// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2019 SUSE

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/livepatch.h>

#define CONSOLE_LOGLEVEL_STATE 1
/* Version 2 supports migration. */
#define CONSOLE_LOGLEVEL_STATE_VERSION 2

static const char *const module_state[] = {
        [MODULE_STATE_LIVE]     = "[MODULE_STATE_LIVE] Normal state",
        [MODULE_STATE_COMING]   = "[MODULE_STATE_COMING] Full formed, running module_init",
        [MODULE_STATE_GOING]    = "[MODULE_STATE_GOING] Going away",
        [MODULE_STATE_UNFORMED] = "[MODULE_STATE_UNFORMED] Still setting it up",
};

static void callback_info(const char *callback, struct klp_object *obj)
{
        if (obj->mod)
                pr_info("%s: %s -> %s\n", callback, obj->mod->name,
                        module_state[obj->mod->state]);
        else
                pr_info("%s: vmlinux\n", callback);
}

static struct klp_patch patch;

static int allocate_loglevel_state(void)
{
        struct klp_state *loglevel_state, *prev_loglevel_state;

        prev_loglevel_state = klp_get_prev_state(CONSOLE_LOGLEVEL_STATE);
        if (prev_loglevel_state) {
                pr_info("%s: space to store console_loglevel already allocated\n",
                __func__);
                return 0;
        }

        loglevel_state = klp_get_state(&patch, CONSOLE_LOGLEVEL_STATE);
        if (!loglevel_state)
                return -EINVAL;

        loglevel_state->data = kzalloc(sizeof(console_loglevel), GFP_KERNEL);
        if (!loglevel_state->data)
                return -ENOMEM;

        pr_info("%s: allocating space to store console_loglevel\n",
                __func__);
        return 0;
}

static void fix_console_loglevel(void)
{
        struct klp_state *loglevel_state, *prev_loglevel_state;

        loglevel_state = klp_get_state(&patch, CONSOLE_LOGLEVEL_STATE);
        if (!loglevel_state)
                return;

        prev_loglevel_state = klp_get_prev_state(CONSOLE_LOGLEVEL_STATE);
        if (prev_loglevel_state) {
                pr_info("%s: taking over the console_loglevel change\n",
                __func__);
                loglevel_state->data = prev_loglevel_state->data;
                return;
        }

        pr_info("%s: fixing console_loglevel\n", __func__);
        *(int *)loglevel_state->data = console_loglevel;
        console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
}

static void restore_console_loglevel(void)
{
        struct klp_state *loglevel_state, *prev_loglevel_state;

        prev_loglevel_state = klp_get_prev_state(CONSOLE_LOGLEVEL_STATE);
        if (prev_loglevel_state) {
                pr_info("%s: passing the console_loglevel change back to the old livepatch\n",
                __func__);
                return;
        }

        loglevel_state = klp_get_state(&patch, CONSOLE_LOGLEVEL_STATE);
        if (!loglevel_state)
                return;

        pr_info("%s: restoring console_loglevel\n", __func__);
        console_loglevel = *(int *)loglevel_state->data;
}

static void free_loglevel_state(void)
{
        struct klp_state *loglevel_state, *prev_loglevel_state;

        prev_loglevel_state = klp_get_prev_state(CONSOLE_LOGLEVEL_STATE);
        if (prev_loglevel_state) {
                pr_info("%s: keeping space to store console_loglevel\n",
                __func__);
                return;
        }

        loglevel_state = klp_get_state(&patch, CONSOLE_LOGLEVEL_STATE);
        if (!loglevel_state)
                return;

        pr_info("%s: freeing space for the stored console_loglevel\n",
                __func__);
        kfree(loglevel_state->data);
}

/* Executed on object patching (ie, patch enablement) */
static int pre_patch_callback(struct klp_object *obj)
{
        callback_info(__func__, obj);
        return allocate_loglevel_state();
}

/* Executed on object unpatching (ie, patch disablement) */
static void post_patch_callback(struct klp_object *obj)
{
        callback_info(__func__, obj);
        fix_console_loglevel();
}

/* Executed on object unpatching (ie, patch disablement) */
static void pre_unpatch_callback(struct klp_object *obj)
{
        callback_info(__func__, obj);
        restore_console_loglevel();
}

/* Executed on object unpatching (ie, patch disablement) */
static void post_unpatch_callback(struct klp_object *obj)
{
        callback_info(__func__, obj);
        free_loglevel_state();
}

static struct klp_func no_funcs[] = {
        {}
};

static struct klp_object objs[] = {
        {
                .name = NULL,   /* vmlinux */
                .funcs = no_funcs,
                .callbacks = {
                        .pre_patch = pre_patch_callback,
                        .post_patch = post_patch_callback,
                        .pre_unpatch = pre_unpatch_callback,
                        .post_unpatch = post_unpatch_callback,
                },
        }, { }
};

static struct klp_state states[] = {
        {
                .id = CONSOLE_LOGLEVEL_STATE,
                .version = CONSOLE_LOGLEVEL_STATE_VERSION,
        }, { }
};

static struct klp_patch patch = {
        .mod = THIS_MODULE,
        .objs = objs,
        .states = states,
        .replace = true,
};

static int test_klp_callbacks_demo_init(void)
{
        return klp_enable_patch(&patch);
}

static void test_klp_callbacks_demo_exit(void)
{
}

module_init(test_klp_callbacks_demo_init);
module_exit(test_klp_callbacks_demo_exit);
MODULE_LICENSE("GPL");
MODULE_INFO(livepatch, "Y");
MODULE_AUTHOR("Petr Mladek <pmladek@suse.com>");
MODULE_DESCRIPTION("Livepatch test: system state modification");