linux-kernel - scanning for LUNs

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Date:	Thu,  4 Apr 2013 08:12:37 -0700
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, ohering@...e.com,
	jbottomley@...allels.com, hch@...radead.org,
	linux-scsi@...r.kernel.org, kys@...rosoft.com
Subject: scanning for LUNs 

Here is the code snippet for scanning LUNS (drivers/scsi/scsi_scan.c in function 
__scsi_scan_target()):

        /*
         * Scan LUN 0, if there is some response, scan further. Ideally, we
         * would not configure LUN 0 until all LUNs are scanned.
         */
        res = scsi_probe_and_add_lun(starget, 0, &bflags, NULL, rescan, NULL);
        if (res == SCSI_SCAN_LUN_PRESENT || res == SCSI_SCAN_TARGET_PRESENT) {
                if (scsi_report_lun_scan(starget, bflags, rescan) != 0)

So, if we don't get a response while scanning LUN0, we will not use scsi_report_lun_scan().
On Hyper-V, the scsi emulation on the host does not treat LUN0 as anything special and we 
could have situations where the only device under a scsi controller is at a location other than 0
or 1. In this case the standard LUN scanning code in Linux fails to detect this device. Is this
behaviour expected? Why is LUN0 treated differently here. Looking at the scsi spec, I am not sure
if this is what is specified. Any help/guidance will be greatly appreciated.

Regards,

K. Y

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