Re: [pve-devel] [PATCH pve-qemu 1/1] add block-commit-replaces option patch

[Fiona Ebner <f.ebner@proxmox.com>]

Hi,

Am 22.04.25 um 13:51 schrieb Alexandre Derumier via pve-devel:
> This is needed for external snapshot live commit,
> when the top blocknode is not the fmt-node.
> (in our case, the throttle-group node is the topnode)
> 
> Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>

I looked into this again and maybe we can avoid this patch. I think all
you need is to specify the 'top-node' when issuing the commit command.

Without specifying "top-node":

> [I] root@pve8a1 ~# cat block-commit.sh
> #!/bin/bash
> rm -f /tmp/backing.qcow2
> rm -f /tmp/top.qcow2
> qemu-img create /tmp/backing.qcow2 -f qcow2 64M
> qemu-img create /tmp/top.qcow2 -f qcow2 64M
> qemu-system-x86_64 --qmp stdio \
> --nodefaults \
> --object throttle-group,id=thrgr0 \
> --blockdev qcow2,node-name=backing0,file.driver=file,file.filename=/tmp/backing.qcow2 \
> --blockdev throttle,node-name=drive-scsi0,throttle-group=thrgr0,file.driver=qcow2,file.node-name=node0,file.file.driver=file,file.file.filename=/tmp/top.qcow2,file.backing=backing0 \
> --device 'virtio-scsi-pci,id=virtioscsi0,bus=pci.0,addr=0x2' \
> --device 'scsi-hd,bus=virtioscsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0' \
> <<EOF
> {"execute": "qmp_capabilities"}
> {"execute": "query-block"}
> {"execute": "block-commit", "arguments": { "device": "drive-scsi0", "base-node": "backing0", "job-id": "commit0" } }
> {"execute": "block-job-complete", "arguments": {"device": "commit0" } }
> {"execute": "query-block"}
> {"execute": "quit"}
> EOF

The result will be:

> {
>   "return": [
>     {
>       "io-status": "ok",
>       "device": "",
>       "locked": false,
>       "removable": false,
>       "inserted": {
>         "iops_rd": 0,
>         "detect_zeroes": "off",
>         "image": {
>           "virtual-size": 67108864,
>           "filename": "/tmp/backing.qcow2",
>           "cluster-size": 65536,
>           "format": "qcow2",
>           "actual-size": 200704,
>           "format-specific": {
>             "type": "qcow2",
>             "data": {
>               "compat": "1.1",
>               "compression-type": "zlib",
>               "lazy-refcounts": false,
>               "refcount-bits": 16,
>               "corrupt": false,
>               "extended-l2": false
>             }
>           },
>           "dirty-flag": false
>         },
>         "iops_wr": 0,
>         "ro": false,
>         "node-name": "backing0",
>         "backing_file_depth": 0,
>         "drv": "qcow2",
>         "iops": 0,
>         "bps_wr": 0,
>         "write_threshold": 0,
>         "encrypted": false,
>         "bps": 0,
>         "bps_rd": 0,
>         "cache": {
>           "no-flush": false,
>           "direct": false,
>           "writeback": true
>         },
>         "file": "/tmp/backing.qcow2"
>       },
>       "qdev": "scsi0",
>       "type": "unknown"
>     }
>   ]
> }

So no throttle group, bad.

But setting "top-node" being the throttle node like here:

> #!/bin/bash
> rm -f /tmp/backing.qcow2
> rm -f /tmp/top.qcow2
> qemu-img create /tmp/backing.qcow2 -f qcow2 64M
> qemu-img create /tmp/top.qcow2 -f qcow2 64M
> qemu-system-x86_64 --qmp stdio \
> --nodefaults \
> --object throttle-group,id=thrgr0 \
> --blockdev qcow2,node-name=backing0,file.driver=file,file.filename=/tmp/backing.qcow2 \
> --blockdev throttle,node-name=drive-scsi0,throttle-group=thrgr0,file.driver=qcow2,file.node-name=node0,file.file.driver=file,file.file.filename=/tmp/top.qcow2,file.backing=backing0 \
> --device 'virtio-scsi-pci,id=virtioscsi0,bus=pci.0,addr=0x2' \
> --device 'scsi-hd,bus=virtioscsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0' \
> <<EOF
> {"execute": "qmp_capabilities"}
> {"execute": "query-block"}
> {"execute": "block-commit", "arguments": { "device": "drive-scsi0", "top-node": "node0", "base-node": "backing0", "job-id": "commit0" } }
> {"execute": "block-job-complete", "arguments": {"device": "commit0" } }
> {"execute": "query-block"}
> {"execute": "quit"}
> EOF

The result will be:

> {
>   "return": [
>     {
>       "io-status": "ok",
>       "device": "",
>       "locked": false,
>       "removable": false,
>       "inserted": {
>         "iops_rd": 0,
>         "detect_zeroes": "off",
>         "image": {
>           "backing-image": {
>             "virtual-size": 67108864,
>             "filename": "/tmp/backing.qcow2",
>             "cluster-size": 65536,
>             "format": "qcow2",
>             "actual-size": 200704,
>             "format-specific": {
>               "type": "qcow2",
>               "data": {
>                 "compat": "1.1",
>                 "compression-type": "zlib",
>                 "lazy-refcounts": false,
>                 "refcount-bits": 16,
>                 "corrupt": false,
>                 "extended-l2": false
>               }
>             },
>             "dirty-flag": false
>           },
>           "virtual-size": 67108864,
>           "filename": "json:{\"throttle-group\": \"thrgr0\", \"driver\": \"throttle\", \"file\": {\"driver\": \"qcow2\", \"file\": {\"driver\": \"file\", \"filename\": \"/tmp/backing.qcow2\"}}}",
>           "cluster-size": 65536,
>           "format": "throttle",
>           "actual-size": 200704,
>           "dirty-flag": false
>         },
>         "iops_wr": 0,
>         "ro": false,
>         "node-name": "drive-scsi0",
>         "backing_file_depth": 1,
>         "drv": "throttle",
>         "iops": 0,
>         "bps_wr": 0,
>         "write_threshold": 0,
>         "encrypted": false,
>         "bps": 0,
>         "bps_rd": 0,
>         "cache": {
>           "no-flush": false,
>           "direct": false,
>           "writeback": true
>         },
>         "file": "json:{\"throttle-group\": \"thrgr0\", \"driver\": \"throttle\", \"file\": {\"driver\": \"qcow2\", \"file\": {\"driver\": \"file\", \"filename\": \"/tmp/backing.qcow2\"}}}"
>       },
>       "qdev": "scsi0",
>       "type": "unknown"
>     }
>   ]
> }

I hope this is what you want?

Probably QEMU does not consider throttle groups when automatically
determining the top-node, so we need to specify it explicitly.

Best Regards,
Fiona


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