linux/fs/netfs/buffered_write.c

// SPDX-License-Identifier: GPL-2.0-only
/* Network filesystem high-level buffered write support.
 *
 * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 */

#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 { … };

static void netfs_set_group(struct folio *folio, struct netfs_group *netfs_group)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * Update i_size and estimate the update to i_blocks to reflect the additional
 * data written into the pagecache until we can find out from the server what
 * the values actually are.
 */
static void netfs_update_i_size(struct netfs_inode *ctx, struct inode *inode,
				loff_t i_size, loff_t pos, size_t copied)
{ … }

/**
 * netfs_perform_write - Copy data into the pagecache.
 * @iocb: The operation parameters
 * @iter: The source buffer
 * @netfs_group: Grouping for dirty pages (eg. ceph snaps).
 *
 * Copy data into pagecache pages attached to the inode specified by @iocb.
 * The caller must hold appropriate inode locks.
 *
 * Dirty pages are tagged with a netfs_folio struct if they're not up to date
 * to indicate the range modified.  Dirty pages may also be tagged with a
 * netfs-specific grouping such that data from an old group gets flushed before
 * a new one is started.
 */
ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
			    struct netfs_group *netfs_group)
{ … }
EXPORT_SYMBOL(…);

/**
 * netfs_buffered_write_iter_locked - write data to a file
 * @iocb:	IO state structure (file, offset, etc.)
 * @from:	iov_iter with data to write
 * @netfs_group: Grouping for dirty pages (eg. ceph snaps).
 *
 * This function does all the work needed for actually writing data to a
 * file. It does all basic checks, removes SUID from the file, updates
 * modification times and calls proper subroutines depending on whether we
 * do direct IO or a standard buffered write.
 *
 * The caller must hold appropriate locks around this function and have called
 * generic_write_checks() already.  The caller is also responsible for doing
 * any necessary syncing afterwards.
 *
 * This function does *not* take care of syncing data in case of O_SYNC write.
 * A caller has to handle it. This is mainly due to the fact that we want to
 * avoid syncing under i_rwsem.
 *
 * Return:
 * * number of bytes written, even for truncated writes
 * * negative error code if no data has been written at all
 */
ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,
					 struct netfs_group *netfs_group)
{ … }
EXPORT_SYMBOL(…);

/**
 * netfs_file_write_iter - write data to a file
 * @iocb: IO state structure
 * @from: iov_iter with data to write
 *
 * Perform a write to a file, writing into the pagecache if possible and doing
 * an unbuffered write instead if not.
 *
 * Return:
 * * Negative error code if no data has been written at all of
 *   vfs_fsync_range() failed for a synchronous write
 * * Number of bytes written, even for truncated writes
 */
ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{ … }
EXPORT_SYMBOL(…);

/*
 * Notification that a previously read-only page is about to become writable.
 * Note that the caller indicates a single page of a multipage folio.
 */
vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_group)
{ … }
EXPORT_SYMBOL(…);