Merge tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linuxgrafted

Pull I3C updates from Alexandre Belloni:
 "A new driver this cycle, for the AMD AXI I3C controller.

  There are also new features such as IBI wakeup support, SETAASA device
  discovery and ACPI support for the the DAA methods, meaning we can now
  communicate with the SPD devices on DDR5 modules.

  New driver:
   - AMD AXI I3C master controller

  Subsystem:
   - I3C Common Command Code (CCC) handling improvements, especially
     around GET CCCs
   - SETAASA device discovery support
   - ACPI support for all existing DAA methods like SETDASA, SETNEWDA as
     well as I2C devices on I3C bus
   - IBI-based wakeup support

  Drivers:
   - dw: SETAASA support
   - mipi-i3c-hci: advertise IBI wakeup capability, AMD_PT I3C
     controller support, PIO queue management support for HCI v1.2
   - renesas: improve suspend to RAM support, add runtime PM support"

* tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux: (70 commits)
  i3c: dw: reduce do_daa time if there's no client
  i3c: mipi-i3c-hci: Add support for AMD_PT I3C controller
  i3c: mipi-i3c-hci: Add PIO queue management support for HCI v1.2
  i3c: mipi-i3c-hci: Fix missing STAT_IBI_STATUS_THLD in PIO mode
  i3c: dw: rename "pclk" to "apb" to match dt-binding
  i3c: dw: make struct dw_i3c_cmd smaller
  i3c: dw: use COMMAND_PORT_TRANSFER_ARG instead of hardcoding
  i3c: renesas: Don't register devices when ENTDAA times out
  i3c: master: dw-i3c-master: fix OD timing for first broadcast
  i3c: mipi-i3c-hci: Advertise IBI wakeup capability
  i3c: mipi-i3c-hci: Factor out i3c_hci_sysdev()
  i3c: mipi-i3c-hci-pci: Propagate I3C wakeup requirements to PCI
  i3c: master: Reject IBI requests from non-IBI-capable devices
  i3c: master: Add helper to query bus wakeup requirements
  i3c: master: Report wakeup events for IBIs
  i3c: master: Support IBI-based wakeup capability
  i3c: master: Fix potential UAF in i3c_device_match()
  i3c: master: Fix potential UAF in i3c_device_uevent()
  i3c: Make dev->desc locking assumptions explicit
  i3c: master: Fix use-after-free of master->this
  ...

1 files changed, 840 insertions, 0 deletions

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
new file mode 100644
index 000000000..7fdfa4f27
--- /dev/null
+++ b/fs/netfs/buffered_read.c
@@ -0,0 +1,840 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Network filesystem high-level buffered read support.
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/task_io_accounting_ops.h>
+#include "internal.h"
+
+static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
+					 unsigned long long *_start,
+					 unsigned long long *_len,
+					 unsigned long long i_size)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	if (cres->ops && cres->ops->expand_readahead)
+		cres->ops->expand_readahead(cres, _start, _len, i_size);
+}
+
+static void netfs_rreq_expand(struct netfs_io_request *rreq,
+			      struct readahead_control *ractl)
+{
+	/* Give the cache a chance to change the request parameters.  The
+	 * resultant request must contain the original region.
+	 */
+	netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
+
+	/* Give the netfs a chance to change the request parameters.  The
+	 * resultant request must contain the original region.
+	 */
+	if (rreq->netfs_ops->expand_readahead)
+		rreq->netfs_ops->expand_readahead(rreq);
+
+	/* Expand the request if the cache wants it to start earlier.  Note
+	 * that the expansion may get further extended if the VM wishes to
+	 * insert THPs and the preferred start and/or end wind up in the middle
+	 * of THPs.
+	 *
+	 * If this is the case, however, the THP size should be an integer
+	 * multiple of the cache granule size, so we get a whole number of
+	 * granules to deal with.
+	 */
+	if (rreq->start  != readahead_pos(ractl) ||
+	    rreq->len != readahead_length(ractl)) {
+		readahead_expand(ractl, rreq->start, rreq->len);
+		rreq->start  = readahead_pos(ractl);
+		rreq->len = readahead_length(ractl);
+
+		trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+				 netfs_read_trace_expanded);
+	}
+}
+
+/*
+ * Begin an operation, and fetch the stored zero point value from the cookie if
+ * available.
+ */
+static int netfs_begin_cache_read(struct netfs_io_request *rreq, struct netfs_inode *ctx)
+{
+	return fscache_begin_read_operation(&rreq->cache_resources, netfs_i_cookie(ctx));
+}
+
+/*
+ * netfs_prepare_read_iterator - Prepare the subreq iterator for I/O
+ * @subreq: The subrequest to be set up
+ *
+ * Prepare the I/O iterator representing the read buffer on a subrequest for
+ * the filesystem to use for I/O (it can be passed directly to a socket).  This
+ * is intended to be called from the ->issue_read() method once the filesystem
+ * has trimmed the request to the size it wants.
+ *
+ * Returns the limited size if successful and -ENOMEM if insufficient memory
+ * available.
+ *
+ * [!] NOTE: This must be run in the same thread as ->issue_read() was called
+ * in as we access the readahead_control struct.
+ */
+static ssize_t netfs_prepare_read_iterator(struct netfs_io_subrequest *subreq,
+					   struct readahead_control *ractl)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+	size_t rsize = subreq->len;
+
+	if (subreq->source == NETFS_DOWNLOAD_FROM_SERVER)
+		rsize = umin(rsize, rreq->io_streams[0].sreq_max_len);
+
+	if (ractl) {
+		/* If we don't have sufficient folios in the rolling buffer,
+		 * extract a folioq's worth from the readahead region at a time
+		 * into the buffer.  Note that this acquires a ref on each page
+		 * that we will need to release later - but we don't want to do
+		 * that until after we've started the I/O.
+		 */
+		struct folio_batch put_batch;
+
+		folio_batch_init(&put_batch);
+		while (rreq->submitted < subreq->start + rsize) {
+			ssize_t added;
+
+			added = rolling_buffer_load_from_ra(&rreq->buffer, ractl,
+							    &put_batch);
+			if (added < 0) {
+				folio_batch_release(&put_batch);
+				return added;
+			}
+			rreq->submitted += added;
+		}
+		folio_batch_release(&put_batch);
+	}
+
+	subreq->len = rsize;
+	if (unlikely(rreq->io_streams[0].sreq_max_segs)) {
+		size_t limit = netfs_limit_iter(&rreq->buffer.iter, 0, rsize,
+						rreq->io_streams[0].sreq_max_segs);
+
+		if (limit < rsize) {
+			subreq->len = limit;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
+		}
+	}
+
+	subreq->io_iter	= rreq->buffer.iter;
+
+	iov_iter_truncate(&subreq->io_iter, subreq->len);
+	rolling_buffer_advance(&rreq->buffer, subreq->len);
+	return subreq->len;
+}
+
+static enum netfs_io_source netfs_cache_prepare_read(struct netfs_io_request *rreq,
+						     struct netfs_io_subrequest *subreq,
+						     loff_t i_size)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+	enum netfs_io_source source;
+
+	if (!cres->ops)
+		return NETFS_DOWNLOAD_FROM_SERVER;
+	source = cres->ops->prepare_read(subreq, i_size);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+	return source;
+
+}
+
+/*
+ * Issue a read against the cache.
+ * - Eats the caller's ref on subreq.
+ */
+static void netfs_read_cache_to_pagecache(struct netfs_io_request *rreq,
+					  struct netfs_io_subrequest *subreq)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	netfs_stat(&netfs_n_rh_read);
+	cres->ops->read(cres, subreq->start, &subreq->io_iter, NETFS_READ_HOLE_IGNORE,
+			netfs_cache_read_terminated, subreq);
+}
+
+void netfs_queue_read(struct netfs_io_request *rreq,
+		      struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_stream *stream = &rreq->io_streams[0];
+
+	__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(&rreq->lock);
+	/* Write IN_PROGRESS before pointer to new subreq */
+	list_add_tail_release(&subreq->rreq_link, &stream->subrequests);
+	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
+		if (!stream->active) {
+			stream->collected_to = subreq->start;
+			/* Store list pointers before active flag */
+			smp_store_release(&stream->active, true);
+		}
+	}
+
+	spin_unlock(&rreq->lock);
+}
+
+static void netfs_issue_read(struct netfs_io_request *rreq,
+			     struct netfs_io_subrequest *subreq)
+{
+	switch (subreq->source) {
+	case NETFS_DOWNLOAD_FROM_SERVER:
+		rreq->netfs_ops->issue_read(subreq);
+		break;
+	case NETFS_READ_FROM_CACHE:
+		netfs_read_cache_to_pagecache(rreq, subreq);
+		break;
+	default:
+		__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
+		subreq->error = 0;
+		iov_iter_zero(subreq->len, &subreq->io_iter);
+		subreq->transferred = subreq->len;
+		netfs_read_subreq_terminated(subreq);
+		break;
+	}
+}
+
+/*
+ * Perform a read to the pagecache from a series of sources of different types,
+ * slicing up the region to be read according to available cache blocks and
+ * network rsize.
+ */
+static void netfs_read_to_pagecache(struct netfs_io_request *rreq,
+				    struct readahead_control *ractl)
+{
+	unsigned long long start = rreq->start;
+	ssize_t size = rreq->len;
+	int ret = 0;
+
+	do {
+		struct netfs_io_subrequest *subreq;
+		enum netfs_io_source source = NETFS_SOURCE_UNKNOWN;
+		ssize_t slice;
+
+		subreq = netfs_alloc_subrequest(rreq);
+		if (!subreq) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		subreq->start	= start;
+		subreq->len	= size;
+
+		netfs_queue_read(rreq, subreq);
+
+		source = netfs_cache_prepare_read(rreq, subreq, rreq->i_size);
+		subreq->source = source;
+		if (source == NETFS_DOWNLOAD_FROM_SERVER) {
+			unsigned long long zero_point = netfs_read_zero_point(rreq->inode);
+			unsigned long long zp = umin(zero_point, rreq->i_size);
+			size_t len = subreq->len;
+
+			if (unlikely(rreq->origin == NETFS_READ_SINGLE))
+				zp = rreq->i_size;
+			if (subreq->start >= zp) {
+				subreq->source = source = NETFS_FILL_WITH_ZEROES;
+				goto fill_with_zeroes;
+			}
+
+			if (len > zp - subreq->start)
+				len = zp - subreq->start;
+			if (len == 0) {
+				pr_err("ZERO-LEN READ: R=%08x[%x] l=%zx/%zx s=%llx z=%llx i=%llx",
+				       rreq->debug_id, subreq->debug_index,
+				       subreq->len, size,
+				       subreq->start, zero_point, rreq->i_size);
+				netfs_cancel_read(subreq, ret);
+				break;
+			}
+			subreq->len = len;
+
+			netfs_stat(&netfs_n_rh_download);
+			if (rreq->netfs_ops->prepare_read) {
+				ret = rreq->netfs_ops->prepare_read(subreq);
+				if (ret < 0) {
+					netfs_cancel_read(subreq, ret);
+					break;
+				}
+				trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+			}
+			goto issue;
+		}
+
+	fill_with_zeroes:
+		if (source == NETFS_FILL_WITH_ZEROES) {
+			subreq->source = NETFS_FILL_WITH_ZEROES;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+			netfs_stat(&netfs_n_rh_zero);
+			goto issue;
+		}
+
+		if (source == NETFS_READ_FROM_CACHE) {
+			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+			goto issue;
+		}
+
+		pr_err("Unexpected read source %u\n", source);
+		WARN_ON_ONCE(1);
+		netfs_cancel_read(subreq, ret);
+		break;
+
+	issue:
+		slice = netfs_prepare_read_iterator(subreq, ractl);
+		if (slice < 0) {
+			ret = slice;
+			netfs_cancel_read(subreq, ret);
+			break;
+		}
+		start += slice;
+		size -= slice;
+		if (size <= 0) {
+			smp_wmb(); /* Write lists before ALL_QUEUED. */
+			set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
+		}
+
+		netfs_issue_read(rreq, subreq);
+
+		if (test_bit(NETFS_RREQ_PAUSE, &rreq->flags))
+			netfs_wait_for_paused_read(rreq);
+		if (test_bit(NETFS_RREQ_FAILED, &rreq->flags))
+			break;
+		cond_resched();
+	} while (size > 0);
+
+	if (unlikely(size > 0)) {
+		smp_wmb(); /* Write lists before ALL_QUEUED. */
+		set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
+		netfs_wake_collector(rreq);
+	}
+
+	/* Defer error return as we may need to wait for outstanding I/O. */
+	cmpxchg(&rreq->error, 0, ret);
+}
+
+/**
+ * netfs_readahead - Helper to manage a read request
+ * @ractl: The description of the readahead request
+ *
+ * Fulfil a readahead request by drawing data from the cache if possible, or
+ * the netfs if not.  Space beyond the EOF is zero-filled.  Multiple I/O
+ * requests from different sources will get munged together.  If necessary, the
+ * readahead window can be expanded in either direction to a more convenient
+ * alighment for RPC efficiency or to make storage in the cache feasible.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+void netfs_readahead(struct readahead_control *ractl)
+{
+	struct netfs_io_request *rreq;
+	struct netfs_inode *ictx = netfs_inode(ractl->mapping->host);
+	unsigned long long start = readahead_pos(ractl);
+	size_t size = readahead_length(ractl);
+	int ret;
+
+	rreq = netfs_alloc_request(ractl->mapping, ractl->file, start, size,
+				   NETFS_READAHEAD);
+	if (IS_ERR(rreq))
+		return;
+
+	__set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags);
+
+	ret = netfs_begin_cache_read(rreq, ictx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto cleanup_free;
+
+	netfs_stat(&netfs_n_rh_readahead);
+	trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+			 netfs_read_trace_readahead);
+
+	netfs_rreq_expand(rreq, ractl);
+
+	rreq->submitted = rreq->start;
+	if (rolling_buffer_init(&rreq->buffer, rreq->debug_id, ITER_DEST, rreq->gfp) < 0)
+		goto cleanup_free;
+	netfs_read_to_pagecache(rreq, ractl);
+
+	return netfs_put_request(rreq, netfs_rreq_trace_put_return);
+
+cleanup_free:
+	return netfs_put_failed_request(rreq);
+}
+EXPORT_SYMBOL(netfs_readahead);
+
+/*
+ * Create a rolling buffer with a single occupying folio.
+ */
+static int netfs_create_singular_buffer(struct netfs_io_request *rreq, struct folio *folio,
+					unsigned int rollbuf_flags)
+{
+	ssize_t added;
+
+	if (rolling_buffer_init(&rreq->buffer, rreq->debug_id, ITER_DEST, rreq->gfp) < 0)
+		return -ENOMEM;
+
+	added = rolling_buffer_append(&rreq->buffer, folio, rollbuf_flags, rreq->gfp);
+	if (added < 0)
+		return added;
+	rreq->submitted = rreq->start + added;
+	return 0;
+}
+
+/*
+ * Read into gaps in a folio partially filled by a streaming write.
+ */
+static int netfs_read_gaps(struct file *file, struct folio *folio)
+{
+	struct netfs_io_request *rreq;
+	struct address_space *mapping = folio->mapping;
+	struct netfs_group *group = netfs_folio_group(folio);
+	struct netfs_folio *finfo = netfs_folio_info(folio);
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	struct folio *sink = NULL;
+	struct bio_vec *bvec;
+	unsigned int from = finfo->dirty_offset;
+	unsigned int to = from + finfo->dirty_len;
+	unsigned int off = 0, i = 0;
+	size_t flen = folio_size(folio);
+	size_t nr_bvec = flen / PAGE_SIZE + 2;
+	size_t part;
+	int ret;
+
+	_enter("%lx", folio->index);
+
+	rreq = netfs_alloc_request(mapping, file, folio_pos(folio), flen, NETFS_READ_GAPS);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto alloc_error;
+	}
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto discard;
+
+	netfs_stat(&netfs_n_rh_read_folio);
+	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_read_gaps);
+
+	/* Fiddle the buffer so that a gap at the beginning and/or a gap at the
+	 * end get copied to, but the middle is discarded.
+	 */
+	ret = -ENOMEM;
+	bvec = kmalloc_objs(*bvec, nr_bvec);
+	if (!bvec)
+		goto discard;
+
+	sink = folio_alloc(GFP_KERNEL, 0);
+	if (!sink) {
+		kfree(bvec);
+		goto discard;
+	}
+
+	trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
+
+	rreq->direct_bv = bvec;
+	rreq->direct_bv_count = nr_bvec;
+	if (from > 0) {
+		bvec_set_folio(&bvec[i++], folio, from, 0);
+		off = from;
+	}
+	while (off < to) {
+		part = min_t(size_t, to - off, PAGE_SIZE);
+		bvec_set_folio(&bvec[i++], sink, part, 0);
+		off += part;
+	}
+	if (to < flen)
+		bvec_set_folio(&bvec[i++], folio, flen - to, to);
+	iov_iter_bvec(&rreq->buffer.iter, ITER_DEST, bvec, i, rreq->len);
+	rreq->submitted = rreq->start + flen;
+
+	netfs_read_to_pagecache(rreq, NULL);
+
+	ret = netfs_wait_for_read(rreq);
+	if (ret >= 0) {
+		if (group)
+			folio_change_private(folio, group);
+		else
+			folio_detach_private(folio);
+		kfree(finfo);
+		trace_netfs_folio(folio, netfs_folio_trace_filled_gaps);
+		flush_dcache_folio(folio);
+		folio_mark_uptodate(folio);
+	}
+
+	if (sink)
+		folio_put(sink);
+	folio_unlock(folio);
+	netfs_put_request(rreq, netfs_rreq_trace_put_return);
+	return ret < 0 ? ret : 0;
+
+discard:
+	netfs_put_failed_request(rreq);
+alloc_error:
+	folio_unlock(folio);
+	return ret;
+}
+
+/**
+ * netfs_read_folio - Helper to manage a read_folio request
+ * @file: The file to read from
+ * @folio: The folio to read
+ *
+ * Fulfil a read_folio request by drawing data from the cache if
+ * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
+ * Multiple I/O requests from different sources will get munged together.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_read_folio(struct file *file, struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+	struct netfs_io_request *rreq;
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	int ret;
+
+	folio_wait_writeback(folio);
+
+	if (folio_test_dirty(folio))
+		return netfs_read_gaps(file, folio);
+
+	_enter("%lx", folio->index);
+
+	rreq = netfs_alloc_request(mapping, file,
+				   folio_pos(folio), folio_size(folio),
+				   NETFS_READPAGE);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto alloc_error;
+	}
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto discard;
+
+	netfs_stat(&netfs_n_rh_read_folio);
+	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
+
+	/* Set up the output buffer */
+	ret = netfs_create_singular_buffer(rreq, folio, 0);
+	if (ret < 0)
+		goto discard;
+
+	netfs_read_to_pagecache(rreq, NULL);
+	ret = netfs_wait_for_read(rreq);
+	netfs_put_request(rreq, netfs_rreq_trace_put_return);
+	return ret < 0 ? ret : 0;
+
+discard:
+	netfs_put_failed_request(rreq);
+alloc_error:
+	folio_unlock(folio);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_read_folio);
+
+/*
+ * Prepare a folio for writing without reading first
+ * @folio: The folio being prepared
+ * @pos: starting position for the write
+ * @len: length of write
+ * @always_fill: T if the folio should always be completely filled/cleared
+ *
+ * In some cases, write_begin doesn't need to read at all:
+ * - full folio write
+ * - write that lies in a folio that is completely beyond EOF
+ * - write that covers the folio from start to EOF or beyond it
+ *
+ * If any of these criteria are met, then zero out the unwritten parts
+ * of the folio and return true. Otherwise, return false.
+ */
+static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
+				 bool always_fill)
+{
+	struct inode *inode = folio_inode(folio);
+	loff_t i_size = i_size_read(inode);
+	size_t offset = offset_in_folio(folio, pos);
+	size_t plen = folio_size(folio);
+
+	if (unlikely(always_fill)) {
+		if (pos - offset + len <= i_size)
+			return false; /* Page entirely before EOF */
+		folio_zero_segment(folio, 0, plen);
+		folio_mark_uptodate(folio);
+		return true;
+	}
+
+	/* Full folio write */
+	if (offset == 0 && len >= plen)
+		return true;
+
+	/* Page entirely beyond the end of the file */
+	if (pos - offset >= i_size)
+		goto zero_out;
+
+	/* Write that covers from the start of the folio to EOF or beyond */
+	if (offset == 0 && (pos + len) >= i_size)
+		goto zero_out;
+
+	return false;
+zero_out:
+	folio_zero_segments(folio, 0, offset, offset + len, plen);
+	return true;
+}
+
+/**
+ * netfs_write_begin - Helper to prepare for writing [DEPRECATED]
+ * @ctx: The netfs context
+ * @file: The file to read from
+ * @mapping: The mapping to read from
+ * @pos: File position at which the write will begin
+ * @len: The length of the write (may extend beyond the end of the folio chosen)
+ * @_folio: Where to put the resultant folio
+ * @_fsdata: Place for the netfs to store a cookie
+ *
+ * Pre-read data for a write-begin request by drawing data from the cache if
+ * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
+ * Multiple I/O requests from different sources will get munged together.
+ *
+ * The calling netfs must provide a table of operations, only one of which,
+ * issue_read, is mandatory.
+ *
+ * The check_write_begin() operation can be provided to check for and flush
+ * conflicting writes once the folio is grabbed and locked.  It is passed a
+ * pointer to the fsdata cookie that gets returned to the VM to be passed to
+ * write_end.  It is permitted to sleep.  It should return 0 if the request
+ * should go ahead or it may return an error.  It may also unlock and put the
+ * folio, provided it sets ``*foliop`` to NULL, in which case a return of 0
+ * will cause the folio to be re-got and the process to be retried.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ *
+ * Note that this should be considered deprecated and netfs_perform_write()
+ * used instead.
+ */
+int netfs_write_begin(struct netfs_inode *ctx,
+		      struct file *file, struct address_space *mapping,
+		      loff_t pos, unsigned int len, struct folio **_folio,
+		      void **_fsdata)
+{
+	struct netfs_io_request *rreq;
+	struct folio *folio;
+	pgoff_t index = pos >> PAGE_SHIFT;
+	int ret;
+
+retry:
+	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+				    mapping_gfp_mask(mapping));
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
+
+	if (ctx->ops->check_write_begin) {
+		/* Allow the netfs (eg. ceph) to flush conflicts. */
+		ret = ctx->ops->check_write_begin(file, pos, len, &folio, _fsdata);
+		if (ret < 0) {
+			trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
+			goto error;
+		}
+		if (!folio)
+			goto retry;
+	}
+
+	if (folio_test_uptodate(folio))
+		goto have_folio;
+
+	/* If the folio is beyond the EOF, we want to clear it - unless it's
+	 * within the cache granule containing the EOF, in which case we need
+	 * to preload the granule.
+	 */
+	if (!netfs_is_cache_maybe_enabled(ctx) &&
+	    netfs_skip_folio_read(folio, pos, len, false)) {
+		netfs_stat(&netfs_n_rh_write_zskip);
+		goto have_folio_no_wait;
+	}
+
+	rreq = netfs_alloc_request(mapping, file,
+				   folio_pos(folio), folio_size(folio),
+				   NETFS_READ_FOR_WRITE);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto error;
+	}
+	rreq->no_unlock_folio	= folio;
+	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto error_put;
+
+	netfs_stat(&netfs_n_rh_write_begin);
+	trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
+
+	/* Set up the output buffer */
+	ret = netfs_create_singular_buffer(rreq, folio, 0);
+	if (ret < 0)
+		goto error_put;
+
+	netfs_read_to_pagecache(rreq, NULL);
+	ret = netfs_wait_for_read(rreq);
+	netfs_put_request(rreq, netfs_rreq_trace_put_return);
+	if (ret < 0)
+		goto error;
+
+have_folio:
+	ret = folio_wait_private_2_killable(folio);
+	if (ret < 0)
+		goto error;
+have_folio_no_wait:
+	*_folio = folio;
+	_leave(" = 0");
+	return 0;
+
+error_put:
+	netfs_put_failed_request(rreq);
+error:
+	if (folio) {
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+	_leave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_write_begin);
+
+/*
+ * Preload the data into a folio we're proposing to write into.
+ */
+int netfs_prefetch_for_write(struct file *file, struct folio *folio,
+			     size_t offset, size_t len)
+{
+	struct netfs_io_request *rreq;
+	struct address_space *mapping = folio->mapping;
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	unsigned long long start = folio_pos(folio);
+	size_t flen = folio_size(folio);
+	int ret;
+
+	_enter("%zx @%llx", flen, start);
+
+	ret = -ENOMEM;
+
+	rreq = netfs_alloc_request(mapping, file, start, flen,
+				   NETFS_READ_FOR_WRITE);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto error;
+	}
+
+	rreq->no_unlock_folio = folio;
+	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto error_put;
+
+	netfs_stat(&netfs_n_rh_write_begin);
+	trace_netfs_read(rreq, start, flen, netfs_read_trace_prefetch_for_write);
+
+	/* Set up the output buffer */
+	ret = netfs_create_singular_buffer(rreq, folio, NETFS_ROLLBUF_PAGECACHE_MARK);
+	if (ret < 0)
+		goto error_put;
+
+	netfs_read_to_pagecache(rreq, NULL);
+	ret = netfs_wait_for_read(rreq);
+	netfs_put_request(rreq, netfs_rreq_trace_put_return);
+	return ret < 0 ? ret : 0;
+
+error_put:
+	netfs_put_failed_request(rreq);
+error:
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/**
+ * netfs_buffered_read_iter - Filesystem buffered I/O read routine
+ * @iocb: kernel I/O control block
+ * @iter: destination for the data read
+ *
+ * This is the ->read_iter() routine for all filesystems that can use the page
+ * cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall be
+ * returned when no data can be read without waiting for I/O requests to
+ * complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O requests
+ * shall be made for the read or for readahead.  When no data can be read,
+ * -EAGAIN shall be returned.  When readahead would be triggered, a partial,
+ * possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t netfs_buffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct netfs_inode *ictx = netfs_inode(inode);
+	ssize_t ret;
+
+	if (WARN_ON_ONCE((iocb->ki_flags & IOCB_DIRECT) ||
+			 test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags)))
+		return -EINVAL;
+
+	ret = netfs_start_io_read(inode);
+	if (ret == 0) {
+		ret = filemap_read(iocb, iter, 0);
+		netfs_end_io_read(inode);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(netfs_buffered_read_iter);
+
+/**
+ * netfs_file_read_iter - Generic filesystem read routine
+ * @iocb: kernel I/O control block
+ * @iter: destination for the data read
+ *
+ * This is the ->read_iter() routine for all filesystems that can use the page
+ * cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall be
+ * returned when no data can be read without waiting for I/O requests to
+ * complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O requests
+ * shall be made for the read or for readahead.  When no data can be read,
+ * -EAGAIN shall be returned.  When readahead would be triggered, a partial,
+ * possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct netfs_inode *ictx = netfs_inode(iocb->ki_filp->f_mapping->host);
+
+	if ((iocb->ki_flags & IOCB_DIRECT) ||
+	    test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags))
+		return netfs_unbuffered_read_iter(iocb, iter);
+
+	return netfs_buffered_read_iter(iocb, iter);
+}
+EXPORT_SYMBOL(netfs_file_read_iter);