// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
 */

#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/srcu.h>
#include <linux/rculist.h>
#include <linux/wait.h>
#include <linux/memcontrol.h>

#include <linux/fsnotify_backend.h>
#include "fsnotify.h"

#include <linux/atomic.h>

/*
 * Final freeing of a group
 */
static void fsnotify_final_destroy_group(struct fsnotify_group *group)
{
        if (group->ops->free_group_priv)
                group->ops->free_group_priv(group);

        mem_cgroup_put(group->memcg);
        mutex_destroy(&group->mark_mutex);

        kfree(group);
}

/*
 * Stop queueing new events for this group. Once this function returns
 * fsnotify_add_event() will not add any new events to the group's queue.
 */
void fsnotify_group_stop_queueing(struct fsnotify_group *group)
{
        spin_lock(&group->notification_lock);
        group->shutdown = true;
        spin_unlock(&group->notification_lock);
}

/*
 * Trying to get rid of a group. Remove all marks, flush all events and release
 * the group reference.
 * Note that another thread calling fsnotify_clear_marks_by_group() may still
 * hold a ref to the group.
 */
void fsnotify_destroy_group(struct fsnotify_group *group)
{
        /*
         * Stop queueing new events. The code below is careful enough to not
         * require this but fanotify needs to stop queuing events even before
         * fsnotify_destroy_group() is called and this makes the other callers
         * of fsnotify_destroy_group() to see the same behavior.
         */
        fsnotify_group_stop_queueing(group);

        /* Clear all marks for this group and queue them for destruction */
        fsnotify_clear_marks_by_group(group, FSNOTIFY_OBJ_TYPE_ANY);

        /*
         * Some marks can still be pinned when waiting for response from
         * userspace. Wait for those now. fsnotify_prepare_user_wait() will
         * not succeed now so this wait is race-free.
         */
        wait_event(group->notification_waitq, !atomic_read(&group->user_waits));

        /*
         * Wait until all marks get really destroyed. We could actually destroy
         * them ourselves instead of waiting for worker to do it, however that
         * would be racy as worker can already be processing some marks before
         * we even entered fsnotify_destroy_group().
         */
        fsnotify_wait_marks_destroyed();

        /*
         * Since we have waited for fsnotify_mark_srcu in
         * fsnotify_mark_destroy_list() there can be no outstanding event
         * notification against this group. So clearing the notification queue
         * of all events is reliable now.
         */
        fsnotify_flush_notify(group);

        /*
         * Destroy overflow event (we cannot use fsnotify_destroy_event() as
         * that deliberately ignores overflow events.
         */
        if (group->overflow_event)
                group->ops->free_event(group, group->overflow_event);

        fsnotify_put_group(group);
}

/*
 * Get reference to a group.
 */
void fsnotify_get_group(struct fsnotify_group *group)
{
        refcount_inc(&group->refcnt);
}

/*
 * Drop a reference to a group.  Free it if it's through.
 */
void fsnotify_put_group(struct fsnotify_group *group)
{
        if (refcount_dec_and_test(&group->refcnt))
                fsnotify_final_destroy_group(group);
}
EXPORT_SYMBOL_GPL(fsnotify_put_group);

static struct fsnotify_group *__fsnotify_alloc_group(
                                const struct fsnotify_ops *ops,
                                int flags, gfp_t gfp)
{
        struct fsnotify_group *group;

        group = kzalloc_obj(struct fsnotify_group, gfp);
        if (!group)
                return ERR_PTR(-ENOMEM);

        /* set to 0 when there a no external references to this group */
        refcount_set(&group->refcnt, 1);
        atomic_set(&group->user_waits, 0);

        spin_lock_init(&group->notification_lock);
        INIT_LIST_HEAD(&group->notification_list);
        init_waitqueue_head(&group->notification_waitq);
        group->max_events = UINT_MAX;

        mutex_init(&group->mark_mutex);
        INIT_LIST_HEAD(&group->marks_list);

        group->ops = ops;
        group->flags = flags;

        return group;
}

/*
 * Create a new fsnotify_group and hold a reference for the group returned.
 */
struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops,
                                            int flags)
{
        gfp_t gfp = (flags & FSNOTIFY_GROUP_USER) ? GFP_KERNEL_ACCOUNT :
                                                    GFP_KERNEL;

        return __fsnotify_alloc_group(ops, flags, gfp);
}
EXPORT_SYMBOL_GPL(fsnotify_alloc_group);

int fsnotify_fasync(int fd, struct file *file, int on)
{
        struct fsnotify_group *group = file->private_data;

        return fasync_helper(fd, file, on, &group->fsn_fa) >= 0 ? 0 : -EIO;
}