TIOCGPTPEER PTY Fallback for Restricted Android Kernels

[Ebola-Chan-bot]

Summary

The standard openpty() call might fail because SELinux blocks open("/dev/pts/N") under certain environments. This PR adds a TIOCGPTPEER ioctl fallback path so the terminal can create PTY sessions on these restricted kernels. It also switches portable-pty from a pinned wezterm git revision to the crates.io release.

Changes

1. New file: src/terminal/pty_fallback.rs (+351 lines)

Why: portable_pty::native_pty_system().openpty() calls open("/dev/pts/N") internally, which might be denied by SELinux in proot environments. The TIOCGPTPEER ioctl obtains the slave fd directly from the master fd, completely bypassing /dev/pts directory access.

Implementation:

• OwnedFd — lightweight RAII fd wrapper implementing Read / Write, maps EIO to EOF
• FallbackMasterPty — implements the portable_pty::MasterPty trait (resize / get_size / try_clone_reader / take_writer)
• FallbackMasterWriter — sends EOT on drop to match portable-pty behaviour
• close_fds_above_stderr() — closes leaked fds after fork
• fallback_open_and_spawn() — public entry point: /dev/ptmx → grantpt → unlockpt → TIOCGPTPEER → set winsize → fork + setsid + TIOCSCTTY → exec child

2. Refactored src/terminal/handlers.rs (create_terminal)

Why: The original code performed all session setup (reader/writer/scrollback/exit waiter) inside a deeply nested match openpty { Ok(pair) => match spawn { Ok(child) => ... } } block. Adding a fallback path would make this nesting unmanageable.

What changed:

• PTY creation is now a two-step try: standard path first, then fallback_open_and_spawn on failure
• Both paths return a unified (Box<dyn MasterPty + Send>, Box<dyn Child + Send + Sync>)
• Session setup code (reader/writer/scrollback/exit waiter) is extracted into a shared section after the PTY creation, eliminating duplication
• native_pty_system() initialization moved closer to its usage point

3. New dependencies: anyhow + libc (Cargo.toml)

Dependency	Version	Purpose
anyhow	1	Error handling in pty_fallback.rs (bail! macro)
libc	0.2	Direct calls to ioctl / grantpt / setsid and other POSIX APIs

4. portable-pty source change

- portable-pty = { git = "https://github.com/wez/wezterm", package = "portable-pty", rev = "1e941fca5c17..." }
+ portable-pty = "0.9.0"

Why: The previous dependency pulled from a pinned revision of the entire wezterm monorepo, resulting in slow fetches and a bloated Cargo.lock. The crates.io 0.9.0 release provides the same API surface with faster builds and fewer transitive dependencies.

[Copilot]

Pull request overview

Adds a Linux TIOCGPTPEER-based PTY creation/spawn fallback for environments where openpty() fails (e.g., SELinux denying /dev/pts/N), and updates portable-pty to the crates.io release to reduce dependency bloat and fetch time.

Changes:

• Introduces src/terminal/pty_fallback.rs implementing a PTY + spawn fallback using /dev/ptmx + TIOCGPTPEER.
• Refactors create_terminal to try standard portable-pty first, then fall back on failure with shared session setup.
• Updates dependencies (portable-pty = 0.9.0) and adds anyhow + libc.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
src/terminal/pty_fallback.rs	New Linux-only PTY fallback implementation using TIOCGPTPEER and Command spawn.
src/terminal/mod.rs	Wires the new pty_fallback module into the terminal module.
src/terminal/handlers.rs	Refactors terminal creation to use a two-stage (standard → fallback) PTY creation path.
Cargo.toml	Adds anyhow + libc, switches portable-pty to crates.io.
Cargo.lock	Lockfile update reflecting new dependency source and resolver updates.

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