fs/ramfs/file-nommu.c

   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 }