linux/fs/netfs/write_issue.c

// 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 ([email protected])
 *
 *
 * 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)
{ … }

/*
 * 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)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/*
 * 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)
{ … }

/*
 * 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)
{ … }

void netfs_reissue_write(struct netfs_io_stream *stream,
			 struct netfs_io_subrequest *subreq)
{ … }

static void netfs_issue_write(struct netfs_io_request *wreq,
			      struct netfs_io_stream *stream)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * Write some of the pending data back to the server
 */
int netfs_writepages(struct address_space *mapping,
		     struct writeback_control *wbc)
{ … }
EXPORT_SYMBOL(…);

/*
 * Begin a write operation for writing through the pagecache.
 */
struct netfs_io_request *netfs_begin_writethrough(struct kiocb *iocb, size_t len)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }