glusterfs_native: able to create multiple shares with identical glusterfs volume as backend

[Ramana Raja]

Glusterfs native driver, maps a share to a GlusterFS volume. So every share uses an unique GlusterFS volume as its backend. But I was able to create two shares with the same GlusterFS volume as the backend. Note this occurred
while testing Manila master branch which had the following commit 4eb57f53c1c705fa3abf2ab0c2973fe709dbe6c8 [that allows glusterfs native driver to be used in multi-backend environment].

The following steps/environment produces the bug .

1. Enable multiple backends with one of the backends using glusterfs_native driver.
2. There are no shares in available state created by the glusterfs_native backend in the Manila db.
3. Issue two requests to create shares of the same size.
 e.g. manila create --share-type glusternative GLUSTERFS 1

Two shares would be created with same GlusterFS volume as their backends.

See below the manila list output. Notice that the 2 shares have identical export locations i.e use same GlusterFS volume as the backend.

ID | Name | Size | Share Proto | Status | Is Public | Share Type | Export location

68ad1d82-9bc9-4130-b131-e4199a2c6aef | None | 1 | GLUSTERFS | available | False | glusternative | 172.16.53.56:/manila-share-volume-1G-1

d40db806-8491-478c-b04e-fe11aecee543 | None | 1 | GLUSTERFS | available | False | glusternative | 172.16.53.56:/manila-share-volume-1G-1

[Ramana Raja (rraja)]

I was unable to reproduce this bug on different setups. This bug was unique to a setup, and so seems to have been caused by some fault in the setup itself, which I was unable to pinpoint, rather than by a bug in the Manila code base.