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# Copyright 2017-present Open Networking Foundation
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
AF_PACKET receive support
When VLAN offload is enabled on the NIC Linux will not deliver the VLAN tag
in the data returned by recv. Instead, it delivers the VLAN TCI in a control
message. Python 2.x doesn't have built-in support for recvmsg, so we have to
use ctypes to call it. The recv function exported by this module reconstructs
the VLAN tag if it was offloaded.
"""
import socket
import struct
from ctypes import *
ETH_P_8021Q = 0x8100
SOL_PACKET = 263
PACKET_AUXDATA = 8
TP_STATUS_VLAN_VALID = 1 << 4
class struct_iovec(Structure):
_fields_ = [
("iov_base", c_void_p),
("iov_len", c_size_t),
]
class struct_msghdr(Structure):
_fields_ = [
("msg_name", c_void_p),
("msg_namelen", c_uint32),
("msg_iov", POINTER(struct_iovec)),
("msg_iovlen", c_size_t),
("msg_control", c_void_p),
("msg_controllen", c_size_t),
("msg_flags", c_int),
]
class struct_cmsghdr(Structure):
_fields_ = [
("cmsg_len", c_size_t),
("cmsg_level", c_int),
("cmsg_type", c_int),
]
class struct_tpacket_auxdata(Structure):
_fields_ = [
("tp_status", c_uint),
("tp_len", c_uint),
("tp_snaplen", c_uint),
("tp_mac", c_ushort),
("tp_net", c_ushort),
("tp_vlan_tci", c_ushort),
("tp_padding", c_ushort),
]
libc = CDLL("libc.so.6")
recvmsg = libc.recvmsg
recvmsg.argtypes = [c_int, POINTER(struct_msghdr), c_int]
recvmsg.retype = c_int
def enable_auxdata(sk):
"""
Ask the kernel to return the VLAN tag in a control message
Must be called on the socket before afpacket.recv.
"""
sk.setsockopt(SOL_PACKET, PACKET_AUXDATA, 1)
def recv(sk, bufsize):
"""
Receive a packet from an AF_PACKET socket
@sk Socket
@bufsize Maximum packet size
"""
buf = create_string_buffer(bufsize)
ctrl_bufsize = sizeof(struct_cmsghdr) + sizeof(struct_tpacket_auxdata) + sizeof(c_size_t)
ctrl_buf = create_string_buffer(ctrl_bufsize)
iov = struct_iovec()
iov.iov_base = cast(buf, c_void_p)
iov.iov_len = bufsize
msghdr = struct_msghdr()
msghdr.msg_name = None
msghdr.msg_namelen = 0
msghdr.msg_iov = pointer(iov)
msghdr.msg_iovlen = 1
msghdr.msg_control = cast(ctrl_buf, c_void_p)
msghdr.msg_controllen = ctrl_bufsize
msghdr.msg_flags = 0
rv = recvmsg(sk.fileno(), byref(msghdr), 0)
if rv < 0:
raise RuntimeError("recvmsg failed: rv=%d", rv)
# The kernel only delivers control messages we ask for. We
# only enabled PACKET_AUXDATA, so we can assume it's the
# only control message.
assert msghdr.msg_controllen >= sizeof(struct_cmsghdr)
cmsghdr = struct_cmsghdr.from_buffer(ctrl_buf) # pylint: disable=E1101
assert cmsghdr.cmsg_level == SOL_PACKET
assert cmsghdr.cmsg_type == PACKET_AUXDATA
auxdata = struct_tpacket_auxdata.from_buffer(ctrl_buf, sizeof(struct_cmsghdr)) # pylint: disable=E1101
if auxdata.tp_vlan_tci != 0 or auxdata.tp_status & TP_STATUS_VLAN_VALID:
# Insert VLAN tag
tag = struct.pack("!HH", ETH_P_8021Q, auxdata.tp_vlan_tci)
return buf.raw[:12] + tag + buf.raw[12:rv]
else:
return buf.raw[:rv]