Function attach_tap

tools/cove_tap_tool/src/attach.rs:12–37

(
    kernel_file: String,
    tap_file_name: String,
    output_file: Option<String>,
)

use std::io::SeekFrom;

pub fn attach_tap(
    kernel_file: String,
    tap_file_name: String,
    output_file: Option<String>,
) -> Result<(), Error> {
    let output_file_name = match output_file {
        Some(f) if kernel_file != f => {
            std::fs::copy(kernel_file, f.clone())?;
            f
        }
        Some(f) => f,
        None => kernel_file,
    };
    let offset = find_placehoder(&output_file_name)?;
    // clear the placeholder
    let mut output_file = OpenOptions::new().write(true).open(output_file_name)?;
    output_file.seek(SeekFrom::Start(offset))?;
    (riscv_cove_tap::ACE_HEADER_SIZE..riscv_cove_tap::ACE_MAX_TAP_SIZE)
        .try_for_each(|_| output_file.write_u8(0u8))?;
    // write expected TAP from the beginning of the offset
    output_file.seek(SeekFrom::Start(offset))?;
    let mut tap_file = OpenOptions::new().read(true).open(tap_file_name)?;
    std::io::copy(&mut tap_file, &mut output_file)?;
    println!("TAP attached successfully");
    Ok(())
}

fn find_placehoder(output_file_name: &str) -> Result<u64, Error> {
    let output_file = OpenOptions::new().read(true).open(output_file_name)?;