1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Copyright (C) 2010 Red Hat, Inc.
 4 * Copyright (c) 2016-2018 Christoph Hellwig.
 5 */
 6#include <linux/module.h>
 7#include <linux/compiler.h>
 8#include <linux/fs.h>
 9#include <linux/iomap.h>
10
11/*
12 * Execute a iomap write on a segment of the mapping that spans a
13 * contiguous range of pages that have identical block mapping state.
14 *
15 * This avoids the need to map pages individually, do individual allocations
16 * for each page and most importantly avoid the need for filesystem specific
17 * locking per page. Instead, all the operations are amortised over the entire
18 * range of pages. It is assumed that the filesystems will lock whatever
19 * resources they require in the iomap_begin call, and release them in the
20 * iomap_end call.
21 */
22loff_t
23iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
24		const struct iomap_ops *ops, void *data, iomap_actor_t actor)
25{
26	struct iomap iomap = { 0 };
27	loff_t written = 0, ret;
28
29	/*
30	 * Need to map a range from start position for length bytes. This can
31	 * span multiple pages - it is only guaranteed to return a range of a
32	 * single type of pages (e.g. all into a hole, all mapped or all
33	 * unwritten). Failure at this point has nothing to undo.
34	 *
35	 * If allocation is required for this range, reserve the space now so
36	 * that the allocation is guaranteed to succeed later on. Once we copy
37	 * the data into the page cache pages, then we cannot fail otherwise we
38	 * expose transient stale data. If the reserve fails, we can safely
39	 * back out at this point as there is nothing to undo.
40	 */
41	ret = ops->iomap_begin(inode, pos, length, flags, &iomap);
42	if (ret)
43		return ret;
44	if (WARN_ON(iomap.offset > pos))
45		return -EIO;
46	if (WARN_ON(iomap.length == 0))
47		return -EIO;
48
49	/*
50	 * Cut down the length to the one actually provided by the filesystem,
51	 * as it might not be able to give us the whole size that we requested.
52	 */
53	if (iomap.offset + iomap.length < pos + length)
54		length = iomap.offset + iomap.length - pos;
55
56	/*
57	 * Now that we have guaranteed that the space allocation will succeed.
58	 * we can do the copy-in page by page without having to worry about
59	 * failures exposing transient data.
60	 */
61	written = actor(inode, pos, length, data, &iomap);
62
63	/*
64	 * Now the data has been copied, commit the range we've copied.  This
65	 * should not fail unless the filesystem has had a fatal error.
66	 */
67	if (ops->iomap_end) {
68		ret = ops->iomap_end(inode, pos, length,
69				     written > 0 ? written : 0,
70				     flags, &iomap);
71	}
72
73	return written ? written : ret;
74}