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Implement WCOW parentless active snapshots and view snapshots

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The WCOW layer support does not support creating sandboxes with no
parent.  Instead, parentless scratch layers must be layed out as a
directory containing only a directory named 'Files', and all data stored
inside 'Files'. At commit-time, this will be converted in-place into a
read-only layer suitable for use as a parent layer.

The WCOW layer support also does not deal with making read-only layers,
i.e. layers that are prepared to be parent layers, visible in a
read-only manner. A bind-mount or junction point cannot be made
read-only, so a view must instead be a small sandbox layer that we can
mount via WCOW, and discard later, to protect the layer against
accidental or deliberate modification.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>
This commit is contained in:
Paul "TBBle" Hampson
2020-07-23 22:13:08 +10:00
committed by Gabriel Adrian Samfira
parent 988ee8ffef
commit 34b07d3e2d
2 changed files with 94 additions and 43 deletions
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47
diff/windows/windows.go
View File

@@ -320,10 +320,13 @@ func mountsToLayerAndParents(mounts []mount.Mount) (string, []string, error) {
return "", nil, fmt.Errorf("number of mounts should always be 1 for Windows layers: %w", errdefs.ErrInvalidArgument)
}
mnt := mounts[0]
if mnt.Type != "windows-layer" {
if mnt.Type != "windows-layer" && mnt.Type != "bind" {
// This is a special case error. When this is received the diff service
// will attempt the next differ in the chain which for Windows is the
// lcow differ that we want.
// TODO: Is there any situation where we actually wanted a "bind" mount to
// fall through to the lcow differ?
return "", nil, fmt.Errorf("windowsDiff does not support layer type %s: %w", mnt.Type, errdefs.ErrNotImplemented)
}
@@ -332,6 +335,30 @@ func mountsToLayerAndParents(mounts []mount.Mount) (string, []string, error) {
return "", nil, err
}
isView := false
for _, o := range mnt.Options {
if o == "ro" {
isView = true
break
}
}
if isView {
if mnt.Type == "bind" && len(parentLayerPaths) != 0 {
return "", nil, fmt.Errorf("unexpected bind-mount View with parents: %w", errdefs.ErrInvalidArgument)
} else if mnt.Type == "bind" {
// rootfs.CreateDiff creates a new, empty View to diff against,
// when diffing something with no parent.
// This makes perfect sense for a walking Diff, but for WCOW,
// we have to recognise this as "diff against nothing"
return "", nil, nil
} else if len(parentLayerPaths) == 0 {
return "", nil, fmt.Errorf("unexpected windows-layer View with no parent: %w", errdefs.ErrInvalidArgument)
}
// Ignore the dummy sandbox.
return parentLayerPaths[0], parentLayerPaths[1:], nil
}
return mnt.Source, parentLayerPaths, nil
}
@@ -346,8 +373,16 @@ func mountPairToLayerStack(lower, upper []mount.Mount) ([]string, error) {
return nil, fmt.Errorf("Upper mount invalid: %w", err)
}
lowerLayer, lowerParentLayerPaths, err := mountsToLayerAndParents(lower)
if errdefs.IsNotImplemented(err) {
// Upper was a windows-layer or bind, lower is not. We can't handle that.
return nil, fmt.Errorf("windowsDiff cannot diff a windows-layer against a non-windows-layer: %w", errdefs.ErrInvalidArgument)
} else if err != nil {
return nil, fmt.Errorf("Lower mount invalid: %w", err)
}
// Trivial case, diff-against-nothing
if len(lower) == 0 {
if lowerLayer == "" {
if len(upperParentLayerPaths) != 0 {
return nil, fmt.Errorf("windowsDiff cannot diff a layer with parents against a null layer: %w", errdefs.ErrInvalidArgument)
}
@@ -358,14 +393,6 @@ func mountPairToLayerStack(lower, upper []mount.Mount) ([]string, error) {
return nil, fmt.Errorf("windowsDiff cannot diff a layer with no parents against another layer: %w", errdefs.ErrInvalidArgument)
}
lowerLayer, lowerParentLayerPaths, err := mountsToLayerAndParents(lower)
if errdefs.IsNotImplemented(err) {
// Upper was a windows-layer, lower is not. We can't handle that.
return nil, fmt.Errorf("windowsDiff cannot diff a windows-layer against a non-windows-layer: %w", errdefs.ErrInvalidArgument)
} else if err != nil {
return nil, fmt.Errorf("Lower mount invalid: %w", err)
}
if upperParentLayerPaths[0] != lowerLayer {
return nil, fmt.Errorf("windowsDiff cannot diff a layer against a layer other than its own parent: %w", errdefs.ErrInvalidArgument)
}

90
snapshots/windows/windows.go
View File

@@ -187,7 +187,7 @@ func (s *snapshotter) Mounts(ctx context.Context, key string) (_ []mount.Mount,
return nil, err
}
return s.mounts(snapshot), nil
return s.mounts(snapshot, key), nil
}
func (s *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) (retErr error) {
@@ -208,7 +208,11 @@ func (s *snapshotter) Commit(ctx context.Context, name, key string, opts ...snap
// If (windowsDiff).Apply was used to populate this layer, then it's already in the 'committed' state.
// See createSnapshot below for more details
if !strings.Contains(key, snapshots.UnpackKeyPrefix) {
if err := s.convertScratchToReadOnlyLayer(ctx, snapshot, path); err != nil {
if len(snapshot.ParentIDs) == 0 {
if err = hcsshim.ConvertToBaseLayer(path); err != nil {
return err
}
} else if err := s.convertScratchToReadOnlyLayer(ctx, snapshot, path); err != nil {
return err
}
}
@@ -299,11 +303,9 @@ func (s *snapshotter) Close() error {
return s.ms.Close()
}
func (s *snapshotter) mounts(sn storage.Snapshot) []mount.Mount {
func (s *snapshotter) mounts(sn storage.Snapshot, key string) []mount.Mount {
var (
roFlag string
source string
parentLayerPaths []string
roFlag string
)
if sn.Kind == snapshots.KindView {
@@ -312,12 +314,19 @@ func (s *snapshotter) mounts(sn storage.Snapshot) []mount.Mount {
roFlag = "rw"
}
if len(sn.ParentIDs) == 0 || sn.Kind == snapshots.KindActive {
source = s.getSnapshotDir(sn.ID)
parentLayerPaths = s.parentIDsToParentPaths(sn.ParentIDs)
} else {
source = s.getSnapshotDir(sn.ParentIDs[0])
parentLayerPaths = s.parentIDsToParentPaths(sn.ParentIDs[1:])
source := s.getSnapshotDir(sn.ID)
parentLayerPaths := s.parentIDsToParentPaths(sn.ParentIDs)
mountType := "windows-layer"
if len(sn.ParentIDs) == 0 {
// A mount of a parentless snapshot is a bind-mount.
mountType = "bind"
// If not being extracted into, then the bind-target is the
// "Files" subdirectory.
if !strings.Contains(key, snapshots.UnpackKeyPrefix) {
source = filepath.Join(source, "Files")
}
}
// error is not checked here, as a string array will never fail to Marshal
@@ -327,7 +336,7 @@ func (s *snapshotter) mounts(sn storage.Snapshot) []mount.Mount {
var mounts []mount.Mount
mounts = append(mounts, mount.Mount{
Source: source,
Type: "windows-layer",
Type: mountType,
Options: []string{
roFlag,
parentLayersOption,
@@ -360,13 +369,22 @@ func (s *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, k
return err
}
// IO/disk space optimization
//
// We only need one sandbox.vhdx for the container. Skip making one for this
// snapshot if this isn't the snapshot that just houses the final sandbox.vhd
// that will be mounted as the containers scratch. Currently the key for a snapshot
// where a layer will be extracted to will have the string `extract-` in it.
if !strings.Contains(key, snapshots.UnpackKeyPrefix) {
if strings.Contains(key, snapshots.UnpackKeyPrefix) {
// IO/disk space optimization: Do nothing
//
// We only need one sandbox.vhdx for the container. Skip making one for this
// snapshot if this isn't the snapshot that just houses the final sandbox.vhd
// that will be mounted as the containers scratch. Currently the key for a snapshot
// where a layer will be extracted to will have the string `extract-` in it.
} else if len(newSnapshot.ParentIDs) == 0 {
// A parentless snapshot is just a bind-mount to a directory named
// "Files". When committed, there'll be some post-processing to fill in the rest
// of the metadata.
filesDir := filepath.Join(snDir, "Files")
if err := os.MkdirAll(filesDir, 0700); err != nil {
return err
}
} else {
parentLayerPaths := s.parentIDsToParentPaths(newSnapshot.ParentIDs)
var snapshotInfo snapshots.Info
@@ -375,22 +393,28 @@ func (s *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, k
}
var sizeInBytes uint64
if sizeGBstr, ok := snapshotInfo.Labels[rootfsSizeInGBLabel]; ok {
log.G(ctx).Warnf("%q label is deprecated, please use %q instead.", rootfsSizeInGBLabel, rootfsSizeInBytesLabel)
if kind == snapshots.KindActive {
if sizeGBstr, ok := snapshotInfo.Labels[rootfsSizeInGBLabel]; ok {
log.G(ctx).Warnf("%q label is deprecated, please use %q instead.", rootfsSizeInGBLabel, rootfsSizeInBytesLabel)
sizeInGB, err := strconv.ParseUint(sizeGBstr, 10, 32)
if err != nil {
return fmt.Errorf("failed to parse label %q=%q: %w", rootfsSizeInGBLabel, sizeGBstr, err)
sizeInGB, err := strconv.ParseUint(sizeGBstr, 10, 32)
if err != nil {
return fmt.Errorf("failed to parse label %q=%q: %w", rootfsSizeInGBLabel, sizeGBstr, err)
}
sizeInBytes = sizeInGB * 1024 * 1024 * 1024
}
sizeInBytes = sizeInGB * 1024 * 1024 * 1024
}
// Prefer the newer label in bytes over the deprecated Windows specific GB variant.
if sizeBytesStr, ok := snapshotInfo.Labels[rootfsSizeInBytesLabel]; ok {
sizeInBytes, err = strconv.ParseUint(sizeBytesStr, 10, 64)
if err != nil {
return fmt.Errorf("failed to parse label %q=%q: %w", rootfsSizeInBytesLabel, sizeBytesStr, err)
// Prefer the newer label in bytes over the deprecated Windows specific GB variant.
if sizeBytesStr, ok := snapshotInfo.Labels[rootfsSizeInBytesLabel]; ok {
sizeInBytes, err = strconv.ParseUint(sizeBytesStr, 10, 64)
if err != nil {
return fmt.Errorf("failed to parse label %q=%q: %w", rootfsSizeInBytesLabel, sizeBytesStr, err)
}
}
} else {
// A view is just a read-write snapshot with a _really_ small sandbox, since we cannot actually
// make a read-only mount or junction point. https://superuser.com/q/881544/112473
sizeInBytes = 1024 * 1024 * 1024
}
var makeUVMScratch bool
@@ -415,7 +439,7 @@ func (s *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, k
return nil, err
}
return s.mounts(newSnapshot), nil
return s.mounts(newSnapshot, key), nil
}
func (s *snapshotter) parentIDsToParentPaths(parentIDs []string) []string {