[SCSI] Make scsi_scan_host work for drivers which find their own targets

If a driver can find its own targets, it can now fill in scan_finished and
(optionally) scan_start in the scsi_host_template.  Then, when it calls
scsi_scan_host(), it will be called back (from a thread if asynchronous
discovery is enabled), first to start the scan, and then at intervals to
check if the scan is completed.

Also make scsi_prep_async_scan and scsi_finish_async_scan static.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

include/scsi/scsi_host.h

@@ -240,6 +240,24 @@ struct scsi_host_template {
 	 */
 	void (* target_destroy)(struct scsi_target *);
 
+	/*
+	 * If a host has the ability to discover targets on its own instead
+	 * of scanning the entire bus, it can fill in this function and
+	 * call scsi_scan_host().  This function will be called periodically
+	 * until it returns 1 with the scsi_host and the elapsed time of
+	 * the scan in jiffies.
+	 *
+	 * Status: OPTIONAL
+	 */
+	int (* scan_finished)(struct Scsi_Host *, unsigned long);
+
+	/*
+	 * If the host wants to be called before the scan starts, but
+	 * after the midlayer has set up ready for the scan, it can fill
+	 * in this function.
+	 */
+	void (* scan_start)(struct Scsi_Host *);
+
 	/*
 	 * fill in this function to allow the queue depth of this host
 	 * to be changeable (on a per device basis).  returns either