Re: [PATCH 2/6] iomap: copy the xfs writeback code to iomap.c

[Andreas Gruenbacher <agruenba@redhat.com>]

On Tue, 30 Jul 2019 at 03:18, Darrick J. Wong <darrick.wong@oracle.com> wrote:
> From: Christoph Hellwig <hch@lst.de>
>
> Takes the xfs writeback code and copies it to iomap.c.  A new structure
> with three methods is added as the abstraction from the generic
> writeback code to the file system.  These methods are used to map
> blocks, submit an ioend, and cancel a page that encountered an error
> before it was added to an ioend.
>
> Note that we temporarily lose the writepage tracing, but that will
> be added back soon.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> [darrick: create the new iomap code, we'll delete the xfs code separately]
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/iomap/buffered-io.c |  548 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iomap.h  |   43 ++++
>  2 files changed, 590 insertions(+), 1 deletion(-)
>
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index e25901ae3ff4..ff1f7d2b4d7a 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1,7 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /*
>   * Copyright (C) 2010 Red Hat, Inc.
> - * Copyright (c) 2016-2018 Christoph Hellwig.
> + * Copyright (c) 2016-2019 Christoph Hellwig.
>   */
>  #include <linux/module.h>
>  #include <linux/compiler.h>
> @@ -12,6 +12,7 @@
>  #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>
> @@ -19,6 +20,8 @@
>
>  #include "../internal.h"
>
> +static struct bio_set iomap_ioend_bioset;
> +
>  static struct iomap_page *
>  iomap_page_create(struct inode *inode, struct page *page)
>  {
> @@ -1071,3 +1074,546 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
>         return block_page_mkwrite_return(ret);
>  }
>  EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
> +
> +static void
> +iomap_finish_page_writeback(struct inode *inode, struct bio_vec *bvec,
> +               int error)
> +{
> +       struct iomap_page *iop = to_iomap_page(bvec->bv_page);
> +
> +       if (error) {
> +               SetPageError(bvec->bv_page);
> +               mapping_set_error(inode->i_mapping, -EIO);
> +       }
> +
> +       WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +       WARN_ON_ONCE(iop && atomic_read(&iop->write_count) <= 0);
> +
> +       if (!iop || atomic_dec_and_test(&iop->write_count))
> +               end_page_writeback(bvec->bv_page);
> +}
> +
> +/*
> + * 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 void
> +iomap_finish_ioend(struct iomap_ioend *ioend, int error)
> +{
> +       struct inode *inode = ioend->io_inode;
> +       struct bio *bio = &ioend->io_inline_bio;
> +       struct bio *last = ioend->io_bio, *next;
> +       u64 start = bio->bi_iter.bi_sector;
> +       bool quiet = bio_flagged(bio, BIO_QUIET);
> +
> +       for (bio = &ioend->io_inline_bio; bio; bio = next) {
> +               struct bio_vec  *bvec;
> +               struct bvec_iter_all iter_all;
> +
> +               /*
> +                * For the last bio, bi_private points to the ioend, so we
> +                * need to explicitly end the iteration here.
> +                */
> +               if (bio == last)
> +                       next = NULL;
> +               else
> +                       next = bio->bi_private;
> +
> +               /* walk each page on bio, ending page IO on them */
> +               bio_for_each_segment_all(bvec, bio, iter_all)
> +                       iomap_finish_page_writeback(inode, bvec, error);
> +               bio_put(bio);
> +       }
> +
> +       if (unlikely(error && !quiet)) {
> +               printk_ratelimited(KERN_ERR
> +                       "%s: writeback error on sector %llu",
> +                       inode->i_sb->s_id, start);
> +       }
> +}
> +
> +void
> +iomap_finish_ioends(struct iomap_ioend *ioend, int error)
> +{
> +       struct list_head tmp;
> +
> +       list_replace_init(&ioend->io_list, &tmp);
> +       iomap_finish_ioend(ioend, error);
> +       while ((ioend = list_pop_entry(&tmp, struct iomap_ioend, io_list)))
> +               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;
> +       return true;
> +}
> +
> +void
> +iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends,
> +               void (*merge_private)(struct iomap_ioend *ioend,
> +                               struct iomap_ioend *next))
> +{
> +       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;
> +               if (next->io_private && merge_private)
> +                       merge_private(ioend, next);
> +       }
> +}
> +EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
> +
> +static int
> +iomap_ioend_compare(void *priv, struct list_head *a, struct list_head *b)
> +{
> +       struct iomap_ioend *ia, *ib;
> +
> +       ia = container_of(a, struct iomap_ioend, io_list);
> +       ib = container_of(b, struct iomap_ioend, io_list);
> +       if (ia->io_offset < ib->io_offset)
> +               return -1;
> +       else 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)
> +{
> +       struct iomap_ioend *ioend = bio->bi_private;
> +
> +       iomap_finish_ioend(ioend, blk_status_to_errno(bio->bi_status));
> +}
> +
> +/*
> + * Submit the bio for an ioend. We are passed an ioend with a bio attached to
> + * it, and we submit that bio. The ioend may be used for multiple bio
> + * submissions, so we only want to allocate an append transaction for the ioend
> + * once. In the case of multiple bio submission, each bio will take an IO
> + * reference to the ioend to ensure that the ioend completion is only done once
> + * all bios have been submitted and the ioend is really done.
> + *
> + * If @error is non-zero, it means that we have a situation where some part of
> + * the submission process has failed after we have marked paged for writeback
> + * and unlocked them. In this situation, we need to fail the bio and ioend
> + * rather than submit it to IO. This typically only happens on a filesystem
> + * shutdown.
> + */
> +static int
> +iomap_submit_ioend(struct iomap_writepage_ctx *wpc, struct iomap_ioend *ioend,
> +               int error)
> +{
> +       ioend->io_bio->bi_private = ioend;
> +       ioend->io_bio->bi_end_io = iomap_writepage_end_bio;
> +
> +       /*
> +        * File systems can perform actions at submit time and/or override
> +        * the end_io handler here for complex operations like copy on write
> +        * extent manipulation or unwritten extent conversions.
> +        */
> +       if (wpc->ops->submit_ioend)
> +               error = wpc->ops->submit_ioend(ioend, error);
> +       if (error) {
> +               /*
> +                * If we are failing the IO now, just mark the ioend with an
> +                * error and finish it.  This will run IO completion immediately
> +                * as there is only one reference to the ioend at this point in
> +                * time.
> +                */
> +               ioend->io_bio->bi_status = errno_to_blk_status(error);
> +               bio_endio(ioend->io_bio);
> +               return error;
> +       }
> +
> +       submit_bio(ioend->io_bio);
> +       return 0;
> +}
> +
> +static struct iomap_ioend *
> +iomap_alloc_ioend(struct inode *inode, struct iomap_writepage_ctx *wpc,
> +               loff_t offset, sector_t sector, struct writeback_control *wbc)
> +{
> +       struct iomap_ioend *ioend;
> +       struct bio *bio;
> +
> +       bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, &iomap_ioend_bioset);
> +       bio_set_dev(bio, wpc->iomap.bdev);
> +       bio->bi_iter.bi_sector = sector;
> +       bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
> +       bio->bi_write_hint = inode->i_write_hint;
> +       wbc_init_bio(wbc, bio);
> +
> +       ioend = container_of(bio, struct iomap_ioend, io_inline_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 = offset;
> +       ioend->io_private = NULL;
> +       ioend->io_bio = bio;
> +       return ioend;
> +}
> +
> +/*
> + * Allocate a new bio, and chain the old bio to the new one.
> + *
> + * Note that we have to do perform the chaining in this unintuitive order
> + * so that the bi_private linkage is set up in the right direction for the
> + * traversal in iomap_finish_ioend().
> + */
> +static struct bio *
> +iomap_chain_bio(struct bio *prev)
> +{
> +       struct bio *new;
> +
> +       new = bio_alloc(GFP_NOFS, BIO_MAX_PAGES);
> +       bio_copy_dev(new, prev);/* also copies over blkcg information */
> +       new->bi_iter.bi_sector = bio_end_sector(prev);
> +       new->bi_opf = prev->bi_opf;
> +       new->bi_write_hint = prev->bi_write_hint;
> +
> +       bio_chain(prev, new);
> +       bio_get(prev);          /* for iomap_finish_ioend */
> +       submit_bio(prev);
> +       return new;
> +}
> +
> +/*
> + * 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.
> + */
> +static void
> +iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
> +               struct iomap_page *iop, struct iomap_writepage_ctx *wpc,
> +               struct writeback_control *wbc, struct list_head *iolist)
> +{
> +       sector_t sector = iomap_sector(&wpc->iomap, offset);
> +       unsigned len = i_blocksize(inode);
> +       unsigned poff = offset & (PAGE_SIZE - 1);
> +       bool merged, same_page = false;
> +
> +       if (!wpc->ioend ||
> +           (wpc->iomap.flags & IOMAP_F_SHARED) !=
> +           (wpc->ioend->io_flags & IOMAP_F_SHARED) ||
> +           wpc->iomap.type != wpc->ioend->io_type ||
> +           sector != bio_end_sector(wpc->ioend->io_bio) ||
> +           offset != wpc->ioend->io_offset + wpc->ioend->io_size) {
> +               if (wpc->ioend)
> +                       list_add(&wpc->ioend->io_list, iolist);
> +               wpc->ioend = iomap_alloc_ioend(inode, wpc, offset, sector, wbc);
> +       }
> +
> +       merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
> +                       &same_page);
> +
> +       if (iop && !same_page)
> +               atomic_inc(&iop->write_count);
> +       if (!merged) {
> +               if (bio_full(wpc->ioend->io_bio, len)) {
> +                       wpc->ioend->io_bio =
> +                               iomap_chain_bio(wpc->ioend->io_bio);
> +               }
> +               bio_add_page(wpc->ioend->io_bio, page, len, poff);
> +       }
> +
> +       wpc->ioend->io_size += len;
> +       wbc_account_cgroup_owner(wbc, page, len);
> +}
> +
> +/*
> + * We implement an immediate ioend submission policy here to avoid needing to
> + * chain multiple ioends and hence nest mempool allocations which can violate
> + * forward progress guarantees we need to provide. The current ioend we are
> + * adding blocks to is cached on the writepage context, and if the new block
> + * does not append to the cached ioend it will create a new ioend and cache that
> + * instead.
> + *
> + * If a new ioend is created and cached, the old ioend is returned and queued
> + * locally for submission once the entire page is processed or an error has been
> + * detected.  While ioends are submitted immediately after they are completed,
> + * 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_writepage_map(struct iomap_writepage_ctx *wpc,
> +               struct writeback_control *wbc, struct inode *inode,
> +               struct page *page, u64 end_offset)
> +{
> +       struct iomap_page *iop = to_iomap_page(page);
> +       struct iomap_ioend *ioend, *next;
> +       unsigned len = i_blocksize(inode);
> +       u64 file_offset; /* file offset of page */
> +       int error = 0, count = 0, i;
> +       LIST_HEAD(submit_list);
> +
> +       WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE && !iop);
> +       WARN_ON_ONCE(iop && atomic_read(&iop->write_count) != 0);

How about this instead?

       if (iop)
               WARN_ON_ONCE(atomic_read(&iop->write_count) != 0);
       else
               WARN_ON_ONCE(i_blocksize(inode) < PAGE_SIZE);

> +
> +       /*
> +        * Walk through the page to find areas to write back. If we run off the
> +        * end of the current map or find the current map invalid, grab a new
> +        * one.
> +        */
> +       for (i = 0, file_offset = page_offset(page);
> +            i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
> +            i++, file_offset += len) {
> +               if (iop && !test_bit(i, iop->uptodate))
> +                       continue;
> +
> +               error = wpc->ops->map_blocks(wpc, inode, file_offset);
> +               if (error)
> +                       break;
> +               if (wpc->iomap.type == IOMAP_HOLE)
> +                       continue;
> +               iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
> +                                &submit_list);
> +               count++;
> +       }
> +
> +       WARN_ON_ONCE(!wpc->ioend && !list_empty(&submit_list));
> +       WARN_ON_ONCE(!PageLocked(page));
> +       WARN_ON_ONCE(PageWriteback(page));
> +
> +       /*
> +        * On error, we have to fail the ioend here because we may have set
> +        * pages under writeback, we have to make sure we run IO completion to
> +        * mark the error state of the IO appropriately, so we can't cancel the
> +        * ioend directly here.  That means we have to mark this page as under
> +        * writeback if we included any blocks from it in the ioend chain so
> +        * that completion treats it correctly.
> +        *
> +        * If we didn't include the page in the ioend, the on error we can
> +        * simply discard and unlock it as there are no other users of the page
> +        * now.  The caller will still need to trigger submission of outstanding
> +        * ioends on the writepage context so they are treated correctly on
> +        * error.
> +        */
> +       if (unlikely(error)) {
> +               if (!count) {
> +                       if (wpc->ops->discard_page)
> +                               wpc->ops->discard_page(page);
> +                       ClearPageUptodate(page);
> +                       unlock_page(page);
> +                       goto done;
> +               }
> +
> +               /*
> +                * If the page was not fully cleaned, we need to ensure that the
> +                * higher layers come back to it correctly.  That means we need
> +                * to keep the page dirty, and for WB_SYNC_ALL writeback we need
> +                * to ensure the PAGECACHE_TAG_TOWRITE index mark is not removed
> +                * so another attempt to write this page in this writeback sweep
> +                * will be made.
> +                */
> +               set_page_writeback_keepwrite(page);
> +       } else {
> +               clear_page_dirty_for_io(page);
> +               set_page_writeback(page);
> +       }
> +
> +       unlock_page(page);
> +
> +       /*
> +        * Preserve the original error if there was one, otherwise catch
> +        * submission errors here and propagate into subsequent ioend
> +        * submissions.
> +        */
> +       list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
> +               int error2;
> +
> +               list_del_init(&ioend->io_list);
> +               error2 = iomap_submit_ioend(wpc, ioend, error);
> +               if (error2 && !error)
> +                       error = error2;
> +       }
> +
> +       /*
> +        * We can end up here with no error and nothing to write only if we race
> +        * with a partial page truncate on a sub-page block sized filesystem.
> +        */
> +       if (!count)
> +               end_page_writeback(page);
> +done:
> +       mapping_set_error(page->mapping, error);
> +       return error;
> +}
> +
> +/*
> + * Write out a dirty page.
> + *
> + * For delalloc space on the page we need to allocate space and flush it.
> + * For unwritten space on the page we need to start the conversion to
> + * regular allocated space.
> + */
> +static int
> +iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> +{
> +       struct iomap_writepage_ctx *wpc = data;
> +       struct inode *inode = page->mapping->host;
> +       pgoff_t end_index;
> +       u64 end_offset;
> +       loff_t offset;
> +
> +       /*
> +        * Refuse to write the page out if we are called from reclaim context.
> +        *
> +        * This avoids stack overflows when called from deeply used stacks in
> +        * random callers for direct reclaim or memcg reclaim.  We explicitly
> +        * allow reclaim from kswapd as the stack usage there is relatively low.
> +        *
> +        * This should never happen except in the case of a VM regression so
> +        * warn about it.
> +        */
> +       if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> +                       PF_MEMALLOC))
> +               goto redirty;
> +
> +       /*
> +        * Given that we do not allow direct reclaim to call us, we should
> +        * never be called while in a filesystem transaction.
> +        */
> +       if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> +               goto redirty;
> +
> +       /*
> +        * Is this page beyond the end of the file?
> +        *
> +        * The page index is less than the end_index, adjust the end_offset
> +        * to the highest offset that this page should represent.
> +        * -----------------------------------------------------
> +        * |                    file mapping           | <EOF> |
> +        * -----------------------------------------------------
> +        * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
> +        * ^--------------------------------^----------|--------
> +        * |     desired writeback range    |      see else    |
> +        * ---------------------------------^------------------|
> +        */
> +       offset = i_size_read(inode);
> +       end_index = offset >> PAGE_SHIFT;
> +       if (page->index < end_index)
> +               end_offset = (loff_t)(page->index + 1) << PAGE_SHIFT;
> +       else {
> +               /*
> +                * Check whether the page to write out is beyond or straddles
> +                * i_size or not.
> +                * -------------------------------------------------------
> +                * |            file mapping                    | <EOF>  |
> +                * -------------------------------------------------------
> +                * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
> +                * ^--------------------------------^-----------|---------
> +                * |                                |      Straddles     |
> +                * ---------------------------------^-----------|--------|
> +                */
> +               unsigned offset_into_page = offset & (PAGE_SIZE - 1);
> +
> +               /*
> +                * Skip the page if it is fully outside i_size, e.g. due to a
> +                * truncate operation that is in progress. We must redirty the
> +                * page so that reclaim stops reclaiming it. Otherwise
> +                * iomap_vm_releasepage() is called on it and gets confused.
> +                *
> +                * Note that the end_index is unsigned long, it would overflow
> +                * if the given offset is greater than 16TB on 32-bit system
> +                * and if we do check the page is fully outside i_size or not
> +                * via "if (page->index >= end_index + 1)" as "end_index + 1"
> +                * will be evaluated to 0.  Hence this page will be redirtied
> +                * and be written out repeatedly which would result in an
> +                * infinite loop, the user program that perform this operation
> +                * will hang.  Instead, we can verify this situation by checking
> +                * if the page to write is totally beyond the i_size or if it's
> +                * offset is just equal to the EOF.
> +                */
> +               if (page->index > end_index ||
> +                   (page->index == end_index && offset_into_page == 0))
> +                       goto redirty;
> +
> +               /*
> +                * The page straddles i_size.  It must be zeroed out on each
> +                * and every writepage invocation because it may be mmapped.
> +                * "A file is mapped in multiples of the page size.  For a file
> +                * that is not a multiple of the page size, the remaining
> +                * memory is zeroed when mapped, and writes to that region are
> +                * not written out to the file."
> +                */
> +               zero_user_segment(page, offset_into_page, PAGE_SIZE);
> +
> +               /* Adjust the end_offset to the end of file */
> +               end_offset = offset;
> +       }
> +
> +       return iomap_writepage_map(wpc, wbc, inode, page, end_offset);
> +
> +redirty:
> +       redirty_page_for_writepage(wbc, page);
> +       unlock_page(page);
> +       return 0;
> +}
> +
> +int
> +iomap_writepage(struct page *page, struct writeback_control *wbc,
> +               struct iomap_writepage_ctx *wpc,
> +               const struct iomap_writeback_ops *ops)
> +{
> +       int ret;
> +
> +       wpc->ops = ops;
> +       ret = iomap_do_writepage(page, wbc, wpc);
> +       if (!wpc->ioend)
> +               return ret;
> +       return iomap_submit_ioend(wpc, wpc->ioend, ret);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepage);
> +
> +int
> +iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
> +               struct iomap_writepage_ctx *wpc,
> +               const struct iomap_writeback_ops *ops)
> +{
> +       int                     ret;
> +
> +       wpc->ops = ops;
> +       ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
> +       if (!wpc->ioend)
> +               return ret;
> +       return iomap_submit_ioend(wpc, wpc->ioend, ret);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepages);
> +
> +static int __init iomap_init(void)
> +{
> +       return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> +                          offsetof(struct iomap_ioend, io_inline_bio),
> +                          BIOSET_NEED_BVECS);
> +}
> +fs_initcall(iomap_init);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index bc499ceae392..834d3923e2f2 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -4,6 +4,7 @@
>
>  #include <linux/atomic.h>
>  #include <linux/bitmap.h>
> +#include <linux/blk_types.h>
>  #include <linux/mm.h>
>  #include <linux/types.h>
>  #include <linux/mm_types.h>
> @@ -12,6 +13,7 @@
>  struct address_space;
>  struct fiemap_extent_info;
>  struct inode;
> +struct iomap_writepage_ctx;
>  struct iov_iter;
>  struct kiocb;
>  struct page;
> @@ -183,6 +185,47 @@ loff_t iomap_seek_data(struct inode *inode, loff_t offset,
>  sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
>                 const struct iomap_ops *ops);
>
> +/*
> + * Structure for writeback I/O completions.
> + */
> +struct iomap_ioend {
> +       struct list_head        io_list;        /* next ioend in chain */
> +       u16                     io_type;
> +       u16                     io_flags;       /* IOMAP_F_* */
> +       struct inode            *io_inode;      /* file being written to */
> +       size_t                  io_size;        /* size of the extent */
> +       loff_t                  io_offset;      /* offset in the file */
> +       void                    *io_private;    /* file system private data */
> +       struct bio              *io_bio;        /* bio being built */
> +       struct bio              io_inline_bio;  /* MUST BE LAST! */
> +};
> +
> +struct iomap_writeback_ops {
> +       int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
> +                               loff_t offset);
> +       int (*submit_ioend)(struct iomap_ioend *ioend, int status);
> +       void (*discard_page)(struct page *page);
> +};
> +
> +struct iomap_writepage_ctx {
> +       struct iomap            iomap;
> +       struct iomap_ioend      *ioend;
> +       const struct iomap_writeback_ops *ops;
> +};
> +
> +void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
> +void iomap_ioend_try_merge(struct iomap_ioend *ioend,
> +               struct list_head *more_ioends,
> +               void (*merge_private)(struct iomap_ioend *ioend,
> +                               struct iomap_ioend *next));
> +void iomap_sort_ioends(struct list_head *ioend_list);
> +int iomap_writepage(struct page *page, struct writeback_control *wbc,
> +               struct iomap_writepage_ctx *wpc,
> +               const struct iomap_writeback_ops *ops);
> +int iomap_writepages(struct address_space *mapping,
> +               struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
> +               const struct iomap_writeback_ops *ops);
> +
>  /*
>   * Flags for direct I/O ->end_io:
>   */
>

Andreas