Re: [Qemu-devel] [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive

[Paolo Bonzini]

Il 22/08/2012 13:04, Cong Meng ha scritto:
>>
>> Cong, what is the limit that the host HBA enforces (and what is the
>> HBA)?  What commands see a problem?  Is it fixed by using scsi-block
>> instead of scsi-generic (if you can use scsi-block at all, i.e. it's not
>> a tape or similar device)?
>>
> I don't see real problem caused by the the queue limits actually. It's a
> bug which Stefan told me.

I'd rather avoid patching the specification if not to solve real (rather
than known-but-theoretical) problems.

>> With scsi-generic, QEMU uses a bounce buffer for non-I/O commands to a
>> SCSI passthrough device, so the only problem in that case should be the
>> maximum segment size.  This could change in the future, but max_segments
>> and max_sectors should not yet be a problem.
> 
> about bounce buffer, do you meat the buffer allocated in
> scsi_send_command() of hw/scsi-generic.c?

Yes.

Paolo