#include <linux/fanotify.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/wait.h>

static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
{
        pr_debug("%s: old=%p new=%p\n", __func__, old, new);

        if (old->to_tell == new->to_tell &&
            old->data_type == new->data_type &&
            old->tgid == new->tgid) {
                switch (old->data_type) {
                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;
                default:
                        BUG();
                };
        }
        return false;
}

/* and the list better be locked by something too! */
static struct fsnotify_event *fanotify_merge(struct list_head *list,
                                             struct fsnotify_event *event)
{
        struct fsnotify_event_holder *test_holder;
        struct fsnotify_event *test_event = NULL;
        struct fsnotify_event *new_event;

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


        list_for_each_entry_reverse(test_holder, list, event_list) {
                if (should_merge(test_holder->event, event)) {
                        test_event = test_holder->event;
                        break;
                }
        }

        if (!test_event)
                return NULL;

        fsnotify_get_event(test_event);

        /* if they are exactly the same we are done */
        if (test_event->mask == event->mask)
                return test_event;

        /*
         * if the refcnt == 2 this is the only queue
         * for this event and so we can update the mask
         * in place.
         */
        if (atomic_read(&test_event->refcnt) == 2) {
                test_event->mask |= event->mask;
                return test_event;
        }

        new_event = fsnotify_clone_event(test_event);

        /* done with test_event */
        fsnotify_put_event(test_event);

        /* couldn't allocate memory, merge was not possible */
        if (unlikely(!new_event))
                return ERR_PTR(-ENOMEM);

        /* build new event and replace it on the list */
        new_event->mask = (test_event->mask | event->mask);
        fsnotify_replace_event(test_holder, new_event);

        /* we hold a reference on new_event from clone_event */
        return new_event;
}

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
static int fanotify_get_response_from_access(struct fsnotify_group *group,
                                             struct fsnotify_event *event)
{
        int ret;

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

        wait_event(group->fanotify_data.access_waitq, event->response ||
                                atomic_read(&group->fanotify_data.bypass_perm));

        if (!event->response) /* bypass_perm set */
                return 0;

        /* userspace responded, convert to something usable */
        spin_lock(&event->lock);
        switch (event->response) {
        case FAN_ALLOW:
                ret = 0;
                break;
        case FAN_DENY:
        default:
                ret = -EPERM;
        }
        event->response = 0;
        spin_unlock(&event->lock);

        pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
                 group, event, ret);
        
        return ret;
}
#endif

static int fanotify_handle_event(struct fsnotify_group *group,
                                 struct fsnotify_mark *inode_mark,
                                 struct fsnotify_mark *fanotify_mark,
                                 struct fsnotify_event *event)
{
        int ret = 0;
        struct fsnotify_event *notify_event = NULL;

        BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
        BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
        BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
        BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
        BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
        BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
        BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
        BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);

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

        notify_event = fsnotify_add_notify_event(group, event, NULL, fanotify_merge);
        if (IS_ERR(notify_event))
                return PTR_ERR(notify_event);

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
        if (event->mask & FAN_ALL_PERM_EVENTS) {
                /* if we merged we need to wait on the new event */
                if (notify_event)
                        event = notify_event;
                ret = fanotify_get_response_from_access(group, event);
        }
#endif

        if (notify_event)
                fsnotify_put_event(notify_event);

        return ret;
}

static bool fanotify_should_send_event(struct fsnotify_group *group,
                                       struct inode *to_tell,
                                       struct fsnotify_mark *inode_mark,
                                       struct fsnotify_mark *vfsmnt_mark,
                                       __u32 event_mask, void *data, int data_type)
{
        __u32 marks_mask, marks_ignored_mask;
        struct path *path = data;

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

        /* if we don't have enough info to send an event to userspace say no */
        if (data_type != FSNOTIFY_EVENT_PATH)
                return false;

        /* sorry, fanotify only gives a damn about files and dirs */
        if (!S_ISREG(path->dentry->d_inode->i_mode) &&
            !S_ISDIR(path->dentry->d_inode->i_mode))
                return false;

        if (inode_mark && vfsmnt_mark) {
                marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
                marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
        } else if (inode_mark) {
                /*
                 * if the event is for a child and this inode doesn't care about
                 * events on the child, don't send it!
                 */
                if ((event_mask & FS_EVENT_ON_CHILD) &&
                    !(inode_mark->mask & FS_EVENT_ON_CHILD))
                        return false;
                marks_mask = inode_mark->mask;
                marks_ignored_mask = inode_mark->ignored_mask;
        } else if (vfsmnt_mark) {
                marks_mask = vfsmnt_mark->mask;
                marks_ignored_mask = vfsmnt_mark->ignored_mask;
        } else {
                BUG();
        }

        if (S_ISDIR(path->dentry->d_inode->i_mode) &&
            (marks_ignored_mask & FS_ISDIR))
                return false;

        if (event_mask & marks_mask & ~marks_ignored_mask)
                return true;

        return false;
}

static void fanotify_free_group_priv(struct fsnotify_group *group)
{
        struct user_struct *user;

        user = group->fanotify_data.user;
        atomic_dec(&user->fanotify_listeners);
        free_uid(user);
}

const struct fsnotify_ops fanotify_fsnotify_ops = {
        .handle_event = fanotify_handle_event,
        .should_send_event = fanotify_should_send_event,
        .free_group_priv = fanotify_free_group_priv,
        .free_event_priv = NULL,
        .freeing_mark = NULL,
};