[CRIU] [PATCH v2] Introduce feature check via RPC

[Pavel Emelyanov]

> @@ -134,6 +144,12 @@ message criu_req {
>  	 * for all request types.
>  	 */
>  	optional bool			keep_open	= 4;
> +	/*
> +	 * feat_chk can be used to query which features
> +	 * are supported by the installed criu/kernel
> +	 * via RPC.
> +	 */
> +	optional int32			feat_chk	= 5;

What if we run out of bits in the future? Another issue with bit-field
in protobuf is that on non-C languages (e.g. Python) bitopts would
look weird. And some features _might_ be non-boolean, but rather an
integers or strings.

Maybe it would be better to introduce the new message with the set of
features that can be requested from criu? For now there will only be
one, the optional bool dirty_track, later we will be able to add more.

>  }
>  
>  /*
> @@ -151,4 +167,5 @@ message criu_resp {
>  	optional criu_page_server_info	ps		= 6;
>  
>  	optional int32			cr_errno	= 7;
> +	optional int32			feat_res	= 8;
>  }
>