Kir Kolyshkin
7bfcba84c0
TL;DR: check for IsExist(err) after a failed MkdirAll() is both
redundant and wrong -- so two reasons to remove it.
Quoting MkdirAll documentation:
> MkdirAll creates a directory named path, along with any necessary
> parents, and returns nil, or else returns an error. If path
> is already a directory, MkdirAll does nothing and returns nil.
This means two things:
1. If a directory to be created already exists, no error is
returned.
2. If the error returned is IsExist (EEXIST), it means there exists
a non-directory with the same name as MkdirAll need to use for
directory. Example: we want to MkdirAll("a/b"), but file "a"
(or "a/b") already exists, so MkdirAll fails.
The above is a theory, based on quoted documentation and my UNIX
knowledge.
3. In practice, though, current MkdirAll implementation [1] returns
ENOTDIR in most of cases described in #2, with the exception when
there is a race between MkdirAll and someone else creating the
last component of MkdirAll argument as a file. In this very case
MkdirAll() will indeed return EEXIST.
Because of #1, IsExist check after MkdirAll is not needed.
Because of #2 and #3, ignoring IsExist error is just plain wrong,
as directory we require is not created. It's cleaner to report
the error now.
[1] https://github.com/golang/go/blob/f9ed2f75/src/os/path.go
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
libnetwork - networking for containers
Libnetwork provides a native Go implementation for connecting containers
The goal of libnetwork is to deliver a robust Container Network Model that provides a consistent programming interface and the required network abstractions for applications.
NOTE: libnetwork project is under heavy development and is not ready for general use.
Design
Please refer to the design for more information.
Using libnetwork
There are many networking solutions available to suit a broad range of use-cases. libnetwork uses a driver / plugin model to support all of these solutions while abstracting the complexity of the driver implementations by exposing a simple and consistent Network Model to users.
// Create a new controller instance
controller, err := libnetwork.New()
if err != nil {
return
}
// Select and configure the network driver
networkType := "bridge"
driverOptions := options.Generic{}
genericOption := make(map[string]interface{})
genericOption[netlabel.GenericData] = driverOptions
err := controller.ConfigureNetworkDriver(networkType, genericOption)
if err != nil {
return
}
// Create a network for containers to join.
// NewNetwork accepts Variadic optional arguments that libnetwork and Drivers can make of
network, err := controller.NewNetwork(networkType, "network1")
if err != nil {
return
}
// For each new container: allocate IP and interfaces. The returned network
// settings will be used for container infos (inspect and such), as well as
// iptables rules for port publishing. This info is contained or accessible
// from the returned endpoint.
ep, err := network.CreateEndpoint("Endpoint1")
if err != nil {
return
}
// A container can join the endpoint by providing the container ID to the join
// api.
// Join accepts Variadic arguments which will be made use of by libnetwork and Drivers
err = ep.Join("container1",
libnetwork.JoinOptionHostname("test"),
libnetwork.JoinOptionDomainname("docker.io"))
if err != nil {
return
}
// libnetwork client can check the endpoint's operational data via the Info() API
epInfo, err := ep.DriverInfo()
mapData, ok := epInfo[netlabel.PortMap]
if ok {
portMapping, ok := mapData.([]netutils.PortBinding)
if ok {
fmt.Printf("Current port mapping for endpoint %s: %v", ep.Name(), portMapping)
}
}
Current Status
Please watch this space for updates on the progress.
Currently libnetwork is nothing more than an attempt to modularize the Docker platform's networking subsystem by moving it into libnetwork as a library.
Future
Please refer to roadmap for more information.
Contributing
Want to hack on libnetwork? Docker's contributions guidelines apply.
Copyright and license
Code and documentation copyright 2015 Docker, inc. Code released under the Apache 2.0 license. Docs released under Creative commons.