IsMountPoint implementation

Author: kkmsft

client/api/filesystem/v1alpha1/api.proto

@@ -16,6 +16,9 @@ service Filesystem {
     // LinkPath creates a local directory symbolic link between a source path 
     // and target path in the host's filesystem
     rpc LinkPath(LinkPathRequest) returns (LinkPathResponse) {}
+
+    //IsMountPoint checks if a given path is mount or not
+    rpc IsMountPoint(IsMountPointRequest) returns (IsMountPointResponse) {}
 }
 
 // Context of the paths used for path prefix validation
@@ -150,3 +153,16 @@ message LinkPathResponse {
     // Error message if any. Empty string indicates success
     string error = 1;
 }
+ 
+message IsMountPointRequest {
+    // The path whose existence we want to check in the host's filesystem
+    string path = 1;
+}
+
+message IsMountPointResponse {
+    // Error message if any. Empty string indicates success
+    string error = 1;
+
+    // Indicates whether the path in PathExistsRequest exists in the host's filesystem
+    bool is_mount_point = 2;
+}

internal/os/filesystem/api.go

@@ -1,10 +1,8 @@
 package filesystem
 
 import (
-	// "fmt"
+	"fmt"
 	"os"
-	// "os/exec"
-	// "runtime"
 )
 
 // Implements the Filesystem OS API calls. All code here should be very simple
@@ -18,7 +16,7 @@ func New() APIImplementor {
 	return APIImplementor{}
 }
 
-func (APIImplementor) PathExists(path string) (bool, error) {
+func pathExists(path string) (bool, error) {
 	_, err := os.Stat(path)
 	if err == nil {
 		return true, nil
@@ -29,6 +27,10 @@ func (APIImplementor) PathExists(path string) (bool, error) {
 	return false, err
 }
 
+func (APIImplementor) PathExists(path string) (bool, error) {
+	return pathExists(path)
+}
+
 func (APIImplementor) Mkdir(path string) error {
 	return os.MkdirAll(path, 0755)
 }
@@ -43,3 +45,33 @@ func (APIImplementor) Rmdir(path string, force bool) error {
 func (APIImplementor) LinkPath(tgt string, src string) error {
 	return os.Symlink(tgt, src)
 }
+
+// IsMountPoint - returns true if its a mount point.
+// A path is considered a mount point if:
+//  - directory exists and
+//  - it is a soft link and
+//  - the target path of the link exists.
+func (APIImplementor) IsMountPoint(tgt string) (bool, error) {
+	// This code is similar to k8s.io/kubernetes/pkg/util/mount except the pathExists usage.
+	// Also in a remote call environment the os error cannot be passed directly back, hence the callers
+	// are expected to perform the isExists check before calling this call in CSI proxy.
+	stat, err := os.Lstat(tgt)
+	if err != nil {
+		return false, err
+	}
+
+	// If its a link and it points to an existing file then its a mount point.
+	if stat.Mode()&os.ModeSymlink != 0 {
+		target, err := os.Readlink(tgt)
+		if err != nil {
+			return false, fmt.Errorf("readlink error: %v", err)
+		}
+		exists, err := pathExists(target)
+		if err != nil {
+			return false, err
+		}
+		return exists, nil
+	}
+
+	return false, nil
+}

internal/server/filesystem/internal/types.go

@@ -123,3 +123,12 @@ type LinkPathResponse struct {
 	// Error message if any. Empty string indicates success
 	Error string
 }
+
+type IsMountPointRequest struct {
+	Path string
+}
+
+type IsMountPointResponse struct {
+	Error        string
+	IsMountPoint bool
+}

internal/server/filesystem/server.go

@@ -25,6 +25,7 @@ type API interface {
 	Mkdir(path string) error
 	Rmdir(path string, force bool) error
 	LinkPath(tgt string, src string) error
+	IsMountPoint(path string) (bool, error)
 }
 
 func NewServer(kubeletCSIPluginsPath string, kubeletPodPath string, hostAPI API) (*Server, error) {
@@ -184,3 +185,17 @@ func (s *Server) LinkPath(ctx context.Context, request *internal.LinkPathRequest
 		Error: errString,
 	}, nil
 }
+
+func (s *Server) IsMountPoint(ctx context.Context, request *internal.IsMountPointRequest, version apiversion.Version) (*internal.IsMountPointResponse, error) {
+	isMount, err := s.hostAPI.IsMountPoint(request.Path)
+	if err != nil {
+		return &internal.IsMountPointResponse{
+			IsMountPoint: false,
+			Error:        err.Error(),
+		}, nil
+	}
+	return &internal.IsMountPointResponse{
+		Error:        "",
+		IsMountPoint: isMount,
+	}, nil
+}