cgroup: generalize obtaining the handles of and notifying cgroup files
cgroup core handles creations and removals of cgroup interface files
as described by cftypes. There are cases where the handle for a given
file instance is necessary, for example, to generate a file modified
event. Currently, this is handled by explicitly matching the callback
method pointer and storing the file handle manually in
cgroup_add_file(). While this simple approach works for cgroup core
files, it can't for controller interface files.
This patch generalizes cgroup interface file handle handling. struct
cgroup_file is defined and each cftype can optionally tell cgroup core
to store the file handle by setting ->file_offset. A file handle
remains accessible as long as the containing css is accessible.
Both "cgroup.procs" and "cgroup.events" are converted to use the new
generic mechanism instead of hooking directly into cgroup_add_file().
Also, cgroup_file_notify() which takes a struct cgroup_file and
generates a file modified event on it is added and replaces explicit
kernfs_notify() invocations.
This generalizes cgroup file handle handling and allows controllers to
generate file modified notifications.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 10d814b..df589a0 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -84,6 +84,17 @@
};
/*
+ * cgroup_file is the handle for a file instance created in a cgroup which
+ * is used, for example, to generate file changed notifications. This can
+ * be obtained by setting cftype->file_offset.
+ */
+struct cgroup_file {
+ /* do not access any fields from outside cgroup core */
+ struct list_head node; /* anchored at css->files */
+ struct kernfs_node *kn;
+};
+
+/*
* Per-subsystem/per-cgroup state maintained by the system. This is the
* fundamental structural building block that controllers deal with.
*
@@ -123,6 +134,9 @@
*/
u64 serial_nr;
+ /* all cgroup_files associated with this css */
+ struct list_head files;
+
/* percpu_ref killing and RCU release */
struct rcu_head rcu_head;
struct work_struct destroy_work;
@@ -226,8 +240,8 @@
int populated_cnt;
struct kernfs_node *kn; /* cgroup kernfs entry */
- struct kernfs_node *procs_kn; /* kn for "cgroup.procs" */
- struct kernfs_node *events_kn; /* kn for "cgroup.events" */
+ struct cgroup_file procs_file; /* handle for "cgroup.procs" */
+ struct cgroup_file events_file; /* handle for "cgroup.events" */
/*
* The bitmask of subsystems enabled on the child cgroups.
@@ -336,6 +350,14 @@
unsigned int flags;
/*
+ * If non-zero, should contain the offset from the start of css to
+ * a struct cgroup_file field. cgroup will record the handle of
+ * the created file into it. The recorded handle can be used as
+ * long as the containing css remains accessible.
+ */
+ unsigned int file_offset;
+
+ /*
* Fields used for internal bookkeeping. Initialized automatically
* during registration.
*/
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 355bf2e..fb717f2 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -490,6 +490,19 @@
pr_cont_kernfs_path(cgrp->kn);
}
+/**
+ * cgroup_file_notify - generate a file modified event for a cgroup_file
+ * @cfile: target cgroup_file
+ *
+ * @cfile must have been obtained by setting cftype->file_offset.
+ */
+static inline void cgroup_file_notify(struct cgroup_file *cfile)
+{
+ /* might not have been created due to one of the CFTYPE selector flags */
+ if (cfile->kn)
+ kernfs_notify(cfile->kn);
+}
+
#else /* !CONFIG_CGROUPS */
struct cgroup_subsys_state;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 06c9d1a..0be276f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -612,8 +612,8 @@
if (!trigger)
break;
- if (cgrp->events_kn)
- kernfs_notify(cgrp->events_kn);
+ cgroup_file_notify(&cgrp->events_file);
+
cgrp = cgroup_parent(cgrp);
} while (cgrp);
}
@@ -1771,6 +1771,7 @@
INIT_LIST_HEAD(&cgrp->self.sibling);
INIT_LIST_HEAD(&cgrp->self.children);
+ INIT_LIST_HEAD(&cgrp->self.files);
INIT_LIST_HEAD(&cgrp->cset_links);
INIT_LIST_HEAD(&cgrp->pidlists);
mutex_init(&cgrp->pidlist_mutex);
@@ -2562,7 +2563,7 @@
cgrp = cgroup_parent(cgrp);
ret = -ENOMEM;
- inode = kernfs_get_inode(sb, cgrp->procs_kn);
+ inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
if (inode) {
ret = inode_permission(inode, MAY_WRITE);
iput(inode);
@@ -3253,10 +3254,14 @@
return ret;
}
- if (cft->write == cgroup_procs_write)
- cgrp->procs_kn = kn;
- else if (cft->seq_show == cgroup_events_show)
- cgrp->events_kn = kn;
+ if (cft->file_offset) {
+ struct cgroup_file *cfile = (void *)css + cft->file_offset;
+
+ kernfs_get(kn);
+ cfile->kn = kn;
+ list_add(&cfile->node, &css->files);
+ }
+
return 0;
}
@@ -4408,6 +4413,7 @@
static struct cftype cgroup_dfl_base_files[] = {
{
.name = "cgroup.procs",
+ .file_offset = offsetof(struct cgroup, procs_file),
.seq_start = cgroup_pidlist_start,
.seq_next = cgroup_pidlist_next,
.seq_stop = cgroup_pidlist_stop,
@@ -4433,6 +4439,7 @@
{
.name = "cgroup.events",
.flags = CFTYPE_NOT_ON_ROOT,
+ .file_offset = offsetof(struct cgroup, events_file),
.seq_show = cgroup_events_show,
},
{ } /* terminate */
@@ -4511,9 +4518,13 @@
container_of(work, struct cgroup_subsys_state, destroy_work);
struct cgroup_subsys *ss = css->ss;
struct cgroup *cgrp = css->cgroup;
+ struct cgroup_file *cfile;
percpu_ref_exit(&css->refcnt);
+ list_for_each_entry(cfile, &css->files, node)
+ kernfs_put(cfile->kn);
+
if (ss) {
/* css free path */
int id = css->id;
@@ -4618,6 +4629,7 @@
css->ss = ss;
INIT_LIST_HEAD(&css->sibling);
INIT_LIST_HEAD(&css->children);
+ INIT_LIST_HEAD(&css->files);
css->serial_nr = css_serial_nr_next++;
if (cgroup_parent(cgrp)) {