fix(net): add packet polling to networking syscalls for first-call readiness (#99)

ryanbreen · claude · web-flow · commit 2532624014ec · 2026-01-16T13:34:52.000-05:00
* fix(ext2): add init_shell and telnetd to filesystem

The telnetd server was trying to exec /bin/init_shell but it wasn't
in the ext2 filesystem, causing the shell to fail to start over telnet.

Now ext2 contains:
- /bin/init_shell (32KB) - interactive shell
- /bin/telnetd (9KB) - telnet server

Co-Authored-By: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;

* fix(net): add packet polling to networking syscalls for first-call readiness

TCP listeners were not detecting pending connections on the first
poll/select/accept call because incoming SYN packets remained
unprocessed in the e1000 driver buffer. The fix ensures process_rx()
and drain_loopback_queue() are called at syscall entry.

Changes:
- Add process_rx() + drain_loopback_queue() to sys_poll, sys_select,
  sys_accept, sys_recvfrom, and sys_read for TcpConnection
- Add first-call accept test (Test 25) without retry loop
- Add TCP listener poll test (Phase 8) verifying POLLIN on first call
- Add TCP listener select test (Phase 8) verifying readiness on first call
- Fix PTY master reference counting for fork/exec scenarios
- Add telnetd to ext2 filesystem and update run.sh for interactive mode

All 226 boot stages pass. Tests verify first-call success without
retry loops, ensuring the fix actually works rather than masking
timing issues.

Co-Authored-By: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;

* fix(tcp): add refcount for fork/close pattern + remove debug output

TCP connections now use reference counting similar to PTY:
- Add refcount field to TcpConnection (AtomicUsize)
- tcp_add_ref() increments count during fork
- tcp_close() only sends FIN when last reference drops
- FdTable::clone() calls tcp_add_ref() for TCP fds

This fixes telnetd where the child closes inherited socket fds,
which was prematurely closing the parent's connection.

Also removes debug output:
- TSS RSP0 updated messages from gdt.rs
- tcp_add_ref/tcp_close debug logs from tcp.rs

Co-Authored-By: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;

---------

Co-authored-by: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;
diff --git a/kernel/src/gdt.rs b/kernel/src/gdt.rs
@@ -178,13 +178,7 @@ pub fn set_kernel_stack(stack_top: VirtAddr) {
     let tss_ptr = TSS_PTR.load(Ordering::Acquire);
     if !tss_ptr.is_null() {
         unsafe {
-            let old_stack = (*tss_ptr).privilege_stack_table[0];
             (*tss_ptr).privilege_stack_table[0] = stack_top;
-            crate::serial_println!(
-                "TSS RSP0 updated: {:#x} -> {:#x}",
-                old_stack.as_u64(),
-                stack_top.as_u64()
-            );
         }
     } else {
         panic!("TSS not initialized");
diff --git a/kernel/src/ipc/fd.rs b/kernel/src/ipc/fd.rs
@@ -205,12 +205,24 @@ impl Clone for FdTable {
 
         let cloned_fds = alloc::boxed::Box::new((*self.fds).clone());
 
-        // Increment pipe reference counts for all cloned pipe fds
+        // Increment reference counts for all cloned fds that need it
         for fd_opt in cloned_fds.iter() {
             if let Some(fd_entry) = fd_opt {
                 match &fd_entry.kind {
                     FdKind::PipeRead(buffer) => buffer.lock().add_reader(),
                     FdKind::PipeWrite(buffer) => buffer.lock().add_writer(),
+                    FdKind::PtyMaster(pty_num) => {
+                        // Increment PTY master reference count for the clone
+                        if let Some(pair) = crate::tty::pty::get(*pty_num) {
+                            let old_count = pair.master_refcount.fetch_add(1, core::sync::atomic::Ordering::SeqCst);
+                            log::debug!("FdTable::clone() - PTY master {} refcount {} -> {}",
+                                pty_num, old_count, old_count + 1);
+                        }
+                    }
+                    FdKind::TcpConnection(conn_id) => {
+                        // Increment TCP connection reference count for the clone
+                        crate::net::tcp::tcp_add_ref(conn_id);
+                    }
                     _ => {}
                 }
             }
@@ -470,9 +482,16 @@ impl Drop for FdTable {
                         log::debug!("FdTable::drop() - releasing devpts directory fd {}", i);
                     }
                     FdKind::PtyMaster(pty_num) => {
-                        // PTY master cleanup - release the PTY pair when master closes
-                        crate::tty::pty::release(pty_num);
-                        log::debug!("FdTable::drop() - released PTY master fd {} (pty {})", i, pty_num);
+                        // PTY master cleanup - decrement refcount, only release when all masters closed
+                        if let Some(pair) = crate::tty::pty::get(pty_num) {
+                            let old_count = pair.master_refcount.fetch_sub(1, core::sync::atomic::Ordering::SeqCst);
+                            log::debug!("FdTable::drop() - PTY master fd {} (pty {}) refcount {} -> {}",
+                                i, pty_num, old_count, old_count - 1);
+                            if old_count == 1 {
+                                crate::tty::pty::release(pty_num);
+                                log::debug!("FdTable::drop() - released PTY {} (last master closed)", pty_num);
+                            }
+                        }
                     }
                     FdKind::PtySlave(_pty_num) => {
                         // PTY slave doesn't own the pair, just decrement reference
diff --git a/kernel/src/net/tcp.rs b/kernel/src/net/tcp.rs
@@ -296,6 +296,8 @@ pub struct TcpConnection {
     pub send_shutdown: bool,
     /// True if SHUT_RD was called (no more receiving)
     pub recv_shutdown: bool,
+    /// Reference count for fork() support - connection is only closed when last fd is closed
+    pub refcount: core::sync::atomic::AtomicUsize,
 }
 
 impl TcpConnection {
@@ -321,6 +323,7 @@ impl TcpConnection {
             owner_pid,
             send_shutdown: false,
             recv_shutdown: false,
+            refcount: core::sync::atomic::AtomicUsize::new(1),
         }
     }
 
@@ -352,6 +355,7 @@ impl TcpConnection {
             owner_pid,
             send_shutdown: false,
             recv_shutdown: false,
+            refcount: core::sync::atomic::AtomicUsize::new(1),
         }
     }
 }
@@ -1034,13 +1038,30 @@ pub fn tcp_shutdown(conn_id: &ConnectionId, shut_rd: bool, shut_wr: bool) {
     }
 }
 
-/// Close a connection
+/// Increment reference count on a TCP connection (called during fork)
+pub fn tcp_add_ref(conn_id: &ConnectionId) {
+    let connections = TCP_CONNECTIONS.lock();
+    if let Some(conn) = connections.get(conn_id) {
+        conn.refcount.fetch_add(1, core::sync::atomic::Ordering::SeqCst);
+    }
+}
+
+/// Close a connection (decrement refcount, only actually close when last reference dropped)
 pub fn tcp_close(conn_id: &ConnectionId) -> Result<(), &'static str> {
     let config = super::config();
 
     let mut connections = TCP_CONNECTIONS.lock();
     let conn = connections.get_mut(conn_id).ok_or("Connection not found")?;
 
+    // Decrement reference count
+    let old_count = conn.refcount.fetch_sub(1, core::sync::atomic::Ordering::SeqCst);
+
+    // Only actually close when last reference is dropped
+    if old_count > 1 {
+        return Ok(());
+    }
+
+    // Last reference - actually close the connection
     match conn.state {
         TcpState::Established => {
             // Send FIN
diff --git a/kernel/src/process/process.rs b/kernel/src/process/process.rs
@@ -275,9 +275,16 @@ impl Process {
                         log::debug!("Process::close_all_fds() - released devpts directory fd {}", fd);
                     }
                     FdKind::PtyMaster(pty_num) => {
-                        // PTY master cleanup - release the PTY pair when master closes
-                        crate::tty::pty::release(pty_num);
-                        log::debug!("Process::close_all_fds() - released PTY master fd {} (pty {})", fd, pty_num);
+                        // PTY master cleanup - decrement refcount, only release when all masters closed
+                        if let Some(pair) = crate::tty::pty::get(pty_num) {
+                            let old_count = pair.master_refcount.fetch_sub(1, core::sync::atomic::Ordering::SeqCst);
+                            log::debug!("Process::close_all_fds() - PTY master fd {} (pty {}) refcount {} -> {}",
+                                fd, pty_num, old_count, old_count - 1);
+                            if old_count == 1 {
+                                crate::tty::pty::release(pty_num);
+                                log::debug!("Process::close_all_fds() - released PTY {} (last master closed)", pty_num);
+                            }
+                        }
                     }
                     FdKind::PtySlave(_pty_num) => {
                         // PTY slave doesn't own the pair, just decrement reference
diff --git a/kernel/src/syscall/handlers.rs b/kernel/src/syscall/handlers.rs
@@ -783,7 +783,8 @@ pub fn sys_read(fd: u64, buf_ptr: u64, count: u64) -> SyscallResult {
         }
         FdKind::TcpConnection(conn_id) => {
             // Read from TCP connection
-            // First drain loopback queue in case there are pending packets
+            // First process any pending network packets
+            crate::net::process_rx();
             crate::net::drain_loopback_queue();
             let mut user_buf = alloc::vec![0u8; count as usize];
             match crate::net::tcp::tcp_recv(conn_id, &mut user_buf) {
@@ -2301,6 +2302,12 @@ pub fn sys_poll(fds_ptr: u64, nfds: u64, _timeout: i32) -> SyscallResult {
 
     log::debug!("sys_poll: fds_ptr={:#x}, nfds={}, timeout={}", fds_ptr, nfds, _timeout);
 
+    // Process any pending network packets before checking fd readiness.
+    // This is critical for TCP listeners - without this, incoming SYN packets
+    // remain unprocessed in the e1000 driver buffer and accept() never sees connections.
+    crate::net::process_rx();
+    crate::net::drain_loopback_queue();
+
     // Validate parameters
     if fds_ptr == 0 && nfds > 0 {
         return SyscallResult::Err(14); // EFAULT
@@ -2429,6 +2436,12 @@ pub fn sys_select(
         nfds, readfds_ptr, writefds_ptr, exceptfds_ptr, _timeout_ptr
     );
 
+    // Process any pending network packets before checking fd readiness.
+    // This is critical for TCP listeners - without this, incoming SYN packets
+    // remain unprocessed in the e1000 driver buffer and accept() never sees connections.
+    crate::net::process_rx();
+    crate::net::drain_loopback_queue();
+
     // Validate nfds - must be non-negative and <= 64 (we only support u64 bitmaps)
     if nfds < 0 {
         log::debug!("sys_select: Invalid nfds {}", nfds);
diff --git a/kernel/src/syscall/pipe.rs b/kernel/src/syscall/pipe.rs
@@ -192,9 +192,19 @@ pub fn sys_close(fd: i32) -> SyscallResult {
                     log::debug!("sys_close: Closed TCP connection fd={}", fd);
                 }
                 FdKind::PtyMaster(pty_num) => {
-                    // PTY master cleanup - release the PTY pair when master closes
-                    crate::tty::pty::release(pty_num);
-                    log::debug!("sys_close: Closed PTY master fd={} (pty {})", fd, pty_num);
+                    // PTY master cleanup - decrement refcount, only release when all masters closed
+                    if let Some(pair) = crate::tty::pty::get(pty_num) {
+                        let old_count = pair.master_refcount.fetch_sub(1, core::sync::atomic::Ordering::SeqCst);
+                        log::debug!("sys_close: PTY master fd={} (pty {}) refcount {} -> {}",
+                            fd, pty_num, old_count, old_count - 1);
+                        if old_count == 1 {
+                            // Last reference - release the PTY pair
+                            crate::tty::pty::release(pty_num);
+                            log::debug!("sys_close: Released PTY {} (last master closed)", pty_num);
+                        }
+                    } else {
+                        log::warn!("sys_close: PTY {} not found for master fd={}", pty_num, fd);
+                    }
                 }
                 FdKind::PtySlave(pty_num) => {
                     // PTY slave doesn't own the pair, just log closure
diff --git a/kernel/src/syscall/socket.rs b/kernel/src/syscall/socket.rs
@@ -312,6 +312,10 @@ pub fn sys_recvfrom(
     src_addr_ptr: u64,
     addrlen_ptr: u64,
 ) -> SyscallResult {
+    // Process any pending network packets before checking for received data.
+    crate::net::process_rx();
+    crate::net::drain_loopback_queue();
+
     // Validate buffer pointer
     if buf_ptr == 0 {
         return SyscallResult::Err(EFAULT as u64);
@@ -471,6 +475,11 @@ pub fn sys_listen(fd: u64, backlog: u64) -> SyscallResult {
 pub fn sys_accept(fd: u64, addr_ptr: u64, addrlen_ptr: u64) -> SyscallResult {
     log::debug!("sys_accept: fd={}", fd);
 
+    // Process any pending network packets before checking for connections.
+    // This ensures incoming SYN packets are handled even if IRQ hasn't fired.
+    crate::net::process_rx();
+    crate::net::drain_loopback_queue();
+
     // Get current thread and process
     let current_thread_id = match crate::per_cpu::current_thread() {
         Some(thread) => thread.id,
diff --git a/run.sh b/run.sh
@@ -1,3 +1,8 @@
 #!/bin/bash
-# Start Breenix in interactive mode
-cargo run -p xtask -- interactive "$@"
+# Start Breenix in interactive mode with telnet port forwarding (2323)
+# Port 2323 is forwarded automatically by qemu-uefi
+#
+# Two windows:
+#   - QEMU window: Type commands here (PS/2 keyboard -> shell)
+#   - This terminal: Watch serial output (debug messages)
+cargo run --release --features testing,external_test_bins,interactive --bin qemu-uefi -- -display cocoa -serial mon:stdio "$@"
diff --git a/scripts/create_ext2_disk.sh b/scripts/create_ext2_disk.sh
@@ -107,6 +107,24 @@ if [[ "$(uname)" == "Darwin" ]]; then
                 echo "  WARNING: hello_world.elf not found"
             fi
 
+            # Copy init_shell for interactive use and telnet
+            if [ -f /binaries/init_shell.elf ]; then
+                cp /binaries/init_shell.elf /mnt/ext2/bin/init_shell
+                chmod 755 /mnt/ext2/bin/init_shell
+                echo "  /bin/init_shell installed"
+            else
+                echo "  WARNING: init_shell.elf not found"
+            fi
+
+            # Copy telnetd for remote access (system daemon, goes in /sbin)
+            if [ -f /binaries/telnetd.elf ]; then
+                cp /binaries/telnetd.elf /mnt/ext2/sbin/telnetd
+                chmod 755 /mnt/ext2/sbin/telnetd
+                echo "  /sbin/telnetd installed"
+            else
+                echo "  WARNING: telnetd.elf not found"
+            fi
+
             # Create test files for filesystem testing
             echo "Hello from ext2!" > /mnt/ext2/hello.txt
             echo "Truncate test file" > /mnt/ext2/trunctest.txt
@@ -209,6 +227,20 @@ else
         echo "  /bin/hello_world installed"
     fi
 
+    # Copy init_shell for interactive use and telnet
+    if [ -f "$USERSPACE_DIR/init_shell.elf" ]; then
+        cp "$USERSPACE_DIR/init_shell.elf" "$MOUNT_DIR/bin/init_shell"
+        chmod 755 "$MOUNT_DIR/bin/init_shell"
+        echo "  /bin/init_shell installed"
+    fi
+
+    # Copy telnetd for remote access (system daemon, goes in /sbin)
+    if [ -f "$USERSPACE_DIR/telnetd.elf" ]; then
+        cp "$USERSPACE_DIR/telnetd.elf" "$MOUNT_DIR/sbin/telnetd"
+        chmod 755 "$MOUNT_DIR/sbin/telnetd"
+        echo "  /sbin/telnetd installed"
+    fi
+
     # Create test files
     echo "Hello from ext2!" > "$MOUNT_DIR/hello.txt"
     echo "Truncate test file" > "$MOUNT_DIR/trunctest.txt"
@@ -265,6 +297,8 @@ if [[ -f "$OUTPUT_FILE" ]]; then
     echo "  /sbin/true, /bin/false - exit status coreutils"
     echo "  /bin/head, tail, wc, which - text processing coreutils"
     echo "  /bin/hello_world - exec test binary (exit code 42)"
+    echo "  /bin/init_shell - interactive shell"
+    echo "  /sbin/telnetd - telnet daemon"
     echo "  /hello.txt - test file (1 line)"
     echo "  /lines.txt - multi-line test file (15 lines) for head/tail/wc"
     echo "  /test/nested.txt - nested test file"
diff --git a/testdata/ext2.img b/testdata/ext2.img
diff --git a/userspace/tests/poll_test.rs b/userspace/tests/poll_test.rs
diff --git a/userspace/tests/select_test.rs b/userspace/tests/select_test.rs
diff --git a/userspace/tests/tcp_socket_test.rs b/userspace/tests/tcp_socket_test.rs
