devshell: Add interactive python shell

Being able to interact with the python context in the Bitbake task execution
environment has long been desireable. This patch introduces such a
mechanism. Executing "bitbake X -c devpyshell" will open a terminal connected
to a python interactive interpretor in the task context so for example you can
run commands like "d.getVar('WORKDIR')"

This version now includes readline support for command history and various other
bug fixes such as exiting cleanly compared to previous versions.

(From OE-Core rev: 36734f34fe6e4b91e293234687e63c02f5b3117e)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oepydevshell-internal.py

@@ -0,0 +1,92 @@
+#!/usr/bin/env python
+
+import os
+import sys
+import time
+import select
+import fcntl
+import termios
+import readline
+import signal
+
+def nonblockingfd(fd):
+    fcntl.fcntl(fd, fcntl.F_SETFL, fcntl.fcntl(fd, fcntl.F_GETFL) | os.O_NONBLOCK)
+
+def echonocbreak(fd):
+    old = termios.tcgetattr(fd)
+    old[3] = old[3] | termios.ECHO | termios.ICANON
+    termios.tcsetattr(fd, termios.TCSADRAIN, old)
+
+def cbreaknoecho(fd):
+    old = termios.tcgetattr(fd)
+    old[3] = old[3] &~ termios.ECHO &~ termios.ICANON
+    termios.tcsetattr(fd, termios.TCSADRAIN, old)
+
+if len(sys.argv) != 3:
+    print("Incorrect parameters")
+    sys.exit(1)
+
+pty = open(sys.argv[1], "w+b", 0)
+parent = int(sys.argv[2])
+
+# Don't buffer output by line endings
+sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
+sys.stdin = os.fdopen(sys.stdin.fileno(), 'r', 0)
+nonblockingfd(pty)
+nonblockingfd(sys.stdin)
+
+
+histfile = os.path.expanduser("~/.oedevpyshell-history")
+readline.parse_and_bind("tab: complete")
+try:
+    readline.read_history_file(histfile)
+except IOError:
+    pass 
+
+try:
+
+    i = ""
+    o = ""
+    # Need cbreak/noecho whilst in select so we trigger on any keypress
+    cbreaknoecho(sys.stdin.fileno())
+    # Send our PID to the other end so they can kill us.
+    pty.write(str(os.getpid()) + "\n")
+    while True:
+        try:
+            writers = []
+            if i:
+                writers.append(sys.stdout)
+            (ready, _, _) = select.select([pty, sys.stdin], writers , [], 0)
+            try:
+                if pty in ready:
+                    i = i + pty.read()
+                if i:
+                    # Write a page at a time to avoid overflowing output 
+                    # d.keys() is a good way to do that
+                    sys.stdout.write(i[:4096])
+                    i = i[4096:]
+                if sys.stdin in ready:
+                    echonocbreak(sys.stdin.fileno())
+                    o = raw_input()
+                    cbreaknoecho(sys.stdin.fileno())
+                    pty.write(o + "\n")
+            except (IOError, OSError) as e:
+                if e.errno == 11:
+                    continue
+                if e.errno == 5:
+                    sys.exit(0)
+                raise
+            except EOFError:
+                sys.exit(0)
+        except KeyboardInterrupt:
+            os.kill(parent, signal.SIGINT)
+
+except SystemExit:
+    pass
+except Exception as e:
+    import traceback
+    print("Exception in oepydehshell-internal: " + str(e))
+    traceback.print_exc()
+    time.sleep(5)
+finally:
+    readline.write_history_file(histfile)