[mirror_ubuntu-bionic-kernel.git] / drivers / block / xen-blkback / xenbus.c

/*  Xenbus code for blkif backend
    Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
    Copyright (C) 2005 XenSource Ltd

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

*/

#define pr_fmt(fmt) "xen-blkback: " fmt

#include <stdarg.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <xen/events.h>
#include <xen/grant_table.h>
#include "common.h"

/* On the XenBus the max length of 'ring-ref%u'. */
#define RINGREF_NAME_LEN (20)

struct backend_info {
        struct xenbus_device    *dev;
        struct xen_blkif        *blkif;
        struct xenbus_watch     backend_watch;
        unsigned                major;
        unsigned                minor;
        char                    *mode;
};

static struct kmem_cache *xen_blkif_cachep;
static void connect(struct backend_info *);
static int connect_ring(struct backend_info *);
static void backend_changed(struct xenbus_watch *, const char *,
                            const char *);
static void xen_blkif_free(struct xen_blkif *blkif);
static void xen_vbd_free(struct xen_vbd *vbd);

struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be)
{
        return be->dev;
}

/*
 * The last request could free the device from softirq context and
 * xen_blkif_free() can sleep.
 */
static void xen_blkif_deferred_free(struct work_struct *work)
{
        struct xen_blkif *blkif;

        blkif = container_of(work, struct xen_blkif, free_work);
        xen_blkif_free(blkif);
}

static int blkback_name(struct xen_blkif *blkif, char *buf)
{
        char *devpath, *devname;
        struct xenbus_device *dev = blkif->be->dev;

        devpath = xenbus_read(XBT_NIL, dev->nodename, "dev", NULL);
        if (IS_ERR(devpath))
                return PTR_ERR(devpath);

        devname = strstr(devpath, "/dev/");
        if (devname != NULL)
                devname += strlen("/dev/");
        else
                devname  = devpath;

        snprintf(buf, TASK_COMM_LEN, "%d.%s", blkif->domid, devname);
        kfree(devpath);

        return 0;
}

static void xen_update_blkif_status(struct xen_blkif *blkif)
{
        int err;
        char name[TASK_COMM_LEN];
        struct xen_blkif_ring *ring;
        int i;

        /* Not ready to connect? */
        if (!blkif->rings || !blkif->rings[0].irq || !blkif->vbd.bdev)
                return;

        /* Already connected? */
        if (blkif->be->dev->state == XenbusStateConnected)
                return;

        /* Attempt to connect: exit if we fail to. */
        connect(blkif->be);
        if (blkif->be->dev->state != XenbusStateConnected)
                return;

        err = blkback_name(blkif, name);
        if (err) {
                xenbus_dev_error(blkif->be->dev, err, "get blkback dev name");
                return;
        }

        err = filemap_write_and_wait(blkif->vbd.bdev->bd_inode->i_mapping);
        if (err) {
                xenbus_dev_error(blkif->be->dev, err, "block flush");
                return;
        }
        invalidate_inode_pages2(blkif->vbd.bdev->bd_inode->i_mapping);

        for (i = 0; i < blkif->nr_rings; i++) {
                ring = &blkif->rings[i];
                ring->xenblkd = kthread_run(xen_blkif_schedule, ring, "%s-%d", name, i);
                if (IS_ERR(ring->xenblkd)) {
                        err = PTR_ERR(ring->xenblkd);
                        ring->xenblkd = NULL;
                        xenbus_dev_fatal(blkif->be->dev, err,
                                        "start %s-%d xenblkd", name, i);
                        goto out;
                }
        }
        return;

out:
        while (--i >= 0) {
                ring = &blkif->rings[i];
                kthread_stop(ring->xenblkd);
        }
        return;
}

static int xen_blkif_alloc_rings(struct xen_blkif *blkif)
{
        unsigned int r;

        blkif->rings = kzalloc(blkif->nr_rings * sizeof(struct xen_blkif_ring), GFP_KERNEL);
        if (!blkif->rings)
                return -ENOMEM;

        for (r = 0; r < blkif->nr_rings; r++) {
                struct xen_blkif_ring *ring = &blkif->rings[r];

                spin_lock_init(&ring->blk_ring_lock);
                init_waitqueue_head(&ring->wq);
                INIT_LIST_HEAD(&ring->pending_free);
                INIT_LIST_HEAD(&ring->persistent_purge_list);
                INIT_WORK(&ring->persistent_purge_work, xen_blkbk_unmap_purged_grants);
                spin_lock_init(&ring->free_pages_lock);
                INIT_LIST_HEAD(&ring->free_pages);

                spin_lock_init(&ring->pending_free_lock);
                init_waitqueue_head(&ring->pending_free_wq);
                init_waitqueue_head(&ring->shutdown_wq);
                ring->blkif = blkif;
                ring->st_print = jiffies;
                ring->active = true;
        }

        return 0;
}

static struct xen_blkif *xen_blkif_alloc(domid_t domid)
{
        struct xen_blkif *blkif;

        BUILD_BUG_ON(MAX_INDIRECT_PAGES > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);

        blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
        if (!blkif)
                return ERR_PTR(-ENOMEM);

        blkif->domid = domid;
        atomic_set(&blkif->refcnt, 1);
        init_completion(&blkif->drain_complete);
        INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);

        return blkif;
}

static int xen_blkif_map(struct xen_blkif_ring *ring, grant_ref_t *gref,
                         unsigned int nr_grefs, unsigned int evtchn)
{
        int err;
        struct xen_blkif *blkif = ring->blkif;

        /* Already connected through? */
        if (ring->irq)
                return 0;

        err = xenbus_map_ring_valloc(blkif->be->dev, gref, nr_grefs,
                                     &ring->blk_ring);
        if (err < 0)
                return err;

        switch (blkif->blk_protocol) {
        case BLKIF_PROTOCOL_NATIVE:
        {
                struct blkif_sring *sring;
                sring = (struct blkif_sring *)ring->blk_ring;
                BACK_RING_INIT(&ring->blk_rings.native, sring,
                               XEN_PAGE_SIZE * nr_grefs);
                break;
        }
        case BLKIF_PROTOCOL_X86_32:
        {
                struct blkif_x86_32_sring *sring_x86_32;
                sring_x86_32 = (struct blkif_x86_32_sring *)ring->blk_ring;
                BACK_RING_INIT(&ring->blk_rings.x86_32, sring_x86_32,
                               XEN_PAGE_SIZE * nr_grefs);
                break;
        }
        case BLKIF_PROTOCOL_X86_64:
        {
                struct blkif_x86_64_sring *sring_x86_64;
                sring_x86_64 = (struct blkif_x86_64_sring *)ring->blk_ring;
                BACK_RING_INIT(&ring->blk_rings.x86_64, sring_x86_64,
                               XEN_PAGE_SIZE * nr_grefs);
                break;
        }
        default:
                BUG();
        }

        err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
                                                    xen_blkif_be_int, 0,
                                                    "blkif-backend", ring);
        if (err < 0) {
                xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
                ring->blk_rings.common.sring = NULL;
                return err;
        }
        ring->irq = err;

        return 0;
}

static int xen_blkif_disconnect(struct xen_blkif *blkif)
{
        struct pending_req *req, *n;
        unsigned int j, r;
        bool busy = false;

        for (r = 0; r < blkif->nr_rings; r++) {
                struct xen_blkif_ring *ring = &blkif->rings[r];
                unsigned int i = 0;

                if (!ring->active)
                        continue;

                if (ring->xenblkd) {
                        kthread_stop(ring->xenblkd);
                        wake_up(&ring->shutdown_wq);
                }

                /* The above kthread_stop() guarantees that at this point we
                 * don't have any discard_io or other_io requests. So, checking
                 * for inflight IO is enough.
                 */
                if (atomic_read(&ring->inflight) > 0) {
                        busy = true;
                        continue;
                }

                if (ring->irq) {
                        unbind_from_irqhandler(ring->irq, ring);
                        ring->irq = 0;
                }

                if (ring->blk_rings.common.sring) {
                        xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
                        ring->blk_rings.common.sring = NULL;
                }

                /* Remove all persistent grants and the cache of ballooned pages. */
                xen_blkbk_free_caches(ring);

                /* Check that there is no request in use */
                list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
                        list_del(&req->free_list);

                        for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++)
                                kfree(req->segments[j]);

                        for (j = 0; j < MAX_INDIRECT_PAGES; j++)
                                kfree(req->indirect_pages[j]);

                        kfree(req);
                        i++;
                }

                BUG_ON(atomic_read(&ring->persistent_gnt_in_use) != 0);
                BUG_ON(!list_empty(&ring->persistent_purge_list));
                BUG_ON(!RB_EMPTY_ROOT(&ring->persistent_gnts));
                BUG_ON(!list_empty(&ring->free_pages));
                BUG_ON(ring->free_pages_num != 0);
                BUG_ON(ring->persistent_gnt_c != 0);
                WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));
                ring->active = false;
        }
        if (busy)
                return -EBUSY;

        blkif->nr_ring_pages = 0;
        /*
         * blkif->rings was allocated in connect_ring, so we should free it in
         * here.
         */
        kfree(blkif->rings);
        blkif->rings = NULL;
        blkif->nr_rings = 0;

        return 0;
}

static void xen_blkif_free(struct xen_blkif *blkif)
{
        WARN_ON(xen_blkif_disconnect(blkif));
        xen_vbd_free(&blkif->vbd);
        kfree(blkif->be->mode);
        kfree(blkif->be);

        /* Make sure everything is drained before shutting down */
        kmem_cache_free(xen_blkif_cachep, blkif);
}

int __init xen_blkif_interface_init(void)
{
        xen_blkif_cachep = kmem_cache_create("blkif_cache",
                                             sizeof(struct xen_blkif),
                                             0, 0, NULL);
        if (!xen_blkif_cachep)
                return -ENOMEM;

        return 0;
}

/*
 *  sysfs interface for VBD I/O requests
 */

#define VBD_SHOW_ALLRING(name, format)                                  \
        static ssize_t show_##name(struct device *_dev,                 \
                                   struct device_attribute *attr,       \
                                   char *buf)                           \
        {                                                               \
                struct xenbus_device *dev = to_xenbus_device(_dev);     \
                struct backend_info *be = dev_get_drvdata(&dev->dev);   \
                struct xen_blkif *blkif = be->blkif;                    \
                unsigned int i;                                         \
                unsigned long long result = 0;                          \
                                                                        \
                if (!blkif->rings)                              \
                        goto out;                                       \
                                                                        \
                for (i = 0; i < blkif->nr_rings; i++) {         \
                        struct xen_blkif_ring *ring = &blkif->rings[i]; \
                                                                        \
                        result += ring->st_##name;                      \
                }                                                       \
                                                                        \
out:                                                                    \
                return sprintf(buf, format, result);                    \
        }                                                               \
        static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)

VBD_SHOW_ALLRING(oo_req,  "%llu\n");
VBD_SHOW_ALLRING(rd_req,  "%llu\n");
VBD_SHOW_ALLRING(wr_req,  "%llu\n");
VBD_SHOW_ALLRING(f_req,  "%llu\n");
VBD_SHOW_ALLRING(ds_req,  "%llu\n");
VBD_SHOW_ALLRING(rd_sect, "%llu\n");
VBD_SHOW_ALLRING(wr_sect, "%llu\n");

static struct attribute *xen_vbdstat_attrs[] = {
        &dev_attr_oo_req.attr,
        &dev_attr_rd_req.attr,
        &dev_attr_wr_req.attr,
        &dev_attr_f_req.attr,
        &dev_attr_ds_req.attr,
        &dev_attr_rd_sect.attr,
        &dev_attr_wr_sect.attr,
        NULL
};

static const struct attribute_group xen_vbdstat_group = {
        .name = "statistics",
        .attrs = xen_vbdstat_attrs,
};

#define VBD_SHOW(name, format, args...)                                 \
        static ssize_t show_##name(struct device *_dev,                 \
                                   struct device_attribute *attr,       \
                                   char *buf)                           \
        {                                                               \
                struct xenbus_device *dev = to_xenbus_device(_dev);     \
                struct backend_info *be = dev_get_drvdata(&dev->dev);   \
                                                                        \
                return sprintf(buf, format, ##args);                    \
        }                                                               \
        static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)

VBD_SHOW(physical_device, "%x:%x\n", be->major, be->minor);
VBD_SHOW(mode, "%s\n", be->mode);

static int xenvbd_sysfs_addif(struct xenbus_device *dev)
{
        int error;

        error = device_create_file(&dev->dev, &dev_attr_physical_device);
        if (error)
                goto fail1;

        error = device_create_file(&dev->dev, &dev_attr_mode);
        if (error)
                goto fail2;

        error = sysfs_create_group(&dev->dev.kobj, &xen_vbdstat_group);
        if (error)
                goto fail3;

        return 0;

fail3:  sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
fail2:  device_remove_file(&dev->dev, &dev_attr_mode);
fail1:  device_remove_file(&dev->dev, &dev_attr_physical_device);
        return error;
}

static void xenvbd_sysfs_delif(struct xenbus_device *dev)
{
        sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
        device_remove_file(&dev->dev, &dev_attr_mode);
        device_remove_file(&dev->dev, &dev_attr_physical_device);
}


static void xen_vbd_free(struct xen_vbd *vbd)
{
        if (vbd->bdev)
                blkdev_put(vbd->bdev, vbd->readonly ? FMODE_READ : FMODE_WRITE);
        vbd->bdev = NULL;
}

static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
                          unsigned major, unsigned minor, int readonly,
                          int cdrom)
{
        struct xen_vbd *vbd;
        struct block_device *bdev;
        struct request_queue *q;

        vbd = &blkif->vbd;
        vbd->handle   = handle;
        vbd->readonly = readonly;
        vbd->type     = 0;

        vbd->pdevice  = MKDEV(major, minor);

        bdev = blkdev_get_by_dev(vbd->pdevice, vbd->readonly ?
                                 FMODE_READ : FMODE_WRITE, NULL);

        if (IS_ERR(bdev)) {
                pr_warn("xen_vbd_create: device %08x could not be opened\n",
                        vbd->pdevice);
                return -ENOENT;
        }

        vbd->bdev = bdev;
        if (vbd->bdev->bd_disk == NULL) {
                pr_warn("xen_vbd_create: device %08x doesn't exist\n",
                        vbd->pdevice);
                xen_vbd_free(vbd);
                return -ENOENT;
        }
        vbd->size = vbd_sz(vbd);

        if (vbd->bdev->bd_disk->flags & GENHD_FL_CD || cdrom)
                vbd->type |= VDISK_CDROM;
        if (vbd->bdev->bd_disk->flags & GENHD_FL_REMOVABLE)
                vbd->type |= VDISK_REMOVABLE;

        q = bdev_get_queue(bdev);
        if (q && test_bit(QUEUE_FLAG_WC, &q->queue_flags))
                vbd->flush_support = true;

        if (q && blk_queue_secure_erase(q))
                vbd->discard_secure = true;

        pr_debug("Successful creation of handle=%04x (dom=%u)\n",
                handle, blkif->domid);
        return 0;
}
static int xen_blkbk_remove(struct xenbus_device *dev)
{
        struct backend_info *be = dev_get_drvdata(&dev->dev);

        pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);

        if (be->major || be->minor)
                xenvbd_sysfs_delif(dev);

        if (be->backend_watch.node) {
                unregister_xenbus_watch(&be->backend_watch);
                kfree(be->backend_watch.node);
                be->backend_watch.node = NULL;
        }

        dev_set_drvdata(&dev->dev, NULL);

        if (be->blkif) {
                xen_blkif_disconnect(be->blkif);

                /* Put the reference we set in xen_blkif_alloc(). */
                xen_blkif_put(be->blkif);
        }

        return 0;
}

int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
                              struct backend_info *be, int state)
{
        struct xenbus_device *dev = be->dev;
        int err;

        err = xenbus_printf(xbt, dev->nodename, "feature-flush-cache",
                            "%d", state);
        if (err)
                dev_warn(&dev->dev, "writing feature-flush-cache (%d)", err);

        return err;
}

static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
{
        struct xenbus_device *dev = be->dev;
        struct xen_blkif *blkif = be->blkif;
        int err;
        int state = 0;
        struct block_device *bdev = be->blkif->vbd.bdev;
        struct request_queue *q = bdev_get_queue(bdev);

        if (!xenbus_read_unsigned(dev->nodename, "discard-enable", 1))
                return;

        if (blk_queue_discard(q)) {
                err = xenbus_printf(xbt, dev->nodename,
                        "discard-granularity", "%u",
                        q->limits.discard_granularity);
                if (err) {
                        dev_warn(&dev->dev, "writing discard-granularity (%d)", err);
                        return;
                }
                err = xenbus_printf(xbt, dev->nodename,
                        "discard-alignment", "%u",
                        q->limits.discard_alignment);
                if (err) {
                        dev_warn(&dev->dev, "writing discard-alignment (%d)", err);
                        return;
                }
                state = 1;
                /* Optional. */
                err = xenbus_printf(xbt, dev->nodename,
                                    "discard-secure", "%d",
                                    blkif->vbd.discard_secure);
                if (err) {
                        dev_warn(&dev->dev, "writing discard-secure (%d)", err);
                        return;
                }
        }
        err = xenbus_printf(xbt, dev->nodename, "feature-discard",
                            "%d", state);
        if (err)
                dev_warn(&dev->dev, "writing feature-discard (%d)", err);
}
int xen_blkbk_barrier(struct xenbus_transaction xbt,
                      struct backend_info *be, int state)
{
        struct xenbus_device *dev = be->dev;
        int err;

        err = xenbus_printf(xbt, dev->nodename, "feature-barrier",
                            "%d", state);
        if (err)
                dev_warn(&dev->dev, "writing feature-barrier (%d)", err);

        return err;
}

/*
 * Entry point to this code when a new device is created.  Allocate the basic
 * structures, and watch the store waiting for the hotplug scripts to tell us
 * the device's physical major and minor numbers.  Switch to InitWait.
 */
static int xen_blkbk_probe(struct xenbus_device *dev,
                           const struct xenbus_device_id *id)
{
        int err;
        struct backend_info *be = kzalloc(sizeof(struct backend_info),
                                          GFP_KERNEL);

        /* match the pr_debug in xen_blkbk_remove */
        pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);

        if (!be) {
                xenbus_dev_fatal(dev, -ENOMEM,
                                 "allocating backend structure");
                return -ENOMEM;
        }
        be->dev = dev;
        dev_set_drvdata(&dev->dev, be);

        be->blkif = xen_blkif_alloc(dev->otherend_id);
        if (IS_ERR(be->blkif)) {
                err = PTR_ERR(be->blkif);
                be->blkif = NULL;
                xenbus_dev_fatal(dev, err, "creating block interface");
                goto fail;
        }

        err = xenbus_printf(XBT_NIL, dev->nodename,
                            "feature-max-indirect-segments", "%u",
                            MAX_INDIRECT_SEGMENTS);
        if (err)
                dev_warn(&dev->dev,
                         "writing %s/feature-max-indirect-segments (%d)",
                         dev->nodename, err);

        /* Multi-queue: advertise how many queues are supported by us.*/
        err = xenbus_printf(XBT_NIL, dev->nodename,
                            "multi-queue-max-queues", "%u", xenblk_max_queues);
        if (err)
                pr_warn("Error writing multi-queue-max-queues\n");

        /* setup back pointer */
        be->blkif->be = be;

        err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
                                   "%s/%s", dev->nodename, "physical-device");
        if (err)
                goto fail;

        err = xenbus_printf(XBT_NIL, dev->nodename, "max-ring-page-order", "%u",
                            xen_blkif_max_ring_order);
        if (err)
                pr_warn("%s write out 'max-ring-page-order' failed\n", __func__);

        err = xenbus_switch_state(dev, XenbusStateInitWait);
        if (err)
                goto fail;

        return 0;

fail:
        pr_warn("%s failed\n", __func__);
        xen_blkbk_remove(dev);
        return err;
}


/*
 * Callback received when the hotplug scripts have placed the physical-device
 * node.  Read it and the mode node, and create a vbd.  If the frontend is
 * ready, connect.
 */
static void backend_changed(struct xenbus_watch *watch,
                            const char *path, const char *token)
{
        int err;
        unsigned major;
        unsigned minor;
        struct backend_info *be
                = container_of(watch, struct backend_info, backend_watch);
        struct xenbus_device *dev = be->dev;
        int cdrom = 0;
        unsigned long handle;
        char *device_type;

        pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);

        err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
                           &major, &minor);
        if (XENBUS_EXIST_ERR(err)) {
                /*
                 * Since this watch will fire once immediately after it is
                 * registered, we expect this.  Ignore it, and wait for the
                 * hotplug scripts.
                 */
                return;
        }
        if (err != 2) {
                xenbus_dev_fatal(dev, err, "reading physical-device");
                return;
        }

        if (be->major | be->minor) {
                if (be->major != major || be->minor != minor)
                        pr_warn("changing physical device (from %x:%x to %x:%x) not supported.\n",
                                be->major, be->minor, major, minor);
                return;
        }

        be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
        if (IS_ERR(be->mode)) {
                err = PTR_ERR(be->mode);
                be->mode = NULL;
                xenbus_dev_fatal(dev, err, "reading mode");
                return;
        }

        device_type = xenbus_read(XBT_NIL, dev->otherend, "device-type", NULL);
        if (!IS_ERR(device_type)) {
                cdrom = strcmp(device_type, "cdrom") == 0;
                kfree(device_type);
        }

        /* Front end dir is a number, which is used as the handle. */
        err = kstrtoul(strrchr(dev->otherend, '/') + 1, 0, &handle);
        if (err) {
                kfree(be->mode);
                be->mode = NULL;
                return;
        }

        be->major = major;
        be->minor = minor;

        err = xen_vbd_create(be->blkif, handle, major, minor,
                             !strchr(be->mode, 'w'), cdrom);

        if (err)
                xenbus_dev_fatal(dev, err, "creating vbd structure");
        else {
                err = xenvbd_sysfs_addif(dev);
                if (err) {
                        xen_vbd_free(&be->blkif->vbd);
                        xenbus_dev_fatal(dev, err, "creating sysfs entries");
                }
        }

        if (err) {
                kfree(be->mode);
                be->mode = NULL;
                be->major = 0;
                be->minor = 0;
        } else {
                /* We're potentially connected now */
                xen_update_blkif_status(be->blkif);
        }
}


/*
 * Callback received when the frontend's state changes.
 */
static void frontend_changed(struct xenbus_device *dev,
                             enum xenbus_state frontend_state)
{
        struct backend_info *be = dev_get_drvdata(&dev->dev);
        int err;

        pr_debug("%s %p %s\n", __func__, dev, xenbus_strstate(frontend_state));

        switch (frontend_state) {
        case XenbusStateInitialising:
                if (dev->state == XenbusStateClosed) {
                        pr_info("%s: prepare for reconnect\n", dev->nodename);
                        xenbus_switch_state(dev, XenbusStateInitWait);
                }
                break;

        case XenbusStateInitialised:
        case XenbusStateConnected:
                /*
                 * Ensure we connect even when two watches fire in
                 * close succession and we miss the intermediate value
                 * of frontend_state.
                 */
                if (dev->state == XenbusStateConnected)
                        break;

                /*
                 * Enforce precondition before potential leak point.
                 * xen_blkif_disconnect() is idempotent.
                 */
                err = xen_blkif_disconnect(be->blkif);
                if (err) {
                        xenbus_dev_fatal(dev, err, "pending I/O");
                        break;
                }

                err = connect_ring(be);
                if (err) {
                        /*
                         * Clean up so that memory resources can be used by
                         * other devices. connect_ring reported already error.
                         */
                        xen_blkif_disconnect(be->blkif);
                        break;
                }
                xen_update_blkif_status(be->blkif);
                break;

        case XenbusStateClosing:
                xenbus_switch_state(dev, XenbusStateClosing);
                break;

        case XenbusStateClosed:
                xen_blkif_disconnect(be->blkif);
                xenbus_switch_state(dev, XenbusStateClosed);
                if (xenbus_dev_is_online(dev))
                        break;
                /* fall through */
                /* if not online */
        case XenbusStateUnknown:
                /* implies xen_blkif_disconnect() via xen_blkbk_remove() */
                device_unregister(&dev->dev);
                break;

        default:
                xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
                                 frontend_state);
                break;
        }
}


/* ** Connection ** */


/*
 * Write the physical details regarding the block device to the store, and
 * switch to Connected state.
 */
static void connect(struct backend_info *be)
{
        struct xenbus_transaction xbt;
        int err;
        struct xenbus_device *dev = be->dev;

        pr_debug("%s %s\n", __func__, dev->otherend);

        /* Supply the information about the device the frontend needs */
again:
        err = xenbus_transaction_start(&xbt);
        if (err) {
                xenbus_dev_fatal(dev, err, "starting transaction");
                return;
        }

        /* If we can't advertise it is OK. */
        xen_blkbk_flush_diskcache(xbt, be, be->blkif->vbd.flush_support);

        xen_blkbk_discard(xbt, be);

        xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);

        err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
        if (err) {
                xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
                                 dev->nodename);
                goto abort;
        }

        err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
                            (unsigned long long)vbd_sz(&be->blkif->vbd));
        if (err) {
                xenbus_dev_fatal(dev, err, "writing %s/sectors",
                                 dev->nodename);
                goto abort;
        }

        /* FIXME: use a typename instead */
        err = xenbus_printf(xbt, dev->nodename, "info", "%u",
                            be->blkif->vbd.type |
                            (be->blkif->vbd.readonly ? VDISK_READONLY : 0));
        if (err) {
                xenbus_dev_fatal(dev, err, "writing %s/info",
                                 dev->nodename);
                goto abort;
        }
        err = xenbus_printf(xbt, dev->nodename, "sector-size", "%lu",
                            (unsigned long)
                            bdev_logical_block_size(be->blkif->vbd.bdev));
        if (err) {
                xenbus_dev_fatal(dev, err, "writing %s/sector-size",
                                 dev->nodename);
                goto abort;
        }
        err = xenbus_printf(xbt, dev->nodename, "physical-sector-size", "%u",
                            bdev_physical_block_size(be->blkif->vbd.bdev));
        if (err)
                xenbus_dev_error(dev, err, "writing %s/physical-sector-size",
                                 dev->nodename);

        err = xenbus_transaction_end(xbt, 0);
        if (err == -EAGAIN)
                goto again;
        if (err)
                xenbus_dev_fatal(dev, err, "ending transaction");

        err = xenbus_switch_state(dev, XenbusStateConnected);
        if (err)
                xenbus_dev_fatal(dev, err, "%s: switching to Connected state",
                                 dev->nodename);

        return;
 abort:
        xenbus_transaction_end(xbt, 1);
}

/*
 * Each ring may have multi pages, depends on "ring-page-order".
 */
static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
{
        unsigned int ring_ref[XENBUS_MAX_RING_GRANTS];
        struct pending_req *req, *n;
        int err, i, j;
        struct xen_blkif *blkif = ring->blkif;
        struct xenbus_device *dev = blkif->be->dev;
        unsigned int ring_page_order, nr_grefs, evtchn;

        err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u",
                          &evtchn);
        if (err != 1) {
                err = -EINVAL;
                xenbus_dev_fatal(dev, err, "reading %s/event-channel", dir);
                return err;
        }

        err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u",
                          &ring_page_order);
        if (err != 1) {
                err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", &ring_ref[0]);
                if (err != 1) {
                        err = -EINVAL;
                        xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir);
                        return err;
                }
                nr_grefs = 1;
        } else {
                unsigned int i;

                if (ring_page_order > xen_blkif_max_ring_order) {
                        err = -EINVAL;
                        xenbus_dev_fatal(dev, err, "%s/request %d ring page order exceed max:%d",
                                         dir, ring_page_order,
                                         xen_blkif_max_ring_order);
                        return err;
                }

                nr_grefs = 1 << ring_page_order;
                for (i = 0; i < nr_grefs; i++) {
                        char ring_ref_name[RINGREF_NAME_LEN];

                        snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
                        err = xenbus_scanf(XBT_NIL, dir, ring_ref_name,
                                           "%u", &ring_ref[i]);
                        if (err != 1) {
                                err = -EINVAL;
                                xenbus_dev_fatal(dev, err, "reading %s/%s",
                                                 dir, ring_ref_name);
                                return err;
                        }
                }
        }
        blkif->nr_ring_pages = nr_grefs;

        for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) {
                req = kzalloc(sizeof(*req), GFP_KERNEL);
                if (!req)
                        goto fail;
                list_add_tail(&req->free_list, &ring->pending_free);
                for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
                        req->segments[j] = kzalloc(sizeof(*req->segments[0]), GFP_KERNEL);
                        if (!req->segments[j])
                                goto fail;
                }
                for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
                        req->indirect_pages[j] = kzalloc(sizeof(*req->indirect_pages[0]),
                                                         GFP_KERNEL);
                        if (!req->indirect_pages[j])
                                goto fail;
                }
        }

        /* Map the shared frame, irq etc. */
        err = xen_blkif_map(ring, ring_ref, nr_grefs, evtchn);
        if (err) {
                xenbus_dev_fatal(dev, err, "mapping ring-ref port %u", evtchn);
                return err;
        }

        return 0;

fail:
        list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
                list_del(&req->free_list);
                for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
                        if (!req->segments[j])
                                break;
                        kfree(req->segments[j]);
                }
                for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
                        if (!req->indirect_pages[j])
                                break;
                        kfree(req->indirect_pages[j]);
                }
                kfree(req);
        }
        return -ENOMEM;

}

static int connect_ring(struct backend_info *be)
{
        struct xenbus_device *dev = be->dev;
        unsigned int pers_grants;
        char protocol[64] = "";
        int err, i;
        char *xspath;
        size_t xspathsize;
        const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
        unsigned int requested_num_queues = 0;

        pr_debug("%s %s\n", __func__, dev->otherend);

        be->blkif->blk_protocol = BLKIF_PROTOCOL_DEFAULT;
        err = xenbus_scanf(XBT_NIL, dev->otherend, "protocol",
                           "%63s", protocol);
        if (err <= 0)
                strcpy(protocol, "unspecified, assuming default");
        else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_NATIVE))
                be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
        else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_32))
                be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_32;
        else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_64))
                be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
        else {
                xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
                return -ENOSYS;
        }
        pers_grants = xenbus_read_unsigned(dev->otherend, "feature-persistent",
                                           0);
        be->blkif->vbd.feature_gnt_persistent = pers_grants;
        be->blkif->vbd.overflow_max_grants = 0;

        /*
         * Read the number of hardware queues from frontend.
         */
        requested_num_queues = xenbus_read_unsigned(dev->otherend,
                                                    "multi-queue-num-queues",
                                                    1);
        if (requested_num_queues > xenblk_max_queues
            || requested_num_queues == 0) {
                /* Buggy or malicious guest. */
                xenbus_dev_fatal(dev, err,
                                "guest requested %u queues, exceeding the maximum of %u.",
                                requested_num_queues, xenblk_max_queues);
                return -ENOSYS;
        }
        be->blkif->nr_rings = requested_num_queues;
        if (xen_blkif_alloc_rings(be->blkif))
                return -ENOMEM;

        pr_info("%s: using %d queues, protocol %d (%s) %s\n", dev->nodename,
                 be->blkif->nr_rings, be->blkif->blk_protocol, protocol,
                 pers_grants ? "persistent grants" : "");

        if (be->blkif->nr_rings == 1)
                return read_per_ring_refs(&be->blkif->rings[0], dev->otherend);
        else {
                xspathsize = strlen(dev->otherend) + xenstore_path_ext_size;
                xspath = kmalloc(xspathsize, GFP_KERNEL);
                if (!xspath) {
                        xenbus_dev_fatal(dev, -ENOMEM, "reading ring references");
                        return -ENOMEM;
                }

                for (i = 0; i < be->blkif->nr_rings; i++) {
                        memset(xspath, 0, xspathsize);
                        snprintf(xspath, xspathsize, "%s/queue-%u", dev->otherend, i);
                        err = read_per_ring_refs(&be->blkif->rings[i], xspath);
                        if (err) {
                                kfree(xspath);
                                return err;
                        }
                }
                kfree(xspath);
        }
        return 0;
}

static const struct xenbus_device_id xen_blkbk_ids[] = {
        { "vbd" },
        { "" }
};

static struct xenbus_driver xen_blkbk_driver = {
        .ids  = xen_blkbk_ids,
        .probe = xen_blkbk_probe,
        .remove = xen_blkbk_remove,
        .otherend_changed = frontend_changed
};

int xen_blkif_xenbus_init(void)
{
        return xenbus_register_backend(&xen_blkbk_driver);
}