[Devel] Re: [RFC] [PATCH] cgroup: accounting and limitation of disk quota

[Serge E. Hallyn]

Quoting anqin (anqin.qin at gmail.com):
> The patch presents a cgroup subsystem to control the usage of disk quota.
> 
> The subsystem for disk quota (disk_cgroup, to be brief) does accounting
> of inode and block allocated by ext3/ext2 filesystem. Simarily as
> filesystem quota, the disk_cgroup can do limitation but without needing
> to open filesytem quota options (e.g. usrquota,grpquota in /etc/fstab).
> 
> The simple usage of disk_cgroup is as follows:
> 
> # mount -t cgroup cgroup /mnt/cgrp
> # lxc-execute -n lxc-template.conf /bin/bash
> # ls /mnt/cgrp/11457/           // <--  11457 is the pid of bash
> ...
> disk.stat
> disk.usage_in_inode
> disk.usage_in_block
> disk.max_usage_in_inode
> disk.max_usage_in_block
> disk.limit_in_inode
> disk.limit_in_inode
> ...
> 
> # echo  3 > /mnt/cgrp/11457/disk.max_usage_in_block
> 
> # touch /tmp/mytestfile1
> # touch /tmp/mytestfile2
> # touch /tmp/mytestfile3
> # touch /tmp/mytestfile4
> touch: cannot touch `/tmp/mytestfile4': Disk quota exceeded
> 
> The disk_cgroup is easily extended to manage complex objects
> of filesystem.
>
> Signed-off-by: An Qin <anqin.qin at gmail.com>

It's probably worth sending this to linux-fsdevel as well as the
ext2 and ext3 maintainers and lists (see MAINTAINERS - at
least linux-ext4 at vger.kernel.org).

> +static struct cgroup_subsys_state *disk_cgroup_create(
> +			struct cgroup_subsys *ss, struct cgroup *cont)
> +{
> +	struct disk_cgroup *disk;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return ERR_PTR(-EPERM);

On the whole it is preferred to let the cgroup uid permissions
handle access control, and not check CAP_SYS_ADMIN for cgroup
creation.

> +	if (!cgroup_is_descendant(cont))
> +		return ERR_PTR(-EPERM);
> +	
> +	disk = kzalloc(sizeof(struct disk_cgroup), GFP_KERNEL);

So you are setting all the limits to 0, with 0 meaning unlimited, at
cgroup create?  What do you think about copying the parent cgroup's 
limits?

> --- linux-2.6.28.5/kernel/Makefile	2009-02-13 01:51:15.000000000 +0800
> +++ linux-2.6.28.5-cgroup-disk-quota/kernel/Makefile	2009-02-19
> 06:52:04.000000000 +0800
> @@ -55,6 +55,7 @@ obj-$(CONFIG_COMPAT) += compat.o
>  obj-$(CONFIG_CGROUPS) += cgroup.o
>  obj-$(CONFIG_CGROUP_DEBUG) += cgroup_debug.o
>  obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
> +obj-$(CONFIG_CGROUP_FREEZER) += cgroup_disk.o

I don't think you wanted to put this under _FREEZER :)

>  obj-$(CONFIG_CPUSETS) += cpuset.o
>  obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
>  obj-$(CONFIG_UTS_NS) += utsname.o

per-container quota has been mentioned before as a desireable
feature so thanks for working on this.

-serge
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