// SPDX-License-Identifier: GPL-2.0
/*
 * Block rq-qos policy for assigning an I/O priority class to requests.
 *
 * Using an rq-qos policy for assigning I/O priority class has two advantages
 * over using the ioprio_set() system call:
 *
 * - This policy is cgroup based so it has all the advantages of cgroups.
 * - While ioprio_set() does not affect page cache writeback I/O, this rq-qos
 *   controller affects page cache writeback I/O for filesystems that support
 *   assiociating a cgroup with writeback I/O. See also
 *   Documentation/admin-guide/cgroup-v2.rst.
 */

#include <linux/blk-mq.h>
#include <linux/blk_types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include "blk-cgroup.h"
#include "blk-ioprio.h"
#include "blk-rq-qos.h"

/**
 * enum prio_policy - I/O priority class policy.
 * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
 * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
 * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
 *              IOPRIO_CLASS_BE.
 * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
 * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
 *
 * See also <linux/ioprio.h>.
 */
enum prio_policy {
        POLICY_NO_CHANGE        = 0,
        POLICY_PROMOTE_TO_RT    = 1,
        POLICY_RESTRICT_TO_BE   = 2,
        POLICY_ALL_TO_IDLE      = 3,
        POLICY_NONE_TO_RT       = 4,
};

static const char *policy_name[] = {
        [POLICY_NO_CHANGE]      = "no-change",
        [POLICY_PROMOTE_TO_RT]  = "promote-to-rt",
        [POLICY_RESTRICT_TO_BE] = "restrict-to-be",
        [POLICY_ALL_TO_IDLE]    = "idle",
        [POLICY_NONE_TO_RT]     = "none-to-rt",
};

static struct blkcg_policy ioprio_policy;

/**
 * struct ioprio_blkcg - Per cgroup data.
 * @cpd: blkcg_policy_data structure.
 * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
 */
struct ioprio_blkcg {
        struct blkcg_policy_data cpd;
        enum prio_policy         prio_policy;
};

static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
{
        return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
                            struct ioprio_blkcg, cpd);
}

static struct ioprio_blkcg *
ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
{
        return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
}

static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
{
        struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));

        seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
        return 0;
}

static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
                                      size_t nbytes, loff_t off)
{
        struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
        int ret;

        if (off != 0)
                return -EIO;
        /* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
        ret = sysfs_match_string(policy_name, buf);
        if (ret < 0)
                return ret;
        blkcg->prio_policy = ret;
        return nbytes;
}

static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
{
        struct ioprio_blkcg *blkcg;

        blkcg = kzalloc_obj(*blkcg, gfp);
        if (!blkcg)
                return NULL;
        blkcg->prio_policy = POLICY_NO_CHANGE;
        return &blkcg->cpd;
}

static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
{
        struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);

        kfree(blkcg);
}

static struct cftype ioprio_files[] = {
        {
                .name           = "prio.class",
                .seq_show       = ioprio_show_prio_policy,
                .write          = ioprio_set_prio_policy,
        },
        { } /* sentinel */
};

static struct blkcg_policy ioprio_policy = {
        .dfl_cftypes    = ioprio_files,
        .legacy_cftypes = ioprio_files,

        .cpd_alloc_fn   = ioprio_alloc_cpd,
        .cpd_free_fn    = ioprio_free_cpd,
};

void blkcg_set_ioprio(struct bio *bio)
{
        struct ioprio_blkcg *blkcg = blkcg_to_ioprio_blkcg(bio->bi_blkg->blkcg);
        u16 prio;

        if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
                return;

        if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
            blkcg->prio_policy == POLICY_NONE_TO_RT) {
                /*
                 * For RT threads, the default priority level is 4 because
                 * task_nice is 0. By promoting non-RT io-priority to RT-class
                 * and default level 4, those requests that are already
                 * RT-class but need a higher io-priority can use ioprio_set()
                 * to achieve this.
                 */
                if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
                        bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
                return;
        }

        /*
         * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
         * correspond to a lower priority. Hence, the max_t() below selects
         * the lower priority of bi_ioprio and the cgroup I/O priority class.
         * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
         * priority is assigned to the bio.
         */
        prio = max_t(u16, bio->bi_ioprio,
                        IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
        if (prio > bio->bi_ioprio)
                bio->bi_ioprio = prio;
}

static int __init ioprio_init(void)
{
        return blkcg_policy_register(&ioprio_policy);
}

static void __exit ioprio_exit(void)
{
        blkcg_policy_unregister(&ioprio_policy);
}

module_init(ioprio_init);
module_exit(ioprio_exit);