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Date: Wed, 25 Nov 2009 17:37:10 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [sneak preview] major scsi overhaul
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To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org

On 11/24/09 14:51, Paul Brook wrote:
> On Tuesday 24 November 2009, Gerd Hoffmann wrote:
>> On 11/16/09 19:53, Paul Brook wrote:
>>> Capping the amount of memory required for a transfer *is* implemented, in
>>> both LSI and virtio-blk.  The exception being SCSI passthrough where the
>>> kernel API makes it impossible.
>>
>> Well.  Figured while doing more testing:  The allowed request size is
>> limited by the kernel, so scsi-generic requests larger than (currently)
>> 128k fail.
>>
>> Now, how to handle *that*?  Is there some way to signal to the guest
>> that the request was to big?
>
> Same as real hardware.  Probably also want to populate the Block Limits VPD
> page appropriately

Some experiements later.

Linux reads the block limits vpd, but seems to ignore the hard limit.

Answering large requests with "Illegal request, Invalid field in CDB" 
doesn't makes linux try smaller requests, instead it reports I/O errors 
to the syslog.

Hmm.

netbsd and winxp don't try large requests in the first place (they do 
64k max).  Other guests not tried yet.

cheers,
   Gerd