Add spec version to runC version cli

[marcosnils]

This PR prints specs versions when runc --version is used.

Sample:

marcos@XPS:~$ ./runc --version
runc version 0.3
spec version 0.2.0

Signed-off-by: Marcos Lilljedahl marcosnils@gmail.com

[wking]

On Tue, Nov 17, 2015 at 02:15:59PM -0800, Marcos Nils wrote:

This PR prints specs versions when runc --version is used.

I'm not sure what the plan is for backwards compatibility, but if
there is an intention to support 1.x and 2.x specs with the same runC
implementation, we may want to extend this to support multiple spec
versions (e.g. the latest 1.x and 2.x spec versions supported by that
runtime). On the other hand, a 2.x spec release is probably a ways
off, and runC currently only supports a single spec release (modulo
SemVer?) anyway, so maybe this UI is good enough for now?

[marcosnils]

@wking if the specs are pulled from the specs repo, how could supporting 1.x and 2.x would exactly work?. Because that will involve having two different versions of the spec in the runc repository?

My thought that the idea was always to support only one major version of the spec, but I might be confused.

[wking]

On Tue, Nov 17, 2015 at 02:35:46PM -0800, Marcos Nils wrote:

@wking if the specs are pulled from the specs repo, how could
supporting 1.x and 2.x would exactly work?. Because that will
involve having two different versions of the spec in the runc
repository?

I'm not sure what the plan is for that. There's no fundamental reason
you can't support two major versions of the spec with a single
runtime, but it might not be something that the runC folks are
interested in. I'm just bringing it up, because if they are
interested in it, this is a place where that would matter.

[mrunalp]

One way to support would be by maintaining different branches but we still need to figure that out.

[tianon]

+1 LGTM especially given that #410 just brought the version constant in line with the tags here, so the runc version is more meaningful again 😄

[mrunalp]

LGTM

[crosbymichael]

LGTM