        if (!mutex_trylock(&ui->ui_mutex))
                return 0;

        if (index != last_page_read + 1) {
                /* Turn off bulk-read if we stop reading sequentially */
                ui->read_in_a_row = 1;
                if (ui->bulk_read)
                        ui->bulk_read = 0;
                goto out_unlock;
        }

        if (!ui->bulk_read) {
                ui->read_in_a_row += 1;
                if (ui->read_in_a_row < 3)
                        goto out_unlock;
                /* Three reads in a row, so switch on bulk-read */
                ui->bulk_read = 1;
        }

        /*
         * If possible, try to use pre-allocated bulk-read information, which
         * is protected by @c->bu_mutex.
         */
        if (mutex_trylock(&c->bu_mutex))
                bu = &c->bu;
        else {
                bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
                if (!bu)
                        goto out_unlock;

                bu->buf = NULL;
                allocated = 1;
        }

        bu->buf_len = c->max_bu_buf_len;
        data_key_init(c, &bu->key, inode->i_ino,
                      page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT);
        err = ubifs_do_bulk_read(c, bu, page);

        if (!allocated)
                mutex_unlock(&c->bu_mutex);
        else
                kfree(bu);

out_unlock:
        mutex_unlock(&ui->ui_mutex);
        return err;
}

static int ubifs_readpage(struct file *file, struct page *page)
{
        if (ubifs_bulk_read(page))
                return 0;
        do_readpage(page);
        unlock_page(page);
        return 0;
}

static int do_writepage(struct page *page, int len)
{
        int err = 0, i, blen;
        unsigned int block;
        void *addr;
        union ubifs_key key;
        struct inode *inode = page->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;

#ifdef UBIFS_DEBUG
        struct ubifs_inode *ui = ubifs_inode(inode);
        spin_lock(&ui->ui_lock);
        ubifs_assert(c, page->index <= ui->synced_i_size >> PAGE_SHIFT);
        spin_unlock(&ui->ui_lock);
#endif

        /* Update radix tree tags */
        set_page_writeback(page);

        addr = kmap(page);
        block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
        i = 0;
        while (len) {
                blen = min_t(int, len, UBIFS_BLOCK_SIZE);
                data_key_init(c, &key, inode->i_ino, block);
                err = ubifs_jnl_write_data(c, inode, &key, addr, blen);
                if (err)
                        break;
                if (++i >= UBIFS_BLOCKS_PER_PAGE)
                        break;
                block += 1;
                addr += blen;
                len -= blen;
        }
        if (err) {
                SetPageError(page);
                ubifs_err(c, "cannot write page %lu of inode %lu, error %d",
                          page->index, inode->i_ino, err);
                ubifs_ro_mode(c, err);
        }

        ubifs_assert(c, PagePrivate(page));
        if (PageChecked(page))
                release_new_page_budget(c);
        else
                release_existing_page_budget(c);

        atomic_long_dec(&c->dirty_pg_cnt);
        detach_page_private(page);
        ClearPageChecked(page);

        kunmap(page);
        unlock_page(page);
        end_page_writeback(page);
        return err;
}

/*
 * When writing-back dirty inodes, VFS first writes-back pages belonging to the
 * inode, then the inode itself. For UBIFS this may cause a problem. Consider a
 * situation when a we have an inode with size 0, then a megabyte of data is
 * appended to the inode, then write-back starts and flushes some amount of the
 * dirty pages, the journal becomes full, commit happens and finishes, and then
 * an unclean reboot happens. When the file system is mounted next time, the
 * inode size would still be 0, but there would be many pages which are beyond
 * the inode size, they would be indexed and consume flash space. Because the
 * journal has been committed, the replay would not be able to detect this
 * situation and correct the inode size. This means UBIFS would have to scan
 * whole index and correct all inode sizes, which is long an unacceptable.
 *
 * To prevent situations like this, UBIFS writes pages back only if they are
 * within the last synchronized inode size, i.e. the size which has been
 * written to the flash media last time. Otherwise, UBIFS forces inode
 * write-back, thus making sure the on-flash inode contains current inode size,
 * and then keeps writing pages back.
 *
 * Some locking issues explanation. 'ubifs_writepage()' first is called with
 * the page locked, and it locks @ui_mutex. However, write-back does take inode
 * @i_mutex, which means other VFS operations may be run on this inode at the
 * same time. And the problematic one is truncation to smaller size, from where
 * we have to call 'truncate_setsize()', which first changes @inode->i_size,
 * then drops the truncated pages. And while dropping the pages, it takes the
 * page lock. This means that 'do_truncation()' cannot call 'truncate_setsize()'
 * with @ui_mutex locked, because it would deadlock with 'ubifs_writepage()'.
 * This means that @inode->i_size is changed while @ui_mutex is unlocked.
 *
 * XXX(truncate): with the new truncate sequence this is not true anymore,
 * and the calls to truncate_setsize can be move around freely.  They should
 * be moved to the very end of the truncate sequence.
 *
 * But in 'ubifs_writepage()' we have to guarantee that we do not write beyond
 * inode size. How do we do this if @inode->i_size may became smaller while we
 * are in the middle of 'ubifs_writepage()'? The UBIFS solution is the
 * @ui->ui_isize "shadow" field which UBIFS uses instead of @inode->i_size
 * internally and updates it under @ui_mutex.
 *
 * Q: why we do not worry that if we race with truncation, we may end up with a
 * situation when the inode is truncated while we are in the middle of
 * 'do_writepage()', so we do write beyond inode size?

 * A: If we are in the middle of 'do_writepage()', truncation would be locked
 * on the page lock and it would not write the truncated inode node to the
 * journal before we have finished.
 */
static int ubifs_writepage(struct page *page, struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        struct ubifs_inode *ui = ubifs_inode(inode);
        loff_t i_size =  i_size_read(inode), synced_i_size;
        pgoff_t end_index = i_size >> PAGE_SHIFT;
        int err, len = i_size & (PAGE_SIZE - 1);
        void *kaddr;

        dbg_gen("ino %lu, pg %lu, pg flags %#lx",
                inode->i_ino, page->index, page->flags);
        ubifs_assert(c, PagePrivate(page));

        /* Is the page fully outside @i_size? (truncate in progress) */
        if (page->index > end_index || (page->index == end_index && !len)) {
                err = 0;
                goto out_unlock;
        }

        spin_lock(&ui->ui_lock);
        synced_i_size = ui->synced_i_size;
        spin_unlock(&ui->ui_lock);

        /* Is the page fully inside @i_size? */
        if (page->index < end_index) {
                if (page->index >= synced_i_size >> PAGE_SHIFT) {
                        err = inode->i_sb->s_op->write_inode(inode, NULL);
                        if (err)
                                goto out_unlock;
                        /*
                         * The inode has been written, but the write-buffer has
                         * not been synchronized, so in case of an unclean
                         * reboot we may end up with some pages beyond inode
                         * size, but they would be in the journal (because
                         * commit flushes write buffers) and recovery would deal
                         * with this.
                         */
                }
                return do_writepage(page, PAGE_SIZE);
        }

        /*
         * 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."
         */
        kaddr = kmap_atomic(page);
        memset(kaddr + len, 0, PAGE_SIZE - len);
        flush_dcache_page(page);
        kunmap_atomic(kaddr);

        if (i_size > synced_i_size) {
                err = inode->i_sb->s_op->write_inode(inode, NULL);
                if (err)
                        goto out_unlock;
        }

        return do_writepage(page, len);

out_unlock:
        unlock_page(page);
        return err;
}

/**
 * do_attr_changes - change inode attributes.
 * @inode: inode to change attributes for
 * @attr: describes attributes to change
 */
static void do_attr_changes(struct inode *inode, const struct iattr *attr)
{
        if (attr->ia_valid & ATTR_UID)
                inode->i_uid = attr->ia_uid;
        if (attr->ia_valid & ATTR_GID)
                inode->i_gid = attr->ia_gid;
        if (attr->ia_valid & ATTR_ATIME)
                inode->i_atime = attr->ia_atime;
        if (attr->ia_valid & ATTR_MTIME)
                inode->i_mtime = attr->ia_mtime;
        if (attr->ia_valid & ATTR_CTIME)
                inode->i_ctime = attr->ia_ctime;
        if (attr->ia_valid & ATTR_MODE) {
                umode_t mode = attr->ia_mode;

                if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
                        mode &= ~S_ISGID;
                inode->i_mode = mode;
        }
}

/**
 * do_truncation - truncate an inode.
 * @c: UBIFS file-system description object
 * @inode: inode to truncate
 * @attr: inode attribute changes description
 *
 * This function implements VFS '->setattr()' call when the inode is truncated
 * to a smaller size. Returns zero in case of success and a negative error code
 * in case of failure.
 */
static int do_truncation(struct ubifs_info *c, struct inode *inode,
                         const struct iattr *attr)
{
        int err;
        struct ubifs_budget_req req;
        loff_t old_size = inode->i_size, new_size = attr->ia_size;
        int offset = new_size & (UBIFS_BLOCK_SIZE - 1), budgeted = 1;
        struct ubifs_inode *ui = ubifs_inode(inode);

        dbg_gen("ino %lu, size %lld -> %lld", inode->i_ino, old_size, new_size);
        memset(&req, 0, sizeof(struct ubifs_budget_req));

        /*
         * If this is truncation to a smaller size, and we do not truncate on a
         * block boundary, budget for changing one data block, because the last
         * block will be re-written.
         */
        if (new_size & (UBIFS_BLOCK_SIZE - 1))
                req.dirtied_page = 1;

        req.dirtied_ino = 1;
        /* A funny way to budget for truncation node */
        req.dirtied_ino_d = UBIFS_TRUN_NODE_SZ;
        err = ubifs_budget_space(c, &req);
        if (err) {
                /*
                 * Treat truncations to zero as deletion and always allow them,
                 * just like we do for '->unlink()'.
                 */
                if (new_size || err != -ENOSPC)
                        return err;
                budgeted = 0;
        }

        truncate_setsize(inode, new_size);

        if (offset) {
                pgoff_t index = new_size >> PAGE_SHIFT;
                struct page *page;

                page = find_lock_page(inode->i_mapping, index);
                if (page) {
                        if (PageDirty(page)) {
                                /*
                                 * 'ubifs_jnl_truncate()' will try to truncate
                                 * the last data node, but it contains
                                 * out-of-date data because the page is dirty.
                                 * Write the page now, so that
                                 * 'ubifs_jnl_truncate()' will see an already
                                 * truncated (and up to date) data node.
                                 */
                                ubifs_assert(c, PagePrivate(page));

                                clear_page_dirty_for_io(page);
                                if (UBIFS_BLOCKS_PER_PAGE_SHIFT)
                                        offset = new_size &
                                                 (PAGE_SIZE - 1);
                                err = do_writepage(page, offset);
                                put_page(page);
                                if (err)
                                        goto out_budg;
                                /*
                                 * We could now tell 'ubifs_jnl_truncate()' not
                                 * to read the last block.
                                 */
                        } else {
                                /*
                                 * We could 'kmap()' the page and pass the data
                                 * to 'ubifs_jnl_truncate()' to save it from
                                 * having to read it.
                                 */
                                unlock_page(page);
                                put_page(page);
                        }
                }
        }

        mutex_lock(&ui->ui_mutex);
        ui->ui_size = inode->i_size;
        /* Truncation changes inode [mc]time */
        inode->i_mtime = inode->i_ctime = current_time(inode);
        /* Other attributes may be changed at the same time as well */
        do_attr_changes(inode, attr);
        err = ubifs_jnl_truncate(c, inode, old_size, new_size);
        mutex_unlock(&ui->ui_mutex);

out_budg:
        if (budgeted)
                ubifs_release_budget(c, &req);
        else {
                c->bi.nospace = c->bi.nospace_rp = 0;
                smp_wmb();
        }
        return err;
}

/**
 * do_setattr - change inode attributes.
 * @c: UBIFS file-system description object
 * @inode: inode to change attributes for
 * @attr: inode attribute changes description
 *
 * This function implements VFS '->setattr()' call for all cases except
 * truncations to smaller size. Returns zero in case of success and a negative
 * error code in case of failure.
 */
static int do_setattr(struct ubifs_info *c, struct inode *inode,
                      const struct iattr *attr)
{
        int err, release;
        loff_t new_size = attr->ia_size;
        struct ubifs_inode *ui = ubifs_inode(inode);
        struct ubifs_budget_req req = { .dirtied_ino = 1,
                                .dirtied_ino_d = ALIGN(ui->data_len, 8) };

        err = ubifs_budget_space(c, &req);
        if (err)
                return err;

        if (attr->ia_valid & ATTR_SIZE) {
                dbg_gen("size %lld -> %lld", inode->i_size, new_size);
                truncate_setsize(inode, new_size);
        }

        mutex_lock(&ui->ui_mutex);
        if (attr->ia_valid & ATTR_SIZE) {
                /* Truncation changes inode [mc]time */
                inode->i_mtime = inode->i_ctime = current_time(inode);
                /* 'truncate_setsize()' changed @i_size, update @ui_size */
                ui->ui_size = inode->i_size;
        }

        do_attr_changes(inode, attr);

        release = ui->dirty;
        if (attr->ia_valid & ATTR_SIZE)
                /*
                 * Inode length changed, so we have to make sure
                 * @I_DIRTY_DATASYNC is set.
                 */
                 __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        else
                mark_inode_dirty_sync(inode);
        mutex_unlock(&ui->ui_mutex);

        if (release)
                ubifs_release_budget(c, &req);
        if (IS_SYNC(inode))
                err = inode->i_sb->s_op->write_inode(inode, NULL);
        return err;
}

int ubifs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
                  struct iattr *attr)
{
        int err;
        struct inode *inode = d_inode(dentry);
        struct ubifs_info *c = inode->i_sb->s_fs_info;

        dbg_gen("ino %lu, mode %#x, ia_valid %#x",
                inode->i_ino, inode->i_mode, attr->ia_valid);
        err = setattr_prepare(&init_user_ns, dentry, attr);
        if (err)
                return err;

        err = dbg_check_synced_i_size(c, inode);
        if (err)
                return err;

        err = fscrypt_prepare_setattr(dentry, attr);
        if (err)
                return err;

        if ((attr->ia_valid & ATTR_SIZE) && attr->ia_size < inode->i_size)
                /* Truncation to a smaller size */
                err = do_truncation(c, inode, attr);
        else
                err = do_setattr(c, inode, attr);

        return err;
}

static void ubifs_invalidate_folio(struct folio *folio, size_t offset,
                                 size_t length)
{
        struct inode *inode = folio->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;

        ubifs_assert(c, folio_test_private(folio));
        if (offset || length < folio_size(folio))
                /* Partial folio remains dirty */
                return;

        if (folio_test_checked(folio))
                release_new_page_budget(c);
        else
                release_existing_page_budget(c);

        atomic_long_dec(&c->dirty_pg_cnt);
        folio_detach_private(folio);
        folio_clear_checked(folio);
}

int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct inode *inode = file->f_mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        int err;

        dbg_gen("syncing inode %lu", inode->i_ino);

        if (c->ro_mount)
                /*
                 * For some really strange reasons VFS does not filter out
                 * 'fsync()' for R/O mounted file-systems as per 2.6.39.
                 */
                return 0;

        err = file_write_and_wait_range(file, start, end);
        if (err)
                return err;
        inode_lock(inode);

        /* Synchronize the inode unless this is a 'datasync()' call. */
        if (!datasync || (inode->i_state & I_DIRTY_DATASYNC)) {
                err = inode->i_sb->s_op->write_inode(inode, NULL);
                if (err)
                        goto out;
        }

        /*
         * Nodes related to this inode may still sit in a write-buffer. Flush
         * them.
         */
        err = ubifs_sync_wbufs_by_inode(c, inode);
out:
        inode_unlock(inode);
        return err;
}

/**
 * mctime_update_needed - check if mtime or ctime update is needed.
 * @inode: the inode to do the check for
 * @now: current time
 *
 * This helper function checks if the inode mtime/ctime should be updated or
 * not. If current values of the time-stamps are within the UBIFS inode time
 * granularity, they are not updated. This is an optimization.
 */
static inline int mctime_update_needed(const struct inode *inode,
                                       const struct timespec64 *now)
{
        if (!timespec64_equal(&inode->i_mtime, now) ||
            !timespec64_equal(&inode->i_ctime, now))
                return 1;
        return 0;
}

/**
 * ubifs_update_time - update time of inode.
 * @inode: inode to update
 *
 * This function updates time of the inode.
 */
int ubifs_update_time(struct inode *inode, struct timespec64 *time,
                             int flags)
{
        struct ubifs_inode *ui = ubifs_inode(inode);
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        struct ubifs_budget_req req = { .dirtied_ino = 1,
                        .dirtied_ino_d = ALIGN(ui->data_len, 8) };
        int err, release;

        if (!IS_ENABLED(CONFIG_UBIFS_ATIME_SUPPORT))
                return generic_update_time(inode, time, flags);

        err = ubifs_budget_space(c, &req);
        if (err)
                return err;

        mutex_lock(&ui->ui_mutex);
        if (flags & S_ATIME)
                inode->i_atime = *time;
        if (flags & S_CTIME)
                inode->i_ctime = *time;
        if (flags & S_MTIME)
                inode->i_mtime = *time;

        release = ui->dirty;
        __mark_inode_dirty(inode, I_DIRTY_SYNC);
        mutex_unlock(&ui->ui_mutex);
        if (release)
                ubifs_release_budget(c, &req);
        return 0;
}

/**
 * update_mctime - update mtime and ctime of an inode.
 * @inode: inode to update
 *
 * This function updates mtime and ctime of the inode if it is not equivalent to
 * current time. Returns zero in case of success and a negative error code in
 * case of failure.
 */
static int update_mctime(struct inode *inode)
{
        struct timespec64 now = current_time(inode);
        struct ubifs_inode *ui = ubifs_inode(inode);
        struct ubifs_info *c = inode->i_sb->s_fs_info;

        if (mctime_update_needed(inode, &now)) {
                int err, release;
                struct ubifs_budget_req req = { .dirtied_ino = 1,
                                .dirtied_ino_d = ALIGN(ui->data_len, 8) };

                err = ubifs_budget_space(c, &req);
                if (err)
                        return err;

                mutex_lock(&ui->ui_mutex);
                inode->i_mtime = inode->i_ctime = current_time(inode);
                release = ui->dirty;
                mark_inode_dirty_sync(inode);
                mutex_unlock(&ui->ui_mutex);
                if (release)
                        ubifs_release_budget(c, &req);
        }

        return 0;
}

static ssize_t ubifs_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        int err = update_mctime(file_inode(iocb->ki_filp));
        if (err)
                return err;

        return generic_file_write_iter(iocb, from);
}

static bool ubifs_dirty_folio(struct address_space *mapping,
                struct folio *folio)
{
        bool ret;
        struct ubifs_info *c = mapping->host->i_sb->s_fs_info;

        ret = filemap_dirty_folio(mapping, folio);
        /*
         * An attempt to dirty a page without budgeting for it - should not
         * happen.
         */
        ubifs_assert(c, ret == false);
        return ret;
}

#ifdef CONFIG_MIGRATION
static int ubifs_migrate_page(struct address_space *mapping,
                struct page *newpage, struct page *page, enum migrate_mode mode)
{
        int rc;

        rc = migrate_page_move_mapping(mapping, newpage, page, 0);
        if (rc != MIGRATEPAGE_SUCCESS)
                return rc;

        if (PagePrivate(page)) {
                detach_page_private(page);
                attach_page_private(newpage, (void *)1);
        }

        if (mode != MIGRATE_SYNC_NO_COPY)
                migrate_page_copy(newpage, page);
        else
                migrate_page_states(newpage, page);
        return MIGRATEPAGE_SUCCESS;
}
#endif

static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags)
{
        struct inode *inode = page->mapping->host;
        struct ubifs_info *c = inode->i_sb->s_fs_info;

        /*
         * An attempt to release a dirty page without budgeting for it - should
         * not happen.
         */
        if (PageWriteback(page))
                return 0;
        ubifs_assert(c, PagePrivate(page));
        ubifs_assert(c, 0);
        detach_page_private(page);
        ClearPageChecked(page);
        return 1;
}

/*
 * mmap()d file has taken write protection fault and is being made writable.
 * UBIFS must ensure page is budgeted for.
 */
static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
{
        struct page *page = vmf->page;
        struct inode *inode = file_inode(vmf->vma->vm_file);
        struct ubifs_info *c = inode->i_sb->s_fs_info;
        struct timespec64 now = current_time(inode);
        struct ubifs_budget_req req = { .new_page = 1 };
        int err, update_time;

        dbg_gen("ino %lu, pg %lu, i_size %lld", inode->i_ino, page->index,
                i_size_read(inode));
        ubifs_assert(c, !c->ro_media && !c->ro_mount);

        if (unlikely(c->ro_error))
                return VM_FAULT_SIGBUS; /* -EROFS */

        /*
         * We have not locked @page so far so we may budget for changing the
         * page. Note, we cannot do this after we locked the page, because
         * budgeting may cause write-back which would cause deadlock.
         *
         * At the moment we do not know whether the page is dirty or not, so we
         * assume that it is not and budget for a new page. We could look at
         * the @PG_private flag and figure this out, but we may race with write
         * back and the page state may change by the time we lock it, so this
         * would need additional care. We do not bother with this at the
         * moment, although it might be good idea to do. Instead, we allocate
         * budget for a new page and amend it later on if the page was in fact
         * dirty.
         *
         * The budgeting-related logic of this function is similar to what we
         * do in 'ubifs_write_begin()' and 'ubifs_write_end()'. Glance there
         * for more comments.
         */
        update_time = mctime_update_needed(inode, &now);
        if (update_time)
                /*
                 * We have to change inode time stamp which requires extra
                 * budgeting.
                 */
                req.dirtied_ino = 1;

        err = ubifs_budget_space(c, &req);
        if (unlikely(err)) {
                if (err == -ENOSPC)
                        ubifs_warn(c, "out of space for mmapped file (inode number %lu)",
                                   inode->i_ino);
                return VM_FAULT_SIGBUS;
        }

        lock_page(page);
        if (unlikely(page->mapping != inode->i_mapping ||
                     page_offset(page) > i_size_read(inode))) {
                /* Page got truncated out from underneath us */
                goto sigbus;
        }

        if (PagePrivate(page))
                release_new_page_budget(c);
        else {
                if (!PageChecked(page))
                        ubifs_convert_page_budget(c);
                attach_page_private(page, (void *)1);
                atomic_long_inc(&c->dirty_pg_cnt);
                __set_page_dirty_nobuffers(page);
        }

        if (update_time) {
                int release;
                struct ubifs_inode *ui = ubifs_inode(inode);

                mutex_lock(&ui->ui_mutex);
                inode->i_mtime = inode->i_ctime = current_time(inode);
                release = ui->dirty;
                mark_inode_dirty_sync(inode);
                mutex_unlock(&ui->ui_mutex);
                if (release)
                        ubifs_release_dirty_inode_budget(c, ui);
        }

        wait_for_stable_page(page);
        return VM_FAULT_LOCKED;

sigbus:
        unlock_page(page);
        ubifs_release_budget(c, &req);
        return VM_FAULT_SIGBUS;
}

static const struct vm_operations_struct ubifs_file_vm_ops = {
        .fault        = filemap_fault,
        .map_pages = filemap_map_pages,
        .page_mkwrite = ubifs_vm_page_mkwrite,
};

static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
        int err;

        err = generic_file_mmap(file, vma);
        if (err)
                return err;
        vma->vm_ops = &ubifs_file_vm_ops;

        if (IS_ENABLED(CONFIG_UBIFS_ATIME_SUPPORT))
                file_accessed(file);

        return 0;
}

static const char *ubifs_get_link(struct dentry *dentry,
                                            struct inode *inode,
                                            struct delayed_call *done)
{
        struct ubifs_inode *ui = ubifs_inode(inode);

        if (!IS_ENCRYPTED(inode))
                return ui->data;

        if (!dentry)
                return ERR_PTR(-ECHILD);

        return fscrypt_get_symlink(inode, ui->data, ui->data_len, done);
}

static int ubifs_symlink_getattr(struct user_namespace *mnt_userns,
                                 const struct path *path, struct kstat *stat,
                                 u32 request_mask, unsigned int query_flags)
{
        ubifs_getattr(mnt_userns, path, stat, request_mask, query_flags);

        if (IS_ENCRYPTED(d_inode(path->dentry)))
                return fscrypt_symlink_getattr(path, stat);
        return 0;
}

const struct address_space_operations ubifs_file_address_operations = {
        .readpage       = ubifs_readpage,
        .writepage      = ubifs_writepage,
        .write_begin    = ubifs_write_begin,
        .write_end      = ubifs_write_end,
        .invalidate_folio = ubifs_invalidate_folio,
        .dirty_folio    = ubifs_dirty_folio,
#ifdef CONFIG_MIGRATION
        .migratepage    = ubifs_migrate_page,
#endif
        .releasepage    = ubifs_releasepage,
};

const struct inode_operations ubifs_file_inode_operations = {
        .setattr     = ubifs_setattr,
        .getattr     = ubifs_getattr,
        .listxattr   = ubifs_listxattr,
        .update_time = ubifs_update_time,
        .fileattr_get = ubifs_fileattr_get,
        .fileattr_set = ubifs_fileattr_set,
};

const struct inode_operations ubifs_symlink_inode_operations = {
        .get_link    = ubifs_get_link,
        .setattr     = ubifs_setattr,
        .getattr     = ubifs_symlink_getattr,
        .listxattr   = ubifs_listxattr,
        .update_time = ubifs_update_time,
};

const struct file_operations ubifs_file_operations = {
        .llseek         = generic_file_llseek,
        .read_iter      = generic_file_read_iter,
        .write_iter     = ubifs_write_iter,
        .mmap           = ubifs_file_mmap,
        .fsync          = ubifs_fsync,
        .unlocked_ioctl = ubifs_ioctl,
        .splice_read    = generic_file_splice_read,
        .splice_write   = iter_file_splice_write,
        .open           = fscrypt_file_open,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = ubifs_compat_ioctl,
#endif
};