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 #include <linux/slab.h>
  25
  26 #include <asm/uaccess.h>
  27 #include "internal.h"
  28
  29 static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
  30 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
  31                                                    unsigned long addr,
  32                                                    unsigned long len,
  33                                                    unsigned long pgoff,
  34                                                    unsigned long flags);
  35 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
  36
  37 static unsigned ramfs_mmap_capabilities(struct file *file)
  38 {
  39         return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
  40                 NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
  41 }
  42
  43 const struct file_operations ramfs_file_operations = {
  44         .mmap_capabilities      = ramfs_mmap_capabilities,
  45         .mmap                   = ramfs_nommu_mmap,
  46         .get_unmapped_area      = ramfs_nommu_get_unmapped_area,
  47         .read                   = new_sync_read,
  48         .read_iter              = generic_file_read_iter,
  49         .write                  = new_sync_write,
  50         .write_iter             = generic_file_write_iter,
  51         .fsync                  = noop_fsync,
  52         .splice_read            = generic_file_splice_read,
  53         .splice_write           = iter_file_splice_write,
  54         .llseek                 = generic_file_llseek,
  55 };
  56
  57 const struct inode_operations ramfs_file_inode_operations = {
  58         .setattr                = ramfs_nommu_setattr,
  59         .getattr                = simple_getattr,
  60 };
  61
  62 /*****************************************************************************/
  63 /*
  64  * add a contiguous set of pages into a ramfs inode when it's truncated from
  65  * size 0 on the assumption that it's going to be used for an mmap of shared
  66  * memory
  67  */
  68 int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
  69 {
  70         unsigned long npages, xpages, loop;
  71         struct page *pages;
  72         unsigned order;
  73         void *data;
  74         int ret;
  75
  76         /* make various checks */
  77         order = get_order(newsize);
  78         if (unlikely(order >= MAX_ORDER))
  79                 return -EFBIG;
  80
  81         ret = inode_newsize_ok(inode, newsize);
  82         if (ret)
  83                 return ret;
  84
  85         i_size_write(inode, newsize);
  86
  87         /* allocate enough contiguous pages to be able to satisfy the
  88          * request */
  89         pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order);
  90         if (!pages)
  91                 return -ENOMEM;
  92
  93         /* split the high-order page into an array of single pages */
  94         xpages = 1UL << order;
  95         npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  96
  97         split_page(pages, order);
  98
  99         /* trim off any pages we don't actually require */
 100         for (loop = npages; loop < xpages; loop++)
 101                 __free_page(pages + loop);
 102
 103         /* clear the memory we allocated */
 104         newsize = PAGE_SIZE * npages;
 105         data = page_address(pages);
 106         memset(data, 0, newsize);
 107
 108         /* attach all the pages to the inode's address space */
 109         for (loop = 0; loop < npages; loop++) {
 110                 struct page *page = pages + loop;
 111
 112                 ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
 113                                         GFP_KERNEL);
 114                 if (ret < 0)
 115                         goto add_error;
 116
 117                 /* prevent the page from being discarded on memory pressure */
 118                 SetPageDirty(page);
 119                 SetPageUptodate(page);
 120
 121                 unlock_page(page);
 122                 put_page(page);
 123         }
 124
 125         return 0;
 126
 127 add_error:
 128         while (loop < npages)
 129                 __free_page(pages + loop++);
 130         return ret;
 131 }
 132
 133 /*****************************************************************************/
 134 /*
 135  *
 136  */
 137 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 138 {
 139         int ret;
 140
 141         /* assume a truncate from zero size is going to be for the purposes of
 142          * shared mmap */
 143         if (size == 0) {
 144                 if (unlikely(newsize >> 32))
 145                         return -EFBIG;
 146
 147                 return ramfs_nommu_expand_for_mapping(inode, newsize);
 148         }
 149
 150         /* check that a decrease in size doesn't cut off any shared mappings */
 151         if (newsize < size) {
 152                 ret = nommu_shrink_inode_mappings(inode, size, newsize);
 153                 if (ret < 0)
 154                         return ret;
 155         }
 156
 157         truncate_setsize(inode, newsize);
 158         return 0;
 159 }
 160
 161 /*****************************************************************************/
 162 /*
 163  * handle a change of attributes
 164  * - we're specifically interested in a change of size
 165  */
 166 static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
 167 {
 168         struct inode *inode = dentry->d_inode;
 169         unsigned int old_ia_valid = ia->ia_valid;
 170         int ret = 0;
 171
 172         /* POSIX UID/GID verification for setting inode attributes */
 173         ret = inode_change_ok(inode, ia);
 174         if (ret)
 175                 return ret;
 176
 177         /* pick out size-changing events */
 178         if (ia->ia_valid & ATTR_SIZE) {
 179                 loff_t size = inode->i_size;
 180
 181                 if (ia->ia_size != size) {
 182                         ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 183                         if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 184                                 goto out;
 185                 } else {
 186                         /* we skipped the truncate but must still update
 187                          * timestamps
 188                          */
 189                         ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 190                 }
 191         }
 192
 193         setattr_copy(inode, ia);
 194  out:
 195         ia->ia_valid = old_ia_valid;
 196         return ret;
 197 }
 198
 199 /*****************************************************************************/
 200 /*
 201  * try to determine where a shared mapping can be made
 202  * - we require that:
 203  *   - the pages to be mapped must exist
 204  *   - the pages be physically contiguous in sequence
 205  */
 206 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 207                                             unsigned long addr, unsigned long len,
 208                                             unsigned long pgoff, unsigned long flags)
 209 {
 210         unsigned long maxpages, lpages, nr, loop, ret;
 211         struct inode *inode = file_inode(file);
 212         struct page **pages = NULL, **ptr, *page;
 213         loff_t isize;
 214
 215         if (!(flags & MAP_SHARED))
 216                 return addr;
 217
 218         /* the mapping mustn't extend beyond the EOF */
 219         lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 220         isize = i_size_read(inode);
 221
 222         ret = -EINVAL;
 223         maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
 224         if (pgoff >= maxpages)
 225                 goto out;
 226
 227         if (maxpages - pgoff < lpages)
 228                 goto out;
 229
 230         /* gang-find the pages */
 231         ret = -ENOMEM;
 232         pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
 233         if (!pages)
 234                 goto out_free;
 235
 236         nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
 237         if (nr != lpages)
 238                 goto out_free_pages; /* leave if some pages were missing */
 239
 240         /* check the pages for physical adjacency */
 241         ptr = pages;
 242         page = *ptr++;
 243         page++;
 244         for (loop = lpages; loop > 1; loop--)
 245                 if (*ptr++ != page++)
 246                         goto out_free_pages;
 247
 248         /* okay - all conditions fulfilled */
 249         ret = (unsigned long) page_address(pages[0]);
 250
 251 out_free_pages:
 252         ptr = pages;
 253         for (loop = nr; loop > 0; loop--)
 254                 put_page(*ptr++);
 255 out_free:
 256         kfree(pages);
 257 out:
 258         return ret;
 259 }
 260
 261 /*****************************************************************************/
 262 /*
 263  * set up a mapping for shared memory segments
 264  */
 265 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
 266 {
 267         if (!(vma->vm_flags & VM_SHARED))
 268                 return -ENOSYS;
 269
 270         file_accessed(file);
 271         vma->vm_ops = &generic_file_vm_ops;
 272         return 0;
 273 }