On 06/01/2016 03:07 PM, Ademar Reis wrote:
On Tue, May 31, 2016 at 07:30:43AM -0300, Cleber Rosa wrote:
I'm replying on top of Cleber because he already said a few
things I was going to say.
On 05/25/2016 05:31 AM, Amador Pahim wrote:
Hi folks,
We have requests to handle the environment variables that we can set to
the tests. This is the RFC in that regard, with a summary of the ideas
already exposed in the original request and some additional planning.
The original request is here:
https://trello.com/c/Ddcly0oG/312-mechanism-to-provide-environment-variables-to-tests-run-on-a-virtual-machine-remote
Motivation
==========
Avocado tests are executed in a fork process or even in a remote
machine. Regardless the fact that Avocado is hard coded to set some
environment variables, they are for internal consumption and user is not
allowed to control/configure its behavior.
You mean this:
http://avocado-framework.readthedocs.io/en/latest/WritingTests.html#environment-variables-for-simple-tests
Right? Basically, the fact that Avocado sets some of the job/test state as
environment variables, that can be used by SIMPLE tests.
The motivation is the request to provide users an interface to set
and/or keep environment variables for test consumption.
I'm not sure if they're necessarily for test consumption. I think
the motivation for the original request was to provide the
standard Unix interface of environment variables for when tests
are run remotely.
If the motivation is basically about setting the env vars when running
tests remotely, than this brings the discussion about the *local*
behavior to:
1. Should Avocado default to the standard UNIX behavior of cloning the
environment?
A: IMHO, yes.
2. Could Avocado have have a feature to start tests in a clean(er)
environment?
A: Possibly yes, but seems low priority. The use case here could be
seen as a plus in predictability, helping to achieve expected test
results in spite of the runner environment. A real world example could
be a CI environment that sets a VERBOSE environment variable. This env
var will be passed over to Avocado, to the test process and finally to a
custom binary (say a benchmark tool) that will produce different output
depending on that environment variable. Doing that type of cleaning in
the test code is possible, but the framework could help with that.
2.1. If Avocado provides a "clean(er) test environment" feature, how to
determine which environment variables are passed along?
A: The "env-keep" approach seems like the obvious way to do it. If
the mechanism is enabled, which I believe should be disabled by default
(see #1), its default list could contain the more or less standard UNIX
environment variables (TERM, SHELL, LANG, etc).
These environment variables can change the behavior of both
Avocado (the runner itself), the tests (after all nothing
prevents the test writer from using them) and all sub-processes
executed by the test.
Right.
Locally, this is standard:
$ TMPDIR=/whatever/tmp VAR=foo ./avocado run test1.py
But when running avocado remotely, there's no way to configure
the environment in the destination. The environment variables set
in the command line below will not be "forwarded" to the remote
environment:
$ TMPDIR=/whatever/tmp VAR=foo ./avocado run test1.py \
--remote...
Right.
Use cases
=========
1) Use the command line or the config file to set the environment
variables in tests processes environment; access those variables from
inside the test.
2) Copy from current environment some environment variable(s) to the
tests processes environment; access those variables from inside the test.
I think we don't even have to go that far. We can simply say the
intention is to set the environment variables in the environment
where Avocado is run. The mechanism is quite standard and well
understood.
And here comes an important point: I don't think this should be a
mechanism to pass variables to tests. Although, again,
environment variables can be used for that purpose, Avocado
should have a proper interface to provide a dictionary of
configuration and variables to each test.
The only valid reason for having such a mechanism to pass *different*
environment variables to tests, talking about local environment, would
be *if and only if* the same environment variable to be set when running
Avocado would change the behavior of Avocado itself. Example:
$ AVOCADO_LOG_EARLY=1 avocado run avocado-self-tests.py
This way, both the first level avocado process (our "real" runner) and
other instances run by the "avocado-self-test.py" code would react to
that variable. *BUT* this seems a corner case, and I wouldn't think it
justifies the implementation of such a feature at this point.
Currently, this is erroneously provided by the multiplexer
(including --mux-inject), but it should be cleaned up in the near
future.
Right.
Proposal
========
- To create a command line option, under the `run` command, to set
environment variables that will be available in tests environment process:
$ avocado run --test-env='FOO=BAR,FOO1=BAR1' passtest.py
I can relate to this use case...
This would be a simple way of doing it, but something like
"--env-keep=FOO,FOO1" could be a better approach (more about it
below). So one would write it this way:
$ FOO=BAR FOO1=BAR1 avocado run --env-keep='FOO,FOO1' passtest.py
Right. Again, the only drawback of --env-keep is something along the
lines of the "AVOCADO_LOG_EARLY" example I gave earlier.
- To create an option in config file with a dictionary of environment
variables to set in test process environment. It can be used as a
replacement or complement to the command line option (with lower priority):
[tests.env]
test_env_vars = {'FOO': 'BAR', 'FOO1': 'BAR1'}
... while putting those in a config file does not seem like something one
would do.
In all cases, and more explicitly in the config file example, this is only
really necessary if/when the environment variable to pass to the test
actually harms Avocado (considering a local execution, that is, in a forked
process).
So, if Avocado and the test, share the use of environment variables by the
same name, then this is a must. Also in the case of execution in other
"runners", such as remote/vm, this can be quite valuable.
I don't like this interface because I think this opens the door
for abuse. Like I said in a previous paragraph, this interface
should not be a mechanism for passing variables to tests.
I can also see it being abused very quickly.
- Create an option in config file with a list of environment variable
names to copy from avocado main process environment to the test process
environment (similar to env_keep in the /etc/sudoers file):
[tests.env]
env_keep = ['FOO', 'FOO1', 'FOO2']
I like this approach because it reinforces the message that we're
keeping (or forwarding) some of the environment variables from
the original environment where the test runner was run.
Then, we need a "env_reset" mentality, and a default list of environment
variables that we forward by default (along the same lines of sudo):
Defaults env_reset
Defaults env_keep = "COLORS DISPLAY HOSTNAME HISTSIZE INPUTRC KDEDIR
LS_COLORS"
Defaults env_keep += "MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS
LC_CTYPE"
Defaults env_keep += "LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT
LC_MESSAGES"
Defaults env_keep += "LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER
LC_TELEPHONE"
Defaults env_keep += "LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET
XAUTHORITY"
Like I briefly mentioned before.
Right, this makes sense. But it also brings the point that we may actually
change the default behavior of keeping environment variables from Avocado in
the tests' process. That is, they would get a much cleaner environment by
default. While this sounds cleaner, it may break a lot of expectations.
I wonder what the motivation would be to clean-up the environment
where tests are run. Can you please elaborate? If we indeed
decide to implement this change, then I would say we should honor
whatever is set in env_keep.
I mentioned before a few points about test predictability, but the other
points that came later also support this idea.
Again, if env-keep is applicable for tests running remotely *only*, this
changes a lot of things. If we're talking about both local and remote,
than all what I said before applies.
For every configuration entry point, the setting have to be respected in
local and remote executions.
Drawbacks
=========
While setting an environment variable, user will be able to change the
behavior of a test and probably the behavior of Avocado itself. Maybe
even the OS behavior as well. We should:
- Warn users about the danger when using such options.
I fail to see where an environment variable, to be set by Avocado in the
test process, can or should impact Avocado itself. If it does, then we'd
probably be doing something wrong. I'm not sure we need warnings that
exceed documenting the intended behavior.
I think the environment has to be set where Avocado is run, not
where tests are run. Which is why I prefer --env-keep and
[env-keep].
So in the case of:
$ FOO=bla avocado run test.py --remote=...
$FOO is available inside the environment where Avocado and its
tests are run, both locally and remotely.
Agreed, but let's just keep in mind that one (very much) corner case
(where the environment may affect Avocado itself).
- Protect Avocado environment variables from overwriting.
About protecting the Avocado's own environment variables: agreed.
This is something that won't need any change. There are variables
which are read by Avocado and others which are written by it.
For example:
* TMPDIR will influence Avocado's behavior (standard Unix
variable)
* AVOCADO_VERSION is written by Avocado. Setting it externally
won't make any difference.
$ TMPDIR=/home/ademar/tmp avocado run examples/tests/env_variables.sh
--show-job-log | grep Temporary
Temporary dir: /home/ademar/tmp/avocado_L9YiE4
$ AVOCADO_VERSION=0 ./scripts/avocado run examples/tests/env_variables.sh
--show-job-log | grep Version
[stdout] Avocado Version: 35.0
Exactly. Now I think I missed that fact that Avocado's own environment
variables are indeed already "protected", because they're set at when
the SIMPLE tests' processes are created, which happens later and thus
takes precedence.
Looking forward to read your comments.
Overall, this is definitely welcome. Let's discuss possible implementation
issues, such as remote/vm support, because it wouldn't be nice to introduce
something like this with too many caveats.
We appear to have different understandings about what this
feature should be about. IMO it should be about the standard unix
environment where Avocado and tests are run. The primary use-case
is for remote/vm support (in other words, whenever there's a
change in the environment).
Then we should make it clear what we want to tackle first. If remote/vm
support is the primary goal, then maybe we should think about
--remote-env/--vm-env options to not poison the discussion and
implementation with the env_reset/env_keep like features.
Thanks.
- Ademar
--
Cleber Rosa
[ Sr Software Engineer - Virtualization Team - Red Hat ]
[ Avocado Test Framework - avocado-framework.github.io ]
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