Re: [pve-devel] [PATCH v1 pve-qemu 1/1] add block-commit-replaces option patch

[DERUMIER, Alexandre via pve-devel]

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> 
> Feel free to cleanup this patch and submit it to qemu devs, you are a
> better C developper than me ^_^

>>I can try to look into it, but could you give some more details how
>>exactly the issue manifests? What parameters are you using for
>>block-commit, how does the graph look like at the time of the
>>operation?
>>What error do you get without your patch or what exactly does not
>>work
>>in the block graph?

I'll try to redo the test today, but if I remember, the block-commit is
working, but the new fmt node (your topnode node0) is not attached to
the throttle group.

Try to dump the graph  before/after




My first try did not result in an error:

> #!/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,fi
> le.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' \
> < {"execute": "qmp_capabilities"}
> {"execute": "query-block"}
> {"execute": "block-commit", "arguments": { "device": "drive-scsi0",
> "top-node": "node0", "base-node": "backing0", "job-id": "commit0" } }
> {"execute": "query-block"}
> {"execute": "quit"}
> EOF



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Re: [pve-devel] [PATCH v3 qemu-server 08/11] blockdev: convert drive_mirror to blockdev_mirror

[DERUMIER, Alexandre via pve-devel]

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> 

>>Upgrading libpve-storage-perl or an external storage plugin while the
>>VM
>>is running could lead to a different result for path() and thus
>>breakage, right?
mmm, yes, you are right


>>If we do need lookup, an idea to get around the character limit is
>>using
>>a hash of the information to generate the node name, e.g.
>>hash("fmt-$volid@$snapname"), hash("file-$volid@$snapname") or
>>whatever

yes, I think it should works

>>is actually needed as unique information. Even if we only use
>>lowercase
>>letters, we have 26 base chars, so 26^31 possible values.

yes, I was think about a hash too, but I was not sure how to convert it
to the alphanum characters (valid char : alphanum , ‘-’, ‘.’ and ‘_’. 
)



>>So hashes with up to
>>
> > > math.log2(26**31)
>>145.71363126237387
>>
>>bits can still fit, which should be more than enough. Even with an
>>enormous number of 2^50 block nodes (realistically, the max values we
>>expect to encounter are more like 2^10), the collision probability
>>(using a simple approximation for the birthday problem) would only be
>>
> > > d=2**145
> > > n=2**50
> > > 1 - math.exp(-(n*n)/(2*d))
>>1.4210854715202004e-14

yes, should be enough

a simple md5 is 128bit, 
sha1 is 160bit(it's 150bits space with extra -,.,- characters)

Do you known a good hash algorithm ?


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