[PATCH v5 4/6] dax: check synchronous mapping is supported

[Pankaj Gupta]

This patch introduces 'daxdev_mapping_supported' helper
which checks if 'MAP_SYNC' is supported with filesystem
mapping. It also checks if corresponding dax_device is
synchronous. Virtio pmem device is asynchronous and
does not not support VM_SYNC. 

Suggested-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
---
 include/linux/dax.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/include/linux/dax.h b/include/linux/dax.h
index b896706a5ee9..4a2a60ffec86 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -38,6 +38,24 @@ void kill_dax(struct dax_device *dax_dev);
 void dax_write_cache(struct dax_device *dax_dev, bool wc);
 bool dax_write_cache_enabled(struct dax_device *dax_dev);
 bool dax_synchronous(struct dax_device *dax_dev);
+
+/*
+ * Callers check if synchronous mapping is enabled for DAX file
+ * and attached dax device is also synchronous.
+ *
+ * dax_synchronous function verifies if dax device is synchronous.
+ * Currently, only virtio pmem device supports asynchronous device
+ * flush.
+ */
+static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
+				struct dax_device *dax_dev)
+{
+	if (!(vma->vm_flags & VM_SYNC))
+		return true;
+	if (!IS_DAX(file_inode(vma->vm_file)))
+		return false;
+	return dax_synchronous(dax_dev);
+}
 #else
 static inline struct dax_device *dax_get_by_host(const char *host)
 {
@@ -69,6 +87,11 @@ static inline bool dax_synchronous(struct dax_device *dax_dev)
 {
 	return true;
 }
+static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
+				struct dax_device *dax_dev)
+{
+	return true;
+}
 #endif
 
 struct writeback_control;
-- 
2.20.1