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Subject: Re: [Qemu-devel] megasas: Unexpected response from lun 1 while
 scanning, scan aborted
To:     Hannes Reinecke <hare@suse.de>
Cc:     qemu-block@nongnu.org, linux-scsi@vger.kernel.org,
        megaraidlinux.pdl@broadcom.com, linux-kernel@vger.kernel.org,
        qemu-devel@nongnu.org
References: <9c3849cf-86c6-4568-bff5-1050b445322d@default>
 <c3a8f877-82bc-44ab-72e8-51f62c0a65ed@suse.de>
From:   Dongli Zhang <dongli.zhang@oracle.com>
Message-ID: <442316ee-8800-275c-85e9-a5d054a28e63@oracle.com>
Date:   Thu, 28 Mar 2019 08:47:13 +0800
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On 3/27/19 7:31 PM, Hannes Reinecke wrote:
> On 3/26/19 5:47 PM, Dongli Zhang wrote:
>> I am reporting an error that the scsi lun cannot initialize successfully when I
>> am emulating megasas scsi controller with qemu.
>>
>> I am not sure if this is issue in qemu or linux kernel.
>>
>> When 'lun=1' is specified, there is "Unexpected response from lun 1 while
>> scanning, scan aborted".
>>
>> Everything works well if 'lun=0' is specified.
>>
>>
>> Below is the qemu cmdline involved:
>>
>> -device megasas,id=scsi0 \
>> -device scsi-hd,drive=drive0,bus=scsi0.0,lun=1 \
>> -drive file=/home/zhang/img/test.img,if=none,id=drive0,format=raw
>>
>>
>> Below is the syslog related to 'scsi|SCSI'
>>
>> # dmesg | grep SCSI
>> [    0.392494] SCSI subsystem initialized
>> [    0.460666] Block layer SCSI generic (bsg) driver version 0.4 loaded (major
>> 251)
>> [    0.706788] sd 1:0:0:0: [sda] Attached SCSI disk
>> # dmesg | grep scsi
>> [    0.511643] scsi host0: Avago SAS based MegaRAID driver
>> [    0.523302] scsi 0:2:0:0: Unexpected response from lun 1 while scanning,
>> scan aborted
>> [    0.540364] scsi host1: ata_piix
>> [    0.540780] scsi host2: ata_piix
>> [    0.702396] scsi 1:0:0:0: Direct-Access     ATA      QEMU HARDDISK    2.5+
>> PQ: 0 ANSI: 5
>>
>> When 'lun=1' is changed to 'lun=0', there is no issue.
>>
>> Thank you very much!
>>
> That's an artifact from the megasas emulation in quemu.
> Megasas (internally) can't handle LUN numbers (the RAID part only knows about
> 'disks'), so I took the decision to not expose devices with LUN != 0.
> Please use a different SCSI target number, not a non-zero LUN number.

The guest kernel is able to detect the disk if lun is always 0, while target
number is changed:

-device scsi-hd,drive=drive0,bus=scsi0.0,channel=0,scsi-id=0,lun=0
-device scsi-hd,drive=drive1,bus=scsi0.0,channel=0,scsi-id=1,lun=0

# dmesg | grep scsi
[    0.935999] scsi host0: ata_piix
[    0.936401] scsi host1: ata_piix
[    1.100945] scsi 0:0:0:0: Direct-Access     ATA      QEMU HARDDISK    2.5+
PQ: 0 ANSI: 5
[    1.102409] sd 0:0:0:0: Attached scsi generic sg0 type 0
[    1.672952] scsi host2: Avago SAS based MegaRAID driver
[    1.683886] scsi 2:2:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.5+
PQ: 0 ANSI: 5
[    1.684915] scsi 2:2:1:0: Direct-Access     QEMU     QEMU HARDDISK    2.5+
PQ: 0 ANSI: 5
[    1.701529] sd 2:2:0:0: Attached scsi generic sg1 type 0
[    1.704795] sd 2:2:1:0: Attached scsi generic sg2 type 0
# dmesg | grep SCSI
[    0.111015] SCSI subsystem initialized
[    0.904712] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 246)
[    1.121174] sd 0:0:0:0: [sda] Attached SCSI disk
[    1.703739] sd 2:2:0:0: [sdb] Attached SCSI disk
[    1.706964] sd 2:2:1:0: [sdc] Attached SCSI disk


If device with LUN != 0 will not be exposed, why not set max_lun = 0 as what
qemu lsi is doing?

diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index a56317e..c966ee0 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -2298,7 +2298,7 @@ static void megasas_scsi_uninit(PCIDevice *d)
 static const struct SCSIBusInfo megasas_scsi_info = {
     .tcq = true,
     .max_target = MFI_MAX_LD,
-    .max_lun = 255,
+    .max_lun = 0,

     .transfer_data = megasas_xfer_complete,
     .get_sg_list = megasas_get_sg_list,


Thank you very much!

Dongli Zhang