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Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode no
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none. |
Date: |
Thu, 18 Jul 2013 11:32:52 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
On 07/18/2013 11:27 AM, Eric Blake wrote:
>> if (!has_format) {
>> - format = mode == NEW_IMAGE_MODE_EXISTING ? NULL :
>> bs->drv->format_name;
>> + format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";
>
> Is this the right thing to do? Or should we do:
>
> if (!has_format) {
> if (mode == NEW_IMAGE_MODE_EXISTING) {
> format = NULL;
> } else {
> format = bs->drv->format_name ?: "qcow2";
> }
> }
>
> That is, I think we should default to doing a backup in the format given
> by the original (what if the original is qed, which also supports
> backing files), and only use qcow2 when there is no guidance whatsoever.
>
> But in practice, I don't care
Well, I _DO_ care about one thing - make sure that the qapi-schema.json
page accurately documents how this variable is defaulted for callers
that don't care about the implications of omitting a format.
Or we could simplify life by making 'format' mandatory for drive-backup;
it was optional for 'drive-mirror' due to incremental implementation,
but for 'drive-backup', we still have the opportunity to do things right
from the first release.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCH V4 0/4] Implement sync modes for drive-backup., Ian Main, 2013/07/17
- [Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup., Ian Main, 2013/07/17
- [Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup., Ian Main, 2013/07/17
- [Qemu-devel] [PATCH V4 2/4] Add tests for sync modes 'TOP' and 'NONE', Ian Main, 2013/07/17
- [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none., Ian Main, 2013/07/17
- Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none., Ian Main, 2013/07/18