cimfs: Add cim layer mount/unmount functionality.

Signed-off-by: Amit Barve <ambarve@microsoft.com>

internal/wclayer/cim/mount.go

@@ -0,0 +1,87 @@
+package cim
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sync"
+
+	"github.com/Microsoft/go-winio/pkg/guid"
+	hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
+	cimfs "github.com/Microsoft/hcsshim/pkg/cimfs"
+)
+
+// a cache of cim layer to its mounted volume - The mount manager plugin currently doesn't have an option of
+// querying a mounted cim to get the volume at which it is mounted, so we maintain a cache of that here
+var (
+	cimMounts       map[string]string = make(map[string]string)
+	cimMountMapLock sync.Mutex
+	// A random GUID used as a namespace for generating cim mount volume GUIDs: 6827367b-c388-4e9b-95ec-961c6d2c936c
+	cimMountNamespace guid.GUID = guid.GUID{Data1: 0x6827367b, Data2: 0xc388, Data3: 0x4e9b, Data4: [8]byte{0x96, 0x1c, 0x6d, 0x2c, 0x93, 0x6c}}
+)
+
+// MountCimLayer mounts the cim at path `cimPath` and returns the mount location of that cim.  This method
+// uses the `CimMountFlagCacheFiles` mount flag when mounting the cim.  The containerID is used to generated
+// the volumeID for the volume at which this CIM is mounted.  containerID is used so that if the shim process
+// crashes for any reason, the mounted cim can be correctly cleaned up during `shim delete` call.
+func MountCimLayer(ctx context.Context, cimPath, containerID string) (string, error) {
+	volumeGUID, err := guid.NewV5(cimMountNamespace, []byte(containerID))
+	if err != nil {
+		return "", fmt.Errorf("generated cim mount GUID: %w", err)
+	}
+
+	vol, err := cimfs.Mount(cimPath, volumeGUID, hcsschema.CimMountFlagCacheFiles)
+	if err != nil {
+		return "", err
+	}
+
+	cimMountMapLock.Lock()
+	defer cimMountMapLock.Unlock()
+	cimMounts[fmt.Sprintf("%s_%s", containerID, cimPath)] = vol
+
+	return vol, nil
+}
+
+// Unmount unmounts the cim at mounted for given container.
+func UnmountCimLayer(ctx context.Context, cimPath, containerID string) error {
+	cimMountMapLock.Lock()
+	defer cimMountMapLock.Unlock()
+	if vol, ok := cimMounts[fmt.Sprintf("%s_%s", containerID, cimPath)]; !ok {
+		return fmt.Errorf("cim %s not mounted", cimPath)
+	} else {
+		delete(cimMounts, fmt.Sprintf("%s_%s", containerID, cimPath))
+		err := cimfs.Unmount(vol)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// GetCimMountPath returns the volume at which a cim is mounted. If the cim is not mounted returns error
+func GetCimMountPath(cimPath, containerID string) (string, error) {
+	cimMountMapLock.Lock()
+	defer cimMountMapLock.Unlock()
+
+	if vol, ok := cimMounts[fmt.Sprintf("%s_%s", containerID, cimPath)]; !ok {
+		return "", fmt.Errorf("cim %s not mounted", cimPath)
+	} else {
+		return vol, nil
+	}
+}
+
+func CleanupContainerMounts(containerID string) error {
+	volumeGUID, err := guid.NewV5(cimMountNamespace, []byte(containerID))
+	if err != nil {
+		return fmt.Errorf("generated cim mount GUID: %w", err)
+	}
+
+	volPath := fmt.Sprintf("\\\\?\\Volume{%s}\\", volumeGUID.String())
+	if _, err := os.Stat(volPath); err == nil {
+		err = cimfs.Unmount(volPath)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}

pkg/cimfs/cim_test.go

@@ -15,6 +15,8 @@ import (
 	"time"
 
 	"github.com/Microsoft/go-winio"
+	"github.com/Microsoft/go-winio/pkg/guid"
+	hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
 	"golang.org/x/sys/windows"
 )
 
@@ -102,7 +104,12 @@ func TestCimReadWrite(t *testing.T) {
 	}
 
 	// mount and read the contents of the cim
-	mountvol, err := Mount(cimPath)
+	volumeGUID, err := guid.NewV4()
+	if err != nil {
+		t.Fatalf("generate cim mount GUID: %s", err)
+	}
+
+	mountvol, err := Mount(cimPath, volumeGUID, hcsschema.CimMountFlagCacheFiles)
 	if err != nil {
 		t.Fatalf("mount cim : %s", err)
 	}

pkg/cimfs/mount_cim.go

@@ -9,7 +9,6 @@ import (
 	"strings"
 
 	"github.com/Microsoft/go-winio/pkg/guid"
-	hcsschema "github.com/Microsoft/hcsshim/internal/hcs/schema2"
 	"github.com/Microsoft/hcsshim/internal/winapi"
 	"github.com/pkg/errors"
 )
@@ -33,22 +32,13 @@ func (e *MountError) Error() string {
 	return s
 }
 
-func MountWithFlags(cimPath string, mountFlags uint32) (string, error) {
-	layerGUID, err := guid.NewV4()
-	if err != nil {
-		return "", &MountError{Cim: cimPath, Op: "Mount", Err: err}
-	}
-	if err := winapi.CimMountImage(filepath.Dir(cimPath), filepath.Base(cimPath), mountFlags, &layerGUID); err != nil {
-		return "", &MountError{Cim: cimPath, Op: "Mount", VolumeGUID: layerGUID, Err: err}
+// Mount mounts the given cim at a volume with given GUID. Returns the full volume
+// path if mount is successful.
+func Mount(cimPath string, volumeGUID guid.GUID, mountFlags uint32) (string, error) {
+	if err := winapi.CimMountImage(filepath.Dir(cimPath), filepath.Base(cimPath), mountFlags, &volumeGUID); err != nil {
+		return "", &MountError{Cim: cimPath, Op: "Mount", VolumeGUID: volumeGUID, Err: err}
 	}
-	return fmt.Sprintf("\\\\?\\Volume{%s}\\", layerGUID.String()), nil
-}
-
-// Mount mounts the cim at path `cimPath` and returns the mount location of that cim.  This method uses the
-// `CimMountFlagCacheRegions` mount flag when mounting the cim, if some other mount flag is desired use the
-// `MountWithFlags` method.
-func Mount(cimPath string) (string, error) {
-	return MountWithFlags(cimPath, hcsschema.CimMountFlagCacheFiles)
+	return fmt.Sprintf("\\\\?\\Volume{%s}\\", volumeGUID.String()), nil
 }
 
 // Unmount unmounts the cim at mounted at path `volumePath`.