avc: denied { ioctl } messages in Android testbed

[mhsmith]

The Android testbed produces a message like this approximately once per test:

W/Thread-2: type=1400 audit(0.0:767): avc: denied { ioctl } for path="pipe:[10138300]" dev="pipefs" ino=10138300 ioctlcmd=0x5413 scontext=u:r:untrusted_app:s0:c162,c256,c512,c768 tcontext=u:r:untrusted_app:s0:c162,c256,c512,c768 tclass=fifo_file permissive=0 app=org.beeware.toga.testbed

This is an SELinux message, probably caused by the pytest-asyncio plugin, which I think uses a pipe as a means of thread synchronization.

It doesn't appear to be causing any problems, it just makes the log harder to read. But I don't want to suppress all "avc: denied" messages, because they often contain useful information about why the app has been blocked from doing something.

[mhsmith]

probably caused by the pytest-asyncio plugin, which I think uses a pipe as a means of thread synchronization.

Actually, it turns out that when you search the NDK headers for 5413, you find TIOCGWINSZ, which is the ioctl used by os.get_terminal_size, which is called by pytest.

Normally this function would raise an OSError ("Inappropriate ioctl for device"). But because we're using Chaquopy's stdio redirection mechanism, which replaces stdout with a pipe, we instead get a PermissionError and this log message.

I worked around this in #1951 by monkey-patching os.get_terminal_size. This should be merged into Chaquopy itself (chaquo/chaquopy#886).