python/qemu: Add ConsoleSocket for optional use in QEMUMachine

We add the ConsoleSocket object, which has a socket interface
and which will consume all arriving characters on the
socket, placing them into an in memory buffer.
This will also provide those chars via recv() as
would a regular socket.
ConsoleSocket also has the option of dumping
the console bytes to a log file.

We also give QEMUMachine the option of using ConsoleSocket
to drain and to use for logging console to a file.
By default QEMUMachine does not use ConsoleSocket.

This is added in preparation for use by basevm.py in a later commit.
This is a workaround we found was needed for basevm.py since
there is a known issue where QEMU will hang waiting
for console characters to be consumed.

Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Cleber Rosa <crosa@redhat.com>
Signed-off-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Peter Puhov <peter.puhov@linaro.org>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200601211421.1277-9-robert.foley@linaro.org>
Message-Id: <20200701135652.1366-13-alex.bennee@linaro.org>

python/qemu/console_socket.py

@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+#
+# This python module implements a ConsoleSocket object which is
+# designed always drain the socket itself, and place
+# the bytes into a in memory buffer for later processing.
+#
+# Optionally a file path can be passed in and we will also
+# dump the characters to this file for debug.
+#
+# Copyright 2020 Linaro
+#
+# Authors:
+#  Robert Foley <robert.foley@linaro.org>
+#
+# This code is licensed under the GPL version 2 or later.  See
+# the COPYING file in the top-level directory.
+#
+import asyncore
+import socket
+import threading
+import io
+import os
+import sys
+from collections import deque
+import time
+import traceback
+
+class ConsoleSocket(asyncore.dispatcher):
+
+    def __init__(self, address, file=None):
+        self._recv_timeout_sec = 300
+        self._buffer = deque()
+        self._asyncore_thread = None
+        self._sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        self._sock.connect(address)
+        self._logfile = None
+        if file:
+            self._logfile = open(file, "w")
+        asyncore.dispatcher.__init__(self, sock=self._sock)
+        self._open = True
+        self._thread_start()
+
+    def _thread_start(self):
+        """Kick off a thread to wait on the asyncore.loop"""
+        if self._asyncore_thread is not None:
+            return
+        self._asyncore_thread = threading.Thread(target=asyncore.loop,
+                                                 kwargs={'timeout':1})
+        self._asyncore_thread.daemon = True
+        self._asyncore_thread.start()
+
+    def handle_close(self):
+        """redirect close to base class"""
+        # Call the base class close, but not self.close() since
+        # handle_close() occurs in the context of the thread which
+        # self.close() attempts to join.
+        asyncore.dispatcher.close(self)
+
+    def close(self):
+        """Close the base object and wait for the thread to terminate"""
+        if self._open:
+            self._open = False
+            asyncore.dispatcher.close(self)
+            if self._asyncore_thread is not None:
+                thread, self._asyncore_thread = self._asyncore_thread, None
+                thread.join()
+            if self._logfile:
+                self._logfile.close()
+                self._logfile = None
+
+    def handle_read(self):
+        """process arriving characters into in memory _buffer"""
+        try:
+            data = asyncore.dispatcher.recv(self, 1)
+            # latin1 is needed since there are some chars
+            # we are receiving that cannot be encoded to utf-8
+            # such as 0xe2, 0x80, 0xA6.
+            string = data.decode("latin1")
+        except:
+            print("Exception seen.")
+            traceback.print_exc()
+            return
+        if self._logfile:
+            self._logfile.write("{}".format(string))
+            self._logfile.flush()
+        for c in string:
+            self._buffer.extend(c)
+
+    def recv(self, n=1, sleep_delay_s=0.1):
+        """Return chars from in memory buffer"""
+        start_time = time.time()
+        while len(self._buffer) < n:
+            time.sleep(sleep_delay_s)
+            elapsed_sec = time.time() - start_time
+            if elapsed_sec > self._recv_timeout_sec:
+                raise socket.timeout
+        chars = ''.join([self._buffer.popleft() for i in range(n)])
+        # We choose to use latin1 to remain consistent with
+        # handle_read() and give back the same data as the user would
+        # receive if they were reading directly from the
+        # socket w/o our intervention.
+        return chars.encode("latin1")
+
+    def set_blocking(self):
+        """Maintain compatibility with socket API"""
+        pass
+
+    def settimeout(self, seconds):
+        """Set current timeout on recv"""
+        self._recv_timeout_sec = seconds