[Bug 1888818] Re: Multi-queue vhost-user fails to reconnect with qemu version >=4.2

[Thomas Huth <1888818@bugs.launchpad.net>]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/277


** Changed in: qemu
       Status: New => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #277
   https://gitlab.com/qemu-project/qemu/-/issues/277

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Title:
  Multi-queue vhost-user fails to reconnect with qemu version >=4.2

Status in QEMU:
  Expired

Bug description:
  Test Environment:
  DPDK version: DPDK v20.08
  Other software versions: qemu4.2.0, qemu5.0.0.
  OS: Linux 4.15.0-20-generic
  Compiler: gcc (Ubuntu 7.3.0-16ubuntu3) 8.4.0
  Hardware platform: Purley.
  Test Setup
  Steps to reproduce
  List the steps to reproduce the issue.

  Test flow
  =========
  1. Launch vhost-user testpmd as port0 with 2 queues:

  ./x86_64-native-linuxapp-gcc/app/testpmd -l 2-4 -n 4 \
      --file-prefix=vhost --vdev 'net_vhost0,iface=vhost-net,queues=2,client=1' -- -i --txd=1024 --rxd=1024 --txq=2 --rxq=2
  testpmd>start

  3. Launch qemu with virtio-net:

   taskset -c 13 \
      qemu-system-x86_64 -name us-vhost-vm1 \
         -cpu host -enable-kvm -m 2048 -object memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on \
         -numa node,memdev=mem \
         -mem-prealloc -monitor unix:/tmp/vm2_monitor.sock,server,nowait -netdev user,id=yinan,hostfwd=tcp:127.0.0.1:6005-:22 -device e1000,netdev=yinan \
         -smp cores=1,sockets=1 -drive file=/home/osimg/ubuntu16.img  \
         -chardev socket,id=char0,path=./vhost-net,server \
         -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce,queues=2 \
         -device virtio-net-pci,mac=52:54:00:00:00:01,netdev=mynet1,mrg_rxbuf=on,csum=on,gso=on,host_tso4=on,guest_tso4=on,mq=on,vectors=15 \
         -vnc :10 -daemonize

  6. Quit testpmd and restart vhost-user :

  testpmd>quit
  ./x86_64-native-linuxapp-gcc/app/testpmd -l 2-4 -n 4 \
      --file-prefix=vhost --vdev 'net_vhost0,iface=vhost-net,queues=2,client=1' -- -i --txd=1024 --rxd=1024 --txq=2 --rxq=2

  Expected Result:
  After the vhost-user is killed then re-launched, the virtio-net can connect back to vhost-user again.

  Actual Result:
  Vhost-user relaunch failed with continous log printed"VHOST_CONFIG: Processing VHOST_USER_SET_FEATURES failed.

  Analysis:
  This is a regression bug, bad commit: c6beefd674f
  When vhost-user quits, QEMU doesnot save acked features for each virtio-net after vhost-user quits. When vhost-user reconnects to QEMU, QEMU sends two different features(one is the true acked feature while the another is 0x40000000) to vhost-user successively which causing vhost-user exits abnormally.

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