[PATCH] scsi: storvsc: Support manual scans for all Hyper-V targets

[Laurence Oberman <loberman@redhat.com>]

The Fibre Channel transport topology created by storvsc exposes only one
dummy remote port per SCSI host. Its scsi_target_id is always zero.

As a result, the FC transport user-scan path performs its remote-port lookup
using target ID 0 and cannot initiate a scan for Target 1 or higher. No SCSI
command is therefore sent to Hyper-V when userspace explicitly requests a
scan of one of these targets.

storvsc itself supports up to STORVSC_FC_MAX_TARGETS and already passes
scmnd->device->id to Hyper-V as vm_srb->target_id. Devices on Target 1 and
higher work when initially discovered and can be rediscovered by a full host
scan, such as the scan triggered after an FC port bounce.

Provide a storvsc-specific user_scan callback that directly invokes
scsi_scan_host_selected(). This bypasses the single-rport lookup in
fc_user_scan() and allows userspace to explicitly scan any target supported
by storvsc.

This avoids requiring storvsc to create and manage one synthetic fc_rport
for every Hyper-V target.

Signed-off-by: Laurence Oberman <loberman@redhat.com>
---
 drivers/scsi/storvsc_drv.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 571ea549152b..80830aa12532 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -33,6 +33,7 @@
 #include <scsi/scsi_dbg.h>
 #include <scsi/scsi_transport_fc.h>
 #include <scsi/scsi_transport.h>
+#include "scsi_priv.h"
 
 /*
  * All wire protocol details (storage protocol between the guest and the host)
@@ -520,6 +521,17 @@ static void storvsc_host_scan(struct work_struct *work)
 	scsi_scan_host(host);
 }
 
+#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
+static int storvsc_user_scan(struct Scsi_Host *host,
+			     unsigned int channel,
+			     unsigned int id,
+			     u64 lun)
+{
+	return scsi_scan_host_selected(host, channel, id, lun,
+				       SCSI_SCAN_MANUAL);
+}
+#endif
+
 static void storvsc_remove_lun(struct work_struct *work)
 {
 	struct storvsc_scan_work *wrk;
@@ -2232,6 +2244,8 @@ static int __init storvsc_drv_init(void)
 	fc_transport_template = fc_attach_transport(&fc_transport_functions);
 	if (!fc_transport_template)
 		return -ENODEV;
+
+	fc_transport_template->user_scan = storvsc_user_scan;
 #endif
 
 	ret = vmbus_driver_register(&storvsc_drv);
-- 
2.55.0