/*
 * net/core/netprio_cgroup.c    Priority Control Group
 *
 *              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 of the License, or (at your option) any later version.
 *
 * Authors:     Neil Horman <nhorman@tuxdriver.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/cgroup.h>
#include <linux/rcupdate.h>
#include <linux/atomic.h>
#include <linux/sched/task.h>

#include <net/rtnetlink.h>
#include <net/pkt_cls.h>
#include <net/sock.h>
#include <net/netprio_cgroup.h>

#include <linux/fdtable.h>

/*
 * netprio allocates per-net_device priomap array which is indexed by
 * css->id.  Limiting css ID to 16bits doesn't lose anything.
 */
#define NETPRIO_ID_MAX          USHRT_MAX

#define PRIOMAP_MIN_SZ          128

/*
 * Extend @dev->priomap so that it's large enough to accommodate
 * @target_idx.  @dev->priomap.priomap_len > @target_idx after successful
 * return.  Must be called under rtnl lock.
 */
static int extend_netdev_table(struct net_device *dev, u32 target_idx)
{
        struct netprio_map *old, *new;
        size_t new_sz, new_len;

        /* is the existing priomap large enough? */
        old = rtnl_dereference(dev->priomap);
        if (old && old->priomap_len > target_idx)
                return 0;

        /*
         * Determine the new size.  Let's keep it power-of-two.  We start
         * from PRIOMAP_MIN_SZ and double it until it's large enough to
         * accommodate @target_idx.
         */
        new_sz = PRIOMAP_MIN_SZ;
        while (true) {
                new_len = (new_sz - offsetof(struct netprio_map, priomap)) /
                        sizeof(new->priomap[0]);
                if (new_len > target_idx)
                        break;
                new_sz *= 2;
                /* overflowed? */
                if (WARN_ON(new_sz < PRIOMAP_MIN_SZ))
                        return -ENOSPC;
        }

        /* allocate & copy */
        new = kzalloc(new_sz, GFP_KERNEL);
        if (!new)
                return -ENOMEM;

        if (old)
                memcpy(new->priomap, old->priomap,
                       old->priomap_len * sizeof(old->priomap[0]));

        new->priomap_len = new_len;

        /* install the new priomap */
        rcu_assign_pointer(dev->priomap, new);
        if (old)
                kfree_rcu(old, rcu);
        return 0;
}

/**
 * netprio_prio - return the effective netprio of a cgroup-net_device pair
 * @css: css part of the target pair
 * @dev: net_device part of the target pair
 *
 * Should be called under RCU read or rtnl lock.
 */
static u32 netprio_prio(struct cgroup_subsys_state *css, struct net_device *dev)
{
        struct netprio_map *map = rcu_dereference_rtnl(dev->priomap);
        int id = css->cgroup->id;

        if (map && id < map->priomap_len)
                return map->priomap[id];
        return 0;
}

/**
 * netprio_set_prio - set netprio on a cgroup-net_device pair
 * @css: css part of the target pair
 * @dev: net_device part of the target pair
 * @prio: prio to set
 *
 * Set netprio to @prio on @css-@dev pair.  Should be called under rtnl
 * lock and may fail under memory pressure for non-zero @prio.
 */
static int netprio_set_prio(struct cgroup_subsys_state *css,
                            struct net_device *dev, u32 prio)
{
        struct netprio_map *map;
        int id = css->cgroup->id;
        int ret;

        /* avoid extending priomap for zero writes */
        map = rtnl_dereference(dev->priomap);
        if (!prio && (!map || map->priomap_len <= id))
                return 0;

        ret = extend_netdev_table(dev, id);
        if (ret)
                return ret;

        map = rtnl_dereference(dev->priomap);
        map->priomap[id] = prio;
        return 0;
}

static struct cgroup_subsys_state *
cgrp_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct cgroup_subsys_state *css;

        css = kzalloc(sizeof(*css), GFP_KERNEL);
        if (!css)
                return ERR_PTR(-ENOMEM);

        return css;
}

static int cgrp_css_online(struct cgroup_subsys_state *css)
{
        struct cgroup_subsys_state *parent_css = css->parent;
        struct net_device *dev;
        int ret = 0;

        if (css->id > NETPRIO_ID_MAX)
                return -ENOSPC;

        if (!parent_css)
                return 0;

        rtnl_lock();
        /*
         * Inherit prios from the parent.  As all prios are set during
         * onlining, there is no need to clear them on offline.
         */
        for_each_netdev(&init_net, dev) {
                u32 prio = netprio_prio(parent_css, dev);

                ret = netprio_set_prio(css, dev, prio);
                if (ret)
                        break;
        }
        rtnl_unlock();
        return ret;
}

static void cgrp_css_free(struct cgroup_subsys_state *css)
{
        kfree(css);
}

static u64 read_prioidx(struct cgroup_subsys_state *css, struct cftype *cft)
{
        return css->cgroup->id;
}

static int read_priomap(struct seq_file *sf, void *v)
{
        struct net_device *dev;

        rcu_read_lock();
        for_each_netdev_rcu(&init_net, dev)
                seq_printf(sf, "%s %u\n", dev->name,
                           netprio_prio(seq_css(sf), dev));
        rcu_read_unlock();
        return 0;
}

static ssize_t write_priomap(struct kernfs_open_file *of,
                             char *buf, size_t nbytes, loff_t off)
{
        char devname[IFNAMSIZ + 1];
        struct net_device *dev;
        u32 prio;
        int ret;

        if (sscanf(buf, "%"__stringify(IFNAMSIZ)"s %u", devname, &prio) != 2)
                return -EINVAL;

        dev = dev_get_by_name(&init_net, devname);
        if (!dev)
                return -ENODEV;

        cgroup_sk_alloc_disable();

        rtnl_lock();

        ret = netprio_set_prio(of_css(of), dev, prio);

        rtnl_unlock();
        dev_put(dev);
        return ret ?: nbytes;
}

static int update_netprio(const void *v, struct file *file, unsigned n)
{
        int err;
        struct socket *sock = sock_from_file(file, &err);
        if (sock) {
                spin_lock(&cgroup_sk_update_lock);
                sock_cgroup_set_prioidx(&sock->sk->sk_cgrp_data,
                                        (unsigned long)v);
                spin_unlock(&cgroup_sk_update_lock);
        }
        return 0;
}

static void net_prio_attach(struct cgroup_taskset *tset)
{
        struct task_struct *p;
        struct cgroup_subsys_state *css;

        cgroup_taskset_for_each(p, css, tset) {
                void *v = (void *)(unsigned long)css->cgroup->id;

                task_lock(p);
                iterate_fd(p->files, 0, update_netprio, v);
                task_unlock(p);
        }
}

static struct cftype ss_files[] = {
        {
                .name = "prioidx",
                .read_u64 = read_prioidx,
        },
        {
                .name = "ifpriomap",
                .seq_show = read_priomap,
                .write = write_priomap,
        },
        { }     /* terminate */
};

struct cgroup_subsys net_prio_cgrp_subsys = {
        .css_alloc      = cgrp_css_alloc,
        .css_online     = cgrp_css_online,
        .css_free       = cgrp_css_free,
        .attach         = net_prio_attach,
        .legacy_cftypes = ss_files,
};

static int netprio_device_event(struct notifier_block *unused,
                                unsigned long event, void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        struct netprio_map *old;

        /*
         * Note this is called with rtnl_lock held so we have update side
         * protection on our rcu assignments
         */

        switch (event) {
        case NETDEV_UNREGISTER:
                old = rtnl_dereference(dev->priomap);
                RCU_INIT_POINTER(dev->priomap, NULL);
                if (old)
                        kfree_rcu(old, rcu);
                break;
        }
        return NOTIFY_DONE;
}

static struct notifier_block netprio_device_notifier = {
        .notifier_call = netprio_device_event
};

static int __init init_cgroup_netprio(void)
{
        register_netdevice_notifier(&netprio_device_notifier);
        return 0;
}

subsys_initcall(init_cgroup_netprio);
MODULE_LICENSE("GPL v2");