Comment 2 for bug 1869903

I will start to do the implementation.
Here is the my initial proposal.

Add 3 configuration in charm-cinder

image-volume-cache-enabled:
   type: boolean
   default: False
   description: Enable the image volume cache

image-volume-cache-max-size-gb:
   type: int
   default: 0
   description: Max size of the image volume cache in GB. 0 => unlimited

image-volume-cache-max-count:
   type: int
   default: 0
   description: Max number of entries allowed in the image volume cache. 0 => unlimited.

When `image-volume-cache-enabled` is enabled, three configuration will be generated in cinder.conf under [DEFAULT]

```
[DEFAULT]
image_volume_cache_enabled = true
image_volume_cache_max_size_gb = 0
image_volume_cache_max_count = 0

```

I propose to put it under [DEFAULT] session to handle the basic situation: there is only 1 backend or all the backends use the same cache settings.

Anyone who are interested in this feature, welcome to leave your comment.