fuse: support per inode DAX in fuse protocol

Expand the fuse protocol to support per inode DAX.

FUSE_HAS_INODE_DAX flag is added indicating if fuse server/client
supporting per inode DAX. It can be conveyed in both FUSE_INIT request and
reply.

FUSE_ATTR_DAX flag is added indicating if DAX shall be enabled for
corresponding file. It is conveyed in FUSE_LOOKUP reply.
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

include/uapi/linux/fuse.h

@@ -193,6 +193,7 @@
  *  - add flags2 to fuse_init_in and fuse_init_out
  *  - add FUSE_SECURITY_CTX init flag
  *  - add security context to create, mkdir, symlink, and mknod requests
+ *  - add FUSE_HAS_INODE_DAX, FUSE_ATTR_DAX
  */
 
 #ifndef _LINUX_FUSE_H
@@ -351,6 +352,7 @@ struct fuse_file_lock {
  * FUSE_INIT_RESERVED: reserved, do not use
  * FUSE_SECURITY_CTX:	add security context to create, mkdir, symlink, and
  *			mknod
+ * FUSE_HAS_INODE_DAX:  use per inode DAX
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -386,6 +388,7 @@ struct fuse_file_lock {
 #define FUSE_INIT_RESERVED	(1 << 31)
 /* bits 32..63 get shifted down 32 bits into the flags2 field */
 #define FUSE_SECURITY_CTX	(1ULL << 32)
+#define FUSE_HAS_INODE_DAX	(1ULL << 33)
 
 /**
  * CUSE INIT request/reply flags
@@ -468,8 +471,10 @@ struct fuse_file_lock {
  * fuse_attr flags
  *
  * FUSE_ATTR_SUBMOUNT: Object is a submount root
+ * FUSE_ATTR_DAX: Enable DAX for this file in per inode DAX mode
  */
 #define FUSE_ATTR_SUBMOUNT      (1 << 0)
+#define FUSE_ATTR_DAX		(1 << 1)
 
 /**
  * Open flags