snapshots/blockfile: deflaky the testsuite

* Use direct-io mode to reduce IO.

* Add testViewHook helper to recovery the backing file since the ext4
  might need writable permission to handle recovery. If the backing file
  needs recovery and it's for View snapshot, the readonly mount will
  cause error.

* Use 8 MiB as capacity to reduce the IO.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

snapshots/blockfile/blockfile_loopsetup_test.go

@@ -26,9 +26,6 @@ import (
 	"testing"
 
 	"github.com/containerd/containerd/mount"
-	"github.com/containerd/continuity/fs"
-	"github.com/containerd/continuity/testutil/loopback"
-	"golang.org/x/sys/unix"
 )
 
 func setupSnapshotter(t *testing.T) ([]Opt, error) {
@@ -37,52 +34,94 @@ func setupSnapshotter(t *testing.T) ([]Opt, error) {
 		t.Skipf("Could not find mkfs.ext4: %v", err)
 	}
 
-	loopbackSize := int64(128 << 20) // 128 MB
+	loopbackSize := int64(8 << 20) // 8 MB
 	if os.Getpagesize() > 4096 {
 		loopbackSize = int64(650 << 20) // 650 MB
 	}
 
-	loop, err := loopback.New(loopbackSize)
+	scratch := filepath.Join(t.TempDir(), "scratch")
+	scratchDevFile, err := os.OpenFile(scratch, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to create %s: %w", scratch, err)
 	}
-	defer loop.Close()
 
-	if out, err := exec.Command(mkfs, loop.Device).CombinedOutput(); err != nil {
+	if err := scratchDevFile.Truncate(loopbackSize); err != nil {
+		scratchDevFile.Close()
+		return nil, fmt.Errorf("failed to resize %s file: %w", scratch, err)
+	}
+
+	if err := scratchDevFile.Sync(); err != nil {
+		scratchDevFile.Close()
+		return nil, fmt.Errorf("failed to sync %s file: %w", scratch, err)
+	}
+	scratchDevFile.Close()
+
+	if out, err := exec.Command(mkfs, scratch).CombinedOutput(); err != nil {
 		return nil, fmt.Errorf("failed to make ext4 filesystem (out: %q): %w", out, err)
 	}
-	// sync after a mkfs on the loopback before trying to mount the device
-	unix.Sync()
 
-	if err := testMount(t, loop.Device); err != nil {
-		return nil, err
-	}
+	defaultOpts := []string{"loop", "direct-io", "sync"}
 
-	scratch := filepath.Join(t.TempDir(), "scratch")
-	err = fs.CopyFile(scratch, loop.File)
-	if err != nil {
+	if err := testMount(t, scratch, defaultOpts); err != nil {
 		return nil, err
 	}
 
 	return []Opt{
 		WithScratchFile(scratch),
 		WithFSType("ext4"),
-		WithMountOptions([]string{"loop", "sync"}),
+		WithMountOptions(defaultOpts),
+		WithRecreateScratch(false), // reduce IO presure in CI
+		withViewHookHelper(testViewHook),
 	}, nil
 }
 
-func testMount(t *testing.T, device string) error {
+func testMount(t *testing.T, scratchFile string, opts []string) error {
 	root, err := os.MkdirTemp(t.TempDir(), "")
 	if err != nil {
 		return err
 	}
 	defer os.RemoveAll(root)
 
-	if out, err := exec.Command("mount", device, root).CombinedOutput(); err != nil {
-		return fmt.Errorf("failed to mount device %s (out: %q): %w", device, out, err)
+	m := []mount.Mount{
+		{
+			Type:    "ext4",
+			Source:  scratchFile,
+			Options: opts,
+		},
 	}
+
+	if err := mount.All(m, root); err != nil {
+		return fmt.Errorf("failed to mount device %s: %w", scratchFile, err)
+	}
+
 	if err := os.Remove(filepath.Join(root, "lost+found")); err != nil {
 		return err
 	}
-	return mount.UnmountAll(root, unix.MNT_DETACH)
+	return mount.UnmountAll(root, 0)
+}
+
+func testViewHook(backingFile string, fsType string, defaultOpts []string) error {
+	root, err := os.MkdirTemp("", "blockfile-testViewHook-XXXX")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(root)
+
+	// FIXME(fuweid): Mount with rw to force fs to handle recover
+	mountOpts := []mount.Mount{
+		{
+			Type:    fsType,
+			Source:  backingFile,
+			Options: defaultOpts,
+		},
+	}
+
+	if err := mount.All(mountOpts, root); err != nil {
+		return fmt.Errorf("failed to mount device %s: %w", backingFile, err)
+	}
+
+	if err := mount.UnmountAll(root, 0); err != nil {
+		return fmt.Errorf("failed to unmount device %s: %w", backingFile, err)
+	}
+	return nil
 }