/*
 *  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)) {
                pr_debug("%s: event=%p\n", __func__, event);

                if (event->data_type == FSNOTIFY_EVENT_PATH)
                        path_put(&event->path);

                BUG_ON(!list_empty(&event->private_data_list));

                kfree(event->file_name);
                put_pid(event->tgid);
                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)
{
        if (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;
}

/*
 * 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_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
                                                 struct fsnotify_event_private_data *priv,
                                                 struct fsnotify_event *(*merge)(struct list_head *,
                                                                                 struct fsnotify_event *))
{
        struct fsnotify_event *return_event = NULL;
        struct fsnotify_event_holder *holder = NULL;
        struct list_head *list = &group->notification_list;

        pr_debug("%s: group=%p event=%p priv=%p\n", __func__, group, event, priv);

        /*
         * 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 ERR_PTR(-ENOMEM);
        }

        mutex_lock(&group->notification_mutex);

        if (group->q_len >= group->max_events) {
                event = q_overflow_event;

                /*
                 * we need to return the overflow event
                 * which means we need a ref
                 */
                fsnotify_get_event(event);
                return_event = event;

                /* sorry, no private data on the overflow event */
                priv = NULL;
        }

        if (!list_empty(list) && merge) {
                struct fsnotify_event *tmp;

                tmp = merge(list, event);
                if (tmp) {
                        mutex_unlock(&group->notification_mutex);

                        if (return_event)
                                fsnotify_put_event(return_event);
                        if (holder != &event->holder)
                                fsnotify_destroy_event_holder(holder);
                        return tmp;
                }
        }

        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);

                if (return_event) {
                        fsnotify_put_event(return_event);
                        return_event = NULL;
                }

                goto alloc_holder;
        }

        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 return_event;
}

/*
 * 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));

        pr_debug("%s: group=%p\n", __func__, group);

        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)
{
        INIT_LIST_HEAD(&event->holder.event_list);
        atomic_set(&event->refcnt, 1);

        spin_lock_init(&event->lock);

        INIT_LIST_HEAD(&event->private_data_list);
}

/*
 * Caller damn well better be holding whatever mutex is protecting the
 * old_holder->event_list and the new_event must be a clean event which
 * cannot be found anywhere else in the kernel.
 */
int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
                           struct fsnotify_event *new_event)
{
        struct fsnotify_event *old_event = old_holder->event;
        struct fsnotify_event_holder *new_holder = &new_event->holder;

        enum event_spinlock_class {
                SPINLOCK_OLD,
                SPINLOCK_NEW,
        };

        pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, new_event);

        /*
         * if the new_event's embedded holder is in use someone
         * screwed up and didn't give us a clean new event.
         */
        BUG_ON(!list_empty(&new_holder->event_list));

        spin_lock_nested(&old_event->lock, SPINLOCK_OLD);
        spin_lock_nested(&new_event->lock, SPINLOCK_NEW);

        new_holder->event = new_event;
        list_replace_init(&old_holder->event_list, &new_holder->event_list);

        spin_unlock(&new_event->lock);
        spin_unlock(&old_event->lock);

        /* event == holder means we are referenced through the in event holder */
        if (old_holder != &old_event->holder)
                fsnotify_destroy_event_holder(old_holder);

        fsnotify_get_event(new_event); /* on the list take reference */
        fsnotify_put_event(old_event); /* off the list, drop reference */

        return 0;
}

struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event)
{
        struct fsnotify_event *event;

        event = kmem_cache_alloc(fsnotify_event_cachep, GFP_KERNEL);
        if (!event)
                return NULL;

        pr_debug("%s: old_event=%p new_event=%p\n", __func__, old_event, event);

        memcpy(event, old_event, sizeof(*event));
        initialize_event(event);

        if (event->name_len) {
                event->file_name = kstrdup(old_event->file_name, GFP_KERNEL);
                if (!event->file_name) {
                        kmem_cache_free(fsnotify_event_cachep, event);
                        return NULL;
                }
        }
        event->tgid = get_pid(old_event->tgid);
        if (event->data_type == FSNOTIFY_EVENT_PATH)
                path_get(&event->path);

        return event;
}

/*
 * 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 unsigned char *name,
                                             u32 cookie, gfp_t gfp)
{
        struct fsnotify_event *event;

        event = kmem_cache_zalloc(fsnotify_event_cachep, gfp);
        if (!event)
                return NULL;

        pr_debug("%s: event=%p to_tell=%p mask=%x data=%p data_type=%d\n",
                 __func__, event, to_tell, mask, data, data_type);

        initialize_event(event);

        if (name) {
                event->file_name = kstrdup(name, gfp);
                if (!event->file_name) {
                        kmem_cache_free(fsnotify_event_cachep, event);
                        return NULL;
                }
                event->name_len = strlen(event->file_name);
        }

        event->tgid = get_pid(task_tgid(current));
        event->sync_cookie = cookie;
        event->to_tell = to_tell;
        event->data_type = data_type;

        switch (data_type) {
        case FSNOTIFY_EVENT_PATH: {
                struct path *path = data;
                event->path.dentry = path->dentry;
                event->path.mnt = path->mnt;
                path_get(&event->path);
                break;
        }
        case FSNOTIFY_EVENT_INODE:
                event->inode = data;
                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);

        q_overflow_event = fsnotify_create_event(NULL, FS_Q_OVERFLOW, NULL,
                                                 FSNOTIFY_EVENT_NONE, NULL, 0,
                                                 GFP_KERNEL);
        if (!q_overflow_event)
                panic("unable to allocate fsnotify q_overflow_event\n");

        return 0;
}
subsys_initcall(fsnotify_notification_init);