Copied from jacobsa/bazilfuse@b378951.

internal/fuseshim/mount_darwin.go

@@ -0,0 +1,131 @@
+package bazilfuse
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+// OS X appears to cap the size of writes to 1 MiB. This constant is also used
+// for sizing receive buffers, so make it as small as it can be without
+// limiting write sizes.
+const maxWrite = 1 << 20
+
+var errNoAvail = errors.New("no available fuse devices")
+
+var errNotLoaded = errors.New("osxfusefs is not loaded")
+
+func loadOSXFUSE() error {
+	cmd := exec.Command("/Library/Filesystems/osxfusefs.fs/Support/load_osxfusefs")
+	cmd.Dir = "/"
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	return err
+}
+
+func openOSXFUSEDev() (*os.File, error) {
+	var f *os.File
+	var err error
+	for i := uint64(0); ; i++ {
+		path := "/dev/osxfuse" + strconv.FormatUint(i, 10)
+		f, err = os.OpenFile(path, os.O_RDWR, 0000)
+		if os.IsNotExist(err) {
+			if i == 0 {
+				// not even the first device was found -> fuse is not loaded
+				return nil, errNotLoaded
+			}
+
+			// we've run out of kernel-provided devices
+			return nil, errNoAvail
+		}
+
+		if err2, ok := err.(*os.PathError); ok && err2.Err == syscall.EBUSY {
+			// try the next one
+			continue
+		}
+
+		if err != nil {
+			return nil, err
+		}
+		return f, nil
+	}
+}
+
+func callMount(dir string, conf *mountConfig, f *os.File, ready chan<- struct{}, errp *error) error {
+	bin := "/Library/Filesystems/osxfusefs.fs/Support/mount_osxfusefs"
+
+	for k, v := range conf.options {
+		if strings.Contains(k, ",") || strings.Contains(v, ",") {
+			// Silly limitation but the mount helper does not
+			// understand any escaping. See TestMountOptionCommaError.
+			return fmt.Errorf("mount options cannot contain commas on darwin: %q=%q", k, v)
+		}
+	}
+	cmd := exec.Command(
+		bin,
+		"-o", conf.getOptions(),
+		// Tell osxfuse-kext how large our buffer is. It must split
+		// writes larger than this into multiple writes.
+		//
+		// OSXFUSE seems to ignore InitResponse.MaxWrite, and uses
+		// this instead.
+		"-o", "iosize="+strconv.FormatUint(maxWrite, 10),
+		// refers to fd passed in cmd.ExtraFiles
+		"3",
+		dir,
+	)
+	cmd.ExtraFiles = []*os.File{f}
+	cmd.Env = os.Environ()
+	cmd.Env = append(cmd.Env, "MOUNT_FUSEFS_CALL_BY_LIB=")
+	// TODO this is used for fs typenames etc, let app influence it
+	cmd.Env = append(cmd.Env, "MOUNT_FUSEFS_DAEMON_PATH="+bin)
+	var buf bytes.Buffer
+	cmd.Stdout = &buf
+	cmd.Stderr = &buf
+
+	err := cmd.Start()
+	if err != nil {
+		return err
+	}
+	go func() {
+		err := cmd.Wait()
+		if err != nil {
+			if buf.Len() > 0 {
+				output := buf.Bytes()
+				output = bytes.TrimRight(output, "\n")
+				msg := err.Error() + ": " + string(output)
+				err = errors.New(msg)
+			}
+		}
+		*errp = err
+		close(ready)
+	}()
+	return err
+}
+
+func mount(dir string, conf *mountConfig, ready chan<- struct{}, errp *error) (*os.File, error) {
+	f, err := openOSXFUSEDev()
+	if err == errNotLoaded {
+		err = loadOSXFUSE()
+		if err != nil {
+			return nil, err
+		}
+		// try again
+		f, err = openOSXFUSEDev()
+	}
+	if err != nil {
+		return nil, err
+	}
+	err = callMount(dir, conf, f, ready, errp)
+	if err != nil {
+		f.Close()
+		return nil, err
+	}
+	return f, nil
+}

internal/fuseshim/mount_freebsd.go

@@ -0,0 +1,44 @@
+package bazilfuse
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// Maximum file write size we are prepared to receive from the kernel.
+const maxWrite = 128 * 1024
+
+func mount(dir string, conf *mountConfig, ready chan<- struct{}, errp *error) (*os.File, error) {
+	for k, v := range conf.options {
+		if strings.Contains(k, ",") || strings.Contains(v, ",") {
+			// Silly limitation but the mount helper does not
+			// understand any escaping. See TestMountOptionCommaError.
+			return nil, fmt.Errorf("mount options cannot contain commas on FreeBSD: %q=%q", k, v)
+		}
+	}
+
+	f, err := os.OpenFile("/dev/fuse", os.O_RDWR, 0000)
+	if err != nil {
+		*errp = err
+		return nil, err
+	}
+
+	cmd := exec.Command(
+		"/sbin/mount_fusefs",
+		"--safe",
+		"-o", conf.getOptions(),
+		"3",
+		dir,
+	)
+	cmd.ExtraFiles = []*os.File{f}
+
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("mount_fusefs: %q, %v", out, err)
+	}
+
+	close(ready)
+	return f, nil
+}

internal/fuseshim/mount_linux.go

@@ -0,0 +1,116 @@
+package bazilfuse
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"os/exec"
+	"sync"
+	"syscall"
+)
+
+// Maximum file write size we are prepared to receive from the kernel. Linux
+// appears to limit writes to 128 KiB.
+const maxWrite = 128 * 1024
+
+func lineLogger(wg *sync.WaitGroup, prefix string, r io.ReadCloser) {
+	defer wg.Done()
+
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		switch line := scanner.Text(); line {
+		case `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.
+			continue
+		default:
+			log.Printf("%s: %s", prefix, line)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		log.Printf("%s, error reading: %v", prefix, err)
+	}
+}
+
+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)
+	}
+	wg.Add(2)
+	go lineLogger(&wg, "mount helper output", stdout)
+	go lineLogger(&wg, "mount helper error", stderr)
+	wg.Wait()
+	if err := cmd.Wait(); err != nil {
+		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
+}

internal/fuseshim/options.go

@@ -0,0 +1,180 @@
+package bazilfuse
+
+import (
+	"errors"
+	"strings"
+)
+
+func dummyOption(conf *mountConfig) error {
+	return nil
+}
+
+// mountConfig holds the configuration for a mount operation.
+// Use it by passing MountOption values to Mount.
+type mountConfig struct {
+	options      map[string]string
+	maxReadahead uint32
+	initFlags    InitFlags
+}
+
+func escapeComma(s string) string {
+	s = strings.Replace(s, `\`, `\\`, -1)
+	s = strings.Replace(s, `,`, `\,`, -1)
+	return s
+}
+
+// getOptions makes a string of options suitable for passing to FUSE
+// mount flag `-o`. Returns an empty string if no options were set.
+// Any platform specific adjustments should happen before the call.
+func (m *mountConfig) getOptions() string {
+	var opts []string
+	for k, v := range m.options {
+		k = escapeComma(k)
+		if v != "" {
+			k += "=" + escapeComma(v)
+		}
+		opts = append(opts, k)
+	}
+	return strings.Join(opts, ",")
+}
+
+type mountOption func(*mountConfig) error
+
+// MountOption is passed to Mount to change the behavior of the mount.
+type MountOption mountOption
+
+// FSName sets the file system name (also called source) that is
+// visible in the list of mounted file systems.
+//
+// FreeBSD ignores this option.
+func FSName(name string) MountOption {
+	return func(conf *mountConfig) error {
+		conf.options["fsname"] = name
+		return nil
+	}
+}
+
+// Subtype sets the subtype of the mount. The main type is always
+// `fuse`. The type in a list of mounted file systems will look like
+// `fuse.foo`.
+//
+// OS X ignores this option.
+// FreeBSD ignores this option.
+func Subtype(fstype string) MountOption {
+	return func(conf *mountConfig) error {
+		conf.options["subtype"] = fstype
+		return nil
+	}
+}
+
+// LocalVolume sets the volume to be local (instead of network),
+// changing the behavior of Finder, Spotlight, and such.
+//
+// OS X only. Others ignore this option.
+func LocalVolume() MountOption {
+	return localVolume
+}
+
+// VolumeName sets the volume name shown in Finder.
+//
+// OS X only. Others ignore this option.
+func VolumeName(name string) MountOption {
+	return volumeName(name)
+}
+
+var ErrCannotCombineAllowOtherAndAllowRoot = errors.New("cannot combine AllowOther and AllowRoot")
+
+// AllowOther allows other users to access the file system.
+//
+// Only one of AllowOther or AllowRoot can be used.
+func AllowOther() MountOption {
+	return func(conf *mountConfig) error {
+		if _, ok := conf.options["allow_root"]; ok {
+			return ErrCannotCombineAllowOtherAndAllowRoot
+		}
+		conf.options["allow_other"] = ""
+		return nil
+	}
+}
+
+// AllowRoot allows other users to access the file system.
+//
+// Only one of AllowOther or AllowRoot can be used.
+//
+// FreeBSD ignores this option.
+func AllowRoot() MountOption {
+	return func(conf *mountConfig) error {
+		if _, ok := conf.options["allow_other"]; ok {
+			return ErrCannotCombineAllowOtherAndAllowRoot
+		}
+		conf.options["allow_root"] = ""
+		return nil
+	}
+}
+
+// DefaultPermissions makes the kernel enforce access control based on
+// the file mode (as in chmod).
+//
+// Without this option, the Node itself decides what is and is not
+// allowed. This is normally ok because FUSE file systems cannot be
+// accessed by other users without AllowOther/AllowRoot.
+//
+// FreeBSD ignores this option.
+func DefaultPermissions() MountOption {
+	return func(conf *mountConfig) error {
+		conf.options["default_permissions"] = ""
+		return nil
+	}
+}
+
+// Set the supplied arbitrary (key, value) pair in the "-o" argument to the
+// fuse mount binary, overriding any previous setting for the key. If value is
+// empty, the '=' will be omitted from the argument.
+func SetOption(key, value string) MountOption {
+	return func(conf *mountConfig) error {
+		conf.options[key] = value
+		return nil
+	}
+}
+
+// ReadOnly makes the mount read-only.
+func ReadOnly() MountOption {
+	return func(conf *mountConfig) error {
+		conf.options["ro"] = ""
+		return nil
+	}
+}
+
+// MaxReadahead sets the number of bytes that can be prefetched for
+// sequential reads. The kernel can enforce a maximum value lower than
+// this.
+//
+// This setting makes the kernel perform speculative reads that do not
+// originate from any client process. This usually tremendously
+// improves read performance.
+func MaxReadahead(n uint32) MountOption {
+	return func(conf *mountConfig) error {
+		conf.maxReadahead = n
+		return nil
+	}
+}
+
+// AsyncRead enables multiple outstanding read requests for the same
+// handle. Without this, there is at most one request in flight at a
+// time.
+func AsyncRead() MountOption {
+	return func(conf *mountConfig) error {
+		conf.initFlags |= InitAsyncRead
+		return nil
+	}
+}
+
+// WritebackCache enables the kernel to buffer writes before sending
+// them to the FUSE server. Without this, writethrough caching is
+// used.
+func WritebackCache() MountOption {
+	return func(conf *mountConfig) error {
+		conf.initFlags |= InitWritebackCache
+		return nil
+	}
+}

internal/fuseshim/options_darwin.go

@@ -0,0 +1,13 @@
+package bazilfuse
+
+func localVolume(conf *mountConfig) error {
+	conf.options["local"] = ""
+	return nil
+}
+
+func volumeName(name string) MountOption {
+	return func(conf *mountConfig) error {
+		conf.options["volname"] = name
+		return nil
+	}
+}

internal/fuseshim/options_freebsd.go

@@ -0,0 +1,9 @@
+package bazilfuse
+
+func localVolume(conf *mountConfig) error {
+	return nil
+}
+
+func volumeName(name string) MountOption {
+	return dummyOption
+}

internal/fuseshim/options_helper_test.go

@@ -0,0 +1,10 @@
+package bazilfuse
+
+// for TestMountOptionCommaError
+func ForTestSetMountOption(k, v string) MountOption {
+	fn := func(conf *mountConfig) error {
+		conf.options[k] = v
+		return nil
+	}
+	return fn
+}

internal/fuseshim/options_linux.go

@@ -0,0 +1,9 @@
+package bazilfuse
+
+func localVolume(conf *mountConfig) error {
+	return nil
+}
+
+func volumeName(name string) MountOption {
+	return dummyOption
+}

internal/fuseshim/options_nocomma_test.go

@@ -0,0 +1,31 @@
+// This file contains tests for platforms that have no escape
+// mechanism for including commas in mount options.
+//
+// +build darwin
+
+package bazilfuse_test
+
+import (
+	"runtime"
+	"testing"
+
+	fuse "github.com/jacobsa/bazilfuse"
+	"github.com/jacobsa/bazilfuse/fs/fstestutil"
+)
+
+func TestMountOptionCommaError(t *testing.T) {
+	t.Parallel()
+	// this test is not tied to any specific option, it just needs
+	// some string content
+	var evil = "FuseTest,Marker"
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.ForTestSetMountOption("fusetest", evil),
+	)
+	if err == nil {
+		mnt.Close()
+		t.Fatal("expected an error about commas")
+	}
+	if g, e := err.Error(), `mount options cannot contain commas on `+runtime.GOOS+`: "fusetest"="FuseTest,Marker"`; g != e {
+		t.Fatalf("wrong error: %q != %q", g, e)
+	}
+}

internal/fuseshim/options_test.go

@@ -0,0 +1,231 @@
+package bazilfuse_test
+
+import (
+	"os"
+	"runtime"
+	"syscall"
+	"testing"
+
+	fuse "github.com/jacobsa/bazilfuse"
+	"github.com/jacobsa/bazilfuse/fs"
+	"github.com/jacobsa/bazilfuse/fs/fstestutil"
+	"golang.org/x/net/context"
+)
+
+func init() {
+	fstestutil.DebugByDefault()
+}
+
+func TestMountOptionFSName(t *testing.T) {
+	if runtime.GOOS == "freebsd" {
+		t.Skip("FreeBSD does not support FSName")
+	}
+	t.Parallel()
+	const name = "FuseTestMarker"
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.FSName(name),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer mnt.Close()
+
+	info, err := fstestutil.GetMountInfo(mnt.Dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := info.FSName, name; g != e {
+		t.Errorf("wrong FSName: %q != %q", g, e)
+	}
+}
+
+func testMountOptionFSNameEvil(t *testing.T, evil string) {
+	if runtime.GOOS == "freebsd" {
+		t.Skip("FreeBSD does not support FSName")
+	}
+	t.Parallel()
+	var name = "FuseTest" + evil + "Marker"
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.FSName(name),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer mnt.Close()
+
+	info, err := fstestutil.GetMountInfo(mnt.Dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := info.FSName, name; g != e {
+		t.Errorf("wrong FSName: %q != %q", g, e)
+	}
+}
+
+func TestMountOptionFSNameEvilComma(t *testing.T) {
+	if runtime.GOOS == "darwin" {
+		// see TestMountOptionCommaError for a test that enforces we
+		// at least give a nice error, instead of corrupting the mount
+		// options
+		t.Skip("TODO: OS X gets this wrong, commas in mount options cannot be escaped at all")
+	}
+	testMountOptionFSNameEvil(t, ",")
+}
+
+func TestMountOptionFSNameEvilSpace(t *testing.T) {
+	testMountOptionFSNameEvil(t, " ")
+}
+
+func TestMountOptionFSNameEvilTab(t *testing.T) {
+	testMountOptionFSNameEvil(t, "\t")
+}
+
+func TestMountOptionFSNameEvilNewline(t *testing.T) {
+	testMountOptionFSNameEvil(t, "\n")
+}
+
+func TestMountOptionFSNameEvilBackslash(t *testing.T) {
+	testMountOptionFSNameEvil(t, `\`)
+}
+
+func TestMountOptionFSNameEvilBackslashDouble(t *testing.T) {
+	// catch double-unescaping, if it were to happen
+	testMountOptionFSNameEvil(t, `\\`)
+}
+
+func TestMountOptionSubtype(t *testing.T) {
+	if runtime.GOOS == "darwin" {
+		t.Skip("OS X does not support Subtype")
+	}
+	if runtime.GOOS == "freebsd" {
+		t.Skip("FreeBSD does not support Subtype")
+	}
+	t.Parallel()
+	const name = "FuseTestMarker"
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.Subtype(name),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer mnt.Close()
+
+	info, err := fstestutil.GetMountInfo(mnt.Dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := info.Type, "fuse."+name; g != e {
+		t.Errorf("wrong Subtype: %q != %q", g, e)
+	}
+}
+
+// TODO test LocalVolume
+
+// TODO test AllowOther; hard because needs system-level authorization
+
+func TestMountOptionAllowOtherThenAllowRoot(t *testing.T) {
+	t.Parallel()
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.AllowOther(),
+		fuse.AllowRoot(),
+	)
+	if err == nil {
+		mnt.Close()
+	}
+	if g, e := err, fuse.ErrCannotCombineAllowOtherAndAllowRoot; g != e {
+		t.Fatalf("wrong error: %v != %v", g, e)
+	}
+}
+
+// TODO test AllowRoot; hard because needs system-level authorization
+
+func TestMountOptionAllowRootThenAllowOther(t *testing.T) {
+	t.Parallel()
+	mnt, err := fstestutil.MountedT(t, fstestutil.SimpleFS{fstestutil.Dir{}}, nil,
+		fuse.AllowRoot(),
+		fuse.AllowOther(),
+	)
+	if err == nil {
+		mnt.Close()
+	}
+	if g, e := err, fuse.ErrCannotCombineAllowOtherAndAllowRoot; g != e {
+		t.Fatalf("wrong error: %v != %v", g, e)
+	}
+}
+
+type unwritableFile struct{}
+
+func (f unwritableFile) Attr(ctx context.Context, a *fuse.Attr) error {
+	a.Mode = 0000
+	return nil
+}
+
+func TestMountOptionDefaultPermissions(t *testing.T) {
+	if runtime.GOOS == "freebsd" {
+		t.Skip("FreeBSD does not support DefaultPermissions")
+	}
+	t.Parallel()
+	mnt, err := fstestutil.MountedT(t,
+		fstestutil.SimpleFS{
+			&fstestutil.ChildMap{"child": unwritableFile{}},
+		},
+		nil,
+		fuse.DefaultPermissions(),
+	)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer mnt.Close()
+
+	// This will be prevented by kernel-level access checking when
+	// DefaultPermissions is used.
+	f, err := os.OpenFile(mnt.Dir+"/child", os.O_WRONLY, 0000)
+	if err == nil {
+		f.Close()
+		t.Fatal("expected an error")
+	}
+	if !os.IsPermission(err) {
+		t.Fatalf("expected a permission error, got %T: %v", err, err)
+	}
+}
+
+type createrDir struct {
+	fstestutil.Dir
+}
+
+var _ fs.NodeCreater = createrDir{}
+
+func (createrDir) Create(ctx context.Context, req *fuse.CreateRequest, resp *fuse.CreateResponse) (fs.Node, fs.Handle, error) {
+	// pick a really distinct error, to identify it later
+	return nil, nil, fuse.Errno(syscall.ENAMETOOLONG)
+}
+
+func TestMountOptionReadOnly(t *testing.T) {
+	t.Parallel()
+	mnt, err := fstestutil.MountedT(t,
+		fstestutil.SimpleFS{createrDir{}},
+		nil,
+		fuse.ReadOnly(),
+	)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer mnt.Close()
+
+	// This will be prevented by kernel-level access checking when
+	// ReadOnly is used.
+	f, err := os.Create(mnt.Dir + "/child")
+	if err == nil {
+		f.Close()
+		t.Fatal("expected an error")
+	}
+	perr, ok := err.(*os.PathError)
+	if !ok {
+		t.Fatalf("expected PathError, got %T: %v", err, err)
+	}
+	if perr.Err != syscall.EROFS {
+		t.Fatalf("expected EROFS, got %T: %v", err, err)
+	}
+}

internal/fuseshim/protocol.go

@@ -0,0 +1,75 @@
+package bazilfuse
+
+import (
+	"fmt"
+)
+
+// Protocol is a FUSE protocol version number.
+type Protocol struct {
+	Major uint32
+	Minor uint32
+}
+
+func (p Protocol) String() string {
+	return fmt.Sprintf("%d.%d", p.Major, p.Minor)
+}
+
+// LT returns whether a is less than b.
+func (a Protocol) LT(b Protocol) bool {
+	return a.Major < b.Major ||
+		(a.Major == b.Major && a.Minor < b.Minor)
+}
+
+// GE returns whether a is greater than or equal to b.
+func (a Protocol) GE(b Protocol) bool {
+	return a.Major > b.Major ||
+		(a.Major == b.Major && a.Minor >= b.Minor)
+}
+
+func (a Protocol) is79() bool {
+	return a.GE(Protocol{7, 9})
+}
+
+// HasAttrBlockSize returns whether Attr.BlockSize is respected by the
+// kernel.
+func (a Protocol) HasAttrBlockSize() bool {
+	return a.is79()
+}
+
+// HasReadWriteFlags returns whether ReadRequest/WriteRequest
+// fields Flags and FileFlags are valid.
+func (a Protocol) HasReadWriteFlags() bool {
+	return a.is79()
+}
+
+// HasGetattrFlags returns whether GetattrRequest field Flags is
+// valid.
+func (a Protocol) HasGetattrFlags() bool {
+	return a.is79()
+}
+
+func (a Protocol) is710() bool {
+	return a.GE(Protocol{7, 10})
+}
+
+// HasOpenNonSeekable returns whether OpenResponse field Flags flag
+// OpenNonSeekable is supported.
+func (a Protocol) HasOpenNonSeekable() bool {
+	return a.is710()
+}
+
+func (a Protocol) is712() bool {
+	return a.GE(Protocol{7, 12})
+}
+
+// HasUmask returns whether CreateRequest/MkdirRequest/MknodRequest
+// field Umask is valid.
+func (a Protocol) HasUmask() bool {
+	return a.is712()
+}
+
+// HasInvalidate returns whether InvalidateNode/InvalidateEntry are
+// supported.
+func (a Protocol) HasInvalidate() bool {
+	return a.is712()
+}