Function walk_dentry_cache 

pub fn walk_dentry_cache<P: PhysicalMemoryProvider>(
    reader: &ObjectReader<P>,
) -> Result<Vec<HiddenDentryInfo>>

Walk the task list and enumerate all open-but-unlinked file descriptors.

For each process, walks task_struct.files -> files_struct.fdt -> fdtable.fd[], then reads file->f_path.dentry->d_inode->i_nlink. Entries with i_nlink == 0 are recorded as hidden.

Gracefully returns Ok(vec![]) if any required symbol is absent.