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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
View File

@ -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.

13
include/linux/cgroup.h
View File

@ -490,6 +490,19 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
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;

26
kernel/cgroup.c
View File

@ -612,8 +612,8 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
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 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
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 @@ static int cgroup_procs_write_permission(struct task_struct *task,
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 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
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 int cgroup_clone_children_write(struct cgroup_subsys_state *css,
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 @@ static struct cftype cgroup_dfl_base_files[] = {
{
.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 @@ static void css_free_work_fn(struct work_struct *work)
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 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
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)) {