Bug 1731522

This is already supported upstream since

commit c6da5913d993f9f5e1650ca1677e11e25b594e2e
Author: Peter Krempa <pkrempa>
Date:   Mon Jun 17 17:17:56 2019 +0200

    qemu: Add support for controling qemu capabilities via the qemu XML namespace
    
    Similarly how we allow adding arbitrary command line arguments and
    environment variables this patch introduces the ability to control
    libvirt's perception of the qemu process by tweaking the capability bits
    for testing purposes.
    
    The idea is to allow developers and users either test a new feature by
    enabling it early or disabling it to see whether it introduced
    regressions.
    
    This feature is not meant for production use though, so users should
    handle it with care.
    
    Signed-off-by: Peter Krempa <pkrempa>
    Reviewed-by: Ján Tomko <jtomko>

Verified on libvirt-6.0.0-17.module+el8.2.0+6257+0d066c28.x86_64 qemu-kvm-4.2.0-17.module+el8.2.0+6141+0f540f16.x86_64

1. Start a VM with following xml:
<domain type='qemu' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>testvm</name>

   [...]

  <qemu:capabilities>
    <qemu:del capability='blockdev'/>
    <qemu:add capability='drive'/>
  </qemu:capabilities>
</domain>

2. Check the qemu cmdline
➜  ~  ps aux|grep qemu|grep drive
qemu      634681  156  1.6 3411400 522080 ?      Sl   22:03   0:32 /usr/libexec/qemu-kvm -name guest=new,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-new/master-key.aes -machine pc-q35-rhel8.2.0,accel=kvm,usb=off,vmport=off,dump-guest-core=off -cpu EPYC-IBPB,x2apic=on,tsc-deadline=on,hypervisor=on,tsc-adjust=on,arch-capabilities=on,ssbd=on,cmp-legacy=on,perfctr-core=on,clzero=on,amd-ssbd=on,virt-ssbd=on,rdctl-no=on,skip-l1dfl-vmentry=on,mds-no=on,monitor=off,svm=off -m 2048 -overcommit mem-lock=off -smp 2,sockets=2,cores=1,threads=1 -uuid 442bbb67-01ac-4329-9b4f-ca90b638da0b -no-user-config -nodefaults -chardev socket,id=charmonitor,fd=29,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global ICH9-LPC.disable_s3=1 -global ICH9-LPC.disable_s4=1 -boot strict=on -device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 -device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 -device pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 -device pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 -device pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 -device pcie-root-port,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 -device pcie-root-port,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 -device qemu-xhci,p2=15,p3=15,id=usb,bus=pci.2,addr=0x0 -device virtio-scsi-pci,id=scsi0,bus=pci.3,addr=0x0 -device virtio-serial-pci,id=virtio-serial0,bus=pci.4,addr=0x0 -drive file=/var/lib/libvirt/images/new.qcow2,format=qcow2,if=none,id=drive-virtio-disk0 -device virtio-blk-pci,scsi=off,bus=pci.7,addr=0x0,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -netdev tap,fd=40,id=hostnet0,vhost=on,vhostfd=38 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:37:9d:99,bus=pci.1,addr=0x0 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -chardev socket,id=charchannel0,fd=41,server,nowait -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0 -chardev spicevmc,id=charchannel1,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0 -device usb-tablet,id=input0,bus=usb.0,port=1 -spice port=5900,addr=0.0.0.0,disable-ticketing,image-compression=off,seamless-migration=on -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pcie.0,addr=0x1 -device ich9-intel-hda,id=sound0,bus=pcie.0,addr=0x1b -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev spicevmc,id=charredir0,name=usbredir -device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev spicevmc,id=charredir1,name=usbredir -device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device virtio-balloon-pci,id=balloon0,bus=pci.5,addr=0x0 -object rng-random,id=objrng0,filename=/dev/urandom -device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.6,addr=0x0 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on

-drive is used instead of -blockdev

Changing this TestOnly BZ as CLOSED CURRENTRELEASE. Please reopen if the issue is not resolved.