Import Xen paravirtual drivers.

MFC after:	2 weeks

1 files changed, 1021 insertions, 0 deletions

diff --git a/sys/dev/xen/blkfront/blkfront.c b/sys/dev/xen/blkfront/blkfront.c
new file mode 100644
index 0000000..c448b81
--- /dev/null
+++ b/sys/dev/xen/blkfront/blkfront.c
@@ -0,0 +1,1021 @@
+/*-
+ * All rights reserved.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+
+/*
+ * XenoBSD block device driver
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/malloc.h>
+#include <sys/kernel.h>
+#include <vm/vm.h>
+#include <vm/pmap.h>
+
+#include <sys/bio.h>
+#include <sys/bus.h>
+#include <sys/conf.h>
+#include <sys/module.h>
+
+#include <machine/bus.h>
+#include <sys/rman.h>
+#include <machine/resource.h>
+#include <machine/intr_machdep.h>
+#include <machine/vmparam.h>
+
+#include <machine/xen/hypervisor.h>
+#include <machine/xen/xen-os.h>
+#include <machine/xen/xen_intr.h>
+#include <machine/xen/xenbus.h>
+#include <machine/xen/evtchn.h>
+#include <xen/interface/grant_table.h>
+
+#include <geom/geom_disk.h>
+#include <machine/xen/xenfunc.h>
+#include <xen/gnttab.h>
+
+#include <dev/xen/blkfront/block.h>
+
+#define    ASSERT(S)       KASSERT(S, (#S))
+/* prototypes */
+struct xb_softc;
+static void xb_startio(struct xb_softc *sc);
+static void connect(struct blkfront_info *);
+static void blkfront_closing(struct xenbus_device *);
+static int blkfront_remove(struct xenbus_device *);
+static int talk_to_backend(struct xenbus_device *, struct blkfront_info *);
+static int setup_blkring(struct xenbus_device *, struct blkfront_info *);
+static void blkif_int(void *);
+#if 0
+static void blkif_restart_queue(void *arg);
+#endif
+static void blkif_recover(struct blkfront_info *);
+static void blkif_completion(struct blk_shadow *);
+static void blkif_free(struct blkfront_info *, int);
+
+#define GRANT_INVALID_REF 0
+#define BLK_RING_SIZE __RING_SIZE((blkif_sring_t *)0, PAGE_SIZE)
+
+LIST_HEAD(xb_softc_list_head, xb_softc) xbsl_head;
+
+/* Control whether runtime update of vbds is enabled. */
+#define ENABLE_VBD_UPDATE 0
+
+#if ENABLE_VBD_UPDATE
+static void vbd_update(void);
+#endif
+
+
+#define BLKIF_STATE_DISCONNECTED 0
+#define BLKIF_STATE_CONNECTED    1
+#define BLKIF_STATE_SUSPENDED    2
+
+#ifdef notyet
+static char *blkif_state_name[] = {
+	[BLKIF_STATE_DISCONNECTED] = "disconnected",
+	[BLKIF_STATE_CONNECTED]    = "connected",
+	[BLKIF_STATE_SUSPENDED]    = "closed",
+};
+
+static char * blkif_status_name[] = {
+	[BLKIF_INTERFACE_STATUS_CLOSED]       = "closed",
+	[BLKIF_INTERFACE_STATUS_DISCONNECTED] = "disconnected",
+	[BLKIF_INTERFACE_STATUS_CONNECTED]    = "connected",
+	[BLKIF_INTERFACE_STATUS_CHANGED]      = "changed",
+};
+#endif
+#define WPRINTK(fmt, args...) printf("[XEN] " fmt, ##args)
+#if 0
+#define DPRINTK(fmt, args...) printf("[XEN] %s:%d" fmt ".\n", __FUNCTION__, __LINE__,##args)
+#else
+#define DPRINTK(fmt, args...) 
+#endif
+
+static grant_ref_t gref_head;
+#define MAXIMUM_OUTSTANDING_BLOCK_REQS \
+    (BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
+
+static void kick_pending_request_queues(struct blkfront_info *);
+static int blkif_open(struct disk *dp);
+static int blkif_close(struct disk *dp);
+static int blkif_ioctl(struct disk *dp, u_long cmd, void *addr, int flag, struct thread *td);
+static int blkif_queue_request(struct bio *bp);
+static void xb_strategy(struct bio *bp);
+
+
+
+/* XXX move to xb_vbd.c when VBD update support is added */
+#define MAX_VBDS 64
+
+#define XBD_SECTOR_SIZE		512	/* XXX: assume for now */
+#define XBD_SECTOR_SHFT		9
+
+static struct mtx blkif_io_lock;
+
+static unsigned long 
+pfn_to_mfn(unsigned long pfn)
+{
+	return (phystomach(pfn << PAGE_SHIFT) >> PAGE_SHIFT);
+}
+
+
+int
+xlvbd_add(blkif_sector_t capacity, int unit, uint16_t vdisk_info, uint16_t sector_size, 
+	  struct blkfront_info *info)
+{
+	struct xb_softc	*sc;
+	int			error = 0;
+    
+	sc = (struct xb_softc *)malloc(sizeof(*sc), M_DEVBUF, M_WAITOK|M_ZERO);
+	sc->xb_unit = unit;
+	sc->xb_info = info;
+	info->sc = sc;
+
+	memset(&sc->xb_disk, 0, sizeof(sc->xb_disk)); 
+	sc->xb_disk = disk_alloc();
+	sc->xb_disk->d_unit = unit;
+	sc->xb_disk->d_open = blkif_open;
+	sc->xb_disk->d_close = blkif_close;
+	sc->xb_disk->d_ioctl = blkif_ioctl;
+	sc->xb_disk->d_strategy = xb_strategy;
+	sc->xb_disk->d_name = "xbd";
+	sc->xb_disk->d_drv1 = sc;
+	sc->xb_disk->d_sectorsize = sector_size;
+
+	/* XXX */
+	sc->xb_disk->d_mediasize = capacity << XBD_SECTOR_SHFT;
+#if 0
+	sc->xb_disk->d_maxsize = DFLTPHYS;
+#else /* XXX: xen can't handle large single i/o requests */
+	sc->xb_disk->d_maxsize = 4096;
+#endif
+#ifdef notyet
+	XENPRINTF("attaching device 0x%x unit %d capacity %llu\n",
+		  xb_diskinfo[sc->xb_unit].device, sc->xb_unit,
+		  sc->xb_disk->d_mediasize);
+#endif
+	sc->xb_disk->d_flags = 0;
+	disk_create(sc->xb_disk, DISK_VERSION_00);
+	bioq_init(&sc->xb_bioq);
+
+	return error;
+}
+
+void
+xlvbd_del(struct blkfront_info *info)
+{
+	struct xb_softc	*sc;
+
+	sc = info->sc;
+	disk_destroy(sc->xb_disk);
+}
+/************************ end VBD support *****************/
+
+/*
+ * Read/write routine for a buffer.  Finds the proper unit, place it on
+ * the sortq and kick the controller.
+ */
+static void
+xb_strategy(struct bio *bp)
+{
+	struct xb_softc	*sc = (struct xb_softc *)bp->bio_disk->d_drv1;
+
+	/* bogus disk? */
+	if (sc == NULL) {
+		bp->bio_error = EINVAL;
+		bp->bio_flags |= BIO_ERROR;
+		goto bad;
+	}
+
+	DPRINTK("");
+
+	/*
+	 * Place it in the queue of disk activities for this disk
+	 */
+	mtx_lock(&blkif_io_lock);
+	bioq_disksort(&sc->xb_bioq, bp);
+
+	xb_startio(sc);
+	mtx_unlock(&blkif_io_lock);
+	return;
+
+ bad:
+	/*
+	 * Correctly set the bio to indicate a failed tranfer.
+	 */
+	bp->bio_resid = bp->bio_bcount;
+	biodone(bp);
+	return;
+}
+
+
+/* Setup supplies the backend dir, virtual device.
+
+We place an event channel and shared frame entries.
+We watch backend to wait if it's ok. */
+static int blkfront_probe(struct xenbus_device *dev,
+			  const struct xenbus_device_id *id)
+{
+	int err, vdevice, i;
+	struct blkfront_info *info;
+
+	/* FIXME: Use dynamic device id if this is not set. */
+	err = xenbus_scanf(XBT_NIL, dev->nodename,
+			   "virtual-device", "%i", &vdevice);
+	if (err != 1) {
+		xenbus_dev_fatal(dev, err, "reading virtual-device");
+		return err;
+	}
+
+	info = malloc(sizeof(*info), M_DEVBUF, M_NOWAIT|M_ZERO);
+	if (info == NULL) {
+		xenbus_dev_fatal(dev, ENOMEM, "allocating info structure");
+		return ENOMEM;
+	}
+	
+	/*
+	 * XXX debug only
+	 */
+	for (i = 0; i < sizeof(*info); i++)
+			if (((uint8_t *)info)[i] != 0)
+					panic("non-null memory");
+
+	info->shadow_free = 0;
+	info->xbdev = dev;
+	info->vdevice = vdevice;
+	info->connected = BLKIF_STATE_DISCONNECTED;
+
+	/* work queue needed ? */
+	for (i = 0; i < BLK_RING_SIZE; i++)
+		info->shadow[i].req.id = i+1;
+	info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;
+
+	/* Front end dir is a number, which is used as the id. */
+	info->handle = strtoul(strrchr(dev->nodename,'/')+1, NULL, 0);
+	dev->dev_driver_data = info;
+
+	err = talk_to_backend(dev, info);
+	if (err) {
+		free(info, M_DEVBUF);
+		dev->dev_driver_data = NULL;
+		return err;
+	}
+
+	return 0;
+}
+
+
+static int blkfront_resume(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev->dev_driver_data;
+	int err;
+
+	DPRINTK("blkfront_resume: %s\n", dev->nodename);
+
+	blkif_free(info, 1);
+
+	err = talk_to_backend(dev, info);
+	if (!err)
+		blkif_recover(info);
+
+	return err;
+}
+
+/* Common code used when first setting up, and when resuming. */
+static int talk_to_backend(struct xenbus_device *dev,
+			   struct blkfront_info *info)
+{
+	const char *message = NULL;
+	struct xenbus_transaction xbt;
+	int err;
+
+	/* Create shared ring, alloc event channel. */
+	err = setup_blkring(dev, info);
+	if (err)
+		goto out;
+
+ again:
+	err = xenbus_transaction_start(&xbt);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "starting transaction");
+		goto destroy_blkring;
+	}
+
+	err = xenbus_printf(xbt, dev->nodename,
+			    "ring-ref","%u", info->ring_ref);
+	if (err) {
+		message = "writing ring-ref";
+		goto abort_transaction;
+	}
+	err = xenbus_printf(xbt, dev->nodename,
+		"event-channel", "%u", irq_to_evtchn_port(info->irq));
+	if (err) {
+		message = "writing event-channel";
+		goto abort_transaction;
+	}
+
+	err = xenbus_transaction_end(xbt, 0);
+	if (err) {
+		if (err == -EAGAIN)
+			goto again;
+		xenbus_dev_fatal(dev, err, "completing transaction");
+		goto destroy_blkring;
+	}
+	xenbus_switch_state(dev, XenbusStateInitialised);
+	
+	return 0;
+
+ abort_transaction:
+	xenbus_transaction_end(xbt, 1);
+	if (message)
+		xenbus_dev_fatal(dev, err, "%s", message);
+ destroy_blkring:
+	blkif_free(info, 0);
+ out:
+	return err;
+}
+
+static int 
+setup_blkring(struct xenbus_device *dev, struct blkfront_info *info)
+{
+	blkif_sring_t *sring;
+	int err;
+
+	info->ring_ref = GRANT_INVALID_REF;
+
+	sring = (blkif_sring_t *)malloc(PAGE_SIZE, M_DEVBUF, M_NOWAIT|M_ZERO);
+	if (sring == NULL) {
+		xenbus_dev_fatal(dev, ENOMEM, "allocating shared ring");
+		return ENOMEM;
+	}
+	SHARED_RING_INIT(sring);
+	FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
+
+	err = xenbus_grant_ring(dev, (vtomach(info->ring.sring) >> PAGE_SHIFT));
+	if (err < 0) {
+		free(sring, M_DEVBUF);
+		info->ring.sring = NULL;
+		goto fail;
+	}
+	info->ring_ref = err;
+	
+	err = bind_listening_port_to_irqhandler(dev->otherend_id,
+		"xbd", (driver_intr_t *)blkif_int, info,
+					INTR_TYPE_BIO | INTR_MPSAFE, NULL);
+	if (err <= 0) {
+		xenbus_dev_fatal(dev, err,
+				 "bind_evtchn_to_irqhandler failed");
+		goto fail;
+	}
+	info->irq = err;
+
+	return 0;
+ fail:
+	blkif_free(info, 0);
+	return err;
+}
+
+
+/**
+ * Callback received when the backend's state changes.
+ */
+static void backend_changed(struct xenbus_device *dev,
+			    XenbusState backend_state)
+{
+	struct blkfront_info *info = dev->dev_driver_data;
+
+	DPRINTK("blkfront:backend_changed.\n");
+
+	switch (backend_state) {
+	case XenbusStateUnknown:
+	case XenbusStateInitialising:
+	case XenbusStateInitWait:
+	case XenbusStateInitialised:
+	case XenbusStateClosed:
+		break;
+
+	case XenbusStateConnected:
+		connect(info);
+		break;
+
+	case XenbusStateClosing:
+		if (info->users > 0)
+			xenbus_dev_error(dev, -EBUSY,
+					 "Device in use; refusing to close");
+		else
+			blkfront_closing(dev);
+#ifdef notyet
+		bd = bdget(info->dev);
+		if (bd == NULL)
+			xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
+
+		down(&bd->bd_sem);
+		if (info->users > 0)
+			xenbus_dev_error(dev, -EBUSY,
+					 "Device in use; refusing to close");
+		else
+			blkfront_closing(dev);
+		up(&bd->bd_sem);
+		bdput(bd);
+#endif
+	}
+}
+
+/* 
+** Invoked when the backend is finally 'ready' (and has told produced 
+** the details about the physical device - #sectors, size, etc). 
+*/
+static void 
+connect(struct blkfront_info *info)
+{
+	unsigned long sectors, sector_size;
+	unsigned int binfo;
+	int err;
+
+        if( (info->connected == BLKIF_STATE_CONNECTED) || 
+	    (info->connected == BLKIF_STATE_SUSPENDED) )
+		return;
+
+	DPRINTK("blkfront.c:connect:%s.\n", info->xbdev->otherend);
+
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+			    "sectors", "%lu", &sectors,
+			    "info", "%u", &binfo,
+			    "sector-size", "%lu", &sector_size,
+			    NULL);
+	if (err) {
+		xenbus_dev_fatal(info->xbdev, err,
+				 "reading backend fields at %s",
+				 info->xbdev->otherend);
+		return;
+	}
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+			    "feature-barrier", "%lu", &info->feature_barrier,
+			    NULL);
+	if (err)
+		info->feature_barrier = 0;
+
+	xlvbd_add(sectors, info->vdevice, binfo, sector_size, info);
+
+	(void)xenbus_switch_state(info->xbdev, XenbusStateConnected); 
+
+	/* Kick pending requests. */
+	mtx_lock(&blkif_io_lock);
+	info->connected = BLKIF_STATE_CONNECTED;
+	kick_pending_request_queues(info);
+	mtx_unlock(&blkif_io_lock);
+
+#if 0
+	add_disk(info->gd);
+#endif
+}
+
+/**
+ * Handle the change of state of the backend to Closing.  We must delete our
+ * device-layer structures now, to ensure that writes are flushed through to
+ * the backend.  Once is this done, we can switch to Closed in
+ * acknowledgement.
+ */
+static void blkfront_closing(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev->dev_driver_data;
+
+	DPRINTK("blkfront_closing: %s removed\n", dev->nodename);
+
+	if (info->mi) {
+		DPRINTK("Calling xlvbd_del\n");
+		xlvbd_del(info);
+		info->mi = NULL;
+	}
+
+	xenbus_switch_state(dev, XenbusStateClosed);
+}
+
+
+static int blkfront_remove(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev->dev_driver_data;
+
+	DPRINTK("blkfront_remove: %s removed\n", dev->nodename);
+
+	blkif_free(info, 0);
+
+	free(info, M_DEVBUF);
+
+	return 0;
+}
+
+
+static inline int 
+GET_ID_FROM_FREELIST(struct blkfront_info *info)
+{
+	unsigned long nfree = info->shadow_free;
+	
+	KASSERT(nfree <= BLK_RING_SIZE, ("free %lu > RING_SIZE", nfree));
+	info->shadow_free = info->shadow[nfree].req.id;
+	info->shadow[nfree].req.id = 0x0fffffee; /* debug */
+	return nfree;
+}
+
+static inline void 
+ADD_ID_TO_FREELIST(struct blkfront_info *info, unsigned long id)
+{
+	info->shadow[id].req.id  = info->shadow_free;
+	info->shadow[id].request = 0;
+	info->shadow_free = id;
+}
+
+static inline void 
+flush_requests(struct blkfront_info *info)
+{
+	int notify;
+
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->ring, notify);
+
+	if (notify)
+		notify_remote_via_irq(info->irq);
+}
+
+static void 
+kick_pending_request_queues(struct blkfront_info *info)
+{
+	/* XXX check if we can't simplify */
+#if 0
+	if (!RING_FULL(&info->ring)) {
+		/* Re-enable calldowns. */
+		blk_start_queue(info->rq);
+		/* Kick things off immediately. */
+		do_blkif_request(info->rq);
+	}
+#endif
+	if (!RING_FULL(&info->ring)) {
+#if 0
+		sc = LIST_FIRST(&xbsl_head);
+		LIST_REMOVE(sc, entry);
+		/* Re-enable calldowns. */
+		blk_start_queue(di->rq);
+#endif
+		/* Kick things off immediately. */
+		xb_startio(info->sc);
+	}
+}
+
+#if 0
+/* XXX */
+static void blkif_restart_queue(void *arg)
+{
+	struct blkfront_info *info = (struct blkfront_info *)arg;
+
+	mtx_lock(&blkif_io_lock);
+	kick_pending_request_queues(info);
+	mtx_unlock(&blkif_io_lock);
+}
+#endif
+
+static void blkif_restart_queue_callback(void *arg)
+{
+#if 0
+	struct blkfront_info *info = (struct blkfront_info *)arg;
+	/* XXX BSD equiv ? */
+
+	schedule_work(&info->work);
+#endif
+}
+
+static int
+blkif_open(struct disk *dp)
+{
+	struct xb_softc	*sc = (struct xb_softc *)dp->d_drv1;
+
+	if (sc == NULL) {
+		printk("xb%d: not found", sc->xb_unit);
+		return (ENXIO);
+	}
+
+	sc->xb_flags |= XB_OPEN;
+	sc->xb_info->users++;
+	return (0);
+}
+
+static int
+blkif_close(struct disk *dp)
+{
+	struct xb_softc	*sc = (struct xb_softc *)dp->d_drv1;
+
+	if (sc == NULL)
+		return (ENXIO);
+	sc->xb_flags &= ~XB_OPEN;
+	if (--(sc->xb_info->users) == 0) {
+		/* Check whether we have been instructed to close.  We will
+		   have ignored this request initially, as the device was
+		   still mounted. */
+		struct xenbus_device * dev = sc->xb_info->xbdev;
+		XenbusState state = xenbus_read_driver_state(dev->otherend);
+
+		if (state == XenbusStateClosing)
+			blkfront_closing(dev);
+	}
+	return (0);
+}
+
+static int
+blkif_ioctl(struct disk *dp, u_long cmd, void *addr, int flag, struct thread *td)
+{
+	struct xb_softc	*sc = (struct xb_softc *)dp->d_drv1;
+
+	if (sc == NULL)
+		return (ENXIO);
+
+	return (ENOTTY);
+}
+
+
+/*
+ * blkif_queue_request
+ *
+ * request block io
+ * 
+ * id: for guest use only.
+ * operation: BLKIF_OP_{READ,WRITE,PROBE}
+ * buffer: buffer to read/write into. this should be a
+ *   virtual address in the guest os.
+ */
+static int blkif_queue_request(struct bio *bp)
+{
+	caddr_t alignbuf;
+	unsigned long  	buffer_ma;
+	blkif_request_t     *ring_req;
+	unsigned long id;
+	unsigned int fsect, lsect;
+	struct xb_softc *sc = (struct xb_softc *)bp->bio_disk->d_drv1;
+	struct blkfront_info *info = sc->xb_info;
+	int ref;
+
+	if (unlikely(sc->xb_info->connected != BLKIF_STATE_CONNECTED))
+		return 1;
+
+	if (gnttab_alloc_grant_references(
+		    BLKIF_MAX_SEGMENTS_PER_REQUEST, &gref_head) < 0) {
+		gnttab_request_free_callback(
+			&info->callback,
+			blkif_restart_queue_callback,
+			info,
+			BLKIF_MAX_SEGMENTS_PER_REQUEST);
+		return 1;
+	}
+
+	/* Check if the buffer is properly aligned */
+	if ((vm_offset_t)bp->bio_data & PAGE_MASK) {
+		int align = (bp->bio_bcount < PAGE_SIZE/2) ? XBD_SECTOR_SIZE : 
+			PAGE_SIZE;
+		caddr_t newbuf = malloc(bp->bio_bcount + align, M_DEVBUF, 
+					M_NOWAIT);
+
+		alignbuf = (char *)roundup2((u_long)newbuf, align);
+
+		/* save a copy of the current buffer */
+		bp->bio_driver1 = newbuf;
+		bp->bio_driver2 = alignbuf;
+
+		/* Copy the data for a write */
+		if (bp->bio_cmd == BIO_WRITE)
+			bcopy(bp->bio_data, alignbuf, bp->bio_bcount);
+	} else
+		alignbuf = bp->bio_data;
+	
+	/* Fill out a communications ring structure. */
+	ring_req 	         = RING_GET_REQUEST(&info->ring, 
+						    info->ring.req_prod_pvt);
+	id		         = GET_ID_FROM_FREELIST(info);
+	info->shadow[id].request = (unsigned long)bp;
+	
+	ring_req->id 	         = id;
+	ring_req->operation 	 = (bp->bio_cmd == BIO_READ) ? BLKIF_OP_READ :
+		BLKIF_OP_WRITE;
+	
+	ring_req->sector_number= (blkif_sector_t)bp->bio_pblkno;
+	ring_req->handle 	  = (blkif_vdev_t)(uintptr_t)sc->xb_disk;
+	
+	ring_req->nr_segments  = 0;	/* XXX not doing scatter/gather since buffer
+					 * chaining is not supported.
+					 */
+
+	buffer_ma = vtomach(alignbuf);
+	fsect = (buffer_ma & PAGE_MASK) >> XBD_SECTOR_SHFT;
+	lsect = fsect + (bp->bio_bcount >> XBD_SECTOR_SHFT) - 1;
+	/* install a grant reference. */
+	ref = gnttab_claim_grant_reference(&gref_head);
+	KASSERT( ref != -ENOSPC, ("grant_reference failed") );
+
+	gnttab_grant_foreign_access_ref(
+		ref,
+		info->xbdev->otherend_id,
+		buffer_ma >> PAGE_SHIFT,
+		ring_req->operation & 1 ); /* ??? */
+	info->shadow[id].frame[ring_req->nr_segments] = 
+		buffer_ma >> PAGE_SHIFT;
+
+	ring_req->seg[ring_req->nr_segments] =
+		(struct blkif_request_segment) {
+			.gref       = ref,
+			.first_sect = fsect, 
+			.last_sect  = lsect };
+
+	ring_req->nr_segments++;
+	KASSERT((buffer_ma & (XBD_SECTOR_SIZE-1)) == 0,
+		("XEN buffer must be sector aligned"));
+	KASSERT(lsect <= 7, 
+		("XEN disk driver data cannot cross a page boundary"));
+	
+	buffer_ma &= ~PAGE_MASK;
+
+	info->ring.req_prod_pvt++;
+
+	/* Keep a private copy so we can reissue requests when recovering. */
+	info->shadow[id].req = *ring_req;
+
+	gnttab_free_grant_references(gref_head);
+
+	return 0;
+}
+
+
+
+/*
+ * Dequeue buffers and place them in the shared communication ring.
+ * Return when no more requests can be accepted or all buffers have 
+ * been queued.
+ *
+ * Signal XEN once the ring has been filled out.
+ */
+static void
+xb_startio(struct xb_softc *sc)
+{
+	struct bio		*bp;
+	int			queued = 0;
+	struct blkfront_info *info = sc->xb_info;
+	DPRINTK("");
+
+	mtx_assert(&blkif_io_lock, MA_OWNED);
+
+	while ((bp = bioq_takefirst(&sc->xb_bioq)) != NULL) {
+
+		if (RING_FULL(&info->ring)) 
+			goto wait;
+    	
+		if (blkif_queue_request(bp)) {
+		wait:
+			bioq_insert_head(&sc->xb_bioq, bp);
+			break;
+		}
+		queued++;
+	}
+
+	if (queued != 0) 
+		flush_requests(sc->xb_info);
+}
+
+static void
+blkif_int(void *xsc)
+{
+	struct xb_softc *sc = NULL;
+	struct bio *bp;
+	blkif_response_t *bret;
+	RING_IDX i, rp;
+	struct blkfront_info *info = xsc;
+	DPRINTK("");
+
+	TRACE_ENTER;
+
+	mtx_lock(&blkif_io_lock);
+
+	if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
+		mtx_unlock(&blkif_io_lock);
+		return;
+	}
+
+ again:
+	rp = info->ring.sring->rsp_prod;
+	rmb(); /* Ensure we see queued responses up to 'rp'. */
+
+	for (i = info->ring.rsp_cons; i != rp; i++) {
+		unsigned long id;
+
+		bret = RING_GET_RESPONSE(&info->ring, i);
+		id   = bret->id;
+		bp   = (struct bio *)info->shadow[id].request;
+
+		blkif_completion(&info->shadow[id]);
+
+		ADD_ID_TO_FREELIST(info, id);
+
+		switch (bret->operation) {
+		case BLKIF_OP_READ:
+			/* had an unaligned buffer that needs to be copied */
+			if (bp->bio_driver1)
+				bcopy(bp->bio_driver2, bp->bio_data, bp->bio_bcount);
+			/* FALLTHROUGH */
+		case BLKIF_OP_WRITE:
+
+			/* free the copy buffer */
+			if (bp->bio_driver1) {
+				free(bp->bio_driver1, M_DEVBUF);
+				bp->bio_driver1 = NULL;
+			}
+
+			if ( unlikely(bret->status != BLKIF_RSP_OKAY) ) {
+				XENPRINTF("Bad return from blkdev data request: %x\n", 
+					  bret->status);
+				bp->bio_flags |= BIO_ERROR;
+			}
+
+			sc = (struct xb_softc *)bp->bio_disk->d_drv1;
+
+			if (bp->bio_flags & BIO_ERROR)
+				bp->bio_error = EIO;
+			else
+				bp->bio_resid = 0;
+
+			biodone(bp);
+			break;
+		default:
+			panic("received invalid operation");
+			break;
+		}
+	}
+
+	info->ring.rsp_cons = i;
+
+	if (i != info->ring.req_prod_pvt) {
+		int more_to_do;
+		RING_FINAL_CHECK_FOR_RESPONSES(&info->ring, more_to_do);
+		if (more_to_do)
+			goto again;
+	} else {
+		info->ring.sring->rsp_event = i + 1;
+	}
+
+	kick_pending_request_queues(info);
+
+	mtx_unlock(&blkif_io_lock);
+}
+
+static void 
+blkif_free(struct blkfront_info *info, int suspend)
+{
+	
+/* Prevent new requests being issued until we fix things up. */
+	mtx_lock(&blkif_io_lock);
+	info->connected = suspend ? 
+		BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED; 
+	mtx_unlock(&blkif_io_lock);
+
+	/* Free resources associated with old device channel. */
+	if (info->ring_ref != GRANT_INVALID_REF) {
+		gnttab_end_foreign_access(info->ring_ref, 0,
+					  info->ring.sring);
+		info->ring_ref = GRANT_INVALID_REF;
+		info->ring.sring = NULL;
+	}
+	if (info->irq)
+		unbind_from_irqhandler(info->irq, info); 
+	info->irq = 0;
+
+}
+
+static void 
+blkif_completion(struct blk_shadow *s)
+{
+	int i;
+
+	for (i = 0; i < s->req.nr_segments; i++)
+		gnttab_end_foreign_access(s->req.seg[i].gref, 0, 0UL);
+}
+
+static void 
+blkif_recover(struct blkfront_info *info)
+{
+	int i, j;
+	blkif_request_t *req;
+	struct blk_shadow *copy;
+
+	/* Stage 1: Make a safe copy of the shadow state. */
+	copy = (struct blk_shadow *)malloc(sizeof(info->shadow), M_DEVBUF, M_NOWAIT|M_ZERO);
+	PANIC_IF(copy == NULL);
+	memcpy(copy, info->shadow, sizeof(info->shadow));
+
+	/* Stage 2: Set up free list. */
+	memset(&info->shadow, 0, sizeof(info->shadow));
+	for (i = 0; i < BLK_RING_SIZE; i++)
+		info->shadow[i].req.id = i+1;
+	info->shadow_free = info->ring.req_prod_pvt;
+	info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;
+
+	/* Stage 3: Find pending requests and requeue them. */
+	for (i = 0; i < BLK_RING_SIZE; i++) {
+		/* Not in use? */
+		if (copy[i].request == 0)
+			continue;
+
+		/* Grab a request slot and copy shadow state into it. */
+		req = RING_GET_REQUEST(
+			&info->ring, info->ring.req_prod_pvt);
+		*req = copy[i].req;
+
+		/* We get a new request id, and must reset the shadow state. */
+		req->id = GET_ID_FROM_FREELIST(info);
+		memcpy(&info->shadow[req->id], &copy[i], sizeof(copy[i]));
+
+		/* Rewrite any grant references invalidated by suspend/resume. */
+		for (j = 0; j < req->nr_segments; j++)
+			gnttab_grant_foreign_access_ref(
+				req->seg[j].gref,
+				info->xbdev->otherend_id,
+				pfn_to_mfn(info->shadow[req->id].frame[j]),
+				0 /* assume not readonly */);
+
+		info->shadow[req->id].req = *req;
+
+		info->ring.req_prod_pvt++;
+	}
+
+	free(copy, M_DEVBUF);
+
+	xenbus_switch_state(info->xbdev, XenbusStateConnected); 
+	
+	/* Now safe for us to use the shared ring */
+	mtx_lock(&blkif_io_lock);
+	info->connected = BLKIF_STATE_CONNECTED;
+	mtx_unlock(&blkif_io_lock);
+
+	/* Send off requeued requests */
+	mtx_lock(&blkif_io_lock);
+	flush_requests(info);
+
+	/* Kick any other new requests queued since we resumed */
+	kick_pending_request_queues(info);
+	mtx_unlock(&blkif_io_lock);
+}
+
+static int
+blkfront_is_ready(struct xenbus_device *dev)
+{
+	struct blkfront_info *info = dev->dev_driver_data;
+
+	return info->is_ready;
+}
+
+static struct xenbus_device_id blkfront_ids[] = {
+	{ "vbd" },
+	{ "" }
+};
+
+
+static struct xenbus_driver blkfront = {
+	.name             = "vbd",
+	.ids              = blkfront_ids,
+	.probe            = blkfront_probe,
+	.remove           = blkfront_remove,
+	.resume           = blkfront_resume,
+	.otherend_changed = backend_changed,
+	.is_ready		  = blkfront_is_ready,
+};
+
+
+
+static void
+xenbus_init(void)
+{
+	xenbus_register_frontend(&blkfront);
+}
+
+MTX_SYSINIT(ioreq, &blkif_io_lock, "BIO LOCK", MTX_NOWITNESS); /* XXX how does one enroll a lock? */
+SYSINIT(xbdev, SI_SUB_PSEUDO, SI_ORDER_SECOND, xenbus_init, NULL);
+
+
+/*
+ * Local variables:
+ * mode: C
+ * c-set-style: "BSD"
+ * c-basic-offset: 8
+ * tab-width: 4
+ * indent-tabs-mode: t
+ * End:
+ */