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cgroup: add cgroup->dummy_css

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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 <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-08-08 20:11:24 -04:00
parent f7d58818ba
commit 67f4c36f83
2 changed files with 15 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/linux/cgroup.h
View File

@ -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;
@ -668,7 +671,13 @@ 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;
}
/**

9
kernel/cgroup.c
View File

@ -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);
@ -2285,7 +2286,7 @@ 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 */
@ -2467,7 +2468,7 @@ 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) {
@ -2477,7 +2478,7 @@ 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;
}
@ -2491,7 +2492,7 @@ 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;
}