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