fsnotify: generic notification queue and waitq
inotify needs to do asyc notification in which event information is stored on a queue until the listener is ready to receive it. This patch implements a generic notification queue for inotify (and later fanotify) to store events to be sent at a later time. Signed-off-by: Eric Paris <eparis@redhat.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Eric Paris
parent
3c5119c05d
commit
a2d8bc6cb4
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@ -13,8 +13,12 @@ extern struct list_head fsnotify_groups;
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/* all bitwise OR of all event types (FS_*) for all fsnotify_groups */
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extern __u32 fsnotify_mask;
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/* destroy all events sitting in this groups notification queue */
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extern void fsnotify_flush_notify(struct fsnotify_group *group);
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/* final kfree of a group */
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extern void fsnotify_final_destroy_group(struct fsnotify_group *group);
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/* run the list of all marks associated with inode and flag them to be freed */
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extern void fsnotify_clear_marks_by_inode(struct inode *inode);
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/*
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@ -22,4 +26,9 @@ extern void fsnotify_clear_marks_by_inode(struct inode *inode);
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* about events that happen to its children.
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*/
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extern void __fsnotify_update_child_dentry_flags(struct inode *inode);
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/* allocate and destroy and event holder to attach events to notification/access queues */
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extern struct fsnotify_event_holder *fsnotify_alloc_event_holder(void);
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extern void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder);
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#endif /* __FS_NOTIFY_FSNOTIFY_H_ */
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@ -91,6 +91,9 @@ static void fsnotify_get_group(struct fsnotify_group *group)
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*/
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void fsnotify_final_destroy_group(struct fsnotify_group *group)
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{
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/* clear the notification queue of all events */
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fsnotify_flush_notify(group);
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if (group->ops->free_group_priv)
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group->ops->free_group_priv(group);
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@ -214,6 +217,12 @@ struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u32 mask,
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group->group_num = group_num;
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group->mask = mask;
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mutex_init(&group->notification_mutex);
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INIT_LIST_HEAD(&group->notification_list);
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init_waitqueue_head(&group->notification_waitq);
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group->q_len = 0;
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group->max_events = UINT_MAX;
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spin_lock_init(&group->mark_lock);
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atomic_set(&group->num_marks, 0);
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INIT_LIST_HEAD(&group->mark_entries);
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@ -16,6 +16,21 @@
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* Basic idea behind the notification queue: An fsnotify group (like inotify)
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* sends the userspace notification about events asyncronously some time after
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* the event happened. When inotify gets an event it will need to add that
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* event to the group notify queue. Since a single event might need to be on
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* multiple group's notification queues we can't add the event directly to each
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* queue and instead add a small "event_holder" to each queue. This event_holder
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* has a pointer back to the original event. Since the majority of events are
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* going to end up on one, and only one, notification queue we embed one
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* event_holder into each event. This means we have a single allocation instead
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* of always needing two. If the embedded event_holder is already in use by
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* another group a new event_holder (from fsnotify_event_holder_cachep) will be
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* allocated and used.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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@ -33,6 +48,21 @@
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#include "fsnotify.h"
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static struct kmem_cache *fsnotify_event_cachep;
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static struct kmem_cache *fsnotify_event_holder_cachep;
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/*
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* This is a magic event we send when the q is too full. Since it doesn't
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* hold real event information we just keep one system wide and use it any time
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* it is needed. It's refcnt is set 1 at kernel init time and will never
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* get set to 0 so it will never get 'freed'
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*/
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static struct fsnotify_event q_overflow_event;
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/* return true if the notify queue is empty, false otherwise */
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bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
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{
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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return list_empty(&group->notification_list) ? true : false;
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}
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void fsnotify_get_event(struct fsnotify_event *event)
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{
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@ -52,9 +82,198 @@ void fsnotify_put_event(struct fsnotify_event *event)
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}
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}
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struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
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{
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return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
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}
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void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
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{
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kmem_cache_free(fsnotify_event_holder_cachep, holder);
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}
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/*
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* Allocate a new event which will be sent to each group's handle_event function
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* if the group was interested in this particular event.
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* check if 2 events contain the same information.
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*/
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static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
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{
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if ((old->mask == new->mask) &&
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(old->to_tell == new->to_tell) &&
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(old->data_type == new->data_type)) {
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switch (old->data_type) {
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case (FSNOTIFY_EVENT_INODE):
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if (old->inode == new->inode)
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return true;
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break;
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case (FSNOTIFY_EVENT_PATH):
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if ((old->path.mnt == new->path.mnt) &&
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(old->path.dentry == new->path.dentry))
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return true;
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case (FSNOTIFY_EVENT_NONE):
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return true;
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};
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}
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return false;
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}
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/*
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* Add an event to the group notification queue. The group can later pull this
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* event off the queue to deal with. If the event is successfully added to the
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* group's notification queue, a reference is taken on event.
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*/
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int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event)
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{
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struct fsnotify_event_holder *holder = NULL;
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struct list_head *list = &group->notification_list;
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struct fsnotify_event_holder *last_holder;
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struct fsnotify_event *last_event;
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/*
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* There is one fsnotify_event_holder embedded inside each fsnotify_event.
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* Check if we expect to be able to use that holder. If not alloc a new
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* holder.
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* For the overflow event it's possible that something will use the in
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* event holder before we get the lock so we may need to jump back and
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* alloc a new holder, this can't happen for most events...
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*/
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if (!list_empty(&event->holder.event_list)) {
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alloc_holder:
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holder = fsnotify_alloc_event_holder();
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if (!holder)
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return -ENOMEM;
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}
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mutex_lock(&group->notification_mutex);
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if (group->q_len >= group->max_events)
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event = &q_overflow_event;
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spin_lock(&event->lock);
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if (list_empty(&event->holder.event_list)) {
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if (unlikely(holder))
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fsnotify_destroy_event_holder(holder);
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holder = &event->holder;
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} else if (unlikely(!holder)) {
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/* between the time we checked above and got the lock the in
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* event holder was used, go back and get a new one */
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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goto alloc_holder;
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}
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if (!list_empty(list)) {
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last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
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last_event = last_holder->event;
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if (event_compare(last_event, event)) {
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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if (holder != &event->holder)
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fsnotify_destroy_event_holder(holder);
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return 0;
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}
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}
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group->q_len++;
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holder->event = event;
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fsnotify_get_event(event);
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list_add_tail(&holder->event_list, list);
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spin_unlock(&event->lock);
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mutex_unlock(&group->notification_mutex);
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wake_up(&group->notification_waitq);
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return 0;
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}
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/*
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* Remove and return the first event from the notification list. There is a
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* reference held on this event since it was on the list. It is the responsibility
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* of the caller to drop this reference.
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*/
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struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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struct fsnotify_event_holder *holder;
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
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event = holder->event;
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spin_lock(&event->lock);
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holder->event = NULL;
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list_del_init(&holder->event_list);
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spin_unlock(&event->lock);
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/* event == holder means we are referenced through the in event holder */
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if (holder != &event->holder)
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fsnotify_destroy_event_holder(holder);
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group->q_len--;
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return event;
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}
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/*
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* This will not remove the event, that must be done with fsnotify_remove_notify_event()
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*/
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struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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struct fsnotify_event_holder *holder;
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BUG_ON(!mutex_is_locked(&group->notification_mutex));
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holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
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event = holder->event;
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return event;
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}
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/*
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* Called when a group is being torn down to clean up any outstanding
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* event notifications.
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*/
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void fsnotify_flush_notify(struct fsnotify_group *group)
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{
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struct fsnotify_event *event;
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mutex_lock(&group->notification_mutex);
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while (!fsnotify_notify_queue_is_empty(group)) {
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event = fsnotify_remove_notify_event(group);
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fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
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}
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mutex_unlock(&group->notification_mutex);
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}
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static void initialize_event(struct fsnotify_event *event)
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{
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event->holder.event = NULL;
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INIT_LIST_HEAD(&event->holder.event_list);
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atomic_set(&event->refcnt, 1);
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spin_lock_init(&event->lock);
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event->path.dentry = NULL;
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event->path.mnt = NULL;
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event->inode = NULL;
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event->data_type = FSNOTIFY_EVENT_NONE;
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event->to_tell = NULL;
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}
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/*
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* fsnotify_create_event - Allocate a new event which will be sent to each
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* group's handle_event function if the group was interested in this
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* particular event.
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*
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* @to_tell the inode which is supposed to receive the event (sometimes a
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* parent of the inode to which the event happened.
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* @mask what actually happened.
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* @data pointer to the object which was actually affected
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* @data_type flag indication if the data is a file, path, inode, nothing...
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*/
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struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
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void *data, int data_type)
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@ -65,14 +284,7 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
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if (!event)
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return NULL;
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atomic_set(&event->refcnt, 1);
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spin_lock_init(&event->lock);
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event->path.dentry = NULL;
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event->path.mnt = NULL;
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event->inode = NULL;
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initialize_event(event);
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event->to_tell = to_tell;
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switch (data_type) {
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@ -114,6 +326,10 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
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__init int fsnotify_notification_init(void)
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{
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fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
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fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
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initialize_event(&q_overflow_event);
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q_overflow_event.mask = FS_Q_OVERFLOW;
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return 0;
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}
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@ -119,6 +119,13 @@ struct fsnotify_group {
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const struct fsnotify_ops *ops; /* how this group handles things */
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/* needed to send notification to userspace */
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struct mutex notification_mutex; /* protect the notification_list */
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struct list_head notification_list; /* list of event_holder this group needs to send to userspace */
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wait_queue_head_t notification_waitq; /* read() on the notification file blocks on this waitq */
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unsigned int q_len; /* events on the queue */
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unsigned int max_events; /* maximum events allowed on the list */
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/* stores all fastapth entries assoc with this group so they can be cleaned on unregister */
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spinlock_t mark_lock; /* protect mark_entries list */
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atomic_t num_marks; /* 1 for each mark entry and 1 for not being
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@ -135,12 +142,33 @@ struct fsnotify_group {
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};
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};
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/*
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* A single event can be queued in multiple group->notification_lists.
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*
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* each group->notification_list will point to an event_holder which in turns points
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* to the actual event that needs to be sent to userspace.
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*
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* Seemed cheaper to create a refcnt'd event and a small holder for every group
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* than create a different event for every group
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*
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*/
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struct fsnotify_event_holder {
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struct fsnotify_event *event;
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struct list_head event_list;
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};
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/*
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* all of the information about the original object we want to now send to
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* a group. If you want to carry more info from the accessing task to the
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* listener this structure is where you need to be adding fields.
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*/
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struct fsnotify_event {
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/*
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* If we create an event we are also likely going to need a holder
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* to link to a group. So embed one holder in the event. Means only
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* one allocation for the common case where we only have one group
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*/
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struct fsnotify_event_holder holder;
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spinlock_t lock; /* protection for the associated event_holder and private_list */
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/* to_tell may ONLY be dereferenced during handle_event(). */
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struct inode *to_tell; /* either the inode the event happened to or its parent */
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@ -264,6 +292,15 @@ extern void fsnotify_put_event(struct fsnotify_event *event);
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extern struct fsnotify_event_private_data *fsnotify_get_priv_from_event(struct fsnotify_group *group,
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struct fsnotify_event *event);
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/* attach the event to the group notification queue */
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extern int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event);
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/* true if the group notification queue is empty */
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extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
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/* return, but do not dequeue the first event on the notification queue */
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extern struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group);
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/* reutnr AND dequeue the first event on the notification queue */
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extern struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group);
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/* functions used to manipulate the marks attached to inodes */
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/* run all marks associated with an inode and update inode->i_fsnotify_mask */
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