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
29static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
30static 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);
35static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
36
37static unsigned ramfs_mmap_capabilities(struct file *file)
38{
39	return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
40		NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
41}
42
43const struct file_operations ramfs_file_operations = {
44	.mmap_capabilities	= ramfs_mmap_capabilities,
45	.mmap			= ramfs_nommu_mmap,
46	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,
47	.read_iter		= generic_file_read_iter,
48	.write_iter		= generic_file_write_iter,
49	.fsync			= noop_fsync,
50	.splice_read		= generic_file_splice_read,
51	.splice_write		= iter_file_splice_write,
52	.llseek			= generic_file_llseek,
53};
54
55const struct inode_operations ramfs_file_inode_operations = {
56	.setattr		= ramfs_nommu_setattr,
57	.getattr		= simple_getattr,
58};
59
60/*****************************************************************************/
61/*
62 * add a contiguous set of pages into a ramfs inode when it's truncated from
63 * size 0 on the assumption that it's going to be used for an mmap of shared
64 * memory
65 */
66int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
67{
68	unsigned long npages, xpages, loop;
69	struct page *pages;
70	unsigned order;
71	void *data;
72	int ret;
73
74	/* make various checks */
75	order = get_order(newsize);
76	if (unlikely(order >= MAX_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(mapping_gfp_mask(inode->i_mapping), 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_KERNEL);
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
125add_error:
126	while (loop < npages)
127		__free_page(pages + loop++);
128	return ret;
129}
130
131/*****************************************************************************/
132/*
133 *
134 */
135static 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 */
164static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
165{
166	struct inode *inode = d_inode(dentry);
167	unsigned int old_ia_valid = ia->ia_valid;
168	int ret = 0;
169
170	/* POSIX UID/GID verification for setting inode attributes */
171	ret = inode_change_ok(inode, ia);
172	if (ret)
173		return ret;
174
175	/* pick out size-changing events */
176	if (ia->ia_valid & ATTR_SIZE) {
177		loff_t size = inode->i_size;
178
179		if (ia->ia_size != size) {
180			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
181			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
182				goto out;
183		} else {
184			/* we skipped the truncate but must still update
185			 * timestamps
186			 */
187			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
188		}
189	}
190
191	setattr_copy(inode, ia);
192 out:
193	ia->ia_valid = old_ia_valid;
194	return ret;
195}
196
197/*****************************************************************************/
198/*
199 * try to determine where a shared mapping can be made
200 * - we require that:
201 *   - the pages to be mapped must exist
202 *   - the pages be physically contiguous in sequence
203 */
204static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
205					    unsigned long addr, unsigned long len,
206					    unsigned long pgoff, unsigned long flags)
207{
208	unsigned long maxpages, lpages, nr, loop, ret;
209	struct inode *inode = file_inode(file);
210	struct page **pages = NULL, **ptr, *page;
211	loff_t isize;
212
213	if (!(flags & MAP_SHARED))
214		return addr;
215
216	/* the mapping mustn't extend beyond the EOF */
217	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
218	isize = i_size_read(inode);
219
220	ret = -EINVAL;
221	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
222	if (pgoff >= maxpages)
223		goto out;
224
225	if (maxpages - pgoff < lpages)
226		goto out;
227
228	/* gang-find the pages */
229	ret = -ENOMEM;
230	pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
231	if (!pages)
232		goto out_free;
233
234	nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
235	if (nr != lpages)
236		goto out_free_pages; /* leave if some pages were missing */
237
238	/* check the pages for physical adjacency */
239	ptr = pages;
240	page = *ptr++;
241	page++;
242	for (loop = lpages; loop > 1; loop--)
243		if (*ptr++ != page++)
244			goto out_free_pages;
245
246	/* okay - all conditions fulfilled */
247	ret = (unsigned long) page_address(pages[0]);
248
249out_free_pages:
250	ptr = pages;
251	for (loop = nr; loop > 0; loop--)
252		put_page(*ptr++);
253out_free:
254	kfree(pages);
255out:
256	return ret;
257}
258
259/*****************************************************************************/
260/*
261 * set up a mapping for shared memory segments
262 */
263static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
264{
265	if (!(vma->vm_flags & VM_SHARED))
266		return -ENOSYS;
267
268	file_accessed(file);
269	vma->vm_ops = &generic_file_vm_ops;
270	return 0;
271}
272