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 v3 qemu-server 11/11] qcow2: add external snapshot support
Date: Mon, 13 Jan 2025 18:58:36 +0000 [thread overview]
Message-ID: <mailman.285.1736794720.441.pve-devel@lists.proxmox.com> (raw)
In-Reply-To: <mailman.282.1736791667.441.pve-devel@lists.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 v3 qemu-server 11/11] qcow2: add external snapshot support
Date: Mon, 13 Jan 2025 18:58:36 +0000
Message-ID: <4fcbe829f838bdce29f9a1492290c700cdcd8944.camel@groupe-cyllene.com>
>
> > > should this maybe have been vdisk_alloc and it just works by
> accident?
> It's not works fine with vdisk_alloc, because the volume need to be
> created without the size specified but with backing file param
> instead.
> (if I remember, qemu-img is looking at the backing file size+metadas
> and set the correct total size for the new volume)
>>I am not sure I follow.. we create a snapshot, but then we pretend it
>>isn't a file with backing file when passing it to qemu? this seems
>>wrong.. IMHO we should just allocate (+format) here, and then let
>>qemu do the backing link up instead of this confusing (and error-
>>prone, as it masks problems that should be a hard error!) call..
>>
>>
>>
>>
> >>Maybe a better way could be to reuse vdisk_alloc, and add backing
> >>file
> >>as param ?
>>
>>that seems.. wrong as well? the file can never be bigger just because
>>it has a backing file right? why can't we just allocate and format
>>the regular volume?
>>I need to redo tests as I don't remember exactly.
>>
>>From memory (I have wrote it 2month ago, sorry ^_^ ) , it was maybe :
>> - related with metadatas prealloc size + lvm size).
>> or (but I need to verify)
>>
>> The "blockdev-snasphot" qmp later, only change the backing-file in
>>memory in the blockgraph, but not inside the file itself. (so after a
>>restart of the process, the chain is borken).
Ok, I have redone tests and verify, this is the second case
The problem is that blockdev-snapshot don't actually rewrite the
backing file inside the qcow2 file.
It still explain on the same link:
https://lists.gnu.org/archive/html/qemu-block/2019-10/msg01404.html
So the only way, is to do it a qcow2 creation.
And then, that's why we need to pass backing=undef with doing blockdev-
add, because if not, qemu will try to open the file the the backing
already opened/locked.
Don't seem to be fixed in last qemu version, and libvirt is still doing
it this way too.
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prev parent reply other threads:[~2025-01-13 18:59 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20241216091229.3142660-1-alexandre.derumier@groupe-cyllene.com>
2024-12-16 9:12 ` [pve-devel] [PATCH v1 pve-qemu 1/1] add block-commit-replaces option patch Alexandre Derumier via pve-devel
2025-01-08 13:27 ` Fabian Grünbichler
2025-01-10 7:55 ` DERUMIER, Alexandre via pve-devel
[not found] ` <34a164520eba035d1db5f70761b0f4aa59fecfa5.camel@groupe-cyllene.com>
2025-01-10 9:15 ` Fiona Ebner
2025-01-10 9:32 ` DERUMIER, Alexandre via pve-devel
[not found] ` <1e45e756801843dd46eb6ce2958d30885ad73bc2.camel@groupe-cyllene.com>
2025-01-13 14:28 ` Fiona Ebner
2025-01-14 10:10 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 01/11] blockdev: cmdline: convert drive to blockdev syntax Alexandre Derumier via pve-devel
2025-01-08 14:17 ` Fabian Grünbichler
2025-01-10 13:50 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 pve-storage 1/3] qcow2: add external snapshot support Alexandre Derumier via pve-devel
2025-01-09 12:36 ` Fabian Grünbichler
2025-01-10 9:10 ` DERUMIER, Alexandre via pve-devel
[not found] ` <f25028d41a9588e82889b3ef869a14f33cbd216e.camel@groupe-cyllene.com>
2025-01-10 11:02 ` Fabian Grünbichler
2025-01-10 11:51 ` DERUMIER, Alexandre via pve-devel
[not found] ` <1caecaa23e5d57030a9e31f2f0e67648f1930d6a.camel@groupe-cyllene.com>
2025-01-10 12:20 ` Fabian Grünbichler
2025-01-10 13:14 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 02/11] blockdev: fix cfg2cmd tests Alexandre Derumier via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 pve-storage 2/3] lvmplugin: add qcow2 snapshot Alexandre Derumier via pve-devel
2025-01-09 13:55 ` Fabian Grünbichler
2025-01-10 10:16 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 03/11] blockdev : convert qemu_driveadd && qemu_drivedel Alexandre Derumier via pve-devel
2025-01-08 14:26 ` Fabian Grünbichler
2025-01-10 14:08 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 pve-storage 3/3] storage: vdisk_free: remove external snapshots Alexandre Derumier via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 04/11] blockdev: vm_devices_list : fix block-query Alexandre Derumier via pve-devel
2025-01-08 14:31 ` Fabian Grünbichler
2025-01-13 7:56 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 05/11] blockdev: convert cdrom media eject/insert Alexandre Derumier via pve-devel
2025-01-08 14:34 ` Fabian Grünbichler
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 06/11] blockdev: block_resize: convert to blockdev Alexandre Derumier via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 07/11] blockdev: nbd_export: block-export-add : use drive-$id for nodename Alexandre Derumier via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 08/11] blockdev: convert drive_mirror to blockdev_mirror Alexandre Derumier via pve-devel
2025-01-08 15:19 ` Fabian Grünbichler
2025-01-13 8:27 ` DERUMIER, Alexandre via pve-devel
[not found] ` <0d0d4c4d73110cf0e692cae0ee65bf7f9a6ce93a.camel@groupe-cyllene.com>
2025-01-13 9:52 ` Fabian Grünbichler
2025-01-13 9:55 ` Fabian Grünbichler
2025-01-13 10:47 ` DERUMIER, Alexandre via pve-devel
2025-01-13 13:42 ` Fiona Ebner
2025-01-14 10:03 ` DERUMIER, Alexandre via pve-devel
[not found] ` <fa38efbd95b57ba57a5628d6acfcda9d5875fa82.camel@groupe-cyllene.com>
2025-01-15 9:39 ` Fiona Ebner
2025-01-15 9:51 ` Fabian Grünbichler
2025-01-15 10:06 ` Fiona Ebner
2025-01-15 10:15 ` Fabian Grünbichler
2025-01-15 10:46 ` Fiona Ebner
2025-01-15 10:50 ` Fabian Grünbichler
2025-01-15 11:01 ` Fiona Ebner
2025-01-15 13:01 ` DERUMIER, Alexandre via pve-devel
2025-01-16 14:56 ` DERUMIER, Alexandre via pve-devel
2025-01-15 10:15 ` DERUMIER, Alexandre via pve-devel
[not found] ` <c1559499319052d6cf10900efd5376c12389a60f.camel@groupe-cyllene.com>
2025-01-13 13:31 ` Fabian Grünbichler
2025-01-20 13:37 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 09/11] blockdev: mirror: change aio on target if io_uring is not default Alexandre Derumier via pve-devel
2025-01-09 9:51 ` Fabian Grünbichler
2025-01-13 8:38 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 10/11] blockdev: add backing_chain support Alexandre Derumier via pve-devel
2025-01-09 11:57 ` Fabian Grünbichler
2025-01-13 8:53 ` DERUMIER, Alexandre via pve-devel
2024-12-16 9:12 ` [pve-devel] [PATCH v3 qemu-server 11/11] qcow2: add external snapshot support Alexandre Derumier via pve-devel
2025-01-09 11:57 ` Fabian Grünbichler
2025-01-09 13:19 ` Fabio Fantoni via pve-devel
2025-01-20 13:44 ` DERUMIER, Alexandre via pve-devel
[not found] ` <3307ec388a763510ec78f97ed9f0de00c87d54b5.camel@groupe-cyllene.com>
2025-01-20 14:29 ` Fabio Fantoni via pve-devel
[not found] ` <6bdfe757-ae04-42e1-b197-c9ddb873e353@m2r.biz>
2025-01-20 14:41 ` DERUMIER, Alexandre via pve-devel
2025-01-13 10:08 ` DERUMIER, Alexandre via pve-devel
[not found] ` <0ae72889042e006d9202e837aac7ecf2b413e1b4.camel@groupe-cyllene.com>
2025-01-13 13:27 ` Fabian Grünbichler
2025-01-13 18:07 ` DERUMIER, Alexandre via pve-devel
2025-01-13 18:58 ` DERUMIER, Alexandre via pve-devel [this message]
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