Make it possible to forcibly close SRP and FC sessions via sysfs

That patch contains the following changes:
* Move the code for creating a "close_sess" sysfs attribute from iscsi-scst to
  the SCST core such that it becomes available for other target drivers. This
  does not change the functionality of iscsi-scst.
* Add code in ib_srpt and qla2x00t to allow a session to be forcibly closed from
  user space.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>




git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@4852 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/include/scst.h

@@ -997,6 +997,19 @@ struct scst_tgt_template {
 	 */
 	ssize_t (*mgmt_cmd) (char *cmd);
 
+	/*
+	 * Forcibly close a session. Note: this function may operate
+	 * asynchronously - there is no guarantee the session will actually
+	 * have been closed at the time this function returns. May be called
+	 * with scst_mutex held. Activity may be suspended while this function
+	 * is invoked. May sleep but must not wait until session
+	 * unregistration finished. Must return 0 upon success and -EINTR if
+	 * the session has not been closed because a signal has been received.
+	 *
+	 * OPTIONAL
+	 */
+	int (*close_session)(struct scst_session *sess);
+
 	/*
 	 * Should return physical transport version. Used in the corresponding
 	 * INQUIRY version descriptor. See SPC for the list of available codes.