orangefs: record userspace version for feature compatbility

The client reports its version to the kernel on startup. We already test
that it is above the minimum version. Now we record it in a global
variable so code elsewhere can consult it before making a request the
client may not understand.
Signed-off-by: Martin Brandenburg <martin@omnibond.com>

fs/orangefs/devorangefs-req.c

@@ -17,6 +17,8 @@
 
 /* this file implements the /dev/pvfs2-req device node */
 
+uint32_t userspace_version;
+
 static int open_access_count;
 
 #define DUMP_DEVICE_ERROR()                                                   \
@@ -387,6 +389,13 @@ static ssize_t orangefs_devreq_write_iter(struct kiocb *iocb,
 		return -EPROTO;
 	}
 
+	if (!userspace_version) {
+		userspace_version = head.version;
+	} else if (userspace_version != head.version) {
+		gossip_err("Error: userspace version changes\n");
+		return -EPROTO;
+	}
+
 	/* remove the op from the in progress hash table */
 	op = orangefs_devreq_remove_op(head.tag);
 	if (!op) {
@@ -527,6 +536,7 @@ static int orangefs_devreq_release(struct inode *inode, struct file *file)
 	gossip_debug(GOSSIP_DEV_DEBUG,
 		     "pvfs2-client-core: device close complete\n");
 	open_access_count = 0;
+	userspace_version = 0;
 	mutex_unlock(&devreq_mutex);
 	return 0;
 }

fs/orangefs/orangefs-kernel.h

@@ -506,6 +506,8 @@ ssize_t orangefs_inode_read(struct inode *inode,
 /*
  * defined in devorangefs-req.c
  */
+extern uint32_t userspace_version;
+
 int orangefs_dev_init(void);
 void orangefs_dev_cleanup(void);
 int is_daemon_in_service(void);