cgull / wsl-forkpty-shim

solib forkpty() shim for Windows Subsystem for Linux beta

Stale and deprecated

Windows Subsystem for Linux has working ptys in the Anniversary update, and long before in the fast ring releases. You don't need this any more.

##forkpty shlib hack##

This is a hack to get ptys somewhat working on Windows 10 fast-ring builds with Bash on Windows / Windows Subsystem for Linux installed. It's mostly intended for programs that use forkpty().

The WSL pty subsystem, as of build 14332, is too incomplete to use with glibc's forkpty(). The blocker I found is that statvfs("/dev/pts/") fails, but I'm sure there are others.

However, the ptys are not completely unusable. This is a simpler implementation that dodges some pty bugs, so that script and (with some hacks) Mosh's mosh-server (and optional termemu example program) can run. It implements forkpty()/openpty()/login_tty(), the core BSD API to ptys. It also implements posix_openpt() and glibc's getpt(). There are still problems:

• TIOC{G,S}WINSZ fail on a pty master or slave.
• I've been unable to make the slave a controlling tty yet via open() or ioctl(..., TIOCSCTTY, ...).
• Device permissions are broken, requiring running as root.
• openpty() works but callers may themselves trip on unimplemented termios features if they don't use login_tty()
• There are several different ways to access ptys: the BSD forkpty() calls, the POSIX API, glibc's API, open() + ioctl(), and more. This only implements a subset.

So...if you use this you get terminal sessions with no controlling pty, no job control, no keyboard interrupts, broken window resize, and some other termios brokenness I haven't investigated yet. As of Build 14332, I think ptys don't even have a real termio implementation, only a stub implementation that copies bytes back and forth and adds CR on output. But it's just barely usable enough to start further work on pty-using programs in WSL.

to use:

make
sudo sh -c 'LD_PRELOAD=./forkpty.so /usr/bin/script /tmp/barf'