Documentation
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Overview ¶
Package netlink contains general netlink behavioral tests (assertions) and documents gotchas in the github.com/vishvananda/netlink module.
Netlink package (RT)NETLINK Handles and the Package Handle ¶
The netlink package API uses a so-called “package handle” for its package-level (RT)NETLINK functions: this is a package-wide instance of a zero value netlink.Handle. The netlink.Handle type is described as “an handle for the netlink requests on a specific network namespace”.
Whenever calling package methods that use this “package handle”, a temporary (RT)NETLINK socket will be set up just for the duration of the method execution and upon returning to the caller torn down (closed) again. Luckily for us, this behavior ensures correct operation when calling netlink package methods from a (hopefully OS-level thread-locked) Go routine currently attached to some other network namespace, or when switching in and out of different network namespaces. It is slightly inefficient but eventually doesn't matter in unit tests.
In contrast, non-zero value netlink.Handle objects obtained via netlink.NewHandleAt create (RT)NETLINK sockets on demand and then keep these sockets until the handle gets explicitly closed.
Netlink Package Handle Creation ¶
For instance, to create a netlink.Handle connected to another network namespace, in our fail-safe form:
import (
"github.com/thediveo/notwork/netns"
)
netnsfd := netns.NewTransient() // ...no explicit close necessary
h := netns.NewNetlinkHandle(netnsfd) // ...no explicit close necessary
Creating (“Adding”) a New Link ¶
When creating a new network interface (“link”) using netlink.LinkAdd the interface index will be automatically updated upon successful creation, by calling netlink.Handle.LinkByName. Now, netlink.LinkByName and netlink.Handle.LinkByName work on the RTNETLINK connection and interface name, but have no way to pass the netlink.LinkAttrs.Namespace field that has been used when creating the link.
The notwork module thus needs to work around this “quirk”.
Source Files