xref: /openbmc/linux/fs/ramfs/file-nommu.c (revision fd589a8f)
1 /* file-nommu.c: no-MMU version of ramfs
2  *
3  * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version
9  * 2 of the License, or (at your option) any later version.
10  */
11 
12 #include <linux/module.h>
13 #include <linux/fs.h>
14 #include <linux/mm.h>
15 #include <linux/pagemap.h>
16 #include <linux/highmem.h>
17 #include <linux/init.h>
18 #include <linux/string.h>
19 #include <linux/backing-dev.h>
20 #include <linux/ramfs.h>
21 #include <linux/pagevec.h>
22 #include <linux/mman.h>
23 #include <linux/sched.h>
24 
25 #include <asm/uaccess.h>
26 #include "internal.h"
27 
28 static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
29 
30 const struct address_space_operations ramfs_aops = {
31 	.readpage		= simple_readpage,
32 	.write_begin		= simple_write_begin,
33 	.write_end		= simple_write_end,
34 	.set_page_dirty		= __set_page_dirty_no_writeback,
35 };
36 
37 const struct file_operations ramfs_file_operations = {
38 	.mmap			= ramfs_nommu_mmap,
39 	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,
40 	.read			= do_sync_read,
41 	.aio_read		= generic_file_aio_read,
42 	.write			= do_sync_write,
43 	.aio_write		= generic_file_aio_write,
44 	.fsync			= simple_sync_file,
45 	.splice_read		= generic_file_splice_read,
46 	.splice_write		= generic_file_splice_write,
47 	.llseek			= generic_file_llseek,
48 };
49 
50 const struct inode_operations ramfs_file_inode_operations = {
51 	.setattr		= ramfs_nommu_setattr,
52 	.getattr		= simple_getattr,
53 };
54 
55 /*****************************************************************************/
56 /*
57  * add a contiguous set of pages into a ramfs inode when it's truncated from
58  * size 0 on the assumption that it's going to be used for an mmap of shared
59  * memory
60  */
61 int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
62 {
63 	unsigned long npages, xpages, loop, limit;
64 	struct page *pages;
65 	unsigned order;
66 	void *data;
67 	int ret;
68 
69 	/* make various checks */
70 	order = get_order(newsize);
71 	if (unlikely(order >= MAX_ORDER))
72 		goto too_big;
73 
74 	limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
75 	if (limit != RLIM_INFINITY && newsize > limit)
76 		goto fsize_exceeded;
77 
78 	if (newsize > inode->i_sb->s_maxbytes)
79 		goto too_big;
80 
81 	i_size_write(inode, newsize);
82 
83 	/* allocate enough contiguous pages to be able to satisfy the
84 	 * request */
85 	pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order);
86 	if (!pages)
87 		return -ENOMEM;
88 
89 	/* split the high-order page into an array of single pages */
90 	xpages = 1UL << order;
91 	npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
92 
93 	split_page(pages, order);
94 
95 	/* trim off any pages we don't actually require */
96 	for (loop = npages; loop < xpages; loop++)
97 		__free_page(pages + loop);
98 
99 	/* clear the memory we allocated */
100 	newsize = PAGE_SIZE * npages;
101 	data = page_address(pages);
102 	memset(data, 0, newsize);
103 
104 	/* attach all the pages to the inode's address space */
105 	for (loop = 0; loop < npages; loop++) {
106 		struct page *page = pages + loop;
107 
108 		ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
109 					GFP_KERNEL);
110 		if (ret < 0)
111 			goto add_error;
112 
113 		/* prevent the page from being discarded on memory pressure */
114 		SetPageDirty(page);
115 
116 		unlock_page(page);
117 	}
118 
119 	return 0;
120 
121  fsize_exceeded:
122 	send_sig(SIGXFSZ, current, 0);
123  too_big:
124 	return -EFBIG;
125 
126  add_error:
127 	while (loop < npages)
128 		__free_page(pages + loop++);
129 	return ret;
130 }
131 
132 /*****************************************************************************/
133 /*
134  * check that file shrinkage doesn't leave any VMAs dangling in midair
135  */
136 static int ramfs_nommu_check_mappings(struct inode *inode,
137 				      size_t newsize, size_t size)
138 {
139 	struct vm_area_struct *vma;
140 	struct prio_tree_iter iter;
141 
142 	/* search for VMAs that fall within the dead zone */
143 	vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
144 			      newsize >> PAGE_SHIFT,
145 			      (size + PAGE_SIZE - 1) >> PAGE_SHIFT
146 			      ) {
147 		/* found one - only interested if it's shared out of the page
148 		 * cache */
149 		if (vma->vm_flags & VM_SHARED)
150 			return -ETXTBSY; /* not quite true, but near enough */
151 	}
152 
153 	return 0;
154 }
155 
156 /*****************************************************************************/
157 /*
158  *
159  */
160 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
161 {
162 	int ret;
163 
164 	/* assume a truncate from zero size is going to be for the purposes of
165 	 * shared mmap */
166 	if (size == 0) {
167 		if (unlikely(newsize >> 32))
168 			return -EFBIG;
169 
170 		return ramfs_nommu_expand_for_mapping(inode, newsize);
171 	}
172 
173 	/* check that a decrease in size doesn't cut off any shared mappings */
174 	if (newsize < size) {
175 		ret = ramfs_nommu_check_mappings(inode, newsize, size);
176 		if (ret < 0)
177 			return ret;
178 	}
179 
180 	ret = vmtruncate(inode, newsize);
181 
182 	return ret;
183 }
184 
185 /*****************************************************************************/
186 /*
187  * handle a change of attributes
188  * - we're specifically interested in a change of size
189  */
190 static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
191 {
192 	struct inode *inode = dentry->d_inode;
193 	unsigned int old_ia_valid = ia->ia_valid;
194 	int ret = 0;
195 
196 	/* POSIX UID/GID verification for setting inode attributes */
197 	ret = inode_change_ok(inode, ia);
198 	if (ret)
199 		return ret;
200 
201 	/* pick out size-changing events */
202 	if (ia->ia_valid & ATTR_SIZE) {
203 		loff_t size = i_size_read(inode);
204 		if (ia->ia_size != size) {
205 			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
206 			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
207 				goto out;
208 		} else {
209 			/* we skipped the truncate but must still update
210 			 * timestamps
211 			 */
212 			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
213 		}
214 	}
215 
216 	ret = inode_setattr(inode, ia);
217  out:
218 	ia->ia_valid = old_ia_valid;
219 	return ret;
220 }
221 
222 /*****************************************************************************/
223 /*
224  * try to determine where a shared mapping can be made
225  * - we require that:
226  *   - the pages to be mapped must exist
227  *   - the pages be physically contiguous in sequence
228  */
229 unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
230 					    unsigned long addr, unsigned long len,
231 					    unsigned long pgoff, unsigned long flags)
232 {
233 	unsigned long maxpages, lpages, nr, loop, ret;
234 	struct inode *inode = file->f_path.dentry->d_inode;
235 	struct page **pages = NULL, **ptr, *page;
236 	loff_t isize;
237 
238 	if (!(flags & MAP_SHARED))
239 		return addr;
240 
241 	/* the mapping mustn't extend beyond the EOF */
242 	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
243 	isize = i_size_read(inode);
244 
245 	ret = -EINVAL;
246 	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
247 	if (pgoff >= maxpages)
248 		goto out;
249 
250 	if (maxpages - pgoff < lpages)
251 		goto out;
252 
253 	/* gang-find the pages */
254 	ret = -ENOMEM;
255 	pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL);
256 	if (!pages)
257 		goto out_free;
258 
259 	nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
260 	if (nr != lpages)
261 		goto out_free_pages; /* leave if some pages were missing */
262 
263 	/* check the pages for physical adjacency */
264 	ptr = pages;
265 	page = *ptr++;
266 	page++;
267 	for (loop = lpages; loop > 1; loop--)
268 		if (*ptr++ != page++)
269 			goto out_free_pages;
270 
271 	/* okay - all conditions fulfilled */
272 	ret = (unsigned long) page_address(pages[0]);
273 
274 out_free_pages:
275 	ptr = pages;
276 	for (loop = nr; loop > 0; loop--)
277 		put_page(*ptr++);
278 out_free:
279 	kfree(pages);
280 out:
281 	return ret;
282 }
283 
284 /*****************************************************************************/
285 /*
286  * set up a mapping for shared memory segments
287  */
288 int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
289 {
290 	if (!(vma->vm_flags & VM_SHARED))
291 		return -ENOSYS;
292 
293 	file_accessed(file);
294 	vma->vm_ops = &generic_file_vm_ops;
295 	return 0;
296 }
297