util.mount_cb will create an unused temporary directory if the passed `device` is already mounted

This bug was originally filed in Launchpad as [LP: #1885327](https://bugs.launchpad.net/cloud-init/+bug/1885327)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-06-26T19:41:56.797827+00:00

date_fix_committed = None

date_fix_released = None

id = 1885327

importance = wishlist

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1885327

milestone = None

owner = oddbloke

owner_name = Dan Watkins

private = False

status = triaged

submitter = oddbloke

submitter_name = Dan Watkins

tags = []

duplicates = []

_Launchpad user **Dan Watkins(oddbloke)** wrote on 2020-06-26T19:41:56.797827+00:00_

The tmpdir creation happens before (and around, as a contextmanager) the determination of whether or not a mount will be needed. This could be improved.

Start by locating util.mount_cb and inspect how it creates the temporary directory relative to checking whether the device is already mounted. The fix is done when an already-mounted device does not cause an unused temporary directory to be created, while normal mounting behavior remains unchanged.

Written by the indexing model from the issue text.