Re: [PATCH RFC v2 1/4] cgroup: implement eventfd-based generic API for notifications

[Kirill A. Shutemov]

Could anybody review the patch?

Thank you.

On Sat, Dec 12, 2009 at 12:59 AM, Kirill A. Shutemov
<kirill@xxxxxxxxxxxxx> 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
> Âunregister_event() must be defined for the control file;
> - write "<event_fd> <control_fd> <args>" to cgroup.event_control.
> ÂInterpretation 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@xxxxxxxxxxxxx>
> ---
> Âinclude/linux/cgroup.h | Â 20 +++++
> Âkernel/cgroup.c    Â| Â215 +++++++++++++++++++++++++++++++++++++++++++++++-
> Â2 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 {
>
> Â Â Â Â/* For RCU-protected deletion */
> Â Â Â Âstruct rcu_head rcu_head;
> +
> + Â Â Â /* List of events which userspace want to recieve */
> + Â Â Â struct list_head event_list;
> + Â Â Â struct mutex event_list_mutex;
> Â};
>
> Â/*
> @@ -362,6 +366,22 @@ struct cftype {
> Â Â Â Âint (*trigger)(struct cgroup *cgrp, unsigned int event);
>
> Â Â Â Âint (*release)(struct inode *inode, struct file *file);
> +
> + Â Â Â /*
> + Â Â Â Â* register_event() callback will be used to add new userspace
> + Â Â Â Â* waiter for changes related to the cftype. Implement it if
> + Â Â Â Â* you want to provide this functionality. Use eventfd_signal()
> + Â Â Â Â* on eventfd to send notification to userspace.
> + Â Â Â Â*/
> + Â Â Â int (*register_event)(struct cgroup *cgrp, struct cftype *cft,
> + Â Â Â Â Â Â Â Â Â Â Â struct eventfd_ctx *eventfd, const char *args);
> + Â Â Â /*
> + Â Â Â Â* unregister_event() callback will be called when userspace
> + Â Â Â Â* close the eventfd. This callback must be implemented, if you
> + Â Â Â Â* provide register_event().
> + Â Â Â Â*/
> + Â Â Â int (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
> + Â Â Â Â Â Â Â Â Â Â Â struct eventfd_ctx *eventfd);
> Â};
>
> Âstruct 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 @@
> Â* ÂBased originally on the cpuset system, extracted by Paul Menage
> Â* ÂCopyright (C) 2006 Google, Inc
> Â*
> + * ÂNotifiactions support
> + * ÂCopyright (C) 2009 Nokia Corporation
> + * ÂAuthor: Kirill A. Shutemov
> + *
> Â* ÂCopyright notices from the original cpuset code:
> Â* Â--------------------------------------------------
> Â* ÂCopyright (C) 2003 BULL SA.
> @@ -51,6 +55,8 @@
> Â#include <linux/pid_namespace.h>
> Â#include <linux/idr.h>
> Â#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
> +#include <linux/eventfd.h>
> +#include <linux/poll.h>
>
> Â#include <asm/atomic.h>
>
> @@ -146,6 +152,36 @@ struct css_id {
> Â Â Â Âunsigned short stack[0]; /* Array of Length (depth+1) */
> Â};
>
> +/*
> + * cgroup_event represents event which userspace want to recieve.
> + */
> +struct cgroup_event {
> + Â Â Â /*
> + Â Â Â Â* Cgroup which the event belongs to.
> + Â Â Â Â*/
> + Â Â Â struct cgroup *cgrp;
> + Â Â Â /*
> + Â Â Â Â* Control file which the event associated.
> + Â Â Â Â*/
> + Â Â Â struct cftype *cft;
> + Â Â Â /*
> + Â Â Â Â* eventfd to signal userspace about the event.
> + Â Â Â Â*/
> + Â Â Â struct eventfd_ctx *eventfd;
> + Â Â Â /*
> + Â Â Â Â* Each of these stored in a list by the cgroup.
> + Â Â Â Â*/
> + Â Â Â struct list_head list;
> + Â Â Â /*
> + Â Â Â Â* All fields below needed to unregister event when
> + Â Â Â Â* userspace closes eventfd.
> + Â Â Â Â*/
> + Â Â Â poll_table pt;
> + Â Â Â wait_queue_head_t *wqh;
> + Â Â Â wait_queue_t wait;
> + Â Â Â struct work_struct remove;
> +};
> +static void cgroup_event_remove(struct cgroup_event *event);
>
> Â/* The list of hierarchy roots */
>
> @@ -734,14 +770,29 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
> Âstatic int cgroup_call_pre_destroy(struct cgroup *cgrp)
> Â{
> Â Â Â Âstruct cgroup_subsys *ss;
> + Â Â Â struct cgroup_event *event, *tmp;
> Â Â Â Âint ret = 0;
>
> Â Â Â Âfor_each_subsys(cgrp->root, ss)
> Â Â Â Â Â Â Â Âif (ss->pre_destroy) {
> Â Â Â Â Â Â Â Â Â Â Â Âret = ss->pre_destroy(ss, cgrp);
> Â Â Â Â Â Â Â Â Â Â Â Âif (ret)
> - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â break;
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â goto out;
> Â Â Â Â Â Â Â Â}
> +
> + Â Â Â /*
> + Â Â Â Â* Unregister events and notify userspace.
> + Â Â Â Â* FIXME: How to avoid race with cgroup_event_remove_work()
> + Â Â Â Â* Â Â Â Âwhich runs from workqueue?
> + Â Â Â Â*/
> + Â Â Â mutex_lock(&cgrp->event_list_mutex);
> + Â Â Â list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
> + Â Â Â Â Â Â Â cgroup_event_remove(event);
> + Â Â Â Â Â Â Â eventfd_signal(event->eventfd, 1);
> + Â Â Â }
> + Â Â Â mutex_unlock(&cgrp->event_list_mutex);
> +
> +out:
> Â Â Â Âreturn ret;
> Â}
>
> @@ -1136,6 +1187,8 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
> Â Â Â ÂINIT_LIST_HEAD(&cgrp->release_list);
> Â Â Â ÂINIT_LIST_HEAD(&cgrp->pidlists);
> Â Â Â Âmutex_init(&cgrp->pidlist_mutex);
> + Â Â Â INIT_LIST_HEAD(&cgrp->event_list);
> + Â Â Â mutex_init(&cgrp->event_list_mutex);
> Â}
>
> Âstatic void init_cgroup_root(struct cgroupfs_root *root)
> @@ -1935,6 +1988,16 @@ static const struct inode_operations cgroup_dir_inode_operations = {
> Â Â Â Â.rename = cgroup_rename,
> Â};
>
> +/*
> + * Check if a file is a control file
> + */
> +static inline struct cftype *__file_cft(struct file *file)
> +{
> + Â Â Â if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
> + Â Â Â Â Â Â Â return ERR_PTR(-EINVAL);
> + Â Â Â return __d_cft(file->f_dentry);
> +}
> +
> Âstatic int cgroup_create_file(struct dentry *dentry, mode_t mode,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âstruct super_block *sb)
> Â{
> @@ -2789,6 +2852,151 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp,
> Â Â Â Âreturn 0;
> Â}
>
> +static inline void cgroup_event_remove(struct cgroup_event *event)
> +{
> + Â Â Â struct cgroup *cgrp = event->cgrp;
> +
> + Â Â Â BUG_ON(event->cft->unregister_event(cgrp, event->cft, event->eventfd));
> + Â Â Â eventfd_ctx_put(event->eventfd);
> + Â Â Â remove_wait_queue(event->wqh, &event->wait);
> + Â Â Â list_del(&event->list);
> + Â Â Â kfree(event);
> +}
> +
> +static void cgroup_event_remove_work(struct work_struct *work)
> +{
> + Â Â Â struct cgroup_event *event = container_of(work, struct cgroup_event,
> + Â Â Â Â Â Â Â Â Â Â Â remove);
> + Â Â Â struct cgroup *cgrp = event->cgrp;
> +
> + Â Â Â mutex_lock(&cgrp->event_list_mutex);
> + Â Â Â cgroup_event_remove(event);
> + Â Â Â mutex_unlock(&cgrp->event_list_mutex);
> +}
> +
> +static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
> + Â Â Â Â Â Â Â int sync, void *key)
> +{
> + Â Â Â struct cgroup_event *event = container_of(wait,
> + Â Â Â Â Â Â Â Â Â Â Â struct cgroup_event, wait);
> + Â Â Â unsigned long flags = (unsigned long)key;
> +
> + Â Â Â if (flags & POLLHUP)
> + Â Â Â Â Â Â Â /*
> + Â Â Â Â Â Â Â Â* This function called with spinlock taken, but
> + Â Â Â Â Â Â Â Â* cgroup_event_remove() may sleep, so we have
> + Â Â Â Â Â Â Â Â* to run it in a workqueue.
> + Â Â Â Â Â Â Â Â*/
> + Â Â Â Â Â Â Â schedule_work(&event->remove);
> +
> + Â Â Â return 0;
> +}
> +
> +static void cgroup_event_ptable_queue_proc(struct file *file,
> + Â Â Â Â Â Â Â wait_queue_head_t *wqh, poll_table *pt)
> +{
> + Â Â Â struct cgroup_event *event = container_of(pt,
> + Â Â Â Â Â Â Â Â Â Â Â struct cgroup_event, pt);
> +
> + Â Â Â event->wqh = wqh;
> + Â Â Â add_wait_queue(wqh, &event->wait);
> +}
> +
> +static int cgroup_write_event_control(struct cgroup *cont, struct cftype *cft,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â const char *buffer)
> +{
> + Â Â Â struct cgroup_event *event = NULL;
> + Â Â Â unsigned int efd, cfd;
> + Â Â Â struct file *efile = NULL;
> + Â Â Â struct file *cfile = NULL;
> + Â Â Â char *endp;
> + Â Â Â int ret;
> +
> + Â Â Â efd = simple_strtoul(buffer, &endp, 10);
> + Â Â Â if (*endp != ' ')
> + Â Â Â Â Â Â Â return -EINVAL;
> + Â Â Â buffer = endp + 1;
> +
> + Â Â Â cfd = simple_strtoul(buffer, &endp, 10);
> + Â Â Â if ((*endp != ' ') && (*endp != '\0'))
> + Â Â Â Â Â Â Â return -EINVAL;
> + Â Â Â buffer = endp + 1;
> +
> + Â Â Â event = kzalloc(sizeof(*event), GFP_KERNEL);
> + Â Â Â if (!event)
> + Â Â Â Â Â Â Â return -ENOMEM;
> + Â Â Â event->cgrp = cont;
> + Â Â Â INIT_LIST_HEAD(&event->list);
> + Â Â Â init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
> + Â Â Â init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
> + Â Â Â INIT_WORK(&event->remove, cgroup_event_remove_work);
> +
> + Â Â Â efile = eventfd_fget(efd);
> + Â Â Â if (IS_ERR(efile)) {
> + Â Â Â Â Â Â Â ret = PTR_ERR(efile);
> + Â Â Â Â Â Â Â goto fail;
> + Â Â Â }
> +
> + Â Â Â event->eventfd = eventfd_ctx_fileget(efile);
> + Â Â Â if (IS_ERR(event->eventfd)) {
> + Â Â Â Â Â Â Â ret = PTR_ERR(event->eventfd);
> + Â Â Â Â Â Â Â goto fail;
> + Â Â Â }
> +
> + Â Â Â cfile = fget(cfd);
> + Â Â Â if (!cfile) {
> + Â Â Â Â Â Â Â ret = -EBADF;
> + Â Â Â Â Â Â Â goto fail;
> + Â Â Â }
> +
> + Â Â Â /* the process need read permission on control file */
> + Â Â Â ret = file_permission(cfile, MAY_READ);
> + Â Â Â if (ret < 0)
> + Â Â Â Â Â Â Â goto fail;
> +
> + Â Â Â event->cft = __file_cft(cfile);
> + Â Â Â if (IS_ERR(event->cft)) {
> + Â Â Â Â Â Â Â ret = PTR_ERR(event->cft);
> + Â Â Â Â Â Â Â goto fail;
> + Â Â Â }
> +
> + Â Â Â if (!event->cft->register_event || !event->cft->unregister_event) {
> + Â Â Â Â Â Â Â ret = -EINVAL;
> + Â Â Â Â Â Â Â goto fail;
> + Â Â Â }
> +
> + Â Â Â ret = event->cft->register_event(cont, event->cft,
> + Â Â Â Â Â Â Â Â Â Â Â event->eventfd, buffer);
> + Â Â Â if (ret)
> + Â Â Â Â Â Â Â goto fail;
> +
> + Â Â Â efile->f_op->poll(efile, &event->pt);
> +
> + Â Â Â mutex_lock(&cont->event_list_mutex);
> + Â Â Â list_add(&event->list, &cont->event_list);
> + Â Â Â mutex_unlock(&cont->event_list_mutex);
> +
> + Â Â Â fput(cfile);
> + Â Â Â fput(efile);
> +
> + Â Â Â return 0;
> +
> +fail:
> + Â Â Â if (!IS_ERR(cfile))
> + Â Â Â Â Â Â Â fput(cfile);
> +
> + Â Â Â if (event && event->eventfd && !IS_ERR(event->eventfd))
> + Â Â Â Â Â Â Â eventfd_ctx_put(event->eventfd);
> +
> + Â Â Â if (!IS_ERR(efile))
> + Â Â Â Â Â Â Â fput(efile);
> +
> + Â Â Â if (event)
> + Â Â Â Â Â Â Â kfree(event);
> +
> + Â Â Â return ret;
> +}
> +
> Â/*
> Â* for the common functions, 'private' gives the type of file
> Â*/
> @@ -2814,6 +3022,11 @@ static struct cftype files[] = {
> Â Â Â Â Â Â Â Â.read_u64 = cgroup_read_notify_on_release,
> Â Â Â Â Â Â Â Â.write_u64 = cgroup_write_notify_on_release,
> Â Â Â Â},
> + Â Â Â {
> + Â Â Â Â Â Â Â .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
> + Â Â Â Â Â Â Â .write_string = cgroup_write_event_control,
> + Â Â Â Â Â Â Â .mode = S_IWUGO,
> + Â Â Â },
> Â};
>
> Âstatic struct cftype cft_release_agent = {
> --
> 1.6.5.3
>
>
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