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device_alias.go
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device_alias.go
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// Copyright 2016 CoreOS, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package util
import (
"fmt"
"os"
"path/filepath"
"time"
)
const (
deviceAliasDir = "/dev_aliases"
retrySymlinkDelay = 10 * time.Millisecond
retrySymlinkTimeout = 30 * time.Second
retrySymlinkCount = int(retrySymlinkTimeout / retrySymlinkDelay)
)
// DeviceAlias returns the aliased form of the supplied path.
// Note device paths in ignition are always absolute.
func DeviceAlias(path string) string {
return filepath.Join(deviceAliasDir, filepath.Clean(path))
}
// evalSymlinks wraps filepath.EvalSymlinks, retrying if it fails
func evalSymlinks(path string) (res string, err error) {
for i := 0; i < retrySymlinkCount; i++ {
res, err = filepath.EvalSymlinks(path)
if err == nil {
return res, nil
} else if os.IsNotExist(err) {
time.Sleep(retrySymlinkDelay)
} else {
return "", err
}
}
return "", fmt.Errorf("Failed to evaluate symlink after %v: %v", retrySymlinkTimeout, err)
}
// CreateDeviceAlias creates a device alias for the supplied path.
// On success the canonicalized path used as the alias target is returned.
func CreateDeviceAlias(path string) (string, error) {
target, err := evalSymlinks(path)
if err != nil {
return "", err
}
alias := DeviceAlias(path)
if err := os.Remove(alias); err != nil {
if !os.IsNotExist(err) {
return "", err
}
if err = os.MkdirAll(filepath.Dir(alias), 0750); err != nil {
return "", err
}
}
if err = os.Symlink(target, alias); err != nil {
return "", err
}
return target, nil
}