[SeaBIOS] [PATCH 0/9] add support for generic lun enumeration

[Roman Kagan]

On Thu, Mar 02, 2017 at 11:14:37AM -0500, Kevin O'Connor wrote:
> On Wed, Mar 01, 2017 at 01:45:33PM +0300, Roman Kagan wrote:
> > A number of SCSI drivers currently only see luns #0 in their targets.
> > 
> > This may be a problem when drives have to be assigned bigger lun
> > numbers, e.g. because the storage controllers don't provide enough
> > target numbers to accomodate all drives.
> > (In particular, I'm about to submit a driver for Hyper-V VMBus SCSI
> > controller which is limited to 2 targets only).
> > 
> > This series adds generic SCSI lun enumeration (either via REPORT LUNS
> > command or sequentially trying every lun), and makes the respective
> > drivers use it.
> 
> Thanks.  Let me make sure I understand this series.  Some scsi
> controllers have hardware specific mechanisms for finding the number
> of luns (usb-msc, megasas, pvscsi) and some controllers use a generic
> REPORT LUNS mechanism (virtio-scsi, esp-scsi, usb-uas, mpt-scsi,
> lsi-scsi).
> 
> The basic difficulty with implementing REPORT LUNS in seabios is that
> the code needs a "struct drive_s" to issue the REPORT LUNS command,
> but since the drive parameters (or even the number of drives) aren't
> known, a dummy "lun0" drive_s must be created just for REPORT LUNS.
> Thus the series breaks the driver xxx_add_lun() functions into
> xxx_init_lun() and xxx_add_lun() so that a dummy lun0 can be created.
> 
> An additional complexity is that the REPORT LUNS mechanism is broken
> in current QEMU on lsi-scsi and mpt-scsi.
> 
> Your goal is to add support for "Hyper-V VMBus SCSI" which also
> requires REPORT LUNS.
> 
> Is the above correct?

Absolutely.  I couldn't have explained it better.

One minor nit is that, strictly speaking, the upcoming vmbus scsi driver
doesn't *require* REPORTS LUNS.  It's just that it would be too limiting
if the users had to stick with lun #0 only like was currently the case
with other drivers: here the number of available targets was only 2, and
thus the number of BIOS-visible disks would be no more than that.

So I thought it was a good idea to start with a series that adds generic
lun enumeration to the SCSI layer, that would lift this limitation for
the future vmbus scsi and could benefit other drivers, too.

Thanks,
Roman.