Module netdev

source code

KVM hypervisor tap device helpers

Functions

[hide private]

_GetTunFeatures(fd, _ioctl=fcntl.ioctl)
Retrieves supported TUN features from file descriptor.

source code

_ProbeTapVnetHdr(fd, _features_fn=_GetTunFeatures)
Check whether to enable the IFF_VNET_HDR flag.

source code

_ProbeTapMqVirtioNet(fd, _features_fn=_GetTunFeatures)
Check whether to enable the IFF_MULTI_QUEUE flag.

source code

tuple

OpenTap(name="", features=None)
Open a new tap device and return its file descriptor.

source code

Variables

[hide private]

TUNSETIFF = 0x400454ca

TUNGETIFF = 0x800454d2

TUNGETFEATURES = 0x800454cf

IFF_TAP = 0x0002

IFF_NO_PI = 0x1000

IFF_ONE_QUEUE = 0x2000

IFF_VNET_HDR = 0x4000

IFF_MULTI_QUEUE = 0x0100

Imports: os, logging, struct, fcntl, errors

Function Details

[hide private]

_GetTunFeatures(fd, _ioctl=fcntl.ioctl)

source code

Retrieves supported TUN features from file descriptor.

See Also: _ProbeTapVnetHdr

_ProbeTapVnetHdr(fd, _features_fn=_GetTunFeatures)

source code

Check whether to enable the IFF_VNET_HDR flag.

To do this, _all_ of the following conditions must be met:

TUNGETFEATURES ioctl() *must* be implemented
TUNGETFEATURES ioctl() result *must* contain the IFF_VNET_HDR flag
TUNGETIFF ioctl() *must* be implemented; reading the kernel code in drivers/net/tun.c there is no way to test this until after the tap device has been created using TUNSETIFF, and there is no way to change the IFF_VNET_HDR flag after creating the interface, catch-22! However both TUNGETIFF and TUNGETFEATURES were introduced in kernel version 2.6.27, thus we can expect TUNGETIFF to be present if TUNGETFEATURES is.

Parameters:

fd (int) - the file descriptor of /dev/net/tun

_ProbeTapMqVirtioNet(fd, _features_fn=_GetTunFeatures)

source code

Check whether to enable the IFF_MULTI_QUEUE flag.

This flag was introduced in Linux kernel 3.8.

Parameters:

fd (int) - the file descriptor of /dev/net/tun

OpenTap(name="", features=None)

source code

Open a new tap device and return its file descriptor.

This is intended to be used by a qemu-type hypervisor together with the -net tap,fd=<fd> or -net tap,fds=x:y:...:z command line parameter.

Parameters:

name (string) - name for the TAP interface being created; if an empty string is passed, the OS will generate a unique name
features (dict) - A dict denoting whether vhost, vnet_hdr, mq netdev features are enabled or not.

Returns: tuple

(ifname, [tapfds], [vhostfds])