[RFC PATCH 2/3] mm/nvdimm: Add page size and struct page size to pfn superblock

[Aneesh Kumar K.V]

This is needed so that we don't wrongly initialize a namespace
which doesn't have enough space reserved for holding struct pages
with the current kernel.

We also increment PFN_MIN_VERSION to make sure that older kernel
won't initialize namespace created with newer kernel.

Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
 drivers/nvdimm/pfn.h      |  9 ++++++---
 drivers/nvdimm/pfn_devs.c | 19 ++++++++++++++++++-
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/nvdimm/pfn.h b/drivers/nvdimm/pfn.h
index 1b10ae5773b6..ba11738ca8a2 100644
--- a/drivers/nvdimm/pfn.h
+++ b/drivers/nvdimm/pfn.h
@@ -25,7 +25,7 @@
  * kernel should fail to initialize that namespace.
  */
 
-#define PFN_MIN_VERSION 0
+#define PFN_MIN_VERSION 1
 
 struct nd_pfn_sb {
        u8 signature[PFN_SIG_LEN];
@@ -42,8 +42,11 @@ struct nd_pfn_sb {
        __le32 end_trunc;
        /* minor-version-2 record the base alignment of the mapping */
        __le32 align;
-       __le16 min_verison;
-       u8 padding[3998];
+       __le16 min_version;
+       /* minor-version-3 record the page size and struct page size */
+       __le16 page_struct_size;
+       __le32 page_size;
+       u8 padding[3992];
        __le64 checksum;
 };
 
diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index 3250de70a7b3..94918a4e6e73 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -462,6 +462,15 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
        if (__le16_to_cpu(pfn_sb->version_minor) < 2)
                pfn_sb->align = 0;
 
+       if (__le16_to_cpu(pfn_sb->version_minor) < 3) {
+               /*
+                * For a large part we use PAGE_SIZE. But we
+                * do have some accounting code using SZ_4K.
+                */
+               pfn_sb->page_struct_size = cpu_to_le16(64);
+               pfn_sb->page_size = cpu_to_le32(SZ_4K);
+       }
+
        switch (le32_to_cpu(pfn_sb->mode)) {
        case PFN_MODE_RAM:
        case PFN_MODE_PMEM:
@@ -477,6 +486,12 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
                align = 1UL << ilog2(offset);
        mode = le32_to_cpu(pfn_sb->mode);
 
+       if (le32_to_cpu(pfn_sb->page_size) != PAGE_SIZE)
+               return -EOPNOTSUPP;
+
+       if (le16_to_cpu(pfn_sb->page_struct_size) != sizeof(struct page))
+               return -EOPNOTSUPP;
+
        if (!nd_pfn->uuid) {
                /*
                 * When probing a namepace via nd_pfn_probe() the uuid
@@ -771,11 +786,13 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
        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->version_minor = cpu_to_le16(3);
        pfn_sb->min_version = cpu_to_le16(PFN_MIN_VERSION);
        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);
+       pfn_sb->page_struct_size = cpu_to_le16(sizeof(struct page));
+       pfn_sb->page_size = cpu_to_le32(PAGE_SIZE);
        checksum = nd_sb_checksum((struct nd_gen_sb *) pfn_sb);
        pfn_sb->checksum = cpu_to_le64(checksum);
 
-- 
2.21.0