scst: Add the 'forward_src' sysfs attribute

Make forwarding source mode configurable per target port instead of
having a compile-time global option.


git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@8776 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/ChangeLog

@@ -1,3 +1,8 @@
+Summary of changes between versions 3.4 and 3.5
+-----------------------------------------------
+- Added the forward_src and forward_dst sysfs attributes. Removed
+  CONFIG_SCST_FORWARD_MODE_PASS_THROUGH.
+
 Summary of changes between versions 3.3 and 3.4
 -----------------------------------------------
 - I/O keeps running at full speed if a LUN is added or removed and also if

scst/README

@@ -343,16 +343,6 @@ 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. See below for more details.
-   Disabled by default for safety.
-
  - CONFIG_SCST_NO_TOTAL_MEM_CHECKS - disables checks of allocated
    memory, see scst_max_cmd_mem below. Allows to avoid 2 global
    variables on the fast path, hence get better multi-queue performance.
@@ -807,6 +797,14 @@ Every target should have at least the following entries:
    until rel_tgt_id becomes unique. This attribute initialized unique by
    SCST by default.
 
+ - forward_src - if set this target port is a forwarding source. This means
+   that commands like COMPARE AND WRITE, EXTENDED COPY and RECEIVE COPY
+   RESULTS are submitted to the SCSI device instead of being handled inside
+   the SCST core. PERSISTENT RESERVE IN and OUT commands are processed by the
+   SCST core, whether or not this mode is enabled. The name 'forwarding_src'
+   refers to the use case where SCSI passthrough is used to send SCSI commands
+   to another H.A. node.
+
  - forward_dst - if set this target port is a forwarding destination. This means
    that it does not check any local SCSI events (reservations, etc.). Those
    event are supposed to be checked at the forwarding source side.
@@ -1986,13 +1984,13 @@ The link between block devices I and J stands for synchronous replication.
 
 Such a setup can be configured as follows:
 
-1. Build SCST with CONFIG_SCST_FORWARD_MODE_PASS_THROUGH enabled in scst.h
+1. Build SCST.
 
 2. Setup on active node internal redirect target, which is going to
 accept redirected commands from the passive node. It must be visible
 only to the passive node.
 
-3. Set "forwarding" attribute for this target to 1. This is necessary to
+3. Set "forward_dst" attribute for this target to 1. This is necessary to
 correctly handle PRs.
 
 4. Export through this target the SAME backend SCST device as being
@@ -2007,7 +2005,8 @@ device on the passive side pointing to the active node.
 *pass-through* handler (scst_disk). Pass-though is needed to redirect
 non-block commands as well: ATS, XCOPY, etc.
 
-7. Set ALUA state to this target as "nonoptimized".
+7. Set ALUA state to this target as "nonoptimized". Set the forward_src
+attribute to one.
 
 That's it on the normal path. Now the initiator(s) would see 2 paths:
 OPTIMIZED going to the active node and NON-OPTIMIZED going to the

scst/include/backport.h

@@ -674,6 +674,20 @@ static inline int __must_check kstrtol(const char *s, unsigned int base,
 {
 	return strict_strtol(s, base, res);
 }
+
+static inline int __must_check kstrtoint(const char *s, unsigned int base,
+					 int *result)
+{
+	long val;
+	int ret = strict_strtol(s, base, &val);
+
+	if (ret)
+		return ret;
+	*result = val;
+	if (*result != val)
+		return -EINVAL;
+	return 0;
+}
 #endif
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4, 17, 0)

scst/include/scst.h

@@ -28,7 +28,6 @@
 
 /** See README for description of those conditional defines **/
 #define CONFIG_SCST_DIF_INJECT_CORRUPTED_TAGS
-/* #define CONFIG_SCST_FORWARD_MODE_PASS_THROUGH */
 #define CONFIG_SCST_NO_TOTAL_MEM_CHECKS
 
 #include <linux/types.h>
@@ -1687,6 +1686,18 @@ struct scst_tgt {
 
 	struct list_head tgt_acg_list; /* target ACG groups */
 
+	/*
+	 * Set if and only if this target port is a forwarding source. If
+	 * enabled, the dev_disk handler submits COMPARE AND WRITE, EXTENDED
+	 * COPY and RECEIVE COPY RESULTS commands to the SCSI device instead
+	 * of handling these inside the SCST core. PERSISTENT RESERVE IN and
+	 * OUT commands are processed by the SCST core, whether or not this
+	 * mode is enabled. The name 'forwarding_src' refers to the use case
+	 * where SCSI passthrough is used to send SCSI commands to another
+	 * H.A. node.
+	 */
+	unsigned tgt_forward_src:1;
+
 	/*
 	 * Set, if this target is forwarding destination, i.e. does not check
 	 * any local SCSI events (reservations, etc.). Those events are

scst/src/dev_handlers/scst_disk.c

@@ -144,6 +144,7 @@ static void disk_detach(struct scst_device *dev)
 
 static int disk_parse(struct scst_cmd *cmd)
 {
+	struct scst_tgt *tgt = cmd->tgt;
 	int res = SCST_CMD_STATE_DEFAULT, rc;
 
 	rc = scst_sbc_generic_parse(cmd);
@@ -152,8 +153,7 @@ 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)) {
+	if (unlikely(tgt->tgt_forward_src && cmd->op_flags & SCST_LOCAL_CMD)) {
 		switch (cmd->cdb[0]) {
 		case COMPARE_AND_WRITE:
 		case EXTENDED_COPY:
@@ -164,7 +164,6 @@ static int disk_parse(struct scst_cmd *cmd)
 			break;
 		}
 	}
-#endif
 
 	cmd->retries = SCST_PASSTHROUGH_RETRIES;
 out:
@@ -286,6 +285,7 @@ out_complete:
 /* Executes command and split CDB, if necessary */
 static enum scst_exec_res disk_exec(struct scst_cmd *cmd)
 {
+	struct scst_tgt *tgt = cmd->tgt;
 	enum scst_exec_res res;
 	int rc;
 	struct disk_work work;
@@ -299,8 +299,7 @@ static enum scst_exec_res disk_exec(struct scst_cmd *cmd)
 
 	TRACE_ENTRY();
 
-#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
-	if (unlikely(cmd->op_flags & SCST_LOCAL_CMD)) {
+	if (unlikely(tgt->tgt_forward_src && cmd->op_flags & SCST_LOCAL_CMD)) {
 		switch (cmd->cdb[0]) {
 		case RESERVE:
 		case RESERVE_10:
@@ -315,7 +314,6 @@ static enum scst_exec_res disk_exec(struct scst_cmd *cmd)
 			break;
 		}
 	}
-#endif
 
 	/*
 	 * For PC requests we are going to submit max_hw_sectors used instead

scst/src/scst_local_cmd.c

@@ -714,15 +714,13 @@ enum scst_exec_res scst_persistent_reserve_in_local(struct scst_cmd *cmd)
 		goto out_done;
 	}
 
-#ifndef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
-	if (dev->scsi_dev != NULL) {
+	if (cmd->tgt->tgt_forward_src && dev->scsi_dev) {
 		PRINT_WARNING("PR commands for pass-through devices not "
 			"supported (device %s)", dev->virt_name);
 		scst_set_cmd_error(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))

scst/src/scst_main.c

@@ -1111,7 +1111,7 @@ static int scst_register_device(struct scsi_device *scsidp)
 
 	dev->scsi_dev = scsidp;
 
-#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	/* For target ports that function as forwarding source. */
 	res = scst_pr_set_file_name(dev, NULL, "%s/%s", SCST_PR_DIR,
 				    dev->virt_name);
 	if (res != 0)
@@ -1120,7 +1120,6 @@ static int scst_register_device(struct scsi_device *scsidp)
 	res = scst_pr_init_dev(dev);
 	if (res != 0)
 		goto out_free_dev;
-#endif
 
 	list_add_tail(&dev->dev_list_entry, &scst_dev_list);
 
@@ -1143,14 +1142,9 @@ out:
 out_del_unlocked:
 	mutex_lock(&scst_mutex);
 	list_del_init(&dev->dev_list_entry);
-	mutex_unlock(&scst_mutex);
 
-	percpu_ref_kill(&dev->refcnt);
-	goto out;
-
-#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	/* If used as a forwarding source (see also tgt_forward_src). */
 	scst_pr_clear_dev(dev);
-#endif
 
 out_free_dev:
 	percpu_ref_kill(&dev->refcnt);
@@ -1193,9 +1187,8 @@ static void scst_unregister_device(struct scsi_device *scsidp)
 
 	list_del_init(&dev->dev_list_entry);
 
-#ifdef CONFIG_SCST_FORWARD_MODE_PASS_THROUGH
+	/* For forwarding sources (see also tgt_forward_src). */
 	scst_pr_clear_dev(dev);
-#endif
 
 	scst_dg_dev_remove_by_dev(dev);
 

scst/src/scst_sysfs.c

@@ -2513,6 +2513,44 @@ static struct kobj_attribute scst_rel_tgt_id =
 	__ATTR(rel_tgt_id, S_IRUGO | S_IWUSR, scst_rel_tgt_id_show,
 	       scst_rel_tgt_id_store);
 
+static ssize_t scst_tgt_forward_src_show(struct kobject *kobj,
+	struct kobj_attribute *attr, char *buf)
+{
+	struct scst_tgt *tgt = container_of(kobj, struct scst_tgt, tgt_kobj);
+
+	return sprintf(buf, "%d\n%s", tgt->tgt_forward_src,
+		       tgt->tgt_forward_src ? SCST_SYSFS_KEY_MARK "\n" : "");
+}
+
+static ssize_t scst_tgt_forward_src_store(struct kobject *kobj,
+	struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct scst_tgt *tgt = container_of(kobj, struct scst_tgt, tgt_kobj);
+	int res, old, new;
+
+	res = kstrtoint(buf, 0, &new);
+	if (res < 0)
+		return res;
+	if (new < 0 || new > 1)
+		return -EINVAL;
+
+	mutex_lock(&scst_mutex);
+	old = tgt->tgt_forward_src;
+	if (old != new) {
+		tgt->tgt_forward_src = new;
+		PRINT_INFO("%s target %s as forwarding source",
+			   tgt->tgt_forward_src ? "Set" : "Clear",
+			   tgt->tgt_name);
+	}
+	mutex_unlock(&scst_mutex);
+
+	return count;
+}
+
+static struct kobj_attribute scst_tgt_forward_src =
+	__ATTR(forward_src, S_IRUGO | S_IWUSR, scst_tgt_forward_src_show,
+	       scst_tgt_forward_src_store);
+
 static ssize_t scst_tgt_forward_dst_show(struct kobject *kobj,
 	struct kobj_attribute *attr, char *buf)
 {
@@ -2885,6 +2923,7 @@ SCST_TGT_SYSFS_STAT_ATTR(cmd_count, none_cmd_count, SCST_DATA_NONE, >> 0);
 
 static struct attribute *scst_tgt_attrs[] = {
 	&scst_rel_tgt_id.attr,
+	&scst_tgt_forward_src.attr,
 	&scst_tgt_forward_dst.attr,
 	&scst_tgt_forwarding.attr,
 	&scst_tgt_comment.attr,