Merge tag 'vfs-6.10.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull netfs updates from Christian Brauner:
 "This reworks the netfslib writeback implementation so that pages read
  from the cache are written to the cache through ->writepages(),
  thereby allowing the fscache page flag to be retired.

  The reworking also:

   - builds on top of the new writeback_iter() infrastructure

   - makes it possible to use vectored write RPCs as discontiguous
     streams of pages can be accommodated

   - makes it easier to do simultaneous content crypto and stream
     division

   - provides support for retrying writes and re-dividing a stream

   - replaces the ->launder_folio() op, so that ->writepages() is used
     instead

   - uses mempools to allocate the netfs_io_request and
     netfs_io_subrequest structs to avoid allocation failure in the
     writeback path

  Some code that uses the fscache page flag is retained for
  compatibility purposes with nfs and ceph. The code is switched to
  using the synonymous private_2 label instead and marked with
  deprecation comments.

  The merge commit contains additional details on the new algorithm that
  I've left out of here as it would probably be excessively detailed.

  On top of the netfslib infrastructure this contains the work to
  convert cifs over to netfslib"

* tag 'vfs-6.10.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (38 commits)
  cifs: Enable large folio support
  cifs: Remove some code that's no longer used, part 3
  cifs: Remove some code that's no longer used, part 2
  cifs: Remove some code that's no longer used, part 1
  cifs: Cut over to using netfslib
  cifs: Implement netfslib hooks
  cifs: Make add_credits_and_wake_if() clear deducted credits
  cifs: Add mempools for cifs_io_request and cifs_io_subrequest structs
  cifs: Set zero_point in the copy_file_range() and remap_file_range()
  cifs: Move cifs_loose_read_iter() and cifs_file_write_iter() to file.c
  cifs: Replace the writedata replay bool with a netfs sreq flag
  cifs: Make wait_mtu_credits take size_t args
  cifs: Use more fields from netfs_io_subrequest
  cifs: Replace cifs_writedata with a wrapper around netfs_io_subrequest
  cifs: Replace cifs_readdata with a wrapper around netfs_io_subrequest
  cifs: Use alternative invalidation to using launder_folio
  netfs, afs: Use writeback retry to deal with alternate keys
  netfs: Miscellaneous tidy ups
  netfs: Remove the old writeback code
  netfs: Cut over to using new writeback code
  ...

1 files changed, 684 insertions, 0 deletions

diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
new file mode 100644
index 000000000000..e190043bc0da
--- /dev/null
+++ b/fs/netfs/write_issue.c
@@ -0,0 +1,684 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Network filesystem high-level (buffered) writeback.
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ *
+ * To support network filesystems with local caching, we manage a situation
+ * that can be envisioned like the following:
+ *
+ *               +---+---+-----+-----+---+----------+
+ *    Folios:    |   |   |     |     |   |          |
+ *               +---+---+-----+-----+---+----------+
+ *
+ *                 +------+------+     +----+----+
+ *    Upload:      |      |      |.....|    |    |
+ *  (Stream 0)     +------+------+     +----+----+
+ *
+ *               +------+------+------+------+------+
+ *    Cache:     |      |      |      |      |      |
+ *  (Stream 1)   +------+------+------+------+------+
+ *
+ * Where we have a sequence of folios of varying sizes that we need to overlay
+ * with multiple parallel streams of I/O requests, where the I/O requests in a
+ * stream may also be of various sizes (in cifs, for example, the sizes are
+ * negotiated with the server; in something like ceph, they may represent the
+ * sizes of storage objects).
+ *
+ * The sequence in each stream may contain gaps and noncontiguous subrequests
+ * may be glued together into single vectored write RPCs.
+ */
+
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include "internal.h"
+
+/*
+ * Kill all dirty folios in the event of an unrecoverable error, starting with
+ * a locked folio we've already obtained from writeback_iter().
+ */
+static void netfs_kill_dirty_pages(struct address_space *mapping,
+				   struct writeback_control *wbc,
+				   struct folio *folio)
+{
+	int error = 0;
+
+	do {
+		enum netfs_folio_trace why = netfs_folio_trace_kill;
+		struct netfs_group *group = NULL;
+		struct netfs_folio *finfo = NULL;
+		void *priv;
+
+		priv = folio_detach_private(folio);
+		if (priv) {
+			finfo = __netfs_folio_info(priv);
+			if (finfo) {
+				/* Kill folio from streaming write. */
+				group = finfo->netfs_group;
+				why = netfs_folio_trace_kill_s;
+			} else {
+				group = priv;
+				if (group == NETFS_FOLIO_COPY_TO_CACHE) {
+					/* Kill copy-to-cache folio */
+					why = netfs_folio_trace_kill_cc;
+					group = NULL;
+				} else {
+					/* Kill folio with group */
+					why = netfs_folio_trace_kill_g;
+				}
+			}
+		}
+
+		trace_netfs_folio(folio, why);
+
+		folio_start_writeback(folio);
+		folio_unlock(folio);
+		folio_end_writeback(folio);
+
+		netfs_put_group(group);
+		kfree(finfo);
+
+	} while ((folio = writeback_iter(mapping, wbc, folio, &error)));
+}
+
+/*
+ * Create a write request and set it up appropriately for the origin type.
+ */
+struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
+						struct file *file,
+						loff_t start,
+						enum netfs_io_origin origin)
+{
+	struct netfs_io_request *wreq;
+	struct netfs_inode *ictx;
+
+	wreq = netfs_alloc_request(mapping, file, start, 0, origin);
+	if (IS_ERR(wreq))
+		return wreq;
+
+	_enter("R=%x", wreq->debug_id);
+
+	ictx = netfs_inode(wreq->inode);
+	if (test_bit(NETFS_RREQ_WRITE_TO_CACHE, &wreq->flags))
+		fscache_begin_write_operation(&wreq->cache_resources, netfs_i_cookie(ictx));
+
+	wreq->contiguity = wreq->start;
+	wreq->cleaned_to = wreq->start;
+	INIT_WORK(&wreq->work, netfs_write_collection_worker);
+
+	wreq->io_streams[0].stream_nr		= 0;
+	wreq->io_streams[0].source		= NETFS_UPLOAD_TO_SERVER;
+	wreq->io_streams[0].prepare_write	= ictx->ops->prepare_write;
+	wreq->io_streams[0].issue_write		= ictx->ops->issue_write;
+	wreq->io_streams[0].collected_to	= start;
+	wreq->io_streams[0].transferred		= LONG_MAX;
+
+	wreq->io_streams[1].stream_nr		= 1;
+	wreq->io_streams[1].source		= NETFS_WRITE_TO_CACHE;
+	wreq->io_streams[1].collected_to	= start;
+	wreq->io_streams[1].transferred		= LONG_MAX;
+	if (fscache_resources_valid(&wreq->cache_resources)) {
+		wreq->io_streams[1].avail	= true;
+		wreq->io_streams[1].prepare_write = wreq->cache_resources.ops->prepare_write_subreq;
+		wreq->io_streams[1].issue_write = wreq->cache_resources.ops->issue_write;
+	}
+
+	return wreq;
+}
+
+/**
+ * netfs_prepare_write_failed - Note write preparation failed
+ * @subreq: The subrequest to mark
+ *
+ * Mark a subrequest to note that preparation for write failed.
+ */
+void netfs_prepare_write_failed(struct netfs_io_subrequest *subreq)
+{
+	__set_bit(NETFS_SREQ_FAILED, &subreq->flags);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prep_failed);
+}
+EXPORT_SYMBOL(netfs_prepare_write_failed);
+
+/*
+ * Prepare a write subrequest.  We need to allocate a new subrequest
+ * if we don't have one.
+ */
+static void netfs_prepare_write(struct netfs_io_request *wreq,
+				struct netfs_io_stream *stream,
+				loff_t start)
+{
+	struct netfs_io_subrequest *subreq;
+
+	subreq = netfs_alloc_subrequest(wreq);
+	subreq->source		= stream->source;
+	subreq->start		= start;
+	subreq->max_len		= ULONG_MAX;
+	subreq->max_nr_segs	= INT_MAX;
+	subreq->stream_nr	= stream->stream_nr;
+
+	_enter("R=%x[%x]", wreq->debug_id, subreq->debug_index);
+
+	trace_netfs_sreq_ref(wreq->debug_id, subreq->debug_index,
+			     refcount_read(&subreq->ref),
+			     netfs_sreq_trace_new);
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+
+	switch (stream->source) {
+	case NETFS_UPLOAD_TO_SERVER:
+		netfs_stat(&netfs_n_wh_upload);
+		subreq->max_len = wreq->wsize;
+		break;
+	case NETFS_WRITE_TO_CACHE:
+		netfs_stat(&netfs_n_wh_write);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	if (stream->prepare_write)
+		stream->prepare_write(subreq);
+
+	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
+
+	/* We add to the end of the list whilst the collector may be walking
+	 * the list.  The collector only goes nextwards and uses the lock to
+	 * remove entries off of the front.
+	 */
+	spin_lock(&wreq->lock);
+	list_add_tail(&subreq->rreq_link, &stream->subrequests);
+	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
+		stream->front = subreq;
+		if (!stream->active) {
+			stream->collected_to = stream->front->start;
+			/* Write list pointers before active flag */
+			smp_store_release(&stream->active, true);
+		}
+	}
+
+	spin_unlock(&wreq->lock);
+
+	stream->construct = subreq;
+}
+
+/*
+ * Set the I/O iterator for the filesystem/cache to use and dispatch the I/O
+ * operation.  The operation may be asynchronous and should call
+ * netfs_write_subrequest_terminated() when complete.
+ */
+static void netfs_do_issue_write(struct netfs_io_stream *stream,
+				 struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *wreq = subreq->rreq;
+
+	_enter("R=%x[%x],%zx", wreq->debug_id, subreq->debug_index, subreq->len);
+
+	if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
+		return netfs_write_subrequest_terminated(subreq, subreq->error, false);
+
+	// TODO: Use encrypted buffer
+	if (test_bit(NETFS_RREQ_USE_IO_ITER, &wreq->flags)) {
+		subreq->io_iter = wreq->io_iter;
+		iov_iter_advance(&subreq->io_iter,
+				 subreq->start + subreq->transferred - wreq->start);
+		iov_iter_truncate(&subreq->io_iter,
+				 subreq->len - subreq->transferred);
+	} else {
+		iov_iter_xarray(&subreq->io_iter, ITER_SOURCE, &wreq->mapping->i_pages,
+				subreq->start + subreq->transferred,
+				subreq->len   - subreq->transferred);
+	}
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+	stream->issue_write(subreq);
+}
+
+void netfs_reissue_write(struct netfs_io_stream *stream,
+			 struct netfs_io_subrequest *subreq)
+{
+	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
+	netfs_do_issue_write(stream, subreq);
+}
+
+static void netfs_issue_write(struct netfs_io_request *wreq,
+			      struct netfs_io_stream *stream)
+{
+	struct netfs_io_subrequest *subreq = stream->construct;
+
+	if (!subreq)
+		return;
+	stream->construct = NULL;
+
+	if (subreq->start + subreq->len > wreq->start + wreq->submitted)
+		wreq->len = wreq->submitted = subreq->start + subreq->len - wreq->start;
+	netfs_do_issue_write(stream, subreq);
+}
+
+/*
+ * Add data to the write subrequest, dispatching each as we fill it up or if it
+ * is discontiguous with the previous.  We only fill one part at a time so that
+ * we can avoid overrunning the credits obtained (cifs) and try to parallelise
+ * content-crypto preparation with network writes.
+ */
+int netfs_advance_write(struct netfs_io_request *wreq,
+			struct netfs_io_stream *stream,
+			loff_t start, size_t len, bool to_eof)
+{
+	struct netfs_io_subrequest *subreq = stream->construct;
+	size_t part;
+
+	if (!stream->avail) {
+		_leave("no write");
+		return len;
+	}
+
+	_enter("R=%x[%x]", wreq->debug_id, subreq ? subreq->debug_index : 0);
+
+	if (subreq && start != subreq->start + subreq->len) {
+		netfs_issue_write(wreq, stream);
+		subreq = NULL;
+	}
+
+	if (!stream->construct)
+		netfs_prepare_write(wreq, stream, start);
+	subreq = stream->construct;
+
+	part = min(subreq->max_len - subreq->len, len);
+	_debug("part %zx/%zx %zx/%zx", subreq->len, subreq->max_len, part, len);
+	subreq->len += part;
+	subreq->nr_segs++;
+
+	if (subreq->len >= subreq->max_len ||
+	    subreq->nr_segs >= subreq->max_nr_segs ||
+	    to_eof) {
+		netfs_issue_write(wreq, stream);
+		subreq = NULL;
+	}
+
+	return part;
+}
+
+/*
+ * Write some of a pending folio data back to the server.
+ */
+static int netfs_write_folio(struct netfs_io_request *wreq,
+			     struct writeback_control *wbc,
+			     struct folio *folio)
+{
+	struct netfs_io_stream *upload = &wreq->io_streams[0];
+	struct netfs_io_stream *cache  = &wreq->io_streams[1];
+	struct netfs_io_stream *stream;
+	struct netfs_group *fgroup; /* TODO: Use this with ceph */
+	struct netfs_folio *finfo;
+	size_t fsize = folio_size(folio), flen = fsize, foff = 0;
+	loff_t fpos = folio_pos(folio), i_size;
+	bool to_eof = false, streamw = false;
+	bool debug = false;
+
+	_enter("");
+
+	/* netfs_perform_write() may shift i_size around the page or from out
+	 * of the page to beyond it, but cannot move i_size into or through the
+	 * page since we have it locked.
+	 */
+	i_size = i_size_read(wreq->inode);
+
+	if (fpos >= i_size) {
+		/* mmap beyond eof. */
+		_debug("beyond eof");
+		folio_start_writeback(folio);
+		folio_unlock(folio);
+		wreq->nr_group_rel += netfs_folio_written_back(folio);
+		netfs_put_group_many(wreq->group, wreq->nr_group_rel);
+		wreq->nr_group_rel = 0;
+		return 0;
+	}
+
+	if (fpos + fsize > wreq->i_size)
+		wreq->i_size = i_size;
+
+	fgroup = netfs_folio_group(folio);
+	finfo = netfs_folio_info(folio);
+	if (finfo) {
+		foff = finfo->dirty_offset;
+		flen = foff + finfo->dirty_len;
+		streamw = true;
+	}
+
+	if (wreq->origin == NETFS_WRITETHROUGH) {
+		to_eof = false;
+		if (flen > i_size - fpos)
+			flen = i_size - fpos;
+	} else if (flen > i_size - fpos) {
+		flen = i_size - fpos;
+		if (!streamw)
+			folio_zero_segment(folio, flen, fsize);
+		to_eof = true;
+	} else if (flen == i_size - fpos) {
+		to_eof = true;
+	}
+	flen -= foff;
+
+	_debug("folio %zx %zx %zx", foff, flen, fsize);
+
+	/* Deal with discontinuities in the stream of dirty pages.  These can
+	 * arise from a number of sources:
+	 *
+	 * (1) Intervening non-dirty pages from random-access writes, multiple
+	 *     flushers writing back different parts simultaneously and manual
+	 *     syncing.
+	 *
+	 * (2) Partially-written pages from write-streaming.
+	 *
+	 * (3) Pages that belong to a different write-back group (eg.  Ceph
+	 *     snapshots).
+	 *
+	 * (4) Actually-clean pages that were marked for write to the cache
+	 *     when they were read.  Note that these appear as a special
+	 *     write-back group.
+	 */
+	if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
+		netfs_issue_write(wreq, upload);
+	} else if (fgroup != wreq->group) {
+		/* We can't write this page to the server yet. */
+		kdebug("wrong group");
+		folio_redirty_for_writepage(wbc, folio);
+		folio_unlock(folio);
+		netfs_issue_write(wreq, upload);
+		netfs_issue_write(wreq, cache);
+		return 0;
+	}
+
+	if (foff > 0)
+		netfs_issue_write(wreq, upload);
+	if (streamw)
+		netfs_issue_write(wreq, cache);
+
+	/* Flip the page to the writeback state and unlock.  If we're called
+	 * from write-through, then the page has already been put into the wb
+	 * state.
+	 */
+	if (wreq->origin == NETFS_WRITEBACK)
+		folio_start_writeback(folio);
+	folio_unlock(folio);
+
+	if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
+		if (!fscache_resources_valid(&wreq->cache_resources)) {
+			trace_netfs_folio(folio, netfs_folio_trace_cancel_copy);
+			netfs_issue_write(wreq, upload);
+			netfs_folio_written_back(folio);
+			return 0;
+		}
+		trace_netfs_folio(folio, netfs_folio_trace_store_copy);
+	} else if (!upload->construct) {
+		trace_netfs_folio(folio, netfs_folio_trace_store);
+	} else {
+		trace_netfs_folio(folio, netfs_folio_trace_store_plus);
+	}
+
+	/* Move the submission point forward to allow for write-streaming data
+	 * not starting at the front of the page.  We don't do write-streaming
+	 * with the cache as the cache requires DIO alignment.
+	 *
+	 * Also skip uploading for data that's been read and just needs copying
+	 * to the cache.
+	 */
+	for (int s = 0; s < NR_IO_STREAMS; s++) {
+		stream = &wreq->io_streams[s];
+		stream->submit_max_len = fsize;
+		stream->submit_off = foff;
+		stream->submit_len = flen;
+		if ((stream->source == NETFS_WRITE_TO_CACHE && streamw) ||
+		    (stream->source == NETFS_UPLOAD_TO_SERVER &&
+		     fgroup == NETFS_FOLIO_COPY_TO_CACHE)) {
+			stream->submit_off = UINT_MAX;
+			stream->submit_len = 0;
+			stream->submit_max_len = 0;
+		}
+	}
+
+	/* Attach the folio to one or more subrequests.  For a big folio, we
+	 * could end up with thousands of subrequests if the wsize is small -
+	 * but we might need to wait during the creation of subrequests for
+	 * network resources (eg. SMB credits).
+	 */
+	for (;;) {
+		ssize_t part;
+		size_t lowest_off = ULONG_MAX;
+		int choose_s = -1;
+
+		/* Always add to the lowest-submitted stream first. */
+		for (int s = 0; s < NR_IO_STREAMS; s++) {
+			stream = &wreq->io_streams[s];
+			if (stream->submit_len > 0 &&
+			    stream->submit_off < lowest_off) {
+				lowest_off = stream->submit_off;
+				choose_s = s;
+			}
+		}
+
+		if (choose_s < 0)
+			break;
+		stream = &wreq->io_streams[choose_s];
+
+		part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
+					   stream->submit_len, to_eof);
+		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
+		stream->submit_off += part;
+		stream->submit_max_len -= part;
+		if (part > stream->submit_len)
+			stream->submit_len = 0;
+		else
+			stream->submit_len -= part;
+		if (part > 0)
+			debug = true;
+	}
+
+	atomic64_set(&wreq->issued_to, fpos + fsize);
+
+	if (!debug)
+		kdebug("R=%x: No submit", wreq->debug_id);
+
+	if (flen < fsize)
+		for (int s = 0; s < NR_IO_STREAMS; s++)
+			netfs_issue_write(wreq, &wreq->io_streams[s]);
+
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * Write some of the pending data back to the server
+ */
+int netfs_writepages(struct address_space *mapping,
+		     struct writeback_control *wbc)
+{
+	struct netfs_inode *ictx = netfs_inode(mapping->host);
+	struct netfs_io_request *wreq = NULL;
+	struct folio *folio;
+	int error = 0;
+
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		mutex_lock(&ictx->wb_lock);
+	else if (!mutex_trylock(&ictx->wb_lock))
+		return 0;
+
+	/* Need the first folio to be able to set up the op. */
+	folio = writeback_iter(mapping, wbc, NULL, &error);
+	if (!folio)
+		goto out;
+
+	wreq = netfs_create_write_req(mapping, NULL, folio_pos(folio), NETFS_WRITEBACK);
+	if (IS_ERR(wreq)) {
+		error = PTR_ERR(wreq);
+		goto couldnt_start;
+	}
+
+	trace_netfs_write(wreq, netfs_write_trace_writeback);
+	netfs_stat(&netfs_n_wh_writepages);
+
+	do {
+		_debug("wbiter %lx %llx", folio->index, wreq->start + wreq->submitted);
+
+		/* It appears we don't have to handle cyclic writeback wrapping. */
+		WARN_ON_ONCE(wreq && folio_pos(folio) < wreq->start + wreq->submitted);
+
+		if (netfs_folio_group(folio) != NETFS_FOLIO_COPY_TO_CACHE &&
+		    unlikely(!test_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))) {
+			set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);
+			wreq->netfs_ops->begin_writeback(wreq);
+		}
+
+		error = netfs_write_folio(wreq, wbc, folio);
+		if (error < 0)
+			break;
+	} while ((folio = writeback_iter(mapping, wbc, folio, &error)));
+
+	for (int s = 0; s < NR_IO_STREAMS; s++)
+		netfs_issue_write(wreq, &wreq->io_streams[s]);
+	smp_wmb(); /* Write lists before ALL_QUEUED. */
+	set_bit(NETFS_RREQ_ALL_QUEUED, &wreq->flags);
+
+	mutex_unlock(&ictx->wb_lock);
+
+	netfs_put_request(wreq, false, netfs_rreq_trace_put_return);
+	_leave(" = %d", error);
+	return error;
+
+couldnt_start:
+	netfs_kill_dirty_pages(mapping, wbc, folio);
+out:
+	mutex_unlock(&ictx->wb_lock);
+	_leave(" = %d", error);
+	return error;
+}
+EXPORT_SYMBOL(netfs_writepages);
+
+/*
+ * Begin a write operation for writing through the pagecache.
+ */
+struct netfs_io_request *netfs_begin_writethrough(struct kiocb *iocb, size_t len)
+{
+	struct netfs_io_request *wreq = NULL;
+	struct netfs_inode *ictx = netfs_inode(file_inode(iocb->ki_filp));
+
+	mutex_lock(&ictx->wb_lock);
+
+	wreq = netfs_create_write_req(iocb->ki_filp->f_mapping, iocb->ki_filp,
+				      iocb->ki_pos, NETFS_WRITETHROUGH);
+	if (IS_ERR(wreq)) {
+		mutex_unlock(&ictx->wb_lock);
+		return wreq;
+	}
+
+	wreq->io_streams[0].avail = true;
+	trace_netfs_write(wreq, netfs_write_trace_writethrough);
+	return wreq;
+}
+
+/*
+ * Advance the state of the write operation used when writing through the
+ * pagecache.  Data has been copied into the pagecache that we need to append
+ * to the request.  If we've added more than wsize then we need to create a new
+ * subrequest.
+ */
+int netfs_advance_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
+			       struct folio *folio, size_t copied, bool to_page_end,
+			       struct folio **writethrough_cache)
+{
+	_enter("R=%x ic=%zu ws=%u cp=%zu tp=%u",
+	       wreq->debug_id, wreq->iter.count, wreq->wsize, copied, to_page_end);
+
+	if (!*writethrough_cache) {
+		if (folio_test_dirty(folio))
+			/* Sigh.  mmap. */
+			folio_clear_dirty_for_io(folio);
+
+		/* We can make multiple writes to the folio... */
+		folio_start_writeback(folio);
+		if (wreq->len == 0)
+			trace_netfs_folio(folio, netfs_folio_trace_wthru);
+		else
+			trace_netfs_folio(folio, netfs_folio_trace_wthru_plus);
+		*writethrough_cache = folio;
+	}
+
+	wreq->len += copied;
+	if (!to_page_end)
+		return 0;
+
+	*writethrough_cache = NULL;
+	return netfs_write_folio(wreq, wbc, folio);
+}
+
+/*
+ * End a write operation used when writing through the pagecache.
+ */
+int netfs_end_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
+			   struct folio *writethrough_cache)
+{
+	struct netfs_inode *ictx = netfs_inode(wreq->inode);
+	int ret;
+
+	_enter("R=%x", wreq->debug_id);
+
+	if (writethrough_cache)
+		netfs_write_folio(wreq, wbc, writethrough_cache);
+
+	netfs_issue_write(wreq, &wreq->io_streams[0]);
+	netfs_issue_write(wreq, &wreq->io_streams[1]);
+	smp_wmb(); /* Write lists before ALL_QUEUED. */
+	set_bit(NETFS_RREQ_ALL_QUEUED, &wreq->flags);
+
+	mutex_unlock(&ictx->wb_lock);
+
+	ret = wreq->error;
+	netfs_put_request(wreq, false, netfs_rreq_trace_put_return);
+	return ret;
+}
+
+/*
+ * Write data to the server without going through the pagecache and without
+ * writing it to the local cache.
+ */
+int netfs_unbuffered_write(struct netfs_io_request *wreq, bool may_wait, size_t len)
+{
+	struct netfs_io_stream *upload = &wreq->io_streams[0];
+	ssize_t part;
+	loff_t start = wreq->start;
+	int error = 0;
+
+	_enter("%zx", len);
+
+	if (wreq->origin == NETFS_DIO_WRITE)
+		inode_dio_begin(wreq->inode);
+
+	while (len) {
+		// TODO: Prepare content encryption
+
+		_debug("unbuffered %zx", len);
+		part = netfs_advance_write(wreq, upload, start, len, false);
+		start += part;
+		len -= part;
+		if (test_bit(NETFS_RREQ_PAUSE, &wreq->flags)) {
+			trace_netfs_rreq(wreq, netfs_rreq_trace_wait_pause);
+			wait_on_bit(&wreq->flags, NETFS_RREQ_PAUSE, TASK_UNINTERRUPTIBLE);
+		}
+		if (test_bit(NETFS_RREQ_FAILED, &wreq->flags))
+			break;
+	}
+
+	netfs_issue_write(wreq, upload);
+
+	smp_wmb(); /* Write lists before ALL_QUEUED. */
+	set_bit(NETFS_RREQ_ALL_QUEUED, &wreq->flags);
+	if (list_empty(&upload->subrequests))
+		netfs_wake_write_collector(wreq, false);
+
+	_leave(" = %d", error);
+	return error;
+}