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.