xattr: Add __vfs_{get,set,remove}xattr helpers

Right now, various places in the kernel check for the existence of
getxattr, setxattr, and removexattr inode operations and directly call
those operations.  Switch to helper functions and test for the IOP_XATTR
flag instead.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

security/smack/smack_lsm.c

@@ -265,14 +265,14 @@ static struct smack_known *smk_fetch(const char *name, struct inode *ip,
 	char *buffer;
 	struct smack_known *skp = NULL;
 
-	if (ip->i_op->getxattr == NULL)
+	if (!(ip->i_opflags & IOP_XATTR))
 		return ERR_PTR(-EOPNOTSUPP);
 
 	buffer = kzalloc(SMK_LONGLABEL, GFP_KERNEL);
 	if (buffer == NULL)
 		return ERR_PTR(-ENOMEM);
 
-	rc = ip->i_op->getxattr(dp, ip, name, buffer, SMK_LONGLABEL);
+	rc = __vfs_getxattr(dp, ip, name, buffer, SMK_LONGLABEL);
 	if (rc < 0)
 		skp = ERR_PTR(rc);
 	else if (rc == 0)
@@ -3520,8 +3520,8 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 		 * It would be curious if the label of the task
 		 * does not match that assigned.
 		 */
-		if (inode->i_op->getxattr == NULL)
-			break;
+		if (!(inode->i_opflags & IOP_XATTR))
+		        break;
 		/*
 		 * Get the dentry for xattr.
 		 */
@@ -3545,12 +3545,12 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 			 */
 			if (isp->smk_flags & SMK_INODE_CHANGED) {
 				isp->smk_flags &= ~SMK_INODE_CHANGED;
-				rc = inode->i_op->setxattr(dp, inode,
+				rc = __vfs_setxattr(dp, inode,
 					XATTR_NAME_SMACKTRANSMUTE,
 					TRANS_TRUE, TRANS_TRUE_SIZE,
 					0);
 			} else {
-				rc = inode->i_op->getxattr(dp, inode,
+				rc = __vfs_getxattr(dp, inode,
 					XATTR_NAME_SMACKTRANSMUTE, trattr,
 					TRANS_TRUE_SIZE);
 				if (rc >= 0 && strncmp(trattr, TRANS_TRUE,