v0.20.0 (Kiviuq)

We are proud to announce the latest version of Unikraft, v0.20.0! This release comes with the much anticipated redesign and implementation of VFS, which brings enhanced performance, better maintainability, and improved compatibility with modern applications. For more info refer to the accompanying blog post.

DEPRECATION NOTICE

The old VFS, vfscore, will be deprecated in Unikraft 0.22.0 (early 2026). For help on transitioning, consult the migration guide or join us on Discord.

COMPATIBILITY NOTICE

The implementation of arch_prctl system call has been migrated from app-elfloader to libposix-process. Configurations using CONFIG_APPELFLOADER_ARCH_PRCTL should now use CONFIG_LIBPOSIX_PROCESS_ARCH_PRCTL.

A summary of the most important changes follows. For the full list of changes see the changelog.

🚀 New Features#

Filesystem & Storage#

• libukfs: New library for the filesystem interface, driver templates and utilities
• libukfs-ramfs: ukfs memory-resident volatile filesystem
• libukfs-devfs: ukfs pseudo-filesystem that provides files under /dev
• libukfs-pseudo: New library home to pseudo-files previously provided by posix-tty; also provides pseudo-files under devfs
• posix-vfs: New library for POSIX-compliant virtual filesystem layer on top of ukfs
• posix-vfs-fstab: New library for mounting filesystems at boot according to predefined tables (fstabs)
• libukpod: Utility library for managing pages-on-demand - used by filesystem drivers
• libuksparsebuf: Utility library for efficient management of sparse buffers - used by filesystem drivers
• libukfile: Add interface to expose & manage file backing memory

Context Management#

• lcpu: Enhanced exception handling with context escape trampolines

System Call and Process#

• libposix-fdio: Support the sendfile() syscall
• libposix-process: Signal the application on system error (SIGSEGV, SIGILL etc.)

Networking#

• virtio-net, liblwip: Support Mergeable RX buffers (VIRTIO_NET_F_MRG_RXBUF)
• virtio-net, liblwip: Support Large Receive Offload (LRO)

🐛 Bug Fixes & Improvements#

Memory Management#

• libukallocbuddy: Refactor to support asymmetric palloc() / pfree() operations
• ukallocpool: Various improvements to enhance performance
• libukvmem: Fix VMA stack population logic
• libukalloc: Ensure sufficient memory allocation for region metadata
• libukallocregion: Various enhancements and improvements

Context Management#

• libuksched: Remove unnecessary ECTX saving/restoration for cooperative thread switching

System Call and Process#

• libposix-process: Refactor the kernel event API
• libposix-process: Fix exit code propagation to termination context

Architecture and Platform#

• lcpu: Align exception handling stacks across architectures

Synchronization & Atomics#

• libuklock: Optimize ukmutex and allow opt-out of atomics in the fast patch.
• libuklock: Introduce semaphore operation to consume all tokens at once

Network Stack#

• virtio-net: Use single descriptor for packets
• virtio-net: Keep event suppression mechanism internal
• virtio-net: Split feature probing and negotiation

Development & Debugging#

• libsyscall-shim: Enhance syscall tracing with pretty-print decoding for socket, filesystem, and process syscalls