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Re: [dm-devel] [PATCH 3/4] scsi_dh_rdac: Adding the match function for rdac device handler



On 11/02/2011 04:23 PM, Moger, Babu wrote:
-----Original Message-----
From: Hannes Reinecke [mailto:hare suse de]
Sent: Wednesday, November 02, 2011 2:21 AM
To: dm-devel redhat com
Subject: Re: [dm-devel] [PATCH 3/4] scsi_dh_rdac: Adding the match
function for rdac device handler

On 11/01/2011 06:19 PM, Moger, Babu wrote:
This patch introduces the match function for rdac device handler.
Without this,
sometimes handler attach fails during the device_add.  The match
function was
introduced by this patch
http://www.spinics.net/lists/linux-scsi/msg54284.html

Signed-off-by: Babu Moger<babu moger netapp com>
---

--- linux/drivers/scsi/device_handler/scsi_dh_rdac.c.orig	2011-10-31
11:25:44.000000000 -0500
+++ linux/drivers/scsi/device_handler/scsi_dh_rdac.c	2011-10-31
11:31:34.000000000 -0500
@@ -819,6 +819,21 @@ static const struct scsi_dh_devlist rdac
   	{NULL, NULL},
   };

+static bool rdac_match(struct scsi_device *sdev)
+{
+	int i;
+
+	for (i = 0; rdac_dev_list[i].vendor; i++) {
+		if (!strncmp(sdev->vendor, rdac_dev_list[i].vendor,
+			strlen(rdac_dev_list[i].vendor))&&
+		    !strncmp(sdev->model, rdac_dev_list[i].model,
+			strlen(rdac_dev_list[i].model))) {
+			return true;
+		}
+	}
+	return false;
+}
+
   static int rdac_bus_attach(struct scsi_device *sdev);
   static void rdac_bus_detach(struct scsi_device *sdev);

@@ -831,6 +846,7 @@ static struct scsi_device_handler rdac_d
   	.attach = rdac_bus_attach,
   	.detach = rdac_bus_detach,
   	.activate = rdac_activate,
+	.match = rdac_match,
   };

   static int rdac_bus_attach(struct scsi_device *sdev)

As stated in the other mail, I guess we would need to have a check
if the LUN is in ALUA mode.
And, btw, the _original_ intention was to allow vendor-specific
device_handler to do some better probing, eg querying some
vendor-specific VPD pages.
Especially for RDAC it would make far more sense to query the
existence and format of one of the RDAC-specific VPD pages (eg 0xC2,
0xC4, or 0xC8) and use that for matching.
Then you could do away with the vendor/model array altogether here
and we wouldn't need to update the rdac handler every time a new
array comes out or has been rebranded by some OEM.

OK. I will add the check for TPGS. I will send the patches tomorrow.
For sending the VPD pages(0xC2, 0xC4 and 0xC8), I think we need be
> little careful here.
This includes sending these commands to every possible device in the
> system. That is what we want to avoid.
I will investigate more on that. That will be my next set of patches
> independent of this.

Fair enough.
As long as it's understood to be an interim solution, then we would only need to check for the TGPS bit. Which has the neat side-effect that we don't actually have to do any I/O to check this, as the information is already present at that time.

While you're at it, could you please add this check for scsi_dh_emc, too? The Clariion is also able to run in dual-mode, so the same check is required there, too.

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)


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