Re: [Qemu-devel] Re: [PATCH 0/5]

[FUJITA Tomonori]

On Wed, 24 Nov 2010 13:38:59 +0000
Stefan Hajnoczi <address@hidden> wrote:

> > This series adds rebased support for the hw/scsi-bsg.c backstore for 
> > scsi-bus
> > compatible HBA emulation in QEMU-KVM on Linux hosts supporting the BSG 
> > driver
> > against current mainline qemu-kvm.git/master code.
> 
> I don't know the Linux SCSI stack, so some basic questions for you :).
> 
> With scsi-generic I can send SCSI commands to a device.  How is bsg
> different?  The bsg code looks cleaner than sg but they both boil down
> to issuing SCSI requests using the Linux block layer AFAICT.
> 
> Can you explain what advantages this patch series brings over scsi-generic?

The main reason why we invented bsg is that we need the common
interface to send non SCSI commands. For example, we already use bsg
for FC stuff:

http://lwn.net/Articles/326338/

We can use the common interface rather than each HW specific interface.

>From the perspective of SCSI, the major advantage of bsg is supporting
bidi commands. I'm not sure qemu will ever need bidi pass through
support though.