storage: dup() newVZDiskBlockDeviceStorageDeviceAttachment file descriptor

In order to solve #201, this
commit adds a `newFileHandleDupFd()` objective-C helper.

This helper calls `dup()` on its file descriptor argument, and wraps it in
a `NSFileHandle` with `closeOnDealloc:true`. This new file handle is
fully independent from its golang counterpart, if the golang `os.File`
holding the file descriptor is closed, the `NSFileHandle` will still be
valid.

This new helper is then used with vz.NewDiskBlockDeviceStorageDeviceAttachment.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>

Author: cfergeau

storage_test.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"testing"
 
@@ -107,6 +106,22 @@ func TestBlockDeviceWithCacheAndSyncMode(t *testing.T) {
 	}
 }
 
+func TestBlockDeviceStorageDeviceAttachmentError(t *testing.T) {
+	if vz.Available(14) {
+		t.Skip("vz.NewDiskBlockDeviceStorageDeviceAttachment is supported from macOS 14")
+	}
+
+	f, err := os.Create(filepath.Join(t.TempDir(), "empty"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+	_, err = vz.NewDiskBlockDeviceStorageDeviceAttachment(f, false, vz.DiskSynchronizationModeNone)
+	if err == nil {
+		t.Fatal("did not get an error with invalid file descriptor")
+	}
+}
+
 func TestBlockDeviceWithDeviceAttachment(t *testing.T) {
 	if vz.Available(12) {
 		t.Skip("vz.NewDiskImageStorageDeviceAttachmentWithCacheAndSync is supported from macOS 12")
@@ -147,11 +162,11 @@ func TestBlockDeviceWithDeviceAttachment(t *testing.T) {
 				if err != nil {
 					t.Fatal(err)
 				}
+				if err := dev.Close(); err != nil {
+					log.Printf("failed to close %s: %s\n", devPath, err)
+				}
+
 			}
-			// `dev` from the block above will be garbage collected and the underlying file descriptor will be closed.
-			// This will trigger an internal virtualization error in the subsequent code.
-			// https://github.com/Code-Hex/vz/issues/201
-			runtime.GC()
 
 			config, err := vz.NewVirtioBlockDeviceConfiguration(attachment)
 			if err != nil {

virtualization_14.m

@@ -30,7 +30,7 @@
  @param error If not nil, assigned with the error if the initialization failed.
  @return An initialized `VZDiskBlockDeviceStorageDeviceAttachment` or nil if there was an error.
  @discussion
-    The file handle is retained by the disk attachment.
+    The file handle is dup()’ed by this function.
     The handle must be open when the virtual machine starts.
 
     The `readOnly` parameter affects how the disk is exposed to the guest operating system
@@ -41,7 +41,10 @@
 {
 #ifdef INCLUDE_TARGET_OSX_14
     if (@available(macOS 14, *)) {
-        NSFileHandle *fileHandle = [[NSFileHandle alloc] initWithFileDescriptor:fileDescriptor];
+        NSFileHandle *fileHandle = newFileHandleDupFd(fileDescriptor, error);
+        if (fileHandle == nil) {
+            return nil;
+        }
         return [[VZDiskBlockDeviceStorageDeviceAttachment alloc]
              initWithFileHandle:fileHandle
                        readOnly:(BOOL)readOnly

virtualization_helper.h

@@ -4,6 +4,7 @@
 #import <Foundation/Foundation.h>
 
 NSDictionary *dumpProcessinfo();
+NSFileHandle *newFileHandleDupFd(int fileDescriptor, void **error);
 
 #define RAISE_REASON_MESSAGE                                                                               \
     "This may possibly be a bug due to library handling errors.\n"                                         \

virtualization_helper.m

@@ -27,4 +27,19 @@
         @"Min Required OS Version" : @__MAC_OS_X_VERSION_MIN_REQUIRED,
 #endif
     };
-}
+}
+
+NSFileHandle *newFileHandleDupFd(int fileDescriptor, void **error)
+{
+    int dupedFd = dup(fileDescriptor);
+    if (dupedFd < 0) {
+        if (error != nil) {
+            *error = [NSError errorWithDomain:NSPOSIXErrorDomain
+                                         code:errno
+                                     userInfo:nil];
+        }
+        return nil;
+    }
+
+    return [[NSFileHandle alloc] initWithFileDescriptor:dupedFd closeOnDealloc:true];
+}