feat: Add experimental umount command

Counterpart to mount, will unmount a squashfuse mounted filesystem via
fusermount.

Fixes sylabs#205

internal/pkg/exp/umount.go

@@ -0,0 +1,93 @@
+// Copyright (c) 2022, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package exp
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os/exec"
+	"path/filepath"
+)
+
+// unmountSquashFS unmounts the filesystem at mountPath.
+func unmountSquashFS(ctx context.Context, mountPath string, uo unmountOpts) error {
+	args := []string{
+		"-u",
+		filepath.Clean(mountPath),
+	}
+	cmd := exec.CommandContext(ctx, uo.fusermountPath, args...) //nolint:gosec
+	cmd.Stdout = uo.stdout
+	cmd.Stderr = uo.stderr
+
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("failed to unmount: %w", err)
+	}
+
+	return nil
+}
+
+// unmountOpts accumulates unmount options.
+type unmountOpts struct {
+	stdout         io.Writer
+	stderr         io.Writer
+	fusermountPath string
+}
+
+// UnmountOpt are used to specify unmount options.
+type UnmountOpt func(*unmountOpts) error
+
+// OptUnmountStdout writes standard output to w.
+func OptUnmountStdout(w io.Writer) UnmountOpt {
+	return func(mo *unmountOpts) error {
+		mo.stdout = w
+		return nil
+	}
+}
+
+// OptUnmountStderr writes standard error to w.
+func OptUnmountStderr(w io.Writer) UnmountOpt {
+	return func(mo *unmountOpts) error {
+		mo.stderr = w
+		return nil
+	}
+}
+
+var errFusermountPathInvalid = errors.New("fusermount path must be relative or absolute")
+
+// OptUnmountFusermountPath sets the path to the fusermount binary.
+func OptUnmountFusermountPath(path string) UnmountOpt {
+	return func(mo *unmountOpts) error {
+		if filepath.Base(path) == path {
+			return errFusermountPathInvalid
+		}
+		mo.fusermountPath = path
+		return nil
+	}
+}
+
+// Unmount the FUSE mounted filesystem at mountPath.
+//
+// Unmount may start one or more underlying processes. By default, stdout and stderr of these
+// processes is discarded. To modify this behavior, consider using OptUnmountStdout and/or
+// OptUnmountStderr.
+//
+// By default, Unmount searches for a fusermount binary in the directories named by the PATH
+// environment variable. To override this behavior, consider using OptUnmountFusermountPath().
+func Unmount(ctx context.Context, mountPath string, opts ...UnmountOpt) error {
+	uo := unmountOpts{
+		fusermountPath: "fusermount",
+	}
+
+	for _, opt := range opts {
+		if err := opt(&uo); err != nil {
+			return fmt.Errorf("%w", err)
+		}
+	}
+
+	return unmountSquashFS(ctx, mountPath, uo)
+}

internal/pkg/exp/umount_test.go

@@ -0,0 +1,139 @@
+// Copyright (c) 2022, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package exp
+
+import (
+	"bufio"
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+var corpus = filepath.Join("..", "..", "..", "test", "images")
+
+func Test_Unmount(t *testing.T) {
+	if _, err := exec.LookPath("squashfuse"); err != nil {
+		t.Skip(" not found, skipping mount tests")
+	}
+	fusermountPath, err := exec.LookPath("fusermount")
+	if err != nil {
+		t.Skip(" not found, skipping mount tests")
+	}
+
+	path, err := os.MkdirTemp("", "siftool-mount-*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		os.RemoveAll(path)
+	})
+
+	tests := []struct {
+		name          string
+		mountSIF      string
+		mountPath     string
+		opts          []UnmountOpt
+		wantErr       bool
+		wantUnmounted bool
+	}{
+		{
+			name:          "Mounted",
+			mountSIF:      filepath.Join(corpus, "one-group.sif"),
+			mountPath:     path,
+			wantErr:       false,
+			wantUnmounted: true,
+		},
+		{
+			name:      "NotMounted",
+			mountSIF:  "",
+			mountPath: path,
+			wantErr:   true,
+		},
+		{
+			name:      "NotSquashfuse",
+			mountSIF:  "",
+			mountPath: "/dev",
+			wantErr:   true,
+		},
+		{
+			name:      "FusermountBare",
+			mountSIF:  "",
+			mountPath: path,
+			opts:      []UnmountOpt{OptUnmountFusermountPath("fusermount")},
+			wantErr:   true,
+		},
+		{
+			name:          "FusermountValid",
+			mountSIF:      filepath.Join(corpus, "one-group.sif"),
+			mountPath:     path,
+			opts:          []UnmountOpt{OptUnmountFusermountPath(fusermountPath)},
+			wantErr:       false,
+			wantUnmounted: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.mountSIF != "" {
+				err := Mount(context.Background(), tt.mountSIF, path)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			err := Unmount(context.Background(), tt.mountPath, tt.opts...)
+
+			if err != nil && !tt.wantErr {
+				t.Errorf("Unexpected error: %s", err)
+			}
+			if err == nil && tt.wantErr {
+				t.Error("Unexpected success")
+			}
+
+			mounted, err := isMounted(tt.mountPath)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if tt.wantUnmounted && mounted {
+				t.Errorf("Expected %s to be unmounted, but it is mounted", tt.mountPath)
+			}
+		})
+	}
+}
+
+var errBadMountInfo = errors.New("bad mount info")
+
+func isMounted(mountPath string) (bool, error) {
+	mountPath, err := filepath.Abs(mountPath)
+	if err != nil {
+		return false, err
+	}
+
+	mi, err := os.Open("/proc/self/mountinfo")
+	if err != nil {
+		return false, fmt.Errorf("failed to open /proc/self/mountinfo: %w", err)
+	}
+	defer mi.Close()
+
+	scanner := bufio.NewScanner(mi)
+	for scanner.Scan() {
+		fields := strings.Split(scanner.Text(), " ")
+		if len(fields) < 5 {
+			return false, fmt.Errorf("not enough mountinfo fields: %w", errBadMountInfo)
+		}
+		//nolint:lll
+		// 1348 63 0:77 / /tmp/siftool-mount-956028386 ro,nosuid,nodev,relatime shared:646 - fuse.squashfuse squashfuse ro,user_id=1000,group_id=100
+		mntTarget := fields[4]
+		if mntTarget == mountPath {
+			return true, nil
+		}
+	}
+	return false, nil
+}