libnvdimm: infrastructure for btt devices

NVDIMM namespaces, in addition to accepting "struct bio" based requests,
also have the capability to perform byte-aligned accesses.  By default
only the bio/block interface is used.  However, if another driver can
make effective use of the byte-aligned capability it can claim namespace
interface and use the byte-aligned ->rw_bytes() interface.

The BTT driver is the initial first consumer of this mechanism to allow
adding atomic sector update semantics to a pmem or blk namespace.  This
patch is the sysfs infrastructure to allow configuring a BTT instance
for a namespace.  Enabling that BTT and performing i/o is in a
subsequent patch.

Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/Kconfig

@@ -33,4 +33,7 @@ config BLK_DEV_PMEM
 
 	  Say Y if you want to use an NVDIMM
 
+config BTT
+	def_bool y
+
 endif

drivers/nvdimm/Makefile

@@ -11,3 +11,4 @@ libnvdimm-y += region_devs.o
 libnvdimm-y += region.o
 libnvdimm-y += namespace_devs.o
 libnvdimm-y += label.o
+libnvdimm-$(CONFIG_BTT) += btt_devs.o

drivers/nvdimm/btt.h

+/*
+ * Block Translation Table library
+ * Copyright (c) 2014-2015, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ */
+
+#ifndef _LINUX_BTT_H
+#define _LINUX_BTT_H
+
+#include <linux/types.h>
+
+#define BTT_SIG_LEN 16
+#define BTT_SIG "BTT_ARENA_INFO\0"
+
+struct btt_sb {
+	u8 signature[BTT_SIG_LEN];
+	u8 uuid[16];
+	u8 parent_uuid[16];
+	__le32 flags;
+	__le16 version_major;
+	__le16 version_minor;
+	__le32 external_lbasize;
+	__le32 external_nlba;
+	__le32 internal_lbasize;
+	__le32 internal_nlba;
+	__le32 nfree;
+	__le32 infosize;
+	__le64 nextoff;
+	__le64 dataoff;
+	__le64 mapoff;
+	__le64 logoff;
+	__le64 info2off;
+	u8 padding[3968];
+	__le64 checksum;
+};
+
+#endif

drivers/nvdimm/bus.c

@@ -14,8 +14,10 @@
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>
 #include <linux/module.h>
+#include <linux/blkdev.h>
 #include <linux/fcntl.h>
 #include <linux/async.h>
+#include <linux/genhd.h>
 #include <linux/ndctl.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -103,6 +105,7 @@ static int nvdimm_bus_probe(struct device *dev)
 
 	dev_dbg(&nvdimm_bus->dev, "%s.probe(%s) = %d\n", dev->driver->name,
 			dev_name(dev), rc);
+
 	if (rc != 0)
 		module_put(provider);
 	return rc;
@@ -163,14 +166,19 @@ static void nd_async_device_unregister(void *d, async_cookie_t cookie)
 	put_device(dev);
 }
 
-void nd_device_register(struct device *dev)
+void __nd_device_register(struct device *dev)
 {
 	dev->bus = &nvdimm_bus_type;
-	device_initialize(dev);
 	get_device(dev);
 	async_schedule_domain(nd_async_device_register, dev,
 			&nd_async_domain);
 }
+
+void nd_device_register(struct device *dev)
+{
+	device_initialize(dev);
+	__nd_device_register(dev);
+}
 EXPORT_SYMBOL(nd_device_register);
 
 void nd_device_unregister(struct device *dev, enum nd_async_mode mode)

drivers/nvdimm/label.c

@@ -666,7 +666,7 @@ static int __blk_label_update(struct nd_region *nd_region,
 
 	/* don't allow updates that consume the last label */
 	if (nfree - alloc < 0 || nfree - alloc + victims < 1) {
-		dev_info(&nsblk->dev, "insufficient label space\n");
+		dev_info(&nsblk->common.dev, "insufficient label space\n");
 		kfree(victim_map);
 		return -ENOSPC;
 	}
@@ -762,7 +762,8 @@ static int __blk_label_update(struct nd_region *nd_region,
 			continue;
 		res = to_resource(ndd, nd_label);
 		res->flags &= ~DPA_RESOURCE_ADJUSTED;
-		dev_vdbg(&nsblk->dev, "assign label[%d] slot: %d\n", l, slot);
+		dev_vdbg(&nsblk->common.dev, "assign label[%d] slot: %d\n",
+				l, slot);
 		nd_mapping->labels[l++] = nd_label;
 	}
 	nd_mapping->labels[l] = NULL;

drivers/nvdimm/nd-core.h

@@ -45,12 +45,14 @@ struct nvdimm {
 bool is_nvdimm(struct device *dev);
 bool is_nd_blk(struct device *dev);
 bool is_nd_pmem(struct device *dev);
+struct nd_btt;
 struct nvdimm_bus *walk_to_nvdimm_bus(struct device *nd_dev);
 int __init nvdimm_bus_init(void);
 void nvdimm_bus_exit(void);
 void nd_region_probe_success(struct nvdimm_bus *nvdimm_bus, struct device *dev);
 struct nd_region;
 void nd_region_create_blk_seed(struct nd_region *nd_region);
+void nd_region_create_btt_seed(struct nd_region *nd_region);
 void nd_region_disable(struct nvdimm_bus *nvdimm_bus, struct device *dev);
 int nvdimm_bus_create_ndctl(struct nvdimm_bus *nvdimm_bus);
 void nvdimm_bus_destroy_ndctl(struct nvdimm_bus *nvdimm_bus);
@@ -58,6 +60,7 @@ void nd_synchronize(void);
 int nvdimm_bus_register_dimms(struct nvdimm_bus *nvdimm_bus);
 int nvdimm_bus_register_regions(struct nvdimm_bus *nvdimm_bus);
 int nvdimm_bus_init_interleave_sets(struct nvdimm_bus *nvdimm_bus);
+void __nd_device_register(struct device *dev);
 int nd_match_dimm(struct device *dev, void *data);
 struct nd_label_id;
 char *nd_label_gen_id(struct nd_label_id *label_id, u8 *uuid, u32 flags);
@@ -77,4 +80,5 @@ struct resource *nsblk_add_resource(struct nd_region *nd_region,
 		resource_size_t start);
 int nvdimm_num_label_slots(struct nvdimm_drvdata *ndd);
 void get_ndd(struct nvdimm_drvdata *ndd);
+resource_size_t __nvdimm_namespace_capacity(struct nd_namespace_common *ndns);
 #endif /* __ND_CORE_H__ */

drivers/nvdimm/nd.h

@@ -19,6 +19,10 @@
 #include <linux/types.h>
 #include "label.h"
 
+enum {
+	SECTOR_SHIFT = 9,
+};
+
 struct nvdimm_drvdata {
 	struct device *dev;
 	int nsindex_size;
@@ -74,7 +78,9 @@ static inline struct nd_namespace_index *to_next_namespace_index(
 struct nd_region {
 	struct device dev;
 	struct ida ns_ida;
+	struct ida btt_ida;
 	struct device *ns_seed;
+	struct device *btt_seed;
 	u16 ndr_mappings;
 	u64 ndr_size;
 	u64 ndr_start;
@@ -94,6 +100,14 @@ static inline unsigned nd_inc_seq(unsigned seq)
 	return next[seq & 3];
 }
 
+struct nd_btt {
+	struct device dev;
+	struct nd_namespace_common *ndns;
+	unsigned long lbasize;
+	u8 *uuid;
+	int id;
+};
+
 enum nd_async_mode {
 	ND_SYNC,
 	ND_ASYNC,
@@ -118,6 +132,30 @@ int nvdimm_init_nsarea(struct nvdimm_drvdata *ndd);
 int nvdimm_init_config_data(struct nvdimm_drvdata *ndd);
 int nvdimm_set_config_data(struct nvdimm_drvdata *ndd, size_t offset,
 		void *buf, size_t len);
+struct nd_btt *to_nd_btt(struct device *dev);
+struct btt_sb;
+u64 nd_btt_sb_checksum(struct btt_sb *btt_sb);
+#if IS_ENABLED(CONFIG_BTT)
+int nd_btt_probe(struct nd_namespace_common *ndns, void *drvdata);
+bool is_nd_btt(struct device *dev);
+struct device *nd_btt_create(struct nd_region *nd_region);
+#else
+static inline nd_btt_probe(struct nd_namespace_common *ndns, void *drvdata)
+{
+	return -ENODEV;
+}
+
+static inline bool is_nd_btt(struct device *dev)
+{
+	return false;
+}
+
+static inline struct device *nd_btt_create(struct nd_region *nd_region)
+{
+	return NULL;
+}
+
+#endif
 struct nd_region *to_nd_region(struct device *dev);
 int nd_region_to_nstype(struct nd_region *nd_region);
 int nd_region_register_namespaces(struct nd_region *nd_region, int *err);
@@ -132,4 +170,6 @@ void nvdimm_free_dpa(struct nvdimm_drvdata *ndd, struct resource *res);
 struct resource *nvdimm_allocate_dpa(struct nvdimm_drvdata *ndd,
 		struct nd_label_id *label_id, resource_size_t start,
 		resource_size_t n);
+resource_size_t nvdimm_namespace_capacity(struct nd_namespace_common *ndns);
+struct nd_namespace_common *nvdimm_namespace_common_probe(struct device *dev);
 #endif /* __ND_H__ */

drivers/nvdimm/pmem.c

@@ -121,44 +121,61 @@ static struct pmem_device *pmem_alloc(struct device *dev,
 		struct resource *res, int id)
 {
 	struct pmem_device *pmem;
-	struct gendisk *disk;
-	int err;
 
-	err = -ENOMEM;
 	pmem = kzalloc(sizeof(*pmem), GFP_KERNEL);
 	if (!pmem)
-		goto out;
+		return ERR_PTR(-ENOMEM);
 
 	pmem->phys_addr = res->start;
 	pmem->size = resource_size(res);
 
-	err = -EINVAL;
-	if (!request_mem_region(pmem->phys_addr, pmem->size, "pmem")) {
+	if (!request_mem_region(pmem->phys_addr, pmem->size, dev_name(dev))) {
 		dev_warn(dev, "could not reserve region [0x%pa:0x%zx]\n",
 				&pmem->phys_addr, pmem->size);
-		goto out_free_dev;
+		kfree(pmem);
+		return ERR_PTR(-EBUSY);
 	}
 
 	/*
 	 * Map the memory as non-cachable, as we can't write back the contents
 	 * of the CPU caches in case of a crash.
 	 */
-	err = -ENOMEM;
 	pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size);
-	if (!pmem->virt_addr)
-		goto out_release_region;
+	if (!pmem->virt_addr) {
+		release_mem_region(pmem->phys_addr, pmem->size);
+		kfree(pmem);
+		return ERR_PTR(-ENXIO);
+	}
+
+	return pmem;
+}
+
+static void pmem_detach_disk(struct pmem_device *pmem)
+{
+	del_gendisk(pmem->pmem_disk);
+	put_disk(pmem->pmem_disk);
+	blk_cleanup_queue(pmem->pmem_queue);
+}
+
+static int pmem_attach_disk(struct nd_namespace_common *ndns,
+		struct pmem_device *pmem)
+{
+	struct nd_region *nd_region = to_nd_region(ndns->dev.parent);
+	struct gendisk *disk;
 
 	pmem->pmem_queue = blk_alloc_queue(GFP_KERNEL);
 	if (!pmem->pmem_queue)
-		goto out_unmap;
+		return -ENOMEM;
 
 	blk_queue_make_request(pmem->pmem_queue, pmem_make_request);
 	blk_queue_max_hw_sectors(pmem->pmem_queue, 1024);
 	blk_queue_bounce_limit(pmem->pmem_queue, BLK_BOUNCE_ANY);
 
 	disk = alloc_disk(0);
-	if (!disk)
-		goto out_free_queue;
+	if (!disk) {
+		blk_cleanup_queue(pmem->pmem_queue);
+		return -ENOMEM;
+	}
 
 	disk->major		= pmem_major;
 	disk->first_minor	= 0;
@@ -166,32 +183,47 @@ static struct pmem_device *pmem_alloc(struct device *dev,
 	disk->private_data	= pmem;
 	disk->queue		= pmem->pmem_queue;
 	disk->flags		= GENHD_FL_EXT_DEVT;
-	sprintf(disk->disk_name, "pmem%d", id);
-	disk->driverfs_dev = dev;
+	sprintf(disk->disk_name, "pmem%d", nd_region->id);
+	disk->driverfs_dev = &ndns->dev;
 	set_capacity(disk, pmem->size >> 9);
 	pmem->pmem_disk = disk;
 
 	add_disk(disk);
 
-	return pmem;
+	return 0;
+}
 
-out_free_queue:
-	blk_cleanup_queue(pmem->pmem_queue);
-out_unmap:
-	iounmap(pmem->virt_addr);
-out_release_region:
-	release_mem_region(pmem->phys_addr, pmem->size);
-out_free_dev:
-	kfree(pmem);
-out:
-	return ERR_PTR(err);
+static int pmem_rw_bytes(struct nd_namespace_common *ndns,
+		resource_size_t offset, void *buf, size_t size, int rw)
+{
+	struct pmem_device *pmem = dev_get_drvdata(ndns->claim);
+
+	if (unlikely(offset + size > pmem->size)) {
+		dev_WARN_ONCE(&ndns->dev, 1, "request out of range\n");
+		return -EFAULT;
+	}
+
+	if (rw == READ)
+		memcpy(buf, pmem->virt_addr + offset, size);
+	else
+		memcpy(pmem->virt_addr + offset, buf, size);
+
+	return 0;
+}
+
+static int nvdimm_namespace_attach_btt(struct nd_namespace_common *ndns)
+{
+	/* TODO */
+	return -ENXIO;
+}
+
+static void nvdimm_namespace_detach_btt(struct nd_namespace_common *ndns)
+{
+	/* TODO */
 }
 
 static void pmem_free(struct pmem_device *pmem)
 {
-	del_gendisk(pmem->pmem_disk);
-	put_disk(pmem->pmem_disk);
-	blk_cleanup_queue(pmem->pmem_queue);
 	iounmap(pmem->virt_addr);
 	release_mem_region(pmem->phys_addr, pmem->size);
 	kfree(pmem);
@@ -200,40 +232,44 @@ static void pmem_free(struct pmem_device *pmem)
 static int nd_pmem_probe(struct device *dev)
 {
 	struct nd_region *nd_region = to_nd_region(dev->parent);
-	struct nd_namespace_io *nsio = to_nd_namespace_io(dev);
+	struct nd_namespace_common *ndns;
+	struct nd_namespace_io *nsio;
 	struct pmem_device *pmem;
+	int rc;
 
-	if (resource_size(&nsio->res) < ND_MIN_NAMESPACE_SIZE) {
-		resource_size_t size = resource_size(&nsio->res);
-
-		dev_dbg(dev, "%s: size: %pa, too small must be at least %#x\n",
-				__func__, &size, ND_MIN_NAMESPACE_SIZE);
-		return -ENODEV;
-	}
-
-	if (nd_region_to_nstype(nd_region) == ND_DEVICE_NAMESPACE_PMEM) {
-		struct nd_namespace_pmem *nspm = to_nd_namespace_pmem(dev);
-
-		if (!nspm->uuid) {
-			dev_dbg(dev, "%s: uuid not set\n", __func__);
-			return -ENODEV;
-		}
-	}
+	ndns = nvdimm_namespace_common_probe(dev);
+	if (IS_ERR(ndns))
+		return PTR_ERR(ndns);
 
+	nsio = to_nd_namespace_io(&ndns->dev);
 	pmem = pmem_alloc(dev, &nsio->res, nd_region->id);
 	if (IS_ERR(pmem))
 		return PTR_ERR(pmem);
 
 	dev_set_drvdata(dev, pmem);
-
-	return 0;
+	ndns->rw_bytes = pmem_rw_bytes;
+	if (is_nd_btt(dev))
+		rc = nvdimm_namespace_attach_btt(ndns);
+	else if (nd_btt_probe(ndns, pmem) == 0) {
+		/* we'll come back as btt-pmem */
+		rc = -ENXIO;
+	} else
+		rc = pmem_attach_disk(ndns, pmem);
+	if (rc)
+		pmem_free(pmem);
+	return rc;
 }
 
 static int nd_pmem_remove(struct device *dev)
 {
 	struct pmem_device *pmem = dev_get_drvdata(dev);
 
+	if (is_nd_btt(dev))
+		nvdimm_namespace_detach_btt(to_nd_btt(dev)->ndns);
+	else
+		pmem_detach_disk(pmem);
 	pmem_free(pmem);
+
 	return 0;
 }
 

drivers/nvdimm/region.c

@@ -33,12 +33,13 @@ static int nd_region_probe(struct device *dev)
 	num_ns->count = rc + err;
 	dev_set_drvdata(dev, num_ns);
 
+	if (rc && err && rc == err)
+		return -ENODEV;
+
+	nd_region->btt_seed = nd_btt_create(nd_region);
 	if (err == 0)
 		return 0;
 
-	if (rc == err)
-		return -ENODEV;
-
 	/*
 	 * Given multiple namespaces per region, we do not want to
 	 * disable all the successfully registered peer namespaces upon
@@ -66,6 +67,7 @@ static int nd_region_remove(struct device *dev)
 	/* flush attribute readers and disable */
 	nvdimm_bus_lock(dev);
 	nd_region->ns_seed = NULL;
+	nd_region->btt_seed = NULL;
 	dev_set_drvdata(dev, NULL);
 	nvdimm_bus_unlock(dev);
 

drivers/nvdimm/region_devs.c

@@ -296,10 +296,28 @@ static ssize_t namespace_seed_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(namespace_seed);
 
+static ssize_t btt_seed_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct nd_region *nd_region = to_nd_region(dev);
+	ssize_t rc;
+
+	nvdimm_bus_lock(dev);
+	if (nd_region->btt_seed)
+		rc = sprintf(buf, "%s\n", dev_name(nd_region->btt_seed));
+	else
+		rc = sprintf(buf, "\n");
+	nvdimm_bus_unlock(dev);
+
+	return rc;
+}
+static DEVICE_ATTR_RO(btt_seed);
+
 static struct attribute *nd_region_attributes[] = {
 	&dev_attr_size.attr,
 	&dev_attr_nstype.attr,
 	&dev_attr_mappings.attr,
+	&dev_attr_btt_seed.attr,
 	&dev_attr_set_cookie.attr,
 	&dev_attr_available_size.attr,
 	&dev_attr_namespace_seed.attr,
@@ -345,15 +363,18 @@ u64 nd_region_interleave_set_cookie(struct nd_region *nd_region)
 
 /*
  * Upon successful probe/remove, take/release a reference on the
- * associated interleave set (if present)
+ * associated interleave set (if present), and plant new btt + namespace
+ * seeds.
  */
 static void nd_region_notify_driver_action(struct nvdimm_bus *nvdimm_bus,
 		struct device *dev, bool probe)
 {
+	struct nd_region *nd_region;
+
 	if (!probe && (is_nd_pmem(dev) || is_nd_blk(dev))) {
-		struct nd_region *nd_region = to_nd_region(dev);
 		int i;
 
+		nd_region = to_nd_region(dev);
 		for (i = 0; i < nd_region->ndr_mappings; i++) {
 			struct nd_mapping *nd_mapping = &nd_region->mapping[i];
 			struct nvdimm_drvdata *ndd = nd_mapping->ndd;
@@ -365,14 +386,21 @@ static void nd_region_notify_driver_action(struct nvdimm_bus *nvdimm_bus,
 			nd_mapping->ndd = NULL;
 			atomic_dec(&nvdimm->busy);
 		}
-	} else if (dev->parent && is_nd_blk(dev->parent) && probe) {
-		struct nd_region *nd_region = to_nd_region(dev->parent);
-
+	}
+	if (dev->parent && is_nd_blk(dev->parent) && probe) {
+		nd_region = to_nd_region(dev->parent);
 		nvdimm_bus_lock(dev);
 		if (nd_region->ns_seed == dev)
 			nd_region_create_blk_seed(nd_region);
 		nvdimm_bus_unlock(dev);
 	}
+	if (is_nd_btt(dev) && probe) {
+		nd_region = to_nd_region(dev->parent);
+		nvdimm_bus_lock(dev);
+		if (nd_region->btt_seed == dev)
+			nd_region_create_btt_seed(nd_region);
+		nvdimm_bus_unlock(dev);
+	}
 }
 
 void nd_region_probe_success(struct nvdimm_bus *nvdimm_bus, struct device *dev)
@@ -546,6 +574,7 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
 	nd_region->provider_data = ndr_desc->provider_data;
 	nd_region->nd_set = ndr_desc->nd_set;
 	ida_init(&nd_region->ns_ida);
+	ida_init(&nd_region->btt_ida);
 	dev = &nd_region->dev;
 	dev_set_name(dev, "region%d", nd_region->id);
 	dev->parent = &nvdimm_bus->dev;

include/linux/nd.h

@@ -12,6 +12,7 @@
  */
 #ifndef __LINUX_ND_H__
 #define __LINUX_ND_H__
+#include <linux/fs.h>
 #include <linux/ndctl.h>
 #include <linux/device.h>
 
@@ -28,13 +29,33 @@ static inline struct nd_device_driver *to_nd_device_driver(
 	return container_of(drv, struct nd_device_driver, drv);
 };
 
+/**
+ * struct nd_namespace_common - core infrastructure of a namespace
+ * @force_raw: ignore other personalities for the namespace (e.g. btt)
+ * @dev: device model node
+ * @claim: when set a another personality has taken ownership of the namespace
+ * @rw_bytes: access the raw namespace capacity with byte-aligned transfers
+ */
+struct nd_namespace_common {
+	int force_raw;
+	struct device dev;
+	struct device *claim;
+	int (*rw_bytes)(struct nd_namespace_common *, resource_size_t offset,
+			void *buf, size_t size, int rw);
+};
+
+static inline struct nd_namespace_common *to_ndns(struct device *dev)
+{
+	return container_of(dev, struct nd_namespace_common, dev);
+}
+
 /**
  * struct nd_namespace_io - infrastructure for loading an nd_pmem instance
  * @dev: namespace device created by the nd region driver
  * @res: struct resource conversion of a NFIT SPA table
  */
 struct nd_namespace_io {
-	struct device dev;
+	struct nd_namespace_common common;
 	struct resource res;
 };
 
@@ -52,7 +73,6 @@ struct nd_namespace_pmem {
 
 /**
  * struct nd_namespace_blk - namespace for dimm-bounded persistent memory
- * @dev: namespace device creation by the nd region driver
  * @alt_name: namespace name supplied in the dimm label
  * @uuid: namespace name supplied in the dimm label
  * @id: ida allocated id
@@ -61,7 +81,7 @@ struct nd_namespace_pmem {
  * @res: discontiguous dpa extents for given dimm
  */
 struct nd_namespace_blk {
-	struct device dev;
+	struct nd_namespace_common common;
 	char *alt_name;
 	u8 *uuid;
 	int id;
@@ -72,7 +92,7 @@ struct nd_namespace_blk {
 
 static inline struct nd_namespace_io *to_nd_namespace_io(struct device *dev)
 {
-	return container_of(dev, struct nd_namespace_io, dev);
+	return container_of(dev, struct nd_namespace_io, common.dev);
 }
 
 static inline struct nd_namespace_pmem *to_nd_namespace_pmem(struct device *dev)
@@ -84,7 +104,40 @@ static inline struct nd_namespace_pmem *to_nd_namespace_pmem(struct device *dev)
 
 static inline struct nd_namespace_blk *to_nd_namespace_blk(struct device *dev)
 {
-	return container_of(dev, struct nd_namespace_blk, dev);
+	return container_of(dev, struct nd_namespace_blk, common.dev);
+}
+
+/**
+ * nvdimm_read_bytes() - synchronously read bytes from an nvdimm namespace
+ * @ndns: device to read
+ * @offset: namespace-relative starting offset
+ * @buf: buffer to fill
+ * @size: transfer length
+ *
+ * @buf is up-to-date upon return from this routine.
+ */
+static inline int nvdimm_read_bytes(struct nd_namespace_common *ndns,
+		resource_size_t offset, void *buf, size_t size)
+{
+	return ndns->rw_bytes(ndns, offset, buf, size, READ);
+}
+
+/**
+ * nvdimm_write_bytes() - synchronously write bytes to an nvdimm namespace
+ * @ndns: device to read
+ * @offset: namespace-relative starting offset
+ * @buf: buffer to drain
+ * @size: transfer length
+ *
+ * NVDIMM Namepaces disks do not implement sectors internally.  Depending on
+ * the @ndns, the contents of @buf may be in cpu cache, platform buffers,
+ * or on backing memory media upon return from this routine.  Flushing
+ * to media is handled internal to the @ndns driver, if at all.
+ */
+static inline int nvdimm_write_bytes(struct nd_namespace_common *ndns,
+		resource_size_t offset, void *buf, size_t size)
+{
+	return ndns->rw_bytes(ndns, offset, buf, size, WRITE);
 }
 
 #define MODULE_ALIAS_ND_DEVICE(type) \