alua.c

/*
 * Copyright (c) 2017 Red Hat, Inc.
 *
 * This file is licensed to you under your choice of the GNU Lesser
 * General Public License, version 2.1 or any later version (LGPLv2.1 or
 * later), or the Apache License 2.0.
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <dirent.h>
#include <inttypes.h>
#include <limits.h>

#include "ccan/list/list.h"

#include <scsi/scsi.h>

#include "libtcmu_log.h"
#include "libtcmu_common.h"
#include "libtcmu_priv.h"
#include "tcmu-runner.h"
#include "tcmur_device.h"
#include "target.h"
#include "alua.h"

static char *tcmu_get_alua_str_setting(struct alua_grp *group,
				       const char *setting)
{
	char path[PATH_MAX];

	snprintf(path, sizeof(path), CFGFS_CORE"/%s/%s/alua/%s/%s",
		 group->dev->tcm_hba_name, group->dev->tcm_dev_name,
		 group->name, setting);
	return tcmu_cfgfs_get_str(path);
}

static int tcmu_get_alua_int_setting(struct alua_grp *group,
				     const char *setting)
{
	char path[PATH_MAX];

	snprintf(path, sizeof(path), CFGFS_CORE"/%s/%s/alua/%s/%s",
		 group->dev->tcm_hba_name, group->dev->tcm_dev_name,
		 group->name, setting);
	return tcmu_cfgfs_get_int(path);
}

static int tcmu_set_alua_int_setting(struct alua_grp *group,
				     const char *setting, int val)
{
	char path[PATH_MAX];

	snprintf(path, sizeof(path), CFGFS_CORE"/%s/%s/alua/%s/%s",
		 group->dev->tcm_hba_name, group->dev->tcm_dev_name,
		 group->name, setting);
	return tcmu_cfgfs_set_u32(path, val);
}

static void tcmu_release_tgt_ports(struct alua_grp *group)
{
	struct tgt_port *port, *port_next;

	list_for_each_safe(&group->tgt_ports, port, port_next, entry) {
		list_del(&port->entry);
		tcmu_free_tgt_port(port);
	}
}

static void tcmu_free_alua_grp(struct alua_grp *group)
{
	tcmu_release_tgt_ports(group);

	if (group->name)
		free(group->name);
	free(group);
}

static struct alua_grp *
tcmu_get_alua_grp(struct tcmu_device *dev, const char *name)
{
	struct tcmur_device *rdev = tcmu_dev_get_private(dev);
	struct alua_grp *group;
	struct tgt_port *port;
	char *str_val, *orig_str_val, *member;
	int val;

	group = calloc(1, sizeof(*group));
	if (!group)
		return NULL;
	list_head_init(&group->tgt_ports);
	list_node_init(&group->entry);
	group->dev = dev;
	group->name = strdup(name);
	if (!group->name)
		goto free_group;

	val = tcmu_get_alua_int_setting(group, "alua_access_state");
	if (val < 0)
		goto free_group;
	group->state = val;

	val = tcmu_get_alua_int_setting(group, "alua_support_active_nonoptimized");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_NON_OPTIMIZED;

	val = tcmu_get_alua_int_setting(group, "alua_support_active_optimized");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_OPTIMIZED;

	val = tcmu_get_alua_int_setting(group, "alua_support_lba_dependent");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_LBA_DEPENDENT;

	val = tcmu_get_alua_int_setting(group, "alua_support_offline");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_OFFLINE;

	val = tcmu_get_alua_int_setting(group, "alua_support_standby");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_STANDBY;

	val = tcmu_get_alua_int_setting(group, "alua_support_transitioning");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_TRANSITIONING;

	val = tcmu_get_alua_int_setting(group, "alua_support_unavailable");
	if (val < 0)
		goto free_group;
	if (val)
		group->supported_states |= ALUA_SUP_UNAVAILABLE;

	val = tcmu_get_alua_int_setting(group, "implicit_trans_secs");
	if (val < 0)
		goto free_group;
	group->implicit_trans_secs = val;

	val = tcmu_get_alua_int_setting(group, "nonop_delay_msecs");
	if (val < 0)
		goto free_group;
	group->nonop_delay_msecs = val;

	val = tcmu_get_alua_int_setting(group, "trans_delay_msecs");
	if (val < 0)
		goto free_group;
	group->trans_delay_msecs = val;

	val = tcmu_get_alua_int_setting(group, "tg_pt_gp_id");
	if (val < 0)
		goto free_group;
	group->id = val;

	val = tcmu_get_alua_int_setting(group, "preferred");
	if (val < 0)
		goto free_group;
	group->pref = val ? true : false;

	str_val = tcmu_get_alua_str_setting(group, "alua_access_status");
	if (!str_val)
		goto free_group;

	if (!strcmp(str_val, "None"))
		group->status = ALUA_STAT_NONE;
	else if (!strcmp(str_val, "Altered by Explicit STPG"))
		group->status = ALUA_STAT_ALTERED_BY_EXPLICIT_STPG;
	else if (!strcmp(str_val, "Altered by Implicit ALUA"))
		group->status = ALUA_STAT_ALTERED_BY_IMPLICIT_ALUA;
	else {
		tcmu_dev_err(dev, "Invalid ALUA status %s", str_val);
		goto free_str_val;
	}
	free(str_val);

	str_val = tcmu_get_alua_str_setting(group, "alua_access_type");
	if (!str_val)
		goto free_group;

	if (!strcmp(str_val, "None")) {
		/*
		 * Assume user wanted to do active-active.
		 * We still want the initiator to use RTPG and we
		 * can manually change states, so report this as
		 * implicit.
		 */
		rdev->failover_type = TCMUR_DEV_FAILOVER_ALL_ACTIVE;

		group->tpgs = TPGS_ALUA_IMPLICIT;
	} else if (!strcmp(str_val, "Implicit")) {
		rdev->failover_type = TCMUR_DEV_FAILOVER_IMPLICIT;

		group->tpgs = TPGS_ALUA_IMPLICIT;
	} else if (!strcmp(str_val, "Explicit")) {
		/*
		 * kernel requires both implicit and explicit so we can
		 * update the state via configfs.
		 */
		tcmu_dev_warn(dev, "Unsupported alua_access_type: Explicit only failover not supported.\n");

		goto free_str_val;
	} else if (!strcmp(str_val, "Implicit and Explicit")) {
		/*
		 * Only report explicit so initiator always sends STPG.
		 * We only need implicit enabled in the kernel so we can
		 * interact with the alua configfs interface.
		 */
		rdev->failover_type = TCMUR_DEV_FAILOVER_EXPLICIT;

		group->tpgs = TPGS_ALUA_EXPLICIT;

		tcmu_dev_warn(dev, "Unsupported alua_access_type: Implicit and Explicit failover not supported.\n");

		goto free_str_val;
	} else {
		tcmu_dev_err(dev, "Invalid ALUA type %s", str_val);
		goto free_str_val;
	}
	free(str_val);

	str_val = orig_str_val = tcmu_get_alua_str_setting(group, "members");
	if (str_val) {
		while ((member = strsep(&str_val, "\n"))) {
			if (!strlen(member))
				continue;

			port = tcmu_get_tgt_port(member);
			if (!port) {
				free(orig_str_val);
				goto free_group;
			}
			port->grp = group;
			group->num_tgt_ports++;
			list_add_tail(&group->tgt_ports, &port->entry);
		}
	}

	free(orig_str_val);
	return group;

free_str_val:
	free(str_val);
free_group:
	tcmu_free_alua_grp(group);
	return NULL;
}

void tcmu_release_alua_grps(struct list_head *group_list)
{
	struct alua_grp *group, *group_next;

	list_for_each_safe(group_list, group, group_next, entry) {
		list_del(&group->entry);
		tcmu_free_alua_grp(group);
	}
}

static int alua_filter(const struct dirent *dir)
{
        return strcmp(dir->d_name, ".") && strcmp(dir->d_name, "..");
}

/**
 * tcmu_get_alua_grps: Fill group_list with the kernel's port groups.
 * @dev: device to get groups for.
 * @group_list: list allocated by the caller to add groups to.
 *
 * User must call tcmu_release_alua_grps when finished with the list of
 * groups.
 *
 * For now, we will only support ALUA if the user has defined groups.
 * tcmu ALUA support was added in 4.11, but not all fabric modules support
 * it. Depending on the kernel version and tools used we could have:
 *
 * 1. The default ALUA group, but empty members.
 * 2. The default ALUA group, and reading/writing to members will return
 *    a error or crash the kernel.
 * 3. The default ALUA group, and members set to it, but some fabric
 *    modules did not report the target port group/tag properly so
 *    we cannot match groups to ports.
 */
int tcmu_get_alua_grps(struct tcmu_device *dev,
			   struct list_head *group_list)
{
	struct alua_grp *group;
	struct dirent **namelist;
	char path[PATH_MAX];
	int i, n;
	int ret = 0;

	snprintf(path, sizeof(path), CFGFS_CORE"/%s/%s/alua",
		 dev->tcm_hba_name, dev->tcm_dev_name);
	n = scandir(path, &namelist, alua_filter, alphasort);
	if (n < 0) {
		tcmu_dev_err(dev, "Could not get ALUA dirs for %s:%s\n",
			     path, strerror(errno));
		return -errno;
	}

	for (i = 0; i < n; i++) {
		if (!strcmp(namelist[i]->d_name, "default_tg_pt_gp"))
			continue;

		group = tcmu_get_alua_grp(dev, namelist[i]->d_name);
		if (!group) {
			tcmu_dev_err(dev, "Could not get alua group %s.\n", namelist[i]->d_name);
			ret = -1;
			goto free_groups;
		}
		list_add_tail(group_list, &group->entry);
	}
	ret = 0;
	goto free_names;

free_groups:
	tcmu_release_alua_grps(group_list);
free_names:
	for (i = 0; i < n; i++)
		free(namelist[i]);
	free(namelist);
	return ret;
}

/*
 * tcmu does not pass up the target port that the command was
 * received on, so if a LUN is exported through multiple ports
 * in different ALUA target port group we do not know which group
 * to use.
 *
 * For now we support one target port group that contains all
 * enabled ports, or for HA configs one local target port group with
 * enabled ports and N remote port groups which are marked disabled
 * on the the local node.
 */
struct tgt_port *tcmu_get_enabled_port(struct list_head *group_list)
{
	struct alua_grp *group;
	struct tgt_port *port;

	list_for_each(group_list, group, entry) {
		list_for_each(&group->tgt_ports, port, entry) {
			if (port->enabled)
				return port;
		}
	}

	return NULL;
}

static int alua_set_state(struct tcmu_device *dev, struct alua_grp *group,
			  uint8_t new_state, uint8_t alua_status)
{
	int ret;

	ret = tcmu_set_alua_int_setting(group, "alua_access_state", new_state);
	if (ret) {
		tcmu_dev_err(dev, "Could not change kernel state to %u\n",
			     new_state);
		return TCMU_STS_EXPL_TRANSITION_ERR;
	}

	ret = tcmu_set_alua_int_setting(group, "alua_access_status", alua_status);
	if (ret)
		/* Ignore. The RTPG status info will be off, but its not used */
		tcmu_dev_err(dev, "Could not set alua_access_status for group %s:%d\n",
			     group->name, group->id);

	group->state = new_state;
	group->status = alua_status;
	return TCMU_STS_OK;
}

/*
 * alua_sync_state - update alua and lock state
 * @dev: tcmu device
 * @group_list: list of alua groups
 * @enabled_group_id: group id of the local enabled alua group
 *
 * If the handler is not able to update the remote nodes's state during ALUA
 * transition handling we update it now.
 */
static int alua_sync_state(struct tcmu_device *dev,
			   struct list_head *group_list,
			   uint16_t enabled_group_id)
{
	struct tcmur_device *rdev = tcmu_dev_get_private(dev);
	struct tcmur_handler *rhandler = tcmu_get_runner_handler(dev);
	struct alua_grp *group;
	uint16_t ao_group_id;
	uint8_t alua_state;
	int ret;

	if (rdev->failover_type == TCMUR_DEV_FAILOVER_IMPLICIT) {
		tcmu_update_dev_lock_state(dev);
		return TCMU_STS_OK;
	}

	if (rdev->failover_type != TCMUR_DEV_FAILOVER_EXPLICIT ||
	    !rhandler->get_lock_tag)
		return TCMU_STS_OK;

	ret = tcmu_get_lock_tag(dev, &ao_group_id);
	if (ret == TCMU_STS_NO_LOCK_HOLDERS) {
		ao_group_id = TCMU_INVALID_LOCK_TAG;
	} else if (ret != TCMU_STS_OK)
		return ret;

	list_for_each(group_list, group, entry) {
		if (ao_group_id == group->id) {
			alua_state = ALUA_ACCESS_STATE_OPTIMIZED;
		} else {
			alua_state = ALUA_ACCESS_STATE_STANDBY;

			if (enabled_group_id == group->id) {
				/*
				 * A node took the lock from us and this is
				 * the first command sent to us so clear
				 * lock state to avoid later blacklist errors.
				 */
				pthread_mutex_lock(&rdev->state_lock);
				if (rdev->lock_state == TCMUR_DEV_LOCK_LOCKED) {
					tcmu_dev_dbg(dev, "Dropping lock\n");
					rdev->lock_state = TCMUR_DEV_LOCK_UNLOCKED;
				}
				pthread_mutex_unlock(&rdev->state_lock);
			}
		}

		tcmu_dev_dbg(dev, "group %hu old state %u new state %u\n",
			     group->id, group->state, alua_state);

		if (alua_state != group->state)
			alua_set_state(dev, group, alua_state,
				       ALUA_STAT_ALTERED_BY_IMPLICIT_ALUA );
	}

	return TCMU_STS_OK;
}

int tcmu_emulate_report_tgt_port_grps(struct tcmu_device *dev,
				      struct list_head *group_list,
				      struct tcmulib_cmd *cmd)
{
	struct alua_grp *group;
	struct tgt_port *port, *enabled_port;
	int ext_hdr = cmd->cdb[1] & 0x20;
	uint32_t off = 4, ret_data_len = 0, ret32;
	uint32_t alloc_len = tcmu_cdb_get_xfer_length(cmd->cdb);
	uint8_t *buf;
	int ret;

	enabled_port = tcmu_get_enabled_port(group_list);
	if (!enabled_port)
		/* unsupported config */
		return TCMU_STS_INVALID_CMD;

	if (alloc_len < 4)
		return TCMU_STS_INVALID_CDB;

	buf = calloc(1, alloc_len);
	if (!buf)
		return TCMU_STS_NO_RESOURCE;

	if (ext_hdr && alloc_len > 5) {
		buf[4] = 0x10;
		/*
		 * assume all groups will have the same value for now.
		 */
		group = list_first_entry(group_list, struct alua_grp,
					 entry);
		if (group)
			buf[5] = group->implicit_trans_secs;
		off = 8;
	}

	ret = alua_sync_state(dev, group_list, enabled_port->grp->id);
	if (ret)
		goto free_buf;

	list_for_each(group_list, group, entry) {
		int next_off = off + 8 + (group->num_tgt_ports * 4);

		if (next_off > alloc_len) {
			ret_data_len += 8 + (group->num_tgt_ports * 4);
			continue;
		}

		if (group->pref)
			buf[off] = 0x80;

		buf[off++] |= group->state;
		buf[off++] |= group->supported_states;
		buf[off++] = (group->id >> 8) & 0xff;
		buf[off++] = group->id & 0xff;
		/* reserved */
		off++;
		buf[off++] = group->status;
		/* vendor specific */
		off++;
		buf[off++] = group->num_tgt_ports;

		ret_data_len += 8;

		list_for_each(&group->tgt_ports, port, entry) {
			/* reserved */
			off += 2;
			buf[off++] = (port->rel_port_id >> 8) & 0xff;
			buf[off++] = port->rel_port_id & 0xff;

			ret_data_len += 4;
		}

	}
	ret32 = htobe32(ret_data_len);
	memcpy(&buf[0], &ret32, 4);

	tcmu_memcpy_into_iovec(cmd->iovec, cmd->iov_cnt, buf, alloc_len);
	ret = TCMU_STS_OK;
free_buf:
	free(buf);
	return ret;
}

bool lock_is_required(struct tcmu_device *dev)
{
	struct tcmur_handler *rhandler = tcmu_get_runner_handler(dev);

	return !!rhandler->lock;
}

static void *alua_lock_thread_fn(void *arg)
{
	struct tcmu_device *dev = arg;

	tcmu_set_thread_name("alua-lock", dev);

	/* TODO: set UA based on bgly's patches */
	tcmu_acquire_dev_lock(dev, -1);
	return NULL;
}

int alua_implicit_transition(struct tcmu_device *dev, struct tcmulib_cmd *cmd)
{
	struct tcmur_device *rdev = tcmu_dev_get_private(dev);
	pthread_attr_t attr;
	int ret = TCMU_STS_OK;

	if (!lock_is_required(dev))
		return ret;

	pthread_mutex_lock(&rdev->state_lock);
	if (rdev->lock_state == TCMUR_DEV_LOCK_LOCKED) {
		goto done;
	} else if (rdev->lock_state == TCMUR_DEV_LOCK_LOCKING) {
		tcmu_dev_dbg(dev, "Lock acquisition operation is already in process.\n");
		ret = TCMU_STS_BUSY;
		goto done;
	}

	tcmu_dev_info(dev, "Starting lock acquisition operation.\n");

	rdev->lock_state = TCMUR_DEV_LOCK_LOCKING;

	/*
	 * Make the lock_thread as detached to fix the memory leakage bug.
	 */
	pthread_attr_init(&attr);
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

	/*
	 * The initiator is going to be queueing commands, so do this
	 * in the background to avoid command timeouts.
	 */
	if (pthread_create(&rdev->lock_thread, &attr, alua_lock_thread_fn,
			   dev)) {
		tcmu_dev_err(dev, "Could not start implicit transition thread:%s\n",
			     strerror(errno));
		rdev->lock_state = TCMUR_DEV_LOCK_UNLOCKED;
		ret = TCMU_STS_IMPL_TRANSITION_ERR;
	} else {
		ret = TCMU_STS_BUSY;
	}

	pthread_attr_destroy(&attr);

done:
	pthread_mutex_unlock(&rdev->state_lock);
	return ret;
}

static bool alua_check_sup_state(uint8_t state, uint8_t sup)
{
	switch (state) {
	case ALUA_ACCESS_STATE_OPTIMIZED:
		if (sup & ALUA_SUP_OPTIMIZED)
			return true;
		return false;
	case ALUA_ACCESS_STATE_NON_OPTIMIZED:
		if (sup & ALUA_SUP_NON_OPTIMIZED)
			return true;
		return false;
	case ALUA_ACCESS_STATE_STANDBY:
		if (sup & ALUA_SUP_STANDBY)
			return true;
		return false;
	case ALUA_ACCESS_STATE_UNAVAILABLE:
		if (sup & ALUA_SUP_UNAVAILABLE)
			return true;
		return false;
	case ALUA_ACCESS_STATE_OFFLINE:
		/*
		 * TODO: support secondary states
		 */
		return false;
	}

	return false;
}

static int tcmu_explicit_transition(struct list_head *group_list,
				    struct alua_grp *group, uint8_t new_state,
				    uint8_t alua_status)
{
	struct tcmu_device *dev = group->dev;
	struct alua_grp *tmp_group;
	int ret;

	tcmu_dev_dbg(dev, "transition group %u new state %u old state %u sup 0x%x\n",
		     group->id, new_state, group->state, group->supported_states);

	if (!alua_check_sup_state(new_state, group->supported_states))
		return TCMU_STS_INVALID_PARAM_LIST;

	switch (new_state) {
	case ALUA_ACCESS_STATE_OPTIMIZED:
		if (!lock_is_required(dev))
			/* just change local state */
			break;

		ret = tcmu_acquire_dev_lock(dev, group->id);
		if (ret == TCMU_STS_HW_ERR) {
			return TCMU_STS_EXPL_TRANSITION_ERR;
		} else if (ret) {
			/*
			 * We should return TCMU_STS_EXPL_TRANSITION_ERR but
			 * we only get 2 retries for that error in windows 2016.
			 * Most likely we temporarily couldn't connect to the
			 * backend and it is dropping the session. Return BUSY
			 * so this can be retried on another path when
			 * the session recovery kicks in.
			 */
			return TCMU_STS_BUSY;
		}

		/*
		 * We only support 1 active group, so set everything else
		 * to standby.
		 */
		list_for_each(group_list, tmp_group, entry) {
			if (group == tmp_group)
				continue;
			alua_set_state(dev, tmp_group,
				       ALUA_ACCESS_STATE_STANDBY, alua_status);
		}
		break;
	case ALUA_ACCESS_STATE_NON_OPTIMIZED:
	case ALUA_ACCESS_STATE_UNAVAILABLE:
	case ALUA_ACCESS_STATE_OFFLINE:
		/* TODO we only support standby and AO */
		tcmu_dev_err(dev, "Ignoring ANO/unavail/offline\n");
		return TCMU_STS_INVALID_PARAM_LIST;
	case ALUA_ACCESS_STATE_STANDBY:
		if (lock_is_required(dev))
			tcmu_release_dev_lock(dev);
		break;
	default:
		return TCMU_STS_INVALID_PARAM_LIST;
	}

	return alua_set_state(dev, group, new_state, alua_status);
}

int tcmu_emulate_set_tgt_port_grps(struct tcmu_device *dev,
				   struct list_head *group_list,
				   struct tcmulib_cmd *cmd)
{
	struct alua_grp *group;
	struct tgt_port *port;
	uint32_t off = 4, param_list_len = tcmu_cdb_get_xfer_length(cmd->cdb);
	uint16_t id, tmp_id;
	char *buf, new_state;
	int found, ret = TCMU_STS_OK;

	port = tcmu_get_enabled_port(group_list);
	if (!port)
		return TCMU_STS_INVALID_CMD;

	if (!param_list_len)
		return TCMU_STS_OK;

	buf = calloc(1, param_list_len);
	if (!buf)
		return TCMU_STS_NO_RESOURCE;

	if (tcmu_memcpy_from_iovec(buf, param_list_len, cmd->iovec,
				   cmd->iov_cnt) != param_list_len) {
		ret = TCMU_STS_INVALID_PARAM_LIST_LEN;
		goto free_buf;
	}

	while (off < param_list_len) {
		new_state = buf[off++] & 0x0f;
		/* reserved */
		off++;
		memcpy(&tmp_id, &buf[off], sizeof(tmp_id));
		id = be16toh(tmp_id);
		off += 2;

		found = 0;
		list_for_each(group_list, group, entry) {
			if (group->id != id)
				continue;

			if (group != port->grp) {
				ret = TCMU_STS_HW_ERR;
				tcmu_dev_err(dev, "Failing STPG for group %d. Unable to transition remote groups.\n",
					     id);
				goto free_buf;
			}

			tcmu_dev_dbg(dev, "Got STPG for group %u\n", id);
			ret = tcmu_explicit_transition(group_list, group,
					new_state,
					ALUA_STAT_ALTERED_BY_EXPLICIT_STPG);
			if (ret != TCMU_STS_OK) {
				tcmu_dev_err(dev, "Failing STPG for group %d\n",
					      id);
				goto free_buf;
			}
			found = 1;
			break;
		}

		if (!found) {
			/*
			 * Could not find what error code to return in SCSI
			 * spec.
			 */
			tcmu_dev_err(dev, "Could not find group for %u for STPG\n",
				      id);
			ret = TCMU_STS_EXPL_TRANSITION_ERR;
			break;
		}
	}

free_buf:
	free(buf);
	return ret;
}

int alua_check_state(struct tcmu_device *dev, struct tcmulib_cmd *cmd)
{
	struct tcmur_device *rdev = tcmu_dev_get_private(dev);

	if (rdev->failover_type == TCMUR_DEV_FAILOVER_EXPLICIT) {
		if (rdev->lock_state != TCMUR_DEV_LOCK_LOCKED) {
			tcmu_dev_dbg(dev, "device lock not held.\n");
			return TCMU_STS_FENCED;
		}
	} else if (rdev->failover_type == TCMUR_DEV_FAILOVER_IMPLICIT) {
		return alua_implicit_transition(dev, cmd);
	}

	return TCMU_STS_OK;
}