Re: [pve-devel] [RFC v3 storage 8/9] plugin: qemu block device: add support for snapshot option

From: Fiona Ebner <f.ebner@proxmox.com>
To: "Proxmox VE development discussion" <pve-devel@lists.proxmox.com>,
	"Fabian Grünbichler" <f.gruenbichler@proxmox.com>
Subject: Re: [pve-devel] [RFC v3 storage 8/9] plugin: qemu block device: add support for snapshot option
Date: Tue, 1 Jul 2025 14:23:00 +0200	[thread overview]
Message-ID: <a68e3ea6-c553-413d-8fd9-797db253b16c@proxmox.com> (raw)
In-Reply-To: <1751283437.oes1jtv4at.astroid@yuna.none>

Am 30.06.25 um 13:40 schrieb Fabian Grünbichler:
> On June 26, 2025 4:40 pm, Fiona Ebner wrote:
>> This is mostly in preparation for external qcow2 snapshot support.
>>
>> For internal qcow2 snapshots, which currently are the only supported
>> variant, it is not possible to attach the snapshot only. If access to
>> that is required it will need to be handled differently, e.g. via a
>> FUSE/NBD export.
> 
> just for the avoidance of doubt since it's only implied and not spelled
> out explicitly - we don't do any such accesses at the moment, right?
> 
> linked clones cannot be done for running VMs, full clones of snapshots
> don't happen within the running VM but via qemu-img convert, and nothing
> else besides replication (which is ZFS specific) and manual `pvesm
> export` calls (which are on the storage level by definition) directly
> reads from a storage snapshot?

Yes, we do not currently have such accesses. Neither the commandline
generation (and thus also not drive hotplug) nor drive-mirror in
qemu-server has support for specifying a snapshot. Yes, we only access
internal qcow2 snapshots via qemu-img. This is just in anticipation for
Alexandre's external snapshot series.

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