/*
 * Xenbus code for netif 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
*/

#include "common.h"
#include <linux/vmalloc.h>
#include <linux/rtnetlink.h>

struct backend_info {
        struct xenbus_device *dev;
        struct xenvif *vif;

        /* This is the state that will be reflected in xenstore when any
         * active hotplug script completes.
         */
        enum xenbus_state state;

        enum xenbus_state frontend_state;
        struct xenbus_watch hotplug_status_watch;
        u8 have_hotplug_status_watch:1;
};

static int connect_rings(struct backend_info *be, struct xenvif_queue *queue);
static void connect(struct backend_info *be);
static int read_xenbus_vif_flags(struct backend_info *be);
static int backend_create_xenvif(struct backend_info *be);
static void unregister_hotplug_status_watch(struct backend_info *be);
static void set_backend_state(struct backend_info *be,
                              enum xenbus_state state);

#ifdef CONFIG_DEBUG_FS
struct dentry *xen_netback_dbg_root = NULL;

static int xenvif_read_io_ring(struct seq_file *m, void *v)
{
        struct xenvif_queue *queue = m->private;
        struct xen_netif_tx_back_ring *tx_ring = &queue->tx;
        struct xen_netif_rx_back_ring *rx_ring = &queue->rx;
        struct netdev_queue *dev_queue;

        if (tx_ring->sring) {
                struct xen_netif_tx_sring *sring = tx_ring->sring;

                seq_printf(m, "Queue %d\nTX: nr_ents %u\n", queue->id,
                           tx_ring->nr_ents);
                seq_printf(m, "req prod %u (%d) cons %u (%d) event %u (%d)\n",
                           sring->req_prod,
                           sring->req_prod - sring->rsp_prod,
                           tx_ring->req_cons,
                           tx_ring->req_cons - sring->rsp_prod,
                           sring->req_event,
                           sring->req_event - sring->rsp_prod);
                seq_printf(m, "rsp prod %u (base) pvt %u (%d) event %u (%d)\n",
                           sring->rsp_prod,
                           tx_ring->rsp_prod_pvt,
                           tx_ring->rsp_prod_pvt - sring->rsp_prod,
                           sring->rsp_event,
                           sring->rsp_event - sring->rsp_prod);
                seq_printf(m, "pending prod %u pending cons %u nr_pending_reqs %u\n",
                           queue->pending_prod,
                           queue->pending_cons,
                           nr_pending_reqs(queue));
                seq_printf(m, "dealloc prod %u dealloc cons %u dealloc_queue %u\n\n",
                           queue->dealloc_prod,
                           queue->dealloc_cons,
                           queue->dealloc_prod - queue->dealloc_cons);
        }

        if (rx_ring->sring) {
                struct xen_netif_rx_sring *sring = rx_ring->sring;

                seq_printf(m, "RX: nr_ents %u\n", rx_ring->nr_ents);
                seq_printf(m, "req prod %u (%d) cons %u (%d) event %u (%d)\n",
                           sring->req_prod,
                           sring->req_prod - sring->rsp_prod,
                           rx_ring->req_cons,
                           rx_ring->req_cons - sring->rsp_prod,
                           sring->req_event,
                           sring->req_event - sring->rsp_prod);
                seq_printf(m, "rsp prod %u (base) pvt %u (%d) event %u (%d)\n\n",
                           sring->rsp_prod,
                           rx_ring->rsp_prod_pvt,
                           rx_ring->rsp_prod_pvt - sring->rsp_prod,
                           sring->rsp_event,
                           sring->rsp_event - sring->rsp_prod);
        }

        seq_printf(m, "NAPI state: %lx NAPI weight: %d TX queue len %u\n"
                   "Credit timer_pending: %d, credit: %lu, usec: %lu\n"
                   "remaining: %lu, expires: %lu, now: %lu\n",
                   queue->napi.state, queue->napi.weight,
                   skb_queue_len(&queue->tx_queue),
                   timer_pending(&queue->credit_timeout),
                   queue->credit_bytes,
                   queue->credit_usec,
                   queue->remaining_credit,
                   queue->credit_timeout.expires,
                   jiffies);

        dev_queue = netdev_get_tx_queue(queue->vif->dev, queue->id);

        seq_printf(m, "\nRx internal queue: len %u max %u pkts %u %s\n",
                   queue->rx_queue_len, queue->rx_queue_max,
                   skb_queue_len(&queue->rx_queue),
                   netif_tx_queue_stopped(dev_queue) ? "stopped" : "running");

        return 0;
}

#define XENVIF_KICK_STR "kick"
#define BUFFER_SIZE     32

static ssize_t
xenvif_write_io_ring(struct file *filp, const char __user *buf, size_t count,
                     loff_t *ppos)
{
        struct xenvif_queue *queue =
                ((struct seq_file *)filp->private_data)->private;
        int len;
        char write[BUFFER_SIZE];

        /* don't allow partial writes and check the length */
        if (*ppos != 0)
                return 0;
        if (count >= sizeof(write))
                return -ENOSPC;

        len = simple_write_to_buffer(write,
                                     sizeof(write) - 1,
                                     ppos,
                                     buf,
                                     count);
        if (len < 0)
                return len;

        write[len] = '\0';

        if (!strncmp(write, XENVIF_KICK_STR, sizeof(XENVIF_KICK_STR) - 1))
                xenvif_interrupt(0, (void *)queue);
        else {
                pr_warn("Unknown command to io_ring_q%d. Available: kick\n",
                        queue->id);
                count = -EINVAL;
        }
        return count;
}

static int xenvif_dump_open(struct inode *inode, struct file *filp)
{
        int ret;
        void *queue = NULL;

        if (inode->i_private)
                queue = inode->i_private;
        ret = single_open(filp, xenvif_read_io_ring, queue);
        filp->f_mode |= FMODE_PWRITE;
        return ret;
}

static const struct file_operations xenvif_dbg_io_ring_ops_fops = {
        .owner = THIS_MODULE,
        .open = xenvif_dump_open,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = single_release,
        .write = xenvif_write_io_ring,
};

static void xenvif_debugfs_addif(struct xenvif *vif)
{
        struct dentry *pfile;
        int i;

        if (IS_ERR_OR_NULL(xen_netback_dbg_root))
                return;

        vif->xenvif_dbg_root = debugfs_create_dir(vif->dev->name,
                                                  xen_netback_dbg_root);
        if (!IS_ERR_OR_NULL(vif->xenvif_dbg_root)) {
                for (i = 0; i < vif->num_queues; ++i) {
                        char filename[sizeof("io_ring_q") + 4];

                        snprintf(filename, sizeof(filename), "io_ring_q%d", i);
                        pfile = debugfs_create_file(filename,
                                                    S_IRUSR | S_IWUSR,
                                                    vif->xenvif_dbg_root,
                                                    &vif->queues[i],
                                                    &xenvif_dbg_io_ring_ops_fops);
                        if (IS_ERR_OR_NULL(pfile))
                                pr_warn("Creation of io_ring file returned %ld!\n",
                                        PTR_ERR(pfile));
                }
        } else
                netdev_warn(vif->dev,
                            "Creation of vif debugfs dir returned %ld!\n",
                            PTR_ERR(vif->xenvif_dbg_root));
}

static void xenvif_debugfs_delif(struct xenvif *vif)
{
        if (IS_ERR_OR_NULL(xen_netback_dbg_root))
                return;

        if (!IS_ERR_OR_NULL(vif->xenvif_dbg_root))
                debugfs_remove_recursive(vif->xenvif_dbg_root);
        vif->xenvif_dbg_root = NULL;
}
#endif /* CONFIG_DEBUG_FS */

static int netback_remove(struct xenbus_device *dev)
{
        struct backend_info *be = dev_get_drvdata(&dev->dev);

        set_backend_state(be, XenbusStateClosed);

        unregister_hotplug_status_watch(be);
        if (be->vif) {
                kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
                xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
                xenvif_free(be->vif);
                be->vif = NULL;
        }
        kfree(be);
        dev_set_drvdata(&dev->dev, NULL);
        return 0;
}


/**
 * Entry point to this code when a new device is created.  Allocate the basic
 * structures and switch to InitWait.
 */
static int netback_probe(struct xenbus_device *dev,
                         const struct xenbus_device_id *id)
{
        const char *message;
        struct xenbus_transaction xbt;
        int err;
        int sg;
        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);

        sg = 1;

        do {
                err = xenbus_transaction_start(&xbt);
                if (err) {
                        xenbus_dev_fatal(dev, err, "starting transaction");
                        goto fail;
                }

                err = xenbus_printf(xbt, dev->nodename, "feature-sg", "%d", sg);
                if (err) {
                        message = "writing feature-sg";
                        goto abort_transaction;
                }

                err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv4",
                                    "%d", sg);
                if (err) {
                        message = "writing feature-gso-tcpv4";
                        goto abort_transaction;
                }

                err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv6",
                                    "%d", sg);
                if (err) {
                        message = "writing feature-gso-tcpv6";
                        goto abort_transaction;
                }

                /* We support partial checksum setup for IPv6 packets */
                err = xenbus_printf(xbt, dev->nodename,
                                    "feature-ipv6-csum-offload",
                                    "%d", 1);
                if (err) {
                        message = "writing feature-ipv6-csum-offload";
                        goto abort_transaction;
                }

                /* We support rx-copy path. */
                err = xenbus_printf(xbt, dev->nodename,
                                    "feature-rx-copy", "%d", 1);
                if (err) {
                        message = "writing feature-rx-copy";
                        goto abort_transaction;
                }

                /*
                 * We don't support rx-flip path (except old guests who don't
                 * grok this feature flag).
                 */
                err = xenbus_printf(xbt, dev->nodename,
                                    "feature-rx-flip", "%d", 0);
                if (err) {
                        message = "writing feature-rx-flip";
                        goto abort_transaction;
                }

                err = xenbus_transaction_end(xbt, 0);
        } while (err == -EAGAIN);

        if (err) {
                xenbus_dev_fatal(dev, err, "completing transaction");
                goto fail;
        }

        /*
         * Split event channels support, this is optional so it is not
         * put inside the above loop.
         */
        err = xenbus_printf(XBT_NIL, dev->nodename,
                            "feature-split-event-channels",
                            "%u", separate_tx_rx_irq);
        if (err)
                pr_debug("Error writing feature-split-event-channels\n");

        /* Multi-queue support: This is an optional feature. */
        err = xenbus_printf(XBT_NIL, dev->nodename,
                            "multi-queue-max-queues", "%u", xenvif_max_queues);
        if (err)
                pr_debug("Error writing multi-queue-max-queues\n");

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

        be->state = XenbusStateInitWait;

        /* This kicks hotplug scripts, so do it immediately. */
        err = backend_create_xenvif(be);
        if (err)
                goto fail;

        return 0;

abort_transaction:
        xenbus_transaction_end(xbt, 1);
        xenbus_dev_fatal(dev, err, "%s", message);
fail:
        pr_debug("failed\n");
        netback_remove(dev);
        return err;
}


/*
 * Handle the creation of the hotplug script environment.  We add the script
 * and vif variables to the environment, for the benefit of the vif-* hotplug
 * scripts.
 */
static int netback_uevent(struct xenbus_device *xdev,
                          struct kobj_uevent_env *env)
{
        struct backend_info *be = dev_get_drvdata(&xdev->dev);
        char *val;

        val = xenbus_read(XBT_NIL, xdev->nodename, "script", NULL);
        if (IS_ERR(val)) {
                int err = PTR_ERR(val);
                xenbus_dev_fatal(xdev, err, "reading script");
                return err;
        } else {
                if (add_uevent_var(env, "script=%s", val)) {
                        kfree(val);
                        return -ENOMEM;
                }
                kfree(val);
        }

        if (!be || !be->vif)
                return 0;

        return add_uevent_var(env, "vif=%s", be->vif->dev->name);
}


static int backend_create_xenvif(struct backend_info *be)
{
        int err;
        long handle;
        struct xenbus_device *dev = be->dev;
        struct xenvif *vif;

        if (be->vif != NULL)
                return 0;

        err = xenbus_scanf(XBT_NIL, dev->nodename, "handle", "%li", &handle);
        if (err != 1) {
                xenbus_dev_fatal(dev, err, "reading handle");
                return (err < 0) ? err : -EINVAL;
        }

        vif = xenvif_alloc(&dev->dev, dev->otherend_id, handle);
        if (IS_ERR(vif)) {
                err = PTR_ERR(vif);
                xenbus_dev_fatal(dev, err, "creating interface");
                return err;
        }
        be->vif = vif;

        kobject_uevent(&dev->dev.kobj, KOBJ_ONLINE);
        return 0;
}

static void backend_disconnect(struct backend_info *be)
{
        if (be->vif) {
#ifdef CONFIG_DEBUG_FS
                xenvif_debugfs_delif(be->vif);
#endif /* CONFIG_DEBUG_FS */
                xenvif_disconnect(be->vif);
        }
}

static void backend_connect(struct backend_info *be)
{
        if (be->vif)
                connect(be);
}

static inline void backend_switch_state(struct backend_info *be,
                                        enum xenbus_state state)
{
        struct xenbus_device *dev = be->dev;

        pr_debug("%s -> %s\n", dev->nodename, xenbus_strstate(state));
        be->state = state;

        /* If we are waiting for a hotplug script then defer the
         * actual xenbus state change.
         */
        if (!be->have_hotplug_status_watch)
                xenbus_switch_state(dev, state);
}

/* Handle backend state transitions:
 *
 * The backend state starts in InitWait and the following transitions are
 * allowed.
 *
 * InitWait -> Connected
 *
 *    ^    \         |
 *    |     \        |
 *    |      \       |
 *    |       \      |
 *    |        \     |
 *    |         \    |
 *    |          V   V
 *
 *  Closed  <-> Closing
 *
 * The state argument specifies the eventual state of the backend and the
 * function transitions to that state via the shortest path.
 */
static void set_backend_state(struct backend_info *be,
                              enum xenbus_state state)
{
        while (be->state != state) {
                switch (be->state) {
                case XenbusStateClosed:
                        switch (state) {
                        case XenbusStateInitWait:
                        case XenbusStateConnected:
                                pr_info("%s: prepare for reconnect\n",
                                        be->dev->nodename);
                                backend_switch_state(be, XenbusStateInitWait);
                                break;
                        case XenbusStateClosing:
                                backend_switch_state(be, XenbusStateClosing);
                                break;
                        default:
                                BUG();
                        }
                        break;
                case XenbusStateInitWait:
                        switch (state) {
                        case XenbusStateConnected:
                                backend_connect(be);
                                backend_switch_state(be, XenbusStateConnected);
                                break;
                        case XenbusStateClosing:
                        case XenbusStateClosed:
                                backend_switch_state(be, XenbusStateClosing);
                                break;
                        default:
                                BUG();
                        }
                        break;
                case XenbusStateConnected:
                        switch (state) {
                        case XenbusStateInitWait:
                        case XenbusStateClosing:
                        case XenbusStateClosed:
                                backend_disconnect(be);
                                backend_switch_state(be, XenbusStateClosing);
                                break;
                        default:
                                BUG();
                        }
                        break;
                case XenbusStateClosing:
                        switch (state) {
                        case XenbusStateInitWait:
                        case XenbusStateConnected:
                        case XenbusStateClosed:
                                backend_switch_state(be, XenbusStateClosed);
                                break;
                        default:
                                BUG();
                        }
                        break;
                default:
                        BUG();
                }
        }
}

/**
 * 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);

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

        be->frontend_state = frontend_state;

        switch (frontend_state) {
        case XenbusStateInitialising:
                set_backend_state(be, XenbusStateInitWait);
                break;

        case XenbusStateInitialised:
                break;

        case XenbusStateConnected:
                set_backend_state(be, XenbusStateConnected);
                break;

        case XenbusStateClosing:
                set_backend_state(be, XenbusStateClosing);
                break;

        case XenbusStateClosed:
                set_backend_state(be, XenbusStateClosed);
                if (xenbus_dev_is_online(dev))
                        break;
                /* fall through if not online */
        case XenbusStateUnknown:
                set_backend_state(be, XenbusStateClosed);
                device_unregister(&dev->dev);
                break;

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


static void xen_net_read_rate(struct xenbus_device *dev,
                              unsigned long *bytes, unsigned long *usec)
{
        char *s, *e;
        unsigned long b, u;
        char *ratestr;

        /* Default to unlimited bandwidth. */
        *bytes = ~0UL;
        *usec = 0;

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

        s = ratestr;
        b = simple_strtoul(s, &e, 10);
        if ((s == e) || (*e != ','))
                goto fail;

        s = e + 1;
        u = simple_strtoul(s, &e, 10);
        if ((s == e) || (*e != '\0'))
                goto fail;

        *bytes = b;
        *usec = u;

        kfree(ratestr);
        return;

 fail:
        pr_warn("Failed to parse network rate limit. Traffic unlimited.\n");
        kfree(ratestr);
}

static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
{
        char *s, *e, *macstr;
        int i;

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

        for (i = 0; i < ETH_ALEN; i++) {
                mac[i] = simple_strtoul(s, &e, 16);
                if ((s == e) || (*e != ((i == ETH_ALEN-1) ? '\0' : ':'))) {
                        kfree(macstr);
                        return -ENOENT;
                }
                s = e+1;
        }

        kfree(macstr);
        return 0;
}

static void unregister_hotplug_status_watch(struct backend_info *be)
{
        if (be->have_hotplug_status_watch) {
                unregister_xenbus_watch(&be->hotplug_status_watch);
                kfree(be->hotplug_status_watch.node);
        }
        be->have_hotplug_status_watch = 0;
}

static void hotplug_status_changed(struct xenbus_watch *watch,
                                   const char **vec,
                                   unsigned int vec_size)
{
        struct backend_info *be = container_of(watch,
                                               struct backend_info,
                                               hotplug_status_watch);
        char *str;
        unsigned int len;

        str = xenbus_read(XBT_NIL, be->dev->nodename, "hotplug-status", &len);
        if (IS_ERR(str))
                return;
        if (len == sizeof("connected")-1 && !memcmp(str, "connected", len)) {
                /* Complete any pending state change */
                xenbus_switch_state(be->dev, be->state);

                /* Not interested in this watch anymore. */
                unregister_hotplug_status_watch(be);
        }
        kfree(str);
}

static void connect(struct backend_info *be)
{
        int err;
        struct xenbus_device *dev = be->dev;
        unsigned long credit_bytes, credit_usec;
        unsigned int queue_index;
        unsigned int requested_num_queues;
        struct xenvif_queue *queue;

        /* Check whether the frontend requested multiple queues
         * and read the number requested.
         */
        err = xenbus_scanf(XBT_NIL, dev->otherend,
                           "multi-queue-num-queues",
                           "%u", &requested_num_queues);
        if (err < 0) {
                requested_num_queues = 1; /* Fall back to single queue */
        } else if (requested_num_queues > xenvif_max_queues) {
                /* buggy or malicious guest */
                xenbus_dev_fatal(dev, err,
                                 "guest requested %u queues, exceeding the maximum of %u.",
                                 requested_num_queues, xenvif_max_queues);
                return;
        }

        err = xen_net_read_mac(dev, be->vif->fe_dev_addr);
        if (err) {
                xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
                return;
        }

        xen_net_read_rate(dev, &credit_bytes, &credit_usec);
        read_xenbus_vif_flags(be);

        /* Use the number of queues requested by the frontend */
        be->vif->queues = vzalloc(requested_num_queues *
                                  sizeof(struct xenvif_queue));
        be->vif->num_queues = requested_num_queues;
        be->vif->stalled_queues = requested_num_queues;

        for (queue_index = 0; queue_index < requested_num_queues; ++queue_index) {
                queue = &be->vif->queues[queue_index];
                queue->vif = be->vif;
                queue->id = queue_index;
                snprintf(queue->name, sizeof(queue->name), "%s-q%u",
                                be->vif->dev->name, queue->id);

                err = xenvif_init_queue(queue);
                if (err) {
                        /* xenvif_init_queue() cleans up after itself on
                         * failure, but we need to clean up any previously
                         * initialised queues. Set num_queues to i so that
                         * earlier queues can be destroyed using the regular
                         * disconnect logic.
                         */
                        be->vif->num_queues = queue_index;
                        goto err;
                }

                queue->remaining_credit = credit_bytes;
                queue->credit_usec = credit_usec;

                err = connect_rings(be, queue);
                if (err) {
                        /* connect_rings() cleans up after itself on failure,
                         * but we need to clean up after xenvif_init_queue() here,
                         * and also clean up any previously initialised queues.
                         */
                        xenvif_deinit_queue(queue);
                        be->vif->num_queues = queue_index;
                        goto err;
                }
        }

#ifdef CONFIG_DEBUG_FS
        xenvif_debugfs_addif(be->vif);
#endif /* CONFIG_DEBUG_FS */

        /* Initialisation completed, tell core driver the number of
         * active queues.
         */
        rtnl_lock();
        netif_set_real_num_tx_queues(be->vif->dev, requested_num_queues);
        netif_set_real_num_rx_queues(be->vif->dev, requested_num_queues);
        rtnl_unlock();

        xenvif_carrier_on(be->vif);

        unregister_hotplug_status_watch(be);
        err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
                                   hotplug_status_changed,
                                   "%s/%s", dev->nodename, "hotplug-status");
        if (!err)
                be->have_hotplug_status_watch = 1;

        netif_tx_wake_all_queues(be->vif->dev);

        return;

err:
        if (be->vif->num_queues > 0)
                xenvif_disconnect(be->vif); /* Clean up existing queues */
        vfree(be->vif->queues);
        be->vif->queues = NULL;
        be->vif->num_queues = 0;
        return;
}


static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
{
        struct xenbus_device *dev = be->dev;
        unsigned int num_queues = queue->vif->num_queues;
        unsigned long tx_ring_ref, rx_ring_ref;
        unsigned int tx_evtchn, rx_evtchn;
        int err;
        char *xspath;
        size_t xspathsize;
        const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */

        /* If the frontend requested 1 queue, or we have fallen back
         * to single queue due to lack of frontend support for multi-
         * queue, expect the remaining XenStore keys in the toplevel
         * directory. Otherwise, expect them in a subdirectory called
         * queue-N.
         */
        if (num_queues == 1) {
                xspath = kzalloc(strlen(dev->otherend) + 1, GFP_KERNEL);
                if (!xspath) {
                        xenbus_dev_fatal(dev, -ENOMEM,
                                         "reading ring references");
                        return -ENOMEM;
                }
                strcpy(xspath, dev->otherend);
        } else {
                xspathsize = strlen(dev->otherend) + xenstore_path_ext_size;
                xspath = kzalloc(xspathsize, GFP_KERNEL);
                if (!xspath) {
                        xenbus_dev_fatal(dev, -ENOMEM,
                                         "reading ring references");
                        return -ENOMEM;
                }
                snprintf(xspath, xspathsize, "%s/queue-%u", dev->otherend,
                         queue->id);
        }

        err = xenbus_gather(XBT_NIL, xspath,
                            "tx-ring-ref", "%lu", &tx_ring_ref,
                            "rx-ring-ref", "%lu", &rx_ring_ref, NULL);
        if (err) {
                xenbus_dev_fatal(dev, err,
                                 "reading %s/ring-ref",
                                 xspath);
                goto err;
        }

        /* Try split event channels first, then single event channel. */
        err = xenbus_gather(XBT_NIL, xspath,
                            "event-channel-tx", "%u", &tx_evtchn,
                            "event-channel-rx", "%u", &rx_evtchn, NULL);
        if (err < 0) {
                err = xenbus_scanf(XBT_NIL, xspath,
                                   "event-channel", "%u", &tx_evtchn);
                if (err < 0) {
                        xenbus_dev_fatal(dev, err,
                                         "reading %s/event-channel(-tx/rx)",
                                         xspath);
                        goto err;
                }
                rx_evtchn = tx_evtchn;
        }

        /* Map the shared frame, irq etc. */
        err = xenvif_connect(queue, tx_ring_ref, rx_ring_ref,
                             tx_evtchn, rx_evtchn);
        if (err) {
                xenbus_dev_fatal(dev, err,
                                 "mapping shared-frames %lu/%lu port tx %u rx %u",
                                 tx_ring_ref, rx_ring_ref,
                                 tx_evtchn, rx_evtchn);
                goto err;
        }

        err = 0;
err: /* Regular return falls through with err == 0 */
        kfree(xspath);
        return err;
}

static int read_xenbus_vif_flags(struct backend_info *be)
{
        struct xenvif *vif = be->vif;
        struct xenbus_device *dev = be->dev;
        unsigned int rx_copy;
        int err, val;

        err = xenbus_scanf(XBT_NIL, dev->otherend, "request-rx-copy", "%u",
                           &rx_copy);
        if (err == -ENOENT) {
                err = 0;
                rx_copy = 0;
        }
        if (err < 0) {
                xenbus_dev_fatal(dev, err, "reading %s/request-rx-copy",
                                 dev->otherend);
                return err;
        }
        if (!rx_copy)
                return -EOPNOTSUPP;

        if (xenbus_scanf(XBT_NIL, dev->otherend,
                         "feature-rx-notify", "%d", &val) < 0)
                val = 0;
        if (!val) {
                /* - Reduce drain timeout to poll more frequently for
                 *   Rx requests.
                 * - Disable Rx stall detection.
                 */
                be->vif->drain_timeout = msecs_to_jiffies(30);
                be->vif->stall_timeout = 0;
        }

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
                         "%d", &val) < 0)
                val = 0;
        vif->can_sg = !!val;

        vif->gso_mask = 0;
        vif->gso_prefix_mask = 0;

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4",
                         "%d", &val) < 0)
                val = 0;
        if (val)
                vif->gso_mask |= GSO_BIT(TCPV4);

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4-prefix",
                         "%d", &val) < 0)
                val = 0;
        if (val)
                vif->gso_prefix_mask |= GSO_BIT(TCPV4);

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv6",
                         "%d", &val) < 0)
                val = 0;
        if (val)
                vif->gso_mask |= GSO_BIT(TCPV6);

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv6-prefix",
                         "%d", &val) < 0)
                val = 0;
        if (val)
                vif->gso_prefix_mask |= GSO_BIT(TCPV6);

        if (vif->gso_mask & vif->gso_prefix_mask) {
                xenbus_dev_fatal(dev, err,
                                 "%s: gso and gso prefix flags are not "
                                 "mutually exclusive",
                                 dev->otherend);
                return -EOPNOTSUPP;
        }

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-no-csum-offload",
                         "%d", &val) < 0)
                val = 0;
        vif->ip_csum = !val;

        if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-ipv6-csum-offload",
                         "%d", &val) < 0)
                val = 0;
        vif->ipv6_csum = !!val;

        return 0;
}

static const struct xenbus_device_id netback_ids[] = {
        { "vif" },
        { "" }
};

static struct xenbus_driver netback_driver = {
        .ids = netback_ids,
        .probe = netback_probe,
        .remove = netback_remove,
        .uevent = netback_uevent,
        .otherend_changed = frontend_changed,
};

int xenvif_xenbus_init(void)
{
        return xenbus_register_backend(&netback_driver);
}

void xenvif_xenbus_fini(void)
{
        return xenbus_unregister_driver(&netback_driver);
}