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

[Eric Blake]

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).

> + * @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 :)

> + *
> + * 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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