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 */
22 loff_t
23 iomap_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 }