[RFC PATCH 3/4] device-dax: Add a NONE type for DAX KMEM persistence

[Srinivas Aji <srinivas.aji@memverge.com>]

The NONE type allows us to format DAX KMEM so that all the memory is
usable as system memory. This does not allow us to store any
persistent data.

Signed-off-by: Srinivas Aji <srinivas.aji@memverge.com>
---
 drivers/dax/kmem.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index df7cfc8ace78..0ca6e14f7e73 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -474,6 +474,46 @@ int kmem_persist_cleanup(struct dev_dax *dev_dax,
 	return 0;
 }
 
+/*
+ * A NONE type for DAX KMEM persistence which does not expose any persistent
+ * device or filesystem on the memory.
+ */
+
+static int kmem_persist_none_format(struct dev_dax *dev_dax)
+{
+	struct kmem_persist_superblock *super =
+		kmap_local_page(dax_kmem_index_to_page(0, dev_dax));
+	super->magic = kmem_persist_magic;
+	super->type = KMEM_PERSIST_NONE;
+	kunmap_local(super);
+	return 0;
+}
+
+static int kmem_persist_none_probe(struct dev_dax *dev_dax, void **data)
+{
+	unsigned long num_pages = dax_kmem_num_pages(dev_dax);
+	unsigned long i;
+
+	for (i = 1; i < num_pages; i++)
+		__free_page(dax_kmem_index_to_page(i, dev_dax));
+
+	*data = NULL;
+	return 0;
+}
+
+static int kmem_persist_none_cleanup(struct dev_dax *dev_dax, void *data)
+{
+	__free_page(dax_kmem_index_to_page(0, dev_dax));
+	return 0;
+}
+
+static struct kmem_persist_ops kmem_persist_none_ops = {
+	.type = KMEM_PERSIST_NONE,
+	.format = kmem_persist_none_format,
+	.probe = kmem_persist_none_probe,
+	.cleanup = kmem_persist_none_cleanup
+};
+
 #endif /* CONFIG_DEV_DAX_KMEM_PERSIST */
 
 static struct dax_device_driver device_dax_kmem_driver = {
@@ -493,6 +533,10 @@ static int __init dax_kmem_init(void)
 	rc = dax_driver_register(&device_dax_kmem_driver);
 	if (rc)
 		kfree_const(kmem_name);
+#ifdef CONFIG_DEV_DAX_KMEM_PERSIST
+	if (rc == 0)
+		kmem_persist_type_register(&kmem_persist_none_ops);
+#endif
 	return rc;
 }
 
-- 
2.30.2