feat: wcow: add support for bind and cache mounts

Currently, mounts are not supported for WCOW builds,
see #5678. This commit introduces support for
bind and cache mounts. The remaining two require
a little more work and consultation with the platform
teams for enlightment.

WIP Checklist:

- [x] Support for bind mounts
- [x] Support for cache mounts
- [x] add frontend/dockerfile integration tests
- [ ] add client integration tests
- [ ] add documentatio
- [ ] add note and plan on the missing feature(s)
	i.e. secret mounts (that need tmpfs)
- [ ] spec out / second attempt for SSH mount

Fixes #5603
Addresses part of #5678

Signed-off-by: Anthony Nandaa <[email protected]>

executor/oci/spec.go

@@ -201,8 +201,8 @@ func GenerateSpec(ctx context.Context, meta executor.Meta, mounts []executor.Mou
 				return nil, nil, err
 			}
 			s.Mounts = append(s.Mounts, specs.Mount{
-				Destination: m.Dest,
-				Type:        mount.Type,
+				Destination: getAbsPath(m.Dest), // for Windows only
+				Type:        getMountType(mount.Type),
 				Source:      mount.Source,
 				Options:     mount.Options,
 			})
@@ -243,6 +243,10 @@ type submounts struct {
 
 func (s *submounts) subMount(m mount.Mount, subPath string) (mount.Mount, error) {
 	if path.Join("/", subPath) == "/" {
+		// for Windows, the mounting by HCS doesn't go through
+		// WCIFS, hence we have to give the direct path of the
+		// mount, which is in the /Files subdirectory.
+		m.Source = getCompleteSourcePath(m.Source)
 		return m, nil
 	}
 	if s.m == nil {

executor/oci/spec_unix.go

@@ -0,0 +1,18 @@
+//go:build !windows
+
+package oci
+
+// no effect for non-Windows
+func getMountType(mType string) string {
+	return mType
+}
+
+// no effect for non-Windows
+func getAbsPath(p string) string {
+	return p
+}
+
+// no effect for non-Windows
+func getCompleteSourcePath(p string) string {
+	return p
+}

executor/oci/spec_windows.go

@@ -110,3 +110,22 @@ func sub(m mount.Mount, subPath string) (mount.Mount, func() error, error) {
 	m.Source = src
 	return m, func() error { return nil }, nil
 }
+
+func getMountType(_ string) string {
+	// HCS shim doesn't expect a named type
+	// for the mount.
+	return ""
+}
+
+// Returns an absolute path, starting with the
+// default drive letter (C:). HCS Shim expects an absolute path.
+func getAbsPath(p string) string {
+	return filepath.Join("C:\\", p)
+}
+
+// For Windows, the mounting by HCS doesn't go through
+// WCIFS, hence we have to give the direct path of the
+// mount, which is in the /Files subdirectory.
+func getCompleteSourcePath(p string) string {
+	return filepath.Join(p, "Files")
+}