fuse, fs: add DirectMount tests & DirectMountStrict option

Reason for adding DirectMountStrict is making the DirectMount
functionality testable, though it may have value for the user
in some cases.

Add defaultRawFileSystem & loopback tests for DirectMount
and DirectMountStrict.

The tests fail right now due to bugs in DirectMount that will be fixed
shortly:

	go-fuse/fuse$ sudo /usr/local/go/bin/go test -run TestDirectMount
	[...]
	2022/12/28 20:19:21 mountDirect: calling syscall.Mount("", "/tmp/TestDirectMount3242971772", "fuse./tmp/go-build1215740", 0x0, "fd=7,rootmode=40000,user_id=0,group_id=0")
	2022/12/28 20:19:21 mount: failed to do direct mount: invalid argument
	[...]

Change-Id: Ibfa2fa141cb43e1f8c7319233c454a3e85fa435e

all.bash

@@ -13,7 +13,11 @@ GOOS=darwin go build ./fuse/... ./fs/... ./example/loopback/...
 # -p 1 .......... Run tests serially, which also means we get live output
 #                 instead of per-package buffering.
 # -count 1 ...... Disable result caching, so we can see flakey tests
-go test -timeout 5m -p 1 -count 1 ./...
+GO_TEST="go test -timeout 5m -p 1 -count 1"
+# Run all tests as current user
+$GO_TEST ./...
+# Direct-mount tests need to run as root
+sudo env PATH=$PATH $GO_TEST -run TestDirectMount ./fs ./fuse
 
 make -C benchmark
 go test ./benchmark -test.bench '.*' -test.cpu 1,2

fs/loopback_linux_test.go

@@ -401,3 +401,15 @@ func TestRoMount(t *testing.T) {
 	tc := newTestCase(t, &testOptions{ro: true})
 	defer tc.Clean()
 }
+
+func TestDirectMount(t *testing.T) {
+	opts := &testOptions{
+		directMount: true,
+	}
+	if os.Geteuid() == 0 {
+		t.Log("running as root, setting DirectMountStrict")
+		opts.directMountStrict = true
+	}
+	tc := newTestCase(t, opts)
+	defer tc.Clean()
+}

fs/simple_test.go

@@ -56,11 +56,13 @@ func (tc *testCase) Clean() {
 }
 
 type testOptions struct {
-	entryCache    bool
-	attrCache     bool
-	suppressDebug bool
-	testDir       string
-	ro            bool
+	entryCache        bool
+	attrCache         bool
+	suppressDebug     bool
+	testDir           string
+	ro                bool
+	directMount       bool // sets MountOptions.DirectMount
+	directMountStrict bool // sets MountOptions.DirectMountStrict
 }
 
 // newTestCase creates the directories `orig` and `mnt` inside a temporary
@@ -107,7 +109,10 @@ func newTestCase(t *testing.T, opts *testOptions) *testCase {
 		Logger:       log.New(os.Stderr, "", 0),
 	})
 
-	mOpts := &fuse.MountOptions{}
+	mOpts := &fuse.MountOptions{
+		DirectMount:       opts.directMount,
+		DirectMountStrict: opts.directMountStrict,
+	}
 	if !opts.suppressDebug {
 		mOpts.Debug = testutil.VerboseTest()
 	}

fuse/api.go

@@ -247,8 +247,15 @@ type MountOptions struct {
 	// If set, fuse will first attempt to use syscall.Mount instead of
 	// fusermount to mount the filesystem. This will not update /etc/mtab
 	// but might be needed if fusermount is not available.
+	// Also, Server.Unmount will attempt syscall.Unmount before calling
+	// fusermount.
 	DirectMount bool
 
+	// DirectMountStrict is like DirectMount but no fallback to fusermount is
+	// performed. If both DirectMount and DirectMountStrict are set,
+	// DirectMountStrict wins.
+	DirectMountStrict bool
+
 	// Options passed to syscall.Mount, the default value used by fusermount
 	// is syscall.MS_NOSUID|syscall.MS_NODEV
 	DirectMountFlags uintptr

fuse/mount_linux.go

@@ -57,6 +57,10 @@ func mountDirect(mountPoint string, opts *MountOptions, ready chan<- error) (fd
 		r = append(r, "allow_other")
 	}
 
+	if opts.Debug {
+		log.Printf("mountDirect: calling syscall.Mount(%q, %q, %q, %#x, %q)",
+			opts.FsName, mountPoint, "fuse."+opts.Name, opts.DirectMountFlags, strings.Join(r, ","))
+	}
 	err = syscall.Mount(opts.FsName, mountPoint, "fuse."+opts.Name, opts.DirectMountFlags, strings.Join(r, ","))
 	if err != nil {
 		syscall.Close(fd)
@@ -125,13 +129,16 @@ func callFusermount(mountPoint string, opts *MountOptions) (fd int, err error) {
 // Create a FUSE FS on the specified mount point.  The returned
 // mount point is always absolute.
 func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {
-	if opts.DirectMount {
+	if opts.DirectMount || opts.DirectMountStrict {
 		fd, err := mountDirect(mountPoint, opts, ready)
 		if err == nil {
 			return fd, nil
 		} else if opts.Debug {
 			log.Printf("mount: failed to do direct mount: %s", err)
 		}
+		if opts.DirectMountStrict {
+			return -1, err
+		}
 	}
 
 	// Magic `/dev/fd/N` mountpoint. See the docs for NewServer() for how this
@@ -157,12 +164,15 @@ func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, e
 }
 
 func unmount(mountPoint string, opts *MountOptions) (err error) {
-	if opts.DirectMount {
+	if opts.DirectMount || opts.DirectMountStrict {
 		// Attempt to directly unmount, if fails fallback to fusermount method
 		err := syscall.Unmount(mountPoint, 0)
 		if err == nil {
 			return nil
 		}
+		if opts.DirectMountStrict {
+			return err
+		}
 	}
 
 	bin, err := fusermountBinary()

fuse/mount_linux_test.go

@@ -3,8 +3,11 @@ package fuse
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 	"syscall"
 	"testing"
+
+	"github.com/moby/sys/mountinfo"
 )
 
 // TestMountDevFd tests the special `/dev/fd/N` mountpoint syntax, where a
@@ -98,3 +101,77 @@ func TestMountMaxWrite(t *testing.T) {
 		})
 	}
 }
+
+// mountCheckOptions mounts a defaultRawFileSystem and extracts the resulting effective
+// mount options from /proc/self/mounts.
+// The mount options are a comma-separated string like this:
+// rw,nosuid,nodev,relatime,user_id=1026,group_id=1026
+func mountCheckOptions(t *testing.T, opts MountOptions) (info mountinfo.Info) {
+	mnt, err := ioutil.TempDir("", t.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+	fs := NewDefaultRawFileSystem()
+	srv, err := NewServer(fs, mnt, &opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Check mount options
+	mounts, err := mountinfo.GetMounts(mountinfo.SingleEntryFilter(mnt))
+	if err != nil {
+		t.Error(err)
+	}
+	if len(mounts) != 1 {
+		t.Errorf("Could not find mountpoint %q in /proc/self/mountinfo", mnt)
+	}
+	orig := *mounts[0]
+	t.Logf("full mountinfo: %#v", orig)
+	// We are only interested in some fields, as the others are arbitrary id numbers
+	// or contain random strings like "/tmp/TestDirectMount1126361240".
+	//
+	// What are all those fields: Look for "/proc/[pid]/mountinfo" in
+	// https://man7.org/linux/man-pages/man5/proc.5.html .
+	info = mountinfo.Info{
+		Options:    orig.Options,
+		Source:     orig.Source,
+		FSType:     orig.FSType,
+		VFSOptions: orig.VFSOptions,
+		Optional:   orig.Optional,
+	}
+	// server needs to run for Unmount to work
+	go srv.Serve()
+	err = srv.Unmount()
+	if err != nil {
+		t.Error(err)
+	}
+	return info
+}
+
+// TestDirectMount checks that DirectMount and DirectMountStrict work and show the
+// same effective mount options in /proc/self/mounts
+func TestDirectMount(t *testing.T) {
+	opts := MountOptions{
+		Debug: true,
+	}
+	// Without DirectMount - i.e. using fusermount
+	t.Log("Normal fusermount mount")
+	o1 := mountCheckOptions(t, opts)
+	// With DirectMount
+	t.Log("DirectMount")
+	opts.DirectMount = true
+	o2 := mountCheckOptions(t, opts)
+	if o2 != o1 {
+		t.Errorf("Effective mount options differ between DirectMount and fusermount mount:\n%#v\n%#v",
+			o2, o1)
+	}
+	// With DirectMountStrict
+	if os.Geteuid() == 0 {
+		t.Log("DirectMountStrict")
+		opts.DirectMountStrict = true
+		o3 := mountCheckOptions(t, opts)
+		if o3 != o1 {
+			t.Errorf("Effective mount options differ between DirectMountStrict and fusermount mount: \n%#v\n%#v",
+				o3, o1)
+		}
+	}
+}

go.mod

@@ -2,8 +2,9 @@ module github.com/hanwen/go-fuse/v2
 
 require (
 	github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348
+	github.com/moby/sys/mountinfo v0.6.2
 	golang.org/x/sync v0.0.0-20201207232520-09787c993a3a
-	golang.org/x/sys v0.0.0-20180830151530-49385e6e1522
+	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a
 )
 
 go 1.13

go.sum

 github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348 h1:MtvEpTB6LX3vkb4ax0b5D2DHbNAUsen0Gx5wZoq3lV4=
 github.com/kylelemons/godebug v0.0.0-20170820004349-d65d576e9348/go.mod h1:B69LEHPfb2qLo0BaaOLcbitczOKLWTsrBG9LczfCD4k=
+github.com/moby/sys/mountinfo v0.6.2 h1:BzJjoreD5BMFNmD9Rus6gdd1pLuecOFPt8wC+Vygl78=
+github.com/moby/sys/mountinfo v0.6.2/go.mod h1:IJb6JQeOklcdMU9F5xQ8ZALD+CUr5VlGpwtX+VE0rpI=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a h1:DcqTD9SDLc+1P/r1EmRBwnVsrOwW+kk2vWf9n+1sGhs=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20180830151530-49385e6e1522 h1:Ve1ORMCxvRmSXBwJK+t3Oy+V2vRW2OetUQBq4rJIkZE=
-golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a h1:dGzPydgVsqGcTRVwiLJ1jVbufYwmzD3LfVPLKsKg+0k=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=