Merge tag 'sched_ext-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tj...

[sfrench/cifs-2.6.git] / fs / iomap / buffered-io.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2010 Red Hat, Inc.
 * Copyright (C) 2016-2023 Christoph Hellwig.
 */
#include <linux/module.h>
#include <linux/compiler.h>
#include <linux/fs.h>
#include <linux/iomap.h>
#include <linux/pagemap.h>
#include <linux/uio.h>
#include <linux/buffer_head.h>
#include <linux/dax.h>
#include <linux/writeback.h>
#include <linux/list_sort.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/sched/signal.h>
#include <linux/migrate.h>
#include "trace.h"

#include "../internal.h"

#define IOEND_BATCH_SIZE        4096

/*
 * Structure allocated for each folio to track per-block uptodate, dirty state
 * and I/O completions.
 */
struct iomap_folio_state {
        spinlock_t              state_lock;
        unsigned int            read_bytes_pending;
        atomic_t                write_bytes_pending;

        /*
         * Each block has two bits in this bitmap:
         * Bits [0..blocks_per_folio) has the uptodate status.
         * Bits [b_p_f...(2*b_p_f))   has the dirty status.
         */
        unsigned long           state[];
};

static struct bio_set iomap_ioend_bioset;

static inline bool ifs_is_fully_uptodate(struct folio *folio,
                struct iomap_folio_state *ifs)
{
        struct inode *inode = folio->mapping->host;

        return bitmap_full(ifs->state, i_blocks_per_folio(inode, folio));
}

static inline bool ifs_block_is_uptodate(struct iomap_folio_state *ifs,
                unsigned int block)
{
        return test_bit(block, ifs->state);
}

static bool ifs_set_range_uptodate(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int first_blk = off >> inode->i_blkbits;
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;

        bitmap_set(ifs->state, first_blk, nr_blks);
        return ifs_is_fully_uptodate(folio, ifs);
}

static void iomap_set_range_uptodate(struct folio *folio, size_t off,
                size_t len)
{
        struct iomap_folio_state *ifs = folio->private;
        unsigned long flags;
        bool uptodate = true;

        if (ifs) {
                spin_lock_irqsave(&ifs->state_lock, flags);
                uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
                spin_unlock_irqrestore(&ifs->state_lock, flags);
        }

        if (uptodate)
                folio_mark_uptodate(folio);
}

static inline bool ifs_block_is_dirty(struct folio *folio,
                struct iomap_folio_state *ifs, int block)
{
        struct inode *inode = folio->mapping->host;
        unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);

        return test_bit(block + blks_per_folio, ifs->state);
}

static unsigned ifs_find_dirty_range(struct folio *folio,
                struct iomap_folio_state *ifs, u64 *range_start, u64 range_end)
{
        struct inode *inode = folio->mapping->host;
        unsigned start_blk =
                offset_in_folio(folio, *range_start) >> inode->i_blkbits;
        unsigned end_blk = min_not_zero(
                offset_in_folio(folio, range_end) >> inode->i_blkbits,
                i_blocks_per_folio(inode, folio));
        unsigned nblks = 1;

        while (!ifs_block_is_dirty(folio, ifs, start_blk))
                if (++start_blk == end_blk)
                        return 0;

        while (start_blk + nblks < end_blk) {
                if (!ifs_block_is_dirty(folio, ifs, start_blk + nblks))
                        break;
                nblks++;
        }

        *range_start = folio_pos(folio) + (start_blk << inode->i_blkbits);
        return nblks << inode->i_blkbits;
}

static unsigned iomap_find_dirty_range(struct folio *folio, u64 *range_start,
                u64 range_end)
{
        struct iomap_folio_state *ifs = folio->private;

        if (*range_start >= range_end)
                return 0;

        if (ifs)
                return ifs_find_dirty_range(folio, ifs, range_start, range_end);
        return range_end - *range_start;
}

static void ifs_clear_range_dirty(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
        unsigned int first_blk = (off >> inode->i_blkbits);
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;
        unsigned long flags;

        spin_lock_irqsave(&ifs->state_lock, flags);
        bitmap_clear(ifs->state, first_blk + blks_per_folio, nr_blks);
        spin_unlock_irqrestore(&ifs->state_lock, flags);
}

static void iomap_clear_range_dirty(struct folio *folio, size_t off, size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs)
                ifs_clear_range_dirty(folio, ifs, off, len);
}

static void ifs_set_range_dirty(struct folio *folio,
                struct iomap_folio_state *ifs, size_t off, size_t len)
{
        struct inode *inode = folio->mapping->host;
        unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
        unsigned int first_blk = (off >> inode->i_blkbits);
        unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
        unsigned int nr_blks = last_blk - first_blk + 1;
        unsigned long flags;

        spin_lock_irqsave(&ifs->state_lock, flags);
        bitmap_set(ifs->state, first_blk + blks_per_folio, nr_blks);
        spin_unlock_irqrestore(&ifs->state_lock, flags);
}

static void iomap_set_range_dirty(struct folio *folio, size_t off, size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        if (ifs)
                ifs_set_range_dirty(folio, ifs, off, len);
}

static struct iomap_folio_state *ifs_alloc(struct inode *inode,
                struct folio *folio, unsigned int flags)
{
        struct iomap_folio_state *ifs = folio->private;
        unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
        gfp_t gfp;

        if (ifs || nr_blocks <= 1)
                return ifs;

        if (flags & IOMAP_NOWAIT)
                gfp = GFP_NOWAIT;
        else
                gfp = GFP_NOFS | __GFP_NOFAIL;

        /*
         * ifs->state tracks two sets of state flags when the
         * filesystem block size is smaller than the folio size.
         * The first state tracks per-block uptodate and the
         * second tracks per-block dirty state.
         */
        ifs = kzalloc(struct_size(ifs, state,
                      BITS_TO_LONGS(2 * nr_blocks)), gfp);
        if (!ifs)
                return ifs;

        spin_lock_init(&ifs->state_lock);
        if (folio_test_uptodate(folio))
                bitmap_set(ifs->state, 0, nr_blocks);
        if (folio_test_dirty(folio))
                bitmap_set(ifs->state, nr_blocks, nr_blocks);
        folio_attach_private(folio, ifs);

        return ifs;
}

static void ifs_free(struct folio *folio)
{
        struct iomap_folio_state *ifs = folio_detach_private(folio);

        if (!ifs)
                return;
        WARN_ON_ONCE(ifs->read_bytes_pending != 0);
        WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending));
        WARN_ON_ONCE(ifs_is_fully_uptodate(folio, ifs) !=
                        folio_test_uptodate(folio));
        kfree(ifs);
}

/*
 * Calculate the range inside the folio that we actually need to read.
 */
static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
                loff_t *pos, loff_t length, size_t *offp, size_t *lenp)
{
        struct iomap_folio_state *ifs = folio->private;
        loff_t orig_pos = *pos;
        loff_t isize = i_size_read(inode);
        unsigned block_bits = inode->i_blkbits;
        unsigned block_size = (1 << block_bits);
        size_t poff = offset_in_folio(folio, *pos);
        size_t plen = min_t(loff_t, folio_size(folio) - poff, length);
        size_t orig_plen = plen;
        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 (ifs) {
                unsigned int i;

                /* move forward for each leading block marked uptodate */
                for (i = first; i <= last; i++) {
                        if (!ifs_block_is_uptodate(ifs, i))
                                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 (ifs_block_is_uptodate(ifs, i)) {
                                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 + orig_plen > isize) {
                unsigned end = offset_in_folio(folio, isize - 1) >> block_bits;

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

        *offp = poff;
        *lenp = plen;
}

static void iomap_finish_folio_read(struct folio *folio, size_t off,
                size_t len, int error)
{
        struct iomap_folio_state *ifs = folio->private;
        bool uptodate = !error;
        bool finished = true;

        if (ifs) {
                unsigned long flags;

                spin_lock_irqsave(&ifs->state_lock, flags);
                if (!error)
                        uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
                ifs->read_bytes_pending -= len;
                finished = !ifs->read_bytes_pending;
                spin_unlock_irqrestore(&ifs->state_lock, flags);
        }

        if (finished)
                folio_end_read(folio, uptodate);
}

static void iomap_read_end_io(struct bio *bio)
{
        int error = blk_status_to_errno(bio->bi_status);
        struct folio_iter fi;

        bio_for_each_folio_all(fi, bio)
                iomap_finish_folio_read(fi.folio, fi.offset, fi.length, error);
        bio_put(bio);
}

struct iomap_readpage_ctx {
        struct folio            *cur_folio;
        bool                    cur_folio_in_bio;
        struct bio              *bio;
        struct readahead_control *rac;
};

/**
 * iomap_read_inline_data - copy inline data into the page cache
 * @iter: iteration structure
 * @folio: folio to copy to
 *
 * Copy the inline data in @iter into @folio and zero out the rest of the folio.
 * Only a single IOMAP_INLINE extent is allowed at the end of each file.
 * Returns zero for success to complete the read, or the usual negative errno.
 */
static int iomap_read_inline_data(const struct iomap_iter *iter,
                struct folio *folio)
{
        const struct iomap *iomap = iomap_iter_srcmap(iter);
        size_t size = i_size_read(iter->inode) - iomap->offset;
        size_t offset = offset_in_folio(folio, iomap->offset);

        if (folio_test_uptodate(folio))
                return 0;

        if (WARN_ON_ONCE(size > iomap->length))
                return -EIO;
        if (offset > 0)
                ifs_alloc(iter->inode, folio, iter->flags);

        folio_fill_tail(folio, offset, iomap->inline_data, size);
        iomap_set_range_uptodate(folio, offset, folio_size(folio) - offset);
        return 0;
}

static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
                loff_t pos)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);

        return srcmap->type != IOMAP_MAPPED ||
                (srcmap->flags & IOMAP_F_NEW) ||
                pos >= i_size_read(iter->inode);
}

static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
                struct iomap_readpage_ctx *ctx, loff_t offset)
{
        const struct iomap *iomap = &iter->iomap;
        loff_t pos = iter->pos + offset;
        loff_t length = iomap_length(iter) - offset;
        struct folio *folio = ctx->cur_folio;
        struct iomap_folio_state *ifs;
        loff_t orig_pos = pos;
        size_t poff, plen;
        sector_t sector;

        if (iomap->type == IOMAP_INLINE)
                return iomap_read_inline_data(iter, folio);

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

        if (iomap_block_needs_zeroing(iter, pos)) {
                folio_zero_range(folio, poff, plen);
                iomap_set_range_uptodate(folio, poff, plen);
                goto done;
        }

        ctx->cur_folio_in_bio = true;
        if (ifs) {
                spin_lock_irq(&ifs->state_lock);
                ifs->read_bytes_pending += plen;
                spin_unlock_irq(&ifs->state_lock);
        }

        sector = iomap_sector(iomap, pos);
        if (!ctx->bio ||
            bio_end_sector(ctx->bio) != sector ||
            !bio_add_folio(ctx->bio, folio, plen, poff)) {
                gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
                gfp_t orig_gfp = gfp;
                unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);

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

                if (ctx->rac) /* same as readahead_gfp_mask */
                        gfp |= __GFP_NORETRY | __GFP_NOWARN;
                ctx->bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs),
                                     REQ_OP_READ, gfp);
                /*
                 * If the bio_alloc fails, try it again for a single page to
                 * avoid having to deal with partial page reads.  This emulates
                 * what do_mpage_read_folio does.
                 */
                if (!ctx->bio) {
                        ctx->bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ,
                                             orig_gfp);
                }
                if (ctx->rac)
                        ctx->bio->bi_opf |= REQ_RAHEAD;
                ctx->bio->bi_iter.bi_sector = sector;
                ctx->bio->bi_end_io = iomap_read_end_io;
                bio_add_folio_nofail(ctx->bio, folio, 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;
}

static loff_t iomap_read_folio_iter(const struct iomap_iter *iter,
                struct iomap_readpage_ctx *ctx)
{
        struct folio *folio = ctx->cur_folio;
        size_t offset = offset_in_folio(folio, iter->pos);
        loff_t length = min_t(loff_t, folio_size(folio) - offset,
                              iomap_length(iter));
        loff_t done, ret;

        for (done = 0; done < length; done += ret) {
                ret = iomap_readpage_iter(iter, ctx, done);
                if (ret <= 0)
                        return ret;
        }

        return done;
}

int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
{
        struct iomap_iter iter = {
                .inode          = folio->mapping->host,
                .pos            = folio_pos(folio),
                .len            = folio_size(folio),
        };
        struct iomap_readpage_ctx ctx = {
                .cur_folio      = folio,
        };
        int ret;

        trace_iomap_readpage(iter.inode, 1);

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_read_folio_iter(&iter, &ctx);

        if (ctx.bio) {
                submit_bio(ctx.bio);
                WARN_ON_ONCE(!ctx.cur_folio_in_bio);
        } else {
                WARN_ON_ONCE(ctx.cur_folio_in_bio);
                folio_unlock(folio);
        }

        /*
         * Just like mpage_readahead and block_read_full_folio, we always
         * return 0 and just set the folio error flag on errors.  This
         * should be cleaned up throughout the stack eventually.
         */
        return 0;
}
EXPORT_SYMBOL_GPL(iomap_read_folio);

static loff_t iomap_readahead_iter(const struct iomap_iter *iter,
                struct iomap_readpage_ctx *ctx)
{
        loff_t length = iomap_length(iter);
        loff_t done, ret;

        for (done = 0; done < length; done += ret) {
                if (ctx->cur_folio &&
                    offset_in_folio(ctx->cur_folio, iter->pos + done) == 0) {
                        if (!ctx->cur_folio_in_bio)
                                folio_unlock(ctx->cur_folio);
                        ctx->cur_folio = NULL;
                }
                if (!ctx->cur_folio) {
                        ctx->cur_folio = readahead_folio(ctx->rac);
                        ctx->cur_folio_in_bio = false;
                }
                ret = iomap_readpage_iter(iter, ctx, done);
                if (ret <= 0)
                        return ret;
        }

        return done;
}

/**
 * iomap_readahead - Attempt to read pages from a file.
 * @rac: Describes the pages to be read.
 * @ops: The operations vector for the filesystem.
 *
 * This function is for filesystems to call to implement their readahead
 * address_space operation.
 *
 * Context: The @ops callbacks may submit I/O (eg to read the addresses of
 * blocks from disc), and may wait for it.  The caller may be trying to
 * access a different page, and so sleeping excessively should be avoided.
 * It may allocate memory, but should avoid costly allocations.  This
 * function is called with memalloc_nofs set, so allocations will not cause
 * the filesystem to be reentered.
 */
void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
{
        struct iomap_iter iter = {
                .inode  = rac->mapping->host,
                .pos    = readahead_pos(rac),
                .len    = readahead_length(rac),
        };
        struct iomap_readpage_ctx ctx = {
                .rac    = rac,
        };

        trace_iomap_readahead(rac->mapping->host, readahead_count(rac));

        while (iomap_iter(&iter, ops) > 0)
                iter.processed = iomap_readahead_iter(&iter, &ctx);

        if (ctx.bio)
                submit_bio(ctx.bio);
        if (ctx.cur_folio) {
                if (!ctx.cur_folio_in_bio)
                        folio_unlock(ctx.cur_folio);
        }
}
EXPORT_SYMBOL_GPL(iomap_readahead);

/*
 * iomap_is_partially_uptodate checks whether blocks within a folio are
 * uptodate or not.
 *
 * Returns true if all blocks which correspond to the specified part
 * of the folio are uptodate.
 */
bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = folio->mapping->host;
        unsigned first, last, i;

        if (!ifs)
                return false;

        /* Caller's range may extend past the end of this folio */
        count = min(folio_size(folio) - from, count);

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

        for (i = first; i <= last; i++)
                if (!ifs_block_is_uptodate(ifs, i))
                        return false;
        return true;
}
EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);

/**
 * iomap_get_folio - get a folio reference for writing
 * @iter: iteration structure
 * @pos: start offset of write
 * @len: Suggested size of folio to create.
 *
 * Returns a locked reference to the folio at @pos, or an error pointer if the
 * folio could not be obtained.
 */
struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len)
{
        fgf_t fgp = FGP_WRITEBEGIN | FGP_NOFS;

        if (iter->flags & IOMAP_NOWAIT)
                fgp |= FGP_NOWAIT;
        fgp |= fgf_set_order(len);

        return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
                        fgp, mapping_gfp_mask(iter->inode->i_mapping));
}
EXPORT_SYMBOL_GPL(iomap_get_folio);

bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags)
{
        trace_iomap_release_folio(folio->mapping->host, folio_pos(folio),
                        folio_size(folio));

        /*
         * If the folio is dirty, we refuse to release our metadata because
         * it may be partially dirty.  Once we track per-block dirty state,
         * we can release the metadata if every block is dirty.
         */
        if (folio_test_dirty(folio))
                return false;
        ifs_free(folio);
        return true;
}
EXPORT_SYMBOL_GPL(iomap_release_folio);

void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len)
{
        trace_iomap_invalidate_folio(folio->mapping->host,
                                        folio_pos(folio) + offset, len);

        /*
         * If we're invalidating the entire folio, clear the dirty state
         * from it and release it to avoid unnecessary buildup of the LRU.
         */
        if (offset == 0 && len == folio_size(folio)) {
                WARN_ON_ONCE(folio_test_writeback(folio));
                folio_cancel_dirty(folio);
                ifs_free(folio);
        }
}
EXPORT_SYMBOL_GPL(iomap_invalidate_folio);

bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio)
{
        struct inode *inode = mapping->host;
        size_t len = folio_size(folio);

        ifs_alloc(inode, folio, 0);
        iomap_set_range_dirty(folio, 0, len);
        return filemap_dirty_folio(mapping, folio);
}
EXPORT_SYMBOL_GPL(iomap_dirty_folio);

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 - 1);
}

static int iomap_read_folio_sync(loff_t block_start, struct folio *folio,
                size_t poff, size_t plen, const struct iomap *iomap)
{
        struct bio_vec bvec;
        struct bio bio;

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

static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
                size_t len, struct folio *folio)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);
        struct iomap_folio_state *ifs;
        loff_t block_size = i_blocksize(iter->inode);
        loff_t block_start = round_down(pos, block_size);
        loff_t block_end = round_up(pos + len, block_size);
        unsigned int nr_blocks = i_blocks_per_folio(iter->inode, folio);
        size_t from = offset_in_folio(folio, pos), to = from + len;
        size_t poff, plen;

        /*
         * If the write or zeroing completely overlaps the current folio, then
         * entire folio will be dirtied so there is no need for
         * per-block state tracking structures to be attached to this folio.
         * For the unshare case, we must read in the ondisk contents because we
         * are not changing pagecache contents.
         */
        if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) &&
            pos + len >= folio_pos(folio) + folio_size(folio))
                return 0;

        ifs = ifs_alloc(iter->inode, folio, iter->flags);
        if ((iter->flags & IOMAP_NOWAIT) && !ifs && nr_blocks > 1)
                return -EAGAIN;

        if (folio_test_uptodate(folio))
                return 0;

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

                if (!(iter->flags & IOMAP_UNSHARE) &&
                    (from <= poff || from >= poff + plen) &&
                    (to <= poff || to >= poff + plen))
                        continue;

                if (iomap_block_needs_zeroing(iter, block_start)) {
                        if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE))
                                return -EIO;
                        folio_zero_segments(folio, poff, from, to, poff + plen);
                } else {
                        int status;

                        if (iter->flags & IOMAP_NOWAIT)
                                return -EAGAIN;

                        status = iomap_read_folio_sync(block_start, folio,
                                        poff, plen, srcmap);
                        if (status)
                                return status;
                }
                iomap_set_range_uptodate(folio, poff, plen);
        } while ((block_start += plen) < block_end);

        return 0;
}

static struct folio *__iomap_get_folio(struct iomap_iter *iter, loff_t pos,
                size_t len)
{
        const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;

        if (folio_ops && folio_ops->get_folio)
                return folio_ops->get_folio(iter, pos, len);
        else
                return iomap_get_folio(iter, pos, len);
}

static void __iomap_put_folio(struct iomap_iter *iter, loff_t pos, size_t ret,
                struct folio *folio)
{
        const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;

        if (folio_ops && folio_ops->put_folio) {
                folio_ops->put_folio(iter->inode, pos, ret, folio);
        } else {
                folio_unlock(folio);
                folio_put(folio);
        }
}

static int iomap_write_begin_inline(const struct iomap_iter *iter,
                struct folio *folio)
{
        /* needs more work for the tailpacking case; disable for now */
        if (WARN_ON_ONCE(iomap_iter_srcmap(iter)->offset != 0))
                return -EIO;
        return iomap_read_inline_data(iter, folio);
}

static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
                size_t len, struct folio **foliop)
{
        const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;
        const struct iomap *srcmap = iomap_iter_srcmap(iter);
        struct folio *folio;
        int status = 0;

        BUG_ON(pos + len > iter->iomap.offset + iter->iomap.length);
        if (srcmap != &iter->iomap)
                BUG_ON(pos + len > srcmap->offset + srcmap->length);

        if (fatal_signal_pending(current))
                return -EINTR;

        if (!mapping_large_folio_support(iter->inode->i_mapping))
                len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));

        folio = __iomap_get_folio(iter, pos, len);
        if (IS_ERR(folio))
                return PTR_ERR(folio);

        /*
         * Now we have a locked folio, before we do anything with it we need to
         * check that the iomap we have cached is not stale. The inode extent
         * mapping can change due to concurrent IO in flight (e.g.
         * IOMAP_UNWRITTEN state can change and memory reclaim could have
         * reclaimed a previously partially written page at this index after IO
         * completion before this write reaches this file offset) and hence we
         * could do the wrong thing here (zero a page range incorrectly or fail
         * to zero) and corrupt data.
         */
        if (folio_ops && folio_ops->iomap_valid) {
                bool iomap_valid = folio_ops->iomap_valid(iter->inode,
                                                         &iter->iomap);
                if (!iomap_valid) {
                        iter->iomap.flags |= IOMAP_F_STALE;
                        status = 0;
                        goto out_unlock;
                }
        }

        if (pos + len > folio_pos(folio) + folio_size(folio))
                len = folio_pos(folio) + folio_size(folio) - pos;

        if (srcmap->type == IOMAP_INLINE)
                status = iomap_write_begin_inline(iter, folio);
        else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
                status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
        else
                status = __iomap_write_begin(iter, pos, len, folio);

        if (unlikely(status))
                goto out_unlock;

        *foliop = folio;
        return 0;

out_unlock:
        __iomap_put_folio(iter, pos, 0, folio);

        return status;
}

static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
                size_t copied, struct folio *folio)
{
        flush_dcache_folio(folio);

        /*
         * The blocks that were entirely written will now be uptodate, so we
         * don't have to worry about a read_folio reading them and overwriting a
         * partial write.  However, if we've encountered a short write and only
         * partially written into a block, it will not be marked uptodate, so a
         * read_folio 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 && !folio_test_uptodate(folio)))
                return false;
        iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len);
        iomap_set_range_dirty(folio, offset_in_folio(folio, pos), copied);
        filemap_dirty_folio(inode->i_mapping, folio);
        return true;
}

static void iomap_write_end_inline(const struct iomap_iter *iter,
                struct folio *folio, loff_t pos, size_t copied)
{
        const struct iomap *iomap = &iter->iomap;
        void *addr;

        WARN_ON_ONCE(!folio_test_uptodate(folio));
        BUG_ON(!iomap_inline_data_valid(iomap));

        flush_dcache_folio(folio);
        addr = kmap_local_folio(folio, pos);
        memcpy(iomap_inline_data(iomap, pos), addr, copied);
        kunmap_local(addr);

        mark_inode_dirty(iter->inode);
}

/*
 * Returns true if all copied bytes have been written to the pagecache,
 * otherwise return false.
 */
static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
                size_t copied, struct folio *folio)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);

        if (srcmap->type == IOMAP_INLINE) {
                iomap_write_end_inline(iter, folio, pos, copied);
                return true;
        }

        if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
                size_t bh_written;

                bh_written = block_write_end(NULL, iter->inode->i_mapping, pos,
                                        len, copied, folio, NULL);
                WARN_ON_ONCE(bh_written != copied && bh_written != 0);
                return bh_written == copied;
        }

        return __iomap_write_end(iter->inode, pos, len, copied, folio);
}

static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
{
        loff_t length = iomap_length(iter);
        loff_t pos = iter->pos;
        ssize_t total_written = 0;
        long status = 0;
        struct address_space *mapping = iter->inode->i_mapping;
        size_t chunk = mapping_max_folio_size(mapping);
        unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0;

        do {
                struct folio *folio;
                loff_t old_size;
                size_t offset;          /* Offset into folio */
                size_t bytes;           /* Bytes to write to folio */
                size_t copied;          /* Bytes copied from user */
                size_t written;         /* Bytes have been written */

                bytes = iov_iter_count(i);
retry:
                offset = pos & (chunk - 1);
                bytes = min(chunk - offset, bytes);
                status = balance_dirty_pages_ratelimited_flags(mapping,
                                                               bdp_flags);
                if (unlikely(status))
                        break;

                if (bytes > length)
                        bytes = length;

                /*
                 * Bring in the user page that we'll 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.
                 *
                 * For async buffered writes the assumption is that the user
                 * page has already been faulted in. This can be optimized by
                 * faulting the user page.
                 */
                if (unlikely(fault_in_iov_iter_readable(i, bytes) == bytes)) {
                        status = -EFAULT;
                        break;
                }

                status = iomap_write_begin(iter, pos, bytes, &folio);
                if (unlikely(status)) {
                        iomap_write_failed(iter->inode, pos, bytes);
                        break;
                }
                if (iter->iomap.flags & IOMAP_F_STALE)
                        break;

                offset = offset_in_folio(folio, pos);
                if (bytes > folio_size(folio) - offset)
                        bytes = folio_size(folio) - offset;

                if (mapping_writably_mapped(mapping))
                        flush_dcache_folio(folio);

                copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
                written = iomap_write_end(iter, pos, bytes, copied, folio) ?
                          copied : 0;

                /*
                 * Update the in-memory inode size after copying the data into
                 * the page cache.  It's up to the file system to write the
                 * updated size to disk, preferably after I/O completion so that
                 * no stale data is exposed.  Only once that's done can we
                 * unlock and release the folio.
                 */
                old_size = iter->inode->i_size;
                if (pos + written > old_size) {
                        i_size_write(iter->inode, pos + written);
                        iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
                }
                __iomap_put_folio(iter, pos, written, folio);

                if (old_size < pos)
                        pagecache_isize_extended(iter->inode, old_size, pos);

                cond_resched();
                if (unlikely(written == 0)) {
                        /*
                         * A short copy made iomap_write_end() reject the
                         * thing entirely.  Might be memory poisoning
                         * halfway through, might be a race with munmap,
                         * might be severe memory pressure.
                         */
                        iomap_write_failed(iter->inode, pos, bytes);
                        iov_iter_revert(i, copied);

                        if (chunk > PAGE_SIZE)
                                chunk /= 2;
                        if (copied) {
                                bytes = copied;
                                goto retry;
                        }
                } else {
                        pos += written;
                        total_written += written;
                        length -= written;
                }
        } while (iov_iter_count(i) && length);

        if (status == -EAGAIN) {
                iov_iter_revert(i, total_written);
                return -EAGAIN;
        }
        return total_written ? total_written : status;
}

ssize_t
iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
                const struct iomap_ops *ops, void *private)
{
        struct iomap_iter iter = {
                .inode          = iocb->ki_filp->f_mapping->host,
                .pos            = iocb->ki_pos,
                .len            = iov_iter_count(i),
                .flags          = IOMAP_WRITE,
                .private        = private,
        };
        ssize_t ret;

        if (iocb->ki_flags & IOCB_NOWAIT)
                iter.flags |= IOMAP_NOWAIT;

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_write_iter(&iter, i);

        if (unlikely(iter.pos == iocb->ki_pos))
                return ret;
        ret = iter.pos - iocb->ki_pos;
        iocb->ki_pos = iter.pos;
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_file_buffered_write);

static void iomap_write_delalloc_ifs_punch(struct inode *inode,
                struct folio *folio, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        unsigned int first_blk, last_blk, i;
        loff_t last_byte;
        u8 blkbits = inode->i_blkbits;
        struct iomap_folio_state *ifs;

        /*
         * When we have per-block dirty tracking, there can be
         * blocks within a folio which are marked uptodate
         * but not dirty. In that case it is necessary to punch
         * out such blocks to avoid leaking any delalloc blocks.
         */
        ifs = folio->private;
        if (!ifs)
                return;

        last_byte = min_t(loff_t, end_byte - 1,
                        folio_pos(folio) + folio_size(folio) - 1);
        first_blk = offset_in_folio(folio, start_byte) >> blkbits;
        last_blk = offset_in_folio(folio, last_byte) >> blkbits;
        for (i = first_blk; i <= last_blk; i++) {
                if (!ifs_block_is_dirty(folio, ifs, i))
                        punch(inode, folio_pos(folio) + (i << blkbits),
                                    1 << blkbits, iomap);
        }
}

static void iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
                loff_t *punch_start_byte, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        if (!folio_test_dirty(folio))
                return;

        /* if dirty, punch up to offset */
        if (start_byte > *punch_start_byte) {
                punch(inode, *punch_start_byte, start_byte - *punch_start_byte,
                                iomap);
        }

        /* Punch non-dirty blocks within folio */
        iomap_write_delalloc_ifs_punch(inode, folio, start_byte, end_byte,
                        iomap, punch);

        /*
         * Make sure the next punch start is correctly bound to
         * the end of this data range, not the end of the folio.
         */
        *punch_start_byte = min_t(loff_t, end_byte,
                                folio_pos(folio) + folio_size(folio));
}

/*
 * Scan the data range passed to us for dirty page cache folios. If we find a
 * dirty folio, punch out the preceding range and update the offset from which
 * the next punch will start from.
 *
 * We can punch out storage reservations under clean pages because they either
 * contain data that has been written back - in which case the delalloc punch
 * over that range is a no-op - or they have been read faults in which case they
 * contain zeroes and we can remove the delalloc backing range and any new
 * writes to those pages will do the normal hole filling operation...
 *
 * This makes the logic simple: we only need to keep the delalloc extents only
 * over the dirty ranges of the page cache.
 *
 * This function uses [start_byte, end_byte) intervals (i.e. open ended) to
 * simplify range iterations.
 */
static void iomap_write_delalloc_scan(struct inode *inode,
                loff_t *punch_start_byte, loff_t start_byte, loff_t end_byte,
                struct iomap *iomap, iomap_punch_t punch)
{
        while (start_byte < end_byte) {
                struct folio    *folio;

                /* grab locked page */
                folio = filemap_lock_folio(inode->i_mapping,
                                start_byte >> PAGE_SHIFT);
                if (IS_ERR(folio)) {
                        start_byte = ALIGN_DOWN(start_byte, PAGE_SIZE) +
                                        PAGE_SIZE;
                        continue;
                }

                iomap_write_delalloc_punch(inode, folio, punch_start_byte,
                                start_byte, end_byte, iomap, punch);

                /* move offset to start of next folio in range */
                start_byte = folio_next_index(folio) << PAGE_SHIFT;
                folio_unlock(folio);
                folio_put(folio);
        }
}

/*
 * Punch out all the delalloc blocks in the range given except for those that
 * have dirty data still pending in the page cache - those are going to be
 * written and so must still retain the delalloc backing for writeback.
 *
 * As we are scanning the page cache for data, we don't need to reimplement the
 * wheel - mapping_seek_hole_data() does exactly what we need to identify the
 * start and end of data ranges correctly even for sub-folio block sizes. This
 * byte range based iteration is especially convenient because it means we
 * don't have to care about variable size folios, nor where the start or end of
 * the data range lies within a folio, if they lie within the same folio or even
 * if there are multiple discontiguous data ranges within the folio.
 *
 * It should be noted that mapping_seek_hole_data() is not aware of EOF, and so
 * can return data ranges that exist in the cache beyond EOF. e.g. a page fault
 * spanning EOF will initialise the post-EOF data to zeroes and mark it up to
 * date. A write page fault can then mark it dirty. If we then fail a write()
 * beyond EOF into that up to date cached range, we allocate a delalloc block
 * beyond EOF and then have to punch it out. Because the range is up to date,
 * mapping_seek_hole_data() will return it, and we will skip the punch because
 * the folio is dirty. THis is incorrect - we always need to punch out delalloc
 * beyond EOF in this case as writeback will never write back and covert that
 * delalloc block beyond EOF. Hence we limit the cached data scan range to EOF,
 * resulting in always punching out the range from the EOF to the end of the
 * range the iomap spans.
 *
 * Intervals are of the form [start_byte, end_byte) (i.e. open ended) because it
 * matches the intervals returned by mapping_seek_hole_data(). i.e. SEEK_DATA
 * returns the start of a data range (start_byte), and SEEK_HOLE(start_byte)
 * returns the end of the data range (data_end). Using closed intervals would
 * require sprinkling this code with magic "+ 1" and "- 1" arithmetic and expose
 * the code to subtle off-by-one bugs....
 */
static void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
                loff_t end_byte, unsigned flags, struct iomap *iomap,
                iomap_punch_t punch)
{
        loff_t punch_start_byte = start_byte;
        loff_t scan_end_byte = min(i_size_read(inode), end_byte);

        /*
         * Lock the mapping to avoid races with page faults re-instantiating
         * folios and dirtying them via ->page_mkwrite whilst we walk the
         * cache and perform delalloc extent removal. Failing to do this can
         * leave dirty pages with no space reservation in the cache.
         */
        filemap_invalidate_lock(inode->i_mapping);
        while (start_byte < scan_end_byte) {
                loff_t          data_end;

                start_byte = mapping_seek_hole_data(inode->i_mapping,
                                start_byte, scan_end_byte, SEEK_DATA);
                /*
                 * If there is no more data to scan, all that is left is to
                 * punch out the remaining range.
                 *
                 * Note that mapping_seek_hole_data is only supposed to return
                 * either an offset or -ENXIO, so WARN on any other error as
                 * that would be an API change without updating the callers.
                 */
                if (start_byte == -ENXIO || start_byte == scan_end_byte)
                        break;
                if (WARN_ON_ONCE(start_byte < 0))
                        goto out_unlock;
                WARN_ON_ONCE(start_byte < punch_start_byte);
                WARN_ON_ONCE(start_byte > scan_end_byte);

                /*
                 * We find the end of this contiguous cached data range by
                 * seeking from start_byte to the beginning of the next hole.
                 */
                data_end = mapping_seek_hole_data(inode->i_mapping, start_byte,
                                scan_end_byte, SEEK_HOLE);
                if (WARN_ON_ONCE(data_end < 0))
                        goto out_unlock;

                /*
                 * If we race with post-direct I/O invalidation of the page cache,
                 * there might be no data left at start_byte.
                 */
                if (data_end == start_byte)
                        continue;

                WARN_ON_ONCE(data_end < start_byte);
                WARN_ON_ONCE(data_end > scan_end_byte);

                iomap_write_delalloc_scan(inode, &punch_start_byte, start_byte,
                                data_end, iomap, punch);

                /* The next data search starts at the end of this one. */
                start_byte = data_end;
        }

        if (punch_start_byte < end_byte)
                punch(inode, punch_start_byte, end_byte - punch_start_byte,
                                iomap);
out_unlock:
        filemap_invalidate_unlock(inode->i_mapping);
}

/*
 * When a short write occurs, the filesystem may need to remove reserved space
 * that was allocated in ->iomap_begin from it's ->iomap_end method. For
 * filesystems that use delayed allocation, we need to punch out delalloc
 * extents from the range that are not dirty in the page cache. As the write can
 * race with page faults, there can be dirty pages over the delalloc extent
 * outside the range of a short write but still within the delalloc extent
 * allocated for this iomap.
 *
 * This function uses [start_byte, end_byte) intervals (i.e. open ended) to
 * simplify range iterations.
 *
 * The punch() callback *must* only punch delalloc extents in the range passed
 * to it. It must skip over all other types of extents in the range and leave
 * them completely unchanged. It must do this punch atomically with respect to
 * other extent modifications.
 *
 * The punch() callback may be called with a folio locked to prevent writeback
 * extent allocation racing at the edge of the range we are currently punching.
 * The locked folio may or may not cover the range being punched, so it is not
 * safe for the punch() callback to lock folios itself.
 *
 * Lock order is:
 *
 * inode->i_rwsem (shared or exclusive)
 *   inode->i_mapping->invalidate_lock (exclusive)
 *     folio_lock()
 *       ->punch
 *         internal filesystem allocation lock
 */
void iomap_file_buffered_write_punch_delalloc(struct inode *inode,
                loff_t pos, loff_t length, ssize_t written, unsigned flags,
                struct iomap *iomap, iomap_punch_t punch)
{
        loff_t                  start_byte;
        loff_t                  end_byte;
        unsigned int            blocksize = i_blocksize(inode);

        if (iomap->type != IOMAP_DELALLOC)
                return;

        /* If we didn't reserve the blocks, we're not allowed to punch them. */
        if (!(iomap->flags & IOMAP_F_NEW))
                return;

        /*
         * start_byte refers to the first unused block after a short write. If
         * nothing was written, round offset down to point at the first block in
         * the range.
         */
        if (unlikely(!written))
                start_byte = round_down(pos, blocksize);
        else
                start_byte = round_up(pos + written, blocksize);
        end_byte = round_up(pos + length, blocksize);

        /* Nothing to do if we've written the entire delalloc extent */
        if (start_byte >= end_byte)
                return;

        iomap_write_delalloc_release(inode, start_byte, end_byte, flags, iomap,
                        punch);
}
EXPORT_SYMBOL_GPL(iomap_file_buffered_write_punch_delalloc);

static loff_t iomap_unshare_iter(struct iomap_iter *iter)
{
        struct iomap *iomap = &iter->iomap;
        loff_t pos = iter->pos;
        loff_t length = iomap_length(iter);
        loff_t written = 0;

        /* Don't bother with blocks that are not shared to start with. */
        if (!(iomap->flags & IOMAP_F_SHARED))
                return length;

        /*
         * Don't bother with holes or unwritten extents.
         *
         * Note that we use srcmap directly instead of iomap_iter_srcmap as
         * unsharing requires providing a separate source map, and the presence
         * of one is a good indicator that unsharing is needed, unlike
         * IOMAP_F_SHARED which can be set for any data that goes into the COW
         * fork for XFS.
         */
        if (iter->srcmap.type == IOMAP_HOLE ||
            iter->srcmap.type == IOMAP_UNWRITTEN)
                return length;

        do {
                struct folio *folio;
                int status;
                size_t offset;
                size_t bytes = min_t(u64, SIZE_MAX, length);
                bool ret;

                status = iomap_write_begin(iter, pos, bytes, &folio);
                if (unlikely(status))
                        return status;
                if (iomap->flags & IOMAP_F_STALE)
                        break;

                offset = offset_in_folio(folio, pos);
                if (bytes > folio_size(folio) - offset)
                        bytes = folio_size(folio) - offset;

                ret = iomap_write_end(iter, pos, bytes, bytes, folio);
                __iomap_put_folio(iter, pos, bytes, folio);
                if (WARN_ON_ONCE(!ret))
                        return -EIO;

                cond_resched();

                pos += bytes;
                written += bytes;
                length -= bytes;

                balance_dirty_pages_ratelimited(iter->inode->i_mapping);
        } while (length > 0);

        return written;
}

int
iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
                const struct iomap_ops *ops)
{
        struct iomap_iter iter = {
                .inode          = inode,
                .pos            = pos,
                .len            = len,
                .flags          = IOMAP_WRITE | IOMAP_UNSHARE,
        };
        int ret;

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_unshare_iter(&iter);
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_file_unshare);

/*
 * Flush the remaining range of the iter and mark the current mapping stale.
 * This is used when zero range sees an unwritten mapping that may have had
 * dirty pagecache over it.
 */
static inline int iomap_zero_iter_flush_and_stale(struct iomap_iter *i)
{
        struct address_space *mapping = i->inode->i_mapping;
        loff_t end = i->pos + i->len - 1;

        i->iomap.flags |= IOMAP_F_STALE;
        return filemap_write_and_wait_range(mapping, i->pos, end);
}

static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
                bool *range_dirty)
{
        const struct iomap *srcmap = iomap_iter_srcmap(iter);
        loff_t pos = iter->pos;
        loff_t length = iomap_length(iter);
        loff_t written = 0;

        /*
         * We must zero subranges of unwritten mappings that might be dirty in
         * pagecache from previous writes. We only know whether the entire range
         * was clean or not, however, and dirty folios may have been written
         * back or reclaimed at any point after mapping lookup.
         *
         * The easiest way to deal with this is to flush pagecache to trigger
         * any pending unwritten conversions and then grab the updated extents
         * from the fs. The flush may change the current mapping, so mark it
         * stale for the iterator to remap it for the next pass to handle
         * properly.
         *
         * Note that holes are treated the same as unwritten because zero range
         * is (ab)used for partial folio zeroing in some cases. Hole backed
         * post-eof ranges can be dirtied via mapped write and the flush
         * triggers writeback time post-eof zeroing.
         */
        if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN) {
                if (*range_dirty) {
                        *range_dirty = false;
                        return iomap_zero_iter_flush_and_stale(iter);
                }
                /* range is clean and already zeroed, nothing to do */
                return length;
        }

        do {
                struct folio *folio;
                int status;
                size_t offset;
                size_t bytes = min_t(u64, SIZE_MAX, length);
                bool ret;

                status = iomap_write_begin(iter, pos, bytes, &folio);
                if (status)
                        return status;
                if (iter->iomap.flags & IOMAP_F_STALE)
                        break;

                offset = offset_in_folio(folio, pos);
                if (bytes > folio_size(folio) - offset)
                        bytes = folio_size(folio) - offset;

                folio_zero_range(folio, offset, bytes);
                folio_mark_accessed(folio);

                ret = iomap_write_end(iter, pos, bytes, bytes, folio);
                __iomap_put_folio(iter, pos, bytes, folio);
                if (WARN_ON_ONCE(!ret))
                        return -EIO;

                pos += bytes;
                length -= bytes;
                written += bytes;
        } while (length > 0);

        if (did_zero)
                *did_zero = true;
        return written;
}

int
iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
                const struct iomap_ops *ops)
{
        struct iomap_iter iter = {
                .inode          = inode,
                .pos            = pos,
                .len            = len,
                .flags          = IOMAP_ZERO,
        };
        int ret;
        bool range_dirty;

        /*
         * Zero range wants to skip pre-zeroed (i.e. unwritten) mappings, but
         * pagecache must be flushed to ensure stale data from previous
         * buffered writes is not exposed. A flush is only required for certain
         * types of mappings, but checking pagecache after mapping lookup is
         * racy with writeback and reclaim.
         *
         * Therefore, check the entire range first and pass along whether any
         * part of it is dirty. If so and an underlying mapping warrants it,
         * flush the cache at that point. This trades off the occasional false
         * positive (and spurious flush, if the dirty data and mapping don't
         * happen to overlap) for simplicity in handling a relatively uncommon
         * situation.
         */
        range_dirty = filemap_range_needs_writeback(inode->i_mapping,
                                        pos, pos + len - 1);

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_zero_iter(&iter, did_zero, &range_dirty);
        return ret;
}
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_folio_mkwrite_iter(struct iomap_iter *iter,
                struct folio *folio)
{
        loff_t length = iomap_length(iter);
        int ret;

        if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
                ret = __block_write_begin_int(folio, iter->pos, length, NULL,
                                              &iter->iomap);
                if (ret)
                        return ret;
                block_commit_write(&folio->page, 0, length);
        } else {
                WARN_ON_ONCE(!folio_test_uptodate(folio));
                folio_mark_dirty(folio);
        }

        return length;
}

vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
{
        struct iomap_iter iter = {
                .inode          = file_inode(vmf->vma->vm_file),
                .flags          = IOMAP_WRITE | IOMAP_FAULT,
        };
        struct folio *folio = page_folio(vmf->page);
        ssize_t ret;

        folio_lock(folio);
        ret = folio_mkwrite_check_truncate(folio, iter.inode);
        if (ret < 0)
                goto out_unlock;
        iter.pos = folio_pos(folio);
        iter.len = ret;
        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_folio_mkwrite_iter(&iter, folio);

        if (ret < 0)
                goto out_unlock;
        folio_wait_stable(folio);
        return VM_FAULT_LOCKED;
out_unlock:
        folio_unlock(folio);
        return vmf_fs_error(ret);
}
EXPORT_SYMBOL_GPL(iomap_page_mkwrite);

static void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
                size_t len)
{
        struct iomap_folio_state *ifs = folio->private;

        WARN_ON_ONCE(i_blocks_per_folio(inode, folio) > 1 && !ifs);
        WARN_ON_ONCE(ifs && atomic_read(&ifs->write_bytes_pending) <= 0);

        if (!ifs || atomic_sub_and_test(len, &ifs->write_bytes_pending))
                folio_end_writeback(folio);
}

/*
 * We're now finished for good with this ioend structure.  Update the page
 * state, release holds on bios, and finally free up memory.  Do not use the
 * ioend after this.
 */
static u32
iomap_finish_ioend(struct iomap_ioend *ioend, int error)
{
        struct inode *inode = ioend->io_inode;
        struct bio *bio = &ioend->io_bio;
        struct folio_iter fi;
        u32 folio_count = 0;

        if (error) {
                mapping_set_error(inode->i_mapping, error);
                if (!bio_flagged(bio, BIO_QUIET)) {
                        pr_err_ratelimited(
"%s: writeback error on inode %lu, offset %lld, sector %llu",
                                inode->i_sb->s_id, inode->i_ino,
                                ioend->io_offset, ioend->io_sector);
                }
        }

        /* walk all folios in bio, ending page IO on them */
        bio_for_each_folio_all(fi, bio) {
                iomap_finish_folio_write(inode, fi.folio, fi.length);
                folio_count++;
        }

        bio_put(bio);   /* frees the ioend */
        return folio_count;
}

/*
 * Ioend completion routine for merged bios. This can only be called from task
 * contexts as merged ioends can be of unbound length. Hence we have to break up
 * the writeback completions into manageable chunks to avoid long scheduler
 * holdoffs. We aim to keep scheduler holdoffs down below 10ms so that we get
 * good batch processing throughput without creating adverse scheduler latency
 * conditions.
 */
void
iomap_finish_ioends(struct iomap_ioend *ioend, int error)
{
        struct list_head tmp;
        u32 completions;

        might_sleep();

        list_replace_init(&ioend->io_list, &tmp);
        completions = iomap_finish_ioend(ioend, error);

        while (!list_empty(&tmp)) {
                if (completions > IOEND_BATCH_SIZE * 8) {
                        cond_resched();
                        completions = 0;
                }
                ioend = list_first_entry(&tmp, struct iomap_ioend, io_list);
                list_del_init(&ioend->io_list);
                completions += iomap_finish_ioend(ioend, error);
        }
}
EXPORT_SYMBOL_GPL(iomap_finish_ioends);

/*
 * We can merge two adjacent ioends if they have the same set of work to do.
 */
static bool
iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
{
        if (ioend->io_bio.bi_status != next->io_bio.bi_status)
                return false;
        if ((ioend->io_flags & IOMAP_F_SHARED) ^
            (next->io_flags & IOMAP_F_SHARED))
                return false;
        if ((ioend->io_type == IOMAP_UNWRITTEN) ^
            (next->io_type == IOMAP_UNWRITTEN))
                return false;
        if (ioend->io_offset + ioend->io_size != next->io_offset)
                return false;
        /*
         * Do not merge physically discontiguous ioends. The filesystem
         * completion functions will have to iterate the physical
         * discontiguities even if we merge the ioends at a logical level, so
         * we don't gain anything by merging physical discontiguities here.
         *
         * We cannot use bio->bi_iter.bi_sector here as it is modified during
         * submission so does not point to the start sector of the bio at
         * completion.
         */
        if (ioend->io_sector + (ioend->io_size >> 9) != next->io_sector)
                return false;
        return true;
}

void
iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends)
{
        struct iomap_ioend *next;

        INIT_LIST_HEAD(&ioend->io_list);

        while ((next = list_first_entry_or_null(more_ioends, struct iomap_ioend,
                        io_list))) {
                if (!iomap_ioend_can_merge(ioend, next))
                        break;
                list_move_tail(&next->io_list, &ioend->io_list);
                ioend->io_size += next->io_size;
        }
}
EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);

static int
iomap_ioend_compare(void *priv, const struct list_head *a,
                const struct list_head *b)
{
        struct iomap_ioend *ia = container_of(a, struct iomap_ioend, io_list);
        struct iomap_ioend *ib = container_of(b, struct iomap_ioend, io_list);

        if (ia->io_offset < ib->io_offset)
                return -1;
        if (ia->io_offset > ib->io_offset)
                return 1;
        return 0;
}

void
iomap_sort_ioends(struct list_head *ioend_list)
{
        list_sort(NULL, ioend_list, iomap_ioend_compare);
}
EXPORT_SYMBOL_GPL(iomap_sort_ioends);

static void iomap_writepage_end_bio(struct bio *bio)
{
        iomap_finish_ioend(iomap_ioend_from_bio(bio),
                        blk_status_to_errno(bio->bi_status));
}

/*
 * Submit the final bio for an ioend.
 *
 * If @error is non-zero, it means that we have a situation where some part of
 * the submission process has failed after we've marked pages for writeback.
 * We cannot cancel ioend directly in that case, so call the bio end I/O handler
 * with the error status here to run the normal I/O completion handler to clear
 * the writeback bit and let the file system proess the errors.
 */
static int iomap_submit_ioend(struct iomap_writepage_ctx *wpc, int error)
{
        if (!wpc->ioend)
                return error;

        /*
         * Let the file systems prepare the I/O submission and hook in an I/O
         * comletion handler.  This also needs to happen in case after a
         * failure happened so that the file system end I/O handler gets called
         * to clean up.
         */
        if (wpc->ops->prepare_ioend)
                error = wpc->ops->prepare_ioend(wpc->ioend, error);

        if (error) {
                wpc->ioend->io_bio.bi_status = errno_to_blk_status(error);
                bio_endio(&wpc->ioend->io_bio);
        } else {
                submit_bio(&wpc->ioend->io_bio);
        }

        wpc->ioend = NULL;
        return error;
}

static struct iomap_ioend *iomap_alloc_ioend(struct iomap_writepage_ctx *wpc,
                struct writeback_control *wbc, struct inode *inode, loff_t pos)
{
        struct iomap_ioend *ioend;
        struct bio *bio;

        bio = bio_alloc_bioset(wpc->iomap.bdev, BIO_MAX_VECS,
                               REQ_OP_WRITE | wbc_to_write_flags(wbc),
                               GFP_NOFS, &iomap_ioend_bioset);
        bio->bi_iter.bi_sector = iomap_sector(&wpc->iomap, pos);
        bio->bi_end_io = iomap_writepage_end_bio;
        wbc_init_bio(wbc, bio);
        bio->bi_write_hint = inode->i_write_hint;

        ioend = iomap_ioend_from_bio(bio);
        INIT_LIST_HEAD(&ioend->io_list);
        ioend->io_type = wpc->iomap.type;
        ioend->io_flags = wpc->iomap.flags;
        ioend->io_inode = inode;
        ioend->io_size = 0;
        ioend->io_offset = pos;
        ioend->io_sector = bio->bi_iter.bi_sector;

        wpc->nr_folios = 0;
        return ioend;
}

static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos)
{
        if ((wpc->iomap.flags & IOMAP_F_SHARED) !=
            (wpc->ioend->io_flags & IOMAP_F_SHARED))
                return false;
        if (wpc->iomap.type != wpc->ioend->io_type)
                return false;
        if (pos != wpc->ioend->io_offset + wpc->ioend->io_size)
                return false;
        if (iomap_sector(&wpc->iomap, pos) !=
            bio_end_sector(&wpc->ioend->io_bio))
                return false;
        /*
         * Limit ioend bio chain lengths to minimise IO completion latency. This
         * also prevents long tight loops ending page writeback on all the
         * folios in the ioend.
         */
        if (wpc->nr_folios >= IOEND_BATCH_SIZE)
                return false;
        return true;
}

/*
 * Test to see if we have an existing ioend structure that we could append to
 * first; otherwise finish off the current ioend and start another.
 *
 * If a new ioend is created and cached, the old ioend is submitted to the block
 * layer instantly.  Batching optimisations are provided by higher level block
 * plugging.
 *
 * At the end of a writeback pass, there will be a cached ioend remaining on the
 * writepage context that the caller will need to submit.
 */
static int iomap_add_to_ioend(struct iomap_writepage_ctx *wpc,
                struct writeback_control *wbc, struct folio *folio,
                struct inode *inode, loff_t pos, unsigned len)
{
        struct iomap_folio_state *ifs = folio->private;
        size_t poff = offset_in_folio(folio, pos);
        int error;

        if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos)) {
new_ioend:
                error = iomap_submit_ioend(wpc, 0);
                if (error)
                        return error;
                wpc->ioend = iomap_alloc_ioend(wpc, wbc, inode, pos);
        }

        if (!bio_add_folio(&wpc->ioend->io_bio, folio, len, poff))
                goto new_ioend;

        if (ifs)
                atomic_add(len, &ifs->write_bytes_pending);
        wpc->ioend->io_size += len;
        wbc_account_cgroup_owner(wbc, &folio->page, len);
        return 0;
}

static int iomap_writepage_map_blocks(struct iomap_writepage_ctx *wpc,
                struct writeback_control *wbc, struct folio *folio,
                struct inode *inode, u64 pos, unsigned dirty_len,
                unsigned *count)
{
        int error;

        do {
                unsigned map_len;

                error = wpc->ops->map_blocks(wpc, inode, pos, dirty_len);
                if (error)
                        break;
                trace_iomap_writepage_map(inode, pos, dirty_len, &wpc->iomap);

                map_len = min_t(u64, dirty_len,
                        wpc->iomap.offset + wpc->iomap.length - pos);
                WARN_ON_ONCE(!folio->private && map_len < dirty_len);

                switch (wpc->iomap.type) {
                case IOMAP_INLINE:
                        WARN_ON_ONCE(1);
                        error = -EIO;
                        break;
                case IOMAP_HOLE:
                        break;
                default:
                        error = iomap_add_to_ioend(wpc, wbc, folio, inode, pos,
                                        map_len);
                        if (!error)
                                (*count)++;
                        break;
                }
                dirty_len -= map_len;
                pos += map_len;
        } while (dirty_len && !error);

        /*
         * We cannot cancel the ioend directly here on error.  We may have
         * already set other pages under writeback and hence we have to run I/O
         * completion to mark the error state of the pages under writeback
         * appropriately.
         *
         * Just let the file system know what portion of the folio failed to
         * map.
         */
        if (error && wpc->ops->discard_folio)
                wpc->ops->discard_folio(folio, pos);
        return error;
}

/*
 * Check interaction of the folio with the file end.
 *
 * If the folio is entirely beyond i_size, return false.  If it straddles
 * i_size, adjust end_pos and zero all data beyond i_size.
 */
static bool iomap_writepage_handle_eof(struct folio *folio, struct inode *inode,
                u64 *end_pos)
{
        u64 isize = i_size_read(inode);

        if (*end_pos > isize) {
                size_t poff = offset_in_folio(folio, isize);
                pgoff_t end_index = isize >> PAGE_SHIFT;

                /*
                 * If the folio is entirely ouside of i_size, skip it.
                 *
                 * This can happen due to a truncate operation that is in
                 * progress and in that case truncate will finish it off once
                 * we've dropped the folio lock.
                 *
                 * Note that the pgoff_t used for end_index is an unsigned long.
                 * If the given offset is greater than 16TB on a 32-bit system,
                 * then if we checked if the folio is fully outside i_size with
                 * "if (folio->index >= end_index + 1)", "end_index + 1" would
                 * overflow and evaluate to 0.  Hence this folio would be
                 * redirtied and written out repeatedly, which would result in
                 * an infinite loop; the user program performing this operation
                 * would hang.  Instead, we can detect this situation by
                 * checking if the folio is totally beyond i_size or if its
                 * offset is just equal to the EOF.
                 */
                if (folio->index > end_index ||
                    (folio->index == end_index && poff == 0))
                        return false;

                /*
                 * The folio 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.
                 *
                 * Also adjust the writeback range to skip all blocks entirely
                 * beyond i_size.
                 */
                folio_zero_segment(folio, poff, folio_size(folio));
                *end_pos = round_up(isize, i_blocksize(inode));
        }

        return true;
}

static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
                struct writeback_control *wbc, struct folio *folio)
{
        struct iomap_folio_state *ifs = folio->private;
        struct inode *inode = folio->mapping->host;
        u64 pos = folio_pos(folio);
        u64 end_pos = pos + folio_size(folio);
        unsigned count = 0;
        int error = 0;
        u32 rlen;

        WARN_ON_ONCE(!folio_test_locked(folio));
        WARN_ON_ONCE(folio_test_dirty(folio));
        WARN_ON_ONCE(folio_test_writeback(folio));

        trace_iomap_writepage(inode, pos, folio_size(folio));

        if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
                folio_unlock(folio);
                return 0;
        }
        WARN_ON_ONCE(end_pos <= pos);

        if (i_blocks_per_folio(inode, folio) > 1) {
                if (!ifs) {
                        ifs = ifs_alloc(inode, folio, 0);
                        iomap_set_range_dirty(folio, 0, end_pos - pos);
                }

                /*
                 * Keep the I/O completion handler from clearing the writeback
                 * bit until we have submitted all blocks by adding a bias to
                 * ifs->write_bytes_pending, which is dropped after submitting
                 * all blocks.
                 */
                WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending) != 0);
                atomic_inc(&ifs->write_bytes_pending);
        }

        /*
         * Set the writeback bit ASAP, as the I/O completion for the single
         * block per folio case happen hit as soon as we're submitting the bio.
         */
        folio_start_writeback(folio);

        /*
         * Walk through the folio to find dirty areas to write back.
         */
        while ((rlen = iomap_find_dirty_range(folio, &pos, end_pos))) {
                error = iomap_writepage_map_blocks(wpc, wbc, folio, inode,
                                pos, rlen, &count);
                if (error)
                        break;
                pos += rlen;
        }

        if (count)
                wpc->nr_folios++;

        /*
         * We can have dirty bits set past end of file in page_mkwrite path
         * while mapping the last partial folio. Hence it's better to clear
         * all the dirty bits in the folio here.
         */
        iomap_clear_range_dirty(folio, 0, folio_size(folio));

        /*
         * Usually the writeback bit is cleared by the I/O completion handler.
         * But we may end up either not actually writing any blocks, or (when
         * there are multiple blocks in a folio) all I/O might have finished
         * already at this point.  In that case we need to clear the writeback
         * bit ourselves right after unlocking the page.
         */
        folio_unlock(folio);
        if (ifs) {
                if (atomic_dec_and_test(&ifs->write_bytes_pending))
                        folio_end_writeback(folio);
        } else {
                if (!count)
                        folio_end_writeback(folio);
        }
        mapping_set_error(inode->i_mapping, error);
        return error;
}

int
iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
                struct iomap_writepage_ctx *wpc,
                const struct iomap_writeback_ops *ops)
{
        struct folio *folio = NULL;
        int error;

        /*
         * Writeback from reclaim context should never happen except in the case
         * of a VM regression so warn about it and refuse to write the data.
         */
        if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC | PF_KSWAPD)) ==
                        PF_MEMALLOC))
                return -EIO;

        wpc->ops = ops;
        while ((folio = writeback_iter(mapping, wbc, folio, &error)))
                error = iomap_writepage_map(wpc, wbc, folio);
        return iomap_submit_ioend(wpc, error);
}
EXPORT_SYMBOL_GPL(iomap_writepages);

static int __init iomap_buffered_init(void)
{
        return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
                           offsetof(struct iomap_ioend, io_bio),
                           BIOSET_NEED_BVECS);
}
fs_initcall(iomap_buffered_init);