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package open
import (
"bytes"
"encoding/json"
"errors"
"fmt"
"os"
"strings"
"github.com/containers/storage/pkg/reexec"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
const (
bindFdToPathCommand = "buildah-bind-fd-to-path"
)
func init() {
reexec.Register(bindFdToPathCommand, bindFdToPathMain)
}
// BindFdToPath creates a bind mount from the open file (which is actually a
// directory) to the specified location. If it succeeds, the caller will need
// to unmount the targetPath when it's finished using it. Regardless, it
// closes the passed-in descriptor.
func BindFdToPath(fd uintptr, targetPath string) error {
f := os.NewFile(fd, "passed-in directory descriptor")
defer func() {
if err := f.Close(); err != nil {
logrus.Debugf("closing descriptor %d after attempting to bind to %q: %v", fd, targetPath, err)
}
}()
pipeReader, pipeWriter, err := os.Pipe()
if err != nil {
return err
}
cmd := reexec.Command(bindFdToPathCommand)
cmd.Stdin = pipeReader
var stdout bytes.Buffer
var stderr bytes.Buffer
cmd.Stdout, cmd.Stderr = &stdout, &stderr
cmd.ExtraFiles = append(cmd.ExtraFiles, f)
err = cmd.Start()
pipeReader.Close()
if err != nil {
pipeWriter.Close()
return fmt.Errorf("starting child: %w", err)
}
encoder := json.NewEncoder(pipeWriter)
if err := encoder.Encode(&targetPath); err != nil {
return fmt.Errorf("sending target path to child: %w", err)
}
pipeWriter.Close()
err = cmd.Wait()
trimmedOutput := strings.TrimSpace(stdout.String()) + strings.TrimSpace(stderr.String())
if err != nil {
if len(trimmedOutput) > 0 {
err = fmt.Errorf("%s: %w", trimmedOutput, err)
}
} else {
if len(trimmedOutput) > 0 {
err = errors.New(trimmedOutput)
}
}
return err
}
func bindFdToPathMain() {
var targetPath string
decoder := json.NewDecoder(os.Stdin)
if err := decoder.Decode(&targetPath); err != nil {
fmt.Fprintf(os.Stderr, "error decoding target path")
os.Exit(1)
}
if err := unix.Fchdir(3); err != nil {
fmt.Fprintf(os.Stderr, "fchdir(): %v", err)
os.Exit(1)
}
if err := unix.Mount(".", targetPath, "bind", unix.MS_BIND, ""); err != nil {
fmt.Fprintf(os.Stderr, "bind-mounting passed-in directory to %q: %v", targetPath, err)
os.Exit(1)
}
os.Exit(0)
}
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