cgroup subsystem API is being converted to use css
(cgroup_subsys_state) as the main handle, which makes things a bit
awkward for subsystem agnostic core features - the "cgroup.*"
interface files and various iterations - a bit awkward as they don't
have a css to use.
This patch adds cgroup->dummy_css which has NULL ->ss and whose only
role is pointing back to the cgroup. This will be used to support
subsystem agnostic features on the coming css based API.
css_parent() is updated to handle dummy_css's. Note that css will
soon grow its own ->parent field and css_parent() will be made
trivial.
Signed-off-by: Tejun Heo <t...@kernel.org>
---
include/linux/cgroup.h | 11 ++++++++++-
kernel/cgroup.c | 9 +++++----
2 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 2e0e9e2..085ca93 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -225,6 +225,9 @@ struct cgroup {
struct list_head pidlists;
struct mutex pidlist_mutex;
+ /* dummy css with NULL ->ss, points back to this cgroup */
+ struct cgroup_subsys_state dummy_css;
+
/* For css percpu_ref killing and RCU-protected deletion */
struct rcu_head rcu_head;
struct work_struct destroy_work;
@@ -669,7 +672,13 @@ struct cgroup_subsys_state *css_parent(struct
cgroup_subsys_state *css)
{
struct cgroup *parent_cgrp = css->cgroup->parent;
- return parent_cgrp ? parent_cgrp->subsys[css->ss->subsys_id] : NULL;
+ if (!parent_cgrp)
+ return NULL;
+
+ if (css->ss)
+ return parent_cgrp->subsys[css->ss->subsys_id];
+ else
+ return &parent_cgrp->dummy_css;
}
/**
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b413e22..bb87c9f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1365,6 +1365,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
INIT_LIST_HEAD(&cgrp->release_list);
INIT_LIST_HEAD(&cgrp->pidlists);
mutex_init(&cgrp->pidlist_mutex);
+ cgrp->dummy_css.cgroup = cgrp;
INIT_LIST_HEAD(&cgrp->event_list);
spin_lock_init(&cgrp->event_list_lock);
simple_xattrs_init(&cgrp->xattrs);
@@ -2278,7 +2279,7 @@ static struct cgroup_subsys_state *cgroup_file_css(struct
cfent *cfe)
if (cft->ss)
return cgrp->subsys[cft->ss->subsys_id];
- return NULL;
+ return &cgrp->dummy_css;
}
/* A buffer size big enough for numbers or short strings */
@@ -2460,7 +2461,7 @@ static int cgroup_file_open(struct inode *inode, struct
file *file)
* unpinned either on open failure or release. This ensures that
* @css stays alive for all file operations.
*/
- if (css && !css_tryget(css))
+ if (css->ss && !css_tryget(css))
return -ENODEV;
if (cft->read_map || cft->read_seq_string) {
@@ -2470,7 +2471,7 @@ static int cgroup_file_open(struct inode *inode, struct
file *file)
err = cft->open(inode, file);
}
- if (css && err)
+ if (css->ss && err)
css_put(css);
return err;
}
@@ -2484,7 +2485,7 @@ static int cgroup_file_release(struct inode *inode,
struct file *file)
if (cft->release)
ret = cft->release(inode, file);
- if (css)
+ if (css->ss)
css_put(css);
return ret;
}
--
1.8.3.1
--
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