image-volume opened too many times when image being importing which is unnecessary

[zhen]

image-volume opened too many times when image being importing which is unnecessary.

```
# glance_store/_drivers/cinder.py #Store.add()

    def add(self, image_id, image_file, image_size, hashing_algo, context=None,
            verifier=None):
...
```

During the import image process, the 'image_size' passed to the add () method is always 0. According to the current logic, when the image is relatively large, the image-volume will be mounted/unmounted frequently because of the dynamic expansion of the mirror volume (for example, image with size 70G need to be mounted/unmounted 70/70 times)

I think when calling the add () method, we can get the actual size of 'stage_image'' in advance and pass it as' image_size''.

[Cyril Roelandt (cyril-roelandt)]

So you can confirm this because you see a lot of "Extending volume X to Y GB", right?

Could you send a patch implementing your idea?

[zhen (zhen001)]

Yes, in addition, after uploading a 70g image to glance (cinder backend of fcsan volume type), It's more than 70 attchments with "mountpoint" as "glance_store" in the table:

```
select count(*) from cinder.volume_attachment where volume_id="b6b7d42e-7f41-4e50-9a66-e2a51e59ec19" and mountpoint="glance_store"\G
*************************** 1. row ***************************
count(*): 73
1 row in set (0.001 sec)
```

Okay, I'll try.