[pve-devel] PVE::Storage::volume_has_feature

[Alexandre DERUMIER]

>>I have found some post on qemu-devel mailing, not recommanding opening twice the file. (1 for qemu-img convert , 1 for online qemu). 


http://lists.gnu.org/archive/html/qemu-devel/2010-09/msg01207.html

"> 
> Will do.
> BTW, my usage case for this patch is online backup the snapshot. That
> means the image is opened with r/w by a running QEMU process, at the
> same time, management tool can backup some snapshots already created
> before on this image. Here management tool can make sure no one take
> snapshot while backup snapshots.
> If I read the QCOW2 code correctly(not easy to read...), no one
> snapshots_offset/nb_snapshots in QCOW2 header, if you don't take a new
> snapshot, so it's OK to copy the snapshot out from the image in my
> usage case, right?

Right, I _think_ this might happen to work, at least with today's code.
Still I discourage having an image opened twice. It's not something that
code changes will take into consideration."

"


----- Mail original ----- 

De: "Alexandre DERUMIER" <aderumier at odiso.com> 
À: "Dietmar Maurer" <dietmar at proxmox.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Lundi 6 Mai 2013 08:09:30 
Objet: Re: [pve-devel] PVE::Storage::volume_has_feature 

But Maybe you are right, 

I have found some post on qemu-devel mailing, not recommanding opening twice the file. (1 for qemu-img convert , 1 for online qemu). 

Maybe it's works, but maybe something bad could happen. 

I'll do a patch to handle running parameter. 


Another thing we need to handle, it's full clone of a vm which is a qcow2 linked clone. 
I think we need to add backing files chain in qemu-img convert parameters. 


----- Mail original ----- 

De: "Alexandre DERUMIER" <aderumier at odiso.com> 
À: "Dietmar Maurer" <dietmar at proxmox.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Lundi 6 Mai 2013 07:52:10 
Objet: Re: [pve-devel] PVE::Storage::volume_has_feature 

>>I thought it is dangerous to access a qcow2 snapshot while the file is in use? 

I'm think it's ok to do it online, I have done (small) tests last month. 
It's just read access, I don't think it can break the volume. 

But I can do test more extensive test again if you want. 


----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Lundi 6 Mai 2013 06:43:09 
Objet: RE: PVE::Storage::volume_has_feature 

See my example ('copy' qcow2 snapshot while VM is running). 

I thought it is dangerous to access a qcow2 snapshot while the file is in use? 

> -----Original Message----- 
> From: Alexandre DERUMIER [mailto:aderumier at odiso.com] 
> Sent: Montag, 06. Mai 2013 06:41 
> To: Dietmar Maurer 
> Cc: pve-devel at pve.proxmox.com 
> Subject: Re: PVE::Storage::volume_has_feature 
> 
> Yes, Currently I don't use use it, because I think we can do snapshots,full clone, 
> linked cloned online or offline for each storage. 
> 
> Do you see a storage with a feature available offline and not online by example 
> ? 
> 
> ----- Mail original ----- 
> 
> De: "Dietmar Maurer" <dietmar at proxmox.com> 
> À: "Alexandre DERUMIER (aderumier at odiso.com)" <aderumier at odiso.com> 
> apsho 
> Cc: pve-devel at pve.proxmox.com 
> Envoyé: Lundi 6 Mai 2013 06:24:05 
> Objet: PVE::Storage::volume_has_feature 
> 
> That function seems to ignore the 'running'parameter, for example: 
> 
> --------test code------ 
> #!/usr/bin/perl -w 
> 
> use strict; 
> use PVE::Storage; 
> 
> my $volid = "local:200/vm-200-disk-1.qcow2"; my $snapname = "firstboot"; my 
> $runnung = 1; 
> 
> my $storecfg = PVE::Storage::config(); 
> 
> die "got unexpected result" if PVE::Storage::volume_has_feature($storecfg, 
> 'copy', $volid, $snapname, 1);; 
> 
> ----- end test code--------- 
> 
> how can we fix that? 
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