Linux 4.19.133

[linux/fpc-iii.git] / fs / iomap.c

/*
 * Copyright (C) 2010 Red Hat, Inc.
 * Copyright (c) 2016-2018 Christoph Hellwig.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */
#include <linux/module.h>
#include <linux/compiler.h>
#include <linux/fs.h>
#include <linux/iomap.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>
#include <linux/migrate.h>
#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/file.h>
#include <linux/uio.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/dax.h>
#include <linux/sched/signal.h>
#include <linux/swap.h>

#include "internal.h"

/*
 * Execute a iomap write on a segment of the mapping that spans a
 * contiguous range of pages that have identical block mapping state.
 *
 * This avoids the need to map pages individually, do individual allocations
 * for each page and most importantly avoid the need for filesystem specific
 * locking per page. Instead, all the operations are amortised over the entire
 * range of pages. It is assumed that the filesystems will lock whatever
 * resources they require in the iomap_begin call, and release them in the
 * iomap_end call.
 */
loff_t
iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
                const struct iomap_ops *ops, void *data, iomap_actor_t actor)
{
        struct iomap iomap = { 0 };
        loff_t written = 0, ret;

        /*
         * Need to map a range from start position for length bytes. This can
         * span multiple pages - it is only guaranteed to return a range of a
         * single type of pages (e.g. all into a hole, all mapped or all
         * unwritten). Failure at this point has nothing to undo.
         *
         * If allocation is required for this range, reserve the space now so
         * that the allocation is guaranteed to succeed later on. Once we copy
         * the data into the page cache pages, then we cannot fail otherwise we
         * expose transient stale data. If the reserve fails, we can safely
         * back out at this point as there is nothing to undo.
         */
        ret = ops->iomap_begin(inode, pos, length, flags, &iomap);
        if (ret)
                return ret;
        if (WARN_ON(iomap.offset > pos))
                return -EIO;
        if (WARN_ON(iomap.length == 0))
                return -EIO;

        /*
         * Cut down the length to the one actually provided by the filesystem,
         * as it might not be able to give us the whole size that we requested.
         */
        if (iomap.offset + iomap.length < pos + length)
                length = iomap.offset + iomap.length - pos;

        /*
         * Now that we have guaranteed that the space allocation will succeed.
         * we can do the copy-in page by page without having to worry about
         * failures exposing transient data.
         */
        written = actor(inode, pos, length, data, &iomap);

        /*
         * Now the data has been copied, commit the range we've copied.  This
         * should not fail unless the filesystem has had a fatal error.
         */
        if (ops->iomap_end) {
                ret = ops->iomap_end(inode, pos, length,
                                     written > 0 ? written : 0,
                                     flags, &iomap);
        }

        return written ? written : ret;
}

static sector_t
iomap_sector(struct iomap *iomap, loff_t pos)
{
        return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
}

static struct iomap_page *
iomap_page_create(struct inode *inode, struct page *page)
{
        struct iomap_page *iop = to_iomap_page(page);

        if (iop || i_blocksize(inode) == PAGE_SIZE)
                return iop;

        iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);
        atomic_set(&iop->read_count, 0);
        atomic_set(&iop->write_count, 0);
        bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);

        /*
         * migrate_page_move_mapping() assumes that pages with private data have
         * their count elevated by 1.
         */
        get_page(page);
        set_page_private(page, (unsigned long)iop);
        SetPagePrivate(page);
        return iop;
}

static void
iomap_page_release(struct page *page)
{
        struct iomap_page *iop = to_iomap_page(page);

        if (!iop)
                return;
        WARN_ON_ONCE(atomic_read(&iop->read_count));
        WARN_ON_ONCE(atomic_read(&iop->write_count));
        ClearPagePrivate(page);
        set_page_private(page, 0);
        put_page(page);
        kfree(iop);
}

/*
 * Calculate the range inside the page that we actually need to read.
 */
static void
iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
                loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)
{
        loff_t orig_pos = *pos;
        loff_t isize = i_size_read(inode);
        unsigned block_bits = inode->i_blkbits;
        unsigned block_size = (1 << block_bits);
        unsigned poff = offset_in_page(*pos);
        unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
        unsigned first = poff >> block_bits;
        unsigned last = (poff + plen - 1) >> block_bits;

        /*
         * If the block size is smaller than the page size we need to check the
         * per-block uptodate status and adjust the offset and length if needed
         * to avoid reading in already uptodate ranges.
         */
        if (iop) {
                unsigned int i;

                /* move forward for each leading block marked uptodate */
                for (i = first; i <= last; i++) {
                        if (!test_bit(i, iop->uptodate))
                                break;
                        *pos += block_size;
                        poff += block_size;
                        plen -= block_size;
                        first++;
                }

                /* truncate len if we find any trailing uptodate block(s) */
                for ( ; i <= last; i++) {
                        if (test_bit(i, iop->uptodate)) {
                                plen -= (last - i + 1) * block_size;
                                last = i - 1;
                                break;
                        }
                }
        }

        /*
         * If the extent spans the block that contains the i_size we need to
         * handle both halves separately so that we properly zero data in the
         * page cache for blocks that are entirely outside of i_size.
         */
        if (orig_pos <= isize && orig_pos + length > isize) {
                unsigned end = offset_in_page(isize - 1) >> block_bits;

                if (first <= end && last > end)
                        plen -= (last - end) * block_size;
        }

        *offp = poff;
        *lenp = plen;
}

static void
iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
{
        struct iomap_page *iop = to_iomap_page(page);
        struct inode *inode = page->mapping->host;
        unsigned first = off >> inode->i_blkbits;
        unsigned last = (off + len - 1) >> inode->i_blkbits;
        unsigned int i;
        bool uptodate = true;

        if (iop) {
                for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
                        if (i >= first && i <= last)
                                set_bit(i, iop->uptodate);
                        else if (!test_bit(i, iop->uptodate))
                                uptodate = false;
                }
        }

        if (uptodate && !PageError(page))
                SetPageUptodate(page);
}

static void
iomap_read_finish(struct iomap_page *iop, struct page *page)
{
        if (!iop || atomic_dec_and_test(&iop->read_count))
                unlock_page(page);
}

static void
iomap_read_page_end_io(struct bio_vec *bvec, int error)
{
        struct page *page = bvec->bv_page;
        struct iomap_page *iop = to_iomap_page(page);

        if (unlikely(error)) {
                ClearPageUptodate(page);
                SetPageError(page);
        } else {
                iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
        }

        iomap_read_finish(iop, page);
}

static void
iomap_read_inline_data(struct inode *inode, struct page *page,
                struct iomap *iomap)
{
        size_t size = i_size_read(inode);
        void *addr;

        if (PageUptodate(page))
                return;

        BUG_ON(page->index);
        BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));

        addr = kmap_atomic(page);
        memcpy(addr, iomap->inline_data, size);
        memset(addr + size, 0, PAGE_SIZE - size);
        kunmap_atomic(addr);
        SetPageUptodate(page);
}

static void
iomap_read_end_io(struct bio *bio)
{
        int error = blk_status_to_errno(bio->bi_status);
        struct bio_vec *bvec;
        int i;

        bio_for_each_segment_all(bvec, bio, i)
                iomap_read_page_end_io(bvec, error);
        bio_put(bio);
}

struct iomap_readpage_ctx {
        struct page             *cur_page;
        bool                    cur_page_in_bio;
        bool                    is_readahead;
        struct bio              *bio;
        struct list_head        *pages;
};

static loff_t
iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
                struct iomap *iomap)
{
        struct iomap_readpage_ctx *ctx = data;
        struct page *page = ctx->cur_page;
        struct iomap_page *iop = iomap_page_create(inode, page);
        bool is_contig = false;
        loff_t orig_pos = pos;
        unsigned poff, plen;
        sector_t sector;

        if (iomap->type == IOMAP_INLINE) {
                WARN_ON_ONCE(pos);
                iomap_read_inline_data(inode, page, iomap);
                return PAGE_SIZE;
        }

        /* zero post-eof blocks as the page may be mapped */
        iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
        if (plen == 0)
                goto done;

        if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) {
                zero_user(page, poff, plen);
                iomap_set_range_uptodate(page, poff, plen);
                goto done;
        }

        ctx->cur_page_in_bio = true;

        /*
         * Try to merge into a previous segment if we can.
         */
        sector = iomap_sector(iomap, pos);
        if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
                if (__bio_try_merge_page(ctx->bio, page, plen, poff))
                        goto done;
                is_contig = true;
        }

        /*
         * If we start a new segment we need to increase the read count, and we
         * need to do so before submitting any previous full bio to make sure
         * that we don't prematurely unlock the page.
         */
        if (iop)
                atomic_inc(&iop->read_count);

        if (!ctx->bio || !is_contig || bio_full(ctx->bio)) {
                gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
                int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;

                if (ctx->bio)
                        submit_bio(ctx->bio);

                if (ctx->is_readahead) /* same as readahead_gfp_mask */
                        gfp |= __GFP_NORETRY | __GFP_NOWARN;
                ctx->bio = bio_alloc(gfp, min(BIO_MAX_PAGES, nr_vecs));
                ctx->bio->bi_opf = REQ_OP_READ;
                if (ctx->is_readahead)
                        ctx->bio->bi_opf |= REQ_RAHEAD;
                ctx->bio->bi_iter.bi_sector = sector;
                bio_set_dev(ctx->bio, iomap->bdev);
                ctx->bio->bi_end_io = iomap_read_end_io;
        }

        __bio_add_page(ctx->bio, page, plen, poff);
done:
        /*
         * Move the caller beyond our range so that it keeps making progress.
         * For that we have to include any leading non-uptodate ranges, but
         * we can skip trailing ones as they will be handled in the next
         * iteration.
         */
        return pos - orig_pos + plen;
}

int
iomap_readpage(struct page *page, const struct iomap_ops *ops)
{
        struct iomap_readpage_ctx ctx = { .cur_page = page };
        struct inode *inode = page->mapping->host;
        unsigned poff;
        loff_t ret;

        for (poff = 0; poff < PAGE_SIZE; poff += ret) {
                ret = iomap_apply(inode, page_offset(page) + poff,
                                PAGE_SIZE - poff, 0, ops, &ctx,
                                iomap_readpage_actor);
                if (ret <= 0) {
                        WARN_ON_ONCE(ret == 0);
                        SetPageError(page);
                        break;
                }
        }

        if (ctx.bio) {
                submit_bio(ctx.bio);
                WARN_ON_ONCE(!ctx.cur_page_in_bio);
        } else {
                WARN_ON_ONCE(ctx.cur_page_in_bio);
                unlock_page(page);
        }

        /*
         * Just like mpage_readpages and block_read_full_page we always
         * return 0 and just mark the page as PageError on errors.  This
         * should be cleaned up all through the stack eventually.
         */
        return 0;
}
EXPORT_SYMBOL_GPL(iomap_readpage);

static struct page *
iomap_next_page(struct inode *inode, struct list_head *pages, loff_t pos,
                loff_t length, loff_t *done)
{
        while (!list_empty(pages)) {
                struct page *page = lru_to_page(pages);

                if (page_offset(page) >= (u64)pos + length)
                        break;

                list_del(&page->lru);
                if (!add_to_page_cache_lru(page, inode->i_mapping, page->index,
                                GFP_NOFS))
                        return page;

                /*
                 * If we already have a page in the page cache at index we are
                 * done.  Upper layers don't care if it is uptodate after the
                 * readpages call itself as every page gets checked again once
                 * actually needed.
                 */
                *done += PAGE_SIZE;
                put_page(page);
        }

        return NULL;
}

static loff_t
iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
                void *data, struct iomap *iomap)
{
        struct iomap_readpage_ctx *ctx = data;
        loff_t done, ret;

        for (done = 0; done < length; done += ret) {
                if (ctx->cur_page && offset_in_page(pos + done) == 0) {
                        if (!ctx->cur_page_in_bio)
                                unlock_page(ctx->cur_page);
                        put_page(ctx->cur_page);
                        ctx->cur_page = NULL;
                }
                if (!ctx->cur_page) {
                        ctx->cur_page = iomap_next_page(inode, ctx->pages,
                                        pos, length, &done);
                        if (!ctx->cur_page)
                                break;
                        ctx->cur_page_in_bio = false;
                }
                ret = iomap_readpage_actor(inode, pos + done, length - done,
                                ctx, iomap);
        }

        return done;
}

int
iomap_readpages(struct address_space *mapping, struct list_head *pages,
                unsigned nr_pages, const struct iomap_ops *ops)
{
        struct iomap_readpage_ctx ctx = {
                .pages          = pages,
                .is_readahead   = true,
        };
        loff_t pos = page_offset(list_entry(pages->prev, struct page, lru));
        loff_t last = page_offset(list_entry(pages->next, struct page, lru));
        loff_t length = last - pos + PAGE_SIZE, ret = 0;

        while (length > 0) {
                ret = iomap_apply(mapping->host, pos, length, 0, ops,
                                &ctx, iomap_readpages_actor);
                if (ret <= 0) {
                        WARN_ON_ONCE(ret == 0);
                        goto done;
                }
                pos += ret;
                length -= ret;
        }
        ret = 0;
done:
        if (ctx.bio)
                submit_bio(ctx.bio);
        if (ctx.cur_page) {
                if (!ctx.cur_page_in_bio)
                        unlock_page(ctx.cur_page);
                put_page(ctx.cur_page);
        }

        /*
         * Check that we didn't lose a page due to the arcance calling
         * conventions..
         */
        WARN_ON_ONCE(!ret && !list_empty(ctx.pages));
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_readpages);

/*
 * iomap_is_partially_uptodate checks whether blocks within a page are
 * uptodate or not.
 *
 * Returns true if all blocks which correspond to a file portion
 * we want to read within the page are uptodate.
 */
int
iomap_is_partially_uptodate(struct page *page, unsigned long from,
                unsigned long count)
{
        struct iomap_page *iop = to_iomap_page(page);
        struct inode *inode = page->mapping->host;
        unsigned len, first, last;
        unsigned i;

        /* Limit range to one page */
        len = min_t(unsigned, PAGE_SIZE - from, count);

        /* First and last blocks in range within page */
        first = from >> inode->i_blkbits;
        last = (from + len - 1) >> inode->i_blkbits;

        if (iop) {
                for (i = first; i <= last; i++)
                        if (!test_bit(i, iop->uptodate))
                                return 0;
                return 1;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);

int
iomap_releasepage(struct page *page, gfp_t gfp_mask)
{
        /*
         * mm accommodates an old ext3 case where clean pages might not have had
         * the dirty bit cleared. Thus, it can send actual dirty pages to
         * ->releasepage() via shrink_active_list(), skip those here.
         */
        if (PageDirty(page) || PageWriteback(page))
                return 0;
        iomap_page_release(page);
        return 1;
}
EXPORT_SYMBOL_GPL(iomap_releasepage);

void
iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)
{
        /*
         * If we are invalidating the entire page, clear the dirty state from it
         * and release it to avoid unnecessary buildup of the LRU.
         */
        if (offset == 0 && len == PAGE_SIZE) {
                WARN_ON_ONCE(PageWriteback(page));
                cancel_dirty_page(page);
                iomap_page_release(page);
        }
}
EXPORT_SYMBOL_GPL(iomap_invalidatepage);

#ifdef CONFIG_MIGRATION
int
iomap_migrate_page(struct address_space *mapping, struct page *newpage,
                struct page *page, enum migrate_mode mode)
{
        int ret;

        ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
        if (ret != MIGRATEPAGE_SUCCESS)
                return ret;

        if (page_has_private(page)) {
                ClearPagePrivate(page);
                get_page(newpage);
                set_page_private(newpage, page_private(page));
                set_page_private(page, 0);
                put_page(page);
                SetPagePrivate(newpage);
        }

        if (mode != MIGRATE_SYNC_NO_COPY)
                migrate_page_copy(newpage, page);
        else
                migrate_page_states(newpage, page);
        return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL_GPL(iomap_migrate_page);
#endif /* CONFIG_MIGRATION */

static void
iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
{
        loff_t i_size = i_size_read(inode);

        /*
         * Only truncate newly allocated pages beyoned EOF, even if the
         * write started inside the existing inode size.
         */
        if (pos + len > i_size)
                truncate_pagecache_range(inode, max(pos, i_size), pos + len);
}

static int
iomap_read_page_sync(struct inode *inode, loff_t block_start, struct page *page,
                unsigned poff, unsigned plen, unsigned from, unsigned to,
                struct iomap *iomap)
{
        struct bio_vec bvec;
        struct bio bio;

        if (iomap->type != IOMAP_MAPPED || block_start >= i_size_read(inode)) {
                zero_user_segments(page, poff, from, to, poff + plen);
                iomap_set_range_uptodate(page, poff, plen);
                return 0;
        }

        bio_init(&bio, &bvec, 1);
        bio.bi_opf = REQ_OP_READ;
        bio.bi_iter.bi_sector = iomap_sector(iomap, block_start);
        bio_set_dev(&bio, iomap->bdev);
        __bio_add_page(&bio, page, plen, poff);
        return submit_bio_wait(&bio);
}

static int
__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,
                struct page *page, struct iomap *iomap)
{
        struct iomap_page *iop = iomap_page_create(inode, page);
        loff_t block_size = i_blocksize(inode);
        loff_t block_start = pos & ~(block_size - 1);
        loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1);
        unsigned from = offset_in_page(pos), to = from + len, poff, plen;
        int status = 0;

        if (PageUptodate(page))
                return 0;

        do {
                iomap_adjust_read_range(inode, iop, &block_start,
                                block_end - block_start, &poff, &plen);
                if (plen == 0)
                        break;

                if ((from > poff && from < poff + plen) ||
                    (to > poff && to < poff + plen)) {
                        status = iomap_read_page_sync(inode, block_start, page,
                                        poff, plen, from, to, iomap);
                        if (status)
                                break;
                }

        } while ((block_start += plen) < block_end);

        return status;
}

static int
iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
                struct page **pagep, struct iomap *iomap)
{
        pgoff_t index = pos >> PAGE_SHIFT;
        struct page *page;
        int status = 0;

        BUG_ON(pos + len > iomap->offset + iomap->length);

        if (fatal_signal_pending(current))
                return -EINTR;

        page = grab_cache_page_write_begin(inode->i_mapping, index, flags);
        if (!page)
                return -ENOMEM;

        if (iomap->type == IOMAP_INLINE)
                iomap_read_inline_data(inode, page, iomap);
        else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
                status = __block_write_begin_int(page, pos, len, NULL, iomap);
        else
                status = __iomap_write_begin(inode, pos, len, page, iomap);
        if (unlikely(status)) {
                unlock_page(page);
                put_page(page);
                page = NULL;

                iomap_write_failed(inode, pos, len);
        }

        *pagep = page;
        return status;
}

int
iomap_set_page_dirty(struct page *page)
{
        struct address_space *mapping = page_mapping(page);
        int newly_dirty;

        if (unlikely(!mapping))
                return !TestSetPageDirty(page);

        /*
         * Lock out page->mem_cgroup migration to keep PageDirty
         * synchronized with per-memcg dirty page counters.
         */
        lock_page_memcg(page);
        newly_dirty = !TestSetPageDirty(page);
        if (newly_dirty)
                __set_page_dirty(page, mapping, 0);
        unlock_page_memcg(page);

        if (newly_dirty)
                __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
        return newly_dirty;
}
EXPORT_SYMBOL_GPL(iomap_set_page_dirty);

static int
__iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
                unsigned copied, struct page *page, struct iomap *iomap)
{
        flush_dcache_page(page);

        /*
         * The blocks that were entirely written will now be uptodate, so we
         * don't have to worry about a readpage reading them and overwriting a
         * partial write.  However if we have encountered a short write and only
         * partially written into a block, it will not be marked uptodate, so a
         * readpage might come in and destroy our partial write.
         *
         * Do the simplest thing, and just treat any short write to a non
         * uptodate page as a zero-length write, and force the caller to redo
         * the whole thing.
         */
        if (unlikely(copied < len && !PageUptodate(page))) {
                copied = 0;
        } else {
                iomap_set_range_uptodate(page, offset_in_page(pos), len);
                iomap_set_page_dirty(page);
        }
        return __generic_write_end(inode, pos, copied, page);
}

static int
iomap_write_end_inline(struct inode *inode, struct page *page,
                struct iomap *iomap, loff_t pos, unsigned copied)
{
        void *addr;

        WARN_ON_ONCE(!PageUptodate(page));
        BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));

        addr = kmap_atomic(page);
        memcpy(iomap->inline_data + pos, addr + pos, copied);
        kunmap_atomic(addr);

        mark_inode_dirty(inode);
        __generic_write_end(inode, pos, copied, page);
        return copied;
}

static int
iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
                unsigned copied, struct page *page, struct iomap *iomap)
{
        int ret;

        if (iomap->type == IOMAP_INLINE) {
                ret = iomap_write_end_inline(inode, page, iomap, pos, copied);
        } else if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
                ret = generic_write_end(NULL, inode->i_mapping, pos, len,
                                copied, page, NULL);
        } else {
                ret = __iomap_write_end(inode, pos, len, copied, page, iomap);
        }

        if (iomap->page_done)
                iomap->page_done(inode, pos, copied, page, iomap);

        if (ret < len)
                iomap_write_failed(inode, pos, len);
        return ret;
}

static loff_t
iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
                struct iomap *iomap)
{
        struct iov_iter *i = data;
        long status = 0;
        ssize_t written = 0;
        unsigned int flags = AOP_FLAG_NOFS;

        do {
                struct page *page;
                unsigned long offset;   /* Offset into pagecache page */
                unsigned long bytes;    /* Bytes to write to page */
                size_t copied;          /* Bytes copied from user */

                offset = offset_in_page(pos);
                bytes = min_t(unsigned long, PAGE_SIZE - offset,
                                                iov_iter_count(i));
again:
                if (bytes > length)
                        bytes = length;

                /*
                 * Bring in the user page that we will copy from _first_.
                 * Otherwise there's a nasty deadlock on copying from the
                 * same page as we're writing to, without it being marked
                 * up-to-date.
                 *
                 * Not only is this an optimisation, but it is also required
                 * to check that the address is actually valid, when atomic
                 * usercopies are used, below.
                 */
                if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
                        status = -EFAULT;
                        break;
                }

                status = iomap_write_begin(inode, pos, bytes, flags, &page,
                                iomap);
                if (unlikely(status))
                        break;

                if (mapping_writably_mapped(inode->i_mapping))
                        flush_dcache_page(page);

                copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);

                flush_dcache_page(page);

                status = iomap_write_end(inode, pos, bytes, copied, page,
                                iomap);
                if (unlikely(status < 0))
                        break;
                copied = status;

                cond_resched();

                iov_iter_advance(i, copied);
                if (unlikely(copied == 0)) {
                        /*
                         * If we were unable to copy any data at all, we must
                         * fall back to a single segment length write.
                         *
                         * If we didn't fallback here, we could livelock
                         * because not all segments in the iov can be copied at
                         * once without a pagefault.
                         */
                        bytes = min_t(unsigned long, PAGE_SIZE - offset,
                                                iov_iter_single_seg_count(i));
                        goto again;
                }
                pos += copied;
                written += copied;
                length -= copied;

                balance_dirty_pages_ratelimited(inode->i_mapping);
        } while (iov_iter_count(i) && length);

        return written ? written : status;
}

ssize_t
iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
                const struct iomap_ops *ops)
{
        struct inode *inode = iocb->ki_filp->f_mapping->host;
        loff_t pos = iocb->ki_pos, ret = 0, written = 0;

        while (iov_iter_count(iter)) {
                ret = iomap_apply(inode, pos, iov_iter_count(iter),
                                IOMAP_WRITE, ops, iter, iomap_write_actor);
                if (ret <= 0)
                        break;
                pos += ret;
                written += ret;
        }

        return written ? written : ret;
}
EXPORT_SYMBOL_GPL(iomap_file_buffered_write);

static struct page *
__iomap_read_page(struct inode *inode, loff_t offset)
{
        struct address_space *mapping = inode->i_mapping;
        struct page *page;

        page = read_mapping_page(mapping, offset >> PAGE_SHIFT, NULL);
        if (IS_ERR(page))
                return page;
        if (!PageUptodate(page)) {
                put_page(page);
                return ERR_PTR(-EIO);
        }
        return page;
}

static loff_t
iomap_dirty_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
                struct iomap *iomap)
{
        long status = 0;
        ssize_t written = 0;

        do {
                struct page *page, *rpage;
                unsigned long offset;   /* Offset into pagecache page */
                unsigned long bytes;    /* Bytes to write to page */

                offset = offset_in_page(pos);
                bytes = min_t(loff_t, PAGE_SIZE - offset, length);

                rpage = __iomap_read_page(inode, pos);
                if (IS_ERR(rpage))
                        return PTR_ERR(rpage);

                status = iomap_write_begin(inode, pos, bytes,
                                           AOP_FLAG_NOFS, &page, iomap);
                put_page(rpage);
                if (unlikely(status))
                        return status;

                WARN_ON_ONCE(!PageUptodate(page));

                status = iomap_write_end(inode, pos, bytes, bytes, page, iomap);
                if (unlikely(status <= 0)) {
                        if (WARN_ON_ONCE(status == 0))
                                return -EIO;
                        return status;
                }

                cond_resched();

                pos += status;
                written += status;
                length -= status;

                balance_dirty_pages_ratelimited(inode->i_mapping);
        } while (length);

        return written;
}

int
iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
                const struct iomap_ops *ops)
{
        loff_t ret;

        while (len) {
                ret = iomap_apply(inode, pos, len, IOMAP_WRITE, ops, NULL,
                                iomap_dirty_actor);
                if (ret <= 0)
                        return ret;
                pos += ret;
                len -= ret;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(iomap_file_dirty);

static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
                unsigned bytes, struct iomap *iomap)
{
        struct page *page;
        int status;

        status = iomap_write_begin(inode, pos, bytes, AOP_FLAG_NOFS, &page,
                                   iomap);
        if (status)
                return status;

        zero_user(page, offset, bytes);
        mark_page_accessed(page);

        return iomap_write_end(inode, pos, bytes, bytes, page, iomap);
}

static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
                struct iomap *iomap)
{
        return __dax_zero_page_range(iomap->bdev, iomap->dax_dev,
                        iomap_sector(iomap, pos & PAGE_MASK), offset, bytes);
}

static loff_t
iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count,
                void *data, struct iomap *iomap)
{
        bool *did_zero = data;
        loff_t written = 0;
        int status;

        /* already zeroed?  we're done. */
        if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
                return count;

        do {
                unsigned offset, bytes;

                offset = offset_in_page(pos);
                bytes = min_t(loff_t, PAGE_SIZE - offset, count);

                if (IS_DAX(inode))
                        status = iomap_dax_zero(pos, offset, bytes, iomap);
                else
                        status = iomap_zero(inode, pos, offset, bytes, iomap);
                if (status < 0)
                        return status;

                pos += bytes;
                count -= bytes;
                written += bytes;
                if (did_zero)
                        *did_zero = true;
        } while (count > 0);

        return written;
}

int
iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
                const struct iomap_ops *ops)
{
        loff_t ret;

        while (len > 0) {
                ret = iomap_apply(inode, pos, len, IOMAP_ZERO,
                                ops, did_zero, iomap_zero_range_actor);
                if (ret <= 0)
                        return ret;

                pos += ret;
                len -= ret;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(iomap_zero_range);

int
iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
                const struct iomap_ops *ops)
{
        unsigned int blocksize = i_blocksize(inode);
        unsigned int off = pos & (blocksize - 1);

        /* Block boundary? Nothing to do */
        if (!off)
                return 0;
        return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops);
}
EXPORT_SYMBOL_GPL(iomap_truncate_page);

static loff_t
iomap_page_mkwrite_actor(struct inode *inode, loff_t pos, loff_t length,
                void *data, struct iomap *iomap)
{
        struct page *page = data;
        int ret;

        if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
                ret = __block_write_begin_int(page, pos, length, NULL, iomap);
                if (ret)
                        return ret;
                block_commit_write(page, 0, length);
        } else {
                WARN_ON_ONCE(!PageUptodate(page));
                iomap_page_create(inode, page);
                set_page_dirty(page);
        }

        return length;
}

int iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
{
        struct page *page = vmf->page;
        struct inode *inode = file_inode(vmf->vma->vm_file);
        unsigned long length;
        loff_t offset, size;
        ssize_t ret;

        lock_page(page);
        size = i_size_read(inode);
        if ((page->mapping != inode->i_mapping) ||
            (page_offset(page) > size)) {
                /* We overload EFAULT to mean page got truncated */
                ret = -EFAULT;
                goto out_unlock;
        }

        /* page is wholly or partially inside EOF */
        if (((page->index + 1) << PAGE_SHIFT) > size)
                length = offset_in_page(size);
        else
                length = PAGE_SIZE;

        offset = page_offset(page);
        while (length > 0) {
                ret = iomap_apply(inode, offset, length,
                                IOMAP_WRITE | IOMAP_FAULT, ops, page,
                                iomap_page_mkwrite_actor);
                if (unlikely(ret <= 0))
                        goto out_unlock;
                offset += ret;
                length -= ret;
        }

        wait_for_stable_page(page);
        return VM_FAULT_LOCKED;
out_unlock:
        unlock_page(page);
        return block_page_mkwrite_return(ret);
}
EXPORT_SYMBOL_GPL(iomap_page_mkwrite);

struct fiemap_ctx {
        struct fiemap_extent_info *fi;
        struct iomap prev;
};

static int iomap_to_fiemap(struct fiemap_extent_info *fi,
                struct iomap *iomap, u32 flags)
{
        switch (iomap->type) {
        case IOMAP_HOLE:
                /* skip holes */
                return 0;
        case IOMAP_DELALLOC:
                flags |= FIEMAP_EXTENT_DELALLOC | FIEMAP_EXTENT_UNKNOWN;
                break;
        case IOMAP_MAPPED:
                break;
        case IOMAP_UNWRITTEN:
                flags |= FIEMAP_EXTENT_UNWRITTEN;
                break;
        case IOMAP_INLINE:
                flags |= FIEMAP_EXTENT_DATA_INLINE;
                break;
        }

        if (iomap->flags & IOMAP_F_MERGED)
                flags |= FIEMAP_EXTENT_MERGED;
        if (iomap->flags & IOMAP_F_SHARED)
                flags |= FIEMAP_EXTENT_SHARED;

        return fiemap_fill_next_extent(fi, iomap->offset,
                        iomap->addr != IOMAP_NULL_ADDR ? iomap->addr : 0,
                        iomap->length, flags);
}

static loff_t
iomap_fiemap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
                struct iomap *iomap)
{
        struct fiemap_ctx *ctx = data;
        loff_t ret = length;

        if (iomap->type == IOMAP_HOLE)
                return length;

        ret = iomap_to_fiemap(ctx->fi, &ctx->prev, 0);
        ctx->prev = *iomap;
        switch (ret) {
        case 0:         /* success */
                return length;
        case 1:         /* extent array full */
                return 0;
        default:
                return ret;
        }
}

int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
                loff_t start, loff_t len, const struct iomap_ops *ops)
{
        struct fiemap_ctx ctx;
        loff_t ret;

        memset(&ctx, 0, sizeof(ctx));
        ctx.fi = fi;
        ctx.prev.type = IOMAP_HOLE;

        ret = fiemap_check_flags(fi, FIEMAP_FLAG_SYNC);
        if (ret)
                return ret;

        if (fi->fi_flags & FIEMAP_FLAG_SYNC) {
                ret = filemap_write_and_wait(inode->i_mapping);
                if (ret)
                        return ret;
        }

        while (len > 0) {
                ret = iomap_apply(inode, start, len, IOMAP_REPORT, ops, &ctx,
                                iomap_fiemap_actor);
                /* inode with no (attribute) mapping will give ENOENT */
                if (ret == -ENOENT)
                        break;
                if (ret < 0)
                        return ret;
                if (ret == 0)
                        break;

                start += ret;
                len -= ret;
        }

        if (ctx.prev.type != IOMAP_HOLE) {
                ret = iomap_to_fiemap(fi, &ctx.prev, FIEMAP_EXTENT_LAST);
                if (ret < 0)
                        return ret;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(iomap_fiemap);

/*
 * Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.
 * Returns true if found and updates @lastoff to the offset in file.
 */
static bool
page_seek_hole_data(struct inode *inode, struct page *page, loff_t *lastoff,
                int whence)
{
        const struct address_space_operations *ops = inode->i_mapping->a_ops;
        unsigned int bsize = i_blocksize(inode), off;
        bool seek_data = whence == SEEK_DATA;
        loff_t poff = page_offset(page);

        if (WARN_ON_ONCE(*lastoff >= poff + PAGE_SIZE))
                return false;

        if (*lastoff < poff) {
                /*
                 * Last offset smaller than the start of the page means we found
                 * a hole:
                 */
                if (whence == SEEK_HOLE)
                        return true;
                *lastoff = poff;
        }

        /*
         * Just check the page unless we can and should check block ranges:
         */
        if (bsize == PAGE_SIZE || !ops->is_partially_uptodate)
                return PageUptodate(page) == seek_data;

        lock_page(page);
        if (unlikely(page->mapping != inode->i_mapping))
                goto out_unlock_not_found;

        for (off = 0; off < PAGE_SIZE; off += bsize) {
                if (offset_in_page(*lastoff) >= off + bsize)
                        continue;
                if (ops->is_partially_uptodate(page, off, bsize) == seek_data) {
                        unlock_page(page);
                        return true;
                }
                *lastoff = poff + off + bsize;
        }

out_unlock_not_found:
        unlock_page(page);
        return false;
}

/*
 * Seek for SEEK_DATA / SEEK_HOLE in the page cache.
 *
 * Within unwritten extents, the page cache determines which parts are holes
 * and which are data: uptodate buffer heads count as data; everything else
 * counts as a hole.
 *
 * Returns the resulting offset on successs, and -ENOENT otherwise.
 */
static loff_t
page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
                int whence)
{
        pgoff_t index = offset >> PAGE_SHIFT;
        pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
        loff_t lastoff = offset;
        struct pagevec pvec;

        if (length <= 0)
                return -ENOENT;

        pagevec_init(&pvec);

        do {
                unsigned nr_pages, i;

                nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping, &index,
                                                end - 1);
                if (nr_pages == 0)
                        break;

                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        if (page_seek_hole_data(inode, page, &lastoff, whence))
                                goto check_range;
                        lastoff = page_offset(page) + PAGE_SIZE;
                }
                pagevec_release(&pvec);
        } while (index < end);

        /* When no page at lastoff and we are not done, we found a hole. */
        if (whence != SEEK_HOLE)
                goto not_found;

check_range:
        if (lastoff < offset + length)
                goto out;
not_found:
        lastoff = -ENOENT;
out:
        pagevec_release(&pvec);
        return lastoff;
}


static loff_t
iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
                      void *data, struct iomap *iomap)
{
        switch (iomap->type) {
        case IOMAP_UNWRITTEN:
                offset = page_cache_seek_hole_data(inode, offset, length,
                                                   SEEK_HOLE);
                if (offset < 0)
                        return length;
                /* fall through */
        case IOMAP_HOLE:
                *(loff_t *)data = offset;
                return 0;
        default:
                return length;
        }
}

loff_t
iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
{
        loff_t size = i_size_read(inode);
        loff_t length = size - offset;
        loff_t ret;

        /* Nothing to be found before or beyond the end of the file. */
        if (offset < 0 || offset >= size)
                return -ENXIO;

        while (length > 0) {
                ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
                                  &offset, iomap_seek_hole_actor);
                if (ret < 0)
                        return ret;
                if (ret == 0)
                        break;

                offset += ret;
                length -= ret;
        }

        return offset;
}
EXPORT_SYMBOL_GPL(iomap_seek_hole);

static loff_t
iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
                      void *data, struct iomap *iomap)
{
        switch (iomap->type) {
        case IOMAP_HOLE:
                return length;
        case IOMAP_UNWRITTEN:
                offset = page_cache_seek_hole_data(inode, offset, length,
                                                   SEEK_DATA);
                if (offset < 0)
                        return length;
                /*FALLTHRU*/
        default:
                *(loff_t *)data = offset;
                return 0;
        }
}

loff_t
iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
{
        loff_t size = i_size_read(inode);
        loff_t length = size - offset;
        loff_t ret;

        /* Nothing to be found before or beyond the end of the file. */
        if (offset < 0 || offset >= size)
                return -ENXIO;

        while (length > 0) {
                ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
                                  &offset, iomap_seek_data_actor);
                if (ret < 0)
                        return ret;
                if (ret == 0)
                        break;

                offset += ret;
                length -= ret;
        }

        if (length <= 0)
                return -ENXIO;
        return offset;
}
EXPORT_SYMBOL_GPL(iomap_seek_data);

/*
 * Private flags for iomap_dio, must not overlap with the public ones in
 * iomap.h:
 */
#define IOMAP_DIO_WRITE_FUA     (1 << 28)
#define IOMAP_DIO_NEED_SYNC     (1 << 29)
#define IOMAP_DIO_WRITE         (1 << 30)
#define IOMAP_DIO_DIRTY         (1 << 31)

struct iomap_dio {
        struct kiocb            *iocb;
        iomap_dio_end_io_t      *end_io;
        loff_t                  i_size;
        loff_t                  size;
        atomic_t                ref;
        unsigned                flags;
        int                     error;
        bool                    wait_for_completion;

        union {
                /* used during submission and for synchronous completion: */
                struct {
                        struct iov_iter         *iter;
                        struct task_struct      *waiter;
                        struct request_queue    *last_queue;
                        blk_qc_t                cookie;
                } submit;

                /* used for aio completion: */
                struct {
                        struct work_struct      work;
                } aio;
        };
};

static ssize_t iomap_dio_complete(struct iomap_dio *dio)
{
        struct kiocb *iocb = dio->iocb;
        struct inode *inode = file_inode(iocb->ki_filp);
        loff_t offset = iocb->ki_pos;
        ssize_t ret;

        if (dio->end_io) {
                ret = dio->end_io(iocb,
                                dio->error ? dio->error : dio->size,
                                dio->flags);
        } else {
                ret = dio->error;
        }

        if (likely(!ret)) {
                ret = dio->size;
                /* check for short read */
                if (offset + ret > dio->i_size &&
                    !(dio->flags & IOMAP_DIO_WRITE))
                        ret = dio->i_size - offset;
                iocb->ki_pos += ret;
        }

        /*
         * Try again to invalidate clean pages which might have been cached by
         * non-direct readahead, or faulted in by get_user_pages() if the source
         * of the write was an mmap'ed region of the file we're writing.  Either
         * one is a pretty crazy thing to do, so we don't support it 100%.  If
         * this invalidation fails, tough, the write still worked...
         *
         * And this page cache invalidation has to be after dio->end_io(), as
         * some filesystems convert unwritten extents to real allocations in
         * end_io() when necessary, otherwise a racing buffer read would cache
         * zeros from unwritten extents.
         */
        if (!dio->error &&
            (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
                int err;
                err = invalidate_inode_pages2_range(inode->i_mapping,
                                offset >> PAGE_SHIFT,
                                (offset + dio->size - 1) >> PAGE_SHIFT);
                if (err)
                        dio_warn_stale_pagecache(iocb->ki_filp);
        }

        /*
         * If this is a DSYNC write, make sure we push it to stable storage now
         * that we've written data.
         */
        if (ret > 0 && (dio->flags & IOMAP_DIO_NEED_SYNC))
                ret = generic_write_sync(iocb, ret);

        inode_dio_end(file_inode(iocb->ki_filp));
        kfree(dio);

        return ret;
}

static void iomap_dio_complete_work(struct work_struct *work)
{
        struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work);
        struct kiocb *iocb = dio->iocb;

        iocb->ki_complete(iocb, iomap_dio_complete(dio), 0);
}

/*
 * Set an error in the dio if none is set yet.  We have to use cmpxchg
 * as the submission context and the completion context(s) can race to
 * update the error.
 */
static inline void iomap_dio_set_error(struct iomap_dio *dio, int ret)
{
        cmpxchg(&dio->error, 0, ret);
}

static void iomap_dio_bio_end_io(struct bio *bio)
{
        struct iomap_dio *dio = bio->bi_private;
        bool should_dirty = (dio->flags & IOMAP_DIO_DIRTY);

        if (bio->bi_status)
                iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));

        if (atomic_dec_and_test(&dio->ref)) {
                if (dio->wait_for_completion) {
                        struct task_struct *waiter = dio->submit.waiter;
                        WRITE_ONCE(dio->submit.waiter, NULL);
                        wake_up_process(waiter);
                } else if (dio->flags & IOMAP_DIO_WRITE) {
                        struct inode *inode = file_inode(dio->iocb->ki_filp);

                        INIT_WORK(&dio->aio.work, iomap_dio_complete_work);
                        queue_work(inode->i_sb->s_dio_done_wq, &dio->aio.work);
                } else {
                        iomap_dio_complete_work(&dio->aio.work);
                }
        }

        if (should_dirty) {
                bio_check_pages_dirty(bio);
        } else {
                struct bio_vec *bvec;
                int i;

                bio_for_each_segment_all(bvec, bio, i)
                        put_page(bvec->bv_page);
                bio_put(bio);
        }
}

static blk_qc_t
iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
                unsigned len)
{
        struct page *page = ZERO_PAGE(0);
        struct bio *bio;

        bio = bio_alloc(GFP_KERNEL, 1);
        bio_set_dev(bio, iomap->bdev);
        bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
        bio->bi_private = dio;
        bio->bi_end_io = iomap_dio_bio_end_io;

        get_page(page);
        __bio_add_page(bio, page, len, 0);
        bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE);

        atomic_inc(&dio->ref);
        return submit_bio(bio);
}

static loff_t
iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
                struct iomap_dio *dio, struct iomap *iomap)
{
        unsigned int blkbits = blksize_bits(bdev_logical_block_size(iomap->bdev));
        unsigned int fs_block_size = i_blocksize(inode), pad;
        unsigned int align = iov_iter_alignment(dio->submit.iter);
        struct iov_iter iter;
        struct bio *bio;
        bool need_zeroout = false;
        bool use_fua = false;
        int nr_pages, ret = 0;
        size_t copied = 0;

        if ((pos | length | align) & ((1 << blkbits) - 1))
                return -EINVAL;

        if (iomap->type == IOMAP_UNWRITTEN) {
                dio->flags |= IOMAP_DIO_UNWRITTEN;
                need_zeroout = true;
        }

        if (iomap->flags & IOMAP_F_SHARED)
                dio->flags |= IOMAP_DIO_COW;

        if (iomap->flags & IOMAP_F_NEW) {
                need_zeroout = true;
        } else if (iomap->type == IOMAP_MAPPED) {
                /*
                 * Use a FUA write if we need datasync semantics, this is a pure
                 * data IO that doesn't require any metadata updates (including
                 * after IO completion such as unwritten extent conversion) and
                 * the underlying device supports FUA. This allows us to avoid
                 * cache flushes on IO completion.
                 */
                if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
                    (dio->flags & IOMAP_DIO_WRITE_FUA) &&
                    blk_queue_fua(bdev_get_queue(iomap->bdev)))
                        use_fua = true;
        }

        /*
         * Operate on a partial iter trimmed to the extent we were called for.
         * We'll update the iter in the dio once we're done with this extent.
         */
        iter = *dio->submit.iter;
        iov_iter_truncate(&iter, length);

        nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
        if (nr_pages <= 0)
                return nr_pages;

        if (need_zeroout) {
                /* zero out from the start of the block to the write offset */
                pad = pos & (fs_block_size - 1);
                if (pad)
                        iomap_dio_zero(dio, iomap, pos - pad, pad);
        }

        do {
                size_t n;
                if (dio->error) {
                        iov_iter_revert(dio->submit.iter, copied);
                        return 0;
                }

                bio = bio_alloc(GFP_KERNEL, nr_pages);
                bio_set_dev(bio, iomap->bdev);
                bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
                bio->bi_write_hint = dio->iocb->ki_hint;
                bio->bi_ioprio = dio->iocb->ki_ioprio;
                bio->bi_private = dio;
                bio->bi_end_io = iomap_dio_bio_end_io;

                ret = bio_iov_iter_get_pages(bio, &iter);
                if (unlikely(ret)) {
                        /*
                         * We have to stop part way through an IO. We must fall
                         * through to the sub-block tail zeroing here, otherwise
                         * this short IO may expose stale data in the tail of
                         * the block we haven't written data to.
                         */
                        bio_put(bio);
                        goto zero_tail;
                }

                n = bio->bi_iter.bi_size;
                if (dio->flags & IOMAP_DIO_WRITE) {
                        bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
                        if (use_fua)
                                bio->bi_opf |= REQ_FUA;
                        else
                                dio->flags &= ~IOMAP_DIO_WRITE_FUA;
                        task_io_account_write(n);
                } else {
                        bio->bi_opf = REQ_OP_READ;
                        if (dio->flags & IOMAP_DIO_DIRTY)
                                bio_set_pages_dirty(bio);
                }

                iov_iter_advance(dio->submit.iter, n);

                dio->size += n;
                pos += n;
                copied += n;

                nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);

                atomic_inc(&dio->ref);

                dio->submit.last_queue = bdev_get_queue(iomap->bdev);
                dio->submit.cookie = submit_bio(bio);
        } while (nr_pages);

        /*
         * We need to zeroout the tail of a sub-block write if the extent type
         * requires zeroing or the write extends beyond EOF. If we don't zero
         * the block tail in the latter case, we can expose stale data via mmap
         * reads of the EOF block.
         */
zero_tail:
        if (need_zeroout ||
            ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
                /* zero out from the end of the write to the end of the block */
                pad = pos & (fs_block_size - 1);
                if (pad)
                        iomap_dio_zero(dio, iomap, pos, fs_block_size - pad);
        }
        return copied ? copied : ret;
}

static loff_t
iomap_dio_hole_actor(loff_t length, struct iomap_dio *dio)
{
        length = iov_iter_zero(length, dio->submit.iter);
        dio->size += length;
        return length;
}

static loff_t
iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
                struct iomap_dio *dio, struct iomap *iomap)
{
        struct iov_iter *iter = dio->submit.iter;
        size_t copied;

        BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));

        if (dio->flags & IOMAP_DIO_WRITE) {
                loff_t size = inode->i_size;

                if (pos > size)
                        memset(iomap->inline_data + size, 0, pos - size);
                copied = copy_from_iter(iomap->inline_data + pos, length, iter);
                if (copied) {
                        if (pos + copied > size)
                                i_size_write(inode, pos + copied);
                        mark_inode_dirty(inode);
                }
        } else {
                copied = copy_to_iter(iomap->inline_data + pos, length, iter);
        }
        dio->size += copied;
        return copied;
}

static loff_t
iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
                void *data, struct iomap *iomap)
{
        struct iomap_dio *dio = data;

        switch (iomap->type) {
        case IOMAP_HOLE:
                if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
                        return -EIO;
                return iomap_dio_hole_actor(length, dio);
        case IOMAP_UNWRITTEN:
                if (!(dio->flags & IOMAP_DIO_WRITE))
                        return iomap_dio_hole_actor(length, dio);
                return iomap_dio_bio_actor(inode, pos, length, dio, iomap);
        case IOMAP_MAPPED:
                return iomap_dio_bio_actor(inode, pos, length, dio, iomap);
        case IOMAP_INLINE:
                return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
        default:
                WARN_ON_ONCE(1);
                return -EIO;
        }
}

/*
 * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO
 * is being issued as AIO or not.  This allows us to optimise pure data writes
 * to use REQ_FUA rather than requiring generic_write_sync() to issue a
 * REQ_FLUSH post write. This is slightly tricky because a single request here
 * can be mapped into multiple disjoint IOs and only a subset of the IOs issued
 * may be pure data writes. In that case, we still need to do a full data sync
 * completion.
 */
ssize_t
iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
                const struct iomap_ops *ops, iomap_dio_end_io_t end_io)
{
        struct address_space *mapping = iocb->ki_filp->f_mapping;
        struct inode *inode = file_inode(iocb->ki_filp);
        size_t count = iov_iter_count(iter);
        loff_t pos = iocb->ki_pos, start = pos;
        loff_t end = iocb->ki_pos + count - 1, ret = 0;
        unsigned int flags = IOMAP_DIRECT;
        bool wait_for_completion = is_sync_kiocb(iocb);
        struct blk_plug plug;
        struct iomap_dio *dio;

        lockdep_assert_held(&inode->i_rwsem);

        if (!count)
                return 0;

        dio = kmalloc(sizeof(*dio), GFP_KERNEL);
        if (!dio)
                return -ENOMEM;

        dio->iocb = iocb;
        atomic_set(&dio->ref, 1);
        dio->size = 0;
        dio->i_size = i_size_read(inode);
        dio->end_io = end_io;
        dio->error = 0;
        dio->flags = 0;

        dio->submit.iter = iter;
        dio->submit.waiter = current;
        dio->submit.cookie = BLK_QC_T_NONE;
        dio->submit.last_queue = NULL;

        if (iov_iter_rw(iter) == READ) {
                if (pos >= dio->i_size)
                        goto out_free_dio;

                if (iter->type == ITER_IOVEC)
                        dio->flags |= IOMAP_DIO_DIRTY;
        } else {
                flags |= IOMAP_WRITE;
                dio->flags |= IOMAP_DIO_WRITE;

                /* for data sync or sync, we need sync completion processing */
                if (iocb->ki_flags & IOCB_DSYNC)
                        dio->flags |= IOMAP_DIO_NEED_SYNC;

                /*
                 * For datasync only writes, we optimistically try using FUA for
                 * this IO.  Any non-FUA write that occurs will clear this flag,
                 * hence we know before completion whether a cache flush is
                 * necessary.
                 */
                if ((iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC)) == IOCB_DSYNC)
                        dio->flags |= IOMAP_DIO_WRITE_FUA;
        }

        if (iocb->ki_flags & IOCB_NOWAIT) {
                if (filemap_range_has_page(mapping, start, end)) {
                        ret = -EAGAIN;
                        goto out_free_dio;
                }
                flags |= IOMAP_NOWAIT;
        }

        ret = filemap_write_and_wait_range(mapping, start, end);
        if (ret)
                goto out_free_dio;

        /*
         * Try to invalidate cache pages for the range we're direct
         * writing.  If this invalidation fails, tough, the write will
         * still work, but racing two incompatible write paths is a
         * pretty crazy thing to do, so we don't support it 100%.
         */
        ret = invalidate_inode_pages2_range(mapping,
                        start >> PAGE_SHIFT, end >> PAGE_SHIFT);
        if (ret)
                dio_warn_stale_pagecache(iocb->ki_filp);
        ret = 0;

        if (iov_iter_rw(iter) == WRITE && !wait_for_completion &&
            !inode->i_sb->s_dio_done_wq) {
                ret = sb_init_dio_done_wq(inode->i_sb);
                if (ret < 0)
                        goto out_free_dio;
        }

        inode_dio_begin(inode);

        blk_start_plug(&plug);
        do {
                ret = iomap_apply(inode, pos, count, flags, ops, dio,
                                iomap_dio_actor);
                if (ret <= 0) {
                        /* magic error code to fall back to buffered I/O */
                        if (ret == -ENOTBLK) {
                                wait_for_completion = true;
                                ret = 0;
                        }
                        break;
                }
                pos += ret;

                if (iov_iter_rw(iter) == READ && pos >= dio->i_size) {
                        /*
                         * We only report that we've read data up to i_size.
                         * Revert iter to a state corresponding to that as
                         * some callers (such as splice code) rely on it.
                         */
                        iov_iter_revert(iter, pos - dio->i_size);
                        break;
                }
        } while ((count = iov_iter_count(iter)) > 0);
        blk_finish_plug(&plug);

        if (ret < 0)
                iomap_dio_set_error(dio, ret);

        /*
         * If all the writes we issued were FUA, we don't need to flush the
         * cache on IO completion. Clear the sync flag for this case.
         */
        if (dio->flags & IOMAP_DIO_WRITE_FUA)
                dio->flags &= ~IOMAP_DIO_NEED_SYNC;

        /*
         * We are about to drop our additional submission reference, which
         * might be the last reference to the dio.  There are three three
         * different ways we can progress here:
         *
         *  (a) If this is the last reference we will always complete and free
         *      the dio ourselves.
         *  (b) If this is not the last reference, and we serve an asynchronous
         *      iocb, we must never touch the dio after the decrement, the
         *      I/O completion handler will complete and free it.
         *  (c) If this is not the last reference, but we serve a synchronous
         *      iocb, the I/O completion handler will wake us up on the drop
         *      of the final reference, and we will complete and free it here
         *      after we got woken by the I/O completion handler.
         */
        dio->wait_for_completion = wait_for_completion;
        if (!atomic_dec_and_test(&dio->ref)) {
                if (!wait_for_completion)
                        return -EIOCBQUEUED;

                for (;;) {
                        set_current_state(TASK_UNINTERRUPTIBLE);
                        if (!READ_ONCE(dio->submit.waiter))
                                break;

                        if (!(iocb->ki_flags & IOCB_HIPRI) ||
                            !dio->submit.last_queue ||
                            !blk_poll(dio->submit.last_queue,
                                         dio->submit.cookie))
                                io_schedule();
                }
                __set_current_state(TASK_RUNNING);
        }

        return iomap_dio_complete(dio);

out_free_dio:
        kfree(dio);
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_dio_rw);

/* Swapfile activation */

#ifdef CONFIG_SWAP
struct iomap_swapfile_info {
        struct iomap iomap;             /* accumulated iomap */
        struct swap_info_struct *sis;
        uint64_t lowest_ppage;          /* lowest physical addr seen (pages) */
        uint64_t highest_ppage;         /* highest physical addr seen (pages) */
        unsigned long nr_pages;         /* number of pages collected */
        int nr_extents;                 /* extent count */
};

/*
 * Collect physical extents for this swap file.  Physical extents reported to
 * the swap code must be trimmed to align to a page boundary.  The logical
 * offset within the file is irrelevant since the swapfile code maps logical
 * page numbers of the swap device to the physical page-aligned extents.
 */
static int iomap_swapfile_add_extent(struct iomap_swapfile_info *isi)
{
        struct iomap *iomap = &isi->iomap;
        unsigned long nr_pages;
        uint64_t first_ppage;
        uint64_t first_ppage_reported;
        uint64_t next_ppage;
        int error;

        /*
         * Round the start up and the end down so that the physical
         * extent aligns to a page boundary.
         */
        first_ppage = ALIGN(iomap->addr, PAGE_SIZE) >> PAGE_SHIFT;
        next_ppage = ALIGN_DOWN(iomap->addr + iomap->length, PAGE_SIZE) >>
                        PAGE_SHIFT;

        /* Skip too-short physical extents. */
        if (first_ppage >= next_ppage)
                return 0;
        nr_pages = next_ppage - first_ppage;

        /*
         * Calculate how much swap space we're adding; the first page contains
         * the swap header and doesn't count.  The mm still wants that first
         * page fed to add_swap_extent, however.
         */
        first_ppage_reported = first_ppage;
        if (iomap->offset == 0)
                first_ppage_reported++;
        if (isi->lowest_ppage > first_ppage_reported)
                isi->lowest_ppage = first_ppage_reported;
        if (isi->highest_ppage < (next_ppage - 1))
                isi->highest_ppage = next_ppage - 1;

        /* Add extent, set up for the next call. */
        error = add_swap_extent(isi->sis, isi->nr_pages, nr_pages, first_ppage);
        if (error < 0)
                return error;
        isi->nr_extents += error;
        isi->nr_pages += nr_pages;
        return 0;
}

/*
 * Accumulate iomaps for this swap file.  We have to accumulate iomaps because
 * swap only cares about contiguous page-aligned physical extents and makes no
 * distinction between written and unwritten extents.
 */
static loff_t iomap_swapfile_activate_actor(struct inode *inode, loff_t pos,
                loff_t count, void *data, struct iomap *iomap)
{
        struct iomap_swapfile_info *isi = data;
        int error;

        switch (iomap->type) {
        case IOMAP_MAPPED:
        case IOMAP_UNWRITTEN:
                /* Only real or unwritten extents. */
                break;
        case IOMAP_INLINE:
                /* No inline data. */
                pr_err("swapon: file is inline\n");
                return -EINVAL;
        default:
                pr_err("swapon: file has unallocated extents\n");
                return -EINVAL;
        }

        /* No uncommitted metadata or shared blocks. */
        if (iomap->flags & IOMAP_F_DIRTY) {
                pr_err("swapon: file is not committed\n");
                return -EINVAL;
        }
        if (iomap->flags & IOMAP_F_SHARED) {
                pr_err("swapon: file has shared extents\n");
                return -EINVAL;
        }

        /* Only one bdev per swap file. */
        if (iomap->bdev != isi->sis->bdev) {
                pr_err("swapon: file is on multiple devices\n");
                return -EINVAL;
        }

        if (isi->iomap.length == 0) {
                /* No accumulated extent, so just store it. */
                memcpy(&isi->iomap, iomap, sizeof(isi->iomap));
        } else if (isi->iomap.addr + isi->iomap.length == iomap->addr) {
                /* Append this to the accumulated extent. */
                isi->iomap.length += iomap->length;
        } else {
                /* Otherwise, add the retained iomap and store this one. */
                error = iomap_swapfile_add_extent(isi);
                if (error)
                        return error;
                memcpy(&isi->iomap, iomap, sizeof(isi->iomap));
        }
        return count;
}

/*
 * Iterate a swap file's iomaps to construct physical extents that can be
 * passed to the swapfile subsystem.
 */
int iomap_swapfile_activate(struct swap_info_struct *sis,
                struct file *swap_file, sector_t *pagespan,
                const struct iomap_ops *ops)
{
        struct iomap_swapfile_info isi = {
                .sis = sis,
                .lowest_ppage = (sector_t)-1ULL,
        };
        struct address_space *mapping = swap_file->f_mapping;
        struct inode *inode = mapping->host;
        loff_t pos = 0;
        loff_t len = ALIGN_DOWN(i_size_read(inode), PAGE_SIZE);
        loff_t ret;

        /*
         * Persist all file mapping metadata so that we won't have any
         * IOMAP_F_DIRTY iomaps.
         */
        ret = vfs_fsync(swap_file, 1);
        if (ret)
                return ret;

        while (len > 0) {
                ret = iomap_apply(inode, pos, len, IOMAP_REPORT,
                                ops, &isi, iomap_swapfile_activate_actor);
                if (ret <= 0)
                        return ret;

                pos += ret;
                len -= ret;
        }

        if (isi.iomap.length) {
                ret = iomap_swapfile_add_extent(&isi);
                if (ret)
                        return ret;
        }

        *pagespan = 1 + isi.highest_ppage - isi.lowest_ppage;
        sis->max = isi.nr_pages;
        sis->pages = isi.nr_pages - 1;
        sis->highest_bit = isi.nr_pages - 1;
        return isi.nr_extents;
}
EXPORT_SYMBOL_GPL(iomap_swapfile_activate);
#endif /* CONFIG_SWAP */

static loff_t
iomap_bmap_actor(struct inode *inode, loff_t pos, loff_t length,
                void *data, struct iomap *iomap)
{
        sector_t *bno = data, addr;

        if (iomap->type == IOMAP_MAPPED) {
                addr = (pos - iomap->offset + iomap->addr) >> inode->i_blkbits;
                if (addr > INT_MAX)
                        WARN(1, "would truncate bmap result\n");
                else
                        *bno = addr;
        }
        return 0;
}

/* legacy ->bmap interface.  0 is the error return (!) */
sector_t
iomap_bmap(struct address_space *mapping, sector_t bno,
                const struct iomap_ops *ops)
{
        struct inode *inode = mapping->host;
        loff_t pos = bno << inode->i_blkbits;
        unsigned blocksize = i_blocksize(inode);

        if (filemap_write_and_wait(mapping))
                return 0;

        bno = 0;
        iomap_apply(inode, pos, blocksize, 0, ops, &bno, iomap_bmap_actor);
        return bno;
}
EXPORT_SYMBOL_GPL(iomap_bmap);