[PATCH -v1 06/11] fsnotify: generic notification queue and waitq

Eric Paris
2009-02-09T21:18:28Z

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>
---

fs/notify/fsnotify.h | 3 +
fs/notify/group.c | 9 ++
fs/notify/notification.c | 181 +++++++++++++++++++++++++++++++++++++-
include/linux/fsnotify_backend.h | 34 +++++++
4 files changed, 223 insertions(+), 4 deletions(-)

diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h
index bad4da9..6d6942c 100644
--- a/fs/notify/fsnotify.h
+++ b/fs/notify/fsnotify.h
@@ -15,8 +15,11 @@ extern struct srcu_struct fsnotify_grp_srcu_struct;
extern struct list_head fsnotify_groups;
extern __u64 fsnotify_mask;

+extern void fsnotify_flush_notif(struct fsnotify_group *group);
+
extern struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u64 mask, void *data, int data_is);

extern void fsnotify_clear_marks_by_group(struct fsnotify_group *group);
extern void fsnotify_clear_marks_by_inode(struct inode *inode, unsigned int flags);
+
#endif /* _LINUX_FSNOTIFY_PRIVATE_H */
diff --git a/fs/notify/group.c b/fs/notify/group.c
index bac7d8d..9168e81 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -91,6 +91,9 @@ void fsnotify_get_group(struct fsnotify_group *group)

static void fsnotify_destroy_group(struct fsnotify_group *group)
{
+ /* clear the notification queue of all events */
+ fsnotify_flush_notif(group);
+
/* clear all inode mark entries for this group */
fsnotify_clear_marks_by_group(group);

@@ -172,6 +175,12 @@ struct fsnotify_group *fsnotify_obtain_group(unsigned int priority, unsigned int
group->group_num = group_num;
group->mask = mask;

+ mutex_init(&group->notification_mutex);
+ INIT_LIST_HEAD(&group->notification_list);
+ init_waitqueue_head(&group->notification_waitq);
+ group->q_len = 0;
+ group->max_events = UINT_MAX;
+
spin_lock_init(&group->mark_lock);
INIT_LIST_HEAD(&group->mark_entries);

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index c893873..3884879 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -33,6 +33,14 @@
#include "fsnotify.h"

static struct kmem_cache *event_kmem_cache;
+static struct kmem_cache *event_holder_kmem_cache;
+static struct fsnotify_event q_overflow_event;
+
+/* return 1 if something is available, return 0 otherwise */
+int fsnotify_check_notif_queue(struct fsnotify_group *group)
+{
+ return !list_empty(&group->notification_list);
+}

void fsnotify_get_event(struct fsnotify_event *event)
{
@@ -58,6 +66,16 @@ void fsnotify_put_event(struct fsnotify_event *event)
}
}

+struct fsnotify_event_holder *alloc_event_holder(void)
+{
+ return kmem_cache_alloc(event_holder_kmem_cache, GFP_KERNEL);
+}
+
+void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder)
+{
+ kmem_cache_free(event_holder_kmem_cache, holder);
+}
+
struct fsnotify_event_private_data *fsnotify_get_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
{
struct fsnotify_event_private_data *lpriv;
@@ -72,14 +90,152 @@ struct fsnotify_event_private_data *fsnotify_get_priv_from_event(struct fsnotify
return priv;
}

-struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u64 mask, void *data, int data_is)
+static inline int event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
+{
+ if ((old->mask == new->mask) &&
+ (old->to_tell == new->to_tell) &&
+ (old->flag == new->flag)) {
+ if ((old->flag == FSNOTIFY_EVENT_INODE) &&
+ (old->inode == new->inode))
+ return 1;
+ else if ((old->flag == FSNOTIFY_EVENT_PATH) &&
+ (old->path.mnt == new->path.mnt) &&
+ (old->path.dentry == new->path.dentry))
+ return 1;
+ else if (old->flag == FSNOTIFY_EVENT_NONE)
+ return 1;
+ }
+ return 0;
+}
+
+/*
+ * we do NOT compare private data when determining if the last event in the
+ * notification queue is the same as this event someone is trying to add
+ */
+int fsnotify_add_notif_event(struct fsnotify_group *group, struct fsnotify_event *event, struct fsnotify_event_private_data *priv)
+{
+ struct fsnotify_event_holder *holder;
+ struct list_head *list = &group->notification_list;
+ struct fsnotify_event_holder *last_holder;
+ struct fsnotify_event *last_event;
+
+ /*
+ * holder locking
+ *
+ * only this task is going to be adding this event to lists, thus only
+ * this task can add the in event holder to a list.
+ *
+ * other tasks may be removing this event from some other group's
+ * notification_list.
+ *
+ * those other tasks will blank the in event holder list under
+ * the holder spinlock. If we see it blank we know that once we
+ * get that lock the in event holder will be ok for us to (re)use.
+ */
+ if (list_empty(&event->holder.event_list))
+ holder = (struct fsnotify_event_holder *)event;
+ else
+ holder = 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(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 != (struct fsnotify_event_holder *)event)
+ fsnotify_destroy_event_holder(holder);
+ return 0;
+ }
+ }
+
+ group->q_len++;
+ holder->event = event;
+
+ fsnotify_get_event(event);
+ list_add_tail(&holder->event_list, list);
+ if (priv)
+ list_add_tail(&priv->event_list, &event->private_data_list);
+ spin_unlock(&event->lock);
+ mutex_unlock(&group->notification_mutex);
+
+ wake_up(&group->notification_waitq);
+ return 0;
+}
+
+/*
+ * must be called with group->notification_mutex held and must know event is present.
+ * it is the responsibility of the caller to call put_event() on the returned
+ * structure
+ */
+struct fsnotify_event *fsnotify_remove_notif_event(struct fsnotify_group *group)
{
struct fsnotify_event *event;
+ struct fsnotify_event_holder *holder;

- event = kmem_cache_alloc(event_kmem_cache, GFP_KERNEL);
- if (!event)
- return NULL;
+ 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 (event != (struct fsnotify_event *)holder)
+ fsnotify_destroy_event_holder(holder);
+
+ group->q_len--;
+
+ return event;
+}
+
+/*
+ * caller must hold group->notification_mutex and must know event is present.
+ * this will not remove the event, that must be done with fsnotify_remove_notif_event()
+ */
+struct fsnotify_event *fsnotify_peek_notif_event(struct fsnotify_group *group)
+{
+ struct fsnotify_event *event;
+ struct fsnotify_event_holder *holder;
+
+ holder = list_first_entry(&group->notification_list, struct fsnotify_event_holder, event_list);
+ event = holder->event;

+ return event;
+}
+
+void fsnotify_flush_notif(struct fsnotify_group *group)
+{
+ struct fsnotify_event *event;
+
+ /* do I really need the mutex here? I think the group is now safe to
+ * play with lockless... */
+ mutex_lock(&group->notification_mutex);
+ while (fsnotify_check_notif_queue(group)) {
+ event = fsnotify_remove_notif_event(group);
+ if (group->ops->free_event_priv)
+ group->ops->free_event_priv(group, event);
+ fsnotify_put_event(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);
@@ -87,9 +243,22 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u64 mask,
event->path.dentry = NULL;
event->path.mnt = NULL;
event->inode = NULL;
+ event->flag = FSNOTIFY_EVENT_NONE;

INIT_LIST_HEAD(&event->private_data_list);

+ event->to_tell = NULL;
+}
+
+struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u64 mask, void *data, int data_is)
+{
+ struct fsnotify_event *event;
+
+ event = kmem_cache_alloc(event_kmem_cache, GFP_KERNEL);
+ if (!event)
+ return NULL;
+
+ initialize_event(event);
event->to_tell = to_tell;

switch (data_is) {
@@ -126,6 +295,10 @@ struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u64 mask,
__init int fsnotify_notification_init(void)
{
event_kmem_cache = kmem_cache_create("fsnotify_event", sizeof(struct fsnotify_event), 0, SLAB_PANIC, NULL);
+ event_holder_kmem_cache = kmem_cache_create("fsnotify_event_holder", sizeof(struct fsnotify_event_holder), 0, SLAB_PANIC, NULL);
+
+ initialize_event(&q_overflow_event);
+ q_overflow_event.mask = FS_Q_OVERFLOW;

return 0;
}
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 2bada0f..6223efa 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -69,6 +69,7 @@
FS_DELETE)

/* when calling fsnotify tell it if the data is a path or inode */
+#define FSNOTIFY_EVENT_NONE 0
#define FSNOTIFY_EVENT_PATH 1
#define FSNOTIFY_EVENT_INODE 2
#define FSNOTIFY_EVENT_FILE 3
@@ -101,6 +102,13 @@ struct fsnotify_group {

const struct fsnotify_ops *ops; /* how this group handles things */

+ /* needed to send notification to userspace */
+ struct mutex notification_mutex; /* protect the notification_list */
+ struct list_head notification_list; /* list of event_holder this group needs to send to userspace */
+ wait_queue_head_t notification_waitq; /* read() on the notification file blocks on this waitq */
+ unsigned int q_len; /* events on the queue */
+ unsigned int max_events; /* maximum events allowed on the list */
+
/* stores all fastapth entries assoc with this group so they can be cleaned on unregister */
spinlock_t mark_lock; /* protect mark_entries list */
struct list_head mark_entries; /* all inode mark entries for this group */
@@ -113,6 +121,21 @@ struct fsnotify_group {
};
};

+/*
+ * A single event can be queued in multiple group->notification_lists.
+ *
+ * each group->notification_list will point to an event_holder which in turns points
+ * to the actual event that needs to be sent to userspace.
+ *
+ * Seemed cheaper to create a refcnt'd event and a small holder for every group
+ * than create a different event for every group
+ *
+ */
+struct fsnotify_event_holder {
+ struct fsnotify_event *event;
+ struct list_head event_list;
+};
+
struct fsnotify_event_private_data {
struct fsnotify_group *group;
struct list_head event_list;
@@ -125,6 +148,12 @@ struct fsnotify_event_private_data {
* listener this structure is where you need to be adding fields.
*/
struct fsnotify_event {
+ /*
+ * If we create an event we are also likely going to need a holder
+ * to link to a group. So embed one holder in the event. Means only
+ * one allocation for the common case where we only have one group
+ */
+ struct fsnotify_event_holder holder;
spinlock_t lock; /* protection for the associated event_holder and private_list */
struct inode *to_tell;
/*
@@ -183,6 +212,11 @@ extern void fsnotify_get_event(struct fsnotify_event *event);
extern void fsnotify_put_event(struct fsnotify_event *event);
extern struct fsnotify_event_private_data *fsnotify_get_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event);

+extern int fsnotify_add_notif_event(struct fsnotify_group *group, struct fsnotify_event *event, struct fsnotify_event_private_data *priv);
+extern int fsnotify_check_notif_queue(struct fsnotify_group *group);
+extern struct fsnotify_event *fsnotify_peek_notif_event(struct fsnotify_group *group);
+extern struct fsnotify_event *fsnotify_remove_notif_event(struct fsnotify_group *group);
+
extern void fsnotify_recalc_inode_mask(struct inode *inode);
extern void fsnotify_init_mark(struct fsnotify_mark_entry *entry, struct fsnotify_group *group, struct inode *inode, __u64 mask);
extern struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group, struct inode *inode);