Revert "cgroup: remove bind() method from cgroup_subsys."
This reverts commit 84cfb6ab484b442d5115eb3baf9db7d74a3ea626. There
are scheduled changes which make use of the removed callback.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Rami Rosen <ramirose@gmail.com>
Cc: Li Zefan <lizefan@huawei.com>
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 2b51e12..638bf17 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -211,9 +211,10 @@
hierarchy, the mount will fail with -EBUSY. Otherwise, a new hierarchy
is activated, associated with the requested subsystems.
-It's not possible to bind a new subsystem to an active cgroup
-hierarchy, or to unbind a subsystem from an active cgroup
-hierarchy.
+It's not currently possible to bind a new subsystem to an active
+cgroup hierarchy, or to unbind a subsystem from an active cgroup
+hierarchy. This may be possible in future, but is fraught with nasty
+error-recovery issues.
When a cgroup filesystem is unmounted, if there are any
child cgroups created below the top-level cgroup, that hierarchy
@@ -381,8 +382,10 @@
Note that specifying 'release_agent' more than once will return failure.
-Note that changing the set of subsystems is only supported when the
-hierarchy consists of a single (root) cgroup.
+Note that changing the set of subsystems is currently only supported
+when the hierarchy consists of a single (root) cgroup. Supporting
+the ability to arbitrarily bind/unbind subsystems from an existing
+cgroup hierarchy is intended to be implemented in the future.
Then under /sys/fs/cgroup/rg1 you can find a tree that corresponds to the
tree of the cgroups in the system. For instance, /sys/fs/cgroup/rg1
@@ -640,6 +643,13 @@
Called during task exit.
+void bind(struct cgroup *root)
+(cgroup_mutex held by caller)
+
+Called when a cgroup subsystem is rebound to a different hierarchy
+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).
4. Extended attribute usage
===========================
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a2b9d4b..45aee0f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -484,6 +484,8 @@
void (*fork)(struct task_struct *task);
void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,
struct task_struct *task);
+ void (*bind)(struct cgroup *root);
+
int subsys_id;
int active;
int disabled;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7bf3ce0..678a22c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1091,12 +1091,16 @@
cgrp->subsys[i]->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
+ if (ss->bind)
+ ss->bind(cgrp);
/* refcount was already taken, and we're keeping it */
} else if (bit & removed_mask) {
/* We're removing this subsystem */
BUG_ON(ss == NULL);
BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
+ if (ss->bind)
+ ss->bind(dummytop);
dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL;
subsys[i]->root = &rootnode;