path: root/fs/netfs/buffered_write.c

// SPDX-License-Identifier: GPL-2.0-only
/* Network filesystem high-level write support.
 *
 * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/export.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/pagevec.h>
#include "internal.h"

/*
 * Determined write method.  Adjust netfs_folio_traces if this is changed.
 */
enum netfs_how_to_modify {
	NETFS_FOLIO_IS_UPTODATE,	/* Folio is uptodate already */
	NETFS_JUST_PREFETCH,		/* We have to read the folio anyway */
	NETFS_WHOLE_FOLIO_MODIFY,	/* We're going to overwrite the whole folio */
	NETFS_MODIFY_AND_CLEAR,		/* We can assume there is no data to be downloaded. */
	NETFS_STREAMING_WRITE,		/* Store incomplete data in non-uptodate page. */
	NETFS_STREAMING_WRITE_CONT,	/* Continue streaming write. */
	NETFS_FLUSH_CONTENT,		/* Flush incompatible content. */
};

static void netfs_cleanup_buffered_write(struct netfs_io_request *wreq);

static void netfs_set_group(struct folio *folio, struct netfs_group *netfs_group)
{
	if (netfs_group && !folio_get_private(folio))
		folio_attach_private(folio, netfs_get_group(netfs_group));
}

#if IS_ENABLED(CONFIG_FSCACHE)
static void netfs_folio_start_fscache(bool caching, struct folio *folio)
{
	if (caching)
		folio_start_fscache(folio);
}
#else
static void netfs_folio_start_fscache(bool caching, struct folio *folio)
{
}
#endif

/*
 * Decide how we should modify a folio.  We might be attempting to do
 * write-streaming, in which case we don't want to a local RMW cycle if we can
 * avoid it.  If we're doing local caching or content crypto, we award that
 * priority over avoiding RMW.  If the file is open readably, then we also
 * assume that we may want to read what we wrote.
 */
static enum netfs_how_to_modify netfs_how_to_modify(struct netfs_inode *ctx,
						    struct file *file,
						    struct folio *folio,
						    void *netfs_group,
						    size_t flen,
						    size_t offset,
						    size_t len,
						    bool maybe_trouble)
{
	struct netfs_folio *finfo = netfs_folio_info(folio);
	loff_t pos = folio_file_pos(folio);

	_enter("");

	if (netfs_folio_group(folio) != netfs_group)
		return NETFS_FLUSH_CONTENT;

	if (folio_test_uptodate(folio))
		return NETFS_FOLIO_IS_UPTODATE;

	if (pos >= ctx->zero_point)
		return NETFS_MODIFY_AND_CLEAR;

	if (!maybe_trouble && offset == 0 && len >= flen)
		return NETFS_WHOLE_FOLIO_MODIFY;

	if (file->f_mode & FMODE_READ)
		goto no_write_streaming;
	if (test_bit(NETFS_ICTX_NO_WRITE_STREAMING, &ctx->flags))
		goto no_write_streaming;

	if (netfs_is_cache_enabled(ctx)) {
		/* We don't want to get a streaming write on a file that loses
		 * caching service temporarily because the backing store got
		 * culled.
		 */
		if (!test_bit(NETFS_ICTX_NO_WRITE_STREAMING, &ctx->flags))
			set_bit(NETFS_ICTX_NO_WRITE_STREAMING, &ctx->flags);
		goto no_write_streaming;
	}

	if (!finfo)
		return NETFS_STREAMING_WRITE;

	/* We can continue a streaming write only if it continues on from the
	 * previous.  If it overlaps, we must flush lest we suffer a partial
	 * copy and disjoint dirty regions.
	 */
	if (offset == finfo->dirty_offset + finfo->dirty_len)
		return NETFS_STREAMING_WRITE_CONT;
	return NETFS_FLUSH_CONTENT;

no_write_streaming:
	if (finfo) {
		netfs_stat(&netfs_n_wh_wstream_conflict);
		return NETFS_FLUSH_CONTENT;
	}
	return NETFS_JUST_PREFETCH;
}

/*
 * Grab a folio for writing and lock it.  Attempt to allocate as large a folio
 * as possible to hold as much of the remaining length as possible in one go.
 */
static struct folio *netfs_grab_folio_for_write(struct address_space *mapping,
						loff_t pos, size_t part)
{
	pgoff_t index = pos / PAGE_SIZE;
	fgf_t fgp_flags = FGP_WRITEBEGIN;

	if (mapping_large_folio_support(mapping))
		fgp_flags