Telnet Server

poll() support for PTY master FDs. Why it matters: telnetd's relay loop multiplexes both the TCP socket and PTY master FD using poll(); without PTY master support the relay would require busy-waiting. Focus on `sys_poll` and `poll` in `kernel/src/arch/x86_64/syscall.rs` while you trace the snippet.

/// poll(fds, nfds, timeout) — check fd readiness.
///
/// For pipe-read fds: report POLLIN if data available or writer closed (EOF).
/// For TTY fds: report POLLIN if stdin has data.
/// Other fds: report requested events (optimistic).
/// If no fds are ready and timeout != 0, yield once and re-check.
fn sys_poll(fds_ptr: u64, nfds: u64, timeout: u64) -> u64 {
    const POLLIN: i16 = 0x001;
    let nfds = nfds as usize;
    if nfds > 256 {
        return NEG_EINVAL;
    }
    let timeout_i = timeout as i64;
    let pid = crate::process::CURRENT_PID.load(core::sync::atomic::Ordering::Relaxed);
    let saved_user_rsp = unsafe { SYSCALL_USER_RSP };

    loop {
        let mut ready_count = 0u64;

        for i in 0..nfds {
            let base = match fds_ptr.checked_add((i * 8) as u64) {
                Some(a) => a,
                None => return NEG_EFAULT,
            };

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Increase MAX_TCP_CONNECTIONS. Why it matters: 1 listening slot plus ≥4 client slots are needed for the multi-session acceptance criteria; the previous limit of 4 was insufficient. Focus on `MAX_TCP_CONNECTIONS` in `kernel/src/net/tcp.rs` while you trace the snippet.

const MAX_TCP_CONNECTIONS: usize = 8;

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Create telnetd/ and xtask build step. Why it matters: integrating telnetd into the existing musl build pipeline ensures it is automatically compiled and placed in the initrd alongside other C userspace binaries. Focus on `build_musl_bins` and `telnetd.c` in `userspace/telnetd/telnetd.c` while you trace the snippet.

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