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 */
23 loff_t
iomap_apply(struct inode * inode,loff_t pos,loff_t length,unsigned flags,const struct iomap_ops * ops,void * data,iomap_actor_t actor)24 iomap_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
87 out:
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 }
100