// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>

#include "notifier-error-inject.h"

static int debugfs_errno_set(void *data, u64 val)
{
        *(int *)data = clamp_t(int, val, -MAX_ERRNO, 0);
        return 0;
}

static int debugfs_errno_get(void *data, u64 *val)
{
        *val = *(int *)data;
        return 0;
}

DEFINE_SIMPLE_ATTRIBUTE_SIGNED(fops_errno, debugfs_errno_get, debugfs_errno_set,
                        "%lld\n");

static struct dentry *debugfs_create_errno(const char *name, umode_t mode,
                                struct dentry *parent, int *value)
{
        return debugfs_create_file(name, mode, parent, value, &fops_errno);
}

static int notifier_err_inject_callback(struct notifier_block *nb,
                                unsigned long val, void *p)
{
        int err = 0;
        struct notifier_err_inject *err_inject =
                container_of(nb, struct notifier_err_inject, nb);
        struct notifier_err_inject_action *action;

        for (action = err_inject->actions; action->name; action++) {
                if (action->val == val) {
                        err = action->error;
                        break;
                }
        }
        if (err)
                pr_info("Injecting error (%d) to %s\n", err, action->name);

        return notifier_from_errno(err);
}

struct dentry *notifier_err_inject_dir;
EXPORT_SYMBOL_GPL(notifier_err_inject_dir);

struct dentry *notifier_err_inject_init(const char *name, struct dentry *parent,
                        struct notifier_err_inject *err_inject, int priority)
{
        struct notifier_err_inject_action *action;
        umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
        struct dentry *dir;
        struct dentry *actions_dir;

        err_inject->nb.notifier_call = notifier_err_inject_callback;
        err_inject->nb.priority = priority;

        dir = debugfs_create_dir(name, parent);

        actions_dir = debugfs_create_dir("actions", dir);

        for (action = err_inject->actions; action->name; action++) {
                struct dentry *action_dir;

                action_dir = debugfs_create_dir(action->name, actions_dir);

                /*
                 * Create debugfs r/w file containing action->error. If
                 * notifier call chain is called with action->val, it will
                 * fail with the error code
                 */
                debugfs_create_errno("error", mode, action_dir, &action->error);
        }
        return dir;
}
EXPORT_SYMBOL_GPL(notifier_err_inject_init);

static int __init err_inject_init(void)
{
        notifier_err_inject_dir =
                debugfs_create_dir("notifier-error-inject", NULL);

        return 0;
}

static void __exit err_inject_exit(void)
{
        debugfs_remove_recursive(notifier_err_inject_dir);
}

module_init(err_inject_init);
module_exit(err_inject_exit);

MODULE_DESCRIPTION("Notifier error injection module");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Akinobu Mita <akinobu.mita@gmail.com>");