Re: [pve-devel] [PATCH pve-storage 08/10] qcow2: add external snapshot support - DERUMIER, Alexandre via pve-devel

From: "DERUMIER, Alexandre via pve-devel" <pve-devel@lists.proxmox.com>
To: "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>,
	"f.gruenbichler@proxmox.com" <f.gruenbichler@proxmox.com>
Cc: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>
Subject: Re: [pve-devel] [PATCH pve-storage 08/10] qcow2: add external snapshot support
Date: Tue, 8 Jul 2025 10:04:26 +0000	[thread overview]
Message-ID: <mailman.1110.1751969075.395.pve-devel@lists.proxmox.com> (raw)
In-Reply-To: <2064112819.2237.1751629966392@webmail.proxmox.com>

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From: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>
To: "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>, "f.gruenbichler@proxmox.com" <f.gruenbichler@proxmox.com>
Subject: Re: [pve-devel] [PATCH pve-storage 08/10] qcow2: add external snapshot support
Date: Tue, 8 Jul 2025 10:04:26 +0000
Message-ID: <27854af70a4fe3a7765d2760098e2f82f3475f17.camel@groupe-cyllene.com>

> +my sub alloc_backed_image {
> +    my ($class, $storeid, $scfg, $volname, $backing_snap) = @_;
> +
> +    my $path = $class->path($scfg, $volname, $storeid);
> +    my $backing_path = $class->path($scfg, $volname, $storeid,
> $backing_snap);

>>should we use a relative path here like we do when doing a linked
>>clone? else
>>it basically means that it is no longer possible to move the storage
>>mountpoint,
>>unless I am mistaken?

ah, it doesn't playing fine with snapshots directory, because current
is renamed && moved to snapshot directory, so it's breaking the
relative path.

1) create snap1
qm snapshot 10000 snap1

 /home/store/images/10000/vm-10000-disk-0.qcow2
     ------>./snapshot/snap-snap1-vm-10000-disk-0.qcow2

2) create a snap2:

 a)rename current to snap2

  mv /home/store/images/10000/vm-10000-disk-0.qcow2
/home/store/images/10000/snapshots/snap-snap2-vm-10000-disk-0.qcow2

b) create the new current with snap2 backing

 /usr/bin/qemu-img create -F qcow2 -b ./snapshots/snap-snap2-vm-10000-
disk-0.qcow2 -f qcow2 /home/store/images/10000/vm-10000-disk-0.qcow2

qemu-img: /home/store/images/10000/vm-10000-disk-0.qcow2: Could not
open backing file: Could not open
'/home/store/images/10000/./snapshots/./snapshots/snap-snap1-vm-10000-
disk-0.qcow2': No such file or directory
Could not open backing image.

same with:
qemu-img info ./snapshots/snap-snap2-vm-10000-disk-0.qcow2 --backing-
chain
qemu-img: Could not open './snapshots/./snapshots/snap-snap1-vm-10000-
disk-0.qcow2': Could not open './snapshots/./snapshots/snap-snap1-vm-
10000-disk-0.qcow2': No such file or directory

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