ipc/shm: Fix shmat mmap nil-page protection

[cris-mirror.git] / fs / iomap.c

/*
 * Copyright (C) 2010 Red Hat, Inc.
 * Copyright (c) 2016 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/mm.h>
#include <linux/swap.h>
#include <linux/pagemap.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 "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;

        /*
         * 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 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_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;

        status = __block_write_begin_int(page, pos, len, NULL, iomap);
        if (unlikely(status)) {
                unlock_page(page);
                put_page(page);
                page = NULL;

                iomap_write_failed(inode, pos, len);
        }

        *pagep = page;
        return status;
}

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

        ret = generic_write_end(NULL, inode->i_mapping, pos, len,
                        copied, page, NULL);
        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;

        /*
         * Copies from kernel address space cannot fail (NFSD is a big user).
         */
        if (!iter_is_iovec(i))
                flags |= AOP_FLAG_UNINTERRUPTIBLE;

        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 = (pos & (PAGE_SIZE - 1));
                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);
                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 = (pos & (PAGE_SIZE - 1));
                bytes = min_t(unsigned long, 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 | AOP_FLAG_UNINTERRUPTIBLE,
                                &page, iomap);
                put_page(rpage);
                if (unlikely(status))
                        return status;

                WARN_ON_ONCE(!PageUptodate(page));

                status = iomap_write_end(inode, pos, bytes, bytes, page);
                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_UNINTERRUPTIBLE | 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);
}

static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
                struct iomap *iomap)
{
        sector_t sector = iomap->blkno +
                (((pos & ~(PAGE_SIZE - 1)) - iomap->offset) >> 9);

        return __dax_zero_page_range(iomap->bdev, sector, 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 = pos & (PAGE_SIZE - 1); /* Within page */
                bytes = min_t(unsigned, 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 blocksize = (1 << inode->i_blkbits);
        unsigned 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;

        ret = __block_write_begin_int(page, pos, length, NULL, iomap);
        if (ret)
                return ret;

        block_commit_write(page, 0, length);
        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 = size & ~PAGE_MASK;
        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;
        }

        set_page_dirty(page);
        wait_for_stable_page(page);
        return 0;
out_unlock:
        unlock_page(page);
        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_UNWRITTEN:
                flags |= FIEMAP_EXTENT_UNWRITTEN;
                break;
        case IOMAP_MAPPED:
                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->blkno != IOMAP_NULL_BLOCK ? iomap->blkno << 9: 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);

/*
 * Private flags for iomap_dio, must not overlap with the public ones in
 * iomap.h:
 */
#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;

        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;
        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 (iocb->ki_pos + ret > dio->i_size &&
                    !(dio->flags & IOMAP_DIO_WRITE))
                        ret = dio->i_size - iocb->ki_pos;
                iocb->ki_pos += 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;
        bool is_write = (dio->flags & IOMAP_DIO_WRITE);
        ssize_t ret;

        ret = iomap_dio_complete(dio);
        if (is_write && ret > 0)
                ret = generic_write_sync(iocb, ret);
        iocb->ki_complete(iocb, ret, 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_error)
                iomap_dio_set_error(dio, bio->bi_error);

        if (atomic_dec_and_test(&dio->ref)) {
                if (is_sync_kiocb(dio->iocb)) {
                        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->bi_bdev = iomap->bdev;
        bio->bi_iter.bi_sector =
                iomap->blkno + ((pos - iomap->offset) >> 9);
        bio->bi_private = dio;
        bio->bi_end_io = iomap_dio_bio_end_io;

        get_page(page);
        if (bio_add_page(bio, page, len, 0) != len)
                BUG();
        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_actor(struct inode *inode, loff_t pos, loff_t length,
                void *data, struct iomap *iomap)
{
        struct iomap_dio *dio = data;
        unsigned blkbits = blksize_bits(bdev_logical_block_size(iomap->bdev));
        unsigned fs_block_size = (1 << inode->i_blkbits), pad;
        unsigned align = iov_iter_alignment(dio->submit.iter);
        struct iov_iter iter;
        struct bio *bio;
        bool need_zeroout = false;
        int nr_pages, ret;

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

        switch (iomap->type) {
        case IOMAP_HOLE:
                if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
                        return -EIO;
                /*FALLTHRU*/
        case IOMAP_UNWRITTEN:
                if (!(dio->flags & IOMAP_DIO_WRITE)) {
                        iov_iter_zero(length, dio->submit.iter);
                        dio->size += length;
                        return length;
                }
                dio->flags |= IOMAP_DIO_UNWRITTEN;
                need_zeroout = true;
                break;
        case IOMAP_MAPPED:
                if (iomap->flags & IOMAP_F_SHARED)
                        dio->flags |= IOMAP_DIO_COW;
                if (iomap->flags & IOMAP_F_NEW)
                        need_zeroout = true;
                break;
        default:
                WARN_ON_ONCE(1);
                return -EIO;
        }

        /*
         * 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 {
                if (dio->error)
                        return 0;

                bio = bio_alloc(GFP_KERNEL, nr_pages);
                bio->bi_bdev = iomap->bdev;
                bio->bi_iter.bi_sector =
                        iomap->blkno + ((pos - iomap->offset) >> 9);
                bio->bi_private = dio;
                bio->bi_end_io = iomap_dio_bio_end_io;

                ret = bio_iov_iter_get_pages(bio, &iter);
                if (unlikely(ret)) {
                        bio_put(bio);
                        return ret;
                }

                if (dio->flags & IOMAP_DIO_WRITE) {
                        bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE);
                        task_io_account_write(bio->bi_iter.bi_size);
                } else {
                        bio_set_op_attrs(bio, REQ_OP_READ, 0);
                        if (dio->flags & IOMAP_DIO_DIRTY)
                                bio_set_pages_dirty(bio);
                }

                dio->size += bio->bi_iter.bi_size;
                pos += bio->bi_iter.bi_size;

                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);

        if (need_zeroout) {
                /* 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);
        }

        iov_iter_advance(dio->submit.iter, length);
        return length;
}

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, end = iocb->ki_pos + count - 1, ret = 0;
        unsigned int flags = IOMAP_DIRECT;
        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;
        if (is_sync_kiocb(iocb)) {
                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 {
                dio->flags |= IOMAP_DIO_WRITE;
                flags |= IOMAP_WRITE;
        }

        if (mapping->nrpages) {
                ret = filemap_write_and_wait_range(mapping, iocb->ki_pos, end);
                if (ret)
                        goto out_free_dio;

                ret = invalidate_inode_pages2_range(mapping,
                                iocb->ki_pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
                WARN_ON_ONCE(ret);
                ret = 0;
        }

        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)
                                ret = 0;
                        break;
                }
                pos += ret;
        } while ((count = iov_iter_count(iter)) > 0);
        blk_finish_plug(&plug);

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

        if (ret >= 0 && iov_iter_rw(iter) == WRITE && !is_sync_kiocb(iocb) &&
                        !inode->i_sb->s_dio_done_wq) {
                ret = sb_init_dio_done_wq(inode->i_sb);
                if (ret < 0)
                        iomap_dio_set_error(dio, ret);
        }

        if (!atomic_dec_and_test(&dio->ref)) {
                if (!is_sync_kiocb(iocb))
                        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_mq_poll(dio->submit.last_queue,
                                         dio->submit.cookie))
                                io_schedule();
                }
                __set_current_state(TASK_RUNNING);
        }

        /*
         * 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...
         */
        if (iov_iter_rw(iter) == WRITE && mapping->nrpages) {
                ret = invalidate_inode_pages2_range(mapping,
                                iocb->ki_pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
                WARN_ON_ONCE(ret);
        }

        return iomap_dio_complete(dio);

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