4 files changed, 272 insertions, 1 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index c0358c30c64f..fd588ff0e296 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -23,6 +23,7 @@ CONTENTS:
   2.1 Basic Usage
   2.2 Attaching processes
   2.3 Mounting hierarchies by name
+  2.4 Notification API
 3. Kernel API
   3.1 Overview
   3.2 Synchronization
@@ -435,6 +436,25 @@ you give a subsystem a name.
 The name of the subsystem appears as part of the hierarchy description
 in /proc/mounts and /proc/<pid>/cgroups.
 
+2.4 Notification API
+--------------------
+
+There is mechanism which allows to get notifications about changing
+status of a cgroup.
+
+To register new notification handler you need:
+ - create a file descriptor for event notification using eventfd(2);
+ - open a control file to be monitored (e.g. memory.usage_in_bytes);
+ - write "<event_fd> <control_fd> <args>" to cgroup.event_control.
+   Interpretation of args is defined by control file implementation;
+
+eventfd will be woken up by control file implementation or when the
+cgroup is removed.
+
+To unregister notification handler just close eventfd.
+
+NOTE: Support of notifications should be implemented for the control
+file. See documentation for the subsystem.
 
 3. Kernel API
 =============
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 2a59d3101e5d..b4f2201321cd 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -235,6 +235,10 @@ struct cgroup {
 
         /* For RCU-protected deletion */
         struct rcu_head rcu_head;
+
+        /* List of events which userspace want to recieve */
+        struct list_head event_list;
+        spinlock_t event_list_lock;
 };
 
 /*
@@ -378,6 +382,26 @@ struct cftype {
         int (*trigger)(struct cgroup *cgrp, unsigned int event);
 
         int (*release)(struct inode *inode, struct file *file);
+
+        /*
+         * register_event() callback will be used to add new userspace
+         * waiter for changes related to the cftype. Implement it if
+         * you want to provide this functionality. Use eventfd_signal()
+         * on eventfd to send notification to userspace.
+         */
+        int (*register_event)(struct cgroup *cgrp, struct cftype *cft,
+                        struct eventfd_ctx *eventfd, const char *args);
+        /*
+         * unregister_event() callback will be called when userspace
+         * closes the eventfd or on cgroup removing.
+         * This callback must be implemented, if you want provide
+         * notification functionality.
+         *
+         * Be careful. It can be called after destroy(), so you have
+         * to keep all nesessary data, until all events are removed.
+         */
+        int (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
+                        struct eventfd_ctx *eventfd);
 };
 
 struct cgroup_scanner {
diff --git a/init/Kconfig b/init/Kconfig
index 089a230e5652..eb77e8ccde1c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -463,6 +463,7 @@ config HAVE_UNSTABLE_SCHED_CLOCK
 
 menuconfig CGROUPS
         boolean "Control Group support"
+        depends on EVENTFD
         help
           This option adds support for grouping sets of processes together, for
           use with process control subsystems such as Cpusets, CFS, memory
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1bf4d6db54ab..ea94984a3895 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4,6 +4,10 @@
  *  Based originally on the cpuset system, extracted by Paul Menage
  *  Copyright (C) 2006 Google, Inc
  *
+ *  Notifications support
+ *  Copyright (C) 2009 Nokia Corporation
+ *  Author: Kirill A. Shutemov
+ *
  *  Copyright notices from the original cpuset code:
  *  --------------------------------------------------
  *  Copyright (C) 2003 BULL SA.
@@ -53,6 +57,8 @@
 #include <linux/pid_namespace.h>
 #include <linux/idr.h>
 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
+#include <linux/eventfd.h>
+#include <linux/poll.h>
 
 #include <asm/atomic.h>
 
@@ -152,6 +158,35 @@ struct css_id {
         unsigned short stack[0]; /* Array of Length (depth+1) */
 };
 
+/*
+ * cgroup_event represents events which userspace want to recieve.
+ */
+struct cgroup_event {
+        /*
+         * Cgroup which the event belongs to.
+         */
+        struct cgroup *cgrp;
+        /*
+         * Control file which the event associated.
+         */
+        struct cftype *cft;
+        /*
+         * eventfd to signal userspace about the event.
+         */
+        struct eventfd_ctx *eventfd;
+        /*
+         * Each of these stored in a list by the cgroup.
+         */
+        struct list_head list;
+        /*
+         * All fields below needed to unregister event when
+         * userspace closes eventfd.
+         */
+        poll_table pt;
+        wait_queue_head_t *wqh;
+        wait_queue_t wait;
+        struct work_struct remove;
+};
 
 /* The list of hierarchy roots */
 
@@ -760,14 +795,28 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
 static int cgroup_call_pre_destroy(struct cgroup *cgrp)
 {
         struct cgroup_subsys *ss;
+        struct cgroup_event *event, *tmp;
         int ret = 0;
 
         for_each_subsys(cgrp->root, ss)
                 if (ss->pre_destroy) {
                         ret = ss->pre_destroy(ss, cgrp);
                         if (ret)
-                                break;
+                                goto out;
                 }
+
+        /*
+         * Unregister events and notify userspace.
+         */
+        spin_lock(&cgrp->event_list_lock);
+        list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
+                list_del(&event->list);
+                eventfd_signal(event->eventfd, 1);
+                schedule_work(&event->remove);
+        }
+        spin_unlock(&cgrp->event_list_lock);
+
+out:
         return ret;
 }
 
@@ -1239,6 +1288,8 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
         INIT_LIST_HEAD(&cgrp->release_list);
         INIT_LIST_HEAD(&cgrp->pidlists);
         mutex_init(&cgrp->pidlist_mutex);
+        INIT_LIST_HEAD(&cgrp->event_list);
+        spin_lock_init(&cgrp->event_list_lock);
 }
 
 static void init_cgroup_root(struct cgroupfs_root *root)
@@ -2077,6 +2128,16 @@ static const struct inode_operations cgroup_dir_inode_operations = {
         .rename = cgroup_rename,
 };
 
+/*
+ * Check if a file is a control file
+ */
+static inline struct cftype *__file_cft(struct file *file)
+{
+        if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
+                return ERR_PTR(-EINVAL);
+        return __d_cft(file->f_dentry);
+}
+
 static int cgroup_create_file(struct dentry *dentry, mode_t mode,
                                 struct super_block *sb)
 {
@@ -2931,6 +2992,166 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp,
 }
 
 /*
+ * Unregister event and free resources.
+ *
+ * Gets called from workqueue.
+ */
+static void cgroup_event_remove(struct work_struct *work)
+{
+        struct cgroup_event *event = container_of(work, struct cgroup_event,
+                        remove);
+        struct cgroup *cgrp = event->cgrp;
+
+        /* TODO: check return code */
+        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
+
+        eventfd_ctx_put(event->eventfd);
+        remove_wait_queue(event->wqh, &event->wait);
+        kfree(event);
+}
+
+/*
+ * Gets called on POLLHUP on eventfd when user closes it.
+ *
+ * Called with wqh->lock held and interrupts disabled.
+ */
+static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
+                int sync, void *key)
+{
+        struct cgroup_event *event = container_of(wait,
+                        struct cgroup_event, wait);
+        struct cgroup *cgrp = event->cgrp;
+        unsigned long flags = (unsigned long)key;
+
+        if (flags & POLLHUP) {
+                spin_lock(&cgrp->event_list_lock);
+                list_del(&event->list);
+                spin_unlock(&cgrp->event_list_lock);
+                /*
+                 * We are in atomic context, but cgroup_event_remove() may
+                 * sleep, so we have to call it in workqueue.
+                 */
+                schedule_work(&event->remove);
+        }
+
+        return 0;
+}
+
+static void cgroup_event_ptable_queue_proc(struct file *file,
+                wait_queue_head_t *wqh, poll_table *pt)
+{
+        struct cgroup_event *event = container_of(pt,
+                        struct cgroup_event, pt);
+
+        event->wqh = wqh;
+        add_wait_queue(wqh, &event->wait);
+}
+
+/*
+ * Parse input and register new cgroup event handler.
+ *
+ * Input must be in format '<event_fd> <control_fd> <args>'.
+ * Interpretation of args is defined by control file implementation.
+ */
+static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
+                                      const char *buffer)
+{
+        struct cgroup_event *event = NULL;
+        unsigned int efd, cfd;
+        struct file *efile = NULL;
+        struct file *cfile = NULL;
+        char *endp;
+        int ret;
+
+        efd = simple_strtoul(buffer, &endp, 10);
+        if (*endp != ' ')
+                return -EINVAL;
+        buffer = endp + 1;
+
+        cfd = simple_strtoul(buffer, &endp, 10);
+        if ((*endp != ' ') && (*endp != '\0'))
+                return -EINVAL;
+        buffer = endp + 1;
+
+        event = kzalloc(sizeof(*event), GFP_KERNEL);
+        if (!event)
+                return -ENOMEM;
+        event->cgrp = cgrp;
+        INIT_LIST_HEAD(&event->list);
+        init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
+        init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
+        INIT_WORK(&event->remove, cgroup_event_remove);
+
+        efile = eventfd_fget(efd);
+        if (IS_ERR(efile)) {
+                ret = PTR_ERR(efile);
+                goto fail;
+        }
+
+        event->eventfd = eventfd_ctx_fileget(efile);
+        if (IS_ERR(event->eventfd)) {
+                ret = PTR_ERR(event->eventfd);
+                goto fail;
+        }
+
+        cfile = fget(cfd);
+        if (!cfile) {
+                ret = -EBADF;
+                goto fail;
+        }
+
+        /* the process need read permission on control file */
+        ret = file_permission(cfile, MAY_READ);
+        if (ret < 0)
+                goto fail;
+
+        event->cft = __file_cft(cfile);
+        if (IS_ERR(event->cft)) {
+                ret = PTR_ERR(event->cft);
+                goto fail;
+        }
+
+        if (!event->cft->register_event || !event->cft->unregister_event) {
+                ret = -EINVAL;
+                goto fail;
+        }
+
+        ret = event->cft->register_event(cgrp, event->cft,
+                        event->eventfd, buffer);
+        if (ret)
+                goto fail;
+
+        if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
+                event->cft->unregister_event(cgrp, event->cft, event->eventfd);
+                ret = 0;
+                goto fail;
+        }
+
+        spin_lock(&cgrp->event_list_lock);
+        list_add(&event->list, &cgrp->event_list);
+        spin_unlock(&cgrp->event_list_lock);
+
+        fput(cfile);
+        fput(efile);
+
+        return 0;
+
+fail:
+        if (cfile)
+                fput(cfile);
+
+        if (event && event->eventfd && !IS_ERR(event->eventfd))
+                eventfd_ctx_put(event->eventfd);
+
+        if (!IS_ERR_OR_NULL(efile))
+                fput(efile);
+
+        kfree(event);
+
+        return ret;
+}
+
+/*
  * for the common functions, 'private' gives the type of file
  */
 /* for hysterical raisins, we can't put this on the older files */
@@ -2955,6 +3176,11 @@ static struct cftype files[] = {
                 .read_u64 = cgroup_read_notify_on_release,
                 .write_u64 = cgroup_write_notify_on_release,
         },
+        {
+                .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
+                .write_string = cgroup_write_event_control,
+                .mode = S_IWUGO,
+        },
 };
 
 static struct cftype cft_release_agent = {