Elements that try to install files to /tmp, /dev or /proc

[Sam Thursfield <sam thursfield codethink co uk>]

Hi
We've been looking at converting Baserock definitions to BuildStream for 
a while now. As we convert more systems we find new issues!

Here is today's:

  https://gitlab.com/baserock/definitions/-/jobs/29659150

There is a series of problems here:

1. genivi/genivi-demo-platform/audiomanager-at-gdp.bst installs files
   to %{install-root}/tmp, for whatever reason. (We can probably just
   stop it from doing that to work around the following issues, but
   they deserve discussing in any case).

2. genivi/genivi-demo-platform/audiomanagerdemo.bst depends on
   audiomanager-at-gdp.bst. Thus it gets a sandbox which has files in
   /tmp. The _sandboxbwrap.py module considers this a bug[1] and raises
   an exception, which should cause the build to abort.

3. The build subprocess never actually aborts, something deadlocks and
   the process runs forever.

I wrote a testcase to reproduce the issue which can be found here:

  https://gitlab.com/BuildStream/buildstream-tests/merge_requests/14

Interestingly the testcase doesn't suffer from the deadlock issue (3) -- 
it exits as expected.


There are two things that need fixing here. Firstly, if we are going to 
raise an exception when an element installs stuff to /tmp we should do 
so at the point that it happens, i.e. when we create the artifact. Or 
should we fix the sandboxbwrap module so that it allows files to be 
installed there ?

Secondly, we shouldn't deadlock :-) I haven't had time to work out what 
causes that -- the fact that it doesn't occur for a small testcase 
suggests that it's something to do with a queue becoming blocked by long 
messages, but that's just a guess so far.

You can (probably) reproduce the above issues by checking out 
https://gitlab.com/baserock/definitions/commit/a1b739ac6c49cd9a57e75dd3466fe55575fce814 
and running `bst build systems/genivi-demo-platform-content.bst`.

Sam

1. 
https://gitlab.com/BuildStream/buildstream/blob/master/buildstream/_sandboxbwrap.py#L294

--
Sam Thursfield, Codethink Ltd.
Office telephone: +44 161 236 5575