(In reply to aihua liang from comment #1)
> Run on qemu-kvm-2-12-0-42-module-el8-2173-537e5cb5-x86_64, don't hit this
> issue.
Adding Regression keyword.
You didn't specify the 'backing-file' option for your 'blockdev-create' commands, so no backing file link is written into the image files. You can still setup a backing chain at runtime with 'blockdev-snapshot', but this doesn't and isn't supposed to update the backing file links.
I would normally close this as NOTABUG, but you claim in comment 1 that you found an old version where this doesn't happen. Can you confirm that you did the exact same steps on the old version? QEMU never had code that was supposed to update the backing file links during blockdev-snapshot.
Retest it on qemu-kvm-2.12.0-60.module+el8+2725+0ab65287.x86_64, it has same result as qemu-kvm-3.1.0-2.module+el8+2606+2c716ad7.x86_64.
According to kevin's comment in comment4, close this bug as NOTABUG.
Description of problem: Incomplete backing-chain info got by "qemu-img info xxx -U --backing-chain" Version-Release number of selected component (if applicable): kernel version: 4.18.0-57.el8.x86_64 qemu-kvm version: qemu-kvm-3.1.0-2.module+el8+2606+2c716ad7.x86_64 How reproducible: 100% Steps to Reproduce: 1.Start guest with iscsi backend: /usr/libexec/qemu-kvm \ -name 'avocado-vt-vm1' \ -machine q35 \ -nodefaults \ -device VGA,bus=pcie.0,addr=0x1 \ -device pcie-root-port,id=pcie_root_port_0,slot=2,chassis=2,addr=0x2,bus=pcie.0 \ -device pcie-root-port,id=pcie_root_port_1,slot=3,chassis=3,addr=0x3,bus=pcie.0 \ -device pcie-root-port,id=pcie_root_port_2,slot=4,chassis=4,addr=0x4,bus=pcie.0 \ -chardev socket,id=qmp_id_qmpmonitor1,path=/var/tmp/monitor-qmpmonitor1-20181225-045358-gDqDsfCu,server,nowait \ -mon chardev=qmp_id_qmpmonitor1,mode=control \ -chardev socket,id=qmp_id_catch_monitor,path=/var/tmp/monitor-catch_monitor-20181225-045358-gDqDsfCu,server,nowait \ -mon chardev=qmp_id_catch_monitor,mode=control \ -device pvpanic,ioport=0x505,id=idHtZPbY \ -chardev socket,id=serial_id_serial0,path=/var/tmp/serial-serial0-20181225-045358-gDqDsfCu,server,nowait \ -device isa-serial,chardev=serial_id_serial0 \ -chardev socket,id=seabioslog_id_20181225-045358-gDqDsfCu,path=/var/tmp/seabios-20181225-045358-gDqDsfCu,server,nowait \ -device isa-debugcon,chardev=seabioslog_id_20181225-045358-gDqDsfCu,iobase=0x402 \ -device pcie-root-port,id=pcie.0-root-port-5,slot=5,chassis=5,addr=0x5,bus=pcie.0 \ -device qemu-xhci,id=usb1,bus=pcie.0-root-port-5,addr=0x0 \ -blockdev driver=file,node-name=driveimage1,filename=/mnt/test/rhel80-64-virtio.raw \ -blockdev node-name=drive_image1,file=driveimage1,driver=raw \ -device pcie-root-port,id=pcie.0-root-port-6,slot=6,chassis=6,addr=0x6,bus=pcie.0 \ -device virtio-blk-pci,id=image1,drive=drive_image1,bootindex=0,bus=pcie.0-root-port-6,addr=0x0 \ -device pcie-root-port,id=pcie.0-root-port-7,slot=7,chassis=7,addr=0x7,bus=pcie.0 \ -device virtio-net-pci,mac=9a:14:15:16:17:18,id=idQJqHNz,vectors=4,netdev=idXGWoum,bus=pcie.0-root-port-7,addr=0x0 \ -netdev tap,id=idXGWoum,vhost=on \ -m 14336 \ -smp 10,maxcpus=10,cores=5,threads=1,sockets=2 \ -cpu 'Broadwell',+kvm_pv_unhalt \ -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \ -vnc :0 \ -rtc base=utc,clock=host,driftfix=slew \ -boot order=cdn,once=c,menu=off,strict=off \ -enable-kvm \ -monitor stdio \ -qmp tcp:0:3000,server,nowait \ 2. Create snapshot image sn1,sn2,sn3,sn4 in previous {'execute':'blockdev-create','arguments':{'options': {'driver':'file','filename':'/root/sn$i','size':21474836480},'job-id':'job1'}} {'execute':'blockdev-add','arguments':{'driver':'file','node-name':'drive_sn$i','filename':'/root/sn$i'}} {'execute':'blockdev-create','arguments':{'options': {'driver': 'qcow2','file':'drive_sn$i','size':21474836480},'job-id':'job2'}} {'execute':'blockdev-add','arguments':{'driver':'qcow2','node-name':'sn$i','file':'drive_sn$i'}} {'execute':'job-dismiss','arguments':{'id':'job1'}} {'execute':'job-dismiss','arguments':{'id':'job2'}} 3. Create snapshot chain "base->sn1->sn2->sn3->sn4" {"execute":"blockdev-snapshot","arguments": {"node":"drive_image1","overlay":"sn1"}} {"execute":"blockdev-snapshot","arguments":{"node":"sn1","overlay":"sn2"}} {"execute":"blockdev-snapshot","arguments":{"node":"sn2","overlay":"sn3"}} {"execute":"blockdev-snapshot","arguments":{"node":"sn3","overlay":"sn4"}} 4. Check block info 4.1 (qemu)info block (qemu) info block sn4: /root/sn4 (qcow2) Attached to: /machine/peripheral/image1/virtio-backend Cache mode: writeback Backing file: /root/sn3 (chain depth: 4) 4.2 (host)#qemu-img info /root/sn4 -U --backing-chain # qemu-img info sn4 -U --backing-chain image: sn4 file format: qcow2 virtual size: 20G (21474836480 bytes) disk size: 196K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false 5. Do block commit from sn3 to sn1: {'execute': 'block-commit', 'arguments': { 'device': 'sn4', 'base-node':'sn1', 'top-node':'sn3','job-id':'j1'}} 6. Check block info: 6.1 (qemu)info block sn4: /root/sn4 (qcow2) Attached to: /machine/peripheral/image1/virtio-backend Cache mode: writeback Backing file: /root/sn1 (chain depth: 2) 6.2(qemu)#qemu-img info /root/sn4 -U --backing-chain image: sn4 file format: qcow2 virtual size: 20G (21474836480 bytes) disk size: 580K cluster_size: 65536 backing file: /root/sn1 backing file format: qcow2 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false image: /root/sn1 file format: qcow2 virtual size: 20G (21474836480 bytes) disk size: 2.0M cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false Actual results: In step4.2, no backing-chains info displayed. In step6.2, base info not displayed. Expected results: In step4.2, all snapshots info should be displayed. In step6.2, base info should also be displayed.