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Linux/fs/ramfs/file-nommu.c

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

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