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