swarm/api: support mounting manifests via FUSE (#3690)

vendor/bazil.org/fuse/mount_linux.go

@@ -0,0 +1,150 @@
+package fuse
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+func handleFusermountStderr(errCh chan<- error) func(line string) (ignore bool) {
+	return func(line string) (ignore bool) {
+		if line == `fusermount: failed to open /etc/fuse.conf: Permission denied` {
+			// Silence this particular message, it occurs way too
+			// commonly and isn't very relevant to whether the mount
+			// succeeds or not.
+			return true
+		}
+
+		const (
+			noMountpointPrefix = `fusermount: failed to access mountpoint `
+			noMountpointSuffix = `: No such file or directory`
+		)
+		if strings.HasPrefix(line, noMountpointPrefix) && strings.HasSuffix(line, noMountpointSuffix) {
+			// re-extract it from the error message in case some layer
+			// changed the path
+			mountpoint := line[len(noMountpointPrefix) : len(line)-len(noMountpointSuffix)]
+			err := &MountpointDoesNotExistError{
+				Path: mountpoint,
+			}
+			select {
+			case errCh <- err:
+				return true
+			default:
+				// not the first error; fall back to logging it
+				return false
+			}
+		}
+
+		return false
+	}
+}
+
+// isBoringFusermountError returns whether the Wait error is
+// uninteresting; exit status 1 is.
+func isBoringFusermountError(err error) bool {
+	if err, ok := err.(*exec.ExitError); ok && err.Exited() {
+		if status, ok := err.Sys().(syscall.WaitStatus); ok && status.ExitStatus() == 1 {
+			return true
+		}
+	}
+	return false
+}
+
+func mount(dir string, conf *mountConfig, ready chan<- struct{}, errp *error) (fusefd *os.File, err error) {
+	// linux mount is never delayed
+	close(ready)
+
+	fds, err := syscall.Socketpair(syscall.AF_FILE, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		return nil, fmt.Errorf("socketpair error: %v", err)
+	}
+
+	writeFile := os.NewFile(uintptr(fds[0]), "fusermount-child-writes")
+	defer writeFile.Close()
+
+	readFile := os.NewFile(uintptr(fds[1]), "fusermount-parent-reads")
+	defer readFile.Close()
+
+	cmd := exec.Command(
+		"fusermount",
+		"-o", conf.getOptions(),
+		"--",
+		dir,
+	)
+	cmd.Env = append(os.Environ(), "_FUSE_COMMFD=3")
+
+	cmd.ExtraFiles = []*os.File{writeFile}
+
+	var wg sync.WaitGroup
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("setting up fusermount stderr: %v", err)
+	}
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		return nil, fmt.Errorf("setting up fusermount stderr: %v", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("fusermount: %v", err)
+	}
+	helperErrCh := make(chan error, 1)
+	wg.Add(2)
+	go lineLogger(&wg, "mount helper output", neverIgnoreLine, stdout)
+	go lineLogger(&wg, "mount helper error", handleFusermountStderr(helperErrCh), stderr)
+	wg.Wait()
+	if err := cmd.Wait(); err != nil {
+		// see if we have a better error to report
+		select {
+		case helperErr := <-helperErrCh:
+			// log the Wait error if it's not what we expected
+			if !isBoringFusermountError(err) {
+				log.Printf("mount helper failed: %v", err)
+			}
+			// and now return what we grabbed from stderr as the real
+			// error
+			return nil, helperErr
+		default:
+			// nope, fall back to generic message
+		}
+
+		return nil, fmt.Errorf("fusermount: %v", err)
+	}
+
+	c, err := net.FileConn(readFile)
+	if err != nil {
+		return nil, fmt.Errorf("FileConn from fusermount socket: %v", err)
+	}
+	defer c.Close()
+
+	uc, ok := c.(*net.UnixConn)
+	if !ok {
+		return nil, fmt.Errorf("unexpected FileConn type; expected UnixConn, got %T", c)
+	}
+
+	buf := make([]byte, 32) // expect 1 byte
+	oob := make([]byte, 32) // expect 24 bytes
+	_, oobn, _, _, err := uc.ReadMsgUnix(buf, oob)
+	scms, err := syscall.ParseSocketControlMessage(oob[:oobn])
+	if err != nil {
+		return nil, fmt.Errorf("ParseSocketControlMessage: %v", err)
+	}
+	if len(scms) != 1 {
+		return nil, fmt.Errorf("expected 1 SocketControlMessage; got scms = %#v", scms)
+	}
+	scm := scms[0]
+	gotFds, err := syscall.ParseUnixRights(&scm)
+	if err != nil {
+		return nil, fmt.Errorf("syscall.ParseUnixRights: %v", err)
+	}
+	if len(gotFds) != 1 {
+		return nil, fmt.Errorf("wanted 1 fd; got %#v", gotFds)
+	}
+	f := os.NewFile(uintptr(gotFds[0]), "/dev/fuse")
+	return f, nil
+}