target: Fix range calculation in WRITE SAME emulation when num blocks == 0

commit 1765fe5e upstream.

When NUMBER OF LOGICAL BLOCKS is 0, WRITE SAME is supposed to write
all the blocks from the specified LBA through the end of the device.
However, dev->transport->get_blocks(dev) (perhaps confusingly) returns
the last valid LBA rather than the number of blocks, so the correct
number of blocks to write starting with lba is

dev->transport->get_blocks(dev) - lba + 1

(nab: Backport roland's for-3.6 patch to for-3.5)
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/target/target_core_cdb.c

@@ -1199,7 +1199,7 @@ int target_emulate_write_same(struct se_task *task)
 	if (num_blocks != 0)
 		range = num_blocks;
 	else
-		range = (dev->transport->get_blocks(dev) - lba);
+		range = (dev->transport->get_blocks(dev) - lba) + 1;
 
 	pr_debug("WRITE_SAME UNMAP: LBA: %llu Range: %llu\n",
 		 (unsigned long long)lba, (unsigned long long)range);