[CRIU] [PATCH 2/2] cg: Add ability to dump custom cgroup properties

[Tycho Andersen]

Hi Cyrill,

On Tue, Apr 12, 2016 at 12:40:40PM +0300, Cyrill Gorcunov wrote:
> We have some common predefined properties such as
> "cpuset.cpus" and etc gathered in @cgp_predefined
> set, but there might be situation when only predefined
> ones are not enough so add ability to specify additional
> properties via --cgroup-props option.
> 
> This option takes either path to a file or plain JSON
> stream which describe the properties to dump.
> 
> For example one may pass
> 
>   --cgroup-props "{\"controller name 1\" : [ \"property-1\", \"property-2\", ... ]}"
> 
> to dump custom properties.
> 
> At moment we require Jansson library to be present in the
> system to support JSON parsing of --cgroup-props. But if
> someone doesn't need custom properties lets don't force
> him to setup Jansson library for nothing, simply compile
> criu without this feature support.

Not related to this patch, but it seems like I've let the list of
predefined properties get fairly out of date (e.g. the entire pids
cgroups, and a bunch of others are missing). It seems to me like we
should have CRIU have a reasonably comprehensive list of cgroup props,
and then leave this for other stuff (like custom cgroups in the vz
kernel or whatever). Does that make sense? If so, I can send a patch,
but probably not until after ubuntu release :)

> +	/*
> +	 * It's either plain JSON stream, then it must
> +	 * start with '{', or it's path to a file to parse.
> +	 */
> +	if (arg[0] == '{') {

Minor thing, but can we do this check the "other" way, i.e. test for
the first char == '/'? It would be legal json to have leading
whitespace, so if some unparser somewhere emitted with a leading space
or \n or something this might break. The filename has to start with a
/ though, so it seems slightly safer.

Tycho