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[Xen-API] RE: Questions about the api

To: 'Tomoiaga Cristian' <cristi@xxxxxxxxxxx>, "xen-api@xxxxxxxxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-API] RE: Questions about the api
From: Dave Scott <Dave.Scott@xxxxxxxxxxxxx>
Date: Thu, 21 Oct 2010 18:16:11 +0100
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Thread-topic: Questions about the api

> Hello everyone,
> I am writing a SR for Nexenta since I haven't found one and zfs seems
> pretty good until now.
> My questions are more related to missing(?) api calls.
> I need to know if I can set the following fields in a VDI for example:
> Is-a-snapshot - there is a get_is_a_snapshot call but not a
> set_is_a_snapshot. Same for snapshot-of. Think it's usefull just in
> case I vdi-forget the snapshot and re introduce it with a scan or in
> other situations.
> parent - there is a get_parent but not a set_parent call, this would be
> nice.

Hm, I think there's no current way for the backend to set these VDI fields: 
they seem to be only ever set by xapi at creation time. You're right that if 
you forget and then re-scan then the metadata will be lost. For most backends 
this isn't a fatal problem (although it might be annoying) but I wonder what 
will happen for LVHD -- it uses the 'is_a_snapshot' as an indicator to decide 
whether to 'inflate' or 'deflate' the LVM LV.

We should consider allowing the backend to read/write these fields. There's 
already precedent for that kind of thing: the backend can call 
VDI.set_virtual_size but it looks read/only to everyone else.

What do others think?


> Of course I can use sm-config for example, to set a parent but still,
> since the field is there I would like to set it myself.
> Thank you!
> Tomoiaga Cristian
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