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