[PATCH RFC v2 1/4] cgroup: implement eventfd-based generic API for notifications
Kirill A. Shutemov
kirill at shutemov.name
Fri Dec 11 14:59:16 PST 2009
This patch introduces write-only file "cgroup.event_control" in every
cgroup.
To register new notification handler you need:
- create an eventfd;
- open a control file to be monitored. Callbacks register_event() and
unregister_event() must be defined for the control file;
- 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.
If you need notification functionality for a control file you have to
implement callbacks register_event() and unregister_event() in the
struct cftype.
Signed-off-by: Kirill A. Shutemov <kirill at shutemov.name>
---
include/linux/cgroup.h | 20 +++++
kernel/cgroup.c | 215 +++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 234 insertions(+), 1 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0008dee..7ad3078 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -220,6 +220,10 @@ struct cgroup {
/* For RCU-protected deletion */
struct rcu_head rcu_head;
+
+ /* List of events which userspace want to recieve */
+ struct list_head event_list;
+ struct mutex event_list_mutex;
};
/*
@@ -362,6 +366,22 @@ 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
+ * close the eventfd. This callback must be implemented, if you
+ * provide register_event().
+ */
+ int (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
+ struct eventfd_ctx *eventfd);
};
struct cgroup_scanner {
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0249f4b..f7ec3ca 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
*
+ * Notifiactions support
+ * Copyright (C) 2009 Nokia Corporation
+ * Author: Kirill A. Shutemov
+ *
* Copyright notices from the original cpuset code:
* --------------------------------------------------
* Copyright (C) 2003 BULL SA.
@@ -51,6 +55,8 @@
#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>
@@ -146,6 +152,36 @@ struct css_id {
unsigned short stack[0]; /* Array of Length (depth+1) */
};
+/*
+ * cgroup_event represents event 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;
+};
+static void cgroup_event_remove(struct cgroup_event *event);
/* The list of hierarchy roots */
@@ -734,14 +770,29 @@ 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.
+ * FIXME: How to avoid race with cgroup_event_remove_work()
+ * which runs from workqueue?
+ */
+ mutex_lock(&cgrp->event_list_mutex);
+ list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
+ cgroup_event_remove(event);
+ eventfd_signal(event->eventfd, 1);
+ }
+ mutex_unlock(&cgrp->event_list_mutex);
+
+out:
return ret;
}
@@ -1136,6 +1187,8 @@ 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);
+ mutex_init(&cgrp->event_list_mutex);
}
static void init_cgroup_root(struct cgroupfs_root *root)
@@ -1935,6 +1988,16 @@ 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)
{
@@ -2789,6 +2852,151 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp,
return 0;
}
+static inline void cgroup_event_remove(struct cgroup_event *event)
+{
+ struct cgroup *cgrp = event->cgrp;
+
+ BUG_ON(event->cft->unregister_event(cgrp, event->cft, event->eventfd));
+ eventfd_ctx_put(event->eventfd);
+ remove_wait_queue(event->wqh, &event->wait);
+ list_del(&event->list);
+ kfree(event);
+}
+
+static void cgroup_event_remove_work(struct work_struct *work)
+{
+ struct cgroup_event *event = container_of(work, struct cgroup_event,
+ remove);
+ struct cgroup *cgrp = event->cgrp;
+
+ mutex_lock(&cgrp->event_list_mutex);
+ cgroup_event_remove(event);
+ mutex_unlock(&cgrp->event_list_mutex);
+}
+
+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);
+ unsigned long flags = (unsigned long)key;
+
+ if (flags & POLLHUP)
+ /*
+ * This function called with spinlock taken, but
+ * cgroup_event_remove() may sleep, so we have
+ * to run it in a 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);
+}
+
+static int cgroup_write_event_control(struct cgroup *cont, 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 = cont;
+ 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_work);
+
+ 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(cont, event->cft,
+ event->eventfd, buffer);
+ if (ret)
+ goto fail;
+
+ efile->f_op->poll(efile, &event->pt);
+
+ mutex_lock(&cont->event_list_mutex);
+ list_add(&event->list, &cont->event_list);
+ mutex_unlock(&cont->event_list_mutex);
+
+ fput(cfile);
+ fput(efile);
+
+ return 0;
+
+fail:
+ if (!IS_ERR(cfile))
+ fput(cfile);
+
+ if (event && event->eventfd && !IS_ERR(event->eventfd))
+ eventfd_ctx_put(event->eventfd);
+
+ if (!IS_ERR(efile))
+ fput(efile);
+
+ if (event)
+ kfree(event);
+
+ return ret;
+}
+
/*
* for the common functions, 'private' gives the type of file
*/
@@ -2814,6 +3022,11 @@ 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 = {
--
1.6.5.3
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