target/file: Fix off-by-one READ_CAPACITY bug for !S_ISBLK export

This patch fixes a bug where FILEIO was incorrectly reporting the number
of logical blocks (+ 1) when using non struct block_device export mode.

It changes fd_get_blocks() to follow all other backend ->get_blocks() cases,
and reduces the calculated dev_size by one dev->dev_attrib.block_size
number of bytes, and also fixes initial fd_block_size assignment at
fd_configure_device() time introduced in commit 0fd97ccf.
Reported-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Reported-by: Badari Pulavarty <pbadari@us.ibm.com>
Tested-by: Badari Pulavarty <pbadari@us.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_file.c

@@ -153,6 +153,7 @@ static int fd_configure_device(struct se_device *dev)
 		struct request_queue *q = bdev_get_queue(inode->i_bdev);
 		unsigned long long dev_size;
 
+		fd_dev->fd_block_size = bdev_logical_block_size(inode->i_bdev);
 		/*
 		 * Determine the number of bytes from i_size_read() minus
 		 * one (1) logical sector from underlying struct block_device
@@ -199,6 +200,7 @@ static int fd_configure_device(struct se_device *dev)
 			goto fail;
 		}
 
+		fd_dev->fd_block_size = FD_BLOCKSIZE;
 		/*
 		 * Limit UNMAP emulation to 8k Number of LBAs (NoLB)
 		 */
@@ -217,9 +219,7 @@ static int fd_configure_device(struct se_device *dev)
 		dev->dev_attrib.max_write_same_len = 0x1000;
 	}
 
-	fd_dev->fd_block_size = dev->dev_attrib.hw_block_size;
-
-	dev->dev_attrib.hw_block_size = FD_BLOCKSIZE;
+	dev->dev_attrib.hw_block_size = fd_dev->fd_block_size;
 	dev->dev_attrib.hw_max_sectors = FD_MAX_SECTORS;
 	dev->dev_attrib.hw_queue_depth = FD_MAX_DEVICE_QUEUE_DEPTH;
 
@@ -694,11 +694,12 @@ static sector_t fd_get_blocks(struct se_device *dev)
 	 * to handle underlying block_device resize operations.
 	 */
 	if (S_ISBLK(i->i_mode))
-		dev_size = (i_size_read(i) - fd_dev->fd_block_size);
+		dev_size = i_size_read(i);
 	else
 		dev_size = fd_dev->fd_dev_size;
 
-	return div_u64(dev_size, dev->dev_attrib.block_size);
+	return div_u64(dev_size - dev->dev_attrib.block_size,
+		       dev->dev_attrib.block_size);
 }
 
 static struct sbc_ops fd_sbc_ops = {