dax: check synchronous mapping is supported

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@suse.cz>
Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 8b535bc..9bd8528 100644 (file)
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -56,6 +56,18 @@ static inline void set_dax_synchronous(struct dax_device *dax_dev)
 {
        __set_dax_synchronous(dax_dev);
 }
+/*
+ * Check if given mapping is supported by the file / underlying device.
+ */
+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)
 {
@@ -90,6 +102,11 @@ static inline bool dax_synchronous(struct dax_device *dax_dev)
 static inline void set_dax_synchronous(struct dax_device *dax_dev)
 {
 }
+static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
+                               struct dax_device *dax_dev)
+{
+       return !(vma->vm_flags & VM_SYNC);
+}
 #endif
 
 struct writeback_control;