ramfs_nommu_get_unmapped

/*****************************************************************************/
/*
 * try to determine where a shared mapping can be made
 * - we require that:
 *   - the pages to be mapped must exist
 *   - the pages be physically contiguous in sequence
 */
static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
                        unsigned long addr, unsigned long len,
                        unsigned long pgoff, unsigned long flags)
{
    unsigned long maxpages, lpages, nr, loop, ret;
    struct inode *inode = file_inode(file);
    struct page **pages = NULL, **ptr, *page;
    loff_t isize;
 
    /* the mapping mustn't extend beyond the EOF */
    lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
    isize = i_size_read(inode);
 
    ret = -ENOSYS;
    maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
    if (pgoff >= maxpages)
        goto out;
 
    if (maxpages - pgoff < lpages)
        goto out;
 
    /* gang-find the pages */
    pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
    if (!pages)
        goto out_free;
 
    nr = find_get_pages(inode->i_mapping, &pgoff, lpages, pages);
    if (nr != lpages)
        goto out_free_pages; /* leave if some pages were missing */
 
    /* check the pages for physical adjacency */
    ptr = pages;
    page = *ptr++;
    page++;
    for (loop = lpages; loop > 1; loop--)
        if (*ptr++ != page++)
            goto out_free_pages;
 
    /* okay - all conditions fulfilled */
    ret = (unsigned long) page_address(pages[0]);
 
out_free_pages:
    ptr = pages;
    for (loop = nr; loop > 0; loop--)
        put_page(*ptr++);
out_free:
    kfree(pages);
out:
    return ret;
}
函数源码
