default to simple_setattr

With the new truncate sequence every filesystem that wants to support file
size changes on disk needs to implement its own ->setattr.  So instead
of calling inode_setattr which supports size changes call into a simple
method that doesn't support this.  simple_setattr is almost what we
want except that it does not mark the inode dirty after changes.  Given
that marking the inode dirty is a no-op for the simple in-memory filesystems
that use simple_setattr currently just add the mark_inode_dirty call.

Also add a WARN_ON for the presence of a truncate method to simple_setattr
to catch new instances of it during the transition period.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/attr.c

@@ -237,13 +237,10 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
 	if (ia_valid & ATTR_SIZE)
 		down_write(&dentry->d_inode->i_alloc_sem);
 
-	if (inode->i_op && inode->i_op->setattr) {
+	if (inode->i_op->setattr)
 		error = inode->i_op->setattr(dentry, attr);
-	} else {
-		error = inode_change_ok(inode, attr);
-		if (!error)
-			error = inode_setattr(inode, attr);
-	}
+	else
+		error = simple_setattr(dentry, attr);
 
 	if (ia_valid & ATTR_SIZE)
 		up_write(&dentry->d_inode->i_alloc_sem);

fs/libfs.c

@@ -370,21 +370,26 @@ int simple_setsize(struct inode *inode, loff_t newsize)
 EXPORT_SYMBOL(simple_setsize);
 
 /**
- * simple_setattr - setattr for simple in-memory filesystem
+ * simple_setattr - setattr for simple filesystem
  * @dentry: dentry
  * @iattr: iattr structure
  *
  * Returns 0 on success, -error on failure.
  *
- * simple_setattr implements setattr for an in-memory filesystem which
- * does not store its own file data or metadata (eg. uses the page cache
- * and inode cache as its data store).
+ * simple_setattr is a simple ->setattr implementation without a proper
+ * implementation of size changes.
+ *
+ * It can either be used for in-memory filesystems or special files
+ * on simple regular filesystems.  Anything that needs to change on-disk
+ * or wire state on size changes needs its own setattr method.
  */
 int simple_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	struct inode *inode = dentry->d_inode;
 	int error;
 
+	WARN_ON_ONCE(inode->i_op->truncate);
+
 	error = inode_change_ok(inode, iattr);
 	if (error)
 		return error;
@@ -396,7 +401,8 @@ int simple_setattr(struct dentry *dentry, struct iattr *iattr)
 	}
 
 	setattr_copy(inode, iattr);
-	return error;
+	mark_inode_dirty(inode);
+	return 0;
 }
 EXPORT_SYMBOL(simple_setattr);