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authorEric Paris <eparis@redhat.com>2009-05-21 17:01:37 -0400
committerEric Paris <eparis@redhat.com>2009-06-11 14:57:53 -0400
commita2d8bc6cb4a3024661baf877242f123787d0c054 (patch)
tree4ff3f93877a8992d5383c14fb6012ab9b1954660 /fs/notify/notification.c
parent3c5119c05d624f95f4967d16b38c9624b816bdb9 (diff)
downloadlinux-linaro-stable-a2d8bc6cb4a3024661baf877242f123787d0c054.tar.gz
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>
Diffstat (limited to 'fs/notify/notification.c')
-rw-r--r--fs/notify/notification.c230
1 files changed, 223 insertions, 7 deletions
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index b8e9a87f8f58..dddecc74e63d 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -16,6 +16,21 @@
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
+/*
+ * Basic idea behind the notification queue: An fsnotify group (like inotify)
+ * sends the userspace notification about events asyncronously some time after
+ * the event happened. When inotify gets an event it will need to add that
+ * event to the group notify queue. Since a single event might need to be on
+ * multiple group's notification queues we can't add the event directly to each
+ * queue and instead add a small "event_holder" to each queue. This event_holder
+ * has a pointer back to the original event. Since the majority of events are
+ * going to end up on one, and only one, notification queue we embed one
+ * event_holder into each event. This means we have a single allocation instead
+ * of always needing two. If the embedded event_holder is already in use by
+ * another group a new event_holder (from fsnotify_event_holder_cachep) will be
+ * allocated and used.
+ */
+
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -33,6 +48,21 @@
#include "fsnotify.h"
static struct kmem_cache *fsnotify_event_cachep;
+static struct kmem_cache *fsnotify_event_holder_cachep;
+/*
+ * This is a magic event we send when the q is too full. Since it doesn't
+ * hold real event information we just keep one system wide and use it any time
+ * it is needed. It's refcnt is set 1 at kernel init time and will never
+ * get set to 0 so it will never get 'freed'
+ */
+static struct fsnotify_event q_overflow_event;
+
+/* return true if the notify queue is empty, false otherwise */
+bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
+{
+ BUG_ON(!mutex_is_locked(&group->notification_mutex));
+ return list_empty(&group->notification_list) ? true : false;
+}
void fsnotify_get_event(struct fsnotify_event *event)
{
@@ -52,19 +82,176 @@ void fsnotify_put_event(struct fsnotify_event *event)
}
}
+struct fsnotify_event_holder *fsnotify_alloc_event_holder(void)
+{
+ return kmem_cache_alloc(fsnotify_event_holder_cachep, GFP_KERNEL);
+}
+
+void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
+{
+ kmem_cache_free(fsnotify_event_holder_cachep, holder);
+}
+
+/*
+ * check if 2 events contain the same information.
+ */
+static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
+{
+ if ((old->mask == new->mask) &&
+ (old->to_tell == new->to_tell) &&
+ (old->data_type == new->data_type)) {
+ switch (old->data_type) {
+ case (FSNOTIFY_EVENT_INODE):
+ if (old->inode == new->inode)
+ return true;
+ break;
+ case (FSNOTIFY_EVENT_PATH):
+ if ((old->path.mnt == new->path.mnt) &&
+ (old->path.dentry == new->path.dentry))
+ return true;
+ case (FSNOTIFY_EVENT_NONE):
+ return true;
+ };
+ }
+ return false;
+}
+
/*
- * Allocate a new event which will be sent to each group's handle_event function
- * if the group was interested in this particular event.
+ * Add an event to the group notification queue. The group can later pull this
+ * event off the queue to deal with. If the event is successfully added to the
+ * group's notification queue, a reference is taken on event.
*/
-struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
- void *data, int data_type)
+int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event)
+{
+ struct fsnotify_event_holder *holder = NULL;
+ struct list_head *list = &group->notification_list;
+ struct fsnotify_event_holder *last_holder;
+ struct fsnotify_event *last_event;
+
+ /*
+ * There is one fsnotify_event_holder embedded inside each fsnotify_event.
+ * Check if we expect to be able to use that holder. If not alloc a new
+ * holder.
+ * For the overflow event it's possible that something will use the in
+ * event holder before we get the lock so we may need to jump back and
+ * alloc a new holder, this can't happen for most events...
+ */
+ if (!list_empty(&event->holder.event_list)) {
+alloc_holder:
+ holder = fsnotify_alloc_event_holder();
+ if (!holder)
+ return -ENOMEM;
+ }
+
+ mutex_lock(&group->notification_mutex);
+
+ if (group->q_len >= group->max_events)
+ event = &q_overflow_event;
+
+ spin_lock(&event->lock);
+
+ if (list_empty(&event->holder.event_list)) {
+ if (unlikely(holder))
+ fsnotify_destroy_event_holder(holder);
+ holder = &event->holder;
+ } else if (unlikely(!holder)) {
+ /* between the time we checked above and got the lock the in
+ * event holder was used, go back and get a new one */
+ spin_unlock(&event->lock);
+ mutex_unlock(&group->notification_mutex);
+ goto alloc_holder;
+ }
+
+ if (!list_empty(list)) {
+ last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
+ last_event = last_holder->event;
+ if (event_compare(last_event, event)) {
+ spin_unlock(&event->lock);
+ mutex_unlock(&group->notification_mutex);
+ if (holder != &event->holder)
+ fsnotify_destroy_event_holder(holder);
+ return 0;
+ }
+ }
+
+ group->q_len++;
+ holder->event = event;
+
+ fsnotify_get_event(event);
+ list_add_tail(&holder->event_list, list);
+ spin_unlock(&event->lock);
+ mutex_unlock(&group->notification_mutex);
+
+ wake_up(&group->notification_waitq);
+ return 0;
+}
+
+/*
+ * Remove and return the first event from the notification list. There is a
+ * reference held on this event since it was on the list. It is the responsibility
+ * of the caller to drop this reference.
+ */
+struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
+ struct fsnotify_event_holder *holder;
- event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
- if (!event)
- return NULL;
+ BUG_ON(!mutex_is_locked(&group->notification_mutex));
+ holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
+
+ event = holder->event;
+
+ spin_lock(&event->lock);
+ holder->event = NULL;
+ list_del_init(&holder->event_list);
+ spin_unlock(&event->lock);
+
+ /* event == holder means we are referenced through the in event holder */
+ if (holder != &event->holder)
+ fsnotify_destroy_event_holder(holder);
+
+ group->q_len--;
+
+ return event;
+}
+
+/*
+ * This will not remove the event, that must be done with fsnotify_remove_notify_event()
+ */
+struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group)
+{
+ struct fsnotify_event *event;
+ struct fsnotify_event_holder *holder;
+
+ BUG_ON(!mutex_is_locked(&group->notification_mutex));
+
+ holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
+ event = holder->event;
+
+ return event;
+}
+
+/*
+ * Called when a group is being torn down to clean up any outstanding
+ * event notifications.
+ */
+void fsnotify_flush_notify(struct fsnotify_group *group)
+{
+ struct fsnotify_event *event;
+
+ mutex_lock(&group->notification_mutex);
+ while (!fsnotify_notify_queue_is_empty(group)) {
+ event = fsnotify_remove_notify_event(group);
+ fsnotify_put_event(event); /* matches fsnotify_add_notify_event */
+ }
+ mutex_unlock(&group->notification_mutex);
+}
+
+static void initialize_event(struct fsnotify_event *event)
+{
+ event->holder.event = NULL;
+ INIT_LIST_HEAD(&event->holder.event_list);
atomic_set(&event->refcnt, 1);
spin_lock_init(&event->lock);
@@ -72,7 +259,32 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
event->path.dentry = NULL;
event->path.mnt = NULL;
event->inode = NULL;
+ event->data_type = FSNOTIFY_EVENT_NONE;
+ event->to_tell = NULL;
+}
+
+/*
+ * fsnotify_create_event - Allocate a new event which will be sent to each
+ * group's handle_event function if the group was interested in this
+ * particular event.
+ *
+ * @to_tell the inode which is supposed to receive the event (sometimes a
+ * parent of the inode to which the event happened.
+ * @mask what actually happened.
+ * @data pointer to the object which was actually affected
+ * @data_type flag indication if the data is a file, path, inode, nothing...
+ */
+struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
+ void *data, int data_type)
+{
+ struct fsnotify_event *event;
+
+ event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
+ if (!event)
+ return NULL;
+
+ initialize_event(event);
event->to_tell = to_tell;
switch (data_type) {
@@ -114,6 +326,10 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
__init int fsnotify_notification_init(void)
{
fsnotify_event_cachep = KMEM_CACHE(fsnotify_event, SLAB_PANIC);
+ fsnotify_event_holder_cachep = KMEM_CACHE(fsnotify_event_holder, SLAB_PANIC);
+
+ initialize_event(&q_overflow_event);
+ q_overflow_event.mask = FS_Q_OVERFLOW;
return 0;
}