vfs_path_lookup

void lookupInode()
{
    struct dentry* root_dentry;
    struct vfsmount* root_mnt;
    const char* filename;
    struct nameidata data;
    int err = 0;

    root_dentry = current->fs->root.dentry;
    root_mnt = current->fs->root.mnt;
    filename = "/mod/case/superblock/tmp";
    //filename = "/boot/vmlinuz-3.0.0-12-generic";
    //filename = "/";
    filename = "/home/danie/filelist.c";
    //filename = "/home/daniel";
    //filename = "/mod/case/superblock/tmp";
    err = vfs_path_lookup(root_dentry,root_mnt,filename,LOOKUP_EXCL,&data);
    printk("lookup %s\n", filename);
    if (err==0)
    {
        struct inode* nodei = data.inode;
        struct address_space* mapping = nodei->i_mapping;
        printk("mapping 0x%08x\n", mapping);
        printk("nr_pages: %d\n", mapping->nrpages);

        //printk("Showing:\n");
        printRawData(sizeof(struct inode),nodei);

    }
    else
        printk("err: %d\n", err);

}

vfs_path_lookup为什么读不到文件，但是能够读到目录？