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From: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Date: Fri, 17 Aug 2012 12:36:19 +1000
Message-Id: <1345170981-7738-1-git-send-email-ronniesahlberg@gmail.com>
Subject: [Qemu-devel] [PATCH] Two trivial patches for iSCSI and blank DVDs
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To: kwolf@redhat.com, qemu-devel@nongnu.org, pbonzini@redhat.com

Kevin, List, Paolo

Please find two trivial patches to the iscsi block driver.

1, If the LUN contains a blank disk then the readcapacity10 data will
contain a ReturnedLogicalBlockAddress of 0. For this case this does not mean that the device contains one readable block and can be read from.
This is a special case for a blank disk that contains no readable blocks at all. This change makes bdrv_getlength()/iscsi_getlength() now rerurn a size of 0  for iSCSI LUNs that contain a blank disk.

2, If the iSCSI LUN contains a blank disk then we can not read or write to it using bdrv_*() functions since there is no bdrv api for writeable mmc devices.
For this case with a blank disk force the use of scsi-generic just like 
we do for tape and mediachanger devices.
This allows the guest to talk directly to the target LUN and write to/burn the disk.


I have confirmed that 

  dvdrecord -dao -ignsize -overburn dev=/dev/sg1 <some-file>.iso

works from a qemu guest to burn an iSCSI cdrom with these patches.

regards
ronnie sahlberg