fs/romfs/mmap-nommu.c

   1 /* NOMMU mmap support for RomFS on MTD devices
   2  *
   3  * Copyright © 2007 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/mm.h>
  13 #include <linux/mtd/super.h>
  14 #include "internal.h"
  15
  16 /*
  17  * try to determine where a shared mapping can be made
  18  * - only supported for NOMMU at the moment (MMU can't doesn't copy private
  19  *   mappings)
  20  * - attempts to map through to the underlying MTD device
  21  */
  22 static unsigned long romfs_get_unmapped_area(struct file *file,
  23                                              unsigned long addr,
  24                                              unsigned long len,
  25                                              unsigned long pgoff,
  26                                              unsigned long flags)
  27 {
  28         struct inode *inode = file->f_mapping->host;
  29         struct mtd_info *mtd = inode->i_sb->s_mtd;
  30         unsigned long isize, offset, maxpages, lpages;
  31
  32         if (!mtd)
  33                 goto cant_map_directly;
  34
  35         /* the mapping mustn't extend beyond the EOF */
  36         lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  37         isize = i_size_read(inode);
  38         offset = pgoff << PAGE_SHIFT;
  39
  40         maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  41         if ((pgoff >= maxpages) || (maxpages - pgoff < lpages))
  42                 return (unsigned long) -EINVAL;
  43
  44         /* we need to call down to the MTD layer to do the actual mapping */
  45         if (mtd->get_unmapped_area) {
  46                 if (addr != 0)
  47                         return (unsigned long) -EINVAL;
  48
  49                 if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
  50                         return (unsigned long) -EINVAL;
  51
  52                 offset += ROMFS_I(inode)->i_dataoffset;
  53                 if (offset > mtd->size - len)
  54                         return (unsigned long) -EINVAL;
  55
  56                 return mtd->get_unmapped_area(mtd, len, offset, flags);
  57         }
  58
  59 cant_map_directly:
  60         return (unsigned long) -ENOSYS;
  61 }
  62
  63 /*
  64  * permit a R/O mapping to be made directly through onto an MTD device if
  65  * possible
  66  */
  67 static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
  68 {
  69         return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
  70 }
  71
  72 const struct file_operations romfs_ro_fops = {
  73         .llseek                 = generic_file_llseek,
  74         .read                   = do_sync_read,
  75         .aio_read               = generic_file_aio_read,
  76         .splice_read            = generic_file_splice_read,
  77         .mmap                   = romfs_mmap,
  78         .get_unmapped_area      = romfs_get_unmapped_area,
  79 };