[linux-block.git] / fs / netfs / buffered_read.c

// 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"

/*
 * Unlock the folios in a read operation.  We need to set PG_fscache on any
 * folios we're going to write back before we unlock them.
 */
void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
{
	struct netfs_io_subrequest *subreq;
	struct folio *folio;
	pgoff_t start_page = rreq->start / PAGE_SIZE;
	pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
	size_t account = 0;
	bool subreq_failed = false;

	XA_STATE(xas, &rreq->mapping->i_pages, start_page);

	if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
		__clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
		list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
			__clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
		}
	}

	/* Walk through the pagecache and the I/O request lists simultaneously.
	 * We may have a mixture of cached and uncached sections and we only
	 * really want to write out the uncached sections.  This is slightly
	 * complicated by the possibility that we might have huge pages with a
	 * mixture inside.
	 */
	subreq = list_first_entry(&rreq->subrequests,
				  struct netfs_io_subrequest, rreq_link);
	subreq_failed = (subreq->error < 0);

	trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);

	rcu_read_lock();
	xas_for_each(&xas, folio, last_page) {
		loff_t pg_end;
		bool pg_failed = false;
		bool folio_started;

		if (xas_retry(&xas, folio))
			continue;

		pg_end = folio_pos(folio) + folio_size(folio) - 1;

		folio_started = false;
		for (;;) {
			loff_t sreq_end;

			if (!subreq) {
				pg_failed = true;
				break;
			}
			if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
				folio_start_fscache(folio);
				folio_started = true;
			}
			pg_failed |= subreq_failed;
			sreq_end = subreq->start + subreq->len - 1;
			if (pg_end < sreq_end)
				break;

			account += subreq->transferred;
			if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
				subreq = list_next_entry(subreq, rreq_link);
				subreq_failed = (subreq->error < 0);
			} else {
				subreq = NULL;
				subreq_failed = false;
			}

			if (pg_end == sreq_end)
				break;
		}

		if (!pg_failed) {
			flush_dcache_folio(folio);
			folio_mark_uptodate(folio);
		}

		if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
			if (folio_index(folio) == rreq->no_unlock_folio &&
			    test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
				_debug("no unlock");
			else
				folio_unlock(folio);
		}
	}
	rcu_read_unlock();

	task_io_account_read(account);
	if (rreq->netfs_ops->done)
		rreq->netfs_ops->done(rreq);
}

static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
					 loff_t *_start, size_t *_len, loff_t 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);
	}
}

/**
 * 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 *ctx = netfs_inode(ractl->mapping->host);
	int ret;

	_enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));

	if (readahead_count(ractl) == 0)
		return;

	rreq = netfs_alloc_request(ractl->mapping, ractl->file,
				   readahead_pos(ractl),
				   readahead_length(ractl),
				   NETFS_READAHEAD);
	if (IS_ERR(rreq))
		return;

	if (ctx->ops->begin_cache_operation) {
		ret = ctx->ops->begin_cache_operation(rreq);
		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);

	/* Drop the refs on the folios here rather than in the cache or
	 * filesystem.  The locks will be dropped in netfs_rreq_unlock().
	 */
	while (readahead_folio(ractl))
		;

	netfs_begin_read(rreq, false);
	return;

cleanup_free:
	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
	return;
}
EXPORT_SYMBOL(netfs_readahead);

/**
 * 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_file_mapping(folio);
	struct netfs_io_request *rreq;
	struct netfs_inode *ctx = netfs_inode(mapping->host);
	int ret;

	_enter("%lx", folio_index(folio));

	rreq = netfs_alloc_request(mapping, file,
				   folio_file_pos(folio), folio_size(folio),
				   NETFS_READPAGE);
	if (IS_ERR(rreq)) {
		ret = PTR_ERR(rreq);
		goto alloc_error;
	}

	if (ctx->ops->begin_cache_operation) {
		ret = ctx->ops->begin_cache_operation(rreq);
		if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
			goto discard;
	}

	netfs_stat(&netfs_n_rh_readpage);
	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
	return netfs_begin_read(rreq, true);

discard:
	netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
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 */
		zero_user_segment(&folio->page, 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:
	zero_user_segments(&folio->page, 0, offset, offset + len, plen);
	return true;
}

/**
 * netfs_write_begin - Helper to prepare for writing
 * @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.  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 provide a table of operations, only one of which,
 * issue_op, 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.
 */
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;

	DEFINE_READAHEAD(ractl, file, NULL, mapping, index);

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 page 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_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_file_pos(folio), folio_size(folio),
				   NETFS_READ_FOR_WRITE);
	if (IS_ERR(rreq)) {
		ret = PTR_ERR(rreq);
		goto error;
	}
	rreq->no_unlock_folio	= folio_index(folio);
	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);

	if (ctx->ops->begin_cache_operation) {
		ret = ctx->ops->begin_cache_operation(rreq);
		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);

	/* Expand the request to meet caching requirements and download
	 * preferences.
	 */
	ractl._nr_pages = folio_nr_pages(folio);
	netfs_rreq_expand(rreq, &ractl);

	/* We hold the folio locks, so we can drop the references */
	folio_get(folio);
	while (readahead_folio(&ractl))
		;

	ret = netfs_begin_read(rreq, true);
	if (ret < 0)
		goto error;

have_folio:
	ret = folio_wait_fscache_killable(folio);
	if (ret < 0)
		goto error;
have_folio_no_wait:
	*_folio = folio;
	_leave(" = 0");
	return 0;

error_put:
	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
error:
	if (folio) {
		folio_unlock(folio);
		folio_put(folio);
	}
	_leave(" = %d", ret);
	return ret;
}
EXPORT_SYMBOL(netfs_write_begin);
Commit	Line	Data
16211268 DH	1	// SPDX-License-Identifier: GPL-2.0-or-later
	2	/* Network filesystem high-level buffered read support.
	3	*
	4	* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
	5	* Written by David Howells (dhowells@redhat.com)
	6	*/
	7
	8	#include <linux/export.h>
	9	#include <linux/task_io_accounting_ops.h>
	10	#include "internal.h"
	11
	12	/*
	13	* Unlock the folios in a read operation. We need to set PG_fscache on any
	14	* folios we're going to write back before we unlock them.
	15	*/
	16	void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
	17	{
	18	struct netfs_io_subrequest *subreq;
	19	struct folio *folio;
16211268 DH	20	pgoff_t start_page = rreq->start / PAGE_SIZE;
16211268 DH	21	pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
5e51c627	22	size_t account = 0;
16211268 DH	23	bool subreq_failed = false;
	24
	25	XA_STATE(xas, &rreq->mapping->i_pages, start_page);
	26
	27	if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
	28	__clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
	29	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
	30	__clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
	31	}
	32	}
	33
	34	/* Walk through the pagecache and the I/O request lists simultaneously.
	35	* We may have a mixture of cached and uncached sections and we only
	36	* really want to write out the uncached sections. This is slightly
	37	* complicated by the possibility that we might have huge pages with a
	38	* mixture inside.
	39	*/
	40	subreq = list_first_entry(&rreq->subrequests,
	41	struct netfs_io_subrequest, rreq_link);
16211268 DH	42	subreq_failed = (subreq->error < 0);
	43
	44	trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
	45
	46	rcu_read_lock();
	47	xas_for_each(&xas, folio, last_page) {
5e51c627	48	loff_t pg_end;
16211268	49	bool pg_failed = false;
df1c357f	50	bool folio_started;
16211268	51
7e043a80 DH	52	if (xas_retry(&xas, folio))
	53	continue;
	54
5e51c627	55	pg_end = folio_pos(folio) + folio_size(folio) - 1;
7e043a80	56
df1c357f	57	folio_started = false;
16211268	58	for (;;) {
5e51c627 DH	59	loff_t sreq_end;
5e51c627 DH	60
16211268 DH	61	if (!subreq) {
	62	pg_failed = true;
	63	break;
	64	}
df1c357f	65	if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
16211268	66	folio_start_fscache(folio);
df1c357f DW	67	folio_started = true;
df1c357f DW	68	}
16211268	69	pg_failed \|= subreq_failed;
5e51c627 DH	70	sreq_end = subreq->start + subreq->len - 1;
5e51c627 DH	71	if (pg_end < sreq_end)
16211268 DH	72	break;
	73
	74	account += subreq->transferred;
16211268 DH	75	if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
	76	subreq = list_next_entry(subreq, rreq_link);
	77	subreq_failed = (subreq->error < 0);
	78	} else {
	79	subreq = NULL;
	80	subreq_failed = false;
	81	}
5e51c627 DH	82
5e51c627 DH	83	if (pg_end == sreq_end)
16211268 DH	84	break;
	85	}
	86
	87	if (!pg_failed) {
	88	flush_dcache_folio(folio);
	89	folio_mark_uptodate(folio);
	90	}
	91
	92	if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
	93	if (folio_index(folio) == rreq->no_unlock_folio &&
	94	test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
	95	_debug("no unlock");
	96	else
	97	folio_unlock(folio);
	98	}
	99	}
	100	rcu_read_unlock();
	101
	102	task_io_account_read(account);
	103	if (rreq->netfs_ops->done)
	104	rreq->netfs_ops->done(rreq);
	105	}
	106
	107	static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
	108	loff_t _start, size_t _len, loff_t i_size)
	109	{
	110	struct netfs_cache_resources *cres = &rreq->cache_resources;
	111
	112	if (cres->ops && cres->ops->expand_readahead)
	113	cres->ops->expand_readahead(cres, _start, _len, i_size);
	114	}
	115
	116	static void netfs_rreq_expand(struct netfs_io_request *rreq,
	117	struct readahead_control *ractl)
	118	{
	119	/* Give the cache a chance to change the request parameters. The
	120	* resultant request must contain the original region.
	121	*/
	122	netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
	123
	124	/* Give the netfs a chance to change the request parameters. The
	125	* resultant request must contain the original region.
	126	*/
	127	if (rreq->netfs_ops->expand_readahead)
	128	rreq->netfs_ops->expand_readahead(rreq);
	129
	130	/* Expand the request if the cache wants it to start earlier. Note
	131	* that the expansion may get further extended if the VM wishes to
	132	* insert THPs and the preferred start and/or end wind up in the middle
	133	* of THPs.
	134	*
	135	* If this is the case, however, the THP size should be an integer
	136	* multiple of the cache granule size, so we get a whole number of
	137	* granules to deal with.
	138	*/
	139	if (rreq->start != readahead_pos(ractl) \|\|
	140	rreq->len != readahead_length(ractl)) {
	141	readahead_expand(ractl, rreq->start, rreq->len);
	142	rreq->start = readahead_pos(ractl);
	143	rreq->len = readahead_length(ractl);
	144
	145	trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
	146	netfs_read_trace_expanded);
	147	}
148	}
149
150	/**
151	* netfs_readahead - Helper to manage a read request
152	* @ractl: The description of the readahead request
153	*
154	* Fulfil a readahead request by drawing data from the cache if possible, or
155	* the netfs if not. Space beyond the EOF is zero-filled. Multiple I/O
156	* requests from different sources will get munged together. If necessary, the
157	* readahead window can be expanded in either direction to a more convenient
158	* alighment for RPC efficiency or to make storage in the cache feasible.
159	*
160	* The calling netfs must initialise a netfs context contiguous to the vfs
161	* inode before calling this.
162	*
163	* This is usable whether or not caching is enabled.
164	*/
165	void netfs_readahead(struct readahead_control *ractl)
166	{
167	struct netfs_io_request *rreq;
874c8ca1	168	struct netfs_inode *ctx = netfs_inode(ractl->mapping->host);
16211268 DH	169	int ret;
	170
	171	_enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
	172
	173	if (readahead_count(ractl) == 0)
	174	return;
	175
	176	rreq = netfs_alloc_request(ractl->mapping, ractl->file,
	177	readahead_pos(ractl),
	178	readahead_length(ractl),
	179	NETFS_READAHEAD);
	180	if (IS_ERR(rreq))
	181	return;
	182
	183	if (ctx->ops->begin_cache_operation) {
	184	ret = ctx->ops->begin_cache_operation(rreq);
	185	if (ret == -ENOMEM \|\| ret == -EINTR \|\| ret == -ERESTARTSYS)
	186	goto cleanup_free;
	187	}
	188
	189	netfs_stat(&netfs_n_rh_readahead);
	190	trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
	191	netfs_read_trace_readahead);
	192
	193	netfs_rreq_expand(rreq, ractl);
	194
	195	/* Drop the refs on the folios here rather than in the cache or
	196	* filesystem. The locks will be dropped in netfs_rreq_unlock().
	197	*/
	198	while (readahead_folio(ractl))
	199	;
	200
	201	netfs_begin_read(rreq, false);
	202	return;
	203
	204	cleanup_free:
	205	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
	206	return;
	207	}
	208	EXPORT_SYMBOL(netfs_readahead);
	209
	210	/**
6c62371b	211	* netfs_read_folio - Helper to manage a read_folio request
16211268	212	* @file: The file to read from
6c62371b	213	* @folio: The folio to read
16211268	214	*
6c62371b MWO	215	* Fulfil a read_folio request by drawing data from the cache if
	216	* possible, or the netfs if not. Space beyond the EOF is zero-filled.
	217	* Multiple I/O requests from different sources will get munged together.
16211268 DH	218	*
	219	* The calling netfs must initialise a netfs context contiguous to the vfs
	220	* inode before calling this.
	221	*
	222	* This is usable whether or not caching is enabled.
	223	*/
6c62371b	224	int netfs_read_folio(struct file file, struct folio folio)
16211268	225	{
16211268 DH	226	struct address_space *mapping = folio_file_mapping(folio);
16211268 DH	227	struct netfs_io_request *rreq;
874c8ca1	228	struct netfs_inode *ctx = netfs_inode(mapping->host);
16211268 DH	229	int ret;
	230
	231	_enter("%lx", folio_index(folio));
	232
	233	rreq = netfs_alloc_request(mapping, file,
	234	folio_file_pos(folio), folio_size(folio),
	235	NETFS_READPAGE);
	236	if (IS_ERR(rreq)) {
	237	ret = PTR_ERR(rreq);
	238	goto alloc_error;
	239	}
	240
	241	if (ctx->ops->begin_cache_operation) {
	242	ret = ctx->ops->begin_cache_operation(rreq);
	243	if (ret == -ENOMEM \|\| ret == -EINTR \|\| ret == -ERESTARTSYS)
	244	goto discard;
	245	}
	246
	247	netfs_stat(&netfs_n_rh_readpage);
	248	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
	249	return netfs_begin_read(rreq, true);
	250
	251	discard:
	252	netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
	253	alloc_error:
	254	folio_unlock(folio);
	255	return ret;
	256	}
6c62371b	257	EXPORT_SYMBOL(netfs_read_folio);
16211268 DH	258
	259	/*
	260	* Prepare a folio for writing without reading first
	261	* @folio: The folio being prepared
	262	* @pos: starting position for the write
	263	* @len: length of write
	264	* @always_fill: T if the folio should always be completely filled/cleared
	265	*
	266	* In some cases, write_begin doesn't need to read at all:
	267	* - full folio write
	268	* - write that lies in a folio that is completely beyond EOF
	269	* - write that covers the folio from start to EOF or beyond it
	270	*
	271	* If any of these criteria are met, then zero out the unwritten parts
	272	* of the folio and return true. Otherwise, return false.
	273	*/
	274	static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
	275	bool always_fill)
	276	{
	277	struct inode *inode = folio_inode(folio);
	278	loff_t i_size = i_size_read(inode);
	279	size_t offset = offset_in_folio(folio, pos);
	280	size_t plen = folio_size(folio);
	281
	282	if (unlikely(always_fill)) {
	283	if (pos - offset + len <= i_size)
	284	return false; /* Page entirely before EOF */
	285	zero_user_segment(&folio->page, 0, plen);
	286	folio_mark_uptodate(folio);
	287	return true;
	288	}
	289
	290	/* Full folio write */
	291	if (offset == 0 && len >= plen)
	292	return true;
	293
	294	/* Page entirely beyond the end of the file */
	295	if (pos - offset >= i_size)
	296	goto zero_out;
	297
	298	/* Write that covers from the start of the folio to EOF or beyond */
	299	if (offset == 0 && (pos + len) >= i_size)
	300	goto zero_out;
	301
	302	return false;
	303	zero_out:
	304	zero_user_segments(&folio->page, 0, offset, offset + len, plen);
	305	return true;
	306	}
	307
	308	/**
	309	* netfs_write_begin - Helper to prepare for writing
e81fb419	310	* @ctx: The netfs context
16211268 DH	311	* @file: The file to read from
	312	* @mapping: The mapping to read from
	313	* @pos: File position at which the write will begin
	314	* @len: The length of the write (may extend beyond the end of the folio chosen)
16211268 DH	315	* @_folio: Where to put the resultant folio
	316	* @_fsdata: Place for the netfs to store a cookie
	317	*
	318	* Pre-read data for a write-begin request by drawing data from the cache if
	319	* possible, or the netfs if not. Space beyond the EOF is zero-filled.
	320	* Multiple I/O requests from different sources will get munged together. If
	321	* necessary, the readahead window can be expanded in either direction to a
	322	* more convenient alighment for RPC efficiency or to make storage in the cache
	323	* feasible.
	324	*
	325	* The calling netfs must provide a table of operations, only one of which,
	326	* issue_op, is mandatory.
	327	*
	328	* The check_write_begin() operation can be provided to check for and flush
	329	* conflicting writes once the folio is grabbed and locked. It is passed a
	330	* pointer to the fsdata cookie that gets returned to the VM to be passed to
	331	* write_end. It is permitted to sleep. It should return 0 if the request
fac47b43 XL	332	* should go ahead or it may return an error. It may also unlock and put the
	333	* folio, provided it sets ``*foliop`` to NULL, in which case a return of 0
	334	* will cause the folio to be re-got and the process to be retried.
16211268 DH	335	*
	336	* The calling netfs must initialise a netfs context contiguous to the vfs
	337	* inode before calling this.
	338	*
	339	* This is usable whether or not caching is enabled.
	340	*/
e81fb419 LT	341	int netfs_write_begin(struct netfs_inode *ctx,
e81fb419 LT	342	struct file file, struct address_space mapping,
de2a9311 MWO	343	loff_t pos, unsigned int len, struct folio **_folio,
de2a9311 MWO	344	void **_fsdata)
16211268 DH	345	{
16211268 DH	346	struct netfs_io_request *rreq;
16211268	347	struct folio *folio;
16211268 DH	348	pgoff_t index = pos >> PAGE_SHIFT;
	349	int ret;
	350
	351	DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
	352
	353	retry:
e999a5c5	354	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
16211268	355	mapping_gfp_mask(mapping));
66dabbb6 CH	356	if (IS_ERR(folio))
66dabbb6 CH	357	return PTR_ERR(folio);
16211268 DH	358
	359	if (ctx->ops->check_write_begin) {
	360	/* Allow the netfs (eg. ceph) to flush conflicts. */
fac47b43	361	ret = ctx->ops->check_write_begin(file, pos, len, &folio, _fsdata);
16211268 DH	362	if (ret < 0) {
16211268 DH	363	trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
16211268 DH	364	goto error;
16211268 DH	365	}
fac47b43 XL	366	if (!folio)
fac47b43 XL	367	goto retry;
16211268 DH	368	}
	369
	370	if (folio_test_uptodate(folio))
	371	goto have_folio;
	372
	373	/* If the page is beyond the EOF, we want to clear it - unless it's
	374	* within the cache granule containing the EOF, in which case we need
	375	* to preload the granule.
	376	*/
	377	if (!netfs_is_cache_enabled(ctx) &&
	378	netfs_skip_folio_read(folio, pos, len, false)) {
	379	netfs_stat(&netfs_n_rh_write_zskip);
	380	goto have_folio_no_wait;
	381	}
	382
	383	rreq = netfs_alloc_request(mapping, file,
	384	folio_file_pos(folio), folio_size(folio),
	385	NETFS_READ_FOR_WRITE);
	386	if (IS_ERR(rreq)) {
	387	ret = PTR_ERR(rreq);
	388	goto error;
	389	}
	390	rreq->no_unlock_folio = folio_index(folio);
	391	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
	392
	393	if (ctx->ops->begin_cache_operation) {
	394	ret = ctx->ops->begin_cache_operation(rreq);
	395	if (ret == -ENOMEM \|\| ret == -EINTR \|\| ret == -ERESTARTSYS)
	396	goto error_put;
	397	}
	398
	399	netfs_stat(&netfs_n_rh_write_begin);
	400	trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
	401
	402	/* Expand the request to meet caching requirements and download
	403	* preferences.
	404	*/
	405	ractl._nr_pages = folio_nr_pages(folio);
	406	netfs_rreq_expand(rreq, &ractl);
	407
	408	/* We hold the folio locks, so we can drop the references */
	409	folio_get(folio);
	410	while (readahead_folio(&ractl))
	411	;
	412
	413	ret = netfs_begin_read(rreq, true);
	414	if (ret < 0)
	415	goto error;
	416
	417	have_folio:
	418	ret = folio_wait_fscache_killable(folio);
	419	if (ret < 0)
	420	goto error;
	421	have_folio_no_wait:
	422	*_folio = folio;
	423	_leave(" = 0");
	424	return 0;
	425
	426	error_put:
	427	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
	428	error:
fac47b43 XL	429	if (folio) {
	430	folio_unlock(folio);
	431	folio_put(folio);
	432	}
16211268 DH	433	_leave(" = %d", ret);
	434	return ret;
	435	}
	436	EXPORT_SYMBOL(netfs_write_begin);