71 lines
1.6 KiB
Go
71 lines
1.6 KiB
Go
package chroot
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import (
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"errors"
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"fmt"
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"os"
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"path/filepath"
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"strings"
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)
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// AvailableDevice finds an available device and returns it. Note that
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// you should externally hold a flock or something in order to guarantee
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// that this device is available across processes.
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func AvailableDevice() (string, error) {
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prefix, err := devicePrefix()
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if err != nil {
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return "", err
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}
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letters := "fghijklmnop"
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for _, letter := range letters {
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device := fmt.Sprintf("/dev/%s%c", prefix, letter)
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// If the block device itself, i.e. /dev/sf, exists, then we
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// can't use any of the numbers either.
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if _, err := os.Stat(device); err == nil {
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continue
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}
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// To be able to build both Paravirtual and HVM images, the unnumbered
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// device and the first numbered one must be available.
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// E.g. /dev/xvdf and /dev/xvdf1
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numbered_device := fmt.Sprintf("%s%d", device, 1)
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if _, err := os.Stat(numbered_device); err != nil {
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return device, nil
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}
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}
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return "", errors.New("available device could not be found")
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}
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// devicePrefix returns the prefix ("sd" or "xvd" or so on) of the devices
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// on the system.
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func devicePrefix() (string, error) {
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available := []string{"sd", "xvd"}
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f, err := os.Open("/sys/block")
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if err != nil {
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return "", err
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}
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defer f.Close()
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dirs, err := f.Readdirnames(-1)
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if dirs != nil && len(dirs) > 0 {
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for _, dir := range dirs {
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dirBase := filepath.Base(dir)
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for _, prefix := range available {
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if strings.HasPrefix(dirBase, prefix) {
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return prefix, nil
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}
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}
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}
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}
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if err != nil {
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return "", err
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}
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return "", errors.New("device prefix could not be detected")
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}
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