libvirt users - Mar 2017 - Re: domain reinitalization detection

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  ?

And related question is how to  resolve virDomainPtr into domain ID ?
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 ?

Any help appreciated
Krzysztof
--------------------------------------------------------------
Intel Research and Development Ireland Limited
Registered in Ireland
Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
Registered Number: 308263


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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=55dc841254bcfda0742d22580723bf4acac172b4;hb=HEAD

Michal

> 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=55dc841254bcfda0742d22580723bf4acac172b4;hb=HEAD

Michal
--------------------------------------------------------------
Intel Research and Development Ireland Limited
Registered in Ireland
Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
Registered Number: 308263


This e-mail and any attachments may contain confidential material for the sole
use of the intended recipient(s). Any review or distribution by others is
strictly prohibited. If you are not the intended recipient, please contact the
sender and delete all copies.