#include <linux/wait.h>
#include <linux/backing-dev.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/writeback.h>
#include <linux/device.h>
#include <trace/events/writeback.h>

static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);

struct backing_dev_info default_backing_dev_info = {
        .name           = "default",
        .ra_pages       = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
        .state          = 0,
        .capabilities   = BDI_CAP_MAP_COPY,
};
EXPORT_SYMBOL_GPL(default_backing_dev_info);

struct backing_dev_info noop_backing_dev_info = {
        .name           = "noop",
        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
};
EXPORT_SYMBOL_GPL(noop_backing_dev_info);

static struct class *bdi_class;

/*
 * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
 * locking.
 */
DEFINE_SPINLOCK(bdi_lock);
LIST_HEAD(bdi_list);

/* bdi_wq serves all asynchronous writeback tasks */
struct workqueue_struct *bdi_wq;

void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
{
        if (wb1 < wb2) {
                spin_lock(&wb1->list_lock);
                spin_lock_nested(&wb2->list_lock, 1);
        } else {
                spin_lock(&wb2->list_lock);
                spin_lock_nested(&wb1->list_lock, 1);
        }
}

#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>
#include <linux/seq_file.h>

static struct dentry *bdi_debug_root;

static void bdi_debug_init(void)
{
        bdi_debug_root = debugfs_create_dir("bdi", NULL);
}

static int bdi_debug_stats_show(struct seq_file *m, void *v)
{
        struct backing_dev_info *bdi = m->private;
        struct bdi_writeback *wb = &bdi->wb;
        unsigned long background_thresh;
        unsigned long dirty_thresh;
        unsigned long bdi_thresh;
        unsigned long nr_dirty, nr_io, nr_more_io;
        struct inode *inode;

        nr_dirty = nr_io = nr_more_io = 0;
        spin_lock(&wb->list_lock);
        list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
                nr_dirty++;
        list_for_each_entry(inode, &wb->b_io, i_wb_list)
                nr_io++;
        list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
                nr_more_io++;
        spin_unlock(&wb->list_lock);

        global_dirty_limits(&background_thresh, &dirty_thresh);
        bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);

#define K(x) ((x) << (PAGE_SHIFT - 10))
        seq_printf(m,
                   "BdiWriteback:       %10lu kB\n"
                   "BdiReclaimable:     %10lu kB\n"
                   "BdiDirtyThresh:     %10lu kB\n"
                   "DirtyThresh:        %10lu kB\n"
                   "BackgroundThresh:   %10lu kB\n"
                   "BdiDirtied:         %10lu kB\n"
                   "BdiWritten:         %10lu kB\n"
                   "BdiWriteBandwidth:  %10lu kBps\n"
                   "b_dirty:            %10lu\n"
                   "b_io:               %10lu\n"
                   "b_more_io:          %10lu\n"
                   "bdi_list:           %10u\n"
                   "state:              %10lx\n",
                   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
                   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
                   K(bdi_thresh),
                   K(dirty_thresh),
                   K(background_thresh),
                   (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
                   (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
                   (unsigned long) K(bdi->write_bandwidth),
                   nr_dirty,
                   nr_io,
                   nr_more_io,
                   !list_empty(&bdi->bdi_list), bdi->state);
#undef K

        return 0;
}

static int bdi_debug_stats_open(struct inode *inode, struct file *file)
{
        return single_open(file, bdi_debug_stats_show, inode->i_private);
}

static const struct file_operations bdi_debug_stats_fops = {
        .open           = bdi_debug_stats_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
{
        bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
        bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
                                               bdi, &bdi_debug_stats_fops);
}

static void bdi_debug_unregister(struct backing_dev_info *bdi)
{
        debugfs_remove(bdi->debug_stats);
        debugfs_remove(bdi->debug_dir);
}
#else
static inline void bdi_debug_init(void)
{
}
static inline void bdi_debug_register(struct backing_dev_info *bdi,
                                      const char *name)
{
}
static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
{
}
#endif

static ssize_t read_ahead_kb_store(struct device *dev,
                                  struct device_attribute *attr,
                                  const char *buf, size_t count)
{
        struct backing_dev_info *bdi = dev_get_drvdata(dev);
        unsigned long read_ahead_kb;
        ssize_t ret;

        ret = kstrtoul(buf, 10, &read_ahead_kb);
        if (ret < 0)
                return ret;

        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);

        return count;
}

#define K(pages) ((pages) << (PAGE_SHIFT - 10))

#define BDI_SHOW(name, expr)                                            \
static ssize_t name##_show(struct device *dev,                          \
                           struct device_attribute *attr, char *page)   \
{                                                                       \
        struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
                                                                        \
        return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
}                                                                       \
static DEVICE_ATTR_RW(name);

BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))

static ssize_t min_ratio_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t count)
{
        struct backing_dev_info *bdi = dev_get_drvdata(dev);
        unsigned int ratio;
        ssize_t ret;

        ret = kstrtouint(buf, 10, &ratio);
        if (ret < 0)
                return ret;

        ret = bdi_set_min_ratio(bdi, ratio);
        if (!ret)
                ret = count;

        return ret;
}
BDI_SHOW(min_ratio, bdi->min_ratio)

static ssize_t max_ratio_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t count)
{
        struct backing_dev_info *bdi = dev_get_drvdata(dev);
        unsigned int ratio;
        ssize_t ret;

        ret = kstrtouint(buf, 10, &ratio);
        if (ret < 0)
                return ret;

        ret = bdi_set_max_ratio(bdi, ratio);
        if (!ret)
                ret = count;

        return ret;
}
BDI_SHOW(max_ratio, bdi->max_ratio)

static ssize_t stable_pages_required_show(struct device *dev,
                                          struct device_attribute *attr,
                                          char *page)
{
        struct backing_dev_info *bdi = dev_get_drvdata(dev);

        return snprintf(page, PAGE_SIZE-1, "%d\n",
                        bdi_cap_stable_pages_required(bdi) ? 1 : 0);
}
static DEVICE_ATTR_RO(stable_pages_required);

static struct attribute *bdi_dev_attrs[] = {
        &dev_attr_read_ahead_kb.attr,
        &dev_attr_min_ratio.attr,
        &dev_attr_max_ratio.attr,
        &dev_attr_stable_pages_required.attr,
        NULL,
};
ATTRIBUTE_GROUPS(bdi_dev);

static __init int bdi_class_init(void)
{
        bdi_class = class_create(THIS_MODULE, "bdi");
        if (IS_ERR(bdi_class))
                return PTR_ERR(bdi_class);

        bdi_class->dev_groups = bdi_dev_groups;
        bdi_debug_init();
        return 0;
}
postcore_initcall(bdi_class_init);

static int __init default_bdi_init(void)
{
        int err;

        bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
                                              WQ_UNBOUND | WQ_SYSFS, 0);
        if (!bdi_wq)
                return -ENOMEM;

        err = bdi_init(&default_backing_dev_info);
        if (!err)
                bdi_register(&default_backing_dev_info, NULL, "default");
        err = bdi_init(&noop_backing_dev_info);

        return err;
}
subsys_initcall(default_bdi_init);

int bdi_has_dirty_io(struct backing_dev_info *bdi)
{
        return wb_has_dirty_io(&bdi->wb);
}

/*
 * This function is used when the first inode for this bdi is marked dirty. It
 * wakes-up the corresponding bdi thread which should then take care of the
 * periodic background write-out of dirty inodes. Since the write-out would
 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 * set up a timer which wakes the bdi thread up later.
 *
 * Note, we wouldn't bother setting up the timer, but this function is on the
 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 * by delaying the wake-up.
 */
void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
{
        unsigned long timeout;

        timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
        mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
}

/*
 * Remove bdi from bdi_list, and ensure that it is no longer visible
 */
static void bdi_remove_from_list(struct backing_dev_info *bdi)
{
        spin_lock_bh(&bdi_lock);
        list_del_rcu(&bdi->bdi_list);
        spin_unlock_bh(&bdi_lock);

        synchronize_rcu_expedited();

        /* bdi_list is now unused, clear it to mark @bdi dying */
        INIT_LIST_HEAD(&bdi->bdi_list);
}

int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                const char *fmt, ...)
{
        va_list args;
        struct device *dev;

        if (bdi->dev)   /* The driver needs to use separate queues per device */
                return 0;

        va_start(args, fmt);
        dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
        va_end(args);
        if (IS_ERR(dev))
                return PTR_ERR(dev);

        bdi->dev = dev;

        bdi_debug_register(bdi, dev_name(dev));
        set_bit(BDI_registered, &bdi->state);

        spin_lock_bh(&bdi_lock);
        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
        spin_unlock_bh(&bdi_lock);

        trace_writeback_bdi_register(bdi);
        return 0;
}
EXPORT_SYMBOL(bdi_register);

int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
{
        return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
}
EXPORT_SYMBOL(bdi_register_dev);

/*
 * Remove bdi from the global list and shutdown any threads we have running
 */
static void bdi_wb_shutdown(struct backing_dev_info *bdi)
{
        if (!bdi_cap_writeback_dirty(bdi))
                return;

        /*
         * Make sure nobody finds us on the bdi_list anymore
         */
        bdi_remove_from_list(bdi);

        /*
         * Drain work list and shutdown the delayed_work.  At this point,
         * @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi
         * is dying and its work_list needs to be drained no matter what.
         */
        mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
        flush_delayed_work(&bdi->wb.dwork);
        WARN_ON(!list_empty(&bdi->work_list));

        /*
         * This shouldn't be necessary unless @bdi for some reason has
         * unflushed dirty IO after work_list is drained.  Do it anyway
         * just in case.
         */
        cancel_delayed_work_sync(&bdi->wb.dwork);
}

/*
 * This bdi is going away now, make sure that no super_blocks point to it
 */
static void bdi_prune_sb(struct backing_dev_info *bdi)
{
        struct super_block *sb;

        spin_lock(&sb_lock);
        list_for_each_entry(sb, &super_blocks, s_list) {
                if (sb->s_bdi == bdi)
                        sb->s_bdi = &default_backing_dev_info;
        }
        spin_unlock(&sb_lock);
}

void bdi_unregister(struct backing_dev_info *bdi)
{
        struct device *dev = bdi->dev;

        if (dev) {
                bdi_set_min_ratio(bdi, 0);
                trace_writeback_bdi_unregister(bdi);
                bdi_prune_sb(bdi);

                bdi_wb_shutdown(bdi);
                bdi_debug_unregister(bdi);

                spin_lock_bh(&bdi->wb_lock);
                bdi->dev = NULL;
                spin_unlock_bh(&bdi->wb_lock);

                device_unregister(dev);
        }
}
EXPORT_SYMBOL(bdi_unregister);

static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
{
        memset(wb, 0, sizeof(*wb));

        wb->bdi = bdi;
        wb->last_old_flush = jiffies;
        INIT_LIST_HEAD(&wb->b_dirty);
        INIT_LIST_HEAD(&wb->b_io);
        INIT_LIST_HEAD(&wb->b_more_io);
        spin_lock_init(&wb->list_lock);
        INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
}

/*
 * Initial write bandwidth: 100 MB/s
 */
#define INIT_BW         (100 << (20 - PAGE_SHIFT))

int bdi_init(struct backing_dev_info *bdi)
{
        int i, err;

        bdi->dev = NULL;

        bdi->min_ratio = 0;
        bdi->max_ratio = 100;
        bdi->max_prop_frac = FPROP_FRAC_BASE;
        spin_lock_init(&bdi->wb_lock);
        INIT_LIST_HEAD(&bdi->bdi_list);
        INIT_LIST_HEAD(&bdi->work_list);

        bdi_wb_init(&bdi->wb, bdi);

        for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
                err = percpu_counter_init(&bdi->bdi_stat[i], 0);
                if (err)
                        goto err;
        }

        bdi->dirty_exceeded = 0;

        bdi->bw_time_stamp = jiffies;
        bdi->written_stamp = 0;

        bdi->balanced_dirty_ratelimit = INIT_BW;
        bdi->dirty_ratelimit = INIT_BW;
        bdi->write_bandwidth = INIT_BW;
        bdi->avg_write_bandwidth = INIT_BW;

        err = fprop_local_init_percpu(&bdi->completions);

        if (err) {
err:
                while (i--)
                        percpu_counter_destroy(&bdi->bdi_stat[i]);
        }

        return err;
}
EXPORT_SYMBOL(bdi_init);

void bdi_destroy(struct backing_dev_info *bdi)
{
        int i;

        /*
         * Splice our entries to the default_backing_dev_info, if this
         * bdi disappears
         */
        if (bdi_has_dirty_io(bdi)) {
                struct bdi_writeback *dst = &default_backing_dev_info.wb;

                bdi_lock_two(&bdi->wb, dst);
                list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
                list_splice(&bdi->wb.b_io, &dst->b_io);
                list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
                spin_unlock(&bdi->wb.list_lock);
                spin_unlock(&dst->list_lock);
        }

        bdi_unregister(bdi);

        /*
         * If bdi_unregister() had already been called earlier, the dwork
         * could still be pending because bdi_prune_sb() can race with the
         * bdi_wakeup_thread_delayed() calls from __mark_inode_dirty().
         */
        cancel_delayed_work_sync(&bdi->wb.dwork);

        for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
                percpu_counter_destroy(&bdi->bdi_stat[i]);

        fprop_local_destroy_percpu(&bdi->completions);
}
EXPORT_SYMBOL(bdi_destroy);

/*
 * For use from filesystems to quickly init and register a bdi associated
 * with dirty writeback
 */
int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
                           unsigned int cap)
{
        int err;

        bdi->name = name;
        bdi->capabilities = cap;
        err = bdi_init(bdi);
        if (err)
                return err;

        err = bdi_register(bdi, NULL, "%.28s-%ld", name,
                           atomic_long_inc_return(&bdi_seq));
        if (err) {
                bdi_destroy(bdi);
                return err;
        }

        return 0;
}
EXPORT_SYMBOL(bdi_setup_and_register);

static wait_queue_head_t congestion_wqh[2] = {
                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
        };
static atomic_t nr_bdi_congested[2];

void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
{
        enum bdi_state bit;
        wait_queue_head_t *wqh = &congestion_wqh[sync];

        bit = sync ? BDI_sync_congested : BDI_async_congested;
        if (test_and_clear_bit(bit, &bdi->state))
                atomic_dec(&nr_bdi_congested[sync]);
        smp_mb__after_clear_bit();
        if (waitqueue_active(wqh))
                wake_up(wqh);
}
EXPORT_SYMBOL(clear_bdi_congested);

void set_bdi_congested(struct backing_dev_info *bdi, int sync)
{
        enum bdi_state bit;

        bit = sync ? BDI_sync_congested : BDI_async_congested;
        if (!test_and_set_bit(bit, &bdi->state))
                atomic_inc(&nr_bdi_congested[sync]);
}
EXPORT_SYMBOL(set_bdi_congested);

/**
 * congestion_wait - wait for a backing_dev to become uncongested
 * @sync: SYNC or ASYNC IO
 * @timeout: timeout in jiffies
 *
 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 * write congestion.  If no backing_devs are congested then just wait for the
 * next write to be completed.
 */
long congestion_wait(int sync, long timeout)
{
        long ret;
        unsigned long start = jiffies;
        DEFINE_WAIT(wait);
        wait_queue_head_t *wqh = &congestion_wqh[sync];

        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
        ret = io_schedule_timeout(timeout);
        finish_wait(wqh, &wait);

        trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
                                        jiffies_to_usecs(jiffies - start));

        return ret;
}
EXPORT_SYMBOL(congestion_wait);

/**
 * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 * @zone: A zone to check if it is heavily congested
 * @sync: SYNC or ASYNC IO
 * @timeout: timeout in jiffies
 *
 * In the event of a congested backing_dev (any backing_dev) and the given
 * @zone has experienced recent congestion, this waits for up to @timeout
 * jiffies for either a BDI to exit congestion of the given @sync queue
 * or a write to complete.
 *
 * In the absence of zone congestion, cond_resched() is called to yield
 * the processor if necessary but otherwise does not sleep.
 *
 * The return value is 0 if the sleep is for the full timeout. Otherwise,
 * it is the number of jiffies that were still remaining when the function
 * returned. return_value == timeout implies the function did not sleep.
 */
long wait_iff_congested(struct zone *zone, int sync, long timeout)
{
        long ret;
        unsigned long start = jiffies;
        DEFINE_WAIT(wait);
        wait_queue_head_t *wqh = &congestion_wqh[sync];

        /*
         * If there is no congestion, or heavy congestion is not being
         * encountered in the current zone, yield if necessary instead
         * of sleeping on the congestion queue
         */
        if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
                        !zone_is_reclaim_congested(zone)) {
                cond_resched();

                /* In case we scheduled, work out time remaining */
                ret = timeout - (jiffies - start);
                if (ret < 0)
                        ret = 0;

                goto out;
        }

        /* Sleep until uncongested or a write happens */
        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
        ret = io_schedule_timeout(timeout);
        finish_wait(wqh, &wait);

out:
        trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
                                        jiffies_to_usecs(jiffies - start));

        return ret;
}
EXPORT_SYMBOL(wait_iff_congested);

int pdflush_proc_obsolete(struct ctl_table *table, int write,
                        void __user *buffer, size_t *lenp, loff_t *ppos)
{
        char kbuf[] = "0\n";

        if (*ppos || *lenp < sizeof(kbuf)) {
                *lenp = 0;
                return 0;
        }

        if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
                return -EFAULT;
        printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
                        table->procname);

        *lenp = 2;
        *ppos += *lenp;
        return 2;
}