fs/ramfs/file-nommu.c

   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
  24 #include <asm/uaccess.h>
  25 #include "internal.h"
  26
  27 static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
  28
  29 const struct address_space_operations ramfs_aops = {
  30         .readpage               = simple_readpage,
  31         .write_begin            = simple_write_begin,
  32         .write_end              = simple_write_end,
  33         .set_page_dirty         = __set_page_dirty_no_writeback,
  34 };
  35
  36 const struct file_operations ramfs_file_operations = {
  37         .mmap                   = ramfs_nommu_mmap,
  38         .get_unmapped_area      = ramfs_nommu_get_unmapped_area,
  39         .read                   = do_sync_read,
  40         .aio_read               = generic_file_aio_read,
  41         .write                  = do_sync_write,
  42         .aio_write              = generic_file_aio_write,
  43         .fsync                  = simple_sync_file,
  44         .splice_read            = generic_file_splice_read,
  45         .splice_write           = generic_file_splice_write,
  46         .llseek                 = generic_file_llseek,
  47 };
  48
  49 const struct inode_operations ramfs_file_inode_operations = {
  50         .setattr                = ramfs_nommu_setattr,
  51         .getattr                = simple_getattr,
  52 };
  53
  54 /*****************************************************************************/
  55 /*
  56  * add a contiguous set of pages into a ramfs inode when it's truncated from
  57  * size 0 on the assumption that it's going to be used for an mmap of shared
  58  * memory
  59  */
  60 int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
  61 {
  62         unsigned long npages, xpages, loop, limit;
  63         struct page *pages;
  64         unsigned order;
  65         void *data;
  66         int ret;
  67
  68         /* make various checks */
  69         order = get_order(newsize);
  70         if (unlikely(order >= MAX_ORDER))
  71                 goto too_big;
  72
  73         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
  74         if (limit != RLIM_INFINITY && newsize > limit)
  75                 goto fsize_exceeded;
  76
  77         if (newsize > inode->i_sb->s_maxbytes)
  78                 goto too_big;
  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(mapping_gfp_mask(inode->i_mapping), 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_KERNEL);
 109                 if (ret < 0)
 110                         goto add_error;
 111
 112                 /* prevent the page from being discarded on memory pressure */
 113                 SetPageDirty(page);
 114
 115                 unlock_page(page);
 116         }
 117
 118         return 0;
 119
 120  fsize_exceeded:
 121         send_sig(SIGXFSZ, current, 0);
 122  too_big:
 123         return -EFBIG;
 124
 125  add_error:
 126         while (loop < npages)
 127                 __free_page(pages + loop++);
 128         return ret;
 129 }
 130
 131 /*****************************************************************************/
 132 /*
 133  * check that file shrinkage doesn't leave any VMAs dangling in midair
 134  */
 135 static int ramfs_nommu_check_mappings(struct inode *inode,
 136                                       size_t newsize, size_t size)
 137 {
 138         struct vm_area_struct *vma;
 139         struct prio_tree_iter iter;
 140
 141         /* search for VMAs that fall within the dead zone */
 142         vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
 143                               newsize >> PAGE_SHIFT,
 144                               (size + PAGE_SIZE - 1) >> PAGE_SHIFT
 145                               ) {
 146                 /* found one - only interested if it's shared out of the page
 147                  * cache */
 148                 if (vma->vm_flags & VM_SHARED)
 149                         return -ETXTBSY; /* not quite true, but near enough */
 150         }
 151
 152         return 0;
 153 }
 154
 155 /*****************************************************************************/
 156 /*
 157  *
 158  */
 159 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 160 {
 161         int ret;
 162
 163         /* assume a truncate from zero size is going to be for the purposes of
 164          * shared mmap */
 165         if (size == 0) {
 166                 if (unlikely(newsize >> 32))
 167                         return -EFBIG;
 168
 169                 return ramfs_nommu_expand_for_mapping(inode, newsize);
 170         }
 171
 172         /* check that a decrease in size doesn't cut off any shared mappings */
 173         if (newsize < size) {
 174                 ret = ramfs_nommu_check_mappings(inode, newsize, size);
 175                 if (ret < 0)
 176                         return ret;
 177         }
 178
 179         ret = vmtruncate(inode, newsize);
 180
 181         return ret;
 182 }
 183
 184 /*****************************************************************************/
 185 /*
 186  * handle a change of attributes
 187  * - we're specifically interested in a change of size
 188  */
 189 static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
 190 {
 191         struct inode *inode = dentry->d_inode;
 192         unsigned int old_ia_valid = ia->ia_valid;
 193         int ret = 0;
 194
 195         /* POSIX UID/GID verification for setting inode attributes */
 196         ret = inode_change_ok(inode, ia);
 197         if (ret)
 198                 return ret;
 199
 200         /* pick out size-changing events */
 201         if (ia->ia_valid & ATTR_SIZE) {
 202                 loff_t size = i_size_read(inode);
 203                 if (ia->ia_size != size) {
 204                         ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 205                         if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 206                                 goto out;
 207                 } else {
 208                         /* we skipped the truncate but must still update
 209                          * timestamps
 210                          */
 211                         ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 212                 }
 213         }
 214
 215         ret = inode_setattr(inode, ia);
 216  out:
 217         ia->ia_valid = old_ia_valid;
 218         return ret;
 219 }
 220
 221 /*****************************************************************************/
 222 /*
 223  * try to determine where a shared mapping can be made
 224  * - we require that:
 225  *   - the pages to be mapped must exist
 226  *   - the pages be physically contiguous in sequence
 227  */
 228 unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 229                                             unsigned long addr, unsigned long len,
 230                                             unsigned long pgoff, unsigned long flags)
 231 {
 232         unsigned long maxpages, lpages, nr, loop, ret;
 233         struct inode *inode = file->f_path.dentry->d_inode;
 234         struct page **pages = NULL, **ptr, *page;
 235         loff_t isize;
 236
 237         if (!(flags & MAP_SHARED))
 238                 return addr;
 239
 240         /* the mapping mustn't extend beyond the EOF */
 241         lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 242         isize = i_size_read(inode);
 243
 244         ret = -EINVAL;
 245         maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
 246         if (pgoff >= maxpages)
 247                 goto out;
 248
 249         if (maxpages - pgoff < lpages)
 250                 goto out;
 251
 252         /* gang-find the pages */
 253         ret = -ENOMEM;
 254         pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL);
 255         if (!pages)
 256                 goto out_free;
 257
 258         nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
 259         if (nr != lpages)
 260                 goto out_free_pages; /* leave if some pages were missing */
 261
 262         /* check the pages for physical adjacency */
 263         ptr = pages;
 264         page = *ptr++;
 265         page++;
 266         for (loop = lpages; loop > 1; loop--)
 267                 if (*ptr++ != page++)
 268                         goto out_free_pages;
 269
 270         /* okay - all conditions fulfilled */
 271         ret = (unsigned long) page_address(pages[0]);
 272
 273 out_free_pages:
 274         ptr = pages;
 275         for (loop = nr; loop > 0; loop--)
 276                 put_page(*ptr++);
 277 out_free:
 278         kfree(pages);
 279 out:
 280         return ret;
 281 }
 282
 283 /*****************************************************************************/
 284 /*
 285  * set up a mapping for shared memory segments
 286  */
 287 int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
 288 {
 289         if (!(vma->vm_flags & VM_SHARED))
 290                 return -ENOSYS;
 291
 292         file_accessed(file);
 293         vma->vm_ops = &generic_file_vm_ops;
 294         return 0;
 295 }