[RFC PATCH 02/12] dax: Save the kva from memremap

[Dave Jiang <dave.jiang@intel.com>]

This patch is partially taken from John Grove's famfs dax series.

Save the kva for memremap because we need direct_access() support.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 drivers/dax/dax-private.h |  4 ++++
 drivers/dax/device.c      | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index c6ae27c982f4..425a515905e5 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -69,6 +69,8 @@ struct dev_dax_range {
  * data while the device is activated in the driver.
  * @region: parent region
  * @dax_dev: core dax functionality
+ * @virt_addr: kva from memremap; used by fsdev_dax
+ * @cached_size: cached size of the memory range for quick access; used by fsdev_dax
  * @align: alignment of this instance
  * @target_node: effective numa node if dev_dax memory range is onlined
  * @dyn_id: is this a dynamic or statically created instance
@@ -83,6 +85,8 @@ struct dev_dax_range {
 struct dev_dax {
 	struct dax_region *region;
 	struct dax_device *dax_dev;
+	void *virt_addr;
+	u64 cached_size;
 	unsigned int align;
 	int target_node;
 	bool dyn_id;
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 62206bcb63a6..4ffa3ef60a57 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -370,6 +370,7 @@ static int dax_open(struct inode *inode, struct file *filp)
 	filp->f_sb_err = file_sample_sb_err(filp);
 	filp->private_data = dev_dax;
 	inode->i_flags = S_DAX;
+	inode->i_size = dev_dax->cached_size;
 
 	return 0;
 }
@@ -408,7 +409,9 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	struct device *dev = &dev_dax->dev;
 	struct dev_pagemap *pgmap;
 	struct inode *inode;
+	u64 data_offset = 0;
 	struct cdev *cdev;
+	u64 len = 0;
 	void *addr;
 	int rc, i;
 
@@ -451,6 +454,7 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 					i, range->start, range->end);
 			return -EBUSY;
 		}
+		len += range_len(range);
 	}
 
 	pgmap->type = MEMORY_DEVICE_GENERIC;
@@ -461,6 +465,21 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	if (IS_ERR(addr))
 		return PTR_ERR(addr);
 
+	/* Detect whether the data is at a non-zero offset into the memory */
+	if (pgmap->range.start != dev_dax->ranges[0].range.start) {
+		u64 phys = dev_dax->ranges[0].range.start;
+		u64 pgmap_phys = dev_dax->pgmap[0].range.start;
+
+		if (!WARN_ON(pgmap_phys > phys))
+			data_offset = phys - pgmap_phys;
+
+		pr_debug("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx\n",
+			 __func__, phys, pgmap_phys, data_offset);
+	}
+
+	dev_dax->virt_addr = addr + data_offset;
+	dev_dax->cached_size = len;
+
 	inode = dax_inode(dax_dev);
 	cdev = inode->i_cdev;
 	cdev_init(cdev, &dax_fops);
-- 
2.53.0