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                 goto too_big;
  73
  74         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
  75         if (limit != RLIM_INFINITY && newsize > limit)
  76                 goto fsize_exceeded;
  77
  78         if (newsize > inode->i_sb->s_maxbytes)
  79                 goto too_big;
  80
  81         i_size_write(inode, newsize);
  82
  83         /* allocate enough contiguous pages to be able to satisfy the
  84          * request */
  85         pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order);
  86         if (!pages)
  87                 return -ENOMEM;
  88
  89         /* split the high-order page into an array of single pages */
  90         xpages = 1UL << order;
  91         npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  92
  93         split_page(pages, order);
  94
  95         /* trim off any pages we don't actually require */
  96         for (loop = npages; loop < xpages; loop++)
  97                 __free_page(pages + loop);
  98
  99         /* clear the memory we allocated */
 100         newsize = PAGE_SIZE * npages;
 101         data = page_address(pages);
 102         memset(data, 0, newsize);
 103
 104         /* attach all the pages to the inode's address space */
 105         for (loop = 0; loop < npages; loop++) {
 106                 struct page *page = pages + loop;
 107
 108                 ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
 109                                         GFP_KERNEL);
 110                 if (ret < 0)
 111                         goto add_error;
 112
 113                 /* prevent the page from being discarded on memory pressure */
 114                 SetPageDirty(page);
 115
 116                 unlock_page(page);
 117         }
 118
 119         return 0;
 120
 121  fsize_exceeded:
 122         send_sig(SIGXFSZ, current, 0);
 123  too_big:
 124         return -EFBIG;
 125
 126  add_error:
 127         while (loop < npages)
 128                 __free_page(pages + loop++);
 129         return ret;
 130 }
 131
 132 /*****************************************************************************/
 133 /*
 134  * check that file shrinkage doesn't leave any VMAs dangling in midair
 135  */
 136 static int ramfs_nommu_check_mappings(struct inode *inode,
 137                                       size_t newsize, size_t size)
 138 {
 139         struct vm_area_struct *vma;
 140         struct prio_tree_iter iter;
 141
 142         /* search for VMAs that fall within the dead zone */
 143         vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
 144                               newsize >> PAGE_SHIFT,
 145                               (size + PAGE_SIZE - 1) >> PAGE_SHIFT
 146                               ) {
 147                 /* found one - only interested if it's shared out of the page
 148                  * cache */
 149                 if (vma->vm_flags & VM_SHARED)
 150                         return -ETXTBSY; /* not quite true, but near enough */
 151         }
 152
 153         return 0;
 154 }
 155
 156 /*****************************************************************************/
 157 /*
 158  *
 159  */
 160 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 161 {
 162         int ret;
 163
 164         /* assume a truncate from zero size is going to be for the purposes of
 165          * shared mmap */
 166         if (size == 0) {
 167                 if (unlikely(newsize >> 32))
 168                         return -EFBIG;
 169
 170                 return ramfs_nommu_expand_for_mapping(inode, newsize);
 171         }
 172
 173         /* check that a decrease in size doesn't cut off any shared mappings */
 174         if (newsize < size) {
 175                 ret = ramfs_nommu_check_mappings(inode, newsize, size);
 176                 if (ret < 0)
 177                         return ret;
 178         }
 179
 180         ret = vmtruncate(inode, newsize);
 181
 182         return ret;
 183 }
 184
 185 /*****************************************************************************/
 186 /*
 187  * handle a change of attributes
 188  * - we're specifically interested in a change of size
 189  */
 190 static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
 191 {
 192         struct inode *inode = dentry->d_inode;
 193         unsigned int old_ia_valid = ia->ia_valid;
 194         int ret = 0;
 195
 196         /* POSIX UID/GID verification for setting inode attributes */
 197         ret = inode_change_ok(inode, ia);
 198         if (ret)
 199                 return ret;
 200
 201         /* pick out size-changing events */
 202         if (ia->ia_valid & ATTR_SIZE) {
 203                 loff_t size = i_size_read(inode);
 204                 if (ia->ia_size != size) {
 205                         ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 206                         if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 207                                 goto out;
 208                 } else {
 209                         /* we skipped the truncate but must still update
 210                          * timestamps
 211                          */
 212                         ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 213                 }
 214         }
 215
 216         ret = inode_setattr(inode, ia);
 217  out:
 218         ia->ia_valid = old_ia_valid;
 219         return ret;
 220 }
 221
 222 /*****************************************************************************/
 223 /*
 224  * try to determine where a shared mapping can be made
 225  * - we require that:
 226  *   - the pages to be mapped must exist
 227  *   - the pages be physically contiguous in sequence
 228  */
 229 unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 230                                             unsigned long addr, unsigned long len,
 231                                             unsigned long pgoff, unsigned long flags)
 232 {
 233         unsigned long maxpages, lpages, nr, loop, ret;
 234         struct inode *inode = file->f_path.dentry->d_inode;
 235         struct page **pages = NULL, **ptr, *page;
 236         loff_t isize;
 237
 238         if (!(flags & MAP_SHARED))
 239                 return addr;
 240
 241         /* the mapping mustn't extend beyond the EOF */
 242         lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 243         isize = i_size_read(inode);
 244
 245         ret = -EINVAL;
 246         maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
 247         if (pgoff >= maxpages)
 248                 goto out;
 249
 250         if (maxpages - pgoff < lpages)
 251                 goto out;
 252
 253         /* gang-find the pages */
 254         ret = -ENOMEM;
 255         pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL);
 256         if (!pages)
 257                 goto out_free;
 258
 259         nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
 260         if (nr != lpages)
 261                 goto out_free_pages; /* leave if some pages were missing */
 262
 263         /* check the pages for physical adjacency */
 264         ptr = pages;
 265         page = *ptr++;
 266         page++;
 267         for (loop = lpages; loop > 1; loop--)
 268                 if (*ptr++ != page++)
 269                         goto out_free_pages;
 270
 271         /* okay - all conditions fulfilled */
 272         ret = (unsigned long) page_address(pages[0]);
 273
 274 out_free_pages:
 275         ptr = pages;
 276         for (loop = nr; loop > 0; loop--)
 277                 put_page(*ptr++);
 278 out_free:
 279         kfree(pages);
 280 out:
 281         return ret;
 282 }
 283
 284 /*****************************************************************************/
 285 /*
 286  * set up a mapping for shared memory segments
 287  */
 288 int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
 289 {
 290         if (!(vma->vm_flags & VM_SHARED))
 291                 return -ENOSYS;
 292
 293         file_accessed(file);
 294         vma->vm_ops = &generic_file_vm_ops;
 295         return 0;
 296 }