Quoting Pavel Emelyanov ([EMAIL PROTECTED]):
> The Documentation/cgroups.txt file contains the info on how
> to write some controller for cgroups subsystem, but even with
> this, one need to write quite a lot of code before developing
> the core (or copy-n-paste it from some other place).
>
> I propose to put this minimal controller into Documentation
> directory to let people copy-n-paste a) from a known place and
> b) a small piece of code.
>
> Besides, many people learn better reading an example rather
> than/along with a document.
>
> Signed-off-by: Pavel Emelyanov <[EMAIL PROTECTED]>
Actually I thought that was the main point of kernel/cgroup_debug.c?
-serge
>
> ---
>
> diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
> index 42d7c4c..66068dc 100644
> --- a/Documentation/cgroups.txt
> +++ b/Documentation/cgroups.txt
> @@ -531,6 +531,9 @@ and root cgroup. Currently this will only involve
> movement between
> the default hierarchy (which never has sub-cgroups) and a hierarchy
> that is being created/destroyed (and hence has no sub-cgroups).
>
> +For a quick start you may want to look at the
> +Documentation/controllers/example.c file.
> +
> 4. Questions
> ============
>
> diff --git a/Documentation/controllers/example.c
> b/Documentation/controllers/example.c
> new file mode 100644
> index 0000000..4a73c77
> --- /dev/null
> +++ b/Documentation/controllers/example.c
> @@ -0,0 +1,134 @@
> +/*
> + * Documentation/controllers/example.c - A simple controller
> + *
> + * Copy and make s/foo/$SUBSYS_NAME/g in it to get a minimal
> + * working code. Don't forget to add a SUBSYS(foo) line in the
> + * include/linux/cgroup_subsys.h file.
> + *
> + */
> +
> +#include <linux/cgroup.h>
> +
> +/*
> + * the foo main structure - it is used to store any info, that
> + * is required from the group of tasks
> + */
> +
> +struct foo_cgroup {
> + /*
> + * put your fields here
> + */
> +
> + struct cgroup_subsys_state css;
> +
> + /*
> + * ... or/and here
> + */
> +};
> +
> +/*
> + * helpers to get the foo_cgroup from a task and a control group
> + */
> +
> +static inline struct foo_cgroup *foo_from_css(struct cgroup_subsys_state
> *css)
> +{
> + return container_of(css, struct foo_cgroup, css);
> +}
> +
> +static inline struct foo_cgroup *foo_from_cgroup(struct cgroup *cg)
> +{
> + return foo_from_css(cgroup_subsys_state(cg, foo_subsys_id));
> +}
> +
> +static inline struct foo_cgroup *foo_from_task(struct task_struct *p)
> +{
> + return foo_from_css(task_subsys_state(p, foo_subsys_id));
> +}
> +
> +/*
> + * foo files
> + */
> +
> +static ssize_t foo_bar_read(struct cgroup *cg, struct cftype *cft,
> + struct file *file, char __user *userbuf,
> + size_t nbytes, loff_t *ppos)
> +{
> + struct foo_cgroup *foo;
> +
> + foo = foo_from_cgroup(cg);
> +
> + /*
> + * produce some output
> + */
> +
> + return nbytes;
> +}
> +
> +static ssize_t foo_bar_write(struct cgroup *cg, struct cftype *cft,
> + struct file *file, const char __user *userbuf,
> + size_t nbytes, loff_t *ppos)
> +{
> + struct foo_cgroup *foo;
> +
> + foo = foo_from_cgroup(cg);
> +
> + /*
> + * read and tune the foo
> + */
> +
> + return nbytes;
> +}
> +
> +static struct cftype foo_files[] = {
> + {
> + .name = "bar",
> + .read = foo_bar_read,
> + .write = foo_bar_write,
> + },
> +};
> +
> +/*
> + * foo subsystem basic callbacks
> + */
> +
> +static struct cgroup_subsys_state *foo_create(struct cgroup_subsys *cs,
> + struct cgroup *cg)
> +{
> + struct foo_cgroup *foo;
> +
> + foo = kmalloc(sizeof(struct foo_cgroup), GFP_KERNEL);
> + if (foo == NULL)
> + return NULL;
> +
> + /*
> + * initialize your fields
> + */
> +
> + return &foo->css;
> +}
> +
> +static void foo_destroy(struct cgroup_subsys *cs, struct cgroup *cg)
> +{
> + struct foo_cgroup *foo;
> +
> + foo = foo_from_cgroup(cg);
> +
> + /*
> + * clean your fields
> + */
> +
> + kfree(foo);
> +}
> +
> +static int foo_populate(struct cgroup_subsys *cs, struct cgroup *cg)
> +{
> + return cgroup_add_files(cg, cs, foo_files, ARRAY_SIZE(foo_files));
> +}
> +
> +struct cgroup_subsys foo_subsys = {
> + .name = "foo",
> + .subsys_id = foo_subsys_id,
> + .create = foo_create,
> + .destroy = foo_destroy,
> + .populate = foo_populate,
> +};
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