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Subject[PATCH 1/3] cgroup : add clone_children control file
This patch is sent as an answer to a previous thread around the ns_cgroup.

https://lists.linux-foundation.org/pipermail/containers/2009-June/018627.html

It adds a control file 'clone_children' for a cgroup.
This control file is a boolean specifying if the child cgroup should
be a clone of the parent cgroup or not. The default value is 'false'.

This flag makes the child cgroup to call the post_clone callback of all
the subsystem, if it is available.

At present, the cpuset is the only one which had implemented the post_clone
callback.

The option can be set at mount time by specifying the 'clone_children' mount
option.

Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Paul Menage <menage@google.com>
---
Documentation/cgroups/cgroups.txt | 14 +++++++++++-
include/linux/cgroup.h | 4 +++
kernel/cgroup.c | 39 +++++++++++++++++++++++++++++++++++++
3 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index b34823f..190018b 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -18,7 +18,8 @@ CONTENTS:
1.2 Why are cgroups needed ?
1.3 How are cgroups implemented ?
1.4 What does notify_on_release do ?
- 1.5 How do I use cgroups ?
+ 1.5 What does clone_children do ?
+ 1.6 How do I use cgroups ?
2. Usage Examples and Syntax
2.1 Basic Usage
2.2 Attaching processes
@@ -293,7 +294,16 @@ notify_on_release in the root cgroup at system boot is disabled
value of their parents notify_on_release setting. The default value of
a cgroup hierarchy's release_agent path is empty.

-1.5 How do I use cgroups ?
+1.5 What does clone_children do ?
+---------------------------------
+
+If the clone_children flag is enabled (1) in a cgroup, then all
+cgroups created beneath will call the post_clone callbacks for each
+subsystem of the newly created cgroup. Usually when this callback is
+implemented for a subsystem, it copies the values of the parent
+subsystem, this is the case for the cpuset.
+
+1.6 How do I use cgroups ?
--------------------------

To start a new job that is to be contained within a cgroup, using
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e3d00fd..f3cbd73 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -154,6 +154,10 @@ enum {
* A thread in rmdir() is wating for this cgroup.
*/
CGRP_WAIT_ON_RMDIR,
+ /*
+ * Clone cgroup values when creating a new child cgroup
+ */
+ CGRP_CLONE_CHILDREN,
};

/* which pidlist file are we talking about? */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3ac6f5b..dfbff78 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -229,6 +229,7 @@ inline int cgroup_is_removed(const struct cgroup *cgrp)
/* bits in struct cgroupfs_root flags field */
enum {
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
+ ROOT_CLONE_CHILDREN, /* mounted subsystems will inherit from parent */
};

static int cgroup_is_releasable(const struct cgroup *cgrp)
@@ -244,6 +245,11 @@ static int notify_on_release(const struct cgroup *cgrp)
return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
}

+static int clone_children(const struct cgroup *cgrp)
+{
+ return test_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+}
+
/*
* for_each_subsys() allows you to iterate on each subsystem attached to
* an active hierarchy
@@ -1038,6 +1044,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
seq_printf(seq, ",%s", ss->name);
if (test_bit(ROOT_NOPREFIX, &root->flags))
seq_puts(seq, ",noprefix");
+ if (test_bit(ROOT_CLONE_CHILDREN, &root->flags))
+ seq_puts(seq, ",clone_children");
if (strlen(root->release_agent_path))
seq_printf(seq, ",release_agent=%s", root->release_agent_path);
if (strlen(root->name))
@@ -1097,6 +1105,8 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
opts->none = true;
} else if (!strcmp(token, "noprefix")) {
set_bit(ROOT_NOPREFIX, &opts->flags);
+ } else if (!strcmp(token, "clone_children")) {
+ set_bit(ROOT_CLONE_CHILDREN, &opts->flags);
} else if (!strncmp(token, "release_agent=", 14)) {
/* Specifying two release agents is forbidden */
if (opts->release_agent)
@@ -1357,6 +1367,8 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
strcpy(root->release_agent_path, opts->release_agent);
if (opts->name)
strcpy(root->name, opts->name);
+ if (test_bit(ROOT_CLONE_CHILDREN, &opts->flags))
+ set_bit(CGRP_CLONE_CHILDREN, &root->top_cgroup.flags);
return root;
}

@@ -3150,6 +3162,23 @@ fail:
return ret;
}

+static u64 cgroup_clone_children_read(struct cgroup *cgrp,
+ struct cftype *cft)
+{
+ return clone_children(cgrp);
+}
+
+static int cgroup_clone_children_write(struct cgroup *cgrp,
+ struct cftype *cft,
+ u64 val)
+{
+ if (val)
+ set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+ else
+ clear_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+ return 0;
+}
+
/*
* for the common functions, 'private' gives the type of file
*/
@@ -3180,6 +3209,11 @@ static struct cftype files[] = {
.write_string = cgroup_write_event_control,
.mode = S_IWUGO,
},
+ {
+ .name = "cgroup.clone_children",
+ .read_u64 = cgroup_clone_children_read,
+ .write_u64 = cgroup_clone_children_write,
+ },
};

static struct cftype cft_release_agent = {
@@ -3309,6 +3343,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (notify_on_release(parent))
set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

+ if (clone_children(parent))
+ set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
+
for_each_subsys(root, ss) {
struct cgroup_subsys_state *css = ss->create(ss, cgrp);

@@ -3323,6 +3360,8 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
goto err_destroy;
}
/* At error, ->destroy() callback has to free assigned ID. */
+ if (clone_children(parent) && ss->post_clone)
+ ss->post_clone(ss, cgrp);
}

cgroup_lock_hierarchy(root);
--
1.7.0.4


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