/*
   * Xen SCSI frontend driver
   *
   * Copyright (c) 2008, FUJITSU Limited
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License version 2
   * as published by the Free Software Foundation; or, when distributed
   * separately from the Linux kernel or incorporated into other
   * software packages, subject to the following license:
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this source file (the "Software"), to deal in the Software without
   * restriction, including without limitation the rights to use, copy, modify,
   * merge, publish, distribute, sublicense, and/or sell copies of the Software,
   * and to permit persons to whom the Software is furnished to do so, subject to
   * the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
   * IN THE SOFTWARE.
   */
  
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/device.h>
  #include <linux/wait.h>
  #include <linux/interrupt.h>
  #include <linux/mutex.h>
  #include <linux/spinlock.h>
  #include <linux/sched.h>
  #include <linux/blkdev.h>
  #include <linux/pfn.h>
  #include <linux/slab.h>
  #include <linux/bitops.h>
  
  #include <scsi/scsi_cmnd.h>
  #include <scsi/scsi_device.h>
  #include <scsi/scsi.h>
  #include <scsi/scsi_host.h>
  
  #include <xen/xen.h>
  #include <xen/xenbus.h>
  #include <xen/grant_table.h>
  #include <xen/events.h>
  #include <xen/page.h>
  
  #include <xen/interface/grant_table.h>
  #include <xen/interface/io/vscsiif.h>
  #include <xen/interface/io/protocols.h>
  
  #include <asm/xen/hypervisor.h>
  
  
  #define GRANT_INVALID_REF	0
  
  #define VSCSIFRONT_OP_ADD_LUN	1
  #define VSCSIFRONT_OP_DEL_LUN	2

  #define VSCSIFRONT_OP_READD_LUN	3

  
  /* Tuning point. */
  #define VSCSIIF_DEFAULT_CMD_PER_LUN 10
  #define VSCSIIF_MAX_TARGET          64
  #define VSCSIIF_MAX_LUN             255
  
  #define VSCSIIF_RING_SIZE	__CONST_RING_SIZE(vscsiif, PAGE_SIZE)
  #define VSCSIIF_MAX_REQS	VSCSIIF_RING_SIZE
  
  #define vscsiif_grants_sg(_sg)	(PFN_UP((_sg) *		\
  				sizeof(struct scsiif_request_segment)))
  
  struct vscsifrnt_shadow {
  	/* command between backend and frontend */
  	unsigned char act;
  	uint16_t rqid;
  
  	unsigned int nr_grants;		/* number of grants in gref[] */
  	struct scsiif_request_segment *sg;	/* scatter/gather elements */
  
  	/* Do reset or abort function. */
  	wait_queue_head_t wq_reset;	/* reset work queue           */
  	int wait_reset;			/* reset work queue condition */
  	int32_t rslt_reset;		/* reset response status:     */
  					/* SUCCESS or FAILED or:      */
  #define RSLT_RESET_WAITING	0
  #define RSLT_RESET_ERR		-1
  
  	/* Requested struct scsi_cmnd is stored from kernel. */
  	struct scsi_cmnd *sc;
  	int gref[vscsiif_grants_sg(SG_ALL) + SG_ALL];
  };
  
  struct vscsifrnt_info {
  	struct xenbus_device *dev;
  
  	struct Scsi_Host *host;
  	int host_active;
  
  	unsigned int evtchn;
  	unsigned int irq;
  
  	grant_ref_t ring_ref;
  	struct vscsiif_front_ring ring;
  	struct vscsiif_response	ring_rsp;
  
  	spinlock_t shadow_lock;
  	DECLARE_BITMAP(shadow_free_bitmap, VSCSIIF_MAX_REQS);
  	struct vscsifrnt_shadow *shadow[VSCSIIF_MAX_REQS];

  	/* Following items are protected by the host lock. */

  	wait_queue_head_t wq_sync;

  	wait_queue_head_t wq_pause;

  	unsigned int wait_ring_available:1;

  	unsigned int waiting_pause:1;
  	unsigned int pause:1;
  	unsigned callers;

  
  	char dev_state_path[64];
  	struct task_struct *curr;
  };
  
  static DEFINE_MUTEX(scsifront_mutex);
  
  static void scsifront_wake_up(struct vscsifrnt_info *info)
  {
  	info->wait_ring_available = 0;
  	wake_up(&info->wq_sync);
  }
  
  static int scsifront_get_rqid(struct vscsifrnt_info *info)
  {
  	unsigned long flags;
  	int free;
  
  	spin_lock_irqsave(&info->shadow_lock, flags);
  
  	free = find_first_bit(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);
  	__clear_bit(free, info->shadow_free_bitmap);
  
  	spin_unlock_irqrestore(&info->shadow_lock, flags);
  
  	return free;
  }
  
  static int _scsifront_put_rqid(struct vscsifrnt_info *info, uint32_t id)
  {
  	int empty = bitmap_empty(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);
  
  	__set_bit(id, info->shadow_free_bitmap);
  	info->shadow[id] = NULL;
  
  	return empty || info->wait_ring_available;
  }
  
  static void scsifront_put_rqid(struct vscsifrnt_info *info, uint32_t id)
  {
  	unsigned long flags;
  	int kick;
  
  	spin_lock_irqsave(&info->shadow_lock, flags);
  	kick = _scsifront_put_rqid(info, id);
  	spin_unlock_irqrestore(&info->shadow_lock, flags);
  
  	if (kick)
  		scsifront_wake_up(info);
  }
  
  static struct vscsiif_request *scsifront_pre_req(struct vscsifrnt_info *info)
  {
  	struct vscsiif_front_ring *ring = &(info->ring);
  	struct vscsiif_request *ring_req;
  	uint32_t id;
  
  	id = scsifront_get_rqid(info);	/* use id in response */
  	if (id >= VSCSIIF_MAX_REQS)
  		return NULL;
  
  	ring_req = RING_GET_REQUEST(&(info->ring), ring->req_prod_pvt);
  
  	ring->req_prod_pvt++;
  
  	ring_req->rqid = (uint16_t)id;
  
  	return ring_req;
  }
  
  static void scsifront_do_request(struct vscsifrnt_info *info)
  {
  	struct vscsiif_front_ring *ring = &(info->ring);
  	int notify;
  
  	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(ring, notify);
  	if (notify)
  		notify_remote_via_irq(info->irq);
  }
  
  static void scsifront_gnttab_done(struct vscsifrnt_info *info, uint32_t id)
  {
  	struct vscsifrnt_shadow *s = info->shadow[id];
  	int i;
  
  	if (s->sc->sc_data_direction == DMA_NONE)
  		return;
  
  	for (i = 0; i < s->nr_grants; i++) {
  		if (unlikely(gnttab_query_foreign_access(s->gref[i]) != 0)) {
  			shost_printk(KERN_ALERT, info->host, KBUILD_MODNAME
  				     "grant still in use by backend
  ");
  			BUG();
  		}
  		gnttab_end_foreign_access(s->gref[i], 0, 0UL);
  	}
  
  	kfree(s->sg);
  }
  
  static void scsifront_cdb_cmd_done(struct vscsifrnt_info *info,
  				   struct vscsiif_response *ring_rsp)
  {
  	struct scsi_cmnd *sc;
  	uint32_t id;
  	uint8_t sense_len;
  
  	id = ring_rsp->rqid;
  	sc = info->shadow[id]->sc;
  
  	BUG_ON(sc == NULL);
  
  	scsifront_gnttab_done(info, id);
  	scsifront_put_rqid(info, id);
  
  	sc->result = ring_rsp->rslt;
  	scsi_set_resid(sc, ring_rsp->residual_len);
  
  	sense_len = min_t(uint8_t, VSCSIIF_SENSE_BUFFERSIZE,
  			  ring_rsp->sense_len);
  
  	if (sense_len)
  		memcpy(sc->sense_buffer, ring_rsp->sense_buffer, sense_len);
  
  	sc->scsi_done(sc);
  }
  
  static void scsifront_sync_cmd_done(struct vscsifrnt_info *info,
  				    struct vscsiif_response *ring_rsp)
  {
  	uint16_t id = ring_rsp->rqid;
  	unsigned long flags;
  	struct vscsifrnt_shadow *shadow = info->shadow[id];
  	int kick;
  
  	spin_lock_irqsave(&info->shadow_lock, flags);
  	shadow->wait_reset = 1;
  	switch (shadow->rslt_reset) {
  	case RSLT_RESET_WAITING:
  		shadow->rslt_reset = ring_rsp->rslt;
  		break;
  	case RSLT_RESET_ERR:
  		kick = _scsifront_put_rqid(info, id);
  		spin_unlock_irqrestore(&info->shadow_lock, flags);
  		kfree(shadow);
  		if (kick)
  			scsifront_wake_up(info);
  		return;
  	default:
  		shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
  			     "bad reset state %d, possibly leaking %u
  ",
  			     shadow->rslt_reset, id);
  		break;
  	}
  	spin_unlock_irqrestore(&info->shadow_lock, flags);
  
  	wake_up(&shadow->wq_reset);
  }

  static void scsifront_do_response(struct vscsifrnt_info *info,
  				  struct vscsiif_response *ring_rsp)
  {
  	if (WARN(ring_rsp->rqid >= VSCSIIF_MAX_REQS ||
  		 test_bit(ring_rsp->rqid, info->shadow_free_bitmap),
  		 "illegal rqid %u returned by backend!
  ", ring_rsp->rqid))
  		return;
  
  	if (info->shadow[ring_rsp->rqid]->act == VSCSIIF_ACT_SCSI_CDB)
  		scsifront_cdb_cmd_done(info, ring_rsp);
  	else
  		scsifront_sync_cmd_done(info, ring_rsp);
  }
  
  static int scsifront_ring_drain(struct vscsifrnt_info *info)

  {
  	struct vscsiif_response *ring_rsp;
  	RING_IDX i, rp;
  	int more_to_do = 0;

  
  	rp = info->ring.sring->rsp_prod;
  	rmb();	/* ordering required respective to dom0 */
  	for (i = info->ring.rsp_cons; i != rp; i++) {

  		ring_rsp = RING_GET_RESPONSE(&info->ring, i);

  		scsifront_do_response(info, ring_rsp);

  	}
  
  	info->ring.rsp_cons = i;
  
  	if (i != info->ring.req_prod_pvt)
  		RING_FINAL_CHECK_FOR_RESPONSES(&info->ring, more_to_do);
  	else
  		info->ring.sring->rsp_event = i + 1;

  	return more_to_do;
  }
  
  static int scsifront_cmd_done(struct vscsifrnt_info *info)
  {
  	int more_to_do;
  	unsigned long flags;
  
  	spin_lock_irqsave(info->host->host_lock, flags);
  
  	more_to_do = scsifront_ring_drain(info);

  	info->wait_ring_available = 0;
  
  	spin_unlock_irqrestore(info->host->host_lock, flags);
  
  	wake_up(&info->wq_sync);
  
  	return more_to_do;
  }
  
  static irqreturn_t scsifront_irq_fn(int irq, void *dev_id)
  {
  	struct vscsifrnt_info *info = dev_id;
  
  	while (scsifront_cmd_done(info))
  		/* Yield point for this unbounded loop. */
  		cond_resched();
  
  	return IRQ_HANDLED;
  }

  static void scsifront_finish_all(struct vscsifrnt_info *info)
  {
  	unsigned i;
  	struct vscsiif_response resp;
  
  	scsifront_ring_drain(info);
  
  	for (i = 0; i < VSCSIIF_MAX_REQS; i++) {
  		if (test_bit(i, info->shadow_free_bitmap))
  			continue;
  		resp.rqid = i;
  		resp.sense_len = 0;
  		resp.rslt = DID_RESET << 16;
  		resp.residual_len = 0;
  		scsifront_do_response(info, &resp);
  	}
  }

  static int map_data_for_request(struct vscsifrnt_info *info,
  				struct scsi_cmnd *sc,
  				struct vscsiif_request *ring_req,
  				struct vscsifrnt_shadow *shadow)
  {
  	grant_ref_t gref_head;
  	struct page *page;
  	int err, ref, ref_cnt = 0;
  	int grant_ro = (sc->sc_data_direction == DMA_TO_DEVICE);
  	unsigned int i, off, len, bytes;
  	unsigned int data_len = scsi_bufflen(sc);
  	unsigned int data_grants = 0, seg_grants = 0;
  	struct scatterlist *sg;

  	struct scsiif_request_segment *seg;
  
  	ring_req->nr_segments = 0;
  	if (sc->sc_data_direction == DMA_NONE || !data_len)
  		return 0;
  
  	scsi_for_each_sg(sc, sg, scsi_sg_count(sc), i)
  		data_grants += PFN_UP(sg->offset + sg->length);
  
  	if (data_grants > VSCSIIF_SG_TABLESIZE) {
  		if (data_grants > info->host->sg_tablesize) {
  			shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
  			     "Unable to map request_buffer for command!
  ");
  			return -E2BIG;
  		}
  		seg_grants = vscsiif_grants_sg(data_grants);
  		shadow->sg = kcalloc(data_grants,

  			sizeof(struct scsiif_request_segment), GFP_ATOMIC);

  		if (!shadow->sg)
  			return -ENOMEM;
  	}
  	seg = shadow->sg ? : ring_req->seg;
  
  	err = gnttab_alloc_grant_references(seg_grants + data_grants,
  					    &gref_head);
  	if (err) {
  		kfree(shadow->sg);
  		shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
  			     "gnttab_alloc_grant_references() error
  ");
  		return -ENOMEM;
  	}
  
  	if (seg_grants) {
  		page = virt_to_page(seg);
  		off = (unsigned long)seg & ~PAGE_MASK;
  		len = sizeof(struct scsiif_request_segment) * data_grants;
  		while (len > 0) {
  			bytes = min_t(unsigned int, len, PAGE_SIZE - off);
  
  			ref = gnttab_claim_grant_reference(&gref_head);
  			BUG_ON(ref == -ENOSPC);

  			gnttab_grant_foreign_access_ref(ref,

  				info->dev->otherend_id,
  				xen_page_to_gfn(page), 1);

  			shadow->gref[ref_cnt] = ref;
  			ring_req->seg[ref_cnt].gref   = ref;
  			ring_req->seg[ref_cnt].offset = (uint16_t)off;
  			ring_req->seg[ref_cnt].length = (uint16_t)bytes;
  
  			page++;
  			len -= bytes;
  			off = 0;
  			ref_cnt++;
  		}
  		BUG_ON(seg_grants < ref_cnt);
  		seg_grants = ref_cnt;
  	}
  
  	scsi_for_each_sg(sc, sg, scsi_sg_count(sc), i) {
  		page = sg_page(sg);
  		off = sg->offset;
  		len = sg->length;
  
  		while (len > 0 && data_len > 0) {
  			/*
  			 * sg sends a scatterlist that is larger than
  			 * the data_len it wants transferred for certain
  			 * IO sizes.
  			 */
  			bytes = min_t(unsigned int, len, PAGE_SIZE - off);
  			bytes = min(bytes, data_len);
  
  			ref = gnttab_claim_grant_reference(&gref_head);
  			BUG_ON(ref == -ENOSPC);

  			gnttab_grant_foreign_access_ref(ref,

  				info->dev->otherend_id,
  				xen_page_to_gfn(page),
  				grant_ro);

  
  			shadow->gref[ref_cnt] = ref;
  			seg->gref   = ref;
  			seg->offset = (uint16_t)off;
  			seg->length = (uint16_t)bytes;
  
  			page++;
  			seg++;
  			len -= bytes;
  			data_len -= bytes;
  			off = 0;
  			ref_cnt++;
  		}
  	}
  
  	if (seg_grants)
  		ring_req->nr_segments = VSCSIIF_SG_GRANT | seg_grants;
  	else
  		ring_req->nr_segments = (uint8_t)ref_cnt;
  	shadow->nr_grants = ref_cnt;
  
  	return 0;
  }
  
  static struct vscsiif_request *scsifront_command2ring(
  		struct vscsifrnt_info *info, struct scsi_cmnd *sc,
  		struct vscsifrnt_shadow *shadow)
  {
  	struct vscsiif_request *ring_req;
  
  	memset(shadow, 0, sizeof(*shadow));
  
  	ring_req = scsifront_pre_req(info);
  	if (!ring_req)
  		return NULL;
  
  	info->shadow[ring_req->rqid] = shadow;
  	shadow->rqid = ring_req->rqid;
  
  	ring_req->id      = sc->device->id;
  	ring_req->lun     = sc->device->lun;
  	ring_req->channel = sc->device->channel;
  	ring_req->cmd_len = sc->cmd_len;
  
  	BUG_ON(sc->cmd_len > VSCSIIF_MAX_COMMAND_SIZE);
  
  	memcpy(ring_req->cmnd, sc->cmnd, sc->cmd_len);
  
  	ring_req->sc_data_direction   = (uint8_t)sc->sc_data_direction;
  	ring_req->timeout_per_command = sc->request->timeout / HZ;
  
  	return ring_req;
  }

  static int scsifront_enter(struct vscsifrnt_info *info)
  {
  	if (info->pause)
  		return 1;
  	info->callers++;
  	return 0;
  }
  
  static void scsifront_return(struct vscsifrnt_info *info)
  {
  	info->callers--;
  	if (info->callers)
  		return;
  
  	if (!info->waiting_pause)
  		return;
  
  	info->waiting_pause = 0;
  	wake_up(&info->wq_pause);
  }

  static int scsifront_queuecommand(struct Scsi_Host *shost,
  				  struct scsi_cmnd *sc)
  {
  	struct vscsifrnt_info *info = shost_priv(shost);
  	struct vscsiif_request *ring_req;
  	struct vscsifrnt_shadow *shadow = scsi_cmd_priv(sc);
  	unsigned long flags;
  	int err;
  	uint16_t rqid;
  
  	spin_lock_irqsave(shost->host_lock, flags);

  	if (scsifront_enter(info)) {
  		spin_unlock_irqrestore(shost->host_lock, flags);
  		return SCSI_MLQUEUE_HOST_BUSY;
  	}

  	if (RING_FULL(&info->ring))
  		goto busy;
  
  	ring_req = scsifront_command2ring(info, sc, shadow);
  	if (!ring_req)
  		goto busy;
  
  	sc->result = 0;
  
  	rqid = ring_req->rqid;
  	ring_req->act = VSCSIIF_ACT_SCSI_CDB;
  
  	shadow->sc  = sc;
  	shadow->act = VSCSIIF_ACT_SCSI_CDB;
  
  	err = map_data_for_request(info, sc, ring_req, shadow);
  	if (err < 0) {
  		pr_debug("%s: err %d
  ", __func__, err);
  		scsifront_put_rqid(info, rqid);

  		scsifront_return(info);

  		spin_unlock_irqrestore(shost->host_lock, flags);
  		if (err == -ENOMEM)
  			return SCSI_MLQUEUE_HOST_BUSY;
  		sc->result = DID_ERROR << 16;
  		sc->scsi_done(sc);
  		return 0;
  	}
  
  	scsifront_do_request(info);

  	scsifront_return(info);

  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	return 0;
  
  busy:

  	scsifront_return(info);

  	spin_unlock_irqrestore(shost->host_lock, flags);
  	pr_debug("%s: busy
  ", __func__);
  	return SCSI_MLQUEUE_HOST_BUSY;
  }
  
  /*
   * Any exception handling (reset or abort) must be forwarded to the backend.
   * We have to wait until an answer is returned. This answer contains the
   * result to be returned to the requestor.
   */
  static int scsifront_action_handler(struct scsi_cmnd *sc, uint8_t act)
  {
  	struct Scsi_Host *host = sc->device->host;
  	struct vscsifrnt_info *info = shost_priv(host);
  	struct vscsifrnt_shadow *shadow, *s = scsi_cmd_priv(sc);
  	struct vscsiif_request *ring_req;
  	int err = 0;
  
  	shadow = kmalloc(sizeof(*shadow), GFP_NOIO);
  	if (!shadow)
  		return FAILED;

  	spin_lock_irq(host->host_lock);

  	for (;;) {

  		if (!RING_FULL(&info->ring)) {
  			ring_req = scsifront_command2ring(info, sc, shadow);
  			if (ring_req)
  				break;
  		}

  		if (err || info->pause) {

  			spin_unlock_irq(host->host_lock);
  			kfree(shadow);
  			return FAILED;
  		}
  		info->wait_ring_available = 1;
  		spin_unlock_irq(host->host_lock);
  		err = wait_event_interruptible(info->wq_sync,
  					       !info->wait_ring_available);
  		spin_lock_irq(host->host_lock);
  	}

  	if (scsifront_enter(info)) {
  		spin_unlock_irq(host->host_lock);
  		return FAILED;
  	}

  	ring_req->act = act;
  	ring_req->ref_rqid = s->rqid;
  
  	shadow->act = act;
  	shadow->rslt_reset = RSLT_RESET_WAITING;
  	init_waitqueue_head(&shadow->wq_reset);
  
  	ring_req->nr_segments = 0;
  
  	scsifront_do_request(info);
  
  	spin_unlock_irq(host->host_lock);
  	err = wait_event_interruptible(shadow->wq_reset, shadow->wait_reset);
  	spin_lock_irq(host->host_lock);
  
  	if (!err) {
  		err = shadow->rslt_reset;
  		scsifront_put_rqid(info, shadow->rqid);
  		kfree(shadow);
  	} else {
  		spin_lock(&info->shadow_lock);
  		shadow->rslt_reset = RSLT_RESET_ERR;
  		spin_unlock(&info->shadow_lock);
  		err = FAILED;
  	}

  	scsifront_return(info);

  	spin_unlock_irq(host->host_lock);
  	return err;
  }
  
  static int scsifront_eh_abort_handler(struct scsi_cmnd *sc)
  {
  	pr_debug("%s
  ", __func__);
  	return scsifront_action_handler(sc, VSCSIIF_ACT_SCSI_ABORT);
  }
  
  static int scsifront_dev_reset_handler(struct scsi_cmnd *sc)
  {
  	pr_debug("%s
  ", __func__);
  	return scsifront_action_handler(sc, VSCSIIF_ACT_SCSI_RESET);
  }
  
  static int scsifront_sdev_configure(struct scsi_device *sdev)
  {
  	struct vscsifrnt_info *info = shost_priv(sdev->host);
  
  	if (info && current == info->curr)
  		xenbus_printf(XBT_NIL, info->dev->nodename,
  			      info->dev_state_path, "%d", XenbusStateConnected);
  
  	return 0;
  }
  
  static void scsifront_sdev_destroy(struct scsi_device *sdev)
  {
  	struct vscsifrnt_info *info = shost_priv(sdev->host);
  
  	if (info && current == info->curr)
  		xenbus_printf(XBT_NIL, info->dev->nodename,
  			      info->dev_state_path, "%d", XenbusStateClosed);
  }
  
  static struct scsi_host_template scsifront_sht = {
  	.module			= THIS_MODULE,
  	.name			= "Xen SCSI frontend driver",
  	.queuecommand		= scsifront_queuecommand,
  	.eh_abort_handler	= scsifront_eh_abort_handler,
  	.eh_device_reset_handler = scsifront_dev_reset_handler,
  	.slave_configure	= scsifront_sdev_configure,
  	.slave_destroy		= scsifront_sdev_destroy,
  	.cmd_per_lun		= VSCSIIF_DEFAULT_CMD_PER_LUN,
  	.can_queue		= VSCSIIF_MAX_REQS,
  	.this_id		= -1,
  	.cmd_size		= sizeof(struct vscsifrnt_shadow),
  	.sg_tablesize		= VSCSIIF_SG_TABLESIZE,
  	.use_clustering		= DISABLE_CLUSTERING,
  	.proc_name		= "scsifront",
  };
  
  static int scsifront_alloc_ring(struct vscsifrnt_info *info)
  {
  	struct xenbus_device *dev = info->dev;
  	struct vscsiif_sring *sring;

  	grant_ref_t gref;

  	int err = -ENOMEM;
  
  	/***** Frontend to Backend ring start *****/
  	sring = (struct vscsiif_sring *)__get_free_page(GFP_KERNEL);
  	if (!sring) {
  		xenbus_dev_fatal(dev, err,
  			"fail to allocate shared ring (Front to Back)");
  		return err;
  	}
  	SHARED_RING_INIT(sring);
  	FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);

  	err = xenbus_grant_ring(dev, sring, 1, &gref);

  	if (err < 0) {
  		free_page((unsigned long)sring);
  		xenbus_dev_fatal(dev, err,
  			"fail to grant shared ring (Front to Back)");
  		return err;
  	}

  	info->ring_ref = gref;

  
  	err = xenbus_alloc_evtchn(dev, &info->evtchn);
  	if (err) {
  		xenbus_dev_fatal(dev, err, "xenbus_alloc_evtchn");
  		goto free_gnttab;
  	}
  
  	err = bind_evtchn_to_irq(info->evtchn);
  	if (err <= 0) {
  		xenbus_dev_fatal(dev, err, "bind_evtchn_to_irq");
  		goto free_gnttab;
  	}
  
  	info->irq = err;
  
  	err = request_threaded_irq(info->irq, NULL, scsifront_irq_fn,
  				   IRQF_ONESHOT, "scsifront", info);
  	if (err) {
  		xenbus_dev_fatal(dev, err, "request_threaded_irq");
  		goto free_irq;
  	}
  
  	return 0;
  
  /* free resource */
  free_irq:
  	unbind_from_irqhandler(info->irq, info);
  free_gnttab:
  	gnttab_end_foreign_access(info->ring_ref, 0,
  				  (unsigned long)info->ring.sring);
  
  	return err;
  }

  static void scsifront_free_ring(struct vscsifrnt_info *info)
  {
  	unbind_from_irqhandler(info->irq, info);
  	gnttab_end_foreign_access(info->ring_ref, 0,
  				  (unsigned long)info->ring.sring);
  }

  static int scsifront_init_ring(struct vscsifrnt_info *info)
  {
  	struct xenbus_device *dev = info->dev;
  	struct xenbus_transaction xbt;
  	int err;
  
  	pr_debug("%s
  ", __func__);
  
  	err = scsifront_alloc_ring(info);
  	if (err)
  		return err;
  	pr_debug("%s: %u %u
  ", __func__, info->ring_ref, info->evtchn);
  
  again:
  	err = xenbus_transaction_start(&xbt);
  	if (err)
  		xenbus_dev_fatal(dev, err, "starting transaction");
  
  	err = xenbus_printf(xbt, dev->nodename, "ring-ref", "%u",
  			    info->ring_ref);
  	if (err) {
  		xenbus_dev_fatal(dev, err, "%s", "writing ring-ref");
  		goto fail;
  	}
  
  	err = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
  			    info->evtchn);
  
  	if (err) {
  		xenbus_dev_fatal(dev, err, "%s", "writing event-channel");
  		goto fail;
  	}
  
  	err = xenbus_transaction_end(xbt, 0);
  	if (err) {
  		if (err == -EAGAIN)
  			goto again;
  		xenbus_dev_fatal(dev, err, "completing transaction");
  		goto free_sring;
  	}
  
  	return 0;
  
  fail:
  	xenbus_transaction_end(xbt, 1);
  free_sring:

  	scsifront_free_ring(info);

  
  	return err;
  }
  
  
  static int scsifront_probe(struct xenbus_device *dev,
  			   const struct xenbus_device_id *id)
  {
  	struct vscsifrnt_info *info;
  	struct Scsi_Host *host;
  	int err = -ENOMEM;
  	char name[TASK_COMM_LEN];
  
  	host = scsi_host_alloc(&scsifront_sht, sizeof(*info));
  	if (!host) {
  		xenbus_dev_fatal(dev, err, "fail to allocate scsi host");
  		return err;
  	}
  	info = (struct vscsifrnt_info *)host->hostdata;
  
  	dev_set_drvdata(&dev->dev, info);
  	info->dev = dev;
  
  	bitmap_fill(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);
  
  	err = scsifront_init_ring(info);
  	if (err) {
  		scsi_host_put(host);
  		return err;
  	}
  
  	init_waitqueue_head(&info->wq_sync);

  	init_waitqueue_head(&info->wq_pause);

  	spin_lock_init(&info->shadow_lock);
  
  	snprintf(name, TASK_COMM_LEN, "vscsiif.%d", host->host_no);
  
  	host->max_id      = VSCSIIF_MAX_TARGET;
  	host->max_channel = 0;
  	host->max_lun     = VSCSIIF_MAX_LUN;
  	host->max_sectors = (host->sg_tablesize - 1) * PAGE_SIZE / 512;
  	host->max_cmd_len = VSCSIIF_MAX_COMMAND_SIZE;
  
  	err = scsi_add_host(host, &dev->dev);
  	if (err) {
  		dev_err(&dev->dev, "fail to add scsi host %d
  ", err);
  		goto free_sring;
  	}
  	info->host = host;
  	info->host_active = 1;
  
  	xenbus_switch_state(dev, XenbusStateInitialised);
  
  	return 0;
  
  free_sring:

  	scsifront_free_ring(info);

  	scsi_host_put(host);
  	return err;
  }

  static int scsifront_resume(struct xenbus_device *dev)
  {
  	struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
  	struct Scsi_Host *host = info->host;
  	int err;
  
  	spin_lock_irq(host->host_lock);
  
  	/* Finish all still pending commands. */
  	scsifront_finish_all(info);
  
  	spin_unlock_irq(host->host_lock);
  
  	/* Reconnect to dom0. */
  	scsifront_free_ring(info);
  	err = scsifront_init_ring(info);
  	if (err) {
  		dev_err(&dev->dev, "fail to resume %d
  ", err);
  		scsi_host_put(host);
  		return err;
  	}
  
  	xenbus_switch_state(dev, XenbusStateInitialised);
  
  	return 0;
  }
  
  static int scsifront_suspend(struct xenbus_device *dev)
  {
  	struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
  	struct Scsi_Host *host = info->host;
  	int err = 0;
  
  	/* No new commands for the backend. */
  	spin_lock_irq(host->host_lock);
  	info->pause = 1;
  	while (info->callers && !err) {
  		info->waiting_pause = 1;
  		info->wait_ring_available = 0;
  		spin_unlock_irq(host->host_lock);
  		wake_up(&info->wq_sync);
  		err = wait_event_interruptible(info->wq_pause,
  					       !info->waiting_pause);
  		spin_lock_irq(host->host_lock);
  	}
  	spin_unlock_irq(host->host_lock);
  	return err;
  }

  static int scsifront_remove(struct xenbus_device *dev)
  {
  	struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
  
  	pr_debug("%s: %s removed
  ", __func__, dev->nodename);
  
  	mutex_lock(&scsifront_mutex);
  	if (info->host_active) {
  		/* Scsi_host not yet removed */
  		scsi_remove_host(info->host);
  		info->host_active = 0;
  	}
  	mutex_unlock(&scsifront_mutex);

  	scsifront_free_ring(info);

  	scsi_host_put(info->host);
  
  	return 0;
  }
  
  static void scsifront_disconnect(struct vscsifrnt_info *info)
  {
  	struct xenbus_device *dev = info->dev;
  	struct Scsi_Host *host = info->host;
  
  	pr_debug("%s: %s disconnect
  ", __func__, dev->nodename);
  
  	/*
  	 * When this function is executed, all devices of
  	 * Frontend have been deleted.
  	 * Therefore, it need not block I/O before remove_host.
  	 */
  
  	mutex_lock(&scsifront_mutex);
  	if (info->host_active) {
  		scsi_remove_host(host);
  		info->host_active = 0;
  	}
  	mutex_unlock(&scsifront_mutex);
  
  	xenbus_frontend_closed(dev);
  }
  
  static void scsifront_do_lun_hotplug(struct vscsifrnt_info *info, int op)
  {
  	struct xenbus_device *dev = info->dev;
  	int i, err = 0;
  	char str[64];
  	char **dir;
  	unsigned int dir_n = 0;
  	unsigned int device_state;
  	unsigned int hst, chn, tgt, lun;
  	struct scsi_device *sdev;
  
  	dir = xenbus_directory(XBT_NIL, dev->otherend, "vscsi-devs", &dir_n);
  	if (IS_ERR(dir))
  		return;
  
  	/* mark current task as the one allowed to modify device states */
  	BUG_ON(info->curr);
  	info->curr = current;
  
  	for (i = 0; i < dir_n; i++) {
  		/* read status */
  		snprintf(str, sizeof(str), "vscsi-devs/%s/state", dir[i]);
  		err = xenbus_scanf(XBT_NIL, dev->otherend, str, "%u",
  				   &device_state);
  		if (XENBUS_EXIST_ERR(err))
  			continue;
  
  		/* virtual SCSI device */
  		snprintf(str, sizeof(str), "vscsi-devs/%s/v-dev", dir[i]);
  		err = xenbus_scanf(XBT_NIL, dev->otherend, str,
  				   "%u:%u:%u:%u", &hst, &chn, &tgt, &lun);
  		if (XENBUS_EXIST_ERR(err))
  			continue;
  
  		/*
  		 * Front device state path, used in slave_configure called
  		 * on successfull scsi_add_device, and in slave_destroy called
  		 * on remove of a device.
  		 */
  		snprintf(info->dev_state_path, sizeof(info->dev_state_path),
  			 "vscsi-devs/%s/state", dir[i]);
  
  		switch (op) {
  		case VSCSIFRONT_OP_ADD_LUN:
  			if (device_state != XenbusStateInitialised)
  				break;
  
  			if (scsi_add_device(info->host, chn, tgt, lun)) {
  				dev_err(&dev->dev, "scsi_add_device
  ");
  				xenbus_printf(XBT_NIL, dev->nodename,
  					      info->dev_state_path,
  					      "%d", XenbusStateClosed);
  			}
  			break;
  		case VSCSIFRONT_OP_DEL_LUN:
  			if (device_state != XenbusStateClosing)
  				break;
  
  			sdev = scsi_device_lookup(info->host, chn, tgt, lun);
  			if (sdev) {
  				scsi_remove_device(sdev);
  				scsi_device_put(sdev);
  			}
  			break;

  		case VSCSIFRONT_OP_READD_LUN:
  			if (device_state == XenbusStateConnected)
  				xenbus_printf(XBT_NIL, dev->nodename,
  					      info->dev_state_path,
  					      "%d", XenbusStateConnected);
  			break;

  		default:
  			break;
  		}
  	}
  
  	info->curr = NULL;
  
  	kfree(dir);
  }
  
  static void scsifront_read_backend_params(struct xenbus_device *dev,
  					  struct vscsifrnt_info *info)
  {

  	unsigned int sg_grant, nr_segs;

  	int ret;
  	struct Scsi_Host *host = info->host;
  
  	ret = xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg-grant", "%u",
  			   &sg_grant);

  	if (ret != 1)
  		sg_grant = 0;
  	nr_segs = min_t(unsigned int, sg_grant, SG_ALL);
  	nr_segs = max_t(unsigned int, nr_segs, VSCSIIF_SG_TABLESIZE);
  	nr_segs = min_t(unsigned int, nr_segs,

  			VSCSIIF_SG_TABLESIZE * PAGE_SIZE /
  			sizeof(struct scsiif_request_segment));

  
  	if (!info->pause && sg_grant)
  		dev_info(&dev->dev, "using up to %d SG entries
  ", nr_segs);
  	else if (info->pause && nr_segs < host->sg_tablesize)
  		dev_warn(&dev->dev,
  			 "SG entries decreased from %d to %u - device may not work properly anymore
  ",
  			 host->sg_tablesize, nr_segs);
  
  	host->sg_tablesize = nr_segs;
  	host->max_sectors = (nr_segs - 1) * PAGE_SIZE / 512;

  }
  
  static void scsifront_backend_changed(struct xenbus_device *dev,
  				      enum xenbus_state backend_state)
  {
  	struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
  
  	pr_debug("%s: %p %u %u
  ", __func__, dev, dev->state, backend_state);
  
  	switch (backend_state) {
  	case XenbusStateUnknown:
  	case XenbusStateInitialising:
  	case XenbusStateInitWait:
  	case XenbusStateInitialised:
  		break;
  
  	case XenbusStateConnected:
  		scsifront_read_backend_params(dev, info);

  
  		if (info->pause) {
  			scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_READD_LUN);
  			xenbus_switch_state(dev, XenbusStateConnected);
  			info->pause = 0;
  			return;
  		}

  		if (xenbus_read_driver_state(dev->nodename) ==
  		    XenbusStateInitialised)
  			scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_ADD_LUN);
  
  		if (dev->state != XenbusStateConnected)
  			xenbus_switch_state(dev, XenbusStateConnected);
  		break;
  
  	case XenbusStateClosed:
  		if (dev->state == XenbusStateClosed)
  			break;
  		/* Missed the backend's Closing state -- fallthrough */
  	case XenbusStateClosing:
  		scsifront_disconnect(info);
  		break;
  
  	case XenbusStateReconfiguring:
  		scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_DEL_LUN);
  		xenbus_switch_state(dev, XenbusStateReconfiguring);
  		break;
  
  	case XenbusStateReconfigured:
  		scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_ADD_LUN);
  		xenbus_switch_state(dev, XenbusStateConnected);
  		break;
  	}
  }
  
  static const struct xenbus_device_id scsifront_ids[] = {
  	{ "vscsi" },
  	{ "" }
  };

  static struct xenbus_driver scsifront_driver = {
  	.ids			= scsifront_ids,

  	.probe			= scsifront_probe,
  	.remove			= scsifront_remove,

  	.resume			= scsifront_resume,
  	.suspend		= scsifront_suspend,

  	.otherend_changed	= scsifront_backend_changed,

  };

  
  static int __init scsifront_init(void)
  {
  	if (!xen_domain())
  		return -ENODEV;
  
  	return xenbus_register_frontend(&scsifront_driver);
  }
  module_init(scsifront_init);
  
  static void __exit scsifront_exit(void)
  {
  	xenbus_unregister_driver(&scsifront_driver);
  }
  module_exit(scsifront_exit);
  
  MODULE_DESCRIPTION("Xen SCSI frontend driver");
  MODULE_LICENSE("GPL");
  MODULE_ALIAS("xen:vscsi");
  MODULE_AUTHOR("Juergen Gross <jgross@suse.com>");