Merge 4.18-rc7 into staging-next

[linux-2.6/btrfs-unstable.git] / drivers / nvdimm / pfn_devs.c

/*
 * Copyright(c) 2013-2016 Intel Corporation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License 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.
 */
#include <linux/memremap.h>
#include <linux/blkdev.h>
#include <linux/device.h>
#include <linux/genhd.h>
#include <linux/sizes.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include "nd-core.h"
#include "pfn.h"
#include "nd.h"

static void nd_pfn_release(struct device *dev)
{
        struct nd_region *nd_region = to_nd_region(dev->parent);
        struct nd_pfn *nd_pfn = to_nd_pfn(dev);

        dev_dbg(dev, "trace\n");
        nd_detach_ndns(&nd_pfn->dev, &nd_pfn->ndns);
        ida_simple_remove(&nd_region->pfn_ida, nd_pfn->id);
        kfree(nd_pfn->uuid);
        kfree(nd_pfn);
}

static struct device_type nd_pfn_device_type = {
        .name = "nd_pfn",
        .release = nd_pfn_release,
};

bool is_nd_pfn(struct device *dev)
{
        return dev ? dev->type == &nd_pfn_device_type : false;
}
EXPORT_SYMBOL(is_nd_pfn);

struct nd_pfn *to_nd_pfn(struct device *dev)
{
        struct nd_pfn *nd_pfn = container_of(dev, struct nd_pfn, dev);

        WARN_ON(!is_nd_pfn(dev));
        return nd_pfn;
}
EXPORT_SYMBOL(to_nd_pfn);

static ssize_t mode_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);

        switch (nd_pfn->mode) {
        case PFN_MODE_RAM:
                return sprintf(buf, "ram\n");
        case PFN_MODE_PMEM:
                return sprintf(buf, "pmem\n");
        default:
                return sprintf(buf, "none\n");
        }
}

static ssize_t mode_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc = 0;

        device_lock(dev);
        nvdimm_bus_lock(dev);
        if (dev->driver)
                rc = -EBUSY;
        else {
                size_t n = len - 1;

                if (strncmp(buf, "pmem\n", n) == 0
                                || strncmp(buf, "pmem", n) == 0) {
                        nd_pfn->mode = PFN_MODE_PMEM;
                } else if (strncmp(buf, "ram\n", n) == 0
                                || strncmp(buf, "ram", n) == 0)
                        nd_pfn->mode = PFN_MODE_RAM;
                else if (strncmp(buf, "none\n", n) == 0
                                || strncmp(buf, "none", n) == 0)
                        nd_pfn->mode = PFN_MODE_NONE;
                else
                        rc = -EINVAL;
        }
        dev_dbg(dev, "result: %zd wrote: %s%s", rc, buf,
                        buf[len - 1] == '\n' ? "" : "\n");
        nvdimm_bus_unlock(dev);
        device_unlock(dev);

        return rc ? rc : len;
}
static DEVICE_ATTR_RW(mode);

static ssize_t align_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);

        return sprintf(buf, "%ld\n", nd_pfn->align);
}

static const unsigned long *nd_pfn_supported_alignments(void)
{
        /*
         * This needs to be a non-static variable because the *_SIZE
         * macros aren't always constants.
         */
        const unsigned long supported_alignments[] = {
                PAGE_SIZE,
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
                HPAGE_PMD_SIZE,
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
                HPAGE_PUD_SIZE,
#endif
#endif
                0,
        };
        static unsigned long data[ARRAY_SIZE(supported_alignments)];

        memcpy(data, supported_alignments, sizeof(data));

        return data;
}

static ssize_t align_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        device_lock(dev);
        nvdimm_bus_lock(dev);
        rc = nd_size_select_store(dev, buf, &nd_pfn->align,
                        nd_pfn_supported_alignments());
        dev_dbg(dev, "result: %zd wrote: %s%s", rc, buf,
                        buf[len - 1] == '\n' ? "" : "\n");
        nvdimm_bus_unlock(dev);
        device_unlock(dev);

        return rc ? rc : len;
}
static DEVICE_ATTR_RW(align);

static ssize_t uuid_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);

        if (nd_pfn->uuid)
                return sprintf(buf, "%pUb\n", nd_pfn->uuid);
        return sprintf(buf, "\n");
}

static ssize_t uuid_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        device_lock(dev);
        rc = nd_uuid_store(dev, &nd_pfn->uuid, buf, len);
        dev_dbg(dev, "result: %zd wrote: %s%s", rc, buf,
                        buf[len - 1] == '\n' ? "" : "\n");
        device_unlock(dev);

        return rc ? rc : len;
}
static DEVICE_ATTR_RW(uuid);

static ssize_t namespace_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        nvdimm_bus_lock(dev);
        rc = sprintf(buf, "%s\n", nd_pfn->ndns
                        ? dev_name(&nd_pfn->ndns->dev) : "");
        nvdimm_bus_unlock(dev);
        return rc;
}

static ssize_t namespace_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        device_lock(dev);
        nvdimm_bus_lock(dev);
        rc = nd_namespace_store(dev, &nd_pfn->ndns, buf, len);
        dev_dbg(dev, "result: %zd wrote: %s%s", rc, buf,
                        buf[len - 1] == '\n' ? "" : "\n");
        nvdimm_bus_unlock(dev);
        device_unlock(dev);

        return rc;
}
static DEVICE_ATTR_RW(namespace);

static ssize_t resource_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        device_lock(dev);
        if (dev->driver) {
                struct nd_pfn_sb *pfn_sb = nd_pfn->pfn_sb;
                u64 offset = __le64_to_cpu(pfn_sb->dataoff);
                struct nd_namespace_common *ndns = nd_pfn->ndns;
                u32 start_pad = __le32_to_cpu(pfn_sb->start_pad);
                struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);

                rc = sprintf(buf, "%#llx\n", (unsigned long long) nsio->res.start
                                + start_pad + offset);
        } else {
                /* no address to convey if the pfn instance is disabled */
                rc = -ENXIO;
        }
        device_unlock(dev);

        return rc;
}
static DEVICE_ATTR_RO(resource);

static ssize_t size_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
        ssize_t rc;

        device_lock(dev);
        if (dev->driver) {
                struct nd_pfn_sb *pfn_sb = nd_pfn->pfn_sb;
                u64 offset = __le64_to_cpu(pfn_sb->dataoff);
                struct nd_namespace_common *ndns = nd_pfn->ndns;
                u32 start_pad = __le32_to_cpu(pfn_sb->start_pad);
                u32 end_trunc = __le32_to_cpu(pfn_sb->end_trunc);
                struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);

                rc = sprintf(buf, "%llu\n", (unsigned long long)
                                resource_size(&nsio->res) - start_pad
                                - end_trunc - offset);
        } else {
                /* no size to convey if the pfn instance is disabled */
                rc = -ENXIO;
        }
        device_unlock(dev);

        return rc;
}
static DEVICE_ATTR_RO(size);

static ssize_t supported_alignments_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        return nd_size_select_show(0, nd_pfn_supported_alignments(), buf);
}
static DEVICE_ATTR_RO(supported_alignments);

static struct attribute *nd_pfn_attributes[] = {
        &dev_attr_mode.attr,
        &dev_attr_namespace.attr,
        &dev_attr_uuid.attr,
        &dev_attr_align.attr,
        &dev_attr_resource.attr,
        &dev_attr_size.attr,
        &dev_attr_supported_alignments.attr,
        NULL,
};

static umode_t pfn_visible(struct kobject *kobj, struct attribute *a, int n)
{
        if (a == &dev_attr_resource.attr)
                return 0400;
        return a->mode;
}

struct attribute_group nd_pfn_attribute_group = {
        .attrs = nd_pfn_attributes,
        .is_visible = pfn_visible,
};

static const struct attribute_group *nd_pfn_attribute_groups[] = {
        &nd_pfn_attribute_group,
        &nd_device_attribute_group,
        &nd_numa_attribute_group,
        NULL,
};

struct device *nd_pfn_devinit(struct nd_pfn *nd_pfn,
                struct nd_namespace_common *ndns)
{
        struct device *dev;

        if (!nd_pfn)
                return NULL;

        nd_pfn->mode = PFN_MODE_NONE;
        nd_pfn->align = PFN_DEFAULT_ALIGNMENT;
        dev = &nd_pfn->dev;
        device_initialize(&nd_pfn->dev);
        if (ndns && !__nd_attach_ndns(&nd_pfn->dev, ndns, &nd_pfn->ndns)) {
                dev_dbg(&ndns->dev, "failed, already claimed by %s\n",
                                dev_name(ndns->claim));
                put_device(dev);
                return NULL;
        }
        return dev;
}

static struct nd_pfn *nd_pfn_alloc(struct nd_region *nd_region)
{
        struct nd_pfn *nd_pfn;
        struct device *dev;

        nd_pfn = kzalloc(sizeof(*nd_pfn), GFP_KERNEL);
        if (!nd_pfn)
                return NULL;

        nd_pfn->id = ida_simple_get(&nd_region->pfn_ida, 0, 0, GFP_KERNEL);
        if (nd_pfn->id < 0) {
                kfree(nd_pfn);
                return NULL;
        }

        dev = &nd_pfn->dev;
        dev_set_name(dev, "pfn%d.%d", nd_region->id, nd_pfn->id);
        dev->groups = nd_pfn_attribute_groups;
        dev->type = &nd_pfn_device_type;
        dev->parent = &nd_region->dev;

        return nd_pfn;
}

struct device *nd_pfn_create(struct nd_region *nd_region)
{
        struct nd_pfn *nd_pfn;
        struct device *dev;

        if (!is_memory(&nd_region->dev))
                return NULL;

        nd_pfn = nd_pfn_alloc(nd_region);
        dev = nd_pfn_devinit(nd_pfn, NULL);

        __nd_device_register(dev);
        return dev;
}

int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
{
        u64 checksum, offset;
        enum nd_pfn_mode mode;
        struct nd_namespace_io *nsio;
        unsigned long align, start_pad;
        struct nd_pfn_sb *pfn_sb = nd_pfn->pfn_sb;
        struct nd_namespace_common *ndns = nd_pfn->ndns;
        const u8 *parent_uuid = nd_dev_to_uuid(&ndns->dev);

        if (!pfn_sb || !ndns)
                return -ENODEV;

        if (!is_memory(nd_pfn->dev.parent))
                return -ENODEV;

        if (nvdimm_read_bytes(ndns, SZ_4K, pfn_sb, sizeof(*pfn_sb), 0))
                return -ENXIO;

        if (memcmp(pfn_sb->signature, sig, PFN_SIG_LEN) != 0)
                return -ENODEV;

        checksum = le64_to_cpu(pfn_sb->checksum);
        pfn_sb->checksum = 0;
        if (checksum != nd_sb_checksum((struct nd_gen_sb *) pfn_sb))
                return -ENODEV;
        pfn_sb->checksum = cpu_to_le64(checksum);

        if (memcmp(pfn_sb->parent_uuid, parent_uuid, 16) != 0)
                return -ENODEV;

        if (__le16_to_cpu(pfn_sb->version_minor) < 1) {
                pfn_sb->start_pad = 0;
                pfn_sb->end_trunc = 0;
        }

        if (__le16_to_cpu(pfn_sb->version_minor) < 2)
                pfn_sb->align = 0;

        switch (le32_to_cpu(pfn_sb->mode)) {
        case PFN_MODE_RAM:
        case PFN_MODE_PMEM:
                break;
        default:
                return -ENXIO;
        }

        align = le32_to_cpu(pfn_sb->align);
        offset = le64_to_cpu(pfn_sb->dataoff);
        start_pad = le32_to_cpu(pfn_sb->start_pad);
        if (align == 0)
                align = 1UL << ilog2(offset);
        mode = le32_to_cpu(pfn_sb->mode);

        if (!nd_pfn->uuid) {
                /*
                 * When probing a namepace via nd_pfn_probe() the uuid
                 * is NULL (see: nd_pfn_devinit()) we init settings from
                 * pfn_sb
                 */
                nd_pfn->uuid = kmemdup(pfn_sb->uuid, 16, GFP_KERNEL);
                if (!nd_pfn->uuid)
                        return -ENOMEM;
                nd_pfn->align = align;
                nd_pfn->mode = mode;
        } else {
                /*
                 * When probing a pfn / dax instance we validate the
                 * live settings against the pfn_sb
                 */
                if (memcmp(nd_pfn->uuid, pfn_sb->uuid, 16) != 0)
                        return -ENODEV;

                /*
                 * If the uuid validates, but other settings mismatch
                 * return EINVAL because userspace has managed to change
                 * the configuration without specifying new
                 * identification.
                 */
                if (nd_pfn->align != align || nd_pfn->mode != mode) {
                        dev_err(&nd_pfn->dev,
                                        "init failed, settings mismatch\n");
                        dev_dbg(&nd_pfn->dev, "align: %lx:%lx mode: %d:%d\n",
                                        nd_pfn->align, align, nd_pfn->mode,
                                        mode);
                        return -EINVAL;
                }
        }

        if (align > nvdimm_namespace_capacity(ndns)) {
                dev_err(&nd_pfn->dev, "alignment: %lx exceeds capacity %llx\n",
                                align, nvdimm_namespace_capacity(ndns));
                return -EINVAL;
        }

        /*
         * These warnings are verbose because they can only trigger in
         * the case where the physical address alignment of the
         * namespace has changed since the pfn superblock was
         * established.
         */
        nsio = to_nd_namespace_io(&ndns->dev);
        if (offset >= resource_size(&nsio->res)) {
                dev_err(&nd_pfn->dev, "pfn array size exceeds capacity of %s\n",
                                dev_name(&ndns->dev));
                return -EBUSY;
        }

        if ((align && !IS_ALIGNED(nsio->res.start + offset + start_pad, align))
                        || !IS_ALIGNED(offset, PAGE_SIZE)) {
                dev_err(&nd_pfn->dev,
                                "bad offset: %#llx dax disabled align: %#lx\n",
                                offset, align);
                return -ENXIO;
        }

        return 0;
}
EXPORT_SYMBOL(nd_pfn_validate);

int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns)
{
        int rc;
        struct nd_pfn *nd_pfn;
        struct device *pfn_dev;
        struct nd_pfn_sb *pfn_sb;
        struct nd_region *nd_region = to_nd_region(ndns->dev.parent);

        if (ndns->force_raw)
                return -ENODEV;

        switch (ndns->claim_class) {
        case NVDIMM_CCLASS_NONE:
        case NVDIMM_CCLASS_PFN:
                break;
        default:
                return -ENODEV;
        }

        nvdimm_bus_lock(&ndns->dev);
        nd_pfn = nd_pfn_alloc(nd_region);
        pfn_dev = nd_pfn_devinit(nd_pfn, ndns);
        nvdimm_bus_unlock(&ndns->dev);
        if (!pfn_dev)
                return -ENOMEM;
        pfn_sb = devm_kzalloc(dev, sizeof(*pfn_sb), GFP_KERNEL);
        nd_pfn = to_nd_pfn(pfn_dev);
        nd_pfn->pfn_sb = pfn_sb;
        rc = nd_pfn_validate(nd_pfn, PFN_SIG);
        dev_dbg(dev, "pfn: %s\n", rc == 0 ? dev_name(pfn_dev) : "<none>");
        if (rc < 0) {
                nd_detach_ndns(pfn_dev, &nd_pfn->ndns);
                put_device(pfn_dev);
        } else
                __nd_device_register(pfn_dev);

        return rc;
}
EXPORT_SYMBOL(nd_pfn_probe);

/*
 * We hotplug memory at section granularity, pad the reserved area from
 * the previous section base to the namespace base address.
 */
static unsigned long init_altmap_base(resource_size_t base)
{
        unsigned long base_pfn = PHYS_PFN(base);

        return PFN_SECTION_ALIGN_DOWN(base_pfn);
}

static unsigned long init_altmap_reserve(resource_size_t base)
{
        unsigned long reserve = PHYS_PFN(SZ_8K);
        unsigned long base_pfn = PHYS_PFN(base);

        reserve += base_pfn - PFN_SECTION_ALIGN_DOWN(base_pfn);
        return reserve;
}

static int __nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap)
{
        struct resource *res = &pgmap->res;
        struct vmem_altmap *altmap = &pgmap->altmap;
        struct nd_pfn_sb *pfn_sb = nd_pfn->pfn_sb;
        u64 offset = le64_to_cpu(pfn_sb->dataoff);
        u32 start_pad = __le32_to_cpu(pfn_sb->start_pad);
        u32 end_trunc = __le32_to_cpu(pfn_sb->end_trunc);
        struct nd_namespace_common *ndns = nd_pfn->ndns;
        struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);
        resource_size_t base = nsio->res.start + start_pad;
        struct vmem_altmap __altmap = {
                .base_pfn = init_altmap_base(base),
                .reserve = init_altmap_reserve(base),
        };

        memcpy(res, &nsio->res, sizeof(*res));
        res->start += start_pad;
        res->end -= end_trunc;

        if (nd_pfn->mode == PFN_MODE_RAM) {
                if (offset < SZ_8K)
                        return -EINVAL;
                nd_pfn->npfns = le64_to_cpu(pfn_sb->npfns);
                pgmap->altmap_valid = false;
        } else if (nd_pfn->mode == PFN_MODE_PMEM) {
                nd_pfn->npfns = PFN_SECTION_ALIGN_UP((resource_size(res)
                                        - offset) / PAGE_SIZE);
                if (le64_to_cpu(nd_pfn->pfn_sb->npfns) > nd_pfn->npfns)
                        dev_info(&nd_pfn->dev,
                                        "number of pfns truncated from %lld to %ld\n",
                                        le64_to_cpu(nd_pfn->pfn_sb->npfns),
                                        nd_pfn->npfns);
                memcpy(altmap, &__altmap, sizeof(*altmap));
                altmap->free = PHYS_PFN(offset - SZ_8K);
                altmap->alloc = 0;
                pgmap->altmap_valid = true;
        } else
                return -ENXIO;

        return 0;
}

static u64 phys_pmem_align_down(struct nd_pfn *nd_pfn, u64 phys)
{
        return min_t(u64, PHYS_SECTION_ALIGN_DOWN(phys),
                        ALIGN_DOWN(phys, nd_pfn->align));
}

static int nd_pfn_init(struct nd_pfn *nd_pfn)
{
        u32 dax_label_reserve = is_nd_dax(&nd_pfn->dev) ? SZ_128K : 0;
        struct nd_namespace_common *ndns = nd_pfn->ndns;
        u32 start_pad = 0, end_trunc = 0;
        resource_size_t start, size;
        struct nd_namespace_io *nsio;
        struct nd_region *nd_region;
        struct nd_pfn_sb *pfn_sb;
        unsigned long npfns;
        phys_addr_t offset;
        const char *sig;
        u64 checksum;
        int rc;

        pfn_sb = devm_kzalloc(&nd_pfn->dev, sizeof(*pfn_sb), GFP_KERNEL);
        if (!pfn_sb)
                return -ENOMEM;

        nd_pfn->pfn_sb = pfn_sb;
        if (is_nd_dax(&nd_pfn->dev))
                sig = DAX_SIG;
        else
                sig = PFN_SIG;
        rc = nd_pfn_validate(nd_pfn, sig);
        if (rc != -ENODEV)
                return rc;

        /* no info block, do init */;
        nd_region = to_nd_region(nd_pfn->dev.parent);
        if (nd_region->ro) {
                dev_info(&nd_pfn->dev,
                                "%s is read-only, unable to init metadata\n",
                                dev_name(&nd_region->dev));
                return -ENXIO;
        }

        memset(pfn_sb, 0, sizeof(*pfn_sb));

        /*
         * Check if pmem collides with 'System RAM' when section aligned and
         * trim it accordingly
         */
        nsio = to_nd_namespace_io(&ndns->dev);
        start = PHYS_SECTION_ALIGN_DOWN(nsio->res.start);
        size = resource_size(&nsio->res);
        if (region_intersects(start, size, IORESOURCE_SYSTEM_RAM,
                                IORES_DESC_NONE) == REGION_MIXED) {
                start = nsio->res.start;
                start_pad = PHYS_SECTION_ALIGN_UP(start) - start;
        }

        start = nsio->res.start;
        size = PHYS_SECTION_ALIGN_UP(start + size) - start;
        if (region_intersects(start, size, IORESOURCE_SYSTEM_RAM,
                                IORES_DESC_NONE) == REGION_MIXED
                        || !IS_ALIGNED(start + resource_size(&nsio->res),
                                nd_pfn->align)) {
                size = resource_size(&nsio->res);
                end_trunc = start + size - phys_pmem_align_down(nd_pfn,
                                start + size);
        }

        if (start_pad + end_trunc)
                dev_info(&nd_pfn->dev, "%s alignment collision, truncate %d bytes\n",
                                dev_name(&ndns->dev), start_pad + end_trunc);

        /*
         * Note, we use 64 here for the standard size of struct page,
         * debugging options may cause it to be larger in which case the
         * implementation will limit the pfns advertised through
         * ->direct_access() to those that are included in the memmap.
         */
        start += start_pad;
        size = resource_size(&nsio->res);
        npfns = PFN_SECTION_ALIGN_UP((size - start_pad - end_trunc - SZ_8K)
                        / PAGE_SIZE);
        if (nd_pfn->mode == PFN_MODE_PMEM) {
                /*
                 * The altmap should be padded out to the block size used
                 * when populating the vmemmap. This *should* be equal to
                 * PMD_SIZE for most architectures.
                 */
                offset = ALIGN(start + SZ_8K + 64 * npfns + dax_label_reserve,
                                max(nd_pfn->align, PMD_SIZE)) - start;
        } else if (nd_pfn->mode == PFN_MODE_RAM)
                offset = ALIGN(start + SZ_8K + dax_label_reserve,
                                nd_pfn->align) - start;
        else
                return -ENXIO;

        if (offset + start_pad + end_trunc >= size) {
                dev_err(&nd_pfn->dev, "%s unable to satisfy requested alignment\n",
                                dev_name(&ndns->dev));
                return -ENXIO;
        }

        npfns = (size - offset - start_pad - end_trunc) / SZ_4K;
        pfn_sb->mode = cpu_to_le32(nd_pfn->mode);
        pfn_sb->dataoff = cpu_to_le64(offset);
        pfn_sb->npfns = cpu_to_le64(npfns);
        memcpy(pfn_sb->signature, sig, PFN_SIG_LEN);
        memcpy(pfn_sb->uuid, nd_pfn->uuid, 16);
        memcpy(pfn_sb->parent_uuid, nd_dev_to_uuid(&ndns->dev), 16);
        pfn_sb->version_major = cpu_to_le16(1);
        pfn_sb->version_minor = cpu_to_le16(2);
        pfn_sb->start_pad = cpu_to_le32(start_pad);
        pfn_sb->end_trunc = cpu_to_le32(end_trunc);
        pfn_sb->align = cpu_to_le32(nd_pfn->align);
        checksum = nd_sb_checksum((struct nd_gen_sb *) pfn_sb);
        pfn_sb->checksum = cpu_to_le64(checksum);

        return nvdimm_write_bytes(ndns, SZ_4K, pfn_sb, sizeof(*pfn_sb), 0);
}

/*
 * Determine the effective resource range and vmem_altmap from an nd_pfn
 * instance.
 */
int nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap)
{
        int rc;

        if (!nd_pfn->uuid || !nd_pfn->ndns)
                return -ENODEV;

        rc = nd_pfn_init(nd_pfn);
        if (rc)
                return rc;

        /* we need a valid pfn_sb before we can init a dev_pagemap */
        return __nvdimm_setup_pfn(nd_pfn, pgmap);
}
EXPORT_SYMBOL_GPL(nvdimm_setup_pfn);