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Date: Sun, 19 Aug 2012 00:20:44 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/2] ISCSI: Force scsi-generic for MMC with
	blank disks
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To: ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org

Il 19/08/2012 00:02, ronnie sahlberg ha scritto:
> On Sun, Aug 19, 2012 at 7:58 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 17/08/2012 04:36, Ronnie Sahlberg ha scritto:
>>> There is no bdrv_* API for the commands for burning a blank MMC disk
>>> so when iSCSI LUNs are specified and the LUN is a MMC device with
>>> 0 available blocks. This is a blank disk so force scsi generic.
>>>
>>> This allows the guest to talk directly to the target to burn data on
>>> the disk.
>>>
>>> Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
>>
>> What happens without the patch?  It's ok that scsi-{hd,cd} does not
>> work, but do scsi-{block,generic} work without the patch?
>>
> 
> Neither of them work, basically because in
> block.c:find_image_format()
> 
> if bs->sg is not set in
> 
>  if (bs->sg || !bdrv_is_inserted(bs)) {
> 
> then we continue to
> 
>   ret = bdrv_pread(bs, 0, buf, sizeof(buf));
> 
> which fails with an error.
> So this patch is basically to prevent find_image_format() from trying
> to read from a blank disk.
> 
> Maybe there is a better way to do this?

Ah, BTW does using -drive ...,format=raw work, or does it hiccup later
again on something else?

Paolo