docker-storage-setup: If metadata volume already exists, do not create new one

[rhvgoyal]

Fixes #39

It can happen that we created a metadata volume and later there was not
enough space to create data volume and script exited, leaving behind
metadata volume. Later if user adds more space to volume group and re-runs
the script, it fails saying metadata volume already exists.

For now fix this by checking if metadata volume exists or not. If it exists
use it (instead of erroring out).

I think ideally we should have cleanup logic and cleanup any logical
volumes created if error happens later. That probably also means
getting rid of "set -e".

Signed-off-by: Vivek Goyal vgoyal@redhat.com

[rhvgoyal]

I think handling of subshells is little different. if checks for exit code. Here is the sample code.
#!/bin/bash

if i=$(exit 1); then
echo "subshell exited with zero status"
exit 0
fi

echo "subshell exited with non-zero status"

[rhvgoyal]

My understanding is that one can not create a zero sized logical volume. So the very fact command exited with success status means, lv exists, that also means that size is greater than 0.

[rhvgoyal]

@cgwalters does above answer your queries?

[cgwalters]

Ok, right. Your patch will likely work, but I find it confusing that we're retrieving the size and not doing anything with it. If we're just trying to verify existence, how about:

if lvs "${VG}/${META_LV_NAME}" &>/dev/null; then
  return 0
fi

?

[rhvgoyal]

Sounds good. I will modify my patch.

[rhvgoyal]

@cgwalters

Refereshed the patch as per your suggestion. Tested and it works. PTAL.

[cgwalters]

👍