Re: [Qemu-devel] megasas: Unexpected response from lun 1 while scanning, scan aborted

[Hannes Reinecke]

On 3/28/19 1:47 AM, Dongli Zhang wrote:
> 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
> > > [ÂÂÂ 0.392494] SCSI subsystem initialized
> > > [ÂÂÂ 0.460666] Block layer SCSI generic (bsg) driver version 0.4 loaded (major
> > > 251)
> > > [ÂÂÂ 0.706788] sd 1:0:0:0: [sda] Attached SCSI disk
> > > # dmesg | grep scsi
> > > [ÂÂÂ 0.511643] scsi host0: Avago SAS based MegaRAID driver
> > > [ÂÂÂ 0.523302] scsi 0:2:0:0: Unexpected response from lun 1 while scanning,
> > > scan aborted
> > > [ÂÂÂ 0.540364] scsi host1: ata_piix
> > > [ÂÂÂ 0.540780] scsi host2: ata_piix
> > > [ÂÂÂ 0.702396] scsi 1:0:0:0: Direct-AccessÂÂÂÂ ATAÂÂÂÂÂ QEMU HARDDISKÂÂÂ 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,
Hmm. Good point.

In _theory_ one could just jbod mode, in which case _all_ LUNs are 
exposed. But then we could probably adjust it, based on which mode is 
selected.
I'll check.

Cheers,

Hannes
--
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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