summaryrefslogtreecommitdiffstats
path: root/fs/notify/notification.c
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--fs/notify/notification.c189
1 files changed, 189 insertions, 0 deletions
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
new file mode 100644
index 000000000..75d79d6d3
--- /dev/null
+++ b/fs/notify/notification.c
@@ -0,0 +1,189 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
+ */
+
+/*
+ * Basic idea behind the notification queue: An fsnotify group (like inotify)
+ * sends the userspace notification about events asynchronously 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>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mount.h>
+#include <linux/mutex.h>
+#include <linux/namei.h>
+#include <linux/path.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+
+#include <linux/atomic.h>
+
+#include <linux/fsnotify_backend.h>
+#include "fsnotify.h"
+
+static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
+
+/**
+ * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
+ * Called from fsnotify_move, which is inlined into filesystem modules.
+ */
+u32 fsnotify_get_cookie(void)
+{
+ return atomic_inc_return(&fsnotify_sync_cookie);
+}
+EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
+
+/* return true if the notify queue is empty, false otherwise */
+bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
+{
+ assert_spin_locked(&group->notification_lock);
+ return list_empty(&group->notification_list) ? true : false;
+}
+
+void fsnotify_destroy_event(struct fsnotify_group *group,
+ struct fsnotify_event *event)
+{
+ /* Overflow events are per-group and we don't want to free them */
+ if (!event || event == group->overflow_event)
+ return;
+ /*
+ * If the event is still queued, we have a problem... Do an unreliable
+ * lockless check first to avoid locking in the common case. The
+ * locking may be necessary for permission events which got removed
+ * from the list by a different CPU than the one freeing the event.
+ */
+ if (!list_empty(&event->list)) {
+ spin_lock(&group->notification_lock);
+ WARN_ON(!list_empty(&event->list));
+ spin_unlock(&group->notification_lock);
+ }
+ group->ops->free_event(event);
+}
+
+/*
+ * Add an event to the group notification queue. The group can later pull this
+ * event off the queue to deal with. The function returns 0 if the event was
+ * added to the queue, 1 if the event was merged with some other queued event,
+ * 2 if the event was not queued - either the queue of events has overflown
+ * or the group is shutting down.
+ */
+int fsnotify_add_event(struct fsnotify_group *group,
+ struct fsnotify_event *event,
+ int (*merge)(struct list_head *,
+ struct fsnotify_event *))
+{
+ int ret = 0;
+ struct list_head *list = &group->notification_list;
+
+ pr_debug("%s: group=%p event=%p\n", __func__, group, event);
+
+ spin_lock(&group->notification_lock);
+
+ if (group->shutdown) {
+ spin_unlock(&group->notification_lock);
+ return 2;
+ }
+
+ if (event == group->overflow_event ||
+ group->q_len >= group->max_events) {
+ ret = 2;
+ /* Queue overflow event only if it isn't already queued */
+ if (!list_empty(&group->overflow_event->list)) {
+ spin_unlock(&group->notification_lock);
+ return ret;
+ }
+ event = group->overflow_event;
+ goto queue;
+ }
+
+ if (!list_empty(list) && merge) {
+ ret = merge(list, event);
+ if (ret) {
+ spin_unlock(&group->notification_lock);
+ return ret;
+ }
+ }
+
+queue:
+ group->q_len++;
+ list_add_tail(&event->list, list);
+ spin_unlock(&group->notification_lock);
+
+ wake_up(&group->notification_waitq);
+ kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
+ return ret;
+}
+
+void fsnotify_remove_queued_event(struct fsnotify_group *group,
+ struct fsnotify_event *event)
+{
+ assert_spin_locked(&group->notification_lock);
+ /*
+ * We need to init list head for the case of overflow event so that
+ * check in fsnotify_add_event() works
+ */
+ list_del_init(&event->list);
+ group->q_len--;
+}
+
+/*
+ * Remove and return the first event from the notification list. It is the
+ * responsibility of the caller to destroy the obtained event
+ */
+struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
+{
+ struct fsnotify_event *event;
+
+ assert_spin_locked(&group->notification_lock);
+
+ pr_debug("%s: group=%p\n", __func__, group);
+
+ event = list_first_entry(&group->notification_list,
+ struct fsnotify_event, list);
+ fsnotify_remove_queued_event(group, event);
+ return event;
+}
+
+/*
+ * This will not remove the event, that must be done with
+ * fsnotify_remove_first_event()
+ */
+struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
+{
+ assert_spin_locked(&group->notification_lock);
+
+ return list_first_entry(&group->notification_list,
+ struct fsnotify_event, list);
+}
+
+/*
+ * 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;
+
+ spin_lock(&group->notification_lock);
+ while (!fsnotify_notify_queue_is_empty(group)) {
+ event = fsnotify_remove_first_event(group);
+ spin_unlock(&group->notification_lock);
+ fsnotify_destroy_event(group, event);
+ spin_lock(&group->notification_lock);
+ }
+ spin_unlock(&group->notification_lock);
+}