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SubjectRe: [PATCH 03/10] cgroup: implement cgroup_add_cftypes() and friends
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Tejun Heo <tj@kernel.org> writes:

> Currently, cgroup directories are populated by subsys->populate()
> callback explicitly creating files on each cgroup creation. This
> level of flexibility isn't needed or desirable. It provides largely
> unused flexibility which call for abuses while severely limiting what
> the core layer can do through the lack of structure and conventions.
>
> Per each cgroup file type, the only distinction that cgroup users is
> making is whether a cgroup is root or not, which can easily be
> expressed with flags.
>
> This patch introduces cgroup_add_cftypes() and its wrapper macros -
> CGROUP_SUBSYS_CFTYPES[_COND](). These deal with cftypes instead of
> individual files - controllers indicate that certain types of files
> exist for certain subsystem. Newly added CFTYPE_*_ON_ROOT flags
> indicate whether a cftype should be excluded or created only on the
> root cgroup.
>
> cgroup_add_cftypes() can be called any time whether the target
> subsystem is currently attached or not. cgroup core will create files
> on the existing cgroups as necessary. CGROUP_SUBSYS_CFTYPES[_COND]()
> are convenience macros controllers so that cftypes can be declared to
> belong to certain cgroup. The COND variant is useful for cases where
> certain files are dependent on boot time parameter.
>
> Further patches will convert the existing users and remove the file
> based interface. Note that this interface allows dynamic addition of
> files to an active controller. This will be used for sub-controller
> modularity and unified hierarchy in the longer term.
>
> This patch implements the new mechanism but doesn't apply it to any
> user.
>

.....

> +/*
> + * Declare cftype array @cfts for cgroup subsys @ss if @cond is %true.
> + * Useful if the files are dependent on boot time parameter.
> + */
> +#define CGROUP_SUBSYS_CFTYPES_COND(ss, cfts, cond) \
> + static int __init __cgroup_cfts_init_##ss_##cfts(void) \
> + { \
> + if ((cond)) \
> + WARN_ON(cgroup_add_cftypes(&ss, cfts)); \
> + return 0; \
> + } \
> + fs_initcall(__cgroup_cfts_init_##ss_##cfts);
> +

Instead of using CGROUP_SUBSYS_CFTYPES_COND, are you ok if other
subsystem called cgroup_add_cftypes ?. I am looking at how this will
impact http://article.gmane.org/gmane.linux.kernel.mm/75470 . With
HugeTLB we cannot do the above.

-aneesh



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