[Qemu-devel] [PATCH v8 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 <address@hidden>
Signed-off-by: Pankaj Gupta <address@hidden>
Reviewed-by: Jan Kara <address@hidden>
---
 include/linux/dax.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/dax.h b/include/linux/dax.h
index c97fc0cc7167..41b4a5db6305 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -41,6 +41,18 @@ 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);
+/*
+ * 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)
 {
@@ -68,6 +80,11 @@ static inline bool dax_write_cache_enabled(struct dax_device 
*dax_dev)
 {
        return false;
 }
+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;
-- 
2.20.1