Re: [PATCH] Add cgroup support for enabling controllers at boot time

[Li Zefan <lizf@cn.fujitsu.com>]

Balbir Singh wrote:
> From: Paul Menage <menage@google.com>
> 
> The effects of cgroup_disable=foo are:
> 
> - foo doesn't show up in /proc/cgroups
> - foo isn't auto-mounted if you mount all cgroups in a single hierarchy
> - foo isn't visible as an individually mountable subsystem
> 
> As a result there will only ever be one call to foo->create(), at init
> time; all processes will stay in this group, and the group will never
> be mounted on a visible hierarchy. Any additional effects (e.g. not
> allocating metadata) are up to the foo subsystem.
> 
> This doesn't handle early_init subsystems (their "disabled" bit isn't
> set be, but it could easily be extended to do so if any of the early_init
> systems wanted it - I think it would just involve some nastier parameter
> processing since it would occur before the command-line argument parser
> had been run.
> 
> [Balbir added Documentation/kernel-parameters updates]
> 
> Signed-off-by: Paul Menage <menage@google.com>
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  Documentation/kernel-parameters.txt |    4 ++++
>  include/linux/cgroup.h              |    1 +
>  kernel/cgroup.c                     |   27 +++++++++++++++++++++++++--
>  3 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff -puN include/linux/cgroup.h~cgroup_disable include/linux/cgroup.h
> --- linux-2.6.25-rc4/include/linux/cgroup.h~cgroup_disable	2008-03-06 12:19:38.000000000 +0530
> +++ linux-2.6.25-rc4-balbir/include/linux/cgroup.h	2008-03-06 12:19:38.000000000 +0530
> @@ -256,6 +256,7 @@ struct cgroup_subsys {
>  	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
>  	int subsys_id;
>  	int active;
> +	int disabled;
>  	int early_init;
>  #define MAX_CGROUP_TYPE_NAMELEN 32
>  	const char *name;
> diff -puN kernel/cgroup.c~cgroup_disable kernel/cgroup.c
> --- linux-2.6.25-rc4/kernel/cgroup.c~cgroup_disable	2008-03-06 12:19:38.000000000 +0530
> +++ linux-2.6.25-rc4-balbir/kernel/cgroup.c	2008-03-06 12:19:38.000000000 +0530
> @@ -782,7 +782,14 @@ static int parse_cgroupfs_options(char *
>  		if (!*token)
>  			return -EINVAL;
>  		if (!strcmp(token, "all")) {
> -			opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
> +			/* Add all non-disabled subsystems */
> +			int i;
> +			opts->subsys_bits = 0;
> +			for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> +				struct cgroup_subsys *ss = subsys[i];
> +				if (!ss->disabled)
> +					opts->subsys_bits |= 1ul << i;
> +			}
>  		} else if (!strcmp(token, "noprefix")) {
>  			set_bit(ROOT_NOPREFIX, &opts->flags);
>  		} else if (!strncmp(token, "release_agent=", 14)) {
> @@ -800,7 +807,8 @@ static int parse_cgroupfs_options(char *
>  			for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>  				ss = subsys[i];
>  				if (!strcmp(token, ss->name)) {
> -					set_bit(i, &opts->subsys_bits);
> +					if (!ss->disabled)
> +						set_bit(i, &opts->subsys_bits);
>  					break;
>  				}
>  			}
> @@ -2604,6 +2612,8 @@ static int proc_cgroupstats_show(struct 
>  	mutex_lock(&cgroup_mutex);
>  	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>  		struct cgroup_subsys *ss = subsys[i];
> +		if (ss->disabled)
> +			continue;
>  		seq_printf(m, "%s\t%lu\t%d\n",
>  			   ss->name, ss->root->subsys_bits,
>  			   ss->root->number_of_cgroups);
> @@ -3010,3 +3020,16 @@ static void cgroup_release_agent(struct 
>  	spin_unlock(&release_list_lock);
>  	mutex_unlock(&cgroup_mutex);
>  }
> +
> +static int __init cgroup_disable(char *str)
> +{
> +	int i;
> +	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> +		struct cgroup_subsys *ss = subsys[i];
> +		if (!strcmp(str, ss->name)) {
> +			ss->disabled = 1;
> +			break;
> +		}
> +	}
> +}
> +__setup("cgroup_disable=", cgroup_disable);
> diff -puN Documentation/kernel-parameters.txt~cgroup_disable Documentation/kernel-parameters.txt
> --- linux-2.6.25-rc4/Documentation/kernel-parameters.txt~cgroup_disable	2008-03-06 17:57:32.000000000 +0530
> +++ linux-2.6.25-rc4-balbir/Documentation/kernel-parameters.txt	2008-03-06 18:00:32.000000000 +0530
> @@ -383,6 +383,10 @@ and is between 256 and 4096 characters. 
>  	ccw_timeout_log [S390]
>  			See Documentation/s390/CommonIO for details.
>  
> +	cgroup_disable= [KNL] Enable disable a particular controller
> +			Format: {name of the controller}
> +			See /proc/cgroups for a list of compiled controllers
> +

The changelog of this patch:
- foo doesn't show up in /proc/cgroups

So a disabled subsystem won't show up in /proc/cgroups. In a previous
mail, I asked whether it will be useful to print out the disable bit
in /proc/cgroups, so we can distinguish a subsystem from disaled and
not-compiled.

>  	checkreqprot	[SELINUX] Set initial checkreqprot flag value.
>  			Format: { "0" | "1" }
>  			See security/selinux/Kconfig help text.
> _
>