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cgroup: generalize obtaining the handles of and notifying cgroup files

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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>
This commit is contained in:
Tejun Heo
2015-09-18 17:54:23 -04:00
parent 4df8dc9031
commit 6f60eade24
3 changed files with 56 additions and 9 deletions
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26
include/linux/cgroup-defs.h
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@@ -83,6 +83,17 @@ enum {
__CFTYPE_NOT_ON_DFL = (1 << 17), /* not on default hierarchy */
};
/*
* 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 @@ struct cgroup_subsys_state {
*/
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 @@ struct cgroup {
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.
@@ -335,6 +349,14 @@ struct cftype {
/* CFTYPE_* flags */
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.