Silence "Exception ignored when trying to write to the signal wakeup fd"

Disable warn_on_full_buffer via set_wakeup_fd. This avoids tons of

    Exception ignored when trying to write to the signal wakeup fd:
    BlockingIOError: [Errno 11] Resource temporarily unavailable

that are currently issued after running complex builds. Only works since
Python 3.7, though, so this remains best-effort. Fortunately, the Debian
in our container image is 3.7.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/libkas.py

@@ -31,6 +31,7 @@ import tempfile
 import asyncio
 import errno
 import pathlib
+import signal
 from subprocess import Popen, PIPE
 from .context import get_context
 
@@ -93,6 +94,13 @@ async def run_cmd_async(cmd, cwd, env=None, fail=True, liveupdate=True):
 
     logo = LogOutput(liveupdate)
 
+    try:
+        orig_fd = signal.set_wakeup_fd(-1, warn_on_full_buffer=False)
+        signal.set_wakeup_fd(orig_fd, warn_on_full_buffer=False)
+    except TypeError:
+        # Python < 3.7 - we tried our best
+        pass
+
     try:
         process = await asyncio.create_subprocess_exec(
             *cmd,