schema: add checkPlatform

[zhouhao3]

Fixes opencontainers/image-tools#39
Signed-off-by: zhouhao zhouhao@cn.fujitsu.com

[stevvooe]

LGTM

[wking]

acf4adc looks good to me, although this is not really about validating descendants (especially for the config platform check). It would be nice to have something like #403 land soonish so we had a generic name for this sort of media-type-map-based verification.

[zhouhao3]

@philips @vbatts @jonboulle @stevvooe PTAL

[jonboulle]

These are SHOULDs, not MUSTs. Why should we validate them?
https://github.com/opencontainers/image-spec/blame/master/config.md#L63

[vbatts]

i'm okay with them being checked, but not to FAIL a validation.

[wking]

On Wed, Nov 30, 2016 at 01:42:16PM -0800, Vincent Batts wrote: i'm okay with them being _checked_, but not to FAIL a validation.

+1. We should probably table this until we settle on strict handling (see the discussion in opencontainers/image-spec#452 and me trying to outline the issue in opencontainers/image-tools#66).

[zhouhao3]

These are SHOULDs, not MUSTs. Why should we validate them?

Because these two are required attributes, and as the specification says: The name of the operating system which the image is built to run on. If it is the verification of the system, only by JSON to restrict the type is not rigorous, it should be the value of its specific judgment.

[zhouhao3]

Due to my mistakes, resulting in this PR can not be updated, I will close this, and then open a new PR.