82 lines
2.6 KiB
Go
82 lines
2.6 KiB
Go
/*
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Copyright 2015 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package io
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import (
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"bytes"
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"fmt"
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"io/ioutil"
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"os"
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"os/exec"
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"github.com/golang/glog"
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)
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// Writer is an interface which allows to write data to a file.
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type Writer interface {
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// WriteFile mimics ioutil.WriteFile.
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WriteFile(filename string, data []byte, perm os.FileMode) error
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}
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// StdWriter implements Writer interface and uses standard libraries
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// for writing data to files.
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type StdWriter struct {
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}
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// WriteFile directly calls ioutil.WriteFile.
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func (writer *StdWriter) WriteFile(filename string, data []byte, perm os.FileMode) error {
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return ioutil.WriteFile(filename, data, perm)
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}
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// NsenterWriter is implementation of Writer interface that allows writing data
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// to file using nsenter command.
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// If a program (e.g. kubelet) runs in a container it may want to write data to
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// a mounted device. Since in Docker, mount propagation mode is set to private,
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// it will not see the mounted device in its own namespace. To work around this
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// limitation one has to first enter hosts namespace (by using 'nsenter') and
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// only then write data.
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type NsenterWriter struct{}
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// WriteFile calls 'nsenter cat - > <the file>' and 'nsenter chmod' to create a
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// file on the host.
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func (writer *NsenterWriter) WriteFile(filename string, data []byte, perm os.FileMode) error {
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cmd := "nsenter"
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baseArgs := []string{
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"--mount=/rootfs/proc/1/ns/mnt",
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"--",
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}
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echoArgs := append(baseArgs, "sh", "-c", fmt.Sprintf("cat > %s", filename))
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glog.V(5).Infof("Command to write data to file: %v %v", cmd, echoArgs)
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command := exec.Command(cmd, echoArgs...)
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command.Stdin = bytes.NewBuffer(data)
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outputBytes, err := command.CombinedOutput()
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if err != nil {
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glog.Errorf("Output from writing to %q: %v", filename, string(outputBytes))
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return err
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}
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chmodArgs := append(baseArgs, "chmod", fmt.Sprintf("%o", perm), filename)
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glog.V(5).Infof("Command to change permissions to file: %v %v", cmd, chmodArgs)
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outputBytes, err = exec.Command(cmd, chmodArgs...).CombinedOutput()
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if err != nil {
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glog.Errorf("Output from chmod command: %v", string(outputBytes))
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return err
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}
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return nil
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}
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