[PATCH 0/5] Support diskless memfd transport for cpr-exec

Currently, cpr-exec requires a file to save and load VM/device state.

Introduce a diskless approach so cpr-exec no longer relies on disk storage
for this state. The main idea is to add a new memfd-based migration
transport: instead of using a file, VM/device state is saved to and loaded
from an inherited memfd.

I tested this with virtio-blk, NVMe VFIO, and virtio-net.

/home/opc/ext4/qemu/build/qemu-system-x86_64 \
-machine q35,dump-guest-core=off,memory-backend=ram0,aux-ram-share=on \
-accel kvm -cpu host \
-name debug-threads=on \
-m 8G -smp 4 \
-object memory-backend-memfd,id=ram0,size=8G,share=on \
-device virtio-blk-pci,drive=drive0,id=virtblk0,num-queues=4 \
-drive file=ol89.qcow2,if=none,id=drive0 \
-object iommufd,id=iommufd0 \
-device vfio-pci,host=0000:82:00.0,iommufd=iommufd0,id=vfio0,x-no-mmap=on \
-device virtio-net-pci,netdev=tapnet,mq=true,vectors=9,mac=52:54:11:22:14:49 \
-netdev tap,id=tapnet,script=qemu-ifup,downscript=no,queues=2,vhost=off \
-vnc :8 -monitor stdio

(qemu) migrate_set_parameter mode cpr-exec

(qemu) migrate_set_parameter cpr-exec-command /home/opc/ext4/qemu/build/qemu-system-x86_64 -machine q35,dump-guest-core=off,memory-backend=ram0,aux-ram-share=on -accel kvm -cpu host -name debug-threads=on -m 8G -smp 4 -object memory-backend-memfd,id=ram0,size=8G,share=on -device virtio-blk-pci,drive=drive0,id=virtblk0,num-queues=4 -drive file=ol89.qcow2,if=none,id=drive0 -object iommufd,id=iommufd0 -device vfio-pci,host=0000:82:00.0,iommufd=iommufd0,id=vfio0,x-no-mmap=on -device virtio-net-pci,netdev=tapnet,mq=true,vectors=9,mac=52:54:11:22:14:49 -netdev tap,id=tapnet,script=qemu-ifup,downscript=no,queues=2,vhost=off -vnc :8 -monitor stdio -incoming defer

(qemu) migrate -d memfd:
QEMU 11.1.50 monitor - type 'help' for more information

(qemu) info status
VM status: paused (inmigrate)

(qemu) migrate_incoming memfd:

(qemu) info status
VM status: running


Dongli Zhang (5):
  migration/qapi: Add memfd migration transport
  migration: Add generic memfd channel helpers
  migration/cpr-exec: Add memfd helpers
  migration/cpr-exec: Support diskless memfd transport
  migration: cpr-exec memfd transport documentation

 docs/devel/migration/CPR.rst | 24 +++++++++++
 migration/channel.c          |  7 +++
 migration/cpr-exec-memfd.c   | 90 +++++++++++++++++++++++++++++++++++++++
 migration/cpr-exec-memfd.h   | 18 ++++++++
 migration/cpr-exec.c         |  9 ++++
 migration/memfd.c            | 90 +++++++++++++++++++++++++++++++++++++++
 migration/memfd.h            | 19 +++++++++
 migration/meson.build        |  2 +
 migration/migration.c        |  9 ++++
 qapi/migration.json          | 32 +++++++++++---
 10 files changed, 295 insertions(+), 5 deletions(-)

base-commit: e8d693e12af9cbb89d724baadfcc08559669e279

Thank you very much!

Dongli Zhang