[Qemu-devel] Re: [QEMU-KVM]: Megasas + TCM_Loop + SG_IO into Windows XP guests

[Hannes Reinecke <hare@suse.de>]

Nicholas A. Bellinger wrote:
> Greetings Hannes and co,
> 
> I have been spending a bit of time trying Megasas HBA emulation +
> TCM_Loop + SG_IO with a Windows XP SP2 KVM guests..  So far, I noticed
> that hw/scsi-generic.c:execute_command_run() using bdev_aio_ioctl()
> appears to be broken for XP guests, which causes the first 36-byte
> INQUIRY sent via SG_IO to never make it back to QEMU and results in the
> win32 LSI drive taking the LUN offline, et al.  Note that everything
> does appear to be functioning as expected in kernel space for the first
> INQUIRY with the TCM_Loop LLD and Linux/SCSI code (AFAICT) and Linux KVM
> guests using megasas emulation are still working.
> 
Now that is really odd. Have you checked if it works with the
'normal' KVM disk backend?

> So, I ended up needing requiring the following quick hack for
> hw/scsi-generic.c:execute_command_run() to make SG_IO function
> synchronously using bdrv_ioctl(), which at least gets LUN registration
> and basic control path CDBs working for the XP guest.
> 
> Here is how it looks in action on a v2.6.34-rc7 host so far:
> 
> http://www.linux-iscsi.org/images/TCM-KVM-megasas-XP-05132010.png
> 
> 
> diff --git a/hw/scsi-generic.c b/hw/scsi-generic.c
> index 6c58742..aa1eb83 100644
> --- a/hw/scsi-generic.c
> +++ b/hw/scsi-generic.c
> @@ -140,6 +140,7 @@ static int execute_command_run(SCSIGenericReq *r,
>  {
>      BlockDriverState *bdrv = r->req.dev->conf.dinfo->bdrv;
>      SCSIGenericState *s = DO_UPCAST(SCSIGenericState, qdev, r->req.dev);
> +    int ret;
>  
>      r->io_header.interface_id = 'S';
>      r->io_header.dxfer_direction = sgdir[r->req.cmd.mode];
> @@ -161,11 +162,16 @@ static int execute_command_run(SCSIGenericReq *r,
>      printf("\n");
>      }
>  #endif
> +#if 0
>      r->req.aiocb = bdrv_aio_ioctl(bdrv, SG_IO, &r->io_header, complete, r);
>      if (r->req.aiocb == NULL) {
>          BADF("execute_command: read failed !\n");
>          return -1;
>      }
> +#else
> +    ret = bdrv_ioctl(bdrv, SG_IO, &r->io_header);
> +    complete((void *)r, ret);
> +#endif
>  
>       *      return 0;
>  }
> 
> 
> Beyond the initial LUN registration and control CDB parts, doing bulk
> DATA_SG_IO traffic is completing successfully (and everything looks sane
> with TCM_Loop and Linux/SCSI) but it appears that the correct blocks are
> not actually getting written/read by megasas.  This appears to be the
> case with both hw/scsi-generic.c and hw/scsi-disk.c modes of operation
> for megasas with the win32 XP guest.
> 
Oh. Hmm.

> So I was wondering if anyone aware of known issues with QEMU
> asynchronous SG_IO into MSFT KVM guests with virtio or hw/lsi53c895a.c,
> or would this be something specific to megasas HBA emulation and XP
> guests..?
> 
> Hannes, which MSFT guest + driver did you get work stable with bulk
> DATA_SG_IO and hw/scsi-disk.c..?
> 
Well, I have two more patches for megasas.
The one is just a cleanup to remove duplicate definitions, but the
other contains a real issue with a misjudged cast in megasas_enqueue_frame().
Not sure if that helps here, but it's worth a try nevertheless.

I'll be sending them with separate mails.

Let's see if I can find some time working on the megasas emulation.
Maybe I find something.
Last time I checked it was with a Windows7 build, but I didn't do
any real tests there. Basically just checking if the system boots up :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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