feat: expose runtime directory-sharing devices with live share swap by jlagedo · Pull Request #216 · Code-Hex/vz

jlagedo · 2026-05-23T21:14:04Z

Summary

This adds support for runtime directory sharing: reading the directory-sharing devices off a running VirtualMachine and hot-swapping the directories a guest sees without recreating the VM.

The Virtualization framework exposes VZVirtioFileSystemDevice as a live device on a started VM, with a read/write share property (macOS 12+). Until now vz only surfaced the configuration side (VirtioFileSystemDeviceConfiguration), so callers could set a share before Start() but never change it afterwards. This PR fills that gap.

What's added

VirtualMachine.DirectorySharingDevices() []*VirtioFileSystemDevice
Returns the live directory-sharing devices on a running VM. Mirrors the existing SocketDevices() / USBControllers() accessors. Returns nil on macOS < 12.

VirtioFileSystemDevice — the runtime device (distinct from VirtioFileSystemDeviceConfiguration):

SetShare(share DirectoryShare) — swaps the directory share on the running device. The mutation runs on the VM's serial dispatch queue, as the framework requires for all VZVirtualMachine interactions.
Share() DirectoryShare — reads back the current share (also on the VM queue), reconstructing the concrete *SingleDirectoryShare / *MultipleDirectoryShare via Obj-C class introspection. Restores get/set symmetry with the underlying share property.

This lets a host add or remove the directories a guest sees while the VM keeps running.

Implementation notes

Follows the established runtime-device pattern (socket.go, usb.go): the device wrapper stores the VM's dispatchQueue and embeds *pointer.
The device wrapper itself uses no release finalizer — these objects are owned by the VM's array (Apple's get-rule), matching VirtioSocketDevice. Only the value returned by Share() is retained on the C side and released via a Go finalizer, since it crosses the boundary as an owned object.
All live calls go through dispatch_sync on the VM queue, consistent with the memory-balloon runtime device.
Gated on macOS 12 in both the Go and Objective-C layers.

Testing

make download_kernel && make test (run locally on Apple silicon, codesigned):

TestDirectorySharingDevices — a configured file-system device is returned from a created VM.
TestVirtioFileSystemDeviceSetShare — boots a VM with a single-directory share, asserts Share() reports *SingleDirectoryShare, mounts in-guest and sees the file; then hot-swaps to a multiple-directory share via SetShare, asserts Share() now reports *MultipleDirectoryShare, remounts in-guest and verifies the swapped-in content is visible while the original file is gone.

Existing TestSingleDirectoryShare / TestMultipleDirectoryShare continue to pass (no regression). go vet ./... is clean.

Test plan

go build ./...
go vet ./...
make test (new + existing shared-directory tests pass, codesigned, real guest)

🤖 Generated with Claude Code

Add VZVirtualMachine.directorySharingDevices() and a runtime VirtioFileSystemDevice type with SetShare(), so a host can change which directories a guest sees on a running VM (macOS 12+) without recreating it. Apple supports this (VZVirtioFileSystemDevice.share is get/set on the runtime device, reachable via VZVirtualMachine.directorySharingDevices), but the binding only exposed the config-time setter. Mirrors the existing SocketDevices() pattern: NSArray -> ToPointerSlice -> wrap each pointer with the VM's serial dispatch queue. SetShare runs the mutation on that queue, as the framework requires. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Expose a Share() getter on the running file system device so the directory share set via SetShare (or at configuration time) can be read back, restoring get/set symmetry with the VZVirtioFileSystemDevice.share property. The getter reads on the VM's serial dispatch queue and reconstructs the concrete *SingleDirectoryShare or *MultipleDirectoryShare via Obj-C class introspection. Add integration tests covering the runtime directory-sharing API: - TestDirectorySharingDevices verifies a configured device is returned. - TestVirtioFileSystemDeviceSetShare boots a VM, asserts the reported share type, hot-swaps single -> multiple share at runtime, and verifies the guest sees the swapped-in content after remount. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

AkihiroSuda · 2026-06-25T04:02:16Z

+		t.Skip("VirtioFileSystemDevice is supported from macOS 12")
+	}
+
+	const tag = "swap"


Why is this called "swap"?
Can be confused with swap filesystem

Good point — renamed the tag to "shared" to avoid confusion with swap space. Fixed in f556faa.

Copilot

Pull request overview

This PR adds runtime (live) support for Virtio directory sharing devices by exposing directory-sharing devices from a VirtualMachine and enabling hot-swapping the guest-visible directory share without recreating the VM (macOS 12+).

Changes:

Add Objective-C bridge functions to fetch VZVirtualMachine.directorySharingDevices and get/set VZVirtioFileSystemDevice.share on the VM dispatch queue.
Introduce a runtime VirtioFileSystemDevice Go wrapper with SetShare/Share plus VirtualMachine.DirectorySharingDevices().
Add integration tests covering runtime device discovery and live share swapping in-guest.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
virtualization_12.m	Adds Obj-C bridge functions for runtime directory-sharing devices and live share get/set on the VM queue.
virtualization_12.h	Declares the new Obj-C bridge function prototypes for Go to call.
shared_directory.go	Adds the runtime `VirtioFileSystemDevice` wrapper and `VirtualMachine.DirectorySharingDevices()` accessor.
shared_directory_test.go	Adds tests verifying runtime device discovery and live share swapping behavior.

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jlagedo · 2026-06-27T03:40:20Z

+func (d *VirtioFileSystemDevice) SetShare(share DirectoryShare) {
+	C.setShareVZVirtioFileSystemDevice(objc.Ptr(d), objc.Ptr(share), d.dispatchQueue)
+}


Fixed in f556faa: SetShare now passes NULL for a nil share instead of panicking.

jlagedo · 2026-06-27T03:40:22Z

+/*!
+ @abstract Return the list of directory sharing devices configured on this virtual machine. Return an empty array if none is configured.
+ @see VZDirectorySharingDevice
+ @see VZVirtualMachineConfiguration
+ */


Fixed in f556faa: doc now references VZVirtualMachine.

- SetShare passes NULL for a nil share instead of panicking - VZVirtualMachine_directorySharingDevices doc references VZVirtualMachine - rename confusing virtiofs test tag "swap" -> "shared" Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

jlagedo and others added 2 commits May 23, 2026 17:46

AkihiroSuda mentioned this pull request Jun 25, 2026

feat: runtime hot-mount (limactl mount add|remove|list) for QEMU and VZ lima-vm/lima#5154

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AkihiroSuda requested review from Code-Hex and Copilot June 25, 2026 04:00

Copilot started reviewing on behalf of AkihiroSuda June 25, 2026 04:01 View session

AkihiroSuda reviewed Jun 25, 2026

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Copilot AI reviewed Jun 25, 2026

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feat: expose runtime directory-sharing devices with live share swap#216

feat: expose runtime directory-sharing devices with live share swap#216
jlagedo wants to merge 3 commits into
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jlagedo commented May 23, 2026

Summary

What's added

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AkihiroSuda Jun 25, 2026

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