1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2017 Red Hat, Inc.
4 * Copyright (c) 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 <linux/pagemap.h>
11 #include <linux/pagevec.h>
12
13 /*
14 * Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.
15 * Returns true if found and updates @lastoff to the offset in file.
16 */
17 static bool
page_seek_hole_data(struct inode * inode,struct page * page,loff_t * lastoff,int whence)18 page_seek_hole_data(struct inode *inode, struct page *page, loff_t *lastoff,
19 int whence)
20 {
21 const struct address_space_operations *ops = inode->i_mapping->a_ops;
22 unsigned int bsize = i_blocksize(inode), off;
23 bool seek_data = whence == SEEK_DATA;
24 loff_t poff = page_offset(page);
25
26 if (WARN_ON_ONCE(*lastoff >= poff + PAGE_SIZE))
27 return false;
28
29 if (*lastoff < poff) {
30 /*
31 * Last offset smaller than the start of the page means we found
32 * a hole:
33 */
34 if (whence == SEEK_HOLE)
35 return true;
36 *lastoff = poff;
37 }
38
39 /*
40 * Just check the page unless we can and should check block ranges:
41 */
42 if (bsize == PAGE_SIZE || !ops->is_partially_uptodate)
43 return PageUptodate(page) == seek_data;
44
45 lock_page(page);
46 if (unlikely(page->mapping != inode->i_mapping))
47 goto out_unlock_not_found;
48
49 for (off = 0; off < PAGE_SIZE; off += bsize) {
50 if (offset_in_page(*lastoff) >= off + bsize)
51 continue;
52 if (ops->is_partially_uptodate(page, off, bsize) == seek_data) {
53 unlock_page(page);
54 return true;
55 }
56 *lastoff = poff + off + bsize;
57 }
58
59 out_unlock_not_found:
60 unlock_page(page);
61 return false;
62 }
63
64 /*
65 * Seek for SEEK_DATA / SEEK_HOLE in the page cache.
66 *
67 * Within unwritten extents, the page cache determines which parts are holes
68 * and which are data: uptodate buffer heads count as data; everything else
69 * counts as a hole.
70 *
71 * Returns the resulting offset on successs, and -ENOENT otherwise.
72 */
73 static loff_t
page_cache_seek_hole_data(struct inode * inode,loff_t offset,loff_t length,int whence)74 page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
75 int whence)
76 {
77 pgoff_t index = offset >> PAGE_SHIFT;
78 pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
79 loff_t lastoff = offset;
80 struct pagevec pvec;
81
82 if (length <= 0)
83 return -ENOENT;
84
85 pagevec_init(&pvec);
86
87 do {
88 unsigned nr_pages, i;
89
90 nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping, &index,
91 end - 1);
92 if (nr_pages == 0)
93 break;
94
95 for (i = 0; i < nr_pages; i++) {
96 struct page *page = pvec.pages[i];
97
98 if (page_seek_hole_data(inode, page, &lastoff, whence))
99 goto check_range;
100 lastoff = page_offset(page) + PAGE_SIZE;
101 }
102 pagevec_release(&pvec);
103 } while (index < end);
104
105 /* When no page at lastoff and we are not done, we found a hole. */
106 if (whence != SEEK_HOLE)
107 goto not_found;
108
109 check_range:
110 if (lastoff < offset + length)
111 goto out;
112 not_found:
113 lastoff = -ENOENT;
114 out:
115 pagevec_release(&pvec);
116 return lastoff;
117 }
118
119
120 static loff_t
iomap_seek_hole_actor(struct inode * inode,loff_t offset,loff_t length,void * data,struct iomap * iomap,struct iomap * srcmap)121 iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
122 void *data, struct iomap *iomap, struct iomap *srcmap)
123 {
124 switch (iomap->type) {
125 case IOMAP_UNWRITTEN:
126 offset = page_cache_seek_hole_data(inode, offset, length,
127 SEEK_HOLE);
128 if (offset < 0)
129 return length;
130 fallthrough;
131 case IOMAP_HOLE:
132 *(loff_t *)data = offset;
133 return 0;
134 default:
135 return length;
136 }
137 }
138
139 loff_t
iomap_seek_hole(struct inode * inode,loff_t offset,const struct iomap_ops * ops)140 iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
141 {
142 loff_t size = i_size_read(inode);
143 loff_t length = size - offset;
144 loff_t ret;
145
146 /* Nothing to be found before or beyond the end of the file. */
147 if (offset < 0 || offset >= size)
148 return -ENXIO;
149
150 while (length > 0) {
151 ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
152 &offset, iomap_seek_hole_actor);
153 if (ret < 0)
154 return ret;
155 if (ret == 0)
156 break;
157
158 offset += ret;
159 length -= ret;
160 }
161
162 return offset;
163 }
164 EXPORT_SYMBOL_GPL(iomap_seek_hole);
165
166 static loff_t
iomap_seek_data_actor(struct inode * inode,loff_t offset,loff_t length,void * data,struct iomap * iomap,struct iomap * srcmap)167 iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
168 void *data, struct iomap *iomap, struct iomap *srcmap)
169 {
170 switch (iomap->type) {
171 case IOMAP_HOLE:
172 return length;
173 case IOMAP_UNWRITTEN:
174 offset = page_cache_seek_hole_data(inode, offset, length,
175 SEEK_DATA);
176 if (offset < 0)
177 return length;
178 fallthrough;
179 default:
180 *(loff_t *)data = offset;
181 return 0;
182 }
183 }
184
185 loff_t
iomap_seek_data(struct inode * inode,loff_t offset,const struct iomap_ops * ops)186 iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
187 {
188 loff_t size = i_size_read(inode);
189 loff_t length = size - offset;
190 loff_t ret;
191
192 /* Nothing to be found before or beyond the end of the file. */
193 if (offset < 0 || offset >= size)
194 return -ENXIO;
195
196 while (length > 0) {
197 ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
198 &offset, iomap_seek_data_actor);
199 if (ret < 0)
200 return ret;
201 if (ret == 0)
202 break;
203
204 offset += ret;
205 length -= ret;
206 }
207
208 if (length <= 0)
209 return -ENXIO;
210 return offset;
211 }
212 EXPORT_SYMBOL_GPL(iomap_seek_data);
213
