[libvirt] [RFC PATCH 03/12] lib: Introduce event for tracking disk backing file write threshold

[Peter Krempa]

On Thu, Feb 23, 2017 at 16:32:45 -0600, Eric Blake wrote:
> On 02/23/2017 01:21 PM, Peter Krempa wrote:
> > When using thin provisioning, management tools need to resize the disk
> > in certain cases. To avoid having them to poll disk fillng introduce an
> 
> Typo, but a different word sounds better:
> 
> s/fillng/usage/
> 
> > event whic will be fired when a given offset of the storage is written
> 
> s/whic/which/
> 
> > by the hypervisor. Together with the API which will be added later, it
> > will allow to register thresholds for given storage backing volumes and
> 
> s/to register/registering/
> 
> > this event will then notify management if the threshold is exceeded.
> > ---
> >  daemon/remote.c                     | 43 ++++++++++++++++
> >  examples/object-events/event-test.c | 19 ++++++++
> >  include/libvirt/libvirt-domain.h    | 31 ++++++++++++
> >  src/conf/domain_event.c             | 97 +++++++++++++++++++++++++++++++++++++
> >  src/conf/domain_event.h             | 15 ++++++
> >  src/libvirt_private.syms            |  2 +
> >  src/remote/remote_driver.c          | 33 +++++++++++++
> >  src/remote/remote_protocol.x        | 18 ++++++-
> >  src/remote_protocol-structs         |  9 ++++
> >  tools/virsh-domain.c                | 21 ++++++++
> >  10 files changed, 287 insertions(+), 1 deletion(-)
> > 
> 
> > +++ b/include/libvirt/libvirt-domain.h
> > @@ -4175,6 +4175,36 @@ typedef void (*virConnectDomainEventAgentLifecycleCallback)(virConnectPtr conn,
> > 
> > 
> >  /**
> > + * virConnectDomainEventBlockThresholdCallback:
> > + * @conn: connection object
> > + * @dom: domain on which the event occurred
> > + * @dev: name associated with the affected disk or storage backing chain
> > + *       element
> > + * @path: for local storage, the path of the backing chain element
> > + * @threshold: threshold
> > + * @excess: WTF
> 
> Supposedly, how much beyond the threshold a write was detected at the
> time the event was fired.  (For example, if I have an 8M file with a
> threshold at 6M, then the guest does a 2M write at offset 5M, threshold
> would be 1M, because the write from 5-7M is 1M beyond my threshold of 6M).

Ummm, yes, I just forgot to update it once I actually written the docs.

> 
> > + * @opaque: application specified data
> > + *
> > + * The callback occurs when the hypervisor detects that the given storage
> > + * element was written beyond the point specified by @threshold. The excess
> > + * data size written beyond @threshold is reported by @excess (if supported
> > + * by the hypervisor, 0 otherwise). The event is useful for thin-provisioned
> > + * storage.
> 
> This description is better than the WTF above :)

Maybe I should pick better strings to make the docs generator shut up
for work in progress code :D

> 
> > + *
> > + * The threshold size can be set via the virDomainSetBlockThreshold API.
> 
> (added later in the series, but documenting now is fine)
> 
> Looks okay
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 




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