cimfs: Add cim layer mount/unmount functionality. (microsoft#1955)

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

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
+}