// SPDX-License-Identifier: GPL-2.0
/*
 * Disk events - monitor disk events like media change and eject request.
 */
#include <linux/export.h>
#include <linux/moduleparam.h>
#include <linux/genhd.h>
#include "blk.h"

struct disk_events {
        struct list_head        node;           /* all disk_event's */
        struct gendisk          *disk;          /* the associated disk */
        spinlock_t              lock;

        struct mutex            block_mutex;    /* protects blocking */
        int                     block;          /* event blocking depth */
        unsigned int            pending;        /* events already sent out */
        unsigned int            clearing;       /* events being cleared */

        long                    poll_msecs;     /* interval, -1 for default */
        struct delayed_work     dwork;
};

static const char *disk_events_strs[] = {
        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "media_change",
        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "eject_request",
};

static char *disk_uevents[] = {
        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "DISK_MEDIA_CHANGE=1",
        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "DISK_EJECT_REQUEST=1",
};

/* list of all disk_events */
static DEFINE_MUTEX(disk_events_mutex);
static LIST_HEAD(disk_events);

/* disable in-kernel polling by default */
static unsigned long disk_events_dfl_poll_msecs;

static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
{
        struct disk_events *ev = disk->ev;
        long intv_msecs = 0;

        /*
         * If device-specific poll interval is set, always use it.  If
         * the default is being used, poll if the POLL flag is set.
         */
        if (ev->poll_msecs >= 0)
                intv_msecs = ev->poll_msecs;
        else if (disk->event_flags & DISK_EVENT_FLAG_POLL)
                intv_msecs = disk_events_dfl_poll_msecs;

        return msecs_to_jiffies(intv_msecs);
}

/**
 * disk_block_events - block and flush disk event checking
 * @disk: disk to block events for
 *
 * On return from this function, it is guaranteed that event checking
 * isn't in progress and won't happen until unblocked by
 * disk_unblock_events().  Events blocking is counted and the actual
 * unblocking happens after the matching number of unblocks are done.
 *
 * Note that this intentionally does not block event checking from
 * disk_clear_events().
 *
 * CONTEXT:
 * Might sleep.
 */
void disk_block_events(struct gendisk *disk)
{
        struct disk_events *ev = disk->ev;
        unsigned long flags;
        bool cancel;

        if (!ev)
                return;

        /*
         * Outer mutex ensures that the first blocker completes canceling
         * the event work before further blockers are allowed to finish.
         */
        mutex_lock(&ev->block_mutex);

        spin_lock_irqsave(&ev->lock, flags);
        cancel = !ev->block++;
        spin_unlock_irqrestore(&ev->lock, flags);

        if (cancel)
                cancel_delayed_work_sync(&disk->ev->dwork);

        mutex_unlock(&ev->block_mutex);
}

static void __disk_unblock_events(struct gendisk *disk, bool check_now)
{
        struct disk_events *ev = disk->ev;
        unsigned long intv;
        unsigned long flags;

        spin_lock_irqsave(&ev->lock, flags);

        if (WARN_ON_ONCE(ev->block <= 0))
                goto out_unlock;

        if (--ev->block)
                goto out_unlock;

        intv = disk_events_poll_jiffies(disk);
        if (check_now)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, 0);
        else if (intv)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, intv);
out_unlock:
        spin_unlock_irqrestore(&ev->lock, flags);
}

/**
 * disk_unblock_events - unblock disk event checking
 * @disk: disk to unblock events for
 *
 * Undo disk_block_events().  When the block count reaches zero, it
 * starts events polling if configured.
 *
 * CONTEXT:
 * Don't care.  Safe to call from irq context.
 */
void disk_unblock_events(struct gendisk *disk)
{
        if (disk->ev)
                __disk_unblock_events(disk, false);
}

/**
 * disk_flush_events - schedule immediate event checking and flushing
 * @disk: disk to check and flush events for
 * @mask: events to flush
 *
 * Schedule immediate event checking on @disk if not blocked.  Events in
 * @mask are scheduled to be cleared from the driver.  Note that this
 * doesn't clear the events from @disk->ev.
 *
 * CONTEXT:
 * If @mask is non-zero must be called with disk->open_mutex held.
 */
void disk_flush_events(struct gendisk *disk, unsigned int mask)
{
        struct disk_events *ev = disk->ev;

        if (!ev)
                return;

        spin_lock_irq(&ev->lock);
        ev->clearing |= mask;
        if (!ev->block)
                mod_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, 0);
        spin_unlock_irq(&ev->lock);
}

static void disk_check_events(struct disk_events *ev,
                              unsigned int *clearing_ptr)
{
        struct gendisk *disk = ev->disk;
        char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
        unsigned int clearing = *clearing_ptr;
        unsigned int events;
        unsigned long intv;
        int nr_events = 0, i;

        /* check events */
        events = disk->fops->check_events(disk, clearing);

        /* accumulate pending events and schedule next poll if necessary */
        spin_lock_irq(&ev->lock);

        events &= ~ev->pending;
        ev->pending |= events;
        *clearing_ptr &= ~clearing;

        intv = disk_events_poll_jiffies(disk);
        if (!ev->block && intv)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, intv);

        spin_unlock_irq(&ev->lock);

        /*
         * Tell userland about new events.  Only the events listed in
         * @disk->events are reported, and only if DISK_EVENT_FLAG_UEVENT
         * is set. Otherwise, events are processed internally but never
         * get reported to userland.
         */
        for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
                if ((events & disk->events & (1 << i)) &&
                    (disk->event_flags & DISK_EVENT_FLAG_UEVENT))
                        envp[nr_events++] = disk_uevents[i];

        if (nr_events)
                kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
}

/**
 * disk_clear_events - synchronously check, clear and return pending events
 * @disk: disk to fetch and clear events from
 * @mask: mask of events to be fetched and cleared
 *
 * Disk events are synchronously checked and pending events in @mask
 * are cleared and returned.  This ignores the block count.
 *
 * CONTEXT:
 * Might sleep.
 */
static unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
{
        struct disk_events *ev = disk->ev;
        unsigned int pending;
        unsigned int clearing = mask;

        if (!ev)
                return 0;

        disk_block_events(disk);

        /*
         * store the union of mask and ev->clearing on the stack so that the
         * race with disk_flush_events does not cause ambiguity (ev->clearing
         * can still be modified even if events are blocked).
         */
        spin_lock_irq(&ev->lock);
        clearing |= ev->clearing;
        ev->clearing = 0;
        spin_unlock_irq(&ev->lock);

        disk_check_events(ev, &clearing);
        /*
         * if ev->clearing is not 0, the disk_flush_events got called in the
         * middle of this function, so we want to run the workfn without delay.
         */
        __disk_unblock_events(disk, ev->clearing ? true : false);

        /* then, fetch and clear pending events */
        spin_lock_irq(&ev->lock);
        pending = ev->pending & mask;
        ev->pending &= ~mask;
        spin_unlock_irq(&ev->lock);
        WARN_ON_ONCE(clearing & mask);

        return pending;
}

/**
 * bdev_check_media_change - check if a removable media has been changed
 * @bdev: block device to check
 *
 * Check whether a removable media has been changed, and attempt to free all
 * dentries and inodes and invalidates all block device page cache entries in
 * that case.
 *
 * Returns %true if the block device changed, or %false if not.
 */
bool bdev_check_media_change(struct block_device *bdev)
{
        unsigned int events;

        events = disk_clear_events(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE |
                                   DISK_EVENT_EJECT_REQUEST);
        if (!(events & DISK_EVENT_MEDIA_CHANGE))
                return false;

        if (__invalidate_device(bdev, true))
                pr_warn("VFS: busy inodes on changed media %s\n",
                        bdev->bd_disk->disk_name);
        set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
        return true;
}
EXPORT_SYMBOL(bdev_check_media_change);

/*
 * Separate this part out so that a different pointer for clearing_ptr can be
 * passed in for disk_clear_events.
 */
static void disk_events_workfn(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct disk_events *ev = container_of(dwork, struct disk_events, dwork);

        disk_check_events(ev, &ev->clearing);
}

/*
 * A disk events enabled device has the following sysfs nodes under
 * its /sys/block/X/ directory.
 *
 * events               : list of all supported events
 * events_async         : list of events which can be detected w/o polling
 *                        (always empty, only for backwards compatibility)
 * events_poll_msecs    : polling interval, 0: disable, -1: system default
 */
static ssize_t __disk_events_show(unsigned int events, char *buf)
{
        const char *delim = "";
        ssize_t pos = 0;
        int i;

        for (i = 0; i < ARRAY_SIZE(disk_events_strs); i++)
                if (events & (1 << i)) {
                        pos += sprintf(buf + pos, "%s%s",
                                       delim, disk_events_strs[i]);
                        delim = " ";
                }
        if (pos)
                pos += sprintf(buf + pos, "\n");
        return pos;
}

static ssize_t disk_events_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        if (!(disk->event_flags & DISK_EVENT_FLAG_UEVENT))
                return 0;
        return __disk_events_show(disk->events, buf);
}

static ssize_t disk_events_async_show(struct device *dev,
                                      struct device_attribute *attr, char *buf)
{
        return 0;
}

static ssize_t disk_events_poll_msecs_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        if (!disk->ev)
                return sprintf(buf, "-1\n");
        return sprintf(buf, "%ld\n", disk->ev->poll_msecs);
}

static ssize_t disk_events_poll_msecs_store(struct device *dev,
                                            struct device_attribute *attr,
                                            const char *buf, size_t count)
{
        struct gendisk *disk = dev_to_disk(dev);
        long intv;

        if (!count || !sscanf(buf, "%ld", &intv))
                return -EINVAL;

        if (intv < 0 && intv != -1)
                return -EINVAL;

        if (!disk->ev)
                return -ENODEV;

        disk_block_events(disk);
        disk->ev->poll_msecs = intv;
        __disk_unblock_events(disk, true);
        return count;
}

DEVICE_ATTR(events, 0444, disk_events_show, NULL);
DEVICE_ATTR(events_async, 0444, disk_events_async_show, NULL);
DEVICE_ATTR(events_poll_msecs, 0644, disk_events_poll_msecs_show,
            disk_events_poll_msecs_store);

/*
 * The default polling interval can be specified by the kernel
 * parameter block.events_dfl_poll_msecs which defaults to 0
 * (disable).  This can also be modified runtime by writing to
 * /sys/module/block/parameters/events_dfl_poll_msecs.
 */
static int disk_events_set_dfl_poll_msecs(const char *val,
                                          const struct kernel_param *kp)
{
        struct disk_events *ev;
        int ret;

        ret = param_set_ulong(val, kp);
        if (ret < 0)
                return ret;

        mutex_lock(&disk_events_mutex);
        list_for_each_entry(ev, &disk_events, node)
                disk_flush_events(ev->disk, 0);
        mutex_unlock(&disk_events_mutex);
        return 0;
}

static const struct kernel_param_ops disk_events_dfl_poll_msecs_param_ops = {
        .set    = disk_events_set_dfl_poll_msecs,
        .get    = param_get_ulong,
};

#undef MODULE_PARAM_PREFIX
#define MODULE_PARAM_PREFIX     "block."

module_param_cb(events_dfl_poll_msecs, &disk_events_dfl_poll_msecs_param_ops,
                &disk_events_dfl_poll_msecs, 0644);

/*
 * disk_{alloc|add|del|release}_events - initialize and destroy disk_events.
 */
void disk_alloc_events(struct gendisk *disk)
{
        struct disk_events *ev;

        if (!disk->fops->check_events || !disk->events)
                return;

        ev = kzalloc(sizeof(*ev), GFP_KERNEL);
        if (!ev) {
                pr_warn("%s: failed to initialize events\n", disk->disk_name);
                return;
        }

        INIT_LIST_HEAD(&ev->node);
        ev->disk = disk;
        spin_lock_init(&ev->lock);
        mutex_init(&ev->block_mutex);
        ev->block = 1;
        ev->poll_msecs = -1;
        INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);

        disk->ev = ev;
}

void disk_add_events(struct gendisk *disk)
{
        if (!disk->ev)
                return;

        mutex_lock(&disk_events_mutex);
        list_add_tail(&disk->ev->node, &disk_events);
        mutex_unlock(&disk_events_mutex);

        /*
         * Block count is initialized to 1 and the following initial
         * unblock kicks it into action.
         */
        __disk_unblock_events(disk, true);
}

void disk_del_events(struct gendisk *disk)
{
        if (disk->ev) {
                disk_block_events(disk);

                mutex_lock(&disk_events_mutex);
                list_del_init(&disk->ev->node);
                mutex_unlock(&disk_events_mutex);
        }
}

void disk_release_events(struct gendisk *disk)
{
        /* the block count should be 1 from disk_del_events() */
        WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
        kfree(disk->ev);
}