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

[Fiona Ebner]

Am 10.01.25 um 08:55 schrieb DERUMIER, Alexandre:
> -------- Message initial --------
> De: Fabian Grünbichler <f.gruenbichler at proxmox.com>
> À: Proxmox VE development discussion <pve-devel at lists.proxmox.com>
> Cc: Alexandre Derumier <alexandre.derumier at groupe-cyllene.com>, Fiona
> Ebner <f.ebner at proxmox.com>
> Objet: Re: [pve-devel] [PATCH v1 pve-qemu 1/1] add block-commit-
> replaces option patch
> Date: 08/01/2025 14:27:02
> 
> 
>> Alexandre Derumier via pve-devel <pve-devel at lists.proxmox.com> hat am
>> 16.12.2024 10:12 CET geschrieben:
> 
>> 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)
> 
>>> so this is needed to workaround a limitation in block-commit? I think
>>> if we need this it should probably be submitted upstream for
>>> inclusion, or we provide our own copy of block-commit with it in the
>>> meantime?
> Yes, it could be submitted upstream (after a little bit of review, I'm
> not too good in C;)).
> 
> It's more a missing option in the qmp syntax, as it's already using 
> blockdev-mirror code in background.
> 
> (redhat don't used throttle group feature until recently, so I think
> they never had seen this problem with block-commit, as their top root
> node was the disk directly, and not the throttle group)

Maybe it could even be a bug then? In many situations, the filter nodes
on top (like throttle groups) are ignored/skipped to get to the actually
interesting block node for certain block operations. Are there any
situations where you wouldn't want to do that in the block-commit case?
There is a dedicated bdrv_skip_filters() function, e.g. used in
stream_prepare(). Would be good to hear what upstream thinks.