Re: [pve-devel] [PATCH qemu-server 01/13] blockdev: cmdline: add blockdev syntax support

From: "Fabian Grünbichler" <f.gruenbichler@proxmox.com>
To: Fiona Ebner <f.ebner@proxmox.com>,
	Proxmox VE development discussion <pve-devel@lists.proxmox.com>
Subject: Re: [pve-devel] [PATCH qemu-server 01/13] blockdev: cmdline: add blockdev syntax support
Date: Thu, 5 Jun 2025 16:17:04 +0200 (CEST)	[thread overview]
Message-ID: <1715554393.3099.1749133024392@webmail.proxmox.com> (raw)
In-Reply-To: <3ae9921d-cc0a-460b-a560-b5edd97c1556@proxmox.com>

> Fiona Ebner <f.ebner@proxmox.com> hat am 05.06.2025 15:23 CEST geschrieben:
> 
>  
> Am 03.06.25 um 09:55 schrieb Alexandre Derumier via pve-devel:
> > +sub encode_nodename {
> > +    my ($type, $volid, $snap) = @_;
> > +
> > +    my $nodename = "$volid";
> > +    $nodename .= "-$snap" if $snap;
> 
> This will lead to clashes in some cases:
> 1. Currently, we allow attaching the same volume multiple times to a
> single guest.
> 2. You can end up with the same name for
> volname = vm-1234-disk-0-foo
> and for
> volname = vm-1234-disk-0, snap = foo
> 
> The latter can be rather easily fixed by just using a character we don't
> usually support for volume names, but not the former. So I'd like to do
> the switch to -blockdev without support for "looking up which node a
> certain volume is" at first. In general, I feel like mixing the switch
> to -blockdev with your larger series is too much at once. We should
> first get the switch to -blockdev completely and cleanly sorted out,
> then we can add your external qcow2 support on top.
> 
> I think we can even rely on auto-generated-by-QEMU node names at first.
> We can later switch to a variant where node names encode additional
> information. Or we could also think about patching QEMU to better fit
> the need for the "looking up which node a certain volume is" feature.
> But I don't think figuring this out should block us right now for the
> switch to "-blockdev".
> 
> I'll try to work out a series that focuses just on the switch to
> "-blockdev" based on your patches during the next week or so. Maybe not
> much else needs to be changed :) The work is certainly greatly appreciated!
> 
> @Fabian opinions?

I think this is a good disentanglement approach, provided we keep anything
"special" required by the qcow2 series in mind while doing so (to avoid
the need for double compat hacks).

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