linux-kernel - Re: [PATCH][DOCUMENTATION] Minimal controller code for a quick start

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Date:	Thu, 7 Feb 2008 12:45:18 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Pavel Emelyanov" <xemul@...nvz.org>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Containers" <containers@...ts.osdl.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][DOCUMENTATION] Minimal controller code for a quick start

On Feb 7, 2008 7:37 AM, Pavel Emelyanov <xemul@...nvz.org> wrote:
> 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).

Good idea.

> +
> +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,
> +       },
> +};

Can you structure this example so as to encourage people to use the
more formatted read/write routines, such as read_int64 and
write_int64?

> +
> +static struct cgroup_subsys_state *foo_create(struct cgroup_subsys *cs,
> +               struct cgroup *cg)
> +{
> +       struct foo_cgroup *foo;
> +

Maybe add a comment here that mentions that if your cgroup needs very
early initialization, you can check for cg->parent being NULL, and
return a statically-constructed structure here. (And set
foo_subsys.early_init = 1)

Paul
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