fuse: allow fine grained attr cache invaldation

This patch adds the infrastructure for more fine grained attribute
invalidation.  Currently only 'atime' is invalidated separately.

The use of this infrastructure is extended to the statx(2) interface, which
for now means that if only 'atime' is invalid and STATX_ATIME is not
specified in the mask argument, then no GETATTR request will be generated.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/fuse_i.h

@@ -80,6 +80,9 @@ struct fuse_inode {
 	/** Time in jiffies until the file attributes are valid */
 	u64 i_time;
 
+	/* Which attributes are invalid */
+	u32 inval_mask;
+
 	/** The sticky bit in inode->i_mode may have been removed, so
 	    preserve the original mode */
 	umode_t orig_i_mode;