Fetch the environments for the default global options

[laijs]

So thus the user doesn't need to specific the global option on every execution.

get the default root path based on the environment OCI_ROOT
get the default criu path based on the environment RUNC_CRIU

[wking]

On Thu, Aug 20, 2015 at 08:00:43PM -0700, Lai Jiangshan wrote:

• get the default root path based on the environment OCI_ROOT
• get the default criu path based on the environment RUNC_CRIU

It seems strange to use two different prefixes (OCI_ and RUNC_). I'm
still not clear on the need to share state via a collaborative
filesystem location (see 1 and my comments in #159), but if we have
all OCI implementations agreeing on where they store their state, I
don't see why we wouldn't have them agree on which CRIU command to
use.

[laijs]

Not all implementation needs CRIU. The hypervisor based implementations[1] don't need it. So criu is runc (or some implementations, not all) specialized option, so the environment starts with prefix RUNC_. And the collaborative root directory is (will be) required for all implementations. so the environment starts with prefix OCI_.

[1] https://github.com/hyperhq/runv

[wking]

On Fri, Aug 21, 2015 at 12:24:24AM -0700, Lai Jiangshan wrote:

Not all implementation needs CRIU. The hypervisor based
implementations[1] don't need it. So criu is runc…

That makes sense, but “we don't all need $X” isn't enough to require
separate namespacing (runV will work fine with OCI_CRIU set). What
you need is “two of us need $X with different semantics”, and I expect
most OCI-related agents will have the same semantics for CRIU. The
first one with a non-standard CRIU requirement can leave the OCI_
namespace and add their own per-implementation variable.

[crosbymichael]

I don't think env vars give us anything there. These are already flags on runc so why add yet another way to change the value?

[wking]

On Mon, Sep 14, 2015 at 04:31:34PM -0700, Michael Crosby wrote:

I don't think env vars give us anything there. These are already
flags on runc so why add yet another way to change the value?

+1 to “we should only have one way to change the value”.

[crosbymichael]

Lets close this and just go for the flags right now for setting these options.