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#include "trace.h"
11
12/*
13 * Execute a iomap write on a segment of the mapping that spans a
14 * contiguous range of pages that have identical block mapping state.
15 *
16 * This avoids the need to map pages individually, do individual allocations
17 * for each page and most importantly avoid the need for filesystem specific
18 * locking per page. Instead, all the operations are amortised over the entire
19 * range of pages. It is assumed that the filesystems will lock whatever
20 * resources they require in the iomap_begin call, and release them in the
21 * iomap_end call.
22 */
23loff_t
24iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
25		const struct iomap_ops *ops, void *data, iomap_actor_t actor)
26{
27	struct iomap iomap = { .type = IOMAP_HOLE };
28	struct iomap srcmap = { .type = IOMAP_HOLE };
29	loff_t written = 0, ret;
30	u64 end;
31
32	trace_iomap_apply(inode, pos, length, flags, ops, actor, _RET_IP_);
33
34	/*
35	 * Need to map a range from start position for length bytes. This can
36	 * span multiple pages - it is only guaranteed to return a range of a
37	 * single type of pages (e.g. all into a hole, all mapped or all
38	 * unwritten). Failure at this point has nothing to undo.
39	 *
40	 * If allocation is required for this range, reserve the space now so
41	 * that the allocation is guaranteed to succeed later on. Once we copy
42	 * the data into the page cache pages, then we cannot fail otherwise we
43	 * expose transient stale data. If the reserve fails, we can safely
44	 * back out at this point as there is nothing to undo.
45	 */
46	ret = ops->iomap_begin(inode, pos, length, flags, &iomap, &srcmap);
47	if (ret)
48		return ret;
49	if (WARN_ON(iomap.offset > pos)) {
50		written = -EIO;
51		goto out;
52	}
53	if (WARN_ON(iomap.length == 0)) {
54		written = -EIO;
55		goto out;
56	}
57
58	trace_iomap_apply_dstmap(inode, &iomap);
59	if (srcmap.type != IOMAP_HOLE)
60		trace_iomap_apply_srcmap(inode, &srcmap);
61
62	/*
63	 * Cut down the length to the one actually provided by the filesystem,
64	 * as it might not be able to give us the whole size that we requested.
65	 */
66	end = iomap.offset + iomap.length;
67	if (srcmap.type != IOMAP_HOLE)
68		end = min(end, srcmap.offset + srcmap.length);
69	if (pos + length > end)
70		length = end - pos;
71
72	/*
73	 * Now that we have guaranteed that the space allocation will succeed,
74	 * we can do the copy-in page by page without having to worry about
75	 * failures exposing transient data.
76	 *
77	 * To support COW operations, we read in data for partially blocks from
78	 * the srcmap if the file system filled it in.  In that case we the
79	 * length needs to be limited to the earlier of the ends of the iomaps.
80	 * If the file system did not provide a srcmap we pass in the normal
81	 * iomap into the actors so that they don't need to have special
82	 * handling for the two cases.
83	 */
84	written = actor(inode, pos, length, data, &iomap,
85			srcmap.type != IOMAP_HOLE ? &srcmap : &iomap);
86
87out:
88	/*
89	 * Now the data has been copied, commit the range we've copied.  This
90	 * should not fail unless the filesystem has had a fatal error.
91	 */
92	if (ops->iomap_end) {
93		ret = ops->iomap_end(inode, pos, length,
94				     written > 0 ? written : 0,
95				     flags, &iomap);
96	}
97
98	return written ? written : ret;
99}