1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* file-nommu.c: no-MMU version of ramfs
3 *
4 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #include <linux/module.h>
9 #include <linux/fs.h>
10 #include <linux/mm.h>
11 #include <linux/pagemap.h>
12 #include <linux/highmem.h>
13 #include <linux/init.h>
14 #include <linux/string.h>
15 #include <linux/backing-dev.h>
16 #include <linux/ramfs.h>
17 #include <linux/folio_batch.h>
18 #include <linux/mman.h>
19 #include <linux/sched.h>
20 #include <linux/slab.h>
21
22 #include <linux/uaccess.h>
23 #include "internal.h"
24
25 static int ramfs_nommu_setattr(struct mnt_idmap *, struct dentry *, struct iattr *);
26 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
27 unsigned long addr,
28 unsigned long len,
29 unsigned long pgoff,
30 unsigned long flags);
31 static int ramfs_nommu_mmap_prepare(struct vm_area_desc *desc);
32
ramfs_mmap_capabilities(struct file * file)33 static unsigned ramfs_mmap_capabilities(struct file *file)
34 {
35 return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
36 NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
37 }
38
39 const struct file_operations ramfs_file_operations = {
40 .mmap_capabilities = ramfs_mmap_capabilities,
41 .mmap_prepare = ramfs_nommu_mmap_prepare,
42 .get_unmapped_area = ramfs_nommu_get_unmapped_area,
43 .read_iter = generic_file_read_iter,
44 .write_iter = generic_file_write_iter,
45 .fsync = noop_fsync,
46 .splice_read = filemap_splice_read,
47 .splice_write = iter_file_splice_write,
48 .llseek = generic_file_llseek,
49 };
50
51 const struct inode_operations ramfs_file_inode_operations = {
52 .setattr = ramfs_nommu_setattr,
53 .getattr = simple_getattr,
54 };
55
56 /*****************************************************************************/
57 /*
58 * add a contiguous set of pages into a ramfs inode when it's truncated from
59 * size 0 on the assumption that it's going to be used for an mmap of shared
60 * memory
61 */
ramfs_nommu_expand_for_mapping(struct inode * inode,size_t newsize)62 int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
63 {
64 unsigned long npages, xpages, loop;
65 struct page *pages;
66 unsigned order;
67 void *data;
68 int ret;
69 gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
70
71 /* make various checks */
72 if (!newsize)
73 return 0;
74
75 order = get_order(newsize);
76 if (unlikely(order > MAX_PAGE_ORDER))
77 return -EFBIG;
78
79 ret = inode_newsize_ok(inode, newsize);
80 if (ret)
81 return ret;
82
83 i_size_write(inode, newsize);
84
85 /* allocate enough contiguous pages to be able to satisfy the
86 * request */
87 pages = alloc_pages(gfp, order);
88 if (!pages)
89 return -ENOMEM;
90
91 /* split the high-order page into an array of single pages */
92 xpages = 1UL << order;
93 npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
94
95 split_page(pages, order);
96
97 /* trim off any pages we don't actually require */
98 for (loop = npages; loop < xpages; loop++)
99 __free_page(pages + loop);
100
101 /* clear the memory we allocated */
102 newsize = PAGE_SIZE * npages;
103 data = page_address(pages);
104 memset(data, 0, newsize);
105
106 /* attach all the pages to the inode's address space */
107 for (loop = 0; loop < npages; loop++) {
108 struct page *page = pages + loop;
109
110 ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
111 gfp);
112 if (ret < 0)
113 goto add_error;
114
115 /* prevent the page from being discarded on memory pressure */
116 SetPageDirty(page);
117 SetPageUptodate(page);
118
119 unlock_page(page);
120 put_page(page);
121 }
122
123 return 0;
124
125 add_error:
126 while (loop < npages)
127 __free_page(pages + loop++);
128 return ret;
129 }
130
131 /*****************************************************************************/
132 /*
133 *
134 */
ramfs_nommu_resize(struct inode * inode,loff_t newsize,loff_t size)135 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
136 {
137 int ret;
138
139 /* assume a truncate from zero size is going to be for the purposes of
140 * shared mmap */
141 if (size == 0) {
142 if (unlikely(newsize >> 32))
143 return -EFBIG;
144
145 return ramfs_nommu_expand_for_mapping(inode, newsize);
146 }
147
148 /* check that a decrease in size doesn't cut off any shared mappings */
149 if (newsize < size) {
150 ret = nommu_shrink_inode_mappings(inode, size, newsize);
151 if (ret < 0)
152 return ret;
153 }
154
155 truncate_setsize(inode, newsize);
156 return 0;
157 }
158
159 /*****************************************************************************/
160 /*
161 * handle a change of attributes
162 * - we're specifically interested in a change of size
163 */
ramfs_nommu_setattr(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * ia)164 static int ramfs_nommu_setattr(struct mnt_idmap *idmap,
165 struct dentry *dentry, struct iattr *ia)
166 {
167 struct inode *inode = d_inode(dentry);
168 unsigned int old_ia_valid = ia->ia_valid;
169 int ret = 0;
170
171 /* POSIX UID/GID verification for setting inode attributes */
172 ret = setattr_prepare(&nop_mnt_idmap, dentry, ia);
173 if (ret)
174 return ret;
175
176 /* pick out size-changing events */
177 if (ia->ia_valid & ATTR_SIZE) {
178 loff_t size = inode->i_size;
179
180 if (ia->ia_size != size) {
181 ret = ramfs_nommu_resize(inode, ia->ia_size, size);
182 if (ret < 0 || ia->ia_valid == ATTR_SIZE)
183 goto out;
184 } else {
185 /* we skipped the truncate but must still update
186 * timestamps
187 */
188 ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
189 }
190 }
191
192 setattr_copy(&nop_mnt_idmap, inode, ia);
193 out:
194 ia->ia_valid = old_ia_valid;
195 return ret;
196 }
197
198 /*****************************************************************************/
199 /*
200 * try to determine where a shared mapping can be made
201 * - we require that:
202 * - the pages to be mapped must exist
203 * - the pages be physically contiguous in sequence
204 */
ramfs_nommu_get_unmapped_area(struct file * file,unsigned long addr,unsigned long len,unsigned long pgoff,unsigned long flags)205 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
206 unsigned long addr, unsigned long len,
207 unsigned long pgoff, unsigned long flags)
208 {
209 unsigned long maxpages, lpages, nr_folios, loop, ret, nr_pages, pfn;
210 struct inode *inode = file_inode(file);
211 struct folio_batch fbatch;
212 loff_t isize;
213
214 /* the mapping mustn't extend beyond the EOF */
215 lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
216 isize = i_size_read(inode);
217
218 ret = -ENOSYS;
219 maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
220 if (pgoff >= maxpages)
221 goto out;
222
223 if (maxpages - pgoff < lpages)
224 goto out;
225
226 /* gang-find the pages */
227 folio_batch_init(&fbatch);
228 nr_pages = 0;
229 repeat:
230 nr_folios = filemap_get_folios_contig(inode->i_mapping, &pgoff,
231 ULONG_MAX, &fbatch);
232 if (!nr_folios) {
233 ret = -ENOSYS;
234 return ret;
235 }
236
237 if (ret == -ENOSYS) {
238 ret = (unsigned long) folio_address(fbatch.folios[0]);
239 pfn = folio_pfn(fbatch.folios[0]);
240 }
241 /* check the pages for physical adjacency */
242 for (loop = 0; loop < nr_folios; loop++) {
243 if (pfn + nr_pages != folio_pfn(fbatch.folios[loop])) {
244 ret = -ENOSYS;
245 goto out_free; /* leave if not physical adjacent */
246 }
247 nr_pages += folio_nr_pages(fbatch.folios[loop]);
248 if (nr_pages >= lpages)
249 goto out_free; /* successfully found desired pages*/
250 }
251
252 if (nr_pages < lpages) {
253 folio_batch_release(&fbatch);
254 goto repeat; /* loop if pages are missing */
255 }
256 /* okay - all conditions fulfilled */
257
258 out_free:
259 folio_batch_release(&fbatch);
260 out:
261 return ret;
262 }
263
264 /*****************************************************************************/
265 /*
266 * set up a mapping for shared memory segments
267 */
ramfs_nommu_mmap_prepare(struct vm_area_desc * desc)268 static int ramfs_nommu_mmap_prepare(struct vm_area_desc *desc)
269 {
270 if (!is_nommu_shared_vma_flags(&desc->vma_flags))
271 return -ENOSYS;
272
273 file_accessed(desc->file);
274 desc->vm_ops = &generic_file_vm_ops;
275 return 0;
276 }
277