pycriu: add criu class

This class is essentially libcriu in python(yet for now it
has only some basic functions such as check/dump/restore).
It is needed to make life for python users even more easier,
i.e. hiding some nasty connection stuff. It is also using
criu swrk(COMM_BIN) communication method, instead of an old
system service, as we no longer recommend it.
Signed-off-by: Ruslan Kuprieiev <rkuprieiev@cloudlinux.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

pycriu/__init__.py

 import rpc
 import images
+from criu import *

pycriu/criu.py

+# Same as libcriu for C.
+
+import socket
+import errno
+import subprocess
+import fcntl
+import os
+import signal
+import sys
+import struct
+
+import rpc
+
+class _criu_comm:
+	"""
+	Base class for communication classes.
+	"""
+	COMM_SK		= 0
+	COMM_FD		= 1
+	COMM_BIN	= 2
+	comm_type	= None
+	comm		= None
+	sk		= None
+
+	def connect(self, daemon):
+		"""
+		Connect to criu and return socket object.
+		daemon -- is for whether or not criu should daemonize if executing criu from binary(comm_bin).
+		"""
+		pass
+
+	def disconnect(self):
+		"""
+		Disconnect from criu.
+		"""
+		pass
+
+
+class _criu_comm_sk(_criu_comm):
+	"""
+	Communication class for unix socket.
+	"""
+	def __init__(self, sk_path):
+		self.comm_type = self.COMM_SK
+		self.comm = sk_path
+
+	def connect(self, daemon):
+		self.sk = socket.socket(socket.AF_UNIX, socket.SOCK_SEQPACKET)
+		self.sk.connect(self.comm)
+
+		return self.sk
+
+	def disconnect(self):
+		self.sk.close()
+
+
+class _criu_comm_fd(_criu_comm):
+	"""
+	Commnunication class for file descriptor.
+	"""
+	def __init__(self, fd):
+		self.comm_type = self.COMM_FD
+		self.comm = fd
+
+	def connect(self, daemon):
+		self.sk = socket.fromfd(self.comm, socket.AF_UNIX, socket.SOCK_SEQPACKET)
+
+		return self.sk
+
+	def disconnect(self):
+		self.sk.close()
+
+class _criu_comm_bin(_criu_comm):
+	"""
+	Communication class for binary.
+	"""
+	def __init__(self, bin_path):
+		self.comm_type = self.COMM_BIN
+		self.comm = bin_path
+		self.swrk = None
+		self.daemon = None
+
+	def connect(self, daemon):
+		# Kind of the same thing we do in libcriu
+		css = socket.socketpair(socket.AF_UNIX, socket.SOCK_SEQPACKET)
+		flags = fcntl.fcntl(css[1], fcntl.F_GETFD)
+		fcntl.fcntl(css[1], fcntl.F_SETFD, flags | fcntl.FD_CLOEXEC)
+
+		self.daemon = daemon
+
+		p = os.fork()
+
+		if p == 0:
+			def exec_criu():
+				os.close(0)
+				os.close(1)
+				os.close(2)
+
+				css[0].send(struct.pack('i', os.getpid()))
+				os.execv(self.comm, [self.comm, 'swrk', "%d" % css[0].fileno()])
+				os._exit(1)
+
+			if daemon:
+				# Python has no daemon(3) alternative,
+				# so we need to mimic it ourself.
+				p = os.fork()
+
+				if p == 0:
+					os.setsid()
+
+					exec_criu()
+				else:
+					os._exit(0)
+			else:
+				exec_criu()
+
+		css[0].close()
+		self.swrk = struct.unpack('i', css[1].recv(4))[0]
+		self.sk = css[1]
+
+		return self.sk
+
+	def disconnect(self):
+		self.sk.close()
+		if not self.daemon:
+			os.waitpid(self.swrk, 0)
+
+
+class CRIUException(Exception):
+	"""
+	Exception class for handling and storing criu errors.
+	"""
+	typ = None
+	_str = None
+
+	def __str__(self):
+		return self._str
+
+
+class CRIUExceptionInternal(CRIUException):
+	"""
+	Exception class for handling and storing internal errors.
+	"""
+	def __init__(self, typ, s):
+		self.typ = typ
+		self._str = "%s failed with internal error: %s" % (rpc.criu_req_type.Name(self.typ), s)
+
+
+class CRIUExceptionExternal(CRIUException):
+	"""
+	Exception class for handling and storing criu RPC errors.
+	"""
+
+	def __init__(self, req_typ, resp_typ, errno):
+		self.typ = req_typ
+		self.resp_typ = resp_typ
+		self.errno = errno
+		self._str = self._gen_error_str()
+
+	def _gen_error_str(self):
+		s = "%s failed: " % (rpc.criu_req_type.Name(self.typ), )
+
+		if self.typ != self.resp_typ:
+			s += "Unxecpected response type %d: " % (self.resp_typ, )
+
+		s += "Error(%d): " % (self.errno, )
+
+		if self.errno == errno.EBADRQC:
+			s += "Bad options"
+
+		if self.typ == rpc.DUMP:
+			if self.errno == errno.ESRCH:
+				s += "No process with such pid"
+
+		if self.typ == rpc.RESTORE:
+			if self.errno == errno.EEXIST:
+				s += "Process with requested pid already exists"
+
+		s += "Unknown"
+
+		return s
+
+
+class criu:
+	"""
+	Call criu through RPC.
+	"""
+	opts		= None #CRIU options in pb format
+
+	_comm		= None #Communication method
+
+	def __init__(self):
+		self.use_binary('criu')
+		self.opts = rpc.criu_opts()
+
+	def use_sk(self, sk_name):
+		"""
+		Access criu using unix socket which that belongs to criu service daemon.
+		"""
+		self._comm = _criu_comm_sk(sk_name)
+
+	def use_fd(self, fd):
+		"""
+		Access criu using provided fd.
+		"""
+		self._comm = _criu_comm_fd(fd)
+
+	def use_binary(self, bin_name):
+		"""
+		Access criu by execing it using provided path to criu binary.
+		"""
+		self._comm = _criu_comm_bin(bin_name)
+
+	def _send_req_and_recv_resp(self, req):
+		"""
+		As simple as send request and receive response.
+		"""
+		# In case of self-dump we need to spawn criu swrk detached
+		# from our current process, as criu has a hard time separating
+		# process resources from its own if criu is located in a same
+		# process tree it is trying to dump.
+		daemon = False
+		if req.type == rpc.DUMP and not req.opts.HasField('pid'):
+			daemon = True
+
+		try:
+			s = self._comm.connect(daemon)
+
+			s.send(req.SerializeToString())
+
+			buf = s.recv(len(s.recv(1, socket.MSG_TRUNC | socket.MSG_PEEK)))
+
+			self._comm.disconnect()
+
+			resp = rpc.criu_resp()
+			resp.ParseFromString(buf)
+		except Exception as e:
+			raise CRIUExceptionInternal(req.type, str(e))
+
+		return resp
+
+	def check(self):
+		"""
+		Checks whether the kernel support is up-to-date.
+		"""
+		req		= rpc.criu_req()
+		req.type	= rpc.CHECK
+
+		resp = self._send_req_and_recv_resp(req)
+
+		if not resp.success:
+			raise CRIUExceptionExternal(req.type, resp.type, resp.cr_errno)
+
+	def dump(self):
+		"""
+		Checkpoint a process/tree identified by opts.pid.
+		"""
+		req 		= rpc.criu_req()
+		req.type	= rpc.DUMP
+		req.opts.MergeFrom(self.opts)
+
+		resp = self._send_req_and_recv_resp(req)
+
+		if not resp.success:
+			raise CRIUExceptionExternal(req.type, resp.type, resp.cr_errno)
+
+		return resp.dump
+
+	def restore(self):
+		"""
+		Restore a process/tree.
+		"""
+		req		= rpc.criu_req()
+		req.type	= rpc.RESTORE
+		req.opts.MergeFrom(self.opts)
+
+		resp = self._send_req_and_recv_resp(req)
+
+		if not resp.success:
+			raise CRIUExceptionExternal(req.type, resp.type, resp.errno)
+
+		return resp.restore