NFS: Add a helper to set attribute barriers

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/inode.c

@@ -1260,6 +1260,22 @@ void nfs_fattr_init(struct nfs_fattr *fattr)
 }
 EXPORT_SYMBOL_GPL(nfs_fattr_init);
 
+/**
+ * nfs_fattr_set_barrier
+ * @fattr: attributes
+ *
+ * Used to set a barrier after an attribute was updated. This
+ * barrier ensures that older attributes from RPC calls that may
+ * have raced with our update cannot clobber these new values.
+ * Note that you are still responsible for ensuring that other
+ * operations which change the attribute on the server do not
+ * collide.
+ */
+void nfs_fattr_set_barrier(struct nfs_fattr *fattr)
+{
+	fattr->gencount = nfs_inc_attr_generation_counter();
+}
+
 struct nfs_fattr *nfs_alloc_fattr(void)
 {
 	struct nfs_fattr *fattr;

include/linux/nfs_fs.h

@@ -369,6 +369,7 @@ extern struct nfs_lock_context *nfs_get_lock_context(struct nfs_open_context *ct
 extern void nfs_put_lock_context(struct nfs_lock_context *l_ctx);
 extern u64 nfs_compat_user_ino64(u64 fileid);
 extern void nfs_fattr_init(struct nfs_fattr *fattr);
+extern void nfs_fattr_set_barrier(struct nfs_fattr *fattr);
 extern unsigned long nfs_inc_attr_generation_counter(void);
 
 extern struct nfs_fattr *nfs_alloc_fattr(void);