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authorJames Smart <james.smart@emulex.com>2013-05-31 17:04:59 -0400
committerJames Bottomley <JBottomley@Parallels.com>2013-06-26 10:48:49 -0700
commitc4a7c922f55116c3e958ff5d5a53f5bf672ccef1 (patch)
tree188d6e93f2969b79027cbbf07c4ea9fef9a54573 /drivers/scsi/lpfc/lpfc_attr.c
parent06f3555125f7fb70242164b6841328af8b7354a8 (diff)
[SCSI] lpfc 8.3.40: Clarified the behavior of the lpfc_max_luns module parameter
Signed-off-by: James Smart <james.smart@emulex.com> Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Diffstat (limited to 'drivers/scsi/lpfc/lpfc_attr.c')
-rw-r--r--drivers/scsi/lpfc/lpfc_attr.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/drivers/scsi/lpfc/lpfc_attr.c b/drivers/scsi/lpfc/lpfc_attr.c
index 3c5625b8b1f4..5cb08ae3e8c2 100644
--- a/drivers/scsi/lpfc/lpfc_attr.c
+++ b/drivers/scsi/lpfc/lpfc_attr.c
@@ -1,7 +1,7 @@
/*******************************************************************
* This file is part of the Emulex Linux Device Driver for *
* Fibre Channel Host Bus Adapters. *
- * Copyright (C) 2004-2012 Emulex. All rights reserved. *
+ * Copyright (C) 2004-2013 Emulex. All rights reserved. *
* EMULEX and SLI are trademarks of Emulex. *
* www.emulex.com *
* Portions Copyright (C) 2004-2005 Christoph Hellwig *
@@ -4070,11 +4070,28 @@ LPFC_VPORT_ATTR(discovery_threads, 32, 1, 64, "Maximum number of ELS commands "
"during discovery");
/*
-# lpfc_max_luns: maximum allowed LUN.
+# lpfc_max_luns: maximum allowed LUN ID. This is the highest LUN ID that
+# will be scanned by the SCSI midlayer when sequential scanning is
+# used; and is also the highest LUN ID allowed when the SCSI midlayer
+# parses REPORT_LUN responses. The lpfc driver has no LUN count or
+# LUN ID limit, but the SCSI midlayer requires this field for the uses
+# above. The lpfc driver limits the default value to 255 for two reasons.
+# As it bounds the sequential scan loop, scanning for thousands of luns
+# on a target can take minutes of wall clock time. Additionally,
+# there are FC targets, such as JBODs, that only recognize 8-bits of
+# LUN ID. When they receive a value greater than 8 bits, they chop off
+# the high order bits. In other words, they see LUN IDs 0, 256, 512,
+# and so on all as LUN ID 0. This causes the linux kernel, which sees
+# valid responses at each of the LUN IDs, to believe there are multiple
+# devices present, when in fact, there is only 1.
+# A customer that is aware of their target behaviors, and the results as
+# indicated above, is welcome to increase the lpfc_max_luns value.
+# As mentioned, this value is not used by the lpfc driver, only the
+# SCSI midlayer.
# Value range is [0,65535]. Default value is 255.
# NOTE: The SCSI layer might probe all allowed LUN on some old targets.
*/
-LPFC_VPORT_ATTR_R(max_luns, 255, 0, 65535, "Maximum allowed LUN");
+LPFC_VPORT_ATTR_R(max_luns, 255, 0, 65535, "Maximum allowed LUN ID");
/*
# lpfc_poll_tmo: .Milliseconds driver will wait between polling FCP ring.