// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2005-2007 Red Hat GmbH
 *
 * A target that delays reads and/or writes and can send
 * them to different devices.
 *
 * This file is released under the GPL.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/delay.h>

#include <linux/device-mapper.h>

#define DM_MSG_PREFIX "delay"

#define SLEEP_SHIFT 3

struct delay_class {
        struct dm_dev *dev;
        sector_t start;
        unsigned int delay;
        unsigned int ops;
};

struct delay_c {
        struct timer_list delay_timer;
        struct mutex process_bios_lock; /* hold while removing bios to be processed from list */
        spinlock_t delayed_bios_lock; /* hold on all accesses to delayed_bios list */
        struct workqueue_struct *kdelayd_wq;
        struct work_struct flush_expired_bios;
        struct list_head delayed_bios;
        struct task_struct *worker;
        unsigned int worker_sleep_us;
        bool may_delay;

        struct delay_class read;
        struct delay_class write;
        struct delay_class flush;

        int argc;
};

struct dm_delay_info {
        struct delay_c *context;
        struct delay_class *class;
        struct list_head list;
        unsigned long expires;
};

static void handle_delayed_timer(struct timer_list *t)
{
        struct delay_c *dc = timer_container_of(dc, t, delay_timer);

        queue_work(dc->kdelayd_wq, &dc->flush_expired_bios);
}

static void queue_timeout(struct delay_c *dc, unsigned long expires)
{
        timer_reduce(&dc->delay_timer, expires);
}

static inline bool delay_is_fast(struct delay_c *dc)
{
        return !!dc->worker;
}

static void flush_bios(struct bio *bio)
{
        struct bio *n;

        while (bio) {
                n = bio->bi_next;
                bio->bi_next = NULL;
                dm_submit_bio_remap(bio, NULL);
                bio = n;
        }
}

static void flush_delayed_bios(struct delay_c *dc, bool flush_all)
{
        struct dm_delay_info *delayed, *next;
        struct bio_list flush_bio_list;
        LIST_HEAD(local_list);
        unsigned long next_expires = 0;
        bool start_timer = false;
        bio_list_init(&flush_bio_list);

        mutex_lock(&dc->process_bios_lock);
        spin_lock(&dc->delayed_bios_lock);
        list_replace_init(&dc->delayed_bios, &local_list);
        spin_unlock(&dc->delayed_bios_lock);
        list_for_each_entry_safe(delayed, next, &local_list, list) {
                cond_resched();
                if (flush_all || time_after_eq(jiffies, delayed->expires)) {
                        struct bio *bio = dm_bio_from_per_bio_data(delayed,
                                                sizeof(struct dm_delay_info));
                        list_del(&delayed->list);
                        bio_list_add(&flush_bio_list, bio);
                        delayed->class->ops--;
                        continue;
                }

                if (!delay_is_fast(dc)) {
                        if (!start_timer) {
                                start_timer = true;
                                next_expires = delayed->expires;
                        } else {
                                next_expires = min(next_expires, delayed->expires);
                        }
                }
        }
        spin_lock(&dc->delayed_bios_lock);
        list_splice(&local_list, &dc->delayed_bios);
        spin_unlock(&dc->delayed_bios_lock);
        mutex_unlock(&dc->process_bios_lock);

        if (start_timer)
                queue_timeout(dc, next_expires);

        flush_bios(bio_list_get(&flush_bio_list));
}

static int flush_worker_fn(void *data)
{
        struct delay_c *dc = data;

        while (!kthread_should_stop()) {
                flush_delayed_bios(dc, false);
                spin_lock(&dc->delayed_bios_lock);
                if (unlikely(list_empty(&dc->delayed_bios))) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        spin_unlock(&dc->delayed_bios_lock);
                        schedule();
                } else {
                        spin_unlock(&dc->delayed_bios_lock);
                        fsleep(dc->worker_sleep_us);
                        cond_resched();
                }
        }

        return 0;
}

static void flush_expired_bios(struct work_struct *work)
{
        struct delay_c *dc;

        dc = container_of(work, struct delay_c, flush_expired_bios);
        flush_delayed_bios(dc, false);
}

static void delay_dtr(struct dm_target *ti)
{
        struct delay_c *dc = ti->private;

        if (dc->kdelayd_wq) {
                timer_shutdown_sync(&dc->delay_timer);
                destroy_workqueue(dc->kdelayd_wq);
        }

        if (dc->read.dev)
                dm_put_device(ti, dc->read.dev);
        if (dc->write.dev)
                dm_put_device(ti, dc->write.dev);
        if (dc->flush.dev)
                dm_put_device(ti, dc->flush.dev);
        if (dc->worker)
                kthread_stop(dc->worker);

        mutex_destroy(&dc->process_bios_lock);

        kfree(dc);
}

static int delay_class_ctr(struct dm_target *ti, struct delay_class *c, char **argv)
{
        int ret;
        unsigned long long tmpll;
        char dummy;

        if (sscanf(argv[1], "%llu%c", &tmpll, &dummy) != 1 || tmpll != (sector_t)tmpll) {
                ti->error = "Invalid device sector";
                return -EINVAL;
        }
        c->start = tmpll;

        if (sscanf(argv[2], "%u%c", &c->delay, &dummy) != 1) {
                ti->error = "Invalid delay";
                return -EINVAL;
        }

        ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &c->dev);
        if (ret) {
                ti->error = "Device lookup failed";
                return ret;
        }

        return 0;
}

/*
 * Mapping parameters:
 *    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
 *
 * With separate write parameters, the first set is only used for reads.
 * Offsets are specified in sectors.
 * Delays are specified in milliseconds.
 */
static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
        struct delay_c *dc;
        int ret;
        unsigned int max_delay, min_delay;

        if (argc != 3 && argc != 6 && argc != 9) {
                ti->error = "Requires exactly 3, 6 or 9 arguments";
                return -EINVAL;
        }

        dc = kzalloc_obj(*dc);
        if (!dc) {
                ti->error = "Cannot allocate context";
                return -ENOMEM;
        }

        ti->private = dc;
        INIT_LIST_HEAD(&dc->delayed_bios);
        mutex_init(&dc->process_bios_lock);
        spin_lock_init(&dc->delayed_bios_lock);
        dc->may_delay = true;
        dc->argc = argc;

        ret = delay_class_ctr(ti, &dc->read, argv);
        if (ret)
                goto bad;
        min_delay = max_delay = dc->read.delay;

        if (argc == 3) {
                ret = delay_class_ctr(ti, &dc->write, argv);
                if (ret)
                        goto bad;
                ret = delay_class_ctr(ti, &dc->flush, argv);
                if (ret)
                        goto bad;
                goto out;
        }

        ret = delay_class_ctr(ti, &dc->write, argv + 3);
        if (ret)
                goto bad;
        max_delay = max(max_delay, dc->write.delay);
        min_delay = min_not_zero(min_delay, dc->write.delay);

        if (argc == 6) {
                ret = delay_class_ctr(ti, &dc->flush, argv + 3);
                if (ret)
                        goto bad;
                goto out;
        }

        ret = delay_class_ctr(ti, &dc->flush, argv + 6);
        if (ret)
                goto bad;
        max_delay = max(max_delay, dc->flush.delay);
        min_delay = min_not_zero(min_delay, dc->flush.delay);

out:
        if (max_delay < 50) {
                if (min_delay >> SLEEP_SHIFT)
                        dc->worker_sleep_us = 1000;
                else
                        dc->worker_sleep_us = (min_delay * 1000) >> SLEEP_SHIFT;
                /*
                 * In case of small requested delays, use kthread instead of
                 * timers and workqueue to achieve better latency.
                 */
                dc->worker = kthread_run(&flush_worker_fn, dc, "dm-delay-flush-worker");
                if (IS_ERR(dc->worker)) {
                        ret = PTR_ERR(dc->worker);
                        dc->worker = NULL;
                        goto bad;
                }
        } else {
                timer_setup(&dc->delay_timer, handle_delayed_timer, 0);
                INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
                dc->kdelayd_wq = alloc_workqueue("kdelayd",
                                                 WQ_MEM_RECLAIM | WQ_PERCPU,
                                                 0);
                if (!dc->kdelayd_wq) {
                        ret = -EINVAL;
                        DMERR("Couldn't start kdelayd");
                        goto bad;
                }
        }

        ti->num_flush_bios = 1;
        ti->num_discard_bios = 1;
        ti->accounts_remapped_io = true;
        ti->per_io_data_size = sizeof(struct dm_delay_info);
        return 0;

bad:
        delay_dtr(ti);
        return ret;
}

static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio)
{
        struct dm_delay_info *delayed;
        unsigned long expires = 0;

        if (!c->delay)
                return DM_MAPIO_REMAPPED;

        delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));

        delayed->context = dc;
        delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay);

        spin_lock(&dc->delayed_bios_lock);
        if (unlikely(!dc->may_delay)) {
                spin_unlock(&dc->delayed_bios_lock);
                return DM_MAPIO_REMAPPED;
        }
        c->ops++;
        list_add_tail(&delayed->list, &dc->delayed_bios);
        spin_unlock(&dc->delayed_bios_lock);

        if (delay_is_fast(dc))
                wake_up_process(dc->worker);
        else
                queue_timeout(dc, expires);

        return DM_MAPIO_SUBMITTED;
}

static void delay_presuspend(struct dm_target *ti)
{
        struct delay_c *dc = ti->private;

        spin_lock(&dc->delayed_bios_lock);
        dc->may_delay = false;
        spin_unlock(&dc->delayed_bios_lock);

        if (!delay_is_fast(dc))
                timer_delete(&dc->delay_timer);
        flush_delayed_bios(dc, true);
}

static void delay_resume(struct dm_target *ti)
{
        struct delay_c *dc = ti->private;

        dc->may_delay = true;
}

static int delay_map(struct dm_target *ti, struct bio *bio)
{
        struct delay_c *dc = ti->private;
        struct delay_class *c;
        struct dm_delay_info *delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));

        if (bio_data_dir(bio) == WRITE) {
                if (unlikely(bio->bi_opf & REQ_PREFLUSH))
                        c = &dc->flush;
                else
                        c = &dc->write;
        } else {
                c = &dc->read;
        }
        delayed->class = c;
        bio_set_dev(bio, c->dev->bdev);
        bio->bi_iter.bi_sector = c->start + dm_target_offset(ti, bio->bi_iter.bi_sector);

        return delay_bio(dc, c, bio);
}

#ifdef CONFIG_BLK_DEV_ZONED
static int delay_report_zones(struct dm_target *ti,
                struct dm_report_zones_args *args, unsigned int nr_zones)
{
        struct delay_c *dc = ti->private;
        struct delay_class *c = &dc->read;

        return dm_report_zones(c->dev->bdev, c->start,
                        c->start + dm_target_offset(ti, args->next_sector),
                        args, nr_zones);
}
#else
#define delay_report_zones      NULL
#endif

#define DMEMIT_DELAY_CLASS(c) \
        DMEMIT("%s %llu %u", (c)->dev->name, (unsigned long long)(c)->start, (c)->delay)

static void delay_status(struct dm_target *ti, status_type_t type,
                         unsigned int status_flags, char *result, unsigned int maxlen)
{
        struct delay_c *dc = ti->private;
        int sz = 0;

        switch (type) {
        case STATUSTYPE_INFO:
                DMEMIT("%u %u %u", dc->read.ops, dc->write.ops, dc->flush.ops);
                break;

        case STATUSTYPE_TABLE:
                DMEMIT_DELAY_CLASS(&dc->read);
                if (dc->argc >= 6) {
                        DMEMIT(" ");
                        DMEMIT_DELAY_CLASS(&dc->write);
                }
                if (dc->argc >= 9) {
                        DMEMIT(" ");
                        DMEMIT_DELAY_CLASS(&dc->flush);
                }
                break;

        case STATUSTYPE_IMA:
                *result = '\0';
                break;
        }
}

static int delay_iterate_devices(struct dm_target *ti,
                                 iterate_devices_callout_fn fn, void *data)
{
        struct delay_c *dc = ti->private;
        int ret = 0;

        ret = fn(ti, dc->read.dev, dc->read.start, ti->len, data);
        if (ret)
                goto out;
        ret = fn(ti, dc->write.dev, dc->write.start, ti->len, data);
        if (ret)
                goto out;
        ret = fn(ti, dc->flush.dev, dc->flush.start, ti->len, data);
        if (ret)
                goto out;

out:
        return ret;
}

static struct target_type delay_target = {
        .name        = "delay",
        .version     = {1, 5, 0},
        .features    = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_ZONED_HM,
        .module      = THIS_MODULE,
        .ctr         = delay_ctr,
        .dtr         = delay_dtr,
        .map         = delay_map,
        .report_zones = delay_report_zones,
        .presuspend  = delay_presuspend,
        .resume      = delay_resume,
        .status      = delay_status,
        .iterate_devices = delay_iterate_devices,
};
module_dm(delay);

MODULE_DESCRIPTION(DM_NAME " delay target");
MODULE_AUTHOR("Heinz Mauelshagen <mauelshagen@redhat.com>");
MODULE_LICENSE("GPL");