Source Code for Module ganeti.hypervisor.hv_kvm.netdev

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  3   
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 29   
 30   
 31  """KVM hypervisor tap device helpers 
 32   
 33  """ 
 34   
 35  import os 
 36  import logging 
 37  import struct 
 38  import fcntl 
 39   
 40  from ganeti import errors 
 41   
 42   
 43  # TUN/TAP driver constants, taken from <linux/if_tun.h> 
 44  # They are architecture-independent and already hardcoded in qemu-kvm source, 
 45  # so we can safely include them here. 
 46  TUNSETIFF = 0x400454ca 
 47  TUNGETIFF = 0x800454d2 
 48  TUNGETFEATURES = 0x800454cf 
 49  IFF_TAP = 0x0002 
 50  IFF_NO_PI = 0x1000 
 51  IFF_ONE_QUEUE = 0x2000 
 52  IFF_VNET_HDR = 0x4000 
 53  IFF_MULTI_QUEUE = 0x0100 
 54   
 55   
 56 -def _GetTunFeatures(fd, _ioctl=fcntl.ioctl): 
 57    """Retrieves supported TUN features from file descriptor. 
 58   
 59    @see: L{_ProbeTapVnetHdr} 
 60   
 61    """ 
 62    req = struct.pack("I", 0) 
 63    try: 
 64      buf = _ioctl(fd, TUNGETFEATURES, req) 
 65    except EnvironmentError, err: 
 66      logging.warning("ioctl(TUNGETFEATURES) failed: %s", err) 
 67      return None 
 68    else: 
 69      (flags, ) = struct.unpack("I", buf) 
 70      return flags 
 71   
 72   
 73 -def _ProbeTapVnetHdr(fd, _features_fn=_GetTunFeatures): 
 74    """Check whether to enable the IFF_VNET_HDR flag. 
 75   
 76    To do this, _all_ of the following conditions must be met: 
 77     1. TUNGETFEATURES ioctl() *must* be implemented 
 78     2. TUNGETFEATURES ioctl() result *must* contain the IFF_VNET_HDR flag 
 79     3. TUNGETIFF ioctl() *must* be implemented; reading the kernel code in 
 80        drivers/net/tun.c there is no way to test this until after the tap device 
 81        has been created using TUNSETIFF, and there is no way to change the 
 82        IFF_VNET_HDR flag after creating the interface, catch-22! However both 
 83        TUNGETIFF and TUNGETFEATURES were introduced in kernel version 2.6.27, 
 84        thus we can expect TUNGETIFF to be present if TUNGETFEATURES is. 
 85   
 86     @type fd: int 
 87     @param fd: the file descriptor of /dev/net/tun 
 88   
 89    """ 
 90    flags = _features_fn(fd) 
 91   
 92    if flags is None: 
 93      # Not supported 
 94      return False 
 95   
 96    result = bool(flags & IFF_VNET_HDR) 
 97   
 98    if not result: 
 99      logging.warning("Kernel does not support IFF_VNET_HDR, not enabling") 
100   
101    return result 
102   
103   
104 -def _ProbeTapMqVirtioNet(fd, _features_fn=_GetTunFeatures): 
105    """Check whether to enable the IFF_MULTI_QUEUE flag. 
106   
107    This flag was introduced in Linux kernel 3.8. 
108   
109     @type fd: int 
110     @param fd: the file descriptor of /dev/net/tun 
111   
112    """ 
113    flags = _features_fn(fd) 
114   
115    if flags is None: 
116      # Not supported 
117      return False 
118   
119    result = bool(flags & IFF_MULTI_QUEUE) 
120   
121    if not result: 
122      logging.warning("Kernel does not support IFF_MULTI_QUEUE, not enabling") 
123   
124    return result 
125   
126   
127 -def OpenTap(name="", features=None): 
128    """Open a new tap device and return its file descriptor. 
129   
130    This is intended to be used by a qemu-type hypervisor together with the -net 
131    tap,fd=<fd> or -net tap,fds=x:y:...:z command line parameter. 
132   
133    @type name: string 
134    @param name: name for the TAP interface being created; if an empty 
135                 string is passed, the OS will generate a unique name 
136   
137    @type features: dict 
138    @param features: A dict denoting whether vhost, vnet_hdr, mq 
139      netdev features are enabled or not. 
140   
141    @return: (ifname, [tapfds], [vhostfds]) 
142    @rtype: tuple 
143   
144    """ 
145    tapfds = [] 
146    vhostfds = [] 
147    if features is None: 
148      features = {} 
149    vhost = features.get("vhost", False) 
150    vnet_hdr = features.get("vnet_hdr", True) 
151    _, virtio_net_queues = features.get("mq", (False, 1)) 
152   
153    for _ in range(virtio_net_queues): 
154      try: 
155        tapfd = os.open("/dev/net/tun", os.O_RDWR) 
156      except EnvironmentError: 
157        raise errors.HypervisorError("Failed to open /dev/net/tun") 
158   
159      flags = IFF_TAP | IFF_NO_PI 
160   
161      if vnet_hdr and _ProbeTapVnetHdr(tapfd): 
162        flags |= IFF_VNET_HDR 
163   
164      # Check if it's ok to enable IFF_MULTI_QUEUE 
165      if virtio_net_queues > 1 and _ProbeTapMqVirtioNet(tapfd): 
166        flags |= IFF_MULTI_QUEUE 
167      else: 
168        flags |= IFF_ONE_QUEUE 
169   
170      # The struct ifreq ioctl request (see netdevice(7)) 
171      ifr = struct.pack("16sh", name, flags) 
172   
173      try: 
174        res = fcntl.ioctl(tapfd, TUNSETIFF, ifr) 
175      except EnvironmentError, err: 
176        raise errors.HypervisorError("Failed to allocate a new TAP device: %s" % 
177                                     err) 
178   
179      if vhost: 
180        # This is done regularly by the qemu process if vhost=on was passed with 
181        # --netdev option. Still, in case of hotplug and if the process does not 
182        # run with root privileges, we have to get the fds and pass them via 
183        # SCM_RIGHTS prior to qemu using them. 
184        try: 
185          vhostfd = os.open("/dev/vhost-net", os.O_RDWR) 
186          vhostfds.append(vhostfd) 
187        except EnvironmentError: 
188          raise errors.HypervisorError("Failed to open /dev/vhost-net") 
189   
190      tapfds.append(tapfd) 
191   
192    # Get the interface name from the ioctl 
193    ifname = struct.unpack("16sh", res)[0].strip("\x00") 
194   
195    return (ifname, tapfds, vhostfds) 
196