/*
 * Copyright (c) 2009, Microsoft Corporation.
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place - Suite 330, Boston, MA 02111-1307 USA.
 *
 * Authors:
 *   Haiyang Zhang <haiyangz@microsoft.com>
 *   Hank Janssen  <hjanssen@microsoft.com>
 */
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/blkdev.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 "osd.h"
#include "logging.h"
#include "version_info.h"
#include "vmbus.h"
#include "storvsc_api.h"


struct host_device_context {
        /* must be 1st field
         * FIXME this is a bug */
        /* point back to our device context */
        struct vm_device *device_ctx;
        struct kmem_cache *request_pool;
        unsigned int port;
        unsigned char path;
        unsigned char target;
};

struct storvsc_cmd_request {
        struct list_head entry;
        struct scsi_cmnd *cmd;

        unsigned int bounce_sgl_count;
        struct scatterlist *bounce_sgl;

        struct hv_storvsc_request request;
        /* !!!DO NOT ADD ANYTHING BELOW HERE!!! */
        /* The extension buffer falls right here and is pointed to by
         * request.Extension;
         * Which sounds like a very bad design... */
};

struct storvsc_driver_context {
        /* !! These must be the first 2 fields !! */
        /* FIXME this is a bug... */
        struct driver_context drv_ctx;
        struct storvsc_driver_object drv_obj;
};

/* Static decl */
static int storvsc_probe(struct device *dev);
static int storvsc_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd);
static int storvsc_device_alloc(struct scsi_device *);
static int storvsc_device_configure(struct scsi_device *);
static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd);
static int storvsc_remove(struct device *dev);

static struct scatterlist *create_bounce_buffer(struct scatterlist *sgl,
                                                unsigned int sg_count,
                                                unsigned int len);
static void destroy_bounce_buffer(struct scatterlist *sgl,
                                  unsigned int sg_count);
static int do_bounce_buffer(struct scatterlist *sgl, unsigned int sg_count);
static unsigned int copy_from_bounce_buffer(struct scatterlist *orig_sgl,
                                            struct scatterlist *bounce_sgl,
                                            unsigned int orig_sgl_count);
static unsigned int copy_to_bounce_buffer(struct scatterlist *orig_sgl,
                                          struct scatterlist *bounce_sgl,
                                          unsigned int orig_sgl_count);

static int storvsc_get_chs(struct scsi_device *sdev, struct block_device *bdev,
                           sector_t capacity, int *info);


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

/* The one and only one */
static struct storvsc_driver_context g_storvsc_drv;

/* Scsi driver */
static struct scsi_host_template scsi_driver = {
        .module =               THIS_MODULE,
        .name =                 "storvsc_host_t",
        .bios_param =           storvsc_get_chs,
        .queuecommand =         storvsc_queuecommand,
        .eh_host_reset_handler =        storvsc_host_reset_handler,
        .slave_alloc =          storvsc_device_alloc,
        .slave_configure =      storvsc_device_configure,
        .cmd_per_lun =          1,
        /* 64 max_queue * 1 target */
        .can_queue =            STORVSC_MAX_IO_REQUESTS*STORVSC_MAX_TARGETS,
        .this_id =              -1,
        /* no use setting to 0 since ll_blk_rw reset it to 1 */
        /* currently 32 */
        .sg_tablesize =         MAX_MULTIPAGE_BUFFER_COUNT,
        /*
         * ENABLE_CLUSTERING allows mutiple physically contig bio_vecs to merge
         * into 1 sg element. If set, we must limit the max_segment_size to
         * PAGE_SIZE, otherwise we may get 1 sg element that represents
         * multiple
         */
        /* physically contig pfns (ie sg[x].length > PAGE_SIZE). */
        .use_clustering =       ENABLE_CLUSTERING,
        /* Make sure we dont get a sg segment crosses a page boundary */
        .dma_boundary =         PAGE_SIZE-1,
};


/*
 * storvsc_drv_init - StorVsc driver initialization.
 */
static int storvsc_drv_init(int (*drv_init)(struct hv_driver *drv))
{
        int ret;
        struct storvsc_driver_object *storvsc_drv_obj = &g_storvsc_drv.drv_obj;
        struct driver_context *drv_ctx = &g_storvsc_drv.drv_ctx;

        storvsc_drv_obj->ring_buffer_size = storvsc_ringbuffer_size;

        /* Callback to client driver to complete the initialization */
        drv_init(&storvsc_drv_obj->base);

        DPRINT_INFO(STORVSC_DRV,
                    "request extension size %u, max outstanding reqs %u",
                    storvsc_drv_obj->request_ext_size,
                    storvsc_drv_obj->max_outstanding_req_per_channel);

        if (storvsc_drv_obj->max_outstanding_req_per_channel <
            STORVSC_MAX_IO_REQUESTS) {
                DPRINT_ERR(STORVSC_DRV,
                           "The number of outstanding io requests (%d) "
                           "is larger than that supported (%d) internally.",
                           STORVSC_MAX_IO_REQUESTS,
                           storvsc_drv_obj->max_outstanding_req_per_channel);
                return -1;
        }

        drv_ctx->driver.name = storvsc_drv_obj->base.name;
        memcpy(&drv_ctx->class_id, &storvsc_drv_obj->base.deviceType,
               sizeof(struct hv_guid));

        drv_ctx->probe = storvsc_probe;
        drv_ctx->remove = storvsc_remove;

        /* The driver belongs to vmbus */
        ret = vmbus_child_driver_register(drv_ctx);

        return ret;
}

static int storvsc_drv_exit_cb(struct device *dev, void *data)
{
        struct device **curr = (struct device **)data;
        *curr = dev;
        return 1; /* stop iterating */
}

static void storvsc_drv_exit(void)
{
        struct storvsc_driver_object *storvsc_drv_obj = &g_storvsc_drv.drv_obj;
        struct driver_context *drv_ctx = &g_storvsc_drv.drv_ctx;
        struct device *current_dev = NULL;
        int ret;

        while (1) {
                current_dev = NULL;

                /* Get the device */
                ret = driver_for_each_device(&drv_ctx->driver, NULL,
                                             (void *) &current_dev,
                                             storvsc_drv_exit_cb);

                if (ret)
                        DPRINT_WARN(STORVSC_DRV,
                                    "driver_for_each_device returned %d", ret);

                if (current_dev == NULL)
                        break;

                /* Initiate removal from the top-down */
                device_unregister(current_dev);
        }

        if (storvsc_drv_obj->base.OnCleanup)
                storvsc_drv_obj->base.OnCleanup(&storvsc_drv_obj->base);

        vmbus_child_driver_unregister(drv_ctx);
        return;
}

/*
 * storvsc_probe - Add a new device for this driver
 */
static int storvsc_probe(struct device *device)
{
        int ret;
        struct driver_context *driver_ctx =
                                driver_to_driver_context(device->driver);
        struct storvsc_driver_context *storvsc_drv_ctx =
                                (struct storvsc_driver_context *)driver_ctx;
        struct storvsc_driver_object *storvsc_drv_obj =
                                &storvsc_drv_ctx->drv_obj;
        struct vm_device *device_ctx = device_to_vm_device(device);
        struct hv_device *device_obj = &device_ctx->device_obj;
        struct Scsi_Host *host;
        struct host_device_context *host_device_ctx;
        struct storvsc_device_info device_info;

        if (!storvsc_drv_obj->base.OnDeviceAdd)
                return -1;

        host = scsi_host_alloc(&scsi_driver,
                               sizeof(struct host_device_context));
        if (!host) {
                DPRINT_ERR(STORVSC_DRV, "unable to allocate scsi host object");
                return -ENOMEM;
        }

        dev_set_drvdata(device, host);

        host_device_ctx = (struct host_device_context *)host->hostdata;
        memset(host_device_ctx, 0, sizeof(struct host_device_context));

        host_device_ctx->port = host->host_no;
        host_device_ctx->device_ctx = device_ctx;

        host_device_ctx->request_pool =
                                kmem_cache_create(dev_name(&device_ctx->device),
                                        sizeof(struct storvsc_cmd_request) +
                                        storvsc_drv_obj->request_ext_size, 0,
                                        SLAB_HWCACHE_ALIGN, NULL);

        if (!host_device_ctx->request_pool) {
                scsi_host_put(host);
                return -ENOMEM;
        }

        device_info.port_number = host->host_no;
        /* Call to the vsc driver to add the device */
        ret = storvsc_drv_obj->base.OnDeviceAdd(device_obj,
                                                (void *)&device_info);
        if (ret != 0) {
                DPRINT_ERR(STORVSC_DRV, "unable to add scsi vsc device");
                kmem_cache_destroy(host_device_ctx->request_pool);
                scsi_host_put(host);
                return -1;
        }

        /* host_device_ctx->port = device_info.PortNumber; */
        host_device_ctx->path = device_info.path_id;
        host_device_ctx->target = device_info.target_id;

        /* max # of devices per target */
        host->max_lun = STORVSC_MAX_LUNS_PER_TARGET;
        /* max # of targets per channel */
        host->max_id = STORVSC_MAX_TARGETS;
        /* max # of channels */
        host->max_channel = STORVSC_MAX_CHANNELS - 1;

        /* Register the HBA and start the scsi bus scan */
        ret = scsi_add_host(host, device);
        if (ret != 0) {
                DPRINT_ERR(STORVSC_DRV, "unable to add scsi host device");

                storvsc_drv_obj->base.OnDeviceRemove(device_obj);

                kmem_cache_destroy(host_device_ctx->request_pool);
                scsi_host_put(host);
                return -1;
        }

        scsi_scan_host(host);
        return ret;
}

/*
 * storvsc_remove - Callback when our device is removed
 */
static int storvsc_remove(struct device *device)
{
        int ret;
        struct driver_context *driver_ctx =
                        driver_to_driver_context(device->driver);
        struct storvsc_driver_context *storvsc_drv_ctx =
                        (struct storvsc_driver_context *)driver_ctx;
        struct storvsc_driver_object *storvsc_drv_obj =
                        &storvsc_drv_ctx->drv_obj;
        struct vm_device *device_ctx = device_to_vm_device(device);
        struct hv_device *device_obj = &device_ctx->device_obj;
        struct Scsi_Host *host = dev_get_drvdata(device);
        struct host_device_context *host_device_ctx =
                        (struct host_device_context *)host->hostdata;


        if (!storvsc_drv_obj->base.OnDeviceRemove)
                return -1;

        /*
         * Call to the vsc driver to let it know that the device is being
         * removed
         */
        ret = storvsc_drv_obj->base.OnDeviceRemove(device_obj);
        if (ret != 0) {
                /* TODO: */
                DPRINT_ERR(STORVSC, "unable to remove vsc device (ret %d)",
                           ret);
        }

        if (host_device_ctx->request_pool) {
                kmem_cache_destroy(host_device_ctx->request_pool);
                host_device_ctx->request_pool = NULL;
        }

        DPRINT_INFO(STORVSC, "removing host adapter (%p)...", host);
        scsi_remove_host(host);

        DPRINT_INFO(STORVSC, "releasing host adapter (%p)...", host);
        scsi_host_put(host);
        return ret;
}

/*
 * storvsc_commmand_completion - Command completion processing
 */
static void storvsc_commmand_completion(struct hv_storvsc_request *request)
{
        struct storvsc_cmd_request *cmd_request =
                (struct storvsc_cmd_request *)request->context;
        struct scsi_cmnd *scmnd = cmd_request->cmd;
        struct host_device_context *host_device_ctx =
                (struct host_device_context *)scmnd->device->host->hostdata;
        void (*scsi_done_fn)(struct scsi_cmnd *);
        struct scsi_sense_hdr sense_hdr;

        /* ASSERT(request == &cmd_request->request); */
        /* ASSERT(scmnd); */
        /* ASSERT((unsigned long)scmnd->host_scribble == */
        /*        (unsigned long)cmd_request); */
        /* ASSERT(scmnd->scsi_done); */

        if (cmd_request->bounce_sgl_count) {
                /* using bounce buffer */
                /* printk("copy_from_bounce_buffer\n"); */

                /* FIXME: We can optimize on writes by just skipping this */
                copy_from_bounce_buffer(scsi_sglist(scmnd),
                                        cmd_request->bounce_sgl,
                                        scsi_sg_count(scmnd));
                destroy_bounce_buffer(cmd_request->bounce_sgl,
                                      cmd_request->bounce_sgl_count);
        }

        scmnd->result = request->status;

        if (scmnd->result) {
                if (scsi_normalize_sense(scmnd->sense_buffer,
                                request->sense_buffer_size, &sense_hdr))
                        scsi_print_sense_hdr("storvsc", &sense_hdr);
        }

        /* ASSERT(request->BytesXfer <= request->data_buffer.Length); */
        scsi_set_resid(scmnd,
                request->data_buffer.Length - request->bytes_xfer);

        scsi_done_fn = scmnd->scsi_done;

        scmnd->host_scribble = NULL;
        scmnd->scsi_done = NULL;

        /* !!DO NOT MODIFY the scmnd after this call */
        scsi_done_fn(scmnd);

        kmem_cache_free(host_device_ctx->request_pool, cmd_request);
}

static int do_bounce_buffer(struct scatterlist *sgl, unsigned int sg_count)
{
        int i;

        /* No need to check */
        if (sg_count < 2)
                return -1;

        /* We have at least 2 sg entries */
        for (i = 0; i < sg_count; i++) {
                if (i == 0) {
                        /* make sure 1st one does not have hole */
                        if (sgl[i].offset + sgl[i].length != PAGE_SIZE)
                                return i;
                } else if (i == sg_count - 1) {
                        /* make sure last one does not have hole */
                        if (sgl[i].offset != 0)
                                return i;
                } else {
                        /* make sure no hole in the middle */
                        if (sgl[i].length != PAGE_SIZE || sgl[i].offset != 0)
                                return i;
                }
        }
        return -1;
}

static struct scatterlist *create_bounce_buffer(struct scatterlist *sgl,
                                                unsigned int sg_count,
                                                unsigned int len)
{
        int i;
        int num_pages;
        struct scatterlist *bounce_sgl;
        struct page *page_buf;

        num_pages = ALIGN_UP(len, PAGE_SIZE) >> PAGE_SHIFT;

        bounce_sgl = kcalloc(num_pages, sizeof(struct scatterlist), GFP_ATOMIC);
        if (!bounce_sgl)
                return NULL;

        for (i = 0; i < num_pages; i++) {
                page_buf = alloc_page(GFP_ATOMIC);
                if (!page_buf)
                        goto cleanup;
                sg_set_page(&bounce_sgl[i], page_buf, 0, 0);
        }

        return bounce_sgl;

cleanup:
        destroy_bounce_buffer(bounce_sgl, num_pages);
        return NULL;
}

static void destroy_bounce_buffer(struct scatterlist *sgl,
                                  unsigned int sg_count)
{
        int i;
        struct page *page_buf;

        for (i = 0; i < sg_count; i++) {
                page_buf = sg_page((&sgl[i]));
                if (page_buf != NULL)
                        __free_page(page_buf);
        }

        kfree(sgl);
}

/* Assume the bounce_sgl has enough room ie using the create_bounce_buffer() */
static unsigned int copy_to_bounce_buffer(struct scatterlist *orig_sgl,
                                          struct scatterlist *bounce_sgl,
                                          unsigned int orig_sgl_count)
{
        int i;
        int j = 0;
        unsigned long src, dest;
        unsigned int srclen, destlen, copylen;
        unsigned int total_copied = 0;
        unsigned long bounce_addr = 0;
        unsigned long src_addr = 0;
        unsigned long flags;

        local_irq_save(flags);

        for (i = 0; i < orig_sgl_count; i++) {
                src_addr = (unsigned long)kmap_atomic(sg_page((&orig_sgl[i])),
                                KM_IRQ0) + orig_sgl[i].offset;
                src = src_addr;
                srclen = orig_sgl[i].length;

                /* ASSERT(orig_sgl[i].offset + orig_sgl[i].length <= PAGE_SIZE); */

                if (bounce_addr == 0)
                        bounce_addr = (unsigned long)kmap_atomic(sg_page((&bounce_sgl[j])), KM_IRQ0);

                while (srclen) {
                        /* assume bounce offset always == 0 */
                        dest = bounce_addr + bounce_sgl[j].length;
                        destlen = PAGE_SIZE - bounce_sgl[j].length;

                        copylen = min(srclen, destlen);
                        memcpy((void *)dest, (void *)src, copylen);

                        total_copied += copylen;
                        bounce_sgl[j].length += copylen;
                        srclen -= copylen;
                        src += copylen;

                        if (bounce_sgl[j].length == PAGE_SIZE) {
                                /* full..move to next entry */
                                kunmap_atomic((void *)bounce_addr, KM_IRQ0);
                                j++;

                                /* if we need to use another bounce buffer */
                                if (srclen || i != orig_sgl_count - 1)
                                        bounce_addr = (unsigned long)kmap_atomic(sg_page((&bounce_sgl[j])), KM_IRQ0);
                        } else if (srclen == 0 && i == orig_sgl_count - 1) {
                                /* unmap the last bounce that is < PAGE_SIZE */
                                kunmap_atomic((void *)bounce_addr, KM_IRQ0);
                        }
                }

                kunmap_atomic((void *)(src_addr - orig_sgl[i].offset), KM_IRQ0);
        }

        local_irq_restore(flags);

        return total_copied;
}

/* Assume the original sgl has enough room */
static unsigned int copy_from_bounce_buffer(struct scatterlist *orig_sgl,
                                            struct scatterlist *bounce_sgl,
                                            unsigned int orig_sgl_count)
{
        int i;
        int j = 0;
        unsigned long src, dest;
        unsigned int srclen, destlen, copylen;
        unsigned int total_copied = 0;
        unsigned long bounce_addr = 0;
        unsigned long dest_addr = 0;
        unsigned long flags;

        local_irq_save(flags);

        for (i = 0; i < orig_sgl_count; i++) {
                dest_addr = (unsigned long)kmap_atomic(sg_page((&orig_sgl[i])),
                                        KM_IRQ0) + orig_sgl[i].offset;
                dest = dest_addr;
                destlen = orig_sgl[i].length;
                /* ASSERT(orig_sgl[i].offset + orig_sgl[i].length <= PAGE_SIZE); */

                if (bounce_addr == 0)
                        bounce_addr = (unsigned long)kmap_atomic(sg_page((&bounce_sgl[j])), KM_IRQ0);

                while (destlen) {
                        src = bounce_addr + bounce_sgl[j].offset;
                        srclen = bounce_sgl[j].length - bounce_sgl[j].offset;

                        copylen = min(srclen, destlen);
                        memcpy((void *)dest, (void *)src, copylen);

                        total_copied += copylen;
                        bounce_sgl[j].offset += copylen;
                        destlen -= copylen;
                        dest += copylen;

                        if (bounce_sgl[j].offset == bounce_sgl[j].length) {
                                /* full */
                                kunmap_atomic((void *)bounce_addr, KM_IRQ0);
                                j++;

                                /* if we need to use another bounce buffer */
                                if (destlen || i != orig_sgl_count - 1)
                                        bounce_addr = (unsigned long)kmap_atomic(sg_page((&bounce_sgl[j])), KM_IRQ0);
                        } else if (destlen == 0 && i == orig_sgl_count - 1) {
                                /* unmap the last bounce that is < PAGE_SIZE */
                                kunmap_atomic((void *)bounce_addr, KM_IRQ0);
                        }
                }

                kunmap_atomic((void *)(dest_addr - orig_sgl[i].offset),
                              KM_IRQ0);
        }

        local_irq_restore(flags);

        return total_copied;
}

/*
 * storvsc_queuecommand - Initiate command processing
 */
static int storvsc_queuecommand_lck(struct scsi_cmnd *scmnd,
                                void (*done)(struct scsi_cmnd *))
{
        int ret;
        struct host_device_context *host_device_ctx =
                (struct host_device_context *)scmnd->device->host->hostdata;
        struct vm_device *device_ctx = host_device_ctx->device_ctx;
        struct driver_context *driver_ctx =
                driver_to_driver_context(device_ctx->device.driver);
        struct storvsc_driver_context *storvsc_drv_ctx =
                (struct storvsc_driver_context *)driver_ctx;
        struct storvsc_driver_object *storvsc_drv_obj =
                &storvsc_drv_ctx->drv_obj;
        struct hv_storvsc_request *request;
        struct storvsc_cmd_request *cmd_request;
        unsigned int request_size = 0;
        int i;
        struct scatterlist *sgl;
        unsigned int sg_count = 0;

        DPRINT_DBG(STORVSC_DRV, "scmnd %p dir %d, use_sg %d buf %p len %d "
                   "queue depth %d tagged %d", scmnd, scmnd->sc_data_direction,
                   scsi_sg_count(scmnd), scsi_sglist(scmnd),
                   scsi_bufflen(scmnd), scmnd->device->queue_depth,
                   scmnd->device->tagged_supported);

        /* If retrying, no need to prep the cmd */
        if (scmnd->host_scribble) {
                /* ASSERT(scmnd->scsi_done != NULL); */

                cmd_request =
                        (struct storvsc_cmd_request *)scmnd->host_scribble;
                DPRINT_INFO(STORVSC_DRV, "retrying scmnd %p cmd_request %p",
                            scmnd, cmd_request);

                goto retry_request;
        }

        /* ASSERT(scmnd->scsi_done == NULL); */
        /* ASSERT(scmnd->host_scribble == NULL); */

        scmnd->scsi_done = done;

        request_size = sizeof(struct storvsc_cmd_request);

        cmd_request = kmem_cache_alloc(host_device_ctx->request_pool,
                                       GFP_ATOMIC);
        if (!cmd_request) {
                DPRINT_ERR(STORVSC_DRV, "scmnd (%p) - unable to allocate "
                           "storvsc_cmd_request...marking queue busy", scmnd);
                scmnd->scsi_done = NULL;
                return SCSI_MLQUEUE_DEVICE_BUSY;
        }

        /* Setup the cmd request */
        cmd_request->bounce_sgl_count = 0;
        cmd_request->bounce_sgl = NULL;
        cmd_request->cmd = scmnd;

        scmnd->host_scribble = (unsigned char *)cmd_request;

        request = &cmd_request->request;

        request->extension =
                (void *)((unsigned long)cmd_request + request_size);
        DPRINT_DBG(STORVSC_DRV, "req %p size %d ext %d", request, request_size,
                   storvsc_drv_obj->request_ext_size);

        /* Build the SRB */
        switch (scmnd->sc_data_direction) {
        case DMA_TO_DEVICE:
                request->type = WRITE_TYPE;
                break;
        case DMA_FROM_DEVICE:
                request->type = READ_TYPE;
                break;
        default:
                request->type = UNKNOWN_TYPE;
                break;
        }

        request->on_io_completion = storvsc_commmand_completion;
        request->context = cmd_request;/* scmnd; */

        /* request->PortId = scmnd->device->channel; */
        request->host = host_device_ctx->port;
        request->bus = scmnd->device->channel;
        request->target_id = scmnd->device->id;
        request->lun_id = scmnd->device->lun;

        /* ASSERT(scmnd->cmd_len <= 16); */
        request->cdb_len = scmnd->cmd_len;
        request->cdb = scmnd->cmnd;

        request->sense_buffer = scmnd->sense_buffer;
        request->sense_buffer_size = SCSI_SENSE_BUFFERSIZE;


        request->data_buffer.Length = scsi_bufflen(scmnd);
        if (scsi_sg_count(scmnd)) {
                sgl = (struct scatterlist *)scsi_sglist(scmnd);
                sg_count = scsi_sg_count(scmnd);

                /* check if we need to bounce the sgl */
                if (do_bounce_buffer(sgl, scsi_sg_count(scmnd)) != -1) {
                        DPRINT_INFO(STORVSC_DRV,
                                    "need to bounce buffer for this scmnd %p",
                                    scmnd);
                        cmd_request->bounce_sgl =
                                create_bounce_buffer(sgl, scsi_sg_count(scmnd),
                                                     scsi_bufflen(scmnd));
                        if (!cmd_request->bounce_sgl) {
                                DPRINT_ERR(STORVSC_DRV,
                                           "unable to create bounce buffer for "
                                           "this scmnd %p", scmnd);

                                scmnd->scsi_done = NULL;
                                scmnd->host_scribble = NULL;
                                kmem_cache_free(host_device_ctx->request_pool,
                                                cmd_request);

                                return SCSI_MLQUEUE_HOST_BUSY;
                        }

                        cmd_request->bounce_sgl_count =
                                ALIGN_UP(scsi_bufflen(scmnd), PAGE_SIZE) >>
                                        PAGE_SHIFT;

                        /*
                         * FIXME: We can optimize on reads by just skipping
                         * this
                         */
                        copy_to_bounce_buffer(sgl, cmd_request->bounce_sgl,
                                              scsi_sg_count(scmnd));

                        sgl = cmd_request->bounce_sgl;
                        sg_count = cmd_request->bounce_sgl_count;
                }

                request->data_buffer.Offset = sgl[0].offset;

                for (i = 0; i < sg_count; i++) {
                        DPRINT_DBG(STORVSC_DRV, "sgl[%d] len %d offset %d\n",
                                   i, sgl[i].length, sgl[i].offset);
                        request->data_buffer.PfnArray[i] =
                                page_to_pfn(sg_page((&sgl[i])));
                }
        } else if (scsi_sglist(scmnd)) {
                /* ASSERT(scsi_bufflen(scmnd) <= PAGE_SIZE); */
                request->data_buffer.Offset =
                        virt_to_phys(scsi_sglist(scmnd)) & (PAGE_SIZE-1);
                request->data_buffer.PfnArray[0] =
                        virt_to_phys(scsi_sglist(scmnd)) >> PAGE_SHIFT;
        }

retry_request:
        /* Invokes the vsc to start an IO */
        ret = storvsc_drv_obj->on_io_request(&device_ctx->device_obj,
                                           &cmd_request->request);
        if (ret == -1) {
                /* no more space */
                DPRINT_ERR(STORVSC_DRV,
                           "scmnd (%p) - queue FULL...marking queue busy",
                           scmnd);

                if (cmd_request->bounce_sgl_count) {
                        /*
                         * FIXME: We can optimize on writes by just skipping
                         * this
                         */
                        copy_from_bounce_buffer(scsi_sglist(scmnd),
                                                cmd_request->bounce_sgl,
                                                scsi_sg_count(scmnd));
                        destroy_bounce_buffer(cmd_request->bounce_sgl,
                                              cmd_request->bounce_sgl_count);
                }

                kmem_cache_free(host_device_ctx->request_pool, cmd_request);

                scmnd->scsi_done = NULL;
                scmnd->host_scribble = NULL;

                ret = SCSI_MLQUEUE_DEVICE_BUSY;
        }

        return ret;
}

static DEF_SCSI_QCMD(storvsc_queuecommand)

static int storvsc_merge_bvec(struct request_queue *q,
                              struct bvec_merge_data *bmd, struct bio_vec *bvec)
{
        /* checking done by caller. */
        return bvec->bv_len;
}

/*
 * storvsc_device_configure - Configure the specified scsi device
 */
static int storvsc_device_alloc(struct scsi_device *sdevice)
{
        DPRINT_DBG(STORVSC_DRV, "sdev (%p) - setting device flag to %d",
                   sdevice, BLIST_SPARSELUN);
        /*
         * This enables luns to be located sparsely. Otherwise, we may not
         * discovered them.
         */
        sdevice->sdev_bflags |= BLIST_SPARSELUN | BLIST_LARGELUN;
        return 0;
}

static int storvsc_device_configure(struct scsi_device *sdevice)
{
        DPRINT_INFO(STORVSC_DRV, "sdev (%p) - curr queue depth %d", sdevice,
                    sdevice->queue_depth);

        DPRINT_INFO(STORVSC_DRV, "sdev (%p) - setting queue depth to %d",
                    sdevice, STORVSC_MAX_IO_REQUESTS);
        scsi_adjust_queue_depth(sdevice, MSG_SIMPLE_TAG,
                                STORVSC_MAX_IO_REQUESTS);

        DPRINT_INFO(STORVSC_DRV, "sdev (%p) - setting max segment size to %ld",
                    sdevice, PAGE_SIZE);
        blk_queue_max_segment_size(sdevice->request_queue, PAGE_SIZE);

        DPRINT_INFO(STORVSC_DRV, "sdev (%p) - adding merge bio vec routine",
                    sdevice);
        blk_queue_merge_bvec(sdevice->request_queue, storvsc_merge_bvec);

        blk_queue_bounce_limit(sdevice->request_queue, BLK_BOUNCE_ANY);
        /* sdevice->timeout = (2000 * HZ);//(75 * HZ); */

        return 0;
}

/*
 * storvsc_host_reset_handler - Reset the scsi HBA
 */
static int storvsc_host_reset_handler(struct scsi_cmnd *scmnd)
{
        int ret;
        struct host_device_context *host_device_ctx =
                (struct host_device_context *)scmnd->device->host->hostdata;
        struct vm_device *device_ctx = host_device_ctx->device_ctx;

        DPRINT_INFO(STORVSC_DRV, "sdev (%p) dev obj (%p) - host resetting...",
                    scmnd->device, &device_ctx->device_obj);

        /* Invokes the vsc to reset the host/bus */
        ret = stor_vsc_on_host_reset(&device_ctx->device_obj);
        if (ret != 0)
                return ret;

        DPRINT_INFO(STORVSC_DRV, "sdev (%p) dev obj (%p) - host reseted",
                    scmnd->device, &device_ctx->device_obj);

        return ret;
}

static int storvsc_get_chs(struct scsi_device *sdev, struct block_device * bdev,
                           sector_t capacity, int *info)
{
        sector_t total_sectors = capacity;
        sector_t cylinder_times_heads = 0;
        sector_t temp = 0;

        int sectors_per_track = 0;
        int heads = 0;
        int cylinders = 0;
        int rem = 0;

        if (total_sectors > (65535 * 16 * 255))
                total_sectors = (65535 * 16 * 255);

        if (total_sectors >= (65535 * 16 * 63)) {
                sectors_per_track = 255;
                heads = 16;

                cylinder_times_heads = total_sectors;
                /* sector_div stores the quotient in cylinder_times_heads */
                rem = sector_div(cylinder_times_heads, sectors_per_track);
        } else {
                sectors_per_track = 17;

                cylinder_times_heads = total_sectors;
                /* sector_div stores the quotient in cylinder_times_heads */
                rem = sector_div(cylinder_times_heads, sectors_per_track);

                temp = cylinder_times_heads + 1023;
                /* sector_div stores the quotient in temp */
                rem = sector_div(temp, 1024);

                heads = temp;

                if (heads < 4)
                        heads = 4;

                if (cylinder_times_heads >= (heads * 1024) || (heads > 16)) {
                        sectors_per_track = 31;
                        heads = 16;

                        cylinder_times_heads = total_sectors;
                        /*
                         * sector_div stores the quotient in
                         * cylinder_times_heads
                         */
                        rem = sector_div(cylinder_times_heads,
                                         sectors_per_track);
                }

                if (cylinder_times_heads >= (heads * 1024)) {
                        sectors_per_track = 63;
                        heads = 16;

                        cylinder_times_heads = total_sectors;
                        /*
                         * sector_div stores the quotient in
                         * cylinder_times_heads
                         */
                        rem = sector_div(cylinder_times_heads,
                                         sectors_per_track);
                }
        }

        temp = cylinder_times_heads;
        /* sector_div stores the quotient in temp */
        rem = sector_div(temp, heads);
        cylinders = temp;

        info[0] = heads;
        info[1] = sectors_per_track;
        info[2] = cylinders;

        DPRINT_INFO(STORVSC_DRV, "CHS (%d, %d, %d)", cylinders, heads,
                    sectors_per_track);

    return 0;
}

static int __init storvsc_init(void)
{
        int ret;

        DPRINT_INFO(STORVSC_DRV, "Storvsc initializing....");
        ret = storvsc_drv_init(stor_vsc_initialize);
        return ret;
}

static void __exit storvsc_exit(void)
{
        storvsc_drv_exit();
}

MODULE_LICENSE("GPL");
MODULE_VERSION(HV_DRV_VERSION);
MODULE_DESCRIPTION("Microsoft Hyper-V virtual storage driver");
module_init(storvsc_init);
module_exit(storvsc_exit);