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From: Li Zefan on 15 Dec 2009 20:50
Kirill A. Shutemov wrote:
> 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(a)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

s/Notifiactions/Notifications

> + * 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.

s/event/events ?

> + */
> +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;
> +};

Please add a blank line here.

> +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);

How can you access event after you kfree()ed it in cgroup_event_remove()?

> + }
> + 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);

I don't think this check is needed.

> + 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

s/called/is called/ ?

> + * cgroup_event_remove() may sleep, so we have
> + * to run it in a workqueue.
> + */
> + schedule_work(&event->remove);

Please use:

if (...) {
...
}

> +
> + 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,

Please consistently use "cgrp"

> + 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);

kfree(NULL) is ok

> +
> + 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,

We want this file to be writable to everyone ?

> + },
> };
>
> static struct cftype cft_release_agent = {
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From: Li Zefan on 15 Dec 2009 21:10
>> +/*
>> + * 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);
>
> I don't think this check is needed.
>

Sorry, please ignore this comment
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