1 files changed, 411 insertions, 0 deletions

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
new file mode 100644
index 000000000000..959b73e756fd
--- /dev/null
+++ b/fs/notify/notification.c
@@ -0,0 +1,411 @@
+/*
+ *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2, or (at your option)
+ *  any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; see the file COPYING.  If not, write to
+ *  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>
+#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 <asm/atomic.h>
+
+#include <linux/fsnotify_backend.h>
+#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;
+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)
+{
+        BUG_ON(!mutex_is_locked(&group->notification_mutex));
+        return list_empty(&group->notification_list) ? true : false;
+}
+
+void fsnotify_get_event(struct fsnotify_event *event)
+{
+        atomic_inc(&event->refcnt);
+}
+
+void fsnotify_put_event(struct fsnotify_event *event)
+{
+        if (!event)
+                return;
+
+        if (atomic_dec_and_test(&event->refcnt)) {
+                if (event->data_type == FSNOTIFY_EVENT_PATH)
+                        path_put(&event->path);
+
+                BUG_ON(!list_empty(&event->private_data_list));
+
+                kfree(event->file_name);
+                kmem_cache_free(fsnotify_event_cachep, 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);
+}
+
+/*
+ * Find the private data that the group previously attached to this event when
+ * the group added the event to the notification queue (fsnotify_add_notify_event)
+ */
+struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group, struct fsnotify_event *event)
+{
+        struct fsnotify_event_private_data *lpriv;
+        struct fsnotify_event_private_data *priv = NULL;
+
+        assert_spin_locked(&event->lock);
+
+        list_for_each_entry(lpriv, &event->private_data_list, event_list) {
+                if (lpriv->group == group) {
+                        priv = lpriv;
+                        list_del(&priv->event_list);
+                        break;
+                }
+        }
+        return priv;
+}
+
+/*
+ * Check if 2 events contain the same information.  We do not compare private data
+ * but at this moment that isn't a problem for any know fsnotify listeners.
+ */
+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;
+}
+
+/*
+ * 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.
+ */
+int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
+                              struct fsnotify_event_private_data *priv)
+{
+        struct fsnotify_event_holder *holder = NULL;
+        struct list_head *list = &group->notification_list;
+        struct fsnotify_event_holder *last_holder;
+        struct fsnotify_event *last_event;
+
+        /* easy to tell if priv was attached to the event */
+        INIT_LIST_HEAD(&priv->event_list);
+
+        /*
+         * 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;
+                /* sorry, no private data on the overflow event */
+                priv = NULL;
+        }
+
+        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 -EEXIST;
+                }
+        }
+
+        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;
+}
+
+/*
+ * 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;
+
+        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;
+        struct fsnotify_event_private_data *priv;
+
+        mutex_lock(&group->notification_mutex);
+        while (!fsnotify_notify_queue_is_empty(group)) {
+                event = fsnotify_remove_notify_event(group);
+                /* if they don't implement free_event_priv they better not have attached any */
+                if (group->ops->free_event_priv) {
+                        spin_lock(&event->lock);
+                        priv = fsnotify_remove_priv_from_event(group, event);
+                        spin_unlock(&event->lock);
+                        if (priv)
+                                group->ops->free_event_priv(priv);
+                }
+                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);
+
+        event->path.dentry = NULL;
+        event->path.mnt = NULL;
+        event->inode = NULL;
+        event->data_type = FSNOTIFY_EVENT_NONE;
+
+        INIT_LIST_HEAD(&event->private_data_list);
+
+        event->to_tell = NULL;
+
+        event->file_name = NULL;
+        event->name_len = 0;
+
+        event->sync_cookie = 0;
+}
+
+/*
+ * 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...
+ * @name the filename, if available
+ */
+struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask, void *data,
+                                             int data_type, const char *name, u32 cookie)
+{
+        struct fsnotify_event *event;
+
+        event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
+        if (!event)
+                return NULL;
+
+        initialize_event(event);
+
+        if (name) {
+                event->file_name = kstrdup(name, GFP_KERNEL);
+                if (!event->file_name) {
+                        kmem_cache_free(fsnotify_event_cachep, event);
+                        return NULL;
+                }
+                event->name_len = strlen(event->file_name);
+        }
+
+        event->sync_cookie = cookie;
+        event->to_tell = to_tell;
+
+        switch (data_type) {
+        case FSNOTIFY_EVENT_FILE: {
+                struct file *file = data;
+                struct path *path = &file->f_path;
+                event->path.dentry = path->dentry;
+                event->path.mnt = path->mnt;
+                path_get(&event->path);
+                event->data_type = FSNOTIFY_EVENT_PATH;
+                break;
+        }
+        case FSNOTIFY_EVENT_PATH: {
+                struct path *path = data;
+                event->path.dentry = path->dentry;
+                event->path.mnt = path->mnt;
+                path_get(&event->path);
+                event->data_type = FSNOTIFY_EVENT_PATH;
+                break;
+        }
+        case FSNOTIFY_EVENT_INODE:
+                event->inode = data;
+                event->data_type = FSNOTIFY_EVENT_INODE;
+                break;
+        case FSNOTIFY_EVENT_NONE:
+                event->inode = NULL;
+                event->path.dentry = NULL;
+                event->path.mnt = NULL;
+                break;
+        default:
+                BUG();
+        }
+
+        event->mask = mask;
+
+        return event;
+}
+
+__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;
+}
+subsys_initcall(fsnotify_notification_init);
+