cgroup: add cgroup->dummy_css
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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 583f8f6..c049992 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1365,6 +1365,7 @@
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 @@
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 @@
* 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 @@
err = cft->open(inode, file);
}
- if (css && err)
+ if (css->ss && err)
css_put(css);
return err;
}
@@ -2491,7 +2492,7 @@
if (cft->release)
ret = cft->release(inode, file);
- if (css)
+ if (css->ss)
css_put(css);
return ret;
}