Merge branch 'nvme-4.13' of git://git.infradead.org/nvme into for-linus

[mirror_ubuntu-artful-kernel.git] / drivers / lightnvm / pblk-rb.c

/*
 * Copyright (C) 2016 CNEX Labs
 * Initial release: Javier Gonzalez <javier@cnexlabs.com>
 *
 * Based upon the circular ringbuffer.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * pblk-rb.c - pblk's write buffer
 */

#include <linux/circ_buf.h>

#include "pblk.h"

static DECLARE_RWSEM(pblk_rb_lock);

void pblk_rb_data_free(struct pblk_rb *rb)
{
        struct pblk_rb_pages *p, *t;

        down_write(&pblk_rb_lock);
        list_for_each_entry_safe(p, t, &rb->pages, list) {
                free_pages((unsigned long)page_address(p->pages), p->order);
                list_del(&p->list);
                kfree(p);
        }
        up_write(&pblk_rb_lock);
}

/*
 * Initialize ring buffer. The data and metadata buffers must be previously
 * allocated and their size must be a power of two
 * (Documentation/circular-buffers.txt)
 */
int pblk_rb_init(struct pblk_rb *rb, struct pblk_rb_entry *rb_entry_base,
                 unsigned int power_size, unsigned int power_seg_sz)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        unsigned int init_entry = 0;
        unsigned int alloc_order = power_size;
        unsigned int max_order = MAX_ORDER - 1;
        unsigned int order, iter;

        down_write(&pblk_rb_lock);
        rb->entries = rb_entry_base;
        rb->seg_size = (1 << power_seg_sz);
        rb->nr_entries = (1 << power_size);
        rb->mem = rb->subm = rb->sync = rb->l2p_update = 0;
        rb->sync_point = EMPTY_ENTRY;

        spin_lock_init(&rb->w_lock);
        spin_lock_init(&rb->s_lock);

        INIT_LIST_HEAD(&rb->pages);

        if (alloc_order >= max_order) {
                order = max_order;
                iter = (1 << (alloc_order - max_order));
        } else {
                order = alloc_order;
                iter = 1;
        }

        do {
                struct pblk_rb_entry *entry;
                struct pblk_rb_pages *page_set;
                void *kaddr;
                unsigned long set_size;
                int i;

                page_set = kmalloc(sizeof(struct pblk_rb_pages), GFP_KERNEL);
                if (!page_set) {
                        up_write(&pblk_rb_lock);
                        return -ENOMEM;
                }

                page_set->order = order;
                page_set->pages = alloc_pages(GFP_KERNEL, order);
                if (!page_set->pages) {
                        kfree(page_set);
                        pblk_rb_data_free(rb);
                        up_write(&pblk_rb_lock);
                        return -ENOMEM;
                }
                kaddr = page_address(page_set->pages);

                entry = &rb->entries[init_entry];
                entry->data = kaddr;
                entry->cacheline = pblk_cacheline_to_addr(init_entry++);
                entry->w_ctx.flags = PBLK_WRITABLE_ENTRY;

                set_size = (1 << order);
                for (i = 1; i < set_size; i++) {
                        entry = &rb->entries[init_entry];
                        entry->cacheline = pblk_cacheline_to_addr(init_entry++);
                        entry->data = kaddr + (i * rb->seg_size);
                        entry->w_ctx.flags = PBLK_WRITABLE_ENTRY;
                        bio_list_init(&entry->w_ctx.bios);
                }

                list_add_tail(&page_set->list, &rb->pages);
                iter--;
        } while (iter > 0);
        up_write(&pblk_rb_lock);

#ifdef CONFIG_NVM_DEBUG
        atomic_set(&rb->inflight_sync_point, 0);
#endif

        /*
         * Initialize rate-limiter, which controls access to the write buffer
         * but user and GC I/O
         */
        pblk_rl_init(&pblk->rl, rb->nr_entries);

        return 0;
}

/*
 * pblk_rb_calculate_size -- calculate the size of the write buffer
 */
unsigned int pblk_rb_calculate_size(unsigned int nr_entries)
{
        /* Alloc a write buffer that can at least fit 128 entries */
        return (1 << max(get_count_order(nr_entries), 7));
}

void *pblk_rb_entries_ref(struct pblk_rb *rb)
{
        return rb->entries;
}

static void clean_wctx(struct pblk_w_ctx *w_ctx)
{
        int flags;

try:
        flags = READ_ONCE(w_ctx->flags);
        if (!(flags & PBLK_SUBMITTED_ENTRY))
                goto try;

        /* Release flags on context. Protect from writes and reads */
        smp_store_release(&w_ctx->flags, PBLK_WRITABLE_ENTRY);
        pblk_ppa_set_empty(&w_ctx->ppa);
        w_ctx->lba = ADDR_EMPTY;
}

#define pblk_rb_ring_count(head, tail, size) CIRC_CNT(head, tail, size)
#define pblk_rb_ring_space(rb, head, tail, size) \
                                        (CIRC_SPACE(head, tail, size))

/*
 * Buffer space is calculated with respect to the back pointer signaling
 * synchronized entries to the media.
 */
static unsigned int pblk_rb_space(struct pblk_rb *rb)
{
        unsigned int mem = READ_ONCE(rb->mem);
        unsigned int sync = READ_ONCE(rb->sync);

        return pblk_rb_ring_space(rb, mem, sync, rb->nr_entries);
}

/*
 * Buffer count is calculated with respect to the submission entry signaling the
 * entries that are available to send to the media
 */
unsigned int pblk_rb_read_count(struct pblk_rb *rb)
{
        unsigned int mem = READ_ONCE(rb->mem);
        unsigned int subm = READ_ONCE(rb->subm);

        return pblk_rb_ring_count(mem, subm, rb->nr_entries);
}

unsigned int pblk_rb_sync_count(struct pblk_rb *rb)
{
        unsigned int mem = READ_ONCE(rb->mem);
        unsigned int sync = READ_ONCE(rb->sync);

        return pblk_rb_ring_count(mem, sync, rb->nr_entries);
}

unsigned int pblk_rb_read_commit(struct pblk_rb *rb, unsigned int nr_entries)
{
        unsigned int subm;

        subm = READ_ONCE(rb->subm);
        /* Commit read means updating submission pointer */
        smp_store_release(&rb->subm,
                                (subm + nr_entries) & (rb->nr_entries - 1));

        return subm;
}

static int __pblk_rb_update_l2p(struct pblk_rb *rb, unsigned int *l2p_upd,
                                unsigned int to_update)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct pblk_line *line;
        struct pblk_rb_entry *entry;
        struct pblk_w_ctx *w_ctx;
        unsigned int user_io = 0, gc_io = 0;
        unsigned int i;
        int flags;

        for (i = 0; i < to_update; i++) {
                entry = &rb->entries[*l2p_upd];
                w_ctx = &entry->w_ctx;

                flags = READ_ONCE(entry->w_ctx.flags);
                if (flags & PBLK_IOTYPE_USER)
                        user_io++;
                else if (flags & PBLK_IOTYPE_GC)
                        gc_io++;
                else
                        WARN(1, "pblk: unknown IO type\n");

                pblk_update_map_dev(pblk, w_ctx->lba, w_ctx->ppa,
                                                        entry->cacheline);

                line = &pblk->lines[pblk_tgt_ppa_to_line(w_ctx->ppa)];
                kref_put(&line->ref, pblk_line_put);
                clean_wctx(w_ctx);
                *l2p_upd = (*l2p_upd + 1) & (rb->nr_entries - 1);
        }

        pblk_rl_out(&pblk->rl, user_io, gc_io);

        return 0;
}

/*
 * When we move the l2p_update pointer, we update the l2p table - lookups will
 * point to the physical address instead of to the cacheline in the write buffer
 * from this moment on.
 */
static int pblk_rb_update_l2p(struct pblk_rb *rb, unsigned int nr_entries,
                              unsigned int mem, unsigned int sync)
{
        unsigned int space, count;
        int ret = 0;

        lockdep_assert_held(&rb->w_lock);

        /* Update l2p only as buffer entries are being overwritten */
        space = pblk_rb_ring_space(rb, mem, rb->l2p_update, rb->nr_entries);
        if (space > nr_entries)
                goto out;

        count = nr_entries - space;
        /* l2p_update used exclusively under rb->w_lock */
        ret = __pblk_rb_update_l2p(rb, &rb->l2p_update, count);

out:
        return ret;
}

/*
 * Update the l2p entry for all sectors stored on the write buffer. This means
 * that all future lookups to the l2p table will point to a device address, not
 * to the cacheline in the write buffer.
 */
void pblk_rb_sync_l2p(struct pblk_rb *rb)
{
        unsigned int sync;
        unsigned int to_update;

        spin_lock(&rb->w_lock);

        /* Protect from reads and writes */
        sync = smp_load_acquire(&rb->sync);

        to_update = pblk_rb_ring_count(sync, rb->l2p_update, rb->nr_entries);
        __pblk_rb_update_l2p(rb, &rb->l2p_update, to_update);

        spin_unlock(&rb->w_lock);
}

/*
 * Write @nr_entries to ring buffer from @data buffer if there is enough space.
 * Typically, 4KB data chunks coming from a bio will be copied to the ring
 * buffer, thus the write will fail if not all incoming data can be copied.
 *
 */
static void __pblk_rb_write_entry(struct pblk_rb *rb, void *data,
                                  struct pblk_w_ctx w_ctx,
                                  struct pblk_rb_entry *entry)
{
        memcpy(entry->data, data, rb->seg_size);

        entry->w_ctx.lba = w_ctx.lba;
        entry->w_ctx.ppa = w_ctx.ppa;
}

void pblk_rb_write_entry_user(struct pblk_rb *rb, void *data,
                              struct pblk_w_ctx w_ctx, unsigned int ring_pos)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct pblk_rb_entry *entry;
        int flags;

        entry = &rb->entries[ring_pos];
        flags = READ_ONCE(entry->w_ctx.flags);
#ifdef CONFIG_NVM_DEBUG
        /* Caller must guarantee that the entry is free */
        BUG_ON(!(flags & PBLK_WRITABLE_ENTRY));
#endif

        __pblk_rb_write_entry(rb, data, w_ctx, entry);

        pblk_update_map_cache(pblk, w_ctx.lba, entry->cacheline);
        flags = w_ctx.flags | PBLK_WRITTEN_DATA;

        /* Release flags on write context. Protect from writes */
        smp_store_release(&entry->w_ctx.flags, flags);
}

void pblk_rb_write_entry_gc(struct pblk_rb *rb, void *data,
                            struct pblk_w_ctx w_ctx, struct pblk_line *gc_line,
                            unsigned int ring_pos)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct pblk_rb_entry *entry;
        int flags;

        entry = &rb->entries[ring_pos];
        flags = READ_ONCE(entry->w_ctx.flags);
#ifdef CONFIG_NVM_DEBUG
        /* Caller must guarantee that the entry is free */
        BUG_ON(!(flags & PBLK_WRITABLE_ENTRY));
#endif

        __pblk_rb_write_entry(rb, data, w_ctx, entry);

        if (!pblk_update_map_gc(pblk, w_ctx.lba, entry->cacheline, gc_line))
                entry->w_ctx.lba = ADDR_EMPTY;

        flags = w_ctx.flags | PBLK_WRITTEN_DATA;

        /* Release flags on write context. Protect from writes */
        smp_store_release(&entry->w_ctx.flags, flags);
}

static int pblk_rb_sync_point_set(struct pblk_rb *rb, struct bio *bio,
                                  unsigned int pos)
{
        struct pblk_rb_entry *entry;
        unsigned int subm, sync_point;
        int flags;

        subm = READ_ONCE(rb->subm);

#ifdef CONFIG_NVM_DEBUG
        atomic_inc(&rb->inflight_sync_point);
#endif

        if (pos == subm)
                return 0;

        sync_point = (pos == 0) ? (rb->nr_entries - 1) : (pos - 1);
        entry = &rb->entries[sync_point];

        flags = READ_ONCE(entry->w_ctx.flags);
        flags |= PBLK_FLUSH_ENTRY;

        /* Release flags on context. Protect from writes */
        smp_store_release(&entry->w_ctx.flags, flags);

        /* Protect syncs */
        smp_store_release(&rb->sync_point, sync_point);

        if (!bio)
                return 0;

        spin_lock_irq(&rb->s_lock);
        bio_list_add(&entry->w_ctx.bios, bio);
        spin_unlock_irq(&rb->s_lock);

        return 1;
}

static int __pblk_rb_may_write(struct pblk_rb *rb, unsigned int nr_entries,
                               unsigned int *pos)
{
        unsigned int mem;
        unsigned int sync;

        sync = READ_ONCE(rb->sync);
        mem = READ_ONCE(rb->mem);

        if (pblk_rb_ring_space(rb, mem, sync, rb->nr_entries) < nr_entries)
                return 0;

        if (pblk_rb_update_l2p(rb, nr_entries, mem, sync))
                return 0;

        *pos = mem;

        return 1;
}

static int pblk_rb_may_write(struct pblk_rb *rb, unsigned int nr_entries,
                             unsigned int *pos)
{
        if (!__pblk_rb_may_write(rb, nr_entries, pos))
                return 0;

        /* Protect from read count */
        smp_store_release(&rb->mem, (*pos + nr_entries) & (rb->nr_entries - 1));
        return 1;
}

void pblk_rb_flush(struct pblk_rb *rb)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        unsigned int mem = READ_ONCE(rb->mem);

        if (pblk_rb_sync_point_set(rb, NULL, mem))
                return;

        pblk_write_should_kick(pblk);
}

static int pblk_rb_may_write_flush(struct pblk_rb *rb, unsigned int nr_entries,
                                   unsigned int *pos, struct bio *bio,
                                   int *io_ret)
{
        unsigned int mem;

        if (!__pblk_rb_may_write(rb, nr_entries, pos))
                return 0;

        mem = (*pos + nr_entries) & (rb->nr_entries - 1);
        *io_ret = NVM_IO_DONE;

        if (bio->bi_opf & REQ_PREFLUSH) {
                struct pblk *pblk = container_of(rb, struct pblk, rwb);

#ifdef CONFIG_NVM_DEBUG
                atomic_long_inc(&pblk->nr_flush);
#endif
                if (pblk_rb_sync_point_set(&pblk->rwb, bio, mem))
                        *io_ret = NVM_IO_OK;
        }

        /* Protect from read count */
        smp_store_release(&rb->mem, mem);
        return 1;
}

/*
 * Atomically check that (i) there is space on the write buffer for the
 * incoming I/O, and (ii) the current I/O type has enough budget in the write
 * buffer (rate-limiter).
 */
int pblk_rb_may_write_user(struct pblk_rb *rb, struct bio *bio,
                           unsigned int nr_entries, unsigned int *pos)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        int io_ret;

        spin_lock(&rb->w_lock);
        io_ret = pblk_rl_user_may_insert(&pblk->rl, nr_entries);
        if (io_ret) {
                spin_unlock(&rb->w_lock);
                return io_ret;
        }

        if (!pblk_rb_may_write_flush(rb, nr_entries, pos, bio, &io_ret)) {
                spin_unlock(&rb->w_lock);
                return NVM_IO_REQUEUE;
        }

        pblk_rl_user_in(&pblk->rl, nr_entries);
        spin_unlock(&rb->w_lock);

        return io_ret;
}

/*
 * Look at pblk_rb_may_write_user comment
 */
int pblk_rb_may_write_gc(struct pblk_rb *rb, unsigned int nr_entries,
                         unsigned int *pos)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);

        spin_lock(&rb->w_lock);
        if (!pblk_rl_gc_may_insert(&pblk->rl, nr_entries)) {
                spin_unlock(&rb->w_lock);
                return 0;
        }

        if (!pblk_rb_may_write(rb, nr_entries, pos)) {
                spin_unlock(&rb->w_lock);
                return 0;
        }

        pblk_rl_gc_in(&pblk->rl, nr_entries);
        spin_unlock(&rb->w_lock);

        return 1;
}

/*
 * The caller of this function must ensure that the backpointer will not
 * overwrite the entries passed on the list.
 */
unsigned int pblk_rb_read_to_bio_list(struct pblk_rb *rb, struct bio *bio,
                                      struct list_head *list,
                                      unsigned int max)
{
        struct pblk_rb_entry *entry, *tentry;
        struct page *page;
        unsigned int read = 0;
        int ret;

        list_for_each_entry_safe(entry, tentry, list, index) {
                if (read > max) {
                        pr_err("pblk: too many entries on list\n");
                        goto out;
                }

                page = virt_to_page(entry->data);
                if (!page) {
                        pr_err("pblk: could not allocate write bio page\n");
                        goto out;
                }

                ret = bio_add_page(bio, page, rb->seg_size, 0);
                if (ret != rb->seg_size) {
                        pr_err("pblk: could not add page to write bio\n");
                        goto out;
                }

                list_del(&entry->index);
                read++;
        }

out:
        return read;
}

/*
 * Read available entries on rb and add them to the given bio. To avoid a memory
 * copy, a page reference to the write buffer is used to be added to the bio.
 *
 * This function is used by the write thread to form the write bio that will
 * persist data on the write buffer to the media.
 */
unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd,
                                 struct bio *bio, unsigned int pos,
                                 unsigned int nr_entries, unsigned int count)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct request_queue *q = pblk->dev->q;
        struct pblk_c_ctx *c_ctx = nvm_rq_to_pdu(rqd);
        struct pblk_rb_entry *entry;
        struct page *page;
        unsigned int pad = 0, to_read = nr_entries;
        unsigned int i;
        int flags;

        if (count < nr_entries) {
                pad = nr_entries - count;
                to_read = count;
        }

        c_ctx->sentry = pos;
        c_ctx->nr_valid = to_read;
        c_ctx->nr_padded = pad;

        for (i = 0; i < to_read; i++) {
                entry = &rb->entries[pos];

                /* A write has been allowed into the buffer, but data is still
                 * being copied to it. It is ok to busy wait.
                 */
try:
                flags = READ_ONCE(entry->w_ctx.flags);
                if (!(flags & PBLK_WRITTEN_DATA)) {
                        io_schedule();
                        goto try;
                }

                page = virt_to_page(entry->data);
                if (!page) {
                        pr_err("pblk: could not allocate write bio page\n");
                        flags &= ~PBLK_WRITTEN_DATA;
                        flags |= PBLK_SUBMITTED_ENTRY;
                        /* Release flags on context. Protect from writes */
                        smp_store_release(&entry->w_ctx.flags, flags);
                        return NVM_IO_ERR;
                }

                if (bio_add_pc_page(q, bio, page, rb->seg_size, 0) !=
                                                                rb->seg_size) {
                        pr_err("pblk: could not add page to write bio\n");
                        flags &= ~PBLK_WRITTEN_DATA;
                        flags |= PBLK_SUBMITTED_ENTRY;
                        /* Release flags on context. Protect from writes */
                        smp_store_release(&entry->w_ctx.flags, flags);
                        return NVM_IO_ERR;
                }

                if (flags & PBLK_FLUSH_ENTRY) {
                        unsigned int sync_point;

                        sync_point = READ_ONCE(rb->sync_point);
                        if (sync_point == pos) {
                                /* Protect syncs */
                                smp_store_release(&rb->sync_point, EMPTY_ENTRY);
                        }

                        flags &= ~PBLK_FLUSH_ENTRY;
#ifdef CONFIG_NVM_DEBUG
                        atomic_dec(&rb->inflight_sync_point);
#endif
                }

                flags &= ~PBLK_WRITTEN_DATA;
                flags |= PBLK_SUBMITTED_ENTRY;

                /* Release flags on context. Protect from writes */
                smp_store_release(&entry->w_ctx.flags, flags);

                pos = (pos + 1) & (rb->nr_entries - 1);
        }

        if (pad) {
                if (pblk_bio_add_pages(pblk, bio, GFP_KERNEL, pad)) {
                        pr_err("pblk: could not pad page in write bio\n");
                        return NVM_IO_ERR;
                }
        }

#ifdef CONFIG_NVM_DEBUG
        atomic_long_add(pad, &((struct pblk *)
                        (container_of(rb, struct pblk, rwb)))->padded_writes);
#endif

        return NVM_IO_OK;
}

/*
 * Copy to bio only if the lba matches the one on the given cache entry.
 * Otherwise, it means that the entry has been overwritten, and the bio should
 * be directed to disk.
 */
int pblk_rb_copy_to_bio(struct pblk_rb *rb, struct bio *bio, sector_t lba,
                        struct ppa_addr ppa, int bio_iter, bool advanced_bio)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct pblk_rb_entry *entry;
        struct pblk_w_ctx *w_ctx;
        struct ppa_addr l2p_ppa;
        u64 pos = pblk_addr_to_cacheline(ppa);
        void *data;
        int flags;
        int ret = 1;


#ifdef CONFIG_NVM_DEBUG
        /* Caller must ensure that the access will not cause an overflow */
        BUG_ON(pos >= rb->nr_entries);
#endif
        entry = &rb->entries[pos];
        w_ctx = &entry->w_ctx;
        flags = READ_ONCE(w_ctx->flags);

        spin_lock(&rb->w_lock);
        spin_lock(&pblk->trans_lock);
        l2p_ppa = pblk_trans_map_get(pblk, lba);
        spin_unlock(&pblk->trans_lock);

        /* Check if the entry has been overwritten or is scheduled to be */
        if (!pblk_ppa_comp(l2p_ppa, ppa) || w_ctx->lba != lba ||
                                                flags & PBLK_WRITABLE_ENTRY) {
                ret = 0;
                goto out;
        }

        /* Only advance the bio if it hasn't been advanced already. If advanced,
         * this bio is at least a partial bio (i.e., it has partially been
         * filled with data from the cache). If part of the data resides on the
         * media, we will read later on
         */
        if (unlikely(!advanced_bio))
                bio_advance(bio, bio_iter * PBLK_EXPOSED_PAGE_SIZE);

        data = bio_data(bio);
        memcpy(data, entry->data, rb->seg_size);

out:
        spin_unlock(&rb->w_lock);
        return ret;
}

struct pblk_w_ctx *pblk_rb_w_ctx(struct pblk_rb *rb, unsigned int pos)
{
        unsigned int entry = pos & (rb->nr_entries - 1);

        return &rb->entries[entry].w_ctx;
}

unsigned int pblk_rb_sync_init(struct pblk_rb *rb, unsigned long *flags)
        __acquires(&rb->s_lock)
{
        if (flags)
                spin_lock_irqsave(&rb->s_lock, *flags);
        else
                spin_lock_irq(&rb->s_lock);

        return rb->sync;
}

void pblk_rb_sync_end(struct pblk_rb *rb, unsigned long *flags)
        __releases(&rb->s_lock)
{
        lockdep_assert_held(&rb->s_lock);

        if (flags)
                spin_unlock_irqrestore(&rb->s_lock, *flags);
        else
                spin_unlock_irq(&rb->s_lock);
}

unsigned int pblk_rb_sync_advance(struct pblk_rb *rb, unsigned int nr_entries)
{
        unsigned int sync;
        unsigned int i;

        lockdep_assert_held(&rb->s_lock);

        sync = READ_ONCE(rb->sync);

        for (i = 0; i < nr_entries; i++)
                sync = (sync + 1) & (rb->nr_entries - 1);

        /* Protect from counts */
        smp_store_release(&rb->sync, sync);

        return sync;
}

unsigned int pblk_rb_sync_point_count(struct pblk_rb *rb)
{
        unsigned int subm, sync_point;
        unsigned int count;

        /* Protect syncs */
        sync_point = smp_load_acquire(&rb->sync_point);
        if (sync_point == EMPTY_ENTRY)
                return 0;

        subm = READ_ONCE(rb->subm);

        /* The sync point itself counts as a sector to sync */
        count = pblk_rb_ring_count(sync_point, subm, rb->nr_entries) + 1;

        return count;
}

/*
 * Scan from the current position of the sync pointer to find the entry that
 * corresponds to the given ppa. This is necessary since write requests can be
 * completed out of order. The assumption is that the ppa is close to the sync
 * pointer thus the search will not take long.
 *
 * The caller of this function must guarantee that the sync pointer will no
 * reach the entry while it is using the metadata associated with it. With this
 * assumption in mind, there is no need to take the sync lock.
 */
struct pblk_rb_entry *pblk_rb_sync_scan_entry(struct pblk_rb *rb,
                                              struct ppa_addr *ppa)
{
        unsigned int sync, subm, count;
        unsigned int i;

        sync = READ_ONCE(rb->sync);
        subm = READ_ONCE(rb->subm);
        count = pblk_rb_ring_count(subm, sync, rb->nr_entries);

        for (i = 0; i < count; i++)
                sync = (sync + 1) & (rb->nr_entries - 1);

        return NULL;
}

int pblk_rb_tear_down_check(struct pblk_rb *rb)
{
        struct pblk_rb_entry *entry;
        int i;
        int ret = 0;

        spin_lock(&rb->w_lock);
        spin_lock_irq(&rb->s_lock);

        if ((rb->mem == rb->subm) && (rb->subm == rb->sync) &&
                                (rb->sync == rb->l2p_update) &&
                                (rb->sync_point == EMPTY_ENTRY)) {
                goto out;
        }

        if (!rb->entries) {
                ret = 1;
                goto out;
        }

        for (i = 0; i < rb->nr_entries; i++) {
                entry = &rb->entries[i];

                if (!entry->data) {
                        ret = 1;
                        goto out;
                }
        }

out:
        spin_unlock(&rb->w_lock);
        spin_unlock_irq(&rb->s_lock);

        return ret;
}

unsigned int pblk_rb_wrap_pos(struct pblk_rb *rb, unsigned int pos)
{
        return (pos & (rb->nr_entries - 1));
}

int pblk_rb_pos_oob(struct pblk_rb *rb, u64 pos)
{
        return (pos >= rb->nr_entries);
}

ssize_t pblk_rb_sysfs(struct pblk_rb *rb, char *buf)
{
        struct pblk *pblk = container_of(rb, struct pblk, rwb);
        struct pblk_c_ctx *c;
        ssize_t offset;
        int queued_entries = 0;

        spin_lock_irq(&rb->s_lock);
        list_for_each_entry(c, &pblk->compl_list, list)
                queued_entries++;
        spin_unlock_irq(&rb->s_lock);

        if (rb->sync_point != EMPTY_ENTRY)
                offset = scnprintf(buf, PAGE_SIZE,
                        "%u\t%u\t%u\t%u\t%u\t%u\t%u - %u/%u/%u - %d\n",
                        rb->nr_entries,
                        rb->mem,
                        rb->subm,
                        rb->sync,
                        rb->l2p_update,
#ifdef CONFIG_NVM_DEBUG
                        atomic_read(&rb->inflight_sync_point),
#else
                        0,
#endif
                        rb->sync_point,
                        pblk_rb_read_count(rb),
                        pblk_rb_space(rb),
                        pblk_rb_sync_point_count(rb),
                        queued_entries);
        else
                offset = scnprintf(buf, PAGE_SIZE,
                        "%u\t%u\t%u\t%u\t%u\t%u\tNULL - %u/%u/%u - %d\n",
                        rb->nr_entries,
                        rb->mem,
                        rb->subm,
                        rb->sync,
                        rb->l2p_update,
#ifdef CONFIG_NVM_DEBUG
                        atomic_read(&rb->inflight_sync_point),
#else
                        0,
#endif
                        pblk_rb_read_count(rb),
                        pblk_rb_space(rb),
                        pblk_rb_sync_point_count(rb),
                        queued_entries);

        return offset;
}