scsi: target: Remove XDWRITEREAD emulated support

This patch removes XDWRITEREAD support because it never fully worked when
it was added in the initial LIO merge and it's been fully broken since 2013
from commit a289008 ("target: Add compare_and_write_post() completion
callback fall through").

The two issues above are:

1. XDWRITEREAD support was just never completed when LIO was merged. We
never did the DISABLE WRITE check and so we never write data out.

2. Since the commit above, we never complete the command. After we do the
XOR, we return from xdreadwrite_callback and that's it. We never send a
response for the command, so the command will always time out and fail.

Since this has been fully broken for almost nine years this patch just
removes emulated support.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mike Christie <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

drivers/target/target_core_sbc.c

@@ -339,68 +339,6 @@ sbc_setup_write_same(struct se_cmd *cmd, unsigned char flags, struct sbc_ops *op
 	return 0;
 }
 
-static sense_reason_t xdreadwrite_callback(struct se_cmd *cmd, bool success,
-					   int *post_ret)
-{
-	unsigned char *buf, *addr;
-	struct scatterlist *sg;
-	unsigned int offset;
-	sense_reason_t ret = TCM_NO_SENSE;
-	int i, count;
-
-	if (!success)
-		return 0;
-
-	/*
-	 * From sbc3r22.pdf section 5.48 XDWRITEREAD (10) command
-	 *
-	 * 1) read the specified logical block(s);
-	 * 2) transfer logical blocks from the data-out buffer;
-	 * 3) XOR the logical blocks transferred from the data-out buffer with
-	 *    the logical blocks read, storing the resulting XOR data in a buffer;
-	 * 4) if the DISABLE WRITE bit is set to zero, then write the logical
-	 *    blocks transferred from the data-out buffer; and
-	 * 5) transfer the resulting XOR data to the data-in buffer.
-	 */
-	buf = kmalloc(cmd->data_length, GFP_KERNEL);
-	if (!buf) {
-		pr_err("Unable to allocate xor_callback buf\n");
-		return TCM_OUT_OF_RESOURCES;
-	}
-	/*
-	 * Copy the scatterlist WRITE buffer located at cmd->t_data_sg
-	 * into the locally allocated *buf
-	 */
-	sg_copy_to_buffer(cmd->t_data_sg,
-			  cmd->t_data_nents,
-			  buf,
-			  cmd->data_length);
-
-	/*
-	 * Now perform the XOR against the BIDI read memory located at
-	 * cmd->t_mem_bidi_list
-	 */
-
-	offset = 0;
-	for_each_sg(cmd->t_bidi_data_sg, sg, cmd->t_bidi_data_nents, count) {
-		addr = kmap_atomic(sg_page(sg));
-		if (!addr) {
-			ret = TCM_OUT_OF_RESOURCES;
-			goto out;
-		}
-
-		for (i = 0; i < sg->length; i++)
-			*(addr + sg->offset + i) ^= *(buf + offset + i);
-
-		offset += sg->length;
-		kunmap_atomic(addr);
-	}
-
-out:
-	kfree(buf);
-	return ret;
-}
-
 static sense_reason_t
 sbc_execute_rw(struct se_cmd *cmd)
 {
@@ -927,47 +865,10 @@ sbc_parse_cdb(struct se_cmd *cmd, struct sbc_ops *ops)
 		cmd->se_cmd_flags |= SCF_SCSI_DATA_CDB;
 		cmd->execute_cmd = sbc_execute_rw;
 		break;
-	case XDWRITEREAD_10:
-		if (cmd->data_direction != DMA_TO_DEVICE ||
-		    !(cmd->se_cmd_flags & SCF_BIDI))
-			return TCM_INVALID_CDB_FIELD;
-		sectors = transport_get_sectors_10(cdb);
-
-		if (sbc_check_dpofua(dev, cmd, cdb))
-			return TCM_INVALID_CDB_FIELD;
-
-		cmd->t_task_lba = transport_lba_32(cdb);
-		cmd->se_cmd_flags |= SCF_SCSI_DATA_CDB;
-
-		/*
-		 * Setup BIDI XOR callback to be run after I/O completion.
-		 */
-		cmd->execute_cmd = sbc_execute_rw;
-		cmd->transport_complete_callback = &xdreadwrite_callback;
-		break;
 	case VARIABLE_LENGTH_CMD:
 	{
 		u16 service_action = get_unaligned_be16(&cdb[8]);
 		switch (service_action) {
-		case XDWRITEREAD_32:
-			sectors = transport_get_sectors_32(cdb);
-
-			if (sbc_check_dpofua(dev, cmd, cdb))
-				return TCM_INVALID_CDB_FIELD;
-			/*
-			 * Use WRITE_32 and READ_32 opcodes for the emulated
-			 * XDWRITE_READ_32 logic.
-			 */
-			cmd->t_task_lba = transport_lba_64_ext(cdb);
-			cmd->se_cmd_flags |= SCF_SCSI_DATA_CDB;
-
-			/*
-			 * Setup BIDI XOR callback to be run during after I/O
-			 * completion.
-			 */
-			cmd->execute_cmd = sbc_execute_rw;
-			cmd->transport_complete_callback = &xdreadwrite_callback;
-			break;
 		case WRITE_SAME_32:
 			sectors = transport_get_sectors_32(cdb);
 			if (!sectors) {