[SCSI] scsi_dh: fix kconfig related build errors

Do not automatically "select" SCSI_DH for dm-multipath. If SCSI_DH
doesn't exist,just do not allow  hardware handlers to be used.

Handle SCSI_DH being a module also. Make sure it doesn't allow DM_MULTIPATH
to be compiled in when SCSI_DH is a module.

[jejb: added comment for Kconfig syntax]
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/md/Kconfig

@@ -252,7 +252,11 @@ config DM_ZERO
 config DM_MULTIPATH
 	tristate "Multipath target"
 	depends on BLK_DEV_DM
-	select SCSI_DH
+	# nasty syntax but means make DM_MULTIPATH independent
+	# of SCSI_DH if the latter isn't defined but if
+	# it is, DM_MULTIPATH must depend on it.  We get a build
+	# error if SCSI_DH=m and DM_MULTIPATH=y
+	depends on SCSI_DH || !SCSI_DH
 	---help---
 	  Allow volume managers to support multipath hardware.
 

drivers/md/dm-mpath.c

@@ -664,6 +664,8 @@ static int parse_hw_handler(struct arg_set *as, struct multipath *m)
 	request_module("scsi_dh_%s", m->hw_handler_name);
 	if (scsi_dh_handler_exist(m->hw_handler_name) == 0) {
 		ti->error = "unknown hardware handler type";
+		kfree(m->hw_handler_name);
+		m->hw_handler_name = NULL;
 		return -EINVAL;
 	}
 	consume(as, hw_argc - 1);

include/scsi/scsi_dh.h

@@ -54,6 +54,16 @@ enum {
 	SCSI_DH_NOSYS,
 	SCSI_DH_DRIVER_MAX,
 };
-
+#if defined(CONFIG_SCSI_DH) || defined(CONFIG_SCSI_DH_MODULE)
 extern int scsi_dh_activate(struct request_queue *);
 extern int scsi_dh_handler_exist(const char *);
+#else
+static inline int scsi_dh_activate(struct request_queue *req)
+{
+	return 0;
+}
+static inline int scsi_dh_handler_exist(const char *name)
+{
+	return 0;
+}
+#endif