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>
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@ -83,6 +83,17 @@ enum {
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__CFTYPE_NOT_ON_DFL = (1 << 17), /* not on default hierarchy */
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};
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/*
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* cgroup_file is the handle for a file instance created in a cgroup which
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* is used, for example, to generate file changed notifications. This can
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* be obtained by setting cftype->file_offset.
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*/
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struct cgroup_file {
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/* do not access any fields from outside cgroup core */
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struct list_head node; /* anchored at css->files */
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struct kernfs_node *kn;
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};
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/*
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* Per-subsystem/per-cgroup state maintained by the system. This is the
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* fundamental structural building block that controllers deal with.
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@ -123,6 +134,9 @@ struct cgroup_subsys_state {
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*/
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u64 serial_nr;
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/* all cgroup_files associated with this css */
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struct list_head files;
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/* percpu_ref killing and RCU release */
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struct rcu_head rcu_head;
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struct work_struct destroy_work;
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@ -226,8 +240,8 @@ struct cgroup {
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int populated_cnt;
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struct kernfs_node *kn; /* cgroup kernfs entry */
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struct kernfs_node *procs_kn; /* kn for "cgroup.procs" */
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struct kernfs_node *events_kn; /* kn for "cgroup.events" */
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struct cgroup_file procs_file; /* handle for "cgroup.procs" */
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struct cgroup_file events_file; /* handle for "cgroup.events" */
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/*
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* The bitmask of subsystems enabled on the child cgroups.
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@ -335,6 +349,14 @@ struct cftype {
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/* CFTYPE_* flags */
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unsigned int flags;
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/*
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* If non-zero, should contain the offset from the start of css to
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* a struct cgroup_file field. cgroup will record the handle of
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* the created file into it. The recorded handle can be used as
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* long as the containing css remains accessible.
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*/
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unsigned int file_offset;
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/*
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* Fields used for internal bookkeeping. Initialized automatically
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* during registration.
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@ -490,6 +490,19 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
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pr_cont_kernfs_path(cgrp->kn);
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}
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/**
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* cgroup_file_notify - generate a file modified event for a cgroup_file
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* @cfile: target cgroup_file
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*
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* @cfile must have been obtained by setting cftype->file_offset.
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*/
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static inline void cgroup_file_notify(struct cgroup_file *cfile)
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{
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/* might not have been created due to one of the CFTYPE selector flags */
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if (cfile->kn)
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kernfs_notify(cfile->kn);
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}
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#else /* !CONFIG_CGROUPS */
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struct cgroup_subsys_state;
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@ -612,8 +612,8 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
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if (!trigger)
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break;
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if (cgrp->events_kn)
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kernfs_notify(cgrp->events_kn);
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cgroup_file_notify(&cgrp->events_file);
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cgrp = cgroup_parent(cgrp);
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} while (cgrp);
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}
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@ -1771,6 +1771,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
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INIT_LIST_HEAD(&cgrp->self.sibling);
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INIT_LIST_HEAD(&cgrp->self.children);
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INIT_LIST_HEAD(&cgrp->self.files);
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INIT_LIST_HEAD(&cgrp->cset_links);
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INIT_LIST_HEAD(&cgrp->pidlists);
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mutex_init(&cgrp->pidlist_mutex);
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@ -2562,7 +2563,7 @@ static int cgroup_procs_write_permission(struct task_struct *task,
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cgrp = cgroup_parent(cgrp);
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ret = -ENOMEM;
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inode = kernfs_get_inode(sb, cgrp->procs_kn);
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inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
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if (inode) {
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ret = inode_permission(inode, MAY_WRITE);
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iput(inode);
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@ -3253,10 +3254,14 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
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return ret;
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}
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if (cft->write == cgroup_procs_write)
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cgrp->procs_kn = kn;
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else if (cft->seq_show == cgroup_events_show)
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cgrp->events_kn = kn;
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if (cft->file_offset) {
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struct cgroup_file *cfile = (void *)css + cft->file_offset;
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kernfs_get(kn);
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cfile->kn = kn;
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list_add(&cfile->node, &css->files);
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}
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return 0;
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}
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@ -4408,6 +4413,7 @@ static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
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static struct cftype cgroup_dfl_base_files[] = {
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{
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.name = "cgroup.procs",
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.file_offset = offsetof(struct cgroup, procs_file),
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.seq_start = cgroup_pidlist_start,
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.seq_next = cgroup_pidlist_next,
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.seq_stop = cgroup_pidlist_stop,
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@ -4433,6 +4439,7 @@ static struct cftype cgroup_dfl_base_files[] = {
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{
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.name = "cgroup.events",
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.flags = CFTYPE_NOT_ON_ROOT,
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.file_offset = offsetof(struct cgroup, events_file),
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.seq_show = cgroup_events_show,
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},
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{ } /* terminate */
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@ -4511,9 +4518,13 @@ static void css_free_work_fn(struct work_struct *work)
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container_of(work, struct cgroup_subsys_state, destroy_work);
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struct cgroup_subsys *ss = css->ss;
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struct cgroup *cgrp = css->cgroup;
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struct cgroup_file *cfile;
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percpu_ref_exit(&css->refcnt);
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list_for_each_entry(cfile, &css->files, node)
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kernfs_put(cfile->kn);
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if (ss) {
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/* css free path */
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int id = css->id;
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@ -4618,6 +4629,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
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css->ss = ss;
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INIT_LIST_HEAD(&css->sibling);
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INIT_LIST_HEAD(&css->children);
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INIT_LIST_HEAD(&css->files);
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css->serial_nr = css_serial_nr_next++;
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if (cgroup_parent(cgrp)) {
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