These changes are the raw update to linux-4.4.6-rt14. Kernel sources

are taken from kernel.org, and rt patch from the rt wiki download page.

During the rebasing, the following patch collided:

Force tick interrupt and get rid of softirq magic(I70131fb85).

Collisions have been removed because its logic was found on the
source already.

Change-Id: I7f57a4081d9deaa0d9ccfc41a6c8daccdee3b769
Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>

1 files changed, 1371 insertions, 0 deletions

diff --git a/kernel/drivers/lightnvm/rrpc.c b/kernel/drivers/lightnvm/rrpc.c
new file mode 100644
index 000000000..134e4faba
--- /dev/null
+++ b/kernel/drivers/lightnvm/rrpc.c
@@ -0,0 +1,1371 @@
+/*
+ * Copyright (C) 2015 IT University of Copenhagen
+ * Initial release: Matias Bjorling <m@bjorling.me>
+ *
+ * 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.
+ *
+ * Implementation of a Round-robin page-based Hybrid FTL for Open-channel SSDs.
+ */
+
+#include "rrpc.h"
+
+static struct kmem_cache *rrpc_gcb_cache, *rrpc_rq_cache;
+static DECLARE_RWSEM(rrpc_lock);
+
+static int rrpc_submit_io(struct rrpc *rrpc, struct bio *bio,
+				struct nvm_rq *rqd, unsigned long flags);
+
+#define rrpc_for_each_lun(rrpc, rlun, i) \
+		for ((i) = 0, rlun = &(rrpc)->luns[0]; \
+			(i) < (rrpc)->nr_luns; (i)++, rlun = &(rrpc)->luns[(i)])
+
+static void rrpc_page_invalidate(struct rrpc *rrpc, struct rrpc_addr *a)
+{
+	struct rrpc_block *rblk = a->rblk;
+	unsigned int pg_offset;
+
+	lockdep_assert_held(&rrpc->rev_lock);
+
+	if (a->addr == ADDR_EMPTY || !rblk)
+		return;
+
+	spin_lock(&rblk->lock);
+
+	div_u64_rem(a->addr, rrpc->dev->pgs_per_blk, &pg_offset);
+	WARN_ON(test_and_set_bit(pg_offset, rblk->invalid_pages));
+	rblk->nr_invalid_pages++;
+
+	spin_unlock(&rblk->lock);
+
+	rrpc->rev_trans_map[a->addr - rrpc->poffset].addr = ADDR_EMPTY;
+}
+
+static void rrpc_invalidate_range(struct rrpc *rrpc, sector_t slba,
+								unsigned len)
+{
+	sector_t i;
+
+	spin_lock(&rrpc->rev_lock);
+	for (i = slba; i < slba + len; i++) {
+		struct rrpc_addr *gp = &rrpc->trans_map[i];
+
+		rrpc_page_invalidate(rrpc, gp);
+		gp->rblk = NULL;
+	}
+	spin_unlock(&rrpc->rev_lock);
+}
+
+static struct nvm_rq *rrpc_inflight_laddr_acquire(struct rrpc *rrpc,
+					sector_t laddr, unsigned int pages)
+{
+	struct nvm_rq *rqd;
+	struct rrpc_inflight_rq *inf;
+
+	rqd = mempool_alloc(rrpc->rq_pool, GFP_ATOMIC);
+	if (!rqd)
+		return ERR_PTR(-ENOMEM);
+
+	inf = rrpc_get_inflight_rq(rqd);
+	if (rrpc_lock_laddr(rrpc, laddr, pages, inf)) {
+		mempool_free(rqd, rrpc->rq_pool);
+		return NULL;
+	}
+
+	return rqd;
+}
+
+static void rrpc_inflight_laddr_release(struct rrpc *rrpc, struct nvm_rq *rqd)
+{
+	struct rrpc_inflight_rq *inf = rrpc_get_inflight_rq(rqd);
+
+	rrpc_unlock_laddr(rrpc, inf);
+
+	mempool_free(rqd, rrpc->rq_pool);
+}
+
+static void rrpc_discard(struct rrpc *rrpc, struct bio *bio)
+{
+	sector_t slba = bio->bi_iter.bi_sector / NR_PHY_IN_LOG;
+	sector_t len = bio->bi_iter.bi_size / RRPC_EXPOSED_PAGE_SIZE;
+	struct nvm_rq *rqd;
+
+	do {
+		rqd = rrpc_inflight_laddr_acquire(rrpc, slba, len);
+		schedule();
+	} while (!rqd);
+
+	if (IS_ERR(rqd)) {
+		pr_err("rrpc: unable to acquire inflight IO\n");
+		bio_io_error(bio);
+		return;
+	}
+
+	rrpc_invalidate_range(rrpc, slba, len);
+	rrpc_inflight_laddr_release(rrpc, rqd);
+}
+
+static int block_is_full(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	return (rblk->next_page == rrpc->dev->pgs_per_blk);
+}
+
+static u64 block_to_addr(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	struct nvm_block *blk = rblk->parent;
+
+	return blk->id * rrpc->dev->pgs_per_blk;
+}
+
+static struct ppa_addr linear_to_generic_addr(struct nvm_dev *dev,
+							struct ppa_addr r)
+{
+	struct ppa_addr l;
+	int secs, pgs, blks, luns;
+	sector_t ppa = r.ppa;
+
+	l.ppa = 0;
+
+	div_u64_rem(ppa, dev->sec_per_pg, &secs);
+	l.g.sec = secs;
+
+	sector_div(ppa, dev->sec_per_pg);
+	div_u64_rem(ppa, dev->sec_per_blk, &pgs);
+	l.g.pg = pgs;
+
+	sector_div(ppa, dev->pgs_per_blk);
+	div_u64_rem(ppa, dev->blks_per_lun, &blks);
+	l.g.blk = blks;
+
+	sector_div(ppa, dev->blks_per_lun);
+	div_u64_rem(ppa, dev->luns_per_chnl, &luns);
+	l.g.lun = luns;
+
+	sector_div(ppa, dev->luns_per_chnl);
+	l.g.ch = ppa;
+
+	return l;
+}
+
+static struct ppa_addr rrpc_ppa_to_gaddr(struct nvm_dev *dev, u64 addr)
+{
+	struct ppa_addr paddr;
+
+	paddr.ppa = addr;
+	return linear_to_generic_addr(dev, paddr);
+}
+
+/* requires lun->lock taken */
+static void rrpc_set_lun_cur(struct rrpc_lun *rlun, struct rrpc_block *rblk)
+{
+	struct rrpc *rrpc = rlun->rrpc;
+
+	BUG_ON(!rblk);
+
+	if (rlun->cur) {
+		spin_lock(&rlun->cur->lock);
+		WARN_ON(!block_is_full(rrpc, rlun->cur));
+		spin_unlock(&rlun->cur->lock);
+	}
+	rlun->cur = rblk;
+}
+
+static struct rrpc_block *rrpc_get_blk(struct rrpc *rrpc, struct rrpc_lun *rlun,
+							unsigned long flags)
+{
+	struct nvm_block *blk;
+	struct rrpc_block *rblk;
+
+	blk = nvm_get_blk(rrpc->dev, rlun->parent, flags);
+	if (!blk)
+		return NULL;
+
+	rblk = &rlun->blocks[blk->id];
+	blk->priv = rblk;
+
+	bitmap_zero(rblk->invalid_pages, rrpc->dev->pgs_per_blk);
+	rblk->next_page = 0;
+	rblk->nr_invalid_pages = 0;
+	atomic_set(&rblk->data_cmnt_size, 0);
+
+	return rblk;
+}
+
+static void rrpc_put_blk(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	nvm_put_blk(rrpc->dev, rblk->parent);
+}
+
+static void rrpc_put_blks(struct rrpc *rrpc)
+{
+	struct rrpc_lun *rlun;
+	int i;
+
+	for (i = 0; i < rrpc->nr_luns; i++) {
+		rlun = &rrpc->luns[i];
+		if (rlun->cur)
+			rrpc_put_blk(rrpc, rlun->cur);
+		if (rlun->gc_cur)
+			rrpc_put_blk(rrpc, rlun->gc_cur);
+	}
+}
+
+static struct rrpc_lun *get_next_lun(struct rrpc *rrpc)
+{
+	int next = atomic_inc_return(&rrpc->next_lun);
+
+	return &rrpc->luns[next % rrpc->nr_luns];
+}
+
+static void rrpc_gc_kick(struct rrpc *rrpc)
+{
+	struct rrpc_lun *rlun;
+	unsigned int i;
+
+	for (i = 0; i < rrpc->nr_luns; i++) {
+		rlun = &rrpc->luns[i];
+		queue_work(rrpc->krqd_wq, &rlun->ws_gc);
+	}
+}
+
+/*
+ * timed GC every interval.
+ */
+static void rrpc_gc_timer(unsigned long data)
+{
+	struct rrpc *rrpc = (struct rrpc *)data;
+
+	rrpc_gc_kick(rrpc);
+	mod_timer(&rrpc->gc_timer, jiffies + msecs_to_jiffies(10));
+}
+
+static void rrpc_end_sync_bio(struct bio *bio)
+{
+	struct completion *waiting = bio->bi_private;
+
+	if (bio->bi_error)
+		pr_err("nvm: gc request failed (%u).\n", bio->bi_error);
+
+	complete(waiting);
+}
+
+/*
+ * rrpc_move_valid_pages -- migrate live data off the block
+ * @rrpc: the 'rrpc' structure
+ * @block: the block from which to migrate live pages
+ *
+ * Description:
+ *   GC algorithms may call this function to migrate remaining live
+ *   pages off the block prior to erasing it. This function blocks
+ *   further execution until the operation is complete.
+ */
+static int rrpc_move_valid_pages(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	struct request_queue *q = rrpc->dev->q;
+	struct rrpc_rev_addr *rev;
+	struct nvm_rq *rqd;
+	struct bio *bio;
+	struct page *page;
+	int slot;
+	int nr_pgs_per_blk = rrpc->dev->pgs_per_blk;
+	u64 phys_addr;
+	DECLARE_COMPLETION_ONSTACK(wait);
+
+	if (bitmap_full(rblk->invalid_pages, nr_pgs_per_blk))
+		return 0;
+
+	bio = bio_alloc(GFP_NOIO, 1);
+	if (!bio) {
+		pr_err("nvm: could not alloc bio to gc\n");
+		return -ENOMEM;
+	}
+
+	page = mempool_alloc(rrpc->page_pool, GFP_NOIO);
+
+	while ((slot = find_first_zero_bit(rblk->invalid_pages,
+					    nr_pgs_per_blk)) < nr_pgs_per_blk) {
+
+		/* Lock laddr */
+		phys_addr = (rblk->parent->id * nr_pgs_per_blk) + slot;
+
+try:
+		spin_lock(&rrpc->rev_lock);
+		/* Get logical address from physical to logical table */
+		rev = &rrpc->rev_trans_map[phys_addr - rrpc->poffset];
+		/* already updated by previous regular write */
+		if (rev->addr == ADDR_EMPTY) {
+			spin_unlock(&rrpc->rev_lock);
+			continue;
+		}
+
+		rqd = rrpc_inflight_laddr_acquire(rrpc, rev->addr, 1);
+		if (IS_ERR_OR_NULL(rqd)) {
+			spin_unlock(&rrpc->rev_lock);
+			schedule();
+			goto try;
+		}
+
+		spin_unlock(&rrpc->rev_lock);
+
+		/* Perform read to do GC */
+		bio->bi_iter.bi_sector = rrpc_get_sector(rev->addr);
+		bio->bi_rw = READ;
+		bio->bi_private = &wait;
+		bio->bi_end_io = rrpc_end_sync_bio;
+
+		/* TODO: may fail when EXP_PG_SIZE > PAGE_SIZE */
+		bio_add_pc_page(q, bio, page, RRPC_EXPOSED_PAGE_SIZE, 0);
+
+		if (rrpc_submit_io(rrpc, bio, rqd, NVM_IOTYPE_GC)) {
+			pr_err("rrpc: gc read failed.\n");
+			rrpc_inflight_laddr_release(rrpc, rqd);
+			goto finished;
+		}
+		wait_for_completion_io(&wait);
+
+		bio_reset(bio);
+		reinit_completion(&wait);
+
+		bio->bi_iter.bi_sector = rrpc_get_sector(rev->addr);
+		bio->bi_rw = WRITE;
+		bio->bi_private = &wait;
+		bio->bi_end_io = rrpc_end_sync_bio;
+
+		bio_add_pc_page(q, bio, page, RRPC_EXPOSED_PAGE_SIZE, 0);
+
+		/* turn the command around and write the data back to a new
+		 * address
+		 */
+		if (rrpc_submit_io(rrpc, bio, rqd, NVM_IOTYPE_GC)) {
+			pr_err("rrpc: gc write failed.\n");
+			rrpc_inflight_laddr_release(rrpc, rqd);
+			goto finished;
+		}
+		wait_for_completion_io(&wait);
+
+		rrpc_inflight_laddr_release(rrpc, rqd);
+
+		bio_reset(bio);
+	}
+
+finished:
+	mempool_free(page, rrpc->page_pool);
+	bio_put(bio);
+
+	if (!bitmap_full(rblk->invalid_pages, nr_pgs_per_blk)) {
+		pr_err("nvm: failed to garbage collect block\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static void rrpc_block_gc(struct work_struct *work)
+{
+	struct rrpc_block_gc *gcb = container_of(work, struct rrpc_block_gc,
+									ws_gc);
+	struct rrpc *rrpc = gcb->rrpc;
+	struct rrpc_block *rblk = gcb->rblk;
+	struct nvm_dev *dev = rrpc->dev;
+
+	pr_debug("nvm: block '%lu' being reclaimed\n", rblk->parent->id);
+
+	if (rrpc_move_valid_pages(rrpc, rblk))
+		goto done;
+
+	nvm_erase_blk(dev, rblk->parent);
+	rrpc_put_blk(rrpc, rblk);
+done:
+	mempool_free(gcb, rrpc->gcb_pool);
+}
+
+/* the block with highest number of invalid pages, will be in the beginning
+ * of the list
+ */
+static struct rrpc_block *rblock_max_invalid(struct rrpc_block *ra,
+							struct rrpc_block *rb)
+{
+	if (ra->nr_invalid_pages == rb->nr_invalid_pages)
+		return ra;
+
+	return (ra->nr_invalid_pages < rb->nr_invalid_pages) ? rb : ra;
+}
+
+/* linearly find the block with highest number of invalid pages
+ * requires lun->lock
+ */
+static struct rrpc_block *block_prio_find_max(struct rrpc_lun *rlun)
+{
+	struct list_head *prio_list = &rlun->prio_list;
+	struct rrpc_block *rblock, *max;
+
+	BUG_ON(list_empty(prio_list));
+
+	max = list_first_entry(prio_list, struct rrpc_block, prio);
+	list_for_each_entry(rblock, prio_list, prio)
+		max = rblock_max_invalid(max, rblock);
+
+	return max;
+}
+
+static void rrpc_lun_gc(struct work_struct *work)
+{
+	struct rrpc_lun *rlun = container_of(work, struct rrpc_lun, ws_gc);
+	struct rrpc *rrpc = rlun->rrpc;
+	struct nvm_lun *lun = rlun->parent;
+	struct rrpc_block_gc *gcb;
+	unsigned int nr_blocks_need;
+
+	nr_blocks_need = rrpc->dev->blks_per_lun / GC_LIMIT_INVERSE;
+
+	if (nr_blocks_need < rrpc->nr_luns)
+		nr_blocks_need = rrpc->nr_luns;
+
+	spin_lock(&lun->lock);
+	while (nr_blocks_need > lun->nr_free_blocks &&
+					!list_empty(&rlun->prio_list)) {
+		struct rrpc_block *rblock = block_prio_find_max(rlun);
+		struct nvm_block *block = rblock->parent;
+
+		if (!rblock->nr_invalid_pages)
+			break;
+
+		list_del_init(&rblock->prio);
+
+		BUG_ON(!block_is_full(rrpc, rblock));
+
+		pr_debug("rrpc: selected block '%lu' for GC\n", block->id);
+
+		gcb = mempool_alloc(rrpc->gcb_pool, GFP_ATOMIC);
+		if (!gcb)
+			break;
+
+		gcb->rrpc = rrpc;
+		gcb->rblk = rblock;
+		INIT_WORK(&gcb->ws_gc, rrpc_block_gc);
+
+		queue_work(rrpc->kgc_wq, &gcb->ws_gc);
+
+		nr_blocks_need--;
+	}
+	spin_unlock(&lun->lock);
+
+	/* TODO: Hint that request queue can be started again */
+}
+
+static void rrpc_gc_queue(struct work_struct *work)
+{
+	struct rrpc_block_gc *gcb = container_of(work, struct rrpc_block_gc,
+									ws_gc);
+	struct rrpc *rrpc = gcb->rrpc;
+	struct rrpc_block *rblk = gcb->rblk;
+	struct nvm_lun *lun = rblk->parent->lun;
+	struct rrpc_lun *rlun = &rrpc->luns[lun->id - rrpc->lun_offset];
+
+	spin_lock(&rlun->lock);
+	list_add_tail(&rblk->prio, &rlun->prio_list);
+	spin_unlock(&rlun->lock);
+
+	mempool_free(gcb, rrpc->gcb_pool);
+	pr_debug("nvm: block '%lu' is full, allow GC (sched)\n",
+							rblk->parent->id);
+}
+
+static const struct block_device_operations rrpc_fops = {
+	.owner		= THIS_MODULE,
+};
+
+static struct rrpc_lun *rrpc_get_lun_rr(struct rrpc *rrpc, int is_gc)
+{
+	unsigned int i;
+	struct rrpc_lun *rlun, *max_free;
+
+	if (!is_gc)
+		return get_next_lun(rrpc);
+
+	/* during GC, we don't care about RR, instead we want to make
+	 * sure that we maintain evenness between the block luns.
+	 */
+	max_free = &rrpc->luns[0];
+	/* prevent GC-ing lun from devouring pages of a lun with
+	 * little free blocks. We don't take the lock as we only need an
+	 * estimate.
+	 */
+	rrpc_for_each_lun(rrpc, rlun, i) {
+		if (rlun->parent->nr_free_blocks >
+					max_free->parent->nr_free_blocks)
+			max_free = rlun;
+	}
+
+	return max_free;
+}
+
+static struct rrpc_addr *rrpc_update_map(struct rrpc *rrpc, sector_t laddr,
+					struct rrpc_block *rblk, u64 paddr)
+{
+	struct rrpc_addr *gp;
+	struct rrpc_rev_addr *rev;
+
+	BUG_ON(laddr >= rrpc->nr_pages);
+
+	gp = &rrpc->trans_map[laddr];
+	spin_lock(&rrpc->rev_lock);
+	if (gp->rblk)
+		rrpc_page_invalidate(rrpc, gp);
+
+	gp->addr = paddr;
+	gp->rblk = rblk;
+
+	rev = &rrpc->rev_trans_map[gp->addr - rrpc->poffset];
+	rev->addr = laddr;
+	spin_unlock(&rrpc->rev_lock);
+
+	return gp;
+}
+
+static u64 rrpc_alloc_addr(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	u64 addr = ADDR_EMPTY;
+
+	spin_lock(&rblk->lock);
+	if (block_is_full(rrpc, rblk))
+		goto out;
+
+	addr = block_to_addr(rrpc, rblk) + rblk->next_page;
+
+	rblk->next_page++;
+out:
+	spin_unlock(&rblk->lock);
+	return addr;
+}
+
+/* Simple round-robin Logical to physical address translation.
+ *
+ * Retrieve the mapping using the active append point. Then update the ap for
+ * the next write to the disk.
+ *
+ * Returns rrpc_addr with the physical address and block. Remember to return to
+ * rrpc->addr_cache when request is finished.
+ */
+static struct rrpc_addr *rrpc_map_page(struct rrpc *rrpc, sector_t laddr,
+								int is_gc)
+{
+	struct rrpc_lun *rlun;
+	struct rrpc_block *rblk;
+	struct nvm_lun *lun;
+	u64 paddr;
+
+	rlun = rrpc_get_lun_rr(rrpc, is_gc);
+	lun = rlun->parent;
+
+	if (!is_gc && lun->nr_free_blocks < rrpc->nr_luns * 4)
+		return NULL;
+
+	spin_lock(&rlun->lock);
+
+	rblk = rlun->cur;
+retry:
+	paddr = rrpc_alloc_addr(rrpc, rblk);
+
+	if (paddr == ADDR_EMPTY) {
+		rblk = rrpc_get_blk(rrpc, rlun, 0);
+		if (rblk) {
+			rrpc_set_lun_cur(rlun, rblk);
+			goto retry;
+		}
+
+		if (is_gc) {
+			/* retry from emergency gc block */
+			paddr = rrpc_alloc_addr(rrpc, rlun->gc_cur);
+			if (paddr == ADDR_EMPTY) {
+				rblk = rrpc_get_blk(rrpc, rlun, 1);
+				if (!rblk) {
+					pr_err("rrpc: no more blocks");
+					goto err;
+				}
+
+				rlun->gc_cur = rblk;
+				paddr = rrpc_alloc_addr(rrpc, rlun->gc_cur);
+			}
+			rblk = rlun->gc_cur;
+		}
+	}
+
+	spin_unlock(&rlun->lock);
+	return rrpc_update_map(rrpc, laddr, rblk, paddr);
+err:
+	spin_unlock(&rlun->lock);
+	return NULL;
+}
+
+static void rrpc_run_gc(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	struct rrpc_block_gc *gcb;
+
+	gcb = mempool_alloc(rrpc->gcb_pool, GFP_ATOMIC);
+	if (!gcb) {
+		pr_err("rrpc: unable to queue block for gc.");
+		return;
+	}
+
+	gcb->rrpc = rrpc;
+	gcb->rblk = rblk;
+
+	INIT_WORK(&gcb->ws_gc, rrpc_gc_queue);
+	queue_work(rrpc->kgc_wq, &gcb->ws_gc);
+}
+
+static void rrpc_end_io_write(struct rrpc *rrpc, struct rrpc_rq *rrqd,
+						sector_t laddr, uint8_t npages)
+{
+	struct rrpc_addr *p;
+	struct rrpc_block *rblk;
+	struct nvm_lun *lun;
+	int cmnt_size, i;
+
+	for (i = 0; i < npages; i++) {
+		p = &rrpc->trans_map[laddr + i];
+		rblk = p->rblk;
+		lun = rblk->parent->lun;
+
+		cmnt_size = atomic_inc_return(&rblk->data_cmnt_size);
+		if (unlikely(cmnt_size == rrpc->dev->pgs_per_blk))
+			rrpc_run_gc(rrpc, rblk);
+	}
+}
+
+static int rrpc_end_io(struct nvm_rq *rqd, int error)
+{
+	struct rrpc *rrpc = container_of(rqd->ins, struct rrpc, instance);
+	struct rrpc_rq *rrqd = nvm_rq_to_pdu(rqd);
+	uint8_t npages = rqd->nr_pages;
+	sector_t laddr = rrpc_get_laddr(rqd->bio) - npages;
+
+	if (bio_data_dir(rqd->bio) == WRITE)
+		rrpc_end_io_write(rrpc, rrqd, laddr, npages);
+
+	if (rrqd->flags & NVM_IOTYPE_GC)
+		return 0;
+
+	rrpc_unlock_rq(rrpc, rqd);
+	bio_put(rqd->bio);
+
+	if (npages > 1)
+		nvm_dev_dma_free(rrpc->dev, rqd->ppa_list, rqd->dma_ppa_list);
+	if (rqd->metadata)
+		nvm_dev_dma_free(rrpc->dev, rqd->metadata, rqd->dma_metadata);
+
+	mempool_free(rqd, rrpc->rq_pool);
+
+	return 0;
+}
+
+static int rrpc_read_ppalist_rq(struct rrpc *rrpc, struct bio *bio,
+			struct nvm_rq *rqd, unsigned long flags, int npages)
+{
+	struct rrpc_inflight_rq *r = rrpc_get_inflight_rq(rqd);
+	struct rrpc_addr *gp;
+	sector_t laddr = rrpc_get_laddr(bio);
+	int is_gc = flags & NVM_IOTYPE_GC;
+	int i;
+
+	if (!is_gc && rrpc_lock_rq(rrpc, bio, rqd)) {
+		nvm_dev_dma_free(rrpc->dev, rqd->ppa_list, rqd->dma_ppa_list);
+		return NVM_IO_REQUEUE;
+	}
+
+	for (i = 0; i < npages; i++) {
+		/* We assume that mapping occurs at 4KB granularity */
+		BUG_ON(!(laddr + i >= 0 && laddr + i < rrpc->nr_pages));
+		gp = &rrpc->trans_map[laddr + i];
+
+		if (gp->rblk) {
+			rqd->ppa_list[i] = rrpc_ppa_to_gaddr(rrpc->dev,
+								gp->addr);
+		} else {
+			BUG_ON(is_gc);
+			rrpc_unlock_laddr(rrpc, r);
+			nvm_dev_dma_free(rrpc->dev, rqd->ppa_list,
+							rqd->dma_ppa_list);
+			return NVM_IO_DONE;
+		}
+	}
+
+	rqd->opcode = NVM_OP_HBREAD;
+
+	return NVM_IO_OK;
+}
+
+static int rrpc_read_rq(struct rrpc *rrpc, struct bio *bio, struct nvm_rq *rqd,
+							unsigned long flags)
+{
+	struct rrpc_rq *rrqd = nvm_rq_to_pdu(rqd);
+	int is_gc = flags & NVM_IOTYPE_GC;
+	sector_t laddr = rrpc_get_laddr(bio);
+	struct rrpc_addr *gp;
+
+	if (!is_gc && rrpc_lock_rq(rrpc, bio, rqd))
+		return NVM_IO_REQUEUE;
+
+	BUG_ON(!(laddr >= 0 && laddr < rrpc->nr_pages));
+	gp = &rrpc->trans_map[laddr];
+
+	if (gp->rblk) {
+		rqd->ppa_addr = rrpc_ppa_to_gaddr(rrpc->dev, gp->addr);
+	} else {
+		BUG_ON(is_gc);
+		rrpc_unlock_rq(rrpc, rqd);
+		return NVM_IO_DONE;
+	}
+
+	rqd->opcode = NVM_OP_HBREAD;
+	rrqd->addr = gp;
+
+	return NVM_IO_OK;
+}
+
+static int rrpc_write_ppalist_rq(struct rrpc *rrpc, struct bio *bio,
+			struct nvm_rq *rqd, unsigned long flags, int npages)
+{
+	struct rrpc_inflight_rq *r = rrpc_get_inflight_rq(rqd);
+	struct rrpc_addr *p;
+	sector_t laddr = rrpc_get_laddr(bio);
+	int is_gc = flags & NVM_IOTYPE_GC;
+	int i;
+
+	if (!is_gc && rrpc_lock_rq(rrpc, bio, rqd)) {
+		nvm_dev_dma_free(rrpc->dev, rqd->ppa_list, rqd->dma_ppa_list);
+		return NVM_IO_REQUEUE;
+	}
+
+	for (i = 0; i < npages; i++) {
+		/* We assume that mapping occurs at 4KB granularity */
+		p = rrpc_map_page(rrpc, laddr + i, is_gc);
+		if (!p) {
+			BUG_ON(is_gc);
+			rrpc_unlock_laddr(rrpc, r);
+			nvm_dev_dma_free(rrpc->dev, rqd->ppa_list,
+							rqd->dma_ppa_list);
+			rrpc_gc_kick(rrpc);
+			return NVM_IO_REQUEUE;
+		}
+
+		rqd->ppa_list[i] = rrpc_ppa_to_gaddr(rrpc->dev,
+								p->addr);
+	}
+
+	rqd->opcode = NVM_OP_HBWRITE;
+
+	return NVM_IO_OK;
+}
+
+static int rrpc_write_rq(struct rrpc *rrpc, struct bio *bio,
+				struct nvm_rq *rqd, unsigned long flags)
+{
+	struct rrpc_rq *rrqd = nvm_rq_to_pdu(rqd);
+	struct rrpc_addr *p;
+	int is_gc = flags & NVM_IOTYPE_GC;
+	sector_t laddr = rrpc_get_laddr(bio);
+
+	if (!is_gc && rrpc_lock_rq(rrpc, bio, rqd))
+		return NVM_IO_REQUEUE;
+
+	p = rrpc_map_page(rrpc, laddr, is_gc);
+	if (!p) {
+		BUG_ON(is_gc);
+		rrpc_unlock_rq(rrpc, rqd);
+		rrpc_gc_kick(rrpc);
+		return NVM_IO_REQUEUE;
+	}
+
+	rqd->ppa_addr = rrpc_ppa_to_gaddr(rrpc->dev, p->addr);
+	rqd->opcode = NVM_OP_HBWRITE;
+	rrqd->addr = p;
+
+	return NVM_IO_OK;
+}
+
+static int rrpc_setup_rq(struct rrpc *rrpc, struct bio *bio,
+			struct nvm_rq *rqd, unsigned long flags, uint8_t npages)
+{
+	if (npages > 1) {
+		rqd->ppa_list = nvm_dev_dma_alloc(rrpc->dev, GFP_KERNEL,
+							&rqd->dma_ppa_list);
+		if (!rqd->ppa_list) {
+			pr_err("rrpc: not able to allocate ppa list\n");
+			return NVM_IO_ERR;
+		}
+
+		if (bio_rw(bio) == WRITE)
+			return rrpc_write_ppalist_rq(rrpc, bio, rqd, flags,
+									npages);
+
+		return rrpc_read_ppalist_rq(rrpc, bio, rqd, flags, npages);
+	}
+
+	if (bio_rw(bio) == WRITE)
+		return rrpc_write_rq(rrpc, bio, rqd, flags);
+
+	return rrpc_read_rq(rrpc, bio, rqd, flags);
+}
+
+static int rrpc_submit_io(struct rrpc *rrpc, struct bio *bio,
+				struct nvm_rq *rqd, unsigned long flags)
+{
+	int err;
+	struct rrpc_rq *rrq = nvm_rq_to_pdu(rqd);
+	uint8_t nr_pages = rrpc_get_pages(bio);
+	int bio_size = bio_sectors(bio) << 9;
+
+	if (bio_size < rrpc->dev->sec_size)
+		return NVM_IO_ERR;
+	else if (bio_size > rrpc->dev->max_rq_size)
+		return NVM_IO_ERR;
+
+	err = rrpc_setup_rq(rrpc, bio, rqd, flags, nr_pages);
+	if (err)
+		return err;
+
+	bio_get(bio);
+	rqd->bio = bio;
+	rqd->ins = &rrpc->instance;
+	rqd->nr_pages = nr_pages;
+	rrq->flags = flags;
+
+	err = nvm_submit_io(rrpc->dev, rqd);
+	if (err) {
+		pr_err("rrpc: I/O submission failed: %d\n", err);
+		return NVM_IO_ERR;
+	}
+
+	return NVM_IO_OK;
+}
+
+static blk_qc_t rrpc_make_rq(struct request_queue *q, struct bio *bio)
+{
+	struct rrpc *rrpc = q->queuedata;
+	struct nvm_rq *rqd;
+	int err;
+
+	if (bio->bi_rw & REQ_DISCARD) {
+		rrpc_discard(rrpc, bio);
+		return BLK_QC_T_NONE;
+	}
+
+	rqd = mempool_alloc(rrpc->rq_pool, GFP_KERNEL);
+	if (!rqd) {
+		pr_err_ratelimited("rrpc: not able to queue bio.");
+		bio_io_error(bio);
+		return BLK_QC_T_NONE;
+	}
+	memset(rqd, 0, sizeof(struct nvm_rq));
+
+	err = rrpc_submit_io(rrpc, bio, rqd, NVM_IOTYPE_NONE);
+	switch (err) {
+	case NVM_IO_OK:
+		return BLK_QC_T_NONE;
+	case NVM_IO_ERR:
+		bio_io_error(bio);
+		break;
+	case NVM_IO_DONE:
+		bio_endio(bio);
+		break;
+	case NVM_IO_REQUEUE:
+		spin_lock(&rrpc->bio_lock);
+		bio_list_add(&rrpc->requeue_bios, bio);
+		spin_unlock(&rrpc->bio_lock);
+		queue_work(rrpc->kgc_wq, &rrpc->ws_requeue);
+		break;
+	}
+
+	mempool_free(rqd, rrpc->rq_pool);
+	return BLK_QC_T_NONE;
+}
+
+static void rrpc_requeue(struct work_struct *work)
+{
+	struct rrpc *rrpc = container_of(work, struct rrpc, ws_requeue);
+	struct bio_list bios;
+	struct bio *bio;
+
+	bio_list_init(&bios);
+
+	spin_lock(&rrpc->bio_lock);
+	bio_list_merge(&bios, &rrpc->requeue_bios);
+	bio_list_init(&rrpc->requeue_bios);
+	spin_unlock(&rrpc->bio_lock);
+
+	while ((bio = bio_list_pop(&bios)))
+		rrpc_make_rq(rrpc->disk->queue, bio);
+}
+
+static void rrpc_gc_free(struct rrpc *rrpc)
+{
+	struct rrpc_lun *rlun;
+	int i;
+
+	if (rrpc->krqd_wq)
+		destroy_workqueue(rrpc->krqd_wq);
+
+	if (rrpc->kgc_wq)
+		destroy_workqueue(rrpc->kgc_wq);
+
+	if (!rrpc->luns)
+		return;
+
+	for (i = 0; i < rrpc->nr_luns; i++) {
+		rlun = &rrpc->luns[i];
+
+		if (!rlun->blocks)
+			break;
+		vfree(rlun->blocks);
+	}
+}
+
+static int rrpc_gc_init(struct rrpc *rrpc)
+{
+	rrpc->krqd_wq = alloc_workqueue("rrpc-lun", WQ_MEM_RECLAIM|WQ_UNBOUND,
+								rrpc->nr_luns);
+	if (!rrpc->krqd_wq)
+		return -ENOMEM;
+
+	rrpc->kgc_wq = alloc_workqueue("rrpc-bg", WQ_MEM_RECLAIM, 1);
+	if (!rrpc->kgc_wq)
+		return -ENOMEM;
+
+	setup_timer(&rrpc->gc_timer, rrpc_gc_timer, (unsigned long)rrpc);
+
+	return 0;
+}
+
+static void rrpc_map_free(struct rrpc *rrpc)
+{
+	vfree(rrpc->rev_trans_map);
+	vfree(rrpc->trans_map);
+}
+
+static int rrpc_l2p_update(u64 slba, u32 nlb, __le64 *entries, void *private)
+{
+	struct rrpc *rrpc = (struct rrpc *)private;
+	struct nvm_dev *dev = rrpc->dev;
+	struct rrpc_addr *addr = rrpc->trans_map + slba;
+	struct rrpc_rev_addr *raddr = rrpc->rev_trans_map;
+	sector_t max_pages = dev->total_pages * (dev->sec_size >> 9);
+	u64 elba = slba + nlb;
+	u64 i;
+
+	if (unlikely(elba > dev->total_pages)) {
+		pr_err("nvm: L2P data from device is out of bounds!\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < nlb; i++) {
+		u64 pba = le64_to_cpu(entries[i]);
+		/* LNVM treats address-spaces as silos, LBA and PBA are
+		 * equally large and zero-indexed.
+		 */
+		if (unlikely(pba >= max_pages && pba != U64_MAX)) {
+			pr_err("nvm: L2P data entry is out of bounds!\n");
+			return -EINVAL;
+		}
+
+		/* Address zero is a special one. The first page on a disk is
+		 * protected. As it often holds internal device boot
+		 * information.
+		 */
+		if (!pba)
+			continue;
+
+		addr[i].addr = pba;
+		raddr[pba].addr = slba + i;
+	}
+
+	return 0;
+}
+
+static int rrpc_map_init(struct rrpc *rrpc)
+{
+	struct nvm_dev *dev = rrpc->dev;
+	sector_t i;
+	int ret;
+
+	rrpc->trans_map = vzalloc(sizeof(struct rrpc_addr) * rrpc->nr_pages);
+	if (!rrpc->trans_map)
+		return -ENOMEM;
+
+	rrpc->rev_trans_map = vmalloc(sizeof(struct rrpc_rev_addr)
+							* rrpc->nr_pages);
+	if (!rrpc->rev_trans_map)
+		return -ENOMEM;
+
+	for (i = 0; i < rrpc->nr_pages; i++) {
+		struct rrpc_addr *p = &rrpc->trans_map[i];
+		struct rrpc_rev_addr *r = &rrpc->rev_trans_map[i];
+
+		p->addr = ADDR_EMPTY;
+		r->addr = ADDR_EMPTY;
+	}
+
+	if (!dev->ops->get_l2p_tbl)
+		return 0;
+
+	/* Bring up the mapping table from device */
+	ret = dev->ops->get_l2p_tbl(dev, 0, dev->total_pages,
+							rrpc_l2p_update, rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: could not read L2P table.\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+
+/* Minimum pages needed within a lun */
+#define PAGE_POOL_SIZE 16
+#define ADDR_POOL_SIZE 64
+
+static int rrpc_core_init(struct rrpc *rrpc)
+{
+	down_write(&rrpc_lock);
+	if (!rrpc_gcb_cache) {
+		rrpc_gcb_cache = kmem_cache_create("rrpc_gcb",
+				sizeof(struct rrpc_block_gc), 0, 0, NULL);
+		if (!rrpc_gcb_cache) {
+			up_write(&rrpc_lock);
+			return -ENOMEM;
+		}
+
+		rrpc_rq_cache = kmem_cache_create("rrpc_rq",
+				sizeof(struct nvm_rq) + sizeof(struct rrpc_rq),
+				0, 0, NULL);
+		if (!rrpc_rq_cache) {
+			kmem_cache_destroy(rrpc_gcb_cache);
+			up_write(&rrpc_lock);
+			return -ENOMEM;
+		}
+	}
+	up_write(&rrpc_lock);
+
+	rrpc->page_pool = mempool_create_page_pool(PAGE_POOL_SIZE, 0);
+	if (!rrpc->page_pool)
+		return -ENOMEM;
+
+	rrpc->gcb_pool = mempool_create_slab_pool(rrpc->dev->nr_luns,
+								rrpc_gcb_cache);
+	if (!rrpc->gcb_pool)
+		return -ENOMEM;
+
+	rrpc->rq_pool = mempool_create_slab_pool(64, rrpc_rq_cache);
+	if (!rrpc->rq_pool)
+		return -ENOMEM;
+
+	spin_lock_init(&rrpc->inflights.lock);
+	INIT_LIST_HEAD(&rrpc->inflights.reqs);
+
+	return 0;
+}
+
+static void rrpc_core_free(struct rrpc *rrpc)
+{
+	mempool_destroy(rrpc->page_pool);
+	mempool_destroy(rrpc->gcb_pool);
+	mempool_destroy(rrpc->rq_pool);
+}
+
+static void rrpc_luns_free(struct rrpc *rrpc)
+{
+	kfree(rrpc->luns);
+}
+
+static int rrpc_luns_init(struct rrpc *rrpc, int lun_begin, int lun_end)
+{
+	struct nvm_dev *dev = rrpc->dev;
+	struct rrpc_lun *rlun;
+	int i, j;
+
+	spin_lock_init(&rrpc->rev_lock);
+
+	rrpc->luns = kcalloc(rrpc->nr_luns, sizeof(struct rrpc_lun),
+								GFP_KERNEL);
+	if (!rrpc->luns)
+		return -ENOMEM;
+
+	/* 1:1 mapping */
+	for (i = 0; i < rrpc->nr_luns; i++) {
+		struct nvm_lun *lun = dev->mt->get_lun(dev, lun_begin + i);
+
+		if (dev->pgs_per_blk >
+				MAX_INVALID_PAGES_STORAGE * BITS_PER_LONG) {
+			pr_err("rrpc: number of pages per block too high.");
+			goto err;
+		}
+
+		rlun = &rrpc->luns[i];
+		rlun->rrpc = rrpc;
+		rlun->parent = lun;
+		INIT_LIST_HEAD(&rlun->prio_list);
+		INIT_WORK(&rlun->ws_gc, rrpc_lun_gc);
+		spin_lock_init(&rlun->lock);
+
+		rrpc->total_blocks += dev->blks_per_lun;
+		rrpc->nr_pages += dev->sec_per_lun;
+
+		rlun->blocks = vzalloc(sizeof(struct rrpc_block) *
+						rrpc->dev->blks_per_lun);
+		if (!rlun->blocks)
+			goto err;
+
+		for (j = 0; j < rrpc->dev->blks_per_lun; j++) {
+			struct rrpc_block *rblk = &rlun->blocks[j];
+			struct nvm_block *blk = &lun->blocks[j];
+
+			rblk->parent = blk;
+			INIT_LIST_HEAD(&rblk->prio);
+			spin_lock_init(&rblk->lock);
+		}
+	}
+
+	return 0;
+err:
+	return -ENOMEM;
+}
+
+static void rrpc_free(struct rrpc *rrpc)
+{
+	rrpc_gc_free(rrpc);
+	rrpc_map_free(rrpc);
+	rrpc_core_free(rrpc);
+	rrpc_luns_free(rrpc);
+
+	kfree(rrpc);
+}
+
+static void rrpc_exit(void *private)
+{
+	struct rrpc *rrpc = private;
+
+	del_timer(&rrpc->gc_timer);
+
+	flush_workqueue(rrpc->krqd_wq);
+	flush_workqueue(rrpc->kgc_wq);
+
+	rrpc_free(rrpc);
+}
+
+static sector_t rrpc_capacity(void *private)
+{
+	struct rrpc *rrpc = private;
+	struct nvm_dev *dev = rrpc->dev;
+	sector_t reserved, provisioned;
+
+	/* cur, gc, and two emergency blocks for each lun */
+	reserved = rrpc->nr_luns * dev->max_pages_per_blk * 4;
+	provisioned = rrpc->nr_pages - reserved;
+
+	if (reserved > rrpc->nr_pages) {
+		pr_err("rrpc: not enough space available to expose storage.\n");
+		return 0;
+	}
+
+	sector_div(provisioned, 10);
+	return provisioned * 9 * NR_PHY_IN_LOG;
+}
+
+/*
+ * Looks up the logical address from reverse trans map and check if its valid by
+ * comparing the logical to physical address with the physical address.
+ * Returns 0 on free, otherwise 1 if in use
+ */
+static void rrpc_block_map_update(struct rrpc *rrpc, struct rrpc_block *rblk)
+{
+	struct nvm_dev *dev = rrpc->dev;
+	int offset;
+	struct rrpc_addr *laddr;
+	u64 paddr, pladdr;
+
+	for (offset = 0; offset < dev->pgs_per_blk; offset++) {
+		paddr = block_to_addr(rrpc, rblk) + offset;
+
+		pladdr = rrpc->rev_trans_map[paddr].addr;
+		if (pladdr == ADDR_EMPTY)
+			continue;
+
+		laddr = &rrpc->trans_map[pladdr];
+
+		if (paddr == laddr->addr) {
+			laddr->rblk = rblk;
+		} else {
+			set_bit(offset, rblk->invalid_pages);
+			rblk->nr_invalid_pages++;
+		}
+	}
+}
+
+static int rrpc_blocks_init(struct rrpc *rrpc)
+{
+	struct rrpc_lun *rlun;
+	struct rrpc_block *rblk;
+	int lun_iter, blk_iter;
+
+	for (lun_iter = 0; lun_iter < rrpc->nr_luns; lun_iter++) {
+		rlun = &rrpc->luns[lun_iter];
+
+		for (blk_iter = 0; blk_iter < rrpc->dev->blks_per_lun;
+								blk_iter++) {
+			rblk = &rlun->blocks[blk_iter];
+			rrpc_block_map_update(rrpc, rblk);
+		}
+	}
+
+	return 0;
+}
+
+static int rrpc_luns_configure(struct rrpc *rrpc)
+{
+	struct rrpc_lun *rlun;
+	struct rrpc_block *rblk;
+	int i;
+
+	for (i = 0; i < rrpc->nr_luns; i++) {
+		rlun = &rrpc->luns[i];
+
+		rblk = rrpc_get_blk(rrpc, rlun, 0);
+		if (!rblk)
+			goto err;
+
+		rrpc_set_lun_cur(rlun, rblk);
+
+		/* Emergency gc block */
+		rblk = rrpc_get_blk(rrpc, rlun, 1);
+		if (!rblk)
+			goto err;
+		rlun->gc_cur = rblk;
+	}
+
+	return 0;
+err:
+	rrpc_put_blks(rrpc);
+	return -EINVAL;
+}
+
+static struct nvm_tgt_type tt_rrpc;
+
+static void *rrpc_init(struct nvm_dev *dev, struct gendisk *tdisk,
+						int lun_begin, int lun_end)
+{
+	struct request_queue *bqueue = dev->q;
+	struct request_queue *tqueue = tdisk->queue;
+	struct rrpc *rrpc;
+	int ret;
+
+	if (!(dev->identity.dom & NVM_RSP_L2P)) {
+		pr_err("nvm: rrpc: device does not support l2p (%x)\n",
+							dev->identity.dom);
+		return ERR_PTR(-EINVAL);
+	}
+
+	rrpc = kzalloc(sizeof(struct rrpc), GFP_KERNEL);
+	if (!rrpc)
+		return ERR_PTR(-ENOMEM);
+
+	rrpc->instance.tt = &tt_rrpc;
+	rrpc->dev = dev;
+	rrpc->disk = tdisk;
+
+	bio_list_init(&rrpc->requeue_bios);
+	spin_lock_init(&rrpc->bio_lock);
+	INIT_WORK(&rrpc->ws_requeue, rrpc_requeue);
+
+	rrpc->nr_luns = lun_end - lun_begin + 1;
+
+	/* simple round-robin strategy */
+	atomic_set(&rrpc->next_lun, -1);
+
+	ret = rrpc_luns_init(rrpc, lun_begin, lun_end);
+	if (ret) {
+		pr_err("nvm: rrpc: could not initialize luns\n");
+		goto err;
+	}
+
+	rrpc->poffset = dev->sec_per_lun * lun_begin;
+	rrpc->lun_offset = lun_begin;
+
+	ret = rrpc_core_init(rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: could not initialize core\n");
+		goto err;
+	}
+
+	ret = rrpc_map_init(rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: could not initialize maps\n");
+		goto err;
+	}
+
+	ret = rrpc_blocks_init(rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: could not initialize state for blocks\n");
+		goto err;
+	}
+
+	ret = rrpc_luns_configure(rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: not enough blocks available in LUNs.\n");
+		goto err;
+	}
+
+	ret = rrpc_gc_init(rrpc);
+	if (ret) {
+		pr_err("nvm: rrpc: could not initialize gc\n");
+		goto err;
+	}
+
+	/* inherit the size from the underlying device */
+	blk_queue_logical_block_size(tqueue, queue_physical_block_size(bqueue));
+	blk_queue_max_hw_sectors(tqueue, queue_max_hw_sectors(bqueue));
+
+	pr_info("nvm: rrpc initialized with %u luns and %llu pages.\n",
+			rrpc->nr_luns, (unsigned long long)rrpc->nr_pages);
+
+	mod_timer(&rrpc->gc_timer, jiffies + msecs_to_jiffies(10));
+
+	return rrpc;
+err:
+	rrpc_free(rrpc);
+	return ERR_PTR(ret);
+}
+
+/* round robin, page-based FTL, and cost-based GC */
+static struct nvm_tgt_type tt_rrpc = {
+	.name		= "rrpc",
+	.version	= {1, 0, 0},
+
+	.make_rq	= rrpc_make_rq,
+	.capacity	= rrpc_capacity,
+	.end_io		= rrpc_end_io,
+
+	.init		= rrpc_init,
+	.exit		= rrpc_exit,
+};
+
+static int __init rrpc_module_init(void)
+{
+	return nvm_register_target(&tt_rrpc);
+}
+
+static void rrpc_module_exit(void)
+{
+	nvm_unregister_target(&tt_rrpc);
+}
+
+module_init(rrpc_module_init);
+module_exit(rrpc_module_exit);
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Block-Device Target for Open-Channel SSDs");