Allow users to specify TMPDIR in containers.conf

[rhatdan]

Currently we hard code TMPDIR environment variable to /var/tmp
if it is not set in the Environment. This causes TMPDIR environment
variable to be ignored if set in containers.conf.

This change now uses the host environment TMPDIR, followed by
containers.conf and then hard codes TMPDIR, if it was not set.

Signed-off-by: Daniel J Walsh dwalsh@redhat.com

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[rhatdan]

Truly fixes #5412

[rhatdan]

@containers/podman-maintainers PTAL

[mheon]

LGTM

[QiWang19]

LGTM

[ashley-cui]

/lgtm

[edsantiago]

I meant to ask earlier if there was any way to test this. I assume that this change updates the precedence, but I couldn't find a way to confirm. How is $TMPDIR visible to a podman command-line user?

[edsantiago]

Self-followup: found a way using unshare:

$ cat ~/.config/containers/containers.conf
[engine]
env = ["TMPDIR=/this/is/set/in/containers.conf"]
$ env -u TMPDIR ./bin/podman unshare /usr/bin/env|grep TMPD
TMPDIR=/this/is/set/in/containers.conf      <--- Good. Pre-8725, this prints /var/tmp
$ TMPDIR=/this/is/set/in/user/environment ./bin/podman unshare /usr/bin/env|grep TMPD
TMPDIR=/this/is/set/in/user/environment     <--- Good. Same thing pre-8725

Day late and dollar short, but /lgtm :-)

I do not plan to write a system test for this: I try hard to avoid mucking with .conf files in system tests due to the risk of not cleaning up properly and causing cascading failures. If anyone objects, and believes we need a regression test for this, please let me know.

[rhatdan]

Sorry I could not figure a good way of testing this out. So I instrumented the tool to see what TMPDIR was set to and then tried every scenario I could try.