xenbus.c

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/*  Xenbus code for blkif backend
    Copyright (C) 2005 Rusty Russell <[email protected]>
    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.

*/

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

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 **,
                unsigned int);

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

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, "blkback.%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];

    /* Not ready to connect? */
    if (!blkif->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);

    blkif->xenblkd = kthread_run(xen_blkif_schedule, blkif, name);
    if (IS_ERR(blkif->xenblkd)) {
        err = PTR_ERR(blkif->xenblkd);
        blkif->xenblkd = NULL;
        xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
    }
}

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

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

    blkif->domid = domid;
    spin_lock_init(&blkif->blk_ring_lock);
    atomic_set(&blkif->refcnt, 1);
    init_waitqueue_head(&blkif->wq);
    init_completion(&blkif->drain_complete);
    atomic_set(&blkif->drain, 0);
    blkif->st_print = jiffies;
    init_waitqueue_head(&blkif->waiting_to_free);

    return blkif;
}

static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
             unsigned int evtchn)
{
    int err;

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

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

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

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

    return 0;
}

static void xen_blkif_disconnect(struct xen_blkif *blkif)
{
    if (blkif->xenblkd) {
        kthread_stop(blkif->xenblkd);
        blkif->xenblkd = NULL;
    }

    atomic_dec(&blkif->refcnt);
    wait_event(blkif->waiting_to_free, atomic_read(&blkif->refcnt) == 0);
    atomic_inc(&blkif->refcnt);

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

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

static void xen_blkif_free(struct xen_blkif *blkif)
{
    if (!atomic_dec_and_test(&blkif->refcnt))
        BUG();
    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(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(oo_req,  "%d\n", be->blkif->st_oo_req);
VBD_SHOW(rd_req,  "%d\n", be->blkif->st_rd_req);
VBD_SHOW(wr_req,  "%d\n", be->blkif->st_wr_req);
VBD_SHOW(f_req,  "%d\n", be->blkif->st_f_req);
VBD_SHOW(ds_req,  "%d\n", be->blkif->st_ds_req);
VBD_SHOW(rd_sect, "%d\n", be->blkif->st_rd_sect);
VBD_SHOW(wr_sect, "%d\n", be->blkif->st_wr_sect);

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

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

    vbd->bdev = bdev;
    if (vbd->bdev->bd_disk == NULL) {
        DPRINTK("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 && q->flush_flags)
        vbd->flush_support = true;

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

    DPRINTK("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);

    DPRINTK("");

    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;
    }

    if (be->blkif) {
        xen_blkif_disconnect(be->blkif);
        xen_vbd_free(&be->blkif->vbd);
        xen_blkif_free(be->blkif);
        be->blkif = NULL;
    }

    kfree(be);
    dev_set_drvdata(&dev->dev, NULL);
    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 (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);
    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;
    }

    /* 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_switch_state(dev, XenbusStateInitWait);
    if (err)
        goto fail;

    return 0;

fail:
    DPRINTK("failed");
    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 **vec, unsigned int len)
{
    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;
    char *device_type;

    DPRINTK("");

    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) &&
        ((be->major != major) || (be->minor != minor))) {
        pr_warn(DRV_PFX "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);
    }

    if (be->major == 0 && be->minor == 0) {
        /* Front end dir is a number, which is used as the handle. */

        char *p = strrchr(dev->otherend, '/') + 1;
        long handle;
        err = strict_strtoul(p, 0, &handle);
        if (err)
            return;

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

        err = xen_vbd_create(be->blkif, handle, major, minor,
                 (NULL == strchr(be->mode, 'w')), cdrom);
        if (err) {
            be->major = 0;
            be->minor = 0;
            xenbus_dev_fatal(dev, err, "creating vbd structure");
            return;
        }

        err = xenvbd_sysfs_addif(dev);
        if (err) {
            xen_vbd_free(&be->blkif->vbd);
            be->major = 0;
            be->minor = 0;
            xenbus_dev_fatal(dev, err, "creating sysfs entries");
            return;
        }

        /* 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;

    DPRINTK("%s", xenbus_strstate(frontend_state));

    switch (frontend_state) {
    case XenbusStateInitialising:
        if (dev->state == XenbusStateClosed) {
            pr_info(DRV_PFX "%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.
         */
        xen_blkif_disconnect(be->blkif);

        err = connect_ring(be);
        if (err)
            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;

    DPRINTK("%s", 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, "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_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);
}


static int connect_ring(struct backend_info *be)
{
    struct xenbus_device *dev = be->dev;
    unsigned long ring_ref;
    unsigned int evtchn;
    char protocol[64] = "";
    int err;

    DPRINTK("%s", dev->otherend);

    err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
                &ring_ref, "event-channel", "%u", &evtchn, NULL);
    if (err) {
        xenbus_dev_fatal(dev, err,
                 "reading %s/ring-ref and event-channel",
                 dev->otherend);
        return err;
    }

    be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
    err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
                "%63s", protocol, NULL);
    if (err)
        strcpy(protocol, "unspecified, assuming native");
    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 -1;
    }
    pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
        ring_ref, evtchn, be->blkif->blk_protocol, protocol);

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

    return 0;
}


/* ** Driver Registration ** */


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


static DEFINE_XENBUS_DRIVER(xen_blkbk, ,
    .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);
}