Re: [libvirt-users] domain reinitalization detection
Listen to the events
I guess that would require running my own
polling thread, right ? I wanted to avoid that ...
Thanks for help
On 06.03.2017 14:14, Matczak, KrzysztofX wrote:
Hello
I'm trying to find out how to detect if domain was destroyed and brought up between
two time moments, let's call it reads.
So far the best approach I could find is to compare domain ID from previous and current
read.
And this is my first question : is that reliable solution ? Or do you know any better ?
Listen to the events. If domain is destroyed/started libvirt fires up an event. The domain
ID is not necessarily unique. For instance:
a) start a domain and assume it's the first one started. It will have ID=1.
b) destroy it.
c) restart libvirtd.
d) start the domain again - it will have ID=1.
This applies to qemu driver, other drivers might have different meaning for domain IDs -
e.g. LXC driver reports PID of the container's init in which case you can make no
assumptions about it.
And related question is how to resolve virDomainPtr into domain ID ?
virDomainGetID().
The only verified way of getting domain ID I know is to memorize
it's UUID, then call virConnectListDomains , then iterate over all returned domain
IDs and resolve each one's pointer using virDomainLookupByID , then get UUID by
virDomainGetUUIDString get domain ID of matching UUID's .
It seems too complex and I expect noticeable performance overhead, so looking for
something lighter.
I'm trying to get current domain ID using API function :
char * virDomainGetMetadata (virDomainPtr domain, int type, const char * uri,
unsigned int flags)
I'm not sure it's relevant function, since domain ID is contained not in
metadata subsection but in opening <domain> markup.
In fact I wasn't even able to get any data using that function call since I
don't know how to construct valid URI. Do you know any doc or examples explaining that
?
Documentation might come handy:
http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainSetMetadata
http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainGetMetadata
or just look into our test suite:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=tests/metadatatest.c;h=55d...
Michal
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