xref: /openbmc/linux/fs/ramfs/file-nommu.c (revision c819e2cf)
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 #include <linux/slab.h>
25 
26 #include <asm/uaccess.h>
27 #include "internal.h"
28 
29 static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
30 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
31 						   unsigned long addr,
32 						   unsigned long len,
33 						   unsigned long pgoff,
34 						   unsigned long flags);
35 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
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			= new_sync_read,
41 	.read_iter		= generic_file_read_iter,
42 	.write			= new_sync_write,
43 	.write_iter		= generic_file_write_iter,
44 	.fsync			= noop_fsync,
45 	.splice_read		= generic_file_splice_read,
46 	.splice_write		= iter_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;
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 		return -EFBIG;
73 
74 	ret = inode_newsize_ok(inode, newsize);
75 	if (ret)
76 		return ret;
77 
78 	i_size_write(inode, newsize);
79 
80 	/* allocate enough contiguous pages to be able to satisfy the
81 	 * request */
82 	pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order);
83 	if (!pages)
84 		return -ENOMEM;
85 
86 	/* split the high-order page into an array of single pages */
87 	xpages = 1UL << order;
88 	npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
89 
90 	split_page(pages, order);
91 
92 	/* trim off any pages we don't actually require */
93 	for (loop = npages; loop < xpages; loop++)
94 		__free_page(pages + loop);
95 
96 	/* clear the memory we allocated */
97 	newsize = PAGE_SIZE * npages;
98 	data = page_address(pages);
99 	memset(data, 0, newsize);
100 
101 	/* attach all the pages to the inode's address space */
102 	for (loop = 0; loop < npages; loop++) {
103 		struct page *page = pages + loop;
104 
105 		ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
106 					GFP_KERNEL);
107 		if (ret < 0)
108 			goto add_error;
109 
110 		/* prevent the page from being discarded on memory pressure */
111 		SetPageDirty(page);
112 		SetPageUptodate(page);
113 
114 		unlock_page(page);
115 		put_page(page);
116 	}
117 
118 	return 0;
119 
120 add_error:
121 	while (loop < npages)
122 		__free_page(pages + loop++);
123 	return ret;
124 }
125 
126 /*****************************************************************************/
127 /*
128  *
129  */
130 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
131 {
132 	int ret;
133 
134 	/* assume a truncate from zero size is going to be for the purposes of
135 	 * shared mmap */
136 	if (size == 0) {
137 		if (unlikely(newsize >> 32))
138 			return -EFBIG;
139 
140 		return ramfs_nommu_expand_for_mapping(inode, newsize);
141 	}
142 
143 	/* check that a decrease in size doesn't cut off any shared mappings */
144 	if (newsize < size) {
145 		ret = nommu_shrink_inode_mappings(inode, size, newsize);
146 		if (ret < 0)
147 			return ret;
148 	}
149 
150 	truncate_setsize(inode, newsize);
151 	return 0;
152 }
153 
154 /*****************************************************************************/
155 /*
156  * handle a change of attributes
157  * - we're specifically interested in a change of size
158  */
159 static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
160 {
161 	struct inode *inode = dentry->d_inode;
162 	unsigned int old_ia_valid = ia->ia_valid;
163 	int ret = 0;
164 
165 	/* POSIX UID/GID verification for setting inode attributes */
166 	ret = inode_change_ok(inode, ia);
167 	if (ret)
168 		return ret;
169 
170 	/* pick out size-changing events */
171 	if (ia->ia_valid & ATTR_SIZE) {
172 		loff_t size = inode->i_size;
173 
174 		if (ia->ia_size != size) {
175 			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
176 			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
177 				goto out;
178 		} else {
179 			/* we skipped the truncate but must still update
180 			 * timestamps
181 			 */
182 			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
183 		}
184 	}
185 
186 	setattr_copy(inode, ia);
187  out:
188 	ia->ia_valid = old_ia_valid;
189 	return ret;
190 }
191 
192 /*****************************************************************************/
193 /*
194  * try to determine where a shared mapping can be made
195  * - we require that:
196  *   - the pages to be mapped must exist
197  *   - the pages be physically contiguous in sequence
198  */
199 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
200 					    unsigned long addr, unsigned long len,
201 					    unsigned long pgoff, unsigned long flags)
202 {
203 	unsigned long maxpages, lpages, nr, loop, ret;
204 	struct inode *inode = file_inode(file);
205 	struct page **pages = NULL, **ptr, *page;
206 	loff_t isize;
207 
208 	if (!(flags & MAP_SHARED))
209 		return addr;
210 
211 	/* the mapping mustn't extend beyond the EOF */
212 	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
213 	isize = i_size_read(inode);
214 
215 	ret = -EINVAL;
216 	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
217 	if (pgoff >= maxpages)
218 		goto out;
219 
220 	if (maxpages - pgoff < lpages)
221 		goto out;
222 
223 	/* gang-find the pages */
224 	ret = -ENOMEM;
225 	pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
226 	if (!pages)
227 		goto out_free;
228 
229 	nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
230 	if (nr != lpages)
231 		goto out_free_pages; /* leave if some pages were missing */
232 
233 	/* check the pages for physical adjacency */
234 	ptr = pages;
235 	page = *ptr++;
236 	page++;
237 	for (loop = lpages; loop > 1; loop--)
238 		if (*ptr++ != page++)
239 			goto out_free_pages;
240 
241 	/* okay - all conditions fulfilled */
242 	ret = (unsigned long) page_address(pages[0]);
243 
244 out_free_pages:
245 	ptr = pages;
246 	for (loop = nr; loop > 0; loop--)
247 		put_page(*ptr++);
248 out_free:
249 	kfree(pages);
250 out:
251 	return ret;
252 }
253 
254 /*****************************************************************************/
255 /*
256  * set up a mapping for shared memory segments
257  */
258 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
259 {
260 	if (!(vma->vm_flags & VM_SHARED))
261 		return -ENOSYS;
262 
263 	file_accessed(file);
264 	vma->vm_ops = &generic_file_vm_ops;
265 	return 0;
266 }
267