// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2009, Microsoft Corporation.
 *
 * Authors:
 *   Haiyang Zhang <haiyangz@microsoft.com>
 *   Hank Janssen  <hjanssen@microsoft.com>
 *   K. Y. Srinivasan <kys@microsoft.com>
 */

#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/completion.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/hyperv.h>
#include <linux/blkdev.h>
#include <linux/dma-mapping.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_tcq.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_devinfo.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_transport_fc.h>
#include <scsi/scsi_transport.h>

/*
 * All wire protocol details (storage protocol between the guest and the host)
 * are consolidated here.
 *
 * Begin protocol definitions.
 */

/*
 * Version history:
 * V1 Beta: 0.1
 * V1 RC < 2008/1/31: 1.0
 * V1 RC > 2008/1/31:  2.0
 * Win7: 4.2
 * Win8: 5.1
 * Win8.1: 6.0
 * Win10: 6.2
 */

#define VMSTOR_PROTO_VERSION(MAJOR_, MINOR_)    ((((MAJOR_) & 0xff) << 8) | \
                                                (((MINOR_) & 0xff)))

#define VMSTOR_PROTO_VERSION_WIN6       VMSTOR_PROTO_VERSION(2, 0)
#define VMSTOR_PROTO_VERSION_WIN7       VMSTOR_PROTO_VERSION(4, 2)
#define VMSTOR_PROTO_VERSION_WIN8       VMSTOR_PROTO_VERSION(5, 1)
#define VMSTOR_PROTO_VERSION_WIN8_1     VMSTOR_PROTO_VERSION(6, 0)
#define VMSTOR_PROTO_VERSION_WIN10      VMSTOR_PROTO_VERSION(6, 2)

/*  Packet structure describing virtual storage requests. */
enum vstor_packet_operation {
        VSTOR_OPERATION_COMPLETE_IO             = 1,
        VSTOR_OPERATION_REMOVE_DEVICE           = 2,
        VSTOR_OPERATION_EXECUTE_SRB             = 3,
        VSTOR_OPERATION_RESET_LUN               = 4,
        VSTOR_OPERATION_RESET_ADAPTER           = 5,
        VSTOR_OPERATION_RESET_BUS               = 6,
        VSTOR_OPERATION_BEGIN_INITIALIZATION    = 7,
        VSTOR_OPERATION_END_INITIALIZATION      = 8,
        VSTOR_OPERATION_QUERY_PROTOCOL_VERSION  = 9,
        VSTOR_OPERATION_QUERY_PROPERTIES        = 10,
        VSTOR_OPERATION_ENUMERATE_BUS           = 11,
        VSTOR_OPERATION_FCHBA_DATA              = 12,
        VSTOR_OPERATION_CREATE_SUB_CHANNELS     = 13,
        VSTOR_OPERATION_MAXIMUM                 = 13
};

/*
 * WWN packet for Fibre Channel HBA
 */

struct hv_fc_wwn_packet {
        u8      primary_active;
        u8      reserved1[3];
        u8      primary_port_wwn[8];
        u8      primary_node_wwn[8];
        u8      secondary_port_wwn[8];
        u8      secondary_node_wwn[8];
};



/*
 * SRB Flag Bits
 */

#define SRB_FLAGS_QUEUE_ACTION_ENABLE           0x00000002
#define SRB_FLAGS_DISABLE_DISCONNECT            0x00000004
#define SRB_FLAGS_DISABLE_SYNCH_TRANSFER        0x00000008
#define SRB_FLAGS_BYPASS_FROZEN_QUEUE           0x00000010
#define SRB_FLAGS_DISABLE_AUTOSENSE             0x00000020
#define SRB_FLAGS_DATA_IN                       0x00000040
#define SRB_FLAGS_DATA_OUT                      0x00000080
#define SRB_FLAGS_NO_DATA_TRANSFER              0x00000000
#define SRB_FLAGS_UNSPECIFIED_DIRECTION (SRB_FLAGS_DATA_IN | SRB_FLAGS_DATA_OUT)
#define SRB_FLAGS_NO_QUEUE_FREEZE               0x00000100
#define SRB_FLAGS_ADAPTER_CACHE_ENABLE          0x00000200
#define SRB_FLAGS_FREE_SENSE_BUFFER             0x00000400

/*
 * This flag indicates the request is part of the workflow for processing a D3.
 */
#define SRB_FLAGS_D3_PROCESSING                 0x00000800
#define SRB_FLAGS_IS_ACTIVE                     0x00010000
#define SRB_FLAGS_ALLOCATED_FROM_ZONE           0x00020000
#define SRB_FLAGS_SGLIST_FROM_POOL              0x00040000
#define SRB_FLAGS_BYPASS_LOCKED_QUEUE           0x00080000
#define SRB_FLAGS_NO_KEEP_AWAKE                 0x00100000
#define SRB_FLAGS_PORT_DRIVER_ALLOCSENSE        0x00200000
#define SRB_FLAGS_PORT_DRIVER_SENSEHASPORT      0x00400000
#define SRB_FLAGS_DONT_START_NEXT_PACKET        0x00800000
#define SRB_FLAGS_PORT_DRIVER_RESERVED          0x0F000000
#define SRB_FLAGS_CLASS_DRIVER_RESERVED         0xF0000000

#define SP_UNTAGGED                     ((unsigned char) ~0)
#define SRB_SIMPLE_TAG_REQUEST          0x20

/*
 * Platform neutral description of a scsi request -
 * this remains the same across the write regardless of 32/64 bit
 * note: it's patterned off the SCSI_PASS_THROUGH structure
 */
#define STORVSC_MAX_CMD_LEN                     0x10

#define POST_WIN7_STORVSC_SENSE_BUFFER_SIZE     0x14
#define PRE_WIN8_STORVSC_SENSE_BUFFER_SIZE      0x12

#define STORVSC_SENSE_BUFFER_SIZE               0x14
#define STORVSC_MAX_BUF_LEN_WITH_PADDING        0x14

/*
 * Sense buffer size changed in win8; have a run-time
 * variable to track the size we should use.  This value will
 * likely change during protocol negotiation but it is valid
 * to start by assuming pre-Win8.
 */
static int sense_buffer_size = PRE_WIN8_STORVSC_SENSE_BUFFER_SIZE;

/*
 * The storage protocol version is determined during the
 * initial exchange with the host.  It will indicate which
 * storage functionality is available in the host.
*/
static int vmstor_proto_version;

#define STORVSC_LOGGING_NONE    0
#define STORVSC_LOGGING_ERROR   1
#define STORVSC_LOGGING_WARN    2

static int logging_level = STORVSC_LOGGING_ERROR;
module_param(logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(logging_level,
        "Logging level, 0 - None, 1 - Error (default), 2 - Warning.");

static inline bool do_logging(int level)
{
        return logging_level >= level;
}

#define storvsc_log(dev, level, fmt, ...)                       \
do {                                                            \
        if (do_logging(level))                                  \
                dev_warn(&(dev)->device, fmt, ##__VA_ARGS__);   \
} while (0)

struct vmscsi_win8_extension {
        /*
         * The following were added in Windows 8
         */
        u16 reserve;
        u8  queue_tag;
        u8  queue_action;
        u32 srb_flags;
        u32 time_out_value;
        u32 queue_sort_ey;
} __packed;

struct vmscsi_request {
        u16 length;
        u8 srb_status;
        u8 scsi_status;

        u8  port_number;
        u8  path_id;
        u8  target_id;
        u8  lun;

        u8  cdb_length;
        u8  sense_info_length;
        u8  data_in;
        u8  reserved;

        u32 data_transfer_length;

        union {
                u8 cdb[STORVSC_MAX_CMD_LEN];
                u8 sense_data[STORVSC_SENSE_BUFFER_SIZE];
                u8 reserved_array[STORVSC_MAX_BUF_LEN_WITH_PADDING];
        };
        /*
         * The following was added in win8.
         */
        struct vmscsi_win8_extension win8_extension;

} __attribute((packed));

/*
 * The list of storage protocols in order of preference.
 */
struct vmstor_protocol {
        int protocol_version;
        int sense_buffer_size;
        int vmscsi_size_delta;
};


static const struct vmstor_protocol vmstor_protocols[] = {
        {
                VMSTOR_PROTO_VERSION_WIN10,
                POST_WIN7_STORVSC_SENSE_BUFFER_SIZE,
                0
        },
        {
                VMSTOR_PROTO_VERSION_WIN8_1,
                POST_WIN7_STORVSC_SENSE_BUFFER_SIZE,
                0
        },
        {
                VMSTOR_PROTO_VERSION_WIN8,
                POST_WIN7_STORVSC_SENSE_BUFFER_SIZE,
                0
        },
        {
                VMSTOR_PROTO_VERSION_WIN7,
                PRE_WIN8_STORVSC_SENSE_BUFFER_SIZE,
                sizeof(struct vmscsi_win8_extension),
        },
        {
                VMSTOR_PROTO_VERSION_WIN6,
                PRE_WIN8_STORVSC_SENSE_BUFFER_SIZE,
                sizeof(struct vmscsi_win8_extension),
        }
};


/*
 * This structure is sent during the initialization phase to get the different
 * properties of the channel.
 */

#define STORAGE_CHANNEL_SUPPORTS_MULTI_CHANNEL          0x1

struct vmstorage_channel_properties {
        u32 reserved;
        u16 max_channel_cnt;
        u16 reserved1;

        u32 flags;
        u32   max_transfer_bytes;

        u64  reserved2;
} __packed;

/*  This structure is sent during the storage protocol negotiations. */
struct vmstorage_protocol_version {
        /* Major (MSW) and minor (LSW) version numbers. */
        u16 major_minor;

        /*
         * Revision number is auto-incremented whenever this file is changed
         * (See FILL_VMSTOR_REVISION macro above).  Mismatch does not
         * definitely indicate incompatibility--but it does indicate mismatched
         * builds.
         * This is only used on the windows side. Just set it to 0.
         */
        u16 revision;
} __packed;

/* Channel Property Flags */
#define STORAGE_CHANNEL_REMOVABLE_FLAG          0x1
#define STORAGE_CHANNEL_EMULATED_IDE_FLAG       0x2

struct vstor_packet {
        /* Requested operation type */
        enum vstor_packet_operation operation;

        /*  Flags - see below for values */
        u32 flags;

        /* Status of the request returned from the server side. */
        u32 status;

        /* Data payload area */
        union {
                /*
                 * Structure used to forward SCSI commands from the
                 * client to the server.
                 */
                struct vmscsi_request vm_srb;

                /* Structure used to query channel properties. */
                struct vmstorage_channel_properties storage_channel_properties;

                /* Used during version negotiations. */
                struct vmstorage_protocol_version version;

                /* Fibre channel address packet */
                struct hv_fc_wwn_packet wwn_packet;

                /* Number of sub-channels to create */
                u16 sub_channel_count;

                /* This will be the maximum of the union members */
                u8  buffer[0x34];
        };
} __packed;

/*
 * Packet Flags:
 *
 * This flag indicates that the server should send back a completion for this
 * packet.
 */

#define REQUEST_COMPLETION_FLAG 0x1

/* Matches Windows-end */
enum storvsc_request_type {
        WRITE_TYPE = 0,
        READ_TYPE,
        UNKNOWN_TYPE,
};

/*
 * SRB status codes and masks; a subset of the codes used here.
 */

#define SRB_STATUS_AUTOSENSE_VALID      0x80
#define SRB_STATUS_QUEUE_FROZEN         0x40
#define SRB_STATUS_INVALID_LUN  0x20
#define SRB_STATUS_SUCCESS      0x01
#define SRB_STATUS_ABORTED      0x02
#define SRB_STATUS_ERROR        0x04
#define SRB_STATUS_DATA_OVERRUN 0x12

#define SRB_STATUS(status) \
        (status & ~(SRB_STATUS_AUTOSENSE_VALID | SRB_STATUS_QUEUE_FROZEN))
/*
 * This is the end of Protocol specific defines.
 */

static int storvsc_ringbuffer_size = (128 * 1024);
static u32 max_outstanding_req_per_channel;
static int storvsc_change_queue_depth(struct scsi_device *sdev, int queue_depth);

static int storvsc_vcpus_per_sub_channel = 4;
static unsigned int storvsc_max_hw_queues;

module_param(storvsc_ringbuffer_size, int, S_IRUGO);
MODULE_PARM_DESC(storvsc_ringbuffer_size, "Ring buffer size (bytes)");

module_param(storvsc_max_hw_queues, uint, 0644);
MODULE_PARM_DESC(storvsc_max_hw_queues, "Maximum number of hardware queues");

module_param(storvsc_vcpus_per_sub_channel, int, S_IRUGO);
MODULE_PARM_DESC(storvsc_vcpus_per_sub_channel, "Ratio of VCPUs to subchannels");

static int ring_avail_percent_lowater = 10;
module_param(ring_avail_percent_lowater, int, S_IRUGO);
MODULE_PARM_DESC(ring_avail_percent_lowater,
                "Select a channel if available ring size > this in percent");

/*
 * Timeout in seconds for all devices managed by this driver.
 */
static int storvsc_timeout = 180;

#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
static struct scsi_transport_template *fc_transport_template;
#endif

static struct scsi_host_template scsi_driver;
static void storvsc_on_channel_callback(void *context);

#define STORVSC_MAX_LUNS_PER_TARGET                     255
#define STORVSC_MAX_TARGETS                             2
#define STORVSC_MAX_CHANNELS                            8

#define STORVSC_FC_MAX_LUNS_PER_TARGET                  255
#define STORVSC_FC_MAX_TARGETS                          128
#define STORVSC_FC_MAX_CHANNELS                         8

#define STORVSC_IDE_MAX_LUNS_PER_TARGET                 64
#define STORVSC_IDE_MAX_TARGETS                         1
#define STORVSC_IDE_MAX_CHANNELS                        1

/*
 * Upper bound on the size of a storvsc packet. vmscsi_size_delta is not
 * included in the calculation because it is set after STORVSC_MAX_PKT_SIZE
 * is used in storvsc_connect_to_vsp
 */
#define STORVSC_MAX_PKT_SIZE (sizeof(struct vmpacket_descriptor) +\
                              sizeof(struct vstor_packet))

struct storvsc_cmd_request {
        struct scsi_cmnd *cmd;

        struct hv_device *device;

        /* Synchronize the request/response if needed */
        struct completion wait_event;

        struct vmbus_channel_packet_multipage_buffer mpb;
        struct vmbus_packet_mpb_array *payload;
        u32 payload_sz;

        struct vstor_packet vstor_packet;
};


/* A storvsc device is a device object that contains a vmbus channel */
struct storvsc_device {
        struct hv_device *device;

        bool     destroy;
        bool     drain_notify;
        atomic_t num_outstanding_req;
        struct Scsi_Host *host;

        wait_queue_head_t waiting_to_drain;

        /*
         * Each unique Port/Path/Target represents 1 channel ie scsi
         * controller. In reality, the pathid, targetid is always 0
         * and the port is set by us
         */
        unsigned int port_number;
        unsigned char path_id;
        unsigned char target_id;

        /*
         * The size of the vmscsi_request has changed in win8. The
         * additional size is because of new elements added to the
         * structure. These elements are valid only when we are talking
         * to a win8 host.
         * Track the correction to size we need to apply. This value
         * will likely change during protocol negotiation but it is
         * valid to start by assuming pre-Win8.
         */
        int vmscsi_size_delta;

        /*
         * Max I/O, the device can support.
         */
        u32   max_transfer_bytes;
        /*
         * Number of sub-channels we will open.
         */
        u16 num_sc;
        struct vmbus_channel **stor_chns;
        /*
         * Mask of CPUs bound to subchannels.
         */
        struct cpumask alloced_cpus;
        /*
         * Serializes modifications of stor_chns[] from storvsc_do_io()
         * and storvsc_change_target_cpu().
         */
        spinlock_t lock;
        /* Used for vsc/vsp channel reset process */
        struct storvsc_cmd_request init_request;
        struct storvsc_cmd_request reset_request;
        /*
         * Currently active port and node names for FC devices.
         */
        u64 node_name;
        u64 port_name;
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        struct fc_rport *rport;
#endif
};

struct hv_host_device {
        struct hv_device *dev;
        unsigned int port;
        unsigned char path;
        unsigned char target;
        struct workqueue_struct *handle_error_wq;
        struct work_struct host_scan_work;
        struct Scsi_Host *host;
};

struct storvsc_scan_work {
        struct work_struct work;
        struct Scsi_Host *host;
        u8 lun;
        u8 tgt_id;
};

static void storvsc_device_scan(struct work_struct *work)
{
        struct storvsc_scan_work *wrk;
        struct scsi_device *sdev;

        wrk = container_of(work, struct storvsc_scan_work, work);

        sdev = scsi_device_lookup(wrk->host, 0, wrk->tgt_id, wrk->lun);
        if (!sdev)
                goto done;
        scsi_rescan_device(&sdev->sdev_gendev);
        scsi_device_put(sdev);

done:
        kfree(wrk);
}

static void storvsc_host_scan(struct work_struct *work)
{
        struct Scsi_Host *host;
        struct scsi_device *sdev;
        struct hv_host_device *host_device =
                container_of(work, struct hv_host_device, host_scan_work);

        host = host_device->host;
        /*
         * Before scanning the host, first check to see if any of the
         * currrently known devices have been hot removed. We issue a
         * "unit ready" command against all currently known devices.
         * This I/O will result in an error for devices that have been
         * removed. As part of handling the I/O error, we remove the device.
         *
         * When a LUN is added or removed, the host sends us a signal to
         * scan the host. Thus we are forced to discover the LUNs that
         * may have been removed this way.
         */
        mutex_lock(&host->scan_mutex);
        shost_for_each_device(sdev, host)
                scsi_test_unit_ready(sdev, 1, 1, NULL);
        mutex_unlock(&host->scan_mutex);
        /*
         * Now scan the host to discover LUNs that may have been added.
         */
        scsi_scan_host(host);
}

static void storvsc_remove_lun(struct work_struct *work)
{
        struct storvsc_scan_work *wrk;
        struct scsi_device *sdev;

        wrk = container_of(work, struct storvsc_scan_work, work);
        if (!scsi_host_get(wrk->host))
                goto done;

        sdev = scsi_device_lookup(wrk->host, 0, wrk->tgt_id, wrk->lun);

        if (sdev) {
                scsi_remove_device(sdev);
                scsi_device_put(sdev);
        }
        scsi_host_put(wrk->host);

done:
        kfree(wrk);
}


/*
 * We can get incoming messages from the host that are not in response to
 * messages that we have sent out. An example of this would be messages
 * received by the guest to notify dynamic addition/removal of LUNs. To
 * deal with potential race conditions where the driver may be in the
 * midst of being unloaded when we might receive an unsolicited message
 * from the host, we have implemented a mechanism to gurantee sequential
 * consistency:
 *
 * 1) Once the device is marked as being destroyed, we will fail all
 *    outgoing messages.
 * 2) We permit incoming messages when the device is being destroyed,
 *    only to properly account for messages already sent out.
 */

static inline struct storvsc_device *get_out_stor_device(
                                        struct hv_device *device)
{
        struct storvsc_device *stor_device;

        stor_device = hv_get_drvdata(device);

        if (stor_device && stor_device->destroy)
                stor_device = NULL;

        return stor_device;
}


static inline void storvsc_wait_to_drain(struct storvsc_device *dev)
{
        dev->drain_notify = true;
        wait_event(dev->waiting_to_drain,
                   atomic_read(&dev->num_outstanding_req) == 0);
        dev->drain_notify = false;
}

static inline struct storvsc_device *get_in_stor_device(
                                        struct hv_device *device)
{
        struct storvsc_device *stor_device;

        stor_device = hv_get_drvdata(device);

        if (!stor_device)
                goto get_in_err;

        /*
         * If the device is being destroyed; allow incoming
         * traffic only to cleanup outstanding requests.
         */

        if (stor_device->destroy  &&
                (atomic_read(&stor_device->num_outstanding_req) == 0))
                stor_device = NULL;

get_in_err:
        return stor_device;

}

static void storvsc_change_target_cpu(struct vmbus_channel *channel, u32 old,
                                      u32 new)
{
        struct storvsc_device *stor_device;
        struct vmbus_channel *cur_chn;
        bool old_is_alloced = false;
        struct hv_device *device;
        unsigned long flags;
        int cpu;

        device = channel->primary_channel ?
                        channel->primary_channel->device_obj
                                : channel->device_obj;
        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return;

        /* See storvsc_do_io() -> get_og_chn(). */
        spin_lock_irqsave(&stor_device->lock, flags);

        /*
         * Determines if the storvsc device has other channels assigned to
         * the "old" CPU to update the alloced_cpus mask and the stor_chns
         * array.
         */
        if (device->channel != channel && device->channel->target_cpu == old) {
                cur_chn = device->channel;
                old_is_alloced = true;
                goto old_is_alloced;
        }
        list_for_each_entry(cur_chn, &device->channel->sc_list, sc_list) {
                if (cur_chn == channel)
                        continue;
                if (cur_chn->target_cpu == old) {
                        old_is_alloced = true;
                        goto old_is_alloced;
                }
        }

old_is_alloced:
        if (old_is_alloced)
                WRITE_ONCE(stor_device->stor_chns[old], cur_chn);
        else
                cpumask_clear_cpu(old, &stor_device->alloced_cpus);

        /* "Flush" the stor_chns array. */
        for_each_possible_cpu(cpu) {
                if (stor_device->stor_chns[cpu] && !cpumask_test_cpu(
                                        cpu, &stor_device->alloced_cpus))
                        WRITE_ONCE(stor_device->stor_chns[cpu], NULL);
        }

        WRITE_ONCE(stor_device->stor_chns[new], channel);
        cpumask_set_cpu(new, &stor_device->alloced_cpus);

        spin_unlock_irqrestore(&stor_device->lock, flags);
}

static u64 storvsc_next_request_id(struct vmbus_channel *channel, u64 rqst_addr)
{
        struct storvsc_cmd_request *request =
                (struct storvsc_cmd_request *)(unsigned long)rqst_addr;

        if (rqst_addr == VMBUS_RQST_INIT)
                return VMBUS_RQST_INIT;
        if (rqst_addr == VMBUS_RQST_RESET)
                return VMBUS_RQST_RESET;

        /*
         * Cannot return an ID of 0, which is reserved for an unsolicited
         * message from Hyper-V.
         */
        return (u64)blk_mq_unique_tag(scsi_cmd_to_rq(request->cmd)) + 1;
}

static void handle_sc_creation(struct vmbus_channel *new_sc)
{
        struct hv_device *device = new_sc->primary_channel->device_obj;
        struct device *dev = &device->device;
        struct storvsc_device *stor_device;
        struct vmstorage_channel_properties props;
        int ret;

        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return;

        memset(&props, 0, sizeof(struct vmstorage_channel_properties));
        new_sc->max_pkt_size = STORVSC_MAX_PKT_SIZE;

        new_sc->next_request_id_callback = storvsc_next_request_id;

        ret = vmbus_open(new_sc,
                         storvsc_ringbuffer_size,
                         storvsc_ringbuffer_size,
                         (void *)&props,
                         sizeof(struct vmstorage_channel_properties),
                         storvsc_on_channel_callback, new_sc);

        /* In case vmbus_open() fails, we don't use the sub-channel. */
        if (ret != 0) {
                dev_err(dev, "Failed to open sub-channel: err=%d\n", ret);
                return;
        }

        new_sc->change_target_cpu_callback = storvsc_change_target_cpu;

        /* Add the sub-channel to the array of available channels. */
        stor_device->stor_chns[new_sc->target_cpu] = new_sc;
        cpumask_set_cpu(new_sc->target_cpu, &stor_device->alloced_cpus);
}

static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
{
        struct device *dev = &device->device;
        struct storvsc_device *stor_device;
        int num_sc;
        struct storvsc_cmd_request *request;
        struct vstor_packet *vstor_packet;
        int ret, t;

        /*
         * If the number of CPUs is artificially restricted, such as
         * with maxcpus=1 on the kernel boot line, Hyper-V could offer
         * sub-channels >= the number of CPUs. These sub-channels
         * should not be created. The primary channel is already created
         * and assigned to one CPU, so check against # CPUs - 1.
         */
        num_sc = min((int)(num_online_cpus() - 1), max_chns);
        if (!num_sc)
                return;

        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return;

        stor_device->num_sc = num_sc;
        request = &stor_device->init_request;
        vstor_packet = &request->vstor_packet;

        /*
         * Establish a handler for dealing with subchannels.
         */
        vmbus_set_sc_create_callback(device->channel, handle_sc_creation);

        /*
         * Request the host to create sub-channels.
         */
        memset(request, 0, sizeof(struct storvsc_cmd_request));
        init_completion(&request->wait_event);
        vstor_packet->operation = VSTOR_OPERATION_CREATE_SUB_CHANNELS;
        vstor_packet->flags = REQUEST_COMPLETION_FLAG;
        vstor_packet->sub_channel_count = num_sc;

        ret = vmbus_sendpacket(device->channel, vstor_packet,
                               (sizeof(struct vstor_packet) -
                               stor_device->vmscsi_size_delta),
                               VMBUS_RQST_INIT,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);

        if (ret != 0) {
                dev_err(dev, "Failed to create sub-channel: err=%d\n", ret);
                return;
        }

        t = wait_for_completion_timeout(&request->wait_event, 10*HZ);
        if (t == 0) {
                dev_err(dev, "Failed to create sub-channel: timed out\n");
                return;
        }

        if (vstor_packet->operation != VSTOR_OPERATION_COMPLETE_IO ||
            vstor_packet->status != 0) {
                dev_err(dev, "Failed to create sub-channel: op=%d, sts=%d\n",
                        vstor_packet->operation, vstor_packet->status);
                return;
        }

        /*
         * We need to do nothing here, because vmbus_process_offer()
         * invokes channel->sc_creation_callback, which will open and use
         * the sub-channel(s).
         */
}

static void cache_wwn(struct storvsc_device *stor_device,
                      struct vstor_packet *vstor_packet)
{
        /*
         * Cache the currently active port and node ww names.
         */
        if (vstor_packet->wwn_packet.primary_active) {
                stor_device->node_name =
                        wwn_to_u64(vstor_packet->wwn_packet.primary_node_wwn);
                stor_device->port_name =
                        wwn_to_u64(vstor_packet->wwn_packet.primary_port_wwn);
        } else {
                stor_device->node_name =
                        wwn_to_u64(vstor_packet->wwn_packet.secondary_node_wwn);
                stor_device->port_name =
                        wwn_to_u64(vstor_packet->wwn_packet.secondary_port_wwn);
        }
}


static int storvsc_execute_vstor_op(struct hv_device *device,
                                    struct storvsc_cmd_request *request,
                                    bool status_check)
{
        struct storvsc_device *stor_device;
        struct vstor_packet *vstor_packet;
        int ret, t;

        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return -ENODEV;

        vstor_packet = &request->vstor_packet;

        init_completion(&request->wait_event);
        vstor_packet->flags = REQUEST_COMPLETION_FLAG;

        ret = vmbus_sendpacket(device->channel, vstor_packet,
                               (sizeof(struct vstor_packet) -
                               stor_device->vmscsi_size_delta),
                               VMBUS_RQST_INIT,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret != 0)
                return ret;

        t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
        if (t == 0)
                return -ETIMEDOUT;

        if (!status_check)
                return ret;

        if (vstor_packet->operation != VSTOR_OPERATION_COMPLETE_IO ||
            vstor_packet->status != 0)
                return -EINVAL;

        return ret;
}

static int storvsc_channel_init(struct hv_device *device, bool is_fc)
{
        struct storvsc_device *stor_device;
        struct storvsc_cmd_request *request;
        struct vstor_packet *vstor_packet;
        int ret, i;
        int max_chns;
        bool process_sub_channels = false;

        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return -ENODEV;

        request = &stor_device->init_request;
        vstor_packet = &request->vstor_packet;

        /*
         * Now, initiate the vsc/vsp initialization protocol on the open
         * channel
         */
        memset(request, 0, sizeof(struct storvsc_cmd_request));
        vstor_packet->operation = VSTOR_OPERATION_BEGIN_INITIALIZATION;
        ret = storvsc_execute_vstor_op(device, request, true);
        if (ret)
                return ret;
        /*
         * Query host supported protocol version.
         */

        for (i = 0; i < ARRAY_SIZE(vmstor_protocols); i++) {
                /* reuse the packet for version range supported */
                memset(vstor_packet, 0, sizeof(struct vstor_packet));
                vstor_packet->operation =
                        VSTOR_OPERATION_QUERY_PROTOCOL_VERSION;

                vstor_packet->version.major_minor =
                        vmstor_protocols[i].protocol_version;

                /*
                 * The revision number is only used in Windows; set it to 0.
                 */
                vstor_packet->version.revision = 0;
                ret = storvsc_execute_vstor_op(device, request, false);
                if (ret != 0)
                        return ret;

                if (vstor_packet->operation != VSTOR_OPERATION_COMPLETE_IO)
                        return -EINVAL;

                if (vstor_packet->status == 0) {
                        vmstor_proto_version =
                                vmstor_protocols[i].protocol_version;

                        sense_buffer_size =
                                vmstor_protocols[i].sense_buffer_size;

                        stor_device->vmscsi_size_delta =
                                vmstor_protocols[i].vmscsi_size_delta;

                        break;
                }
        }

        if (vstor_packet->status != 0)
                return -EINVAL;


        memset(vstor_packet, 0, sizeof(struct vstor_packet));
        vstor_packet->operation = VSTOR_OPERATION_QUERY_PROPERTIES;
        ret = storvsc_execute_vstor_op(device, request, true);
        if (ret != 0)
                return ret;

        /*
         * Check to see if multi-channel support is there.
         * Hosts that implement protocol version of 5.1 and above
         * support multi-channel.
         */
        max_chns = vstor_packet->storage_channel_properties.max_channel_cnt;

        /*
         * Allocate state to manage the sub-channels.
         * We allocate an array based on the numbers of possible CPUs
         * (Hyper-V does not support cpu online/offline).
         * This Array will be sparseley populated with unique
         * channels - primary + sub-channels.
         * We will however populate all the slots to evenly distribute
         * the load.
         */
        stor_device->stor_chns = kcalloc(num_possible_cpus(), sizeof(void *),
                                         GFP_KERNEL);
        if (stor_device->stor_chns == NULL)
                return -ENOMEM;

        device->channel->change_target_cpu_callback = storvsc_change_target_cpu;

        stor_device->stor_chns[device->channel->target_cpu] = device->channel;
        cpumask_set_cpu(device->channel->target_cpu,
                        &stor_device->alloced_cpus);

        if (vmstor_proto_version >= VMSTOR_PROTO_VERSION_WIN8) {
                if (vstor_packet->storage_channel_properties.flags &
                    STORAGE_CHANNEL_SUPPORTS_MULTI_CHANNEL)
                        process_sub_channels = true;
        }
        stor_device->max_transfer_bytes =
                vstor_packet->storage_channel_properties.max_transfer_bytes;

        if (!is_fc)
                goto done;

        /*

         * For FC devices retrieve FC HBA data.
         */
        memset(vstor_packet, 0, sizeof(struct vstor_packet));
        vstor_packet->operation = VSTOR_OPERATION_FCHBA_DATA;
        ret = storvsc_execute_vstor_op(device, request, true);
        if (ret != 0)
                return ret;

        /*
         * Cache the currently active port and node ww names.
         */
        cache_wwn(stor_device, vstor_packet);

done:

        memset(vstor_packet, 0, sizeof(struct vstor_packet));
        vstor_packet->operation = VSTOR_OPERATION_END_INITIALIZATION;
        ret = storvsc_execute_vstor_op(device, request, true);
        if (ret != 0)
                return ret;

        if (process_sub_channels)
                handle_multichannel_storage(device, max_chns);

        return ret;
}

static void storvsc_handle_error(struct vmscsi_request *vm_srb,
                                struct scsi_cmnd *scmnd,
                                struct Scsi_Host *host,
                                u8 asc, u8 ascq)
{
        struct storvsc_scan_work *wrk;
        void (*process_err_fn)(struct work_struct *work);
        struct hv_host_device *host_dev = shost_priv(host);

        /*
         * In some situations, Hyper-V sets multiple bits in the
         * srb_status, such as ABORTED and ERROR. So process them
         * individually, with the most specific bits first.
         */

        if (vm_srb->srb_status & SRB_STATUS_INVALID_LUN) {
                set_host_byte(scmnd, DID_NO_CONNECT);
                process_err_fn = storvsc_remove_lun;
                goto do_work;
        }

        if (vm_srb->srb_status & SRB_STATUS_ABORTED) {
                if (vm_srb->srb_status & SRB_STATUS_AUTOSENSE_VALID &&
                    /* Capacity data has changed */
                    (asc == 0x2a) && (ascq == 0x9)) {
                        process_err_fn = storvsc_device_scan;
                        /*
                         * Retry the I/O that triggered this.
                         */
                        set_host_byte(scmnd, DID_REQUEUE);
                        goto do_work;
                }
        }

        if (vm_srb->srb_status & SRB_STATUS_ERROR) {
                /*
                 * Let upper layer deal with error when
                 * sense message is present.
                 */
                if (vm_srb->srb_status & SRB_STATUS_AUTOSENSE_VALID)
                        return;

                /*
                 * If there is an error; offline the device since all
                 * error recovery strategies would have already been
                 * deployed on the host side. However, if the command
                 * were a pass-through command deal with it appropriately.
                 */
                switch (scmnd->cmnd[0]) {
                case ATA_16:
                case ATA_12:
                        set_host_byte(scmnd, DID_PASSTHROUGH);
                        break;
                /*
                 * On some Hyper-V hosts TEST_UNIT_READY command can
                 * return SRB_STATUS_ERROR. Let the upper level code
                 * deal with it based on the sense information.
                 */
                case TEST_UNIT_READY:
                        break;
                default:
                        set_host_byte(scmnd, DID_ERROR);
                }
        }
        return;

do_work:
        /*
         * We need to schedule work to process this error; schedule it.
         */
        wrk = kmalloc(sizeof(struct storvsc_scan_work), GFP_ATOMIC);
        if (!wrk) {
                set_host_byte(scmnd, DID_TARGET_FAILURE);
                return;
        }

        wrk->host = host;
        wrk->lun = vm_srb->lun;
        wrk->tgt_id = vm_srb->target_id;
        INIT_WORK(&wrk->work, process_err_fn);
        queue_work(host_dev->handle_error_wq, &wrk->work);
}


static void storvsc_command_completion(struct storvsc_cmd_request *cmd_request,
                                       struct storvsc_device *stor_dev)
{
        struct scsi_cmnd *scmnd = cmd_request->cmd;
        struct scsi_sense_hdr sense_hdr;
        struct vmscsi_request *vm_srb;
        u32 data_transfer_length;
        struct Scsi_Host *host;
        u32 payload_sz = cmd_request->payload_sz;
        void *payload = cmd_request->payload;
        bool sense_ok;

        host = stor_dev->host;

        vm_srb = &cmd_request->vstor_packet.vm_srb;
        data_transfer_length = vm_srb->data_transfer_length;

        scmnd->result = vm_srb->scsi_status;

        if (scmnd->result) {
                sense_ok = scsi_normalize_sense(scmnd->sense_buffer,
                                SCSI_SENSE_BUFFERSIZE, &sense_hdr);

                if (sense_ok && do_logging(STORVSC_LOGGING_WARN))
                        scsi_print_sense_hdr(scmnd->device, "storvsc",
                                             &sense_hdr);
        }

        if (vm_srb->srb_status != SRB_STATUS_SUCCESS) {
                storvsc_handle_error(vm_srb, scmnd, host, sense_hdr.asc,
                                         sense_hdr.ascq);
                /*
                 * The Windows driver set data_transfer_length on
                 * SRB_STATUS_DATA_OVERRUN. On other errors, this value
                 * is untouched.  In these cases we set it to 0.
                 */
                if (vm_srb->srb_status != SRB_STATUS_DATA_OVERRUN)
                        data_transfer_length = 0;
        }

        /* Validate data_transfer_length (from Hyper-V) */
        if (data_transfer_length > cmd_request->payload->range.len)
                data_transfer_length = cmd_request->payload->range.len;

        scsi_set_resid(scmnd,
                cmd_request->payload->range.len - data_transfer_length);

        scsi_done(scmnd);

        if (payload_sz >
                sizeof(struct vmbus_channel_packet_multipage_buffer))
                kfree(payload);
}

static void storvsc_on_io_completion(struct storvsc_device *stor_device,
                                  struct vstor_packet *vstor_packet,
                                  struct storvsc_cmd_request *request)
{
        struct vstor_packet *stor_pkt;
        struct hv_device *device = stor_device->device;

        stor_pkt = &request->vstor_packet;

        /*
         * The current SCSI handling on the host side does
         * not correctly handle:
         * INQUIRY command with page code parameter set to 0x80
         * MODE_SENSE command with cmd[2] == 0x1c
         *
         * Setup srb and scsi status so this won't be fatal.
         * We do this so we can distinguish truly fatal failues
         * (srb status == 0x4) and off-line the device in that case.
         */

        if ((stor_pkt->vm_srb.cdb[0] == INQUIRY) ||
           (stor_pkt->vm_srb.cdb[0] == MODE_SENSE)) {
                vstor_packet->vm_srb.scsi_status = 0;
                vstor_packet->vm_srb.srb_status = SRB_STATUS_SUCCESS;
        }

        /* Copy over the status...etc */
        stor_pkt->vm_srb.scsi_status = vstor_packet->vm_srb.scsi_status;
        stor_pkt->vm_srb.srb_status = vstor_packet->vm_srb.srb_status;

        /*
         * Copy over the sense_info_length, but limit to the known max
         * size if Hyper-V returns a bad value.
         */
        stor_pkt->vm_srb.sense_info_length = min_t(u8, sense_buffer_size,
                vstor_packet->vm_srb.sense_info_length);

        if (vstor_packet->vm_srb.scsi_status != 0 ||
            vstor_packet->vm_srb.srb_status != SRB_STATUS_SUCCESS) {

                /*
                 * Log TEST_UNIT_READY errors only as warnings. Hyper-V can
                 * return errors when detecting devices using TEST_UNIT_READY,
                 * and logging these as errors produces unhelpful noise.
                 */
                int loglevel = (stor_pkt->vm_srb.cdb[0] == TEST_UNIT_READY) ?
                        STORVSC_LOGGING_WARN : STORVSC_LOGGING_ERROR;

                storvsc_log(device, loglevel,
                        "tag#%d cmd 0x%x status: scsi 0x%x srb 0x%x hv 0x%x\n",
                        scsi_cmd_to_rq(request->cmd)->tag,
                        stor_pkt->vm_srb.cdb[0],
                        vstor_packet->vm_srb.scsi_status,
                        vstor_packet->vm_srb.srb_status,
                        vstor_packet->status);
        }

        if (vstor_packet->vm_srb.scsi_status == SAM_STAT_CHECK_CONDITION &&
            (vstor_packet->vm_srb.srb_status & SRB_STATUS_AUTOSENSE_VALID))
                memcpy(request->cmd->sense_buffer,
                       vstor_packet->vm_srb.sense_data,
                       stor_pkt->vm_srb.sense_info_length);

        stor_pkt->vm_srb.data_transfer_length =
                vstor_packet->vm_srb.data_transfer_length;

        storvsc_command_completion(request, stor_device);

        if (atomic_dec_and_test(&stor_device->num_outstanding_req) &&
                stor_device->drain_notify)
                wake_up(&stor_device->waiting_to_drain);
}

static void storvsc_on_receive(struct storvsc_device *stor_device,
                             struct vstor_packet *vstor_packet,
                             struct storvsc_cmd_request *request)
{
        struct hv_host_device *host_dev;
        switch (vstor_packet->operation) {
        case VSTOR_OPERATION_COMPLETE_IO:
                storvsc_on_io_completion(stor_device, vstor_packet, request);
                break;

        case VSTOR_OPERATION_REMOVE_DEVICE:
        case VSTOR_OPERATION_ENUMERATE_BUS:
                host_dev = shost_priv(stor_device->host);
                queue_work(
                        host_dev->handle_error_wq, &host_dev->host_scan_work);
                break;

        case VSTOR_OPERATION_FCHBA_DATA:
                cache_wwn(stor_device, vstor_packet);
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
                fc_host_node_name(stor_device->host) = stor_device->node_name;
                fc_host_port_name(stor_device->host) = stor_device->port_name;
#endif
                break;
        default:
                break;
        }
}

static void storvsc_on_channel_callback(void *context)
{
        struct vmbus_channel *channel = (struct vmbus_channel *)context;
        const struct vmpacket_descriptor *desc;
        struct hv_device *device;
        struct storvsc_device *stor_device;
        struct Scsi_Host *shost;

        if (channel->primary_channel != NULL)
                device = channel->primary_channel->device_obj;
        else
                device = channel->device_obj;

        stor_device = get_in_stor_device(device);
        if (!stor_device)
                return;

        shost = stor_device->host;

        foreach_vmbus_pkt(desc, channel) {
                struct vstor_packet *packet = hv_pkt_data(desc);
                struct storvsc_cmd_request *request = NULL;
                u32 pktlen = hv_pkt_datalen(desc);
                u64 rqst_id = desc->trans_id;
                u32 minlen = rqst_id ? sizeof(struct vstor_packet) -
                        stor_device->vmscsi_size_delta : sizeof(enum vstor_packet_operation);

                if (pktlen < minlen) {
                        dev_err(&device->device,
                                "Invalid pkt: id=%llu, len=%u, minlen=%u\n",
                                rqst_id, pktlen, minlen);
                        continue;
                }

                if (rqst_id == VMBUS_RQST_INIT) {
                        request = &stor_device->init_request;
                } else if (rqst_id == VMBUS_RQST_RESET) {
                        request = &stor_device->reset_request;
                } else {
                        /* Hyper-V can send an unsolicited message with ID of 0 */
                        if (rqst_id == 0) {
                                /*
                                 * storvsc_on_receive() looks at the vstor_packet in the message
                                 * from the ring buffer.
                                 *
                                 * - If the operation in the vstor_packet is COMPLETE_IO, then
                                 *   we call storvsc_on_io_completion(), and dereference the
                                 *   guest memory address.  Make sure we don't call
                                 *   storvsc_on_io_completion() with a guest memory address
                                 *   that is zero if Hyper-V were to construct and send such
                                 *   a bogus packet.
                                 *
                                 * - If the operation in the vstor_packet is FCHBA_DATA, then
                                 *   we call cache_wwn(), and access the data payload area of
                                 *   the packet (wwn_packet); however, there is no guarantee
                                 *   that the packet is big enough to contain such area.
                                 *   Future-proof the code by rejecting such a bogus packet.
                                 */
                                if (packet->operation == VSTOR_OPERATION_COMPLETE_IO ||
                                    packet->operation == VSTOR_OPERATION_FCHBA_DATA) {
                                        dev_err(&device->device, "Invalid packet with ID of 0\n");
                                        continue;
                                }
                        } else {
                                struct scsi_cmnd *scmnd;

                                /* Transaction 'rqst_id' corresponds to tag 'rqst_id - 1' */
                                scmnd = scsi_host_find_tag(shost, rqst_id - 1);
                                if (scmnd == NULL) {
                                        dev_err(&device->device, "Incorrect transaction ID\n");
                                        continue;
                                }
                                request = (struct storvsc_cmd_request *)scsi_cmd_priv(scmnd);
                                scsi_dma_unmap(scmnd);
                        }

                        storvsc_on_receive(stor_device, packet, request);
                        continue;
                }

                memcpy(&request->vstor_packet, packet,
                       (sizeof(struct vstor_packet) - stor_device->vmscsi_size_delta));
                complete(&request->wait_event);
        }
}

static int storvsc_connect_to_vsp(struct hv_device *device, u32 ring_size,
                                  bool is_fc)
{
        struct vmstorage_channel_properties props;
        int ret;

        memset(&props, 0, sizeof(struct vmstorage_channel_properties));

        device->channel->max_pkt_size = STORVSC_MAX_PKT_SIZE;
        device->channel->next_request_id_callback = storvsc_next_request_id;

        ret = vmbus_open(device->channel,
                         ring_size,
                         ring_size,
                         (void *)&props,
                         sizeof(struct vmstorage_channel_properties),
                         storvsc_on_channel_callback, device->channel);

        if (ret != 0)
                return ret;

        ret = storvsc_channel_init(device, is_fc);

        return ret;
}

static int storvsc_dev_remove(struct hv_device *device)
{
        struct storvsc_device *stor_device;

        stor_device = hv_get_drvdata(device);

        stor_device->destroy = true;

        /* Make sure flag is set before waiting */
        wmb();

        /*
         * At this point, all outbound traffic should be disable. We
         * only allow inbound traffic (responses) to proceed so that
         * outstanding requests can be completed.
         */

        storvsc_wait_to_drain(stor_device);

        /*
         * Since we have already drained, we don't need to busy wait
         * as was done in final_release_stor_device()
         * Note that we cannot set the ext pointer to NULL until
         * we have drained - to drain the outgoing packets, we need to
         * allow incoming packets.
         */
        hv_set_drvdata(device, NULL);

        /* Close the channel */
        vmbus_close(device->channel);

        kfree(stor_device->stor_chns);
        kfree(stor_device);
        return 0;
}

static struct vmbus_channel *get_og_chn(struct storvsc_device *stor_device,
                                        u16 q_num)
{
        u16 slot = 0;
        u16 hash_qnum;
        const struct cpumask *node_mask;
        int num_channels, tgt_cpu;

        if (stor_device->num_sc == 0) {
                stor_device->stor_chns[q_num] = stor_device->device->channel;
                return stor_device->device->channel;
        }

        /*
         * Our channel array is sparsley populated and we
         * initiated I/O on a processor/hw-q that does not
         * currently have a designated channel. Fix this.
         * The strategy is simple:
         * I. Ensure NUMA locality
         * II. Distribute evenly (best effort)
         */

        node_mask = cpumask_of_node(cpu_to_node(q_num));

        num_channels = 0;
        for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
                if (cpumask_test_cpu(tgt_cpu, node_mask))
                        num_channels++;
        }
        if (num_channels == 0) {
                stor_device->stor_chns[q_num] = stor_device->device->channel;
                return stor_device->device->channel;
        }

        hash_qnum = q_num;
        while (hash_qnum >= num_channels)
                hash_qnum -= num_channels;

        for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
                if (!cpumask_test_cpu(tgt_cpu, node_mask))
                        continue;
                if (slot == hash_qnum)
                        break;
                slot++;
        }

        stor_device->stor_chns[q_num] = stor_device->stor_chns[tgt_cpu];

        return stor_device->stor_chns[q_num];
}


static int storvsc_do_io(struct hv_device *device,
                         struct storvsc_cmd_request *request, u16 q_num)
{
        struct storvsc_device *stor_device;
        struct vstor_packet *vstor_packet;
        struct vmbus_channel *outgoing_channel, *channel;
        unsigned long flags;
        int ret = 0;
        const struct cpumask *node_mask;
        int tgt_cpu;

        vstor_packet = &request->vstor_packet;
        stor_device = get_out_stor_device(device);

        if (!stor_device)
                return -ENODEV;


        request->device  = device;
        /*
         * Select an appropriate channel to send the request out.
         */
        /* See storvsc_change_target_cpu(). */
        outgoing_channel = READ_ONCE(stor_device->stor_chns[q_num]);
        if (outgoing_channel != NULL) {
                if (outgoing_channel->target_cpu == q_num) {
                        /*
                         * Ideally, we want to pick a different channel if
                         * available on the same NUMA node.
                         */
                        node_mask = cpumask_of_node(cpu_to_node(q_num));
                        for_each_cpu_wrap(tgt_cpu,
                                 &stor_device->alloced_cpus, q_num + 1) {
                                if (!cpumask_test_cpu(tgt_cpu, node_mask))
                                        continue;
                                if (tgt_cpu == q_num)
                                        continue;
                                channel = READ_ONCE(
                                        stor_device->stor_chns[tgt_cpu]);
                                if (channel == NULL)
                                        continue;
                                if (hv_get_avail_to_write_percent(
                                                        &channel->outbound)
                                                > ring_avail_percent_lowater) {
                                        outgoing_channel = channel;
                                        goto found_channel;
                                }
                        }

                        /*
                         * All the other channels on the same NUMA node are
                         * busy. Try to use the channel on the current CPU
                         */
                        if (hv_get_avail_to_write_percent(
                                                &outgoing_channel->outbound)
                                        > ring_avail_percent_lowater)
                                goto found_channel;

                        /*
                         * If we reach here, all the channels on the current
                         * NUMA node are busy. Try to find a channel in
                         * other NUMA nodes
                         */
                        for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
                                if (cpumask_test_cpu(tgt_cpu, node_mask))
                                        continue;
                                channel = READ_ONCE(
                                        stor_device->stor_chns[tgt_cpu]);
                                if (channel == NULL)
                                        continue;
                                if (hv_get_avail_to_write_percent(
                                                        &channel->outbound)
                                                > ring_avail_percent_lowater) {
                                        outgoing_channel = channel;
                                        goto found_channel;
                                }
                        }
                }
        } else {
                spin_lock_irqsave(&stor_device->lock, flags);
                outgoing_channel = stor_device->stor_chns[q_num];
                if (outgoing_channel != NULL) {
                        spin_unlock_irqrestore(&stor_device->lock, flags);
                        goto found_channel;
                }
                outgoing_channel = get_og_chn(stor_device, q_num);
                spin_unlock_irqrestore(&stor_device->lock, flags);
        }

found_channel:
        vstor_packet->flags |= REQUEST_COMPLETION_FLAG;

        vstor_packet->vm_srb.length = (sizeof(struct vmscsi_request) -
                                        stor_device->vmscsi_size_delta);


        vstor_packet->vm_srb.sense_info_length = sense_buffer_size;


        vstor_packet->vm_srb.data_transfer_length =
        request->payload->range.len;

        vstor_packet->operation = VSTOR_OPERATION_EXECUTE_SRB;

        if (request->payload->range.len) {

                ret = vmbus_sendpacket_mpb_desc(outgoing_channel,
                                request->payload, request->payload_sz,
                                vstor_packet,
                                (sizeof(struct vstor_packet) -
                                stor_device->vmscsi_size_delta),
                                (unsigned long)request);
        } else {
                ret = vmbus_sendpacket(outgoing_channel, vstor_packet,
                               (sizeof(struct vstor_packet) -
                                stor_device->vmscsi_size_delta),
                               (unsigned long)request,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        }

        if (ret != 0)
                return ret;

        atomic_inc(&stor_device->num_outstanding_req);

        return ret;
}

static int storvsc_device_alloc(struct scsi_device *sdevice)
{
        /*
         * Set blist flag to permit the reading of the VPD pages even when
         * the target may claim SPC-2 compliance. MSFT targets currently
         * claim SPC-2 compliance while they implement post SPC-2 features.
         * With this flag we can correctly handle WRITE_SAME_16 issues.
         *
         * Hypervisor reports SCSI_UNKNOWN type for DVD ROM device but
         * still supports REPORT LUN.
         */
        sdevice->sdev_bflags = BLIST_REPORTLUN2 | BLIST_TRY_VPD_PAGES;

        return 0;
}

static int storvsc_device_configure(struct scsi_device *sdevice)
{
        blk_queue_rq_timeout(sdevice->request_queue, (storvsc_timeout * HZ));

        sdevice->no_write_same = 1;

        /*
         * If the host is WIN8 or WIN8 R2, claim conformance to SPC-3
         * if the device is a MSFT virtual device.  If the host is
         * WIN10 or newer, allow write_same.
         */
        if (!strncmp(sdevice->vendor, "Msft", 4)) {
                switch (vmstor_proto_version) {
                case VMSTOR_PROTO_VERSION_WIN8:
                case VMSTOR_PROTO_VERSION_WIN8_1:
                        sdevice->scsi_level = SCSI_SPC_3;
                        break;
                }

                if (vmstor_proto_version >= VMSTOR_PROTO_VERSION_WIN10)
                        sdevice->no_write_same = 0;
        }

        return 0;
}

static int storvsc_get_chs(struct scsi_device *sdev, struct block_device * bdev,
                           sector_t capacity, int *info)
{
        sector_t nsect = capacity;
        sector_t cylinders = nsect;
        int heads, sectors_pt;

        /*
         * We are making up these values; let us keep it simple.
         */
        heads = 0xff;
        sectors_pt = 0x3f;      /* Sectors per track */
        sector_div(cylinders, heads * sectors_pt);
        if ((sector_t)(cylinders + 1) * heads * sectors_pt < nsect)
                cylinders = 0xffff;

        info[0] = heads;
        info[1] = sectors_pt;
        info[2] = (int)cylinders;

        return 0;
}

static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
{
        struct hv_host_device *host_dev = shost_priv(scmnd->device->host);
        struct hv_device *device = host_dev->dev;

        struct storvsc_device *stor_device;
        struct storvsc_cmd_request *request;
        struct vstor_packet *vstor_packet;
        int ret, t;

        stor_device = get_out_stor_device(device);
        if (!stor_device)
                return FAILED;

        request = &stor_device->reset_request;
        vstor_packet = &request->vstor_packet;
        memset(vstor_packet, 0, sizeof(struct vstor_packet));

        init_completion(&request->wait_event);

        vstor_packet->operation = VSTOR_OPERATION_RESET_BUS;
        vstor_packet->flags = REQUEST_COMPLETION_FLAG;
        vstor_packet->vm_srb.path_id = stor_device->path_id;

        ret = vmbus_sendpacket(device->channel, vstor_packet,
                               (sizeof(struct vstor_packet) -
                                stor_device->vmscsi_size_delta),
                               VMBUS_RQST_RESET,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret != 0)
                return FAILED;

        t = wait_for_completion_timeout(&request->wait_event, 5*HZ);
        if (t == 0)
                return TIMEOUT_ERROR;


        /*
         * At this point, all outstanding requests in the adapter
         * should have been flushed out and return to us
         * There is a potential race here where the host may be in
         * the process of responding when we return from here.
         * Just wait for all in-transit packets to be accounted for
         * before we return from here.
         */
        storvsc_wait_to_drain(stor_device);

        return SUCCESS;
}

/*
 * The host guarantees to respond to each command, although I/O latencies might
 * be unbounded on Azure.  Reset the timer unconditionally to give the host a
 * chance to perform EH.
 */
static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd *scmnd)
{
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        if (scmnd->device->host->transportt == fc_transport_template)
                return fc_eh_timed_out(scmnd);
#endif
        return BLK_EH_RESET_TIMER;
}

static bool storvsc_scsi_cmd_ok(struct scsi_cmnd *scmnd)
{
        bool allowed = true;
        u8 scsi_op = scmnd->cmnd[0];

        switch (scsi_op) {
        /* the host does not handle WRITE_SAME, log accident usage */
        case WRITE_SAME:
        /*
         * smartd sends this command and the host does not handle
         * this. So, don't send it.
         */
        case SET_WINDOW:
                set_host_byte(scmnd, DID_ERROR);
                allowed = false;
                break;
        default:
                break;
        }
        return allowed;
}

static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
{
        int ret;
        struct hv_host_device *host_dev = shost_priv(host);
        struct hv_device *dev = host_dev->dev;
        struct storvsc_cmd_request *cmd_request = scsi_cmd_priv(scmnd);
        struct scatterlist *sgl;
        struct vmscsi_request *vm_srb;
        struct vmbus_packet_mpb_array  *payload;
        u32 payload_sz;
        u32 length;

        if (vmstor_proto_version <= VMSTOR_PROTO_VERSION_WIN8) {
                /*
                 * On legacy hosts filter unimplemented commands.
                 * Future hosts are expected to correctly handle
                 * unsupported commands. Furthermore, it is
                 * possible that some of the currently
                 * unsupported commands maybe supported in
                 * future versions of the host.
                 */
                if (!storvsc_scsi_cmd_ok(scmnd)) {
                        scsi_done(scmnd);
                        return 0;
                }
        }

        /* Setup the cmd request */
        cmd_request->cmd = scmnd;

        memset(&cmd_request->vstor_packet, 0, sizeof(struct vstor_packet));
        vm_srb = &cmd_request->vstor_packet.vm_srb;
        vm_srb->win8_extension.time_out_value = 60;

        vm_srb->win8_extension.srb_flags |=
                SRB_FLAGS_DISABLE_SYNCH_TRANSFER;

        if (scmnd->device->tagged_supported) {
                vm_srb->win8_extension.srb_flags |=
                (SRB_FLAGS_QUEUE_ACTION_ENABLE | SRB_FLAGS_NO_QUEUE_FREEZE);
                vm_srb->win8_extension.queue_tag = SP_UNTAGGED;
                vm_srb->win8_extension.queue_action = SRB_SIMPLE_TAG_REQUEST;
        }

        /* Build the SRB */
        switch (scmnd->sc_data_direction) {
        case DMA_TO_DEVICE:
                vm_srb->data_in = WRITE_TYPE;
                vm_srb->win8_extension.srb_flags |= SRB_FLAGS_DATA_OUT;
                break;
        case DMA_FROM_DEVICE:
                vm_srb->data_in = READ_TYPE;
                vm_srb->win8_extension.srb_flags |= SRB_FLAGS_DATA_IN;
                break;
        case DMA_NONE:
                vm_srb->data_in = UNKNOWN_TYPE;
                vm_srb->win8_extension.srb_flags |= SRB_FLAGS_NO_DATA_TRANSFER;
                break;
        default:
                /*
                 * This is DMA_BIDIRECTIONAL or something else we are never
                 * supposed to see here.
                 */
                WARN(1, "Unexpected data direction: %d\n",
                     scmnd->sc_data_direction);
                return -EINVAL;
        }


        vm_srb->port_number = host_dev->port;
        vm_srb->path_id = scmnd->device->channel;
        vm_srb->target_id = scmnd->device->id;
        vm_srb->lun = scmnd->device->lun;

        vm_srb->cdb_length = scmnd->cmd_len;

        memcpy(vm_srb->cdb, scmnd->cmnd, vm_srb->cdb_length);

        sgl = (struct scatterlist *)scsi_sglist(scmnd);

        length = scsi_bufflen(scmnd);
        payload = (struct vmbus_packet_mpb_array *)&cmd_request->mpb;
        payload_sz = sizeof(cmd_request->mpb);

        if (scsi_sg_count(scmnd)) {
                unsigned long offset_in_hvpg = offset_in_hvpage(sgl->offset);
                unsigned int hvpg_count = HVPFN_UP(offset_in_hvpg + length);
                struct scatterlist *sg;
                unsigned long hvpfn, hvpfns_to_add;
                int j, i = 0, sg_count;

                if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {

                        payload_sz = (hvpg_count * sizeof(u64) +
                                      sizeof(struct vmbus_packet_mpb_array));
                        payload = kzalloc(payload_sz, GFP_ATOMIC);
                        if (!payload)
                                return SCSI_MLQUEUE_DEVICE_BUSY;
                }

                payload->range.len = length;
                payload->range.offset = offset_in_hvpg;

                sg_count = scsi_dma_map(scmnd);
                if (sg_count < 0) {
                        ret = SCSI_MLQUEUE_DEVICE_BUSY;
                        goto err_free_payload;
                }

                for_each_sg(sgl, sg, sg_count, j) {
                        /*
                         * Init values for the current sgl entry. hvpfns_to_add
                         * is in units of Hyper-V size pages. Handling the
                         * PAGE_SIZE != HV_HYP_PAGE_SIZE case also handles
                         * values of sgl->offset that are larger than PAGE_SIZE.
                         * Such offsets are handled even on other than the first
                         * sgl entry, provided they are a multiple of PAGE_SIZE.
                         */
                        hvpfn = HVPFN_DOWN(sg_dma_address(sg));
                        hvpfns_to_add = HVPFN_UP(sg_dma_address(sg) +
                                                 sg_dma_len(sg)) - hvpfn;

                        /*
                         * Fill the next portion of the PFN array with
                         * sequential Hyper-V PFNs for the continguous physical
                         * memory described by the sgl entry. The end of the
                         * last sgl should be reached at the same time that
                         * the PFN array is filled.
                         */
                        while (hvpfns_to_add--)
                                payload->range.pfn_array[i++] = hvpfn++;
                }
        }

        cmd_request->payload = payload;
        cmd_request->payload_sz = payload_sz;

        /* Invokes the vsc to start an IO */
        ret = storvsc_do_io(dev, cmd_request, get_cpu());
        put_cpu();

        if (ret == -EAGAIN) {
                /* no more space */
                ret = SCSI_MLQUEUE_DEVICE_BUSY;
                goto err_free_payload;
        }

        return 0;

err_free_payload:
        if (payload_sz > sizeof(cmd_request->mpb))
                kfree(payload);

        return ret;
}

static struct scsi_host_template scsi_driver = {
        .module =               THIS_MODULE,
        .name =                 "storvsc_host_t",
        .cmd_size =             sizeof(struct storvsc_cmd_request),
        .bios_param =           storvsc_get_chs,
        .queuecommand =         storvsc_queuecommand,
        .eh_host_reset_handler =        storvsc_host_reset_handler,
        .proc_name =            "storvsc_host",
        .eh_timed_out =         storvsc_eh_timed_out,
        .slave_alloc =          storvsc_device_alloc,
        .slave_configure =      storvsc_device_configure,
        .cmd_per_lun =          2048,
        .this_id =              -1,
        /* Ensure there are no gaps in presented sgls */
        .virt_boundary_mask =   PAGE_SIZE-1,
        .no_write_same =        1,
        .track_queue_depth =    1,
        .change_queue_depth =   storvsc_change_queue_depth,
};

enum {
        SCSI_GUID,
        IDE_GUID,
        SFC_GUID,
};

static const struct hv_vmbus_device_id id_table[] = {
        /* SCSI guid */
        { HV_SCSI_GUID,
          .driver_data = SCSI_GUID
        },
        /* IDE guid */
        { HV_IDE_GUID,
          .driver_data = IDE_GUID
        },
        /* Fibre Channel GUID */
        {
          HV_SYNTHFC_GUID,
          .driver_data = SFC_GUID
        },
        { },
};

MODULE_DEVICE_TABLE(vmbus, id_table);

static const struct { guid_t guid; } fc_guid = { HV_SYNTHFC_GUID };

static bool hv_dev_is_fc(struct hv_device *hv_dev)
{
        return guid_equal(&fc_guid.guid, &hv_dev->dev_type);
}

static int storvsc_probe(struct hv_device *device,
                        const struct hv_vmbus_device_id *dev_id)
{
        int ret;
        int num_cpus = num_online_cpus();
        int num_present_cpus = num_present_cpus();
        struct Scsi_Host *host;
        struct hv_host_device *host_dev;
        bool dev_is_ide = ((dev_id->driver_data == IDE_GUID) ? true : false);
        bool is_fc = ((dev_id->driver_data == SFC_GUID) ? true : false);
        int target = 0;
        struct storvsc_device *stor_device;
        int max_luns_per_target;
        int max_targets;
        int max_channels;
        int max_sub_channels = 0;

        /*
         * Based on the windows host we are running on,
         * set state to properly communicate with the host.
         */

        if (vmbus_proto_version < VERSION_WIN8) {
                max_luns_per_target = STORVSC_IDE_MAX_LUNS_PER_TARGET;
                max_targets = STORVSC_IDE_MAX_TARGETS;
                max_channels = STORVSC_IDE_MAX_CHANNELS;
        } else {
                max_luns_per_target = STORVSC_MAX_LUNS_PER_TARGET;
                max_targets = STORVSC_MAX_TARGETS;
                max_channels = STORVSC_MAX_CHANNELS;
                /*
                 * On Windows8 and above, we support sub-channels for storage
                 * on SCSI and FC controllers.
                 * The number of sub-channels offerred is based on the number of
                 * VCPUs in the guest.
                 */
                if (!dev_is_ide)
                        max_sub_channels =
                                (num_cpus - 1) / storvsc_vcpus_per_sub_channel;
        }

        scsi_driver.can_queue = max_outstanding_req_per_channel *
                                (max_sub_channels + 1) *
                                (100 - ring_avail_percent_lowater) / 100;

        host = scsi_host_alloc(&scsi_driver,
                               sizeof(struct hv_host_device));
        if (!host)
                return -ENOMEM;

        host_dev = shost_priv(host);
        memset(host_dev, 0, sizeof(struct hv_host_device));

        host_dev->port = host->host_no;
        host_dev->dev = device;
        host_dev->host = host;


        stor_device = kzalloc(sizeof(struct storvsc_device), GFP_KERNEL);
        if (!stor_device) {
                ret = -ENOMEM;
                goto err_out0;
        }

        stor_device->destroy = false;
        init_waitqueue_head(&stor_device->waiting_to_drain);
        stor_device->device = device;
        stor_device->host = host;
        stor_device->vmscsi_size_delta = sizeof(struct vmscsi_win8_extension);
        spin_lock_init(&stor_device->lock);
        hv_set_drvdata(device, stor_device);
        dma_set_min_align_mask(&device->device, HV_HYP_PAGE_SIZE - 1);

        stor_device->port_number = host->host_no;
        ret = storvsc_connect_to_vsp(device, storvsc_ringbuffer_size, is_fc);
        if (ret)
                goto err_out1;

        host_dev->path = stor_device->path_id;
        host_dev->target = stor_device->target_id;

        switch (dev_id->driver_data) {
        case SFC_GUID:
                host->max_lun = STORVSC_FC_MAX_LUNS_PER_TARGET;
                host->max_id = STORVSC_FC_MAX_TARGETS;
                host->max_channel = STORVSC_FC_MAX_CHANNELS - 1;
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
                host->transportt = fc_transport_template;
#endif
                break;

        case SCSI_GUID:
                host->max_lun = max_luns_per_target;
                host->max_id = max_targets;
                host->max_channel = max_channels - 1;
                break;

        default:
                host->max_lun = STORVSC_IDE_MAX_LUNS_PER_TARGET;
                host->max_id = STORVSC_IDE_MAX_TARGETS;
                host->max_channel = STORVSC_IDE_MAX_CHANNELS - 1;
                break;
        }
        /* max cmd length */
        host->max_cmd_len = STORVSC_MAX_CMD_LEN;

        /*
         * set the table size based on the info we got
         * from the host.
         */
        host->sg_tablesize = (stor_device->max_transfer_bytes >> PAGE_SHIFT);
        /*
         * For non-IDE disks, the host supports multiple channels.
         * Set the number of HW queues we are supporting.
         */
        if (!dev_is_ide) {
                if (storvsc_max_hw_queues > num_present_cpus) {
                        storvsc_max_hw_queues = 0;
                        storvsc_log(device, STORVSC_LOGGING_WARN,
                                "Resetting invalid storvsc_max_hw_queues value to default.\n");
                }
                if (storvsc_max_hw_queues)
                        host->nr_hw_queues = storvsc_max_hw_queues;
                else
                        host->nr_hw_queues = num_present_cpus;
        }

        /*
         * Set the error handler work queue.
         */
        host_dev->handle_error_wq =
                        alloc_ordered_workqueue("storvsc_error_wq_%d",
                                                WQ_MEM_RECLAIM,
                                                host->host_no);
        if (!host_dev->handle_error_wq) {
                ret = -ENOMEM;
                goto err_out2;
        }
        INIT_WORK(&host_dev->host_scan_work, storvsc_host_scan);
        /* Register the HBA and start the scsi bus scan */
        ret = scsi_add_host(host, &device->device);
        if (ret != 0)
                goto err_out3;

        if (!dev_is_ide) {
                scsi_scan_host(host);
        } else {
                target = (device->dev_instance.b[5] << 8 |
                         device->dev_instance.b[4]);
                ret = scsi_add_device(host, 0, target, 0);
                if (ret)
                        goto err_out4;
        }
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        if (host->transportt == fc_transport_template) {
                struct fc_rport_identifiers ids = {
                        .roles = FC_PORT_ROLE_FCP_DUMMY_INITIATOR,
                };

                fc_host_node_name(host) = stor_device->node_name;
                fc_host_port_name(host) = stor_device->port_name;
                stor_device->rport = fc_remote_port_add(host, 0, &ids);
                if (!stor_device->rport) {
                        ret = -ENOMEM;
                        goto err_out4;
                }
        }
#endif
        return 0;

err_out4:
        scsi_remove_host(host);

err_out3:
        destroy_workqueue(host_dev->handle_error_wq);

err_out2:
        /*
         * Once we have connected with the host, we would need to
         * to invoke storvsc_dev_remove() to rollback this state and
         * this call also frees up the stor_device; hence the jump around
         * err_out1 label.
         */
        storvsc_dev_remove(device);
        goto err_out0;

err_out1:
        kfree(stor_device->stor_chns);
        kfree(stor_device);

err_out0:
        scsi_host_put(host);
        return ret;
}

/* Change a scsi target's queue depth */
static int storvsc_change_queue_depth(struct scsi_device *sdev, int queue_depth)
{
        if (queue_depth > scsi_driver.can_queue)
                queue_depth = scsi_driver.can_queue;

        return scsi_change_queue_depth(sdev, queue_depth);
}

static int storvsc_remove(struct hv_device *dev)
{
        struct storvsc_device *stor_device = hv_get_drvdata(dev);
        struct Scsi_Host *host = stor_device->host;
        struct hv_host_device *host_dev = shost_priv(host);

#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        if (host->transportt == fc_transport_template) {
                fc_remote_port_delete(stor_device->rport);
                fc_remove_host(host);
        }
#endif
        destroy_workqueue(host_dev->handle_error_wq);
        scsi_remove_host(host);
        storvsc_dev_remove(dev);
        scsi_host_put(host);

        return 0;
}

static int storvsc_suspend(struct hv_device *hv_dev)
{
        struct storvsc_device *stor_device = hv_get_drvdata(hv_dev);
        struct Scsi_Host *host = stor_device->host;
        struct hv_host_device *host_dev = shost_priv(host);

        storvsc_wait_to_drain(stor_device);

        drain_workqueue(host_dev->handle_error_wq);

        vmbus_close(hv_dev->channel);

        kfree(stor_device->stor_chns);
        stor_device->stor_chns = NULL;

        cpumask_clear(&stor_device->alloced_cpus);

        return 0;
}

static int storvsc_resume(struct hv_device *hv_dev)
{
        int ret;

        ret = storvsc_connect_to_vsp(hv_dev, storvsc_ringbuffer_size,
                                     hv_dev_is_fc(hv_dev));
        return ret;
}

static struct hv_driver storvsc_drv = {
        .name = KBUILD_MODNAME,
        .id_table = id_table,
        .probe = storvsc_probe,
        .remove = storvsc_remove,
        .suspend = storvsc_suspend,
        .resume = storvsc_resume,
        .driver = {
                .probe_type = PROBE_PREFER_ASYNCHRONOUS,
        },
};

#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
static struct fc_function_template fc_transport_functions = {
        .show_host_node_name = 1,
        .show_host_port_name = 1,
};
#endif

static int __init storvsc_drv_init(void)
{
        int ret;

        /*
         * Divide the ring buffer data size (which is 1 page less
         * than the ring buffer size since that page is reserved for
         * the ring buffer indices) by the max request size (which is
         * vmbus_channel_packet_multipage_buffer + struct vstor_packet + u64)
         *
         * The computation underestimates max_outstanding_req_per_channel
         * for Win7 and older hosts because it does not take into account
         * the vmscsi_size_delta correction to the max request size.
         */
        max_outstanding_req_per_channel =
                ((storvsc_ringbuffer_size - PAGE_SIZE) /
                ALIGN(MAX_MULTIPAGE_BUFFER_PACKET +
                sizeof(struct vstor_packet) + sizeof(u64),
                sizeof(u64)));

#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        fc_transport_template = fc_attach_transport(&fc_transport_functions);
        if (!fc_transport_template)
                return -ENODEV;
#endif

        ret = vmbus_driver_register(&storvsc_drv);

#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        if (ret)
                fc_release_transport(fc_transport_template);
#endif

        return ret;
}

static void __exit storvsc_drv_exit(void)
{
        vmbus_driver_unregister(&storvsc_drv);
#if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
        fc_release_transport(fc_transport_template);
#endif
}

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Microsoft Hyper-V virtual storage driver");
module_init(storvsc_drv_init);
module_exit(storvsc_drv_exit);