scst: add forwarding pass-through mode

git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@6805 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/README

@@ -353,6 +353,15 @@ in/out in Makefile and scst.h:
    functionality is working only if dif_mode doesn't contain dev_store
    and dif_type is 1.
 
+ - CONFIG_SCST_FORWARD_MODE_PASS_THROUGH - if defined, the pass-through
+   subsystem starts working in the forwarding mode, where reservation
+   commands processed locally and not passed to the backend SCSI device,
+   while COMPARE AND WRITE, EXTENDED COPY and RECEIVE COPY RESULTS
+   commands, which normally processed locally by the SCST core, not
+   processed locally, but passed to the backend device. Intended to be
+   used to implement NON-OPTIMIZED ALUA state together with "forwarding"
+   target attribute on the remote node. Disabled by default for safety.
+
 HIGHMEM kernel configurations are fully supported, but not recommended
 for performance reasons, except for scst_user, where they are not
 supported, because this module deals with user supplied memory on a

scst/README_in-tree

@@ -243,6 +243,15 @@ your favorite kernel configuration Makefile target, e.g. "make xconfig":
    functionality is working only if dif_mode doesn't contain dev_store
    and dif_type is 1.
 
+ - CONFIG_SCST_FORWARD_MODE_PASS_THROUGH - if defined, the pass-through
+   subsystem starts working in the forwarding mode, where reservation
+   commands processed locally and not passed to the backend SCSI device,
+   while COMPARE AND WRITE, EXTENDED COPY and RECEIVE COPY RESULTS
+   commands, which normally processed locally by the SCST core, not
+   processed locally, but passed to the backend device. Intended to be
+   used to implement NON-OPTIMIZED ALUA state together with "forwarding"
+   target attribute on the remote node. Disabled by default for safety.
+
 HIGHMEM kernel configurations are fully supported, but not recommended
 for performance reasons.
 

scst/include/scst.h

@@ -29,6 +29,7 @@
 
 /** See README for description of those conditional defines **/
 #define CONFIG_SCST_DIF_INJECT_CORRUPTED_TAGS
+/* #define CONFIG_SCST_FORWARD_MODE_PASS_THROUGH */
 
 #include <linux/types.h>
 #ifndef INSIDE_KERNEL_TREE

scst/src/dev_handlers/scst_disk.c

@@ -268,6 +268,20 @@ static int disk_parse(struct scst_cmd *cmd)
 		goto out;
 	}
 
+#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	if (unlikely(cmd->op_flags & SCST_LOCAL_CMD)) {
+		switch (cmd->cdb[0]) {
+		case COMPARE_AND_WRITE:
+		case EXTENDED_COPY:
+		case RECEIVE_COPY_RESULTS:
+			TRACE_DBG("Clearing LOCAL CMD flag for cmd %p "
+				"(op %s)", cmd, cmd->op_name);
+			cmd->op_flags &= ~SCST_LOCAL_CMD;
+			break;
+		}
+	}
+#endif
+
 	cmd->retries = SCST_PASSTHROUGH_RETRIES;
 out:
 	return res;
@@ -398,6 +412,24 @@ static int disk_exec(struct scst_cmd *cmd)
 
 	TRACE_ENTRY();
 
+#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	if (unlikely(cmd->op_flags & SCST_LOCAL_CMD)) {
+		switch (cmd->cdb[0]) {
+		case RESERVE:
+		case RESERVE_10:
+		case RELEASE:
+		case RELEASE_10:
+			TRACE_DBG("Skipping LOCAL cmd %p (op %s)",
+				cmd, cmd->op_name);
+			goto out_done;
+		case PERSISTENT_RESERVE_IN:
+		case PERSISTENT_RESERVE_OUT:
+			sBUG();
+			break;
+		}
+	}
+#endif
+
 	/*
 	 * For PC requests we are going to submit max_hw_sectors used instead
 	 * of max_sectors.

scst/src/scst_main.c

@@ -1178,6 +1178,17 @@ static int scst_register_device(struct scsi_device *scsidp)
 
 	dev->scsi_dev = scsidp;
 
+#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	res = scst_pr_set_file_name(dev, NULL, "%s/%s", SCST_PR_DIR,
+				    dev->virt_name);
+	if (res != 0)
+		goto out_free_dev;
+
+	res = scst_pr_init_dev(dev);
+	if (res != 0)
+		goto out_free_dev;
+#endif
+
 	list_add_tail(&dev->dev_list_entry, &scst_dev_list);
 
 #ifdef CONFIG_SCST_PROC
@@ -1225,6 +1236,10 @@ out_del_locked:
 	list_del_init(&dev->dev_list_entry);
 #endif
 
+#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	scst_pr_clear_dev(dev);
+#endif
+
 out_free_dev:
 	scst_free_device(dev);
 
@@ -1284,6 +1299,10 @@ static void scst_unregister_device(struct scsi_device *scsidp)
 
 	list_del_init(&dev->dev_list_entry);
 
+#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	scst_pr_clear_dev(dev);
+#endif
+
 	scst_dg_dev_remove_by_dev(dev);
 
 	scst_assign_dev_handler(dev, &scst_null_devtype);

scst/src/scst_targ.c

@@ -2959,6 +2959,7 @@ static int scst_persistent_reserve_in_local(struct scst_cmd *cmd)
 		goto out_done;
 	}
 
+#ifndef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
 	if (dev->scsi_dev != NULL) {
 		PRINT_WARNING("PR commands for pass-through devices not "
 			"supported (device %s)", dev->virt_name);
@@ -2966,6 +2967,7 @@ static int scst_persistent_reserve_in_local(struct scst_cmd *cmd)
 			SCST_LOAD_SENSE(scst_sense_invalid_opcode));
 		goto out_done;
 	}
+#endif
 
 	buffer_size = scst_get_buf_full_sense(cmd, &buffer);
 	if (unlikely(buffer_size <= 0))