Merge tag 'kvm-s390-master-4.15-2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[mirror_ubuntu-disco-kernel.git] / drivers / nvme / target / loop.c

/*
 * NVMe over Fabrics loopback device.
 * Copyright (c) 2015-2016 HGST, a Western Digital Company.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/scatterlist.h>
#include <linux/blk-mq.h>
#include <linux/nvme.h>
#include <linux/module.h>
#include <linux/parser.h>
#include "nvmet.h"
#include "../host/nvme.h"
#include "../host/fabrics.h"

#define NVME_LOOP_MAX_SEGMENTS          256

struct nvme_loop_iod {
        struct nvme_request     nvme_req;
        struct nvme_command     cmd;
        struct nvme_completion  rsp;
        struct nvmet_req        req;
        struct nvme_loop_queue  *queue;
        struct work_struct      work;
        struct sg_table         sg_table;
        struct scatterlist      first_sgl[];
};

struct nvme_loop_ctrl {
        struct nvme_loop_queue  *queues;

        struct blk_mq_tag_set   admin_tag_set;

        struct list_head        list;
        struct blk_mq_tag_set   tag_set;
        struct nvme_loop_iod    async_event_iod;
        struct nvme_ctrl        ctrl;

        struct nvmet_ctrl       *target_ctrl;
};

static inline struct nvme_loop_ctrl *to_loop_ctrl(struct nvme_ctrl *ctrl)
{
        return container_of(ctrl, struct nvme_loop_ctrl, ctrl);
}

enum nvme_loop_queue_flags {
        NVME_LOOP_Q_LIVE        = 0,
};

struct nvme_loop_queue {
        struct nvmet_cq         nvme_cq;
        struct nvmet_sq         nvme_sq;
        struct nvme_loop_ctrl   *ctrl;
        unsigned long           flags;
};

static struct nvmet_port *nvmet_loop_port;

static LIST_HEAD(nvme_loop_ctrl_list);
static DEFINE_MUTEX(nvme_loop_ctrl_mutex);

static void nvme_loop_queue_response(struct nvmet_req *nvme_req);
static void nvme_loop_delete_ctrl(struct nvmet_ctrl *ctrl);

static struct nvmet_fabrics_ops nvme_loop_ops;

static inline int nvme_loop_queue_idx(struct nvme_loop_queue *queue)
{
        return queue - queue->ctrl->queues;
}

static void nvme_loop_complete_rq(struct request *req)
{
        struct nvme_loop_iod *iod = blk_mq_rq_to_pdu(req);

        nvme_cleanup_cmd(req);
        sg_free_table_chained(&iod->sg_table, true);
        nvme_complete_rq(req);
}

static struct blk_mq_tags *nvme_loop_tagset(struct nvme_loop_queue *queue)
{
        u32 queue_idx = nvme_loop_queue_idx(queue);

        if (queue_idx == 0)
                return queue->ctrl->admin_tag_set.tags[queue_idx];
        return queue->ctrl->tag_set.tags[queue_idx - 1];
}

static void nvme_loop_queue_response(struct nvmet_req *req)
{
        struct nvme_loop_queue *queue =
                container_of(req->sq, struct nvme_loop_queue, nvme_sq);
        struct nvme_completion *cqe = req->rsp;

        /*
         * AEN requests are special as they don't time out and can
         * survive any kind of queue freeze and often don't respond to
         * aborts.  We don't even bother to allocate a struct request
         * for them but rather special case them here.
         */
        if (unlikely(nvme_loop_queue_idx(queue) == 0 &&
                        cqe->command_id >= NVME_AQ_BLK_MQ_DEPTH)) {
                nvme_complete_async_event(&queue->ctrl->ctrl, cqe->status,
                                &cqe->result);
        } else {
                struct request *rq;

                rq = blk_mq_tag_to_rq(nvme_loop_tagset(queue), cqe->command_id);
                if (!rq) {
                        dev_err(queue->ctrl->ctrl.device,
                                "tag 0x%x on queue %d not found\n",
                                cqe->command_id, nvme_loop_queue_idx(queue));
                        return;
                }

                nvme_end_request(rq, cqe->status, cqe->result);
        }
}

static void nvme_loop_execute_work(struct work_struct *work)
{
        struct nvme_loop_iod *iod =
                container_of(work, struct nvme_loop_iod, work);

        nvmet_req_execute(&iod->req);
}

static enum blk_eh_timer_return
nvme_loop_timeout(struct request *rq, bool reserved)
{
        struct nvme_loop_iod *iod = blk_mq_rq_to_pdu(rq);

        /* queue error recovery */
        nvme_reset_ctrl(&iod->queue->ctrl->ctrl);

        /* fail with DNR on admin cmd timeout */
        nvme_req(rq)->status = NVME_SC_ABORT_REQ | NVME_SC_DNR;

        return BLK_EH_HANDLED;
}

static inline blk_status_t nvme_loop_is_ready(struct nvme_loop_queue *queue,
                struct request *rq)
{
        if (unlikely(!test_bit(NVME_LOOP_Q_LIVE, &queue->flags)))
                return nvmf_check_init_req(&queue->ctrl->ctrl, rq);
        return BLK_STS_OK;
}

static blk_status_t nvme_loop_queue_rq(struct blk_mq_hw_ctx *hctx,
                const struct blk_mq_queue_data *bd)
{
        struct nvme_ns *ns = hctx->queue->queuedata;
        struct nvme_loop_queue *queue = hctx->driver_data;
        struct request *req = bd->rq;
        struct nvme_loop_iod *iod = blk_mq_rq_to_pdu(req);
        blk_status_t ret;

        ret = nvme_loop_is_ready(queue, req);
        if (unlikely(ret))
                return ret;

        ret = nvme_setup_cmd(ns, req, &iod->cmd);
        if (ret)
                return ret;

        iod->cmd.common.flags |= NVME_CMD_SGL_METABUF;
        iod->req.port = nvmet_loop_port;
        if (!nvmet_req_init(&iod->req, &queue->nvme_cq,
                        &queue->nvme_sq, &nvme_loop_ops)) {
                nvme_cleanup_cmd(req);
                blk_mq_start_request(req);
                nvme_loop_queue_response(&iod->req);
                return BLK_STS_OK;
        }

        if (blk_rq_bytes(req)) {
                iod->sg_table.sgl = iod->first_sgl;
                if (sg_alloc_table_chained(&iod->sg_table,
                                blk_rq_nr_phys_segments(req),
                                iod->sg_table.sgl))
                        return BLK_STS_RESOURCE;

                iod->req.sg = iod->sg_table.sgl;
                iod->req.sg_cnt = blk_rq_map_sg(req->q, req, iod->sg_table.sgl);
                iod->req.transfer_len = blk_rq_bytes(req);
        }

        blk_mq_start_request(req);

        schedule_work(&iod->work);
        return BLK_STS_OK;
}

static void nvme_loop_submit_async_event(struct nvme_ctrl *arg)
{
        struct nvme_loop_ctrl *ctrl = to_loop_ctrl(arg);
        struct nvme_loop_queue *queue = &ctrl->queues[0];
        struct nvme_loop_iod *iod = &ctrl->async_event_iod;

        memset(&iod->cmd, 0, sizeof(iod->cmd));
        iod->cmd.common.opcode = nvme_admin_async_event;
        iod->cmd.common.command_id = NVME_AQ_BLK_MQ_DEPTH;
        iod->cmd.common.flags |= NVME_CMD_SGL_METABUF;

        if (!nvmet_req_init(&iod->req, &queue->nvme_cq, &queue->nvme_sq,
                        &nvme_loop_ops)) {
                dev_err(ctrl->ctrl.device, "failed async event work\n");
                return;
        }

        schedule_work(&iod->work);
}

static int nvme_loop_init_iod(struct nvme_loop_ctrl *ctrl,
                struct nvme_loop_iod *iod, unsigned int queue_idx)
{
        iod->req.cmd = &iod->cmd;
        iod->req.rsp = &iod->rsp;
        iod->queue = &ctrl->queues[queue_idx];
        INIT_WORK(&iod->work, nvme_loop_execute_work);
        return 0;
}

static int nvme_loop_init_request(struct blk_mq_tag_set *set,
                struct request *req, unsigned int hctx_idx,
                unsigned int numa_node)
{
        struct nvme_loop_ctrl *ctrl = set->driver_data;

        return nvme_loop_init_iod(ctrl, blk_mq_rq_to_pdu(req),
                        (set == &ctrl->tag_set) ? hctx_idx + 1 : 0);
}

static int nvme_loop_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
                unsigned int hctx_idx)
{
        struct nvme_loop_ctrl *ctrl = data;
        struct nvme_loop_queue *queue = &ctrl->queues[hctx_idx + 1];

        BUG_ON(hctx_idx >= ctrl->ctrl.queue_count);

        hctx->driver_data = queue;
        return 0;
}

static int nvme_loop_init_admin_hctx(struct blk_mq_hw_ctx *hctx, void *data,
                unsigned int hctx_idx)
{
        struct nvme_loop_ctrl *ctrl = data;
        struct nvme_loop_queue *queue = &ctrl->queues[0];

        BUG_ON(hctx_idx != 0);

        hctx->driver_data = queue;
        return 0;
}

static const struct blk_mq_ops nvme_loop_mq_ops = {
        .queue_rq       = nvme_loop_queue_rq,
        .complete       = nvme_loop_complete_rq,
        .init_request   = nvme_loop_init_request,
        .init_hctx      = nvme_loop_init_hctx,
        .timeout        = nvme_loop_timeout,
};

static const struct blk_mq_ops nvme_loop_admin_mq_ops = {
        .queue_rq       = nvme_loop_queue_rq,
        .complete       = nvme_loop_complete_rq,
        .init_request   = nvme_loop_init_request,
        .init_hctx      = nvme_loop_init_admin_hctx,
        .timeout        = nvme_loop_timeout,
};

static void nvme_loop_destroy_admin_queue(struct nvme_loop_ctrl *ctrl)
{
        clear_bit(NVME_LOOP_Q_LIVE, &ctrl->queues[0].flags);
        nvmet_sq_destroy(&ctrl->queues[0].nvme_sq);
        blk_cleanup_queue(ctrl->ctrl.admin_q);
        blk_mq_free_tag_set(&ctrl->admin_tag_set);
}

static void nvme_loop_free_ctrl(struct nvme_ctrl *nctrl)
{
        struct nvme_loop_ctrl *ctrl = to_loop_ctrl(nctrl);

        if (list_empty(&ctrl->list))
                goto free_ctrl;

        mutex_lock(&nvme_loop_ctrl_mutex);
        list_del(&ctrl->list);
        mutex_unlock(&nvme_loop_ctrl_mutex);

        if (nctrl->tagset) {
                blk_cleanup_queue(ctrl->ctrl.connect_q);
                blk_mq_free_tag_set(&ctrl->tag_set);
        }
        kfree(ctrl->queues);
        nvmf_free_options(nctrl->opts);
free_ctrl:
        kfree(ctrl);
}

static void nvme_loop_destroy_io_queues(struct nvme_loop_ctrl *ctrl)
{
        int i;

        for (i = 1; i < ctrl->ctrl.queue_count; i++) {
                clear_bit(NVME_LOOP_Q_LIVE, &ctrl->queues[i].flags);
                nvmet_sq_destroy(&ctrl->queues[i].nvme_sq);
        }
}

static int nvme_loop_init_io_queues(struct nvme_loop_ctrl *ctrl)
{
        struct nvmf_ctrl_options *opts = ctrl->ctrl.opts;
        unsigned int nr_io_queues;
        int ret, i;

        nr_io_queues = min(opts->nr_io_queues, num_online_cpus());
        ret = nvme_set_queue_count(&ctrl->ctrl, &nr_io_queues);
        if (ret || !nr_io_queues)
                return ret;

        dev_info(ctrl->ctrl.device, "creating %d I/O queues.\n", nr_io_queues);

        for (i = 1; i <= nr_io_queues; i++) {
                ctrl->queues[i].ctrl = ctrl;
                ret = nvmet_sq_init(&ctrl->queues[i].nvme_sq);
                if (ret)
                        goto out_destroy_queues;

                ctrl->ctrl.queue_count++;
        }

        return 0;

out_destroy_queues:
        nvme_loop_destroy_io_queues(ctrl);
        return ret;
}

static int nvme_loop_connect_io_queues(struct nvme_loop_ctrl *ctrl)
{
        int i, ret;

        for (i = 1; i < ctrl->ctrl.queue_count; i++) {
                ret = nvmf_connect_io_queue(&ctrl->ctrl, i);
                if (ret)
                        return ret;
                set_bit(NVME_LOOP_Q_LIVE, &ctrl->queues[i].flags);
        }

        return 0;
}

static int nvme_loop_configure_admin_queue(struct nvme_loop_ctrl *ctrl)
{
        int error;

        memset(&ctrl->admin_tag_set, 0, sizeof(ctrl->admin_tag_set));
        ctrl->admin_tag_set.ops = &nvme_loop_admin_mq_ops;
        ctrl->admin_tag_set.queue_depth = NVME_AQ_MQ_TAG_DEPTH;
        ctrl->admin_tag_set.reserved_tags = 2; /* connect + keep-alive */
        ctrl->admin_tag_set.numa_node = NUMA_NO_NODE;
        ctrl->admin_tag_set.cmd_size = sizeof(struct nvme_loop_iod) +
                SG_CHUNK_SIZE * sizeof(struct scatterlist);
        ctrl->admin_tag_set.driver_data = ctrl;
        ctrl->admin_tag_set.nr_hw_queues = 1;
        ctrl->admin_tag_set.timeout = ADMIN_TIMEOUT;
        ctrl->admin_tag_set.flags = BLK_MQ_F_NO_SCHED;

        ctrl->queues[0].ctrl = ctrl;
        error = nvmet_sq_init(&ctrl->queues[0].nvme_sq);
        if (error)
                return error;
        ctrl->ctrl.queue_count = 1;

        error = blk_mq_alloc_tag_set(&ctrl->admin_tag_set);
        if (error)
                goto out_free_sq;
        ctrl->ctrl.admin_tagset = &ctrl->admin_tag_set;

        ctrl->ctrl.admin_q = blk_mq_init_queue(&ctrl->admin_tag_set);
        if (IS_ERR(ctrl->ctrl.admin_q)) {
                error = PTR_ERR(ctrl->ctrl.admin_q);
                goto out_free_tagset;
        }

        error = nvmf_connect_admin_queue(&ctrl->ctrl);
        if (error)
                goto out_cleanup_queue;

        set_bit(NVME_LOOP_Q_LIVE, &ctrl->queues[0].flags);

        error = nvmf_reg_read64(&ctrl->ctrl, NVME_REG_CAP, &ctrl->ctrl.cap);
        if (error) {
                dev_err(ctrl->ctrl.device,
                        "prop_get NVME_REG_CAP failed\n");
                goto out_cleanup_queue;
        }

        ctrl->ctrl.sqsize =
                min_t(int, NVME_CAP_MQES(ctrl->ctrl.cap), ctrl->ctrl.sqsize);

        error = nvme_enable_ctrl(&ctrl->ctrl, ctrl->ctrl.cap);
        if (error)
                goto out_cleanup_queue;

        ctrl->ctrl.max_hw_sectors =
                (NVME_LOOP_MAX_SEGMENTS - 1) << (PAGE_SHIFT - 9);

        error = nvme_init_identify(&ctrl->ctrl);
        if (error)
                goto out_cleanup_queue;

        return 0;

out_cleanup_queue:
        blk_cleanup_queue(ctrl->ctrl.admin_q);
out_free_tagset:
        blk_mq_free_tag_set(&ctrl->admin_tag_set);
out_free_sq:
        nvmet_sq_destroy(&ctrl->queues[0].nvme_sq);
        return error;
}

static void nvme_loop_shutdown_ctrl(struct nvme_loop_ctrl *ctrl)
{
        if (ctrl->ctrl.queue_count > 1) {
                nvme_stop_queues(&ctrl->ctrl);
                blk_mq_tagset_busy_iter(&ctrl->tag_set,
                                        nvme_cancel_request, &ctrl->ctrl);
                nvme_loop_destroy_io_queues(ctrl);
        }

        if (ctrl->ctrl.state == NVME_CTRL_LIVE)
                nvme_shutdown_ctrl(&ctrl->ctrl);

        blk_mq_quiesce_queue(ctrl->ctrl.admin_q);
        blk_mq_tagset_busy_iter(&ctrl->admin_tag_set,
                                nvme_cancel_request, &ctrl->ctrl);
        blk_mq_unquiesce_queue(ctrl->ctrl.admin_q);
        nvme_loop_destroy_admin_queue(ctrl);
}

static void nvme_loop_delete_ctrl_host(struct nvme_ctrl *ctrl)
{
        nvme_loop_shutdown_ctrl(to_loop_ctrl(ctrl));
}

static void nvme_loop_delete_ctrl(struct nvmet_ctrl *nctrl)
{
        struct nvme_loop_ctrl *ctrl;

        mutex_lock(&nvme_loop_ctrl_mutex);
        list_for_each_entry(ctrl, &nvme_loop_ctrl_list, list) {
                if (ctrl->ctrl.cntlid == nctrl->cntlid)
                        nvme_delete_ctrl(&ctrl->ctrl);
        }
        mutex_unlock(&nvme_loop_ctrl_mutex);
}

static void nvme_loop_reset_ctrl_work(struct work_struct *work)
{
        struct nvme_loop_ctrl *ctrl =
                container_of(work, struct nvme_loop_ctrl, ctrl.reset_work);
        bool changed;
        int ret;

        nvme_stop_ctrl(&ctrl->ctrl);
        nvme_loop_shutdown_ctrl(ctrl);

        ret = nvme_loop_configure_admin_queue(ctrl);
        if (ret)
                goto out_disable;

        ret = nvme_loop_init_io_queues(ctrl);
        if (ret)
                goto out_destroy_admin;

        ret = nvme_loop_connect_io_queues(ctrl);
        if (ret)
                goto out_destroy_io;

        blk_mq_update_nr_hw_queues(&ctrl->tag_set,
                        ctrl->ctrl.queue_count - 1);

        changed = nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_LIVE);
        WARN_ON_ONCE(!changed);

        nvme_start_ctrl(&ctrl->ctrl);

        return;

out_destroy_io:
        nvme_loop_destroy_io_queues(ctrl);
out_destroy_admin:
        nvme_loop_destroy_admin_queue(ctrl);
out_disable:
        dev_warn(ctrl->ctrl.device, "Removing after reset failure\n");
        nvme_uninit_ctrl(&ctrl->ctrl);
        nvme_put_ctrl(&ctrl->ctrl);
}

static const struct nvme_ctrl_ops nvme_loop_ctrl_ops = {
        .name                   = "loop",
        .module                 = THIS_MODULE,
        .flags                  = NVME_F_FABRICS,
        .reg_read32             = nvmf_reg_read32,
        .reg_read64             = nvmf_reg_read64,
        .reg_write32            = nvmf_reg_write32,
        .free_ctrl              = nvme_loop_free_ctrl,
        .submit_async_event     = nvme_loop_submit_async_event,
        .delete_ctrl            = nvme_loop_delete_ctrl_host,
};

static int nvme_loop_create_io_queues(struct nvme_loop_ctrl *ctrl)
{
        int ret;

        ret = nvme_loop_init_io_queues(ctrl);
        if (ret)
                return ret;

        memset(&ctrl->tag_set, 0, sizeof(ctrl->tag_set));
        ctrl->tag_set.ops = &nvme_loop_mq_ops;
        ctrl->tag_set.queue_depth = ctrl->ctrl.opts->queue_size;
        ctrl->tag_set.reserved_tags = 1; /* fabric connect */
        ctrl->tag_set.numa_node = NUMA_NO_NODE;
        ctrl->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
        ctrl->tag_set.cmd_size = sizeof(struct nvme_loop_iod) +
                SG_CHUNK_SIZE * sizeof(struct scatterlist);
        ctrl->tag_set.driver_data = ctrl;
        ctrl->tag_set.nr_hw_queues = ctrl->ctrl.queue_count - 1;
        ctrl->tag_set.timeout = NVME_IO_TIMEOUT;
        ctrl->ctrl.tagset = &ctrl->tag_set;

        ret = blk_mq_alloc_tag_set(&ctrl->tag_set);
        if (ret)
                goto out_destroy_queues;

        ctrl->ctrl.connect_q = blk_mq_init_queue(&ctrl->tag_set);
        if (IS_ERR(ctrl->ctrl.connect_q)) {
                ret = PTR_ERR(ctrl->ctrl.connect_q);
                goto out_free_tagset;
        }

        ret = nvme_loop_connect_io_queues(ctrl);
        if (ret)
                goto out_cleanup_connect_q;

        return 0;

out_cleanup_connect_q:
        blk_cleanup_queue(ctrl->ctrl.connect_q);
out_free_tagset:
        blk_mq_free_tag_set(&ctrl->tag_set);
out_destroy_queues:
        nvme_loop_destroy_io_queues(ctrl);
        return ret;
}

static struct nvme_ctrl *nvme_loop_create_ctrl(struct device *dev,
                struct nvmf_ctrl_options *opts)
{
        struct nvme_loop_ctrl *ctrl;
        bool changed;
        int ret;

        ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
        if (!ctrl)
                return ERR_PTR(-ENOMEM);
        ctrl->ctrl.opts = opts;
        INIT_LIST_HEAD(&ctrl->list);

        INIT_WORK(&ctrl->ctrl.reset_work, nvme_loop_reset_ctrl_work);

        ret = nvme_init_ctrl(&ctrl->ctrl, dev, &nvme_loop_ctrl_ops,
                                0 /* no quirks, we're perfect! */);
        if (ret)
                goto out_put_ctrl;

        ret = -ENOMEM;

        ctrl->ctrl.sqsize = opts->queue_size - 1;
        ctrl->ctrl.kato = opts->kato;

        ctrl->queues = kcalloc(opts->nr_io_queues + 1, sizeof(*ctrl->queues),
                        GFP_KERNEL);
        if (!ctrl->queues)
                goto out_uninit_ctrl;

        ret = nvme_loop_configure_admin_queue(ctrl);
        if (ret)
                goto out_free_queues;

        if (opts->queue_size > ctrl->ctrl.maxcmd) {
                /* warn if maxcmd is lower than queue_size */
                dev_warn(ctrl->ctrl.device,
                        "queue_size %zu > ctrl maxcmd %u, clamping down\n",
                        opts->queue_size, ctrl->ctrl.maxcmd);
                opts->queue_size = ctrl->ctrl.maxcmd;
        }

        if (opts->nr_io_queues) {
                ret = nvme_loop_create_io_queues(ctrl);
                if (ret)
                        goto out_remove_admin_queue;
        }

        nvme_loop_init_iod(ctrl, &ctrl->async_event_iod, 0);

        dev_info(ctrl->ctrl.device,
                 "new ctrl: \"%s\"\n", ctrl->ctrl.opts->subsysnqn);

        nvme_get_ctrl(&ctrl->ctrl);

        changed = nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_LIVE);
        WARN_ON_ONCE(!changed);

        mutex_lock(&nvme_loop_ctrl_mutex);
        list_add_tail(&ctrl->list, &nvme_loop_ctrl_list);
        mutex_unlock(&nvme_loop_ctrl_mutex);

        nvme_start_ctrl(&ctrl->ctrl);

        return &ctrl->ctrl;

out_remove_admin_queue:
        nvme_loop_destroy_admin_queue(ctrl);
out_free_queues:
        kfree(ctrl->queues);
out_uninit_ctrl:
        nvme_uninit_ctrl(&ctrl->ctrl);
out_put_ctrl:
        nvme_put_ctrl(&ctrl->ctrl);
        if (ret > 0)
                ret = -EIO;
        return ERR_PTR(ret);
}

static int nvme_loop_add_port(struct nvmet_port *port)
{
        /*
         * XXX: disalow adding more than one port so
         * there is no connection rejections when a
         * a subsystem is assigned to a port for which
         * loop doesn't have a pointer.
         * This scenario would be possible if we allowed
         * more than one port to be added and a subsystem
         * was assigned to a port other than nvmet_loop_port.
         */

        if (nvmet_loop_port)
                return -EPERM;

        nvmet_loop_port = port;
        return 0;
}

static void nvme_loop_remove_port(struct nvmet_port *port)
{
        if (port == nvmet_loop_port)
                nvmet_loop_port = NULL;
}

static struct nvmet_fabrics_ops nvme_loop_ops = {
        .owner          = THIS_MODULE,
        .type           = NVMF_TRTYPE_LOOP,
        .add_port       = nvme_loop_add_port,
        .remove_port    = nvme_loop_remove_port,
        .queue_response = nvme_loop_queue_response,
        .delete_ctrl    = nvme_loop_delete_ctrl,
};

static struct nvmf_transport_ops nvme_loop_transport = {
        .name           = "loop",
        .create_ctrl    = nvme_loop_create_ctrl,
};

static int __init nvme_loop_init_module(void)
{
        int ret;

        ret = nvmet_register_transport(&nvme_loop_ops);
        if (ret)
                return ret;

        ret = nvmf_register_transport(&nvme_loop_transport);
        if (ret)
                nvmet_unregister_transport(&nvme_loop_ops);

        return ret;
}

static void __exit nvme_loop_cleanup_module(void)
{
        struct nvme_loop_ctrl *ctrl, *next;

        nvmf_unregister_transport(&nvme_loop_transport);
        nvmet_unregister_transport(&nvme_loop_ops);

        mutex_lock(&nvme_loop_ctrl_mutex);
        list_for_each_entry_safe(ctrl, next, &nvme_loop_ctrl_list, list)
                nvme_delete_ctrl(&ctrl->ctrl);
        mutex_unlock(&nvme_loop_ctrl_mutex);

        flush_workqueue(nvme_wq);
}

module_init(nvme_loop_init_module);
module_exit(nvme_loop_cleanup_module);

MODULE_LICENSE("GPL v2");
MODULE_ALIAS("nvmet-transport-254"); /* 254 == NVMF_TRTYPE_LOOP */