Remove zpool altroot when creating datasets.

[kostaslambda]

poudriere breaks if the zpool it's given to use has the altroot property set, as its internal dataset mountpoints are different than the path they were actually mounted on.

Specifically, if the zpool has altroot set, all mounted datasets will have altroot prepended to their mountpoint. When setting BASEFS, the user would naturally take that into account and include altroot in the path. The setting would look something like: BASEFS=<altroot>/rest/of/path. However, what happens is that the BASEFS mountpoint is actually <altroot><altroot>/rest/of/path, while poudriere thinks it's <altroot>/rest/of/path.

To fix the problem, simply check if altroot is set and remove it from the mount path at the point of the dataset creation. The dataset will be prepended with altroot, which will match the path poudriere knows about.

[kostaslambda]

ping?

[bdrewery]

Why the $() for this? We don't need a subshell for the test; we may avoid a fork if NO_ZFS is set.
We need to set a default value or unset altroot too for NO_ZFS.

altroot=
if [ -z "${NO_ZFS}" ]; then
  altroot=$(zpool get -Ho value altroot "${ZPOOL}")
fi

Or

altroot=
[ -n "${NO_ZFS}" ] || altroot=$(zpool get -Ho value altroot "${ZPOOL}")

The test && test will exit with set -e, even if in a subshell. Using || won't exit.

# sh -c 'set -e; foo=$(false && true); echo here'; echo $?
1
# sh -c 'set -e; foo=$(false && true) || :; echo here'; echo $?
here
0
# sh -c 'set -e; foo=$(false || true); echo here'; echo $?
here
0

[kostaslambda]

Done. Thanks for the detailed example. My shell-fu is not very strong :)

[bdrewery]

altroot seems like a temporary thing. What's the use case for something like this?

[kostaslambda]

I came across this while trying to use poudriere on TrueNAS, which sets altroot=/mnt for all pools. Maybe it's uncommon for people to use that property, but it could still happen.

I've also changed the commit message, as it was wrong and maybe a bit convoluted. Let me know what you think.