iscsi: Set number of blocks to 0 for blank CDROM devices

The number of blocks of the device is used to compute the device size
in bdrv_getlength()/iscsi_getlength().
For MMC devices, the ReturnedLogicalBlockAddress in the READCAPACITY10
has a special meaning when it is 0.
In this case it does not mean that LBA 0 is the last accessible LBA,
and thus the device has 1 readable block, but instead it means that the
disc is blank and there are no readable blocks.

This change ensures that when the iSCSI LUN is loaded with a blank
DVD-R disk or similar that bdrv_getlength() will return the correct
size of the device as 0 bytes.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/block/iscsi.c b/block/iscsi.c
index 4828b83..0b96165 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -721,7 +721,12 @@ iscsi_readcapacity10_cb(struct iscsi_context *iscsi, int status,
     }
 
     itask->iscsilun->block_size = rc10->block_size;
-    itask->iscsilun->num_blocks = rc10->lba + 1;
+    if (rc10->lba == 0) {
+        /* blank disk loaded */
+        itask->iscsilun->num_blocks = 0;
+    } else {
+        itask->iscsilun->num_blocks = rc10->lba + 1;
+    }
     itask->bs->total_sectors    = itask->iscsilun->num_blocks *
                                itask->iscsilun->block_size / BDRV_SECTOR_SIZE ;