mmap-nommu.c

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/* NOMMU mmap support for RomFS on MTD devices
 *
 * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/mm.h>
#include <linux/mtd/super.h>
#include "internal.h"

/*
 * try to determine where a shared mapping can be made
 * - only supported for NOMMU at the moment (MMU can't doesn't copy private
 *   mappings)
 * - attempts to map through to the underlying MTD device
 */
static unsigned long romfs_get_unmapped_area(struct file *file,
                         unsigned long addr,
                         unsigned long len,
                         unsigned long pgoff,
                         unsigned long flags)
{
    struct inode *inode = file->f_mapping->host;
    struct mtd_info *mtd = inode->i_sb->s_mtd;
    unsigned long isize, offset, maxpages, lpages;
    int ret;

    if (!mtd)
        return (unsigned long) -ENOSYS;

    /* the mapping mustn't extend beyond the EOF */
    lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
    isize = i_size_read(inode);
    offset = pgoff << PAGE_SHIFT;

    maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
    if ((pgoff >= maxpages) || (maxpages - pgoff < lpages))
        return (unsigned long) -EINVAL;

    if (addr != 0)
        return (unsigned long) -EINVAL;

    if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
        return (unsigned long) -EINVAL;

    offset += ROMFS_I(inode)->i_dataoffset;
    if (offset > mtd->size - len)
        return (unsigned long) -EINVAL;

    ret = mtd_get_unmapped_area(mtd, len, offset, flags);
    if (ret == -EOPNOTSUPP)
        ret = -ENOSYS;
    return (unsigned long) ret;
}

/*
 * permit a R/O mapping to be made directly through onto an MTD device if
 * possible
 */
static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
{
    return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
}

const struct file_operations romfs_ro_fops = {
    .llseek         = generic_file_llseek,
    .read           = do_sync_read,
    .aio_read       = generic_file_aio_read,
    .splice_read        = generic_file_splice_read,
    .mmap           = romfs_mmap,
    .get_unmapped_area  = romfs_get_unmapped_area,
};