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