[v7,14/18] xen: add implementations of xen-block connect and disconnect functions...
diff mbox series

Message ID 20181220171439.11159-15-paul.durrant@citrix.com
State New
Headers show
Series
  • Xen PV backend 'qdevification'
Related show

Commit Message

Paul Durrant Dec. 20, 2018, 5:14 p.m. UTC
...and wire in the dataplane.

This patch adds the remaining code to make the xen-block XenDevice
functional. The parameters that a block frontend expects to find are
populated in the backend xenstore area, and the 'ring-ref' and
'event-channel' values specified in the frontend xenstore area are
mapped/bound and used to set up the dataplane.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony Perard <anthony.perard@citrix.com>
---
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>

v5:
 - Re-base

v3:
 - Add missing return statement to xen_block_realize()
 - Set device name to 'vbd' now the backend is functional
 - Add an unplug handler
 - Move backend watch code from subsequent patch since it's now needed
   to handle unplug

v2:
 - Tidy up header inclusions
 - Stop leaking ring_ref on error
 - Auto-create drive for CDRom devices
---
 hw/block/xen-block.c       | 166 ++++++++++++++++++++++++++++++++
 hw/xen/trace-events        |   3 +
 hw/xen/xen-bus.c           | 187 ++++++++++++++++++++++++++++++++-----
 include/hw/xen/xen-block.h |   9 ++
 include/hw/xen/xen-bus.h   |  14 ++-
 5 files changed, 353 insertions(+), 26 deletions(-)

Patch
diff mbox series

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 3a963b0383..a7c37c185a 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -10,7 +10,13 @@ 
 #include "qapi/error.h"
 #include "qapi/visitor.h"
 #include "hw/hw.h"
+#include "hw/xen/xen_common.h"
+#include "hw/block/xen_blkif.h"
 #include "hw/xen/xen-block.h"
+#include "sysemu/blockdev.h"
+#include "sysemu/block-backend.h"
+#include "sysemu/iothread.h"
+#include "dataplane/xen-block.h"
 #include "trace.h"
 
 static char *xen_block_get_name(XenDevice *xendev, Error **errp)
@@ -28,6 +34,8 @@  static void xen_block_disconnect(XenDevice *xendev, Error **errp)
     XenBlockVdev *vdev = &blockdev->props.vdev;
 
     trace_xen_block_disconnect(type, vdev->disk, vdev->partition);
+
+    xen_block_dataplane_stop(blockdev->dataplane);
 }
 
 static void xen_block_connect(XenDevice *xendev, Error **errp)
@@ -35,8 +43,72 @@  static void xen_block_connect(XenDevice *xendev, Error **errp)
     XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
     const char *type = object_get_typename(OBJECT(blockdev));
     XenBlockVdev *vdev = &blockdev->props.vdev;
+    unsigned int order, nr_ring_ref, *ring_ref, event_channel, protocol;
+    char *str;
 
     trace_xen_block_connect(type, vdev->disk, vdev->partition);
+
+    if (xen_device_frontend_scanf(xendev, "ring-page-order", "%u",
+                                  &order) != 1) {
+        nr_ring_ref = 1;
+        ring_ref = g_new(unsigned int, nr_ring_ref);
+
+        if (xen_device_frontend_scanf(xendev, "ring-ref", "%u",
+                                      &ring_ref[0]) != 1) {
+            error_setg(errp, "failed to read ring-ref");
+            g_free(ring_ref);
+            return;
+        }
+    } else if (order <= blockdev->props.max_ring_page_order) {
+        unsigned int i;
+
+        nr_ring_ref = 1 << order;
+        ring_ref = g_new(unsigned int, nr_ring_ref);
+
+        for (i = 0; i < nr_ring_ref; i++) {
+            const char *key = g_strdup_printf("ring-ref%u", i);
+
+            if (xen_device_frontend_scanf(xendev, key, "%u",
+                                          &ring_ref[i]) != 1) {
+                error_setg(errp, "failed to read %s", key);
+                g_free((gpointer)key);
+                g_free(ring_ref);
+                return;
+            }
+
+            g_free((gpointer)key);
+        }
+    } else {
+        error_setg(errp, "invalid ring-page-order (%d)", order);
+        return;
+    }
+
+    if (xen_device_frontend_scanf(xendev, "event-channel", "%u",
+                                  &event_channel) != 1) {
+        error_setg(errp, "failed to read event-channel");
+        g_free(ring_ref);
+        return;
+    }
+
+    if (xen_device_frontend_scanf(xendev, "protocol", "%ms",
+                                  &str) != 1) {
+        protocol = BLKIF_PROTOCOL_NATIVE;
+    } else {
+        if (strcmp(str, XEN_IO_PROTO_ABI_X86_32) == 0) {
+            protocol = BLKIF_PROTOCOL_X86_32;
+        } else if (strcmp(str, XEN_IO_PROTO_ABI_X86_64) == 0) {
+            protocol = BLKIF_PROTOCOL_X86_64;
+        } else {
+            protocol = BLKIF_PROTOCOL_NATIVE;
+        }
+
+        free(str);
+    }
+
+    xen_block_dataplane_start(blockdev->dataplane, ring_ref, nr_ring_ref,
+                              event_channel, protocol, errp);
+
+    g_free(ring_ref);
 }
 
 static void xen_block_unrealize(XenDevice *xendev, Error **errp)
@@ -56,6 +128,9 @@  static void xen_block_unrealize(XenDevice *xendev, Error **errp)
     /* Disconnect from the frontend in case this has not already happened */
     xen_block_disconnect(xendev, NULL);
 
+    xen_block_dataplane_destroy(blockdev->dataplane);
+    blockdev->dataplane = NULL;
+
     if (blockdev_class->unrealize) {
         blockdev_class->unrealize(blockdev, errp);
     }
@@ -68,6 +143,7 @@  static void xen_block_realize(XenDevice *xendev, Error **errp)
         XEN_BLOCK_DEVICE_GET_CLASS(xendev);
     const char *type = object_get_typename(OBJECT(blockdev));
     XenBlockVdev *vdev = &blockdev->props.vdev;
+    BlockConf *conf = &blockdev->props.conf;
     Error *local_err = NULL;
 
     if (vdev->type == XEN_BLOCK_VDEV_TYPE_INVALID) {
@@ -81,8 +157,62 @@  static void xen_block_realize(XenDevice *xendev, Error **errp)
         blockdev_class->realize(blockdev, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
+            return;
         }
     }
+
+    /*
+     * The blkif protocol does not deal with removable media, so it must
+     * always be present, even for CDRom devices.
+     */
+    assert(conf->blk);
+    if (!blk_is_inserted(conf->blk)) {
+        error_setg(errp, "device needs media, but drive is empty");
+        return;
+    }
+
+    if (!blkconf_apply_backend_options(conf, blockdev->info & VDISK_READONLY,
+                                       false, errp)) {
+        return;
+    }
+
+    if (!(blockdev->info & VDISK_CDROM) &&
+        !blkconf_geometry(conf, NULL, 65535, 255, 255, errp)) {
+        return;
+    }
+
+    blkconf_blocksizes(conf);
+
+    if (conf->logical_block_size > conf->physical_block_size) {
+        error_setg(
+            errp, "logical_block_size > physical_block_size not supported");
+        return;
+    }
+
+    blk_set_guest_block_size(conf->blk, conf->logical_block_size);
+
+    if (conf->discard_granularity > 0) {
+        xen_device_backend_printf(xendev, "feature-discard", "%u", 1);
+    }
+
+    xen_device_backend_printf(xendev, "feature-flush-cache", "%u", 1);
+    xen_device_backend_printf(xendev, "max-ring-page-order", "%u",
+                              blockdev->props.max_ring_page_order);
+    xen_device_backend_printf(xendev, "info", "%u", blockdev->info);
+
+    xen_device_frontend_printf(xendev, "virtual-device", "%lu",
+                               vdev->number);
+    xen_device_frontend_printf(xendev, "device-type", "%s",
+                               blockdev->device_type);
+
+    xen_device_backend_printf(xendev, "sector-size", "%u",
+                              conf->logical_block_size);
+    xen_device_backend_printf(xendev, "sectors", "%lu",
+                              blk_getlength(conf->blk) /
+                              conf->logical_block_size);
+
+    blockdev->dataplane =
+        xen_block_dataplane_create(xendev, conf, blockdev->props.iothread);
 }
 
 static void xen_block_frontend_changed(XenDevice *xendev,
@@ -331,6 +461,11 @@  const PropertyInfo xen_block_prop_vdev = {
 static Property xen_block_props[] = {
     DEFINE_PROP("vdev", XenBlockDevice, props.vdev,
                 xen_block_prop_vdev, XenBlockVdev),
+    DEFINE_BLOCK_PROPERTIES(XenBlockDevice, props.conf),
+    DEFINE_PROP_UINT32("max-ring-page-order", XenBlockDevice,
+                       props.max_ring_page_order, 4),
+    DEFINE_PROP_LINK("iothread", XenBlockDevice, props.iothread,
+                     TYPE_IOTHREAD, IOThread *),
     DEFINE_PROP_END_OF_LIST()
 };
 
@@ -339,6 +474,7 @@  static void xen_block_class_init(ObjectClass *class, void *data)
     DeviceClass *dev_class = DEVICE_CLASS(class);
     XenDeviceClass *xendev_class = XEN_DEVICE_CLASS(class);
 
+    xendev_class->device = "vbd";
     xendev_class->get_name = xen_block_get_name;
     xendev_class->realize = xen_block_realize;
     xendev_class->frontend_changed = xen_block_frontend_changed;
@@ -363,7 +499,18 @@  static void xen_disk_unrealize(XenBlockDevice *blockdev, Error **errp)
 
 static void xen_disk_realize(XenBlockDevice *blockdev, Error **errp)
 {
+    BlockConf *conf = &blockdev->props.conf;
+
     trace_xen_disk_realize();
+
+    blockdev->device_type = "disk";
+
+    if (!conf->blk) {
+        error_setg(errp, "drive property not set");
+        return;
+    }
+
+    blockdev->info = blk_is_read_only(conf->blk) ? VDISK_READONLY : 0;
 }
 
 static void xen_disk_class_init(ObjectClass *class, void *data)
@@ -391,7 +538,26 @@  static void xen_cdrom_unrealize(XenBlockDevice *blockdev, Error **errp)
 
 static void xen_cdrom_realize(XenBlockDevice *blockdev, Error **errp)
 {
+    BlockConf *conf = &blockdev->props.conf;
+
     trace_xen_cdrom_realize();
+
+    blockdev->device_type = "cdrom";
+
+    if (!conf->blk) {
+        int rc;
+
+        /* Set up an empty drive */
+        conf->blk = blk_new(0, BLK_PERM_ALL);
+
+        rc = blk_attach_dev(conf->blk, DEVICE(blockdev));
+        if (!rc) {
+            error_setg_errno(errp, -rc, "failed to create drive");
+            return;
+        }
+    }
+
+    blockdev->info = VDISK_READONLY | VDISK_CDROM;
 }
 
 static void xen_cdrom_class_init(ObjectClass *class, void *data)
diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index 22055b5894..d4651bdb30 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -22,8 +22,11 @@  xen_bus_watch(const char *token) "token: %s"
 xen_device_realize(const char *type, char *name) "type: %s name: %s"
 xen_device_unrealize(const char *type, char *name) "type: %s name: %s"
 xen_device_backend_state(const char *type, char *name, const char *state) "type: %s name: %s -> %s"
+xen_device_backend_online(const char *type, char *name, bool online) "type: %s name: %s -> %u"
+xen_device_backend_changed(const char *type, char *name) "type: %s name: %s"
 xen_device_frontend_state(const char *type, char *name, const char *state) "type: %s name: %s -> %s"
 xen_device_frontend_changed(const char *type, char *name) "type: %s name: %s"
+xen_device_unplug(const char *type, char *name) "type: %s name: %s"
 
 # include/hw/xen/xen-bus-helper.c
 xs_node_create(const char *node) "%s"
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 9443f27d44..a22aa49921 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -48,6 +48,54 @@  static char *xen_device_get_frontend_path(XenDevice *xendev)
                            xendev->frontend_id, device, xendev->name);
 }
 
+static void xen_device_unplug(XenDevice *xendev, Error **errp)
+{
+    XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
+    const char *type = object_get_typename(OBJECT(xendev));
+    Error *local_err = NULL;
+    xs_transaction_t tid;
+
+    trace_xen_device_unplug(type, xendev->name);
+
+    /* Mimic the way the Xen toolstack does an unplug */
+again:
+    tid = xs_transaction_start(xenbus->xsh);
+    if (tid == XBT_NULL) {
+        error_setg_errno(errp, errno, "failed xs_transaction_start");
+        return;
+    }
+
+    xs_node_printf(xenbus->xsh, tid, xendev->backend_path, "online",
+                   &local_err, "%u", 0);
+    if (local_err) {
+        goto abort;
+    }
+
+    xs_node_printf(xenbus->xsh, tid, xendev->backend_path, "state",
+                   &local_err, "%u", XenbusStateClosing);
+    if (local_err) {
+        goto abort;
+    }
+
+    if (!xs_transaction_end(xenbus->xsh, tid, false)) {
+        if (errno == EAGAIN) {
+            goto again;
+        }
+
+        error_setg_errno(errp, errno, "failed xs_transaction_end");
+    }
+
+    return;
+
+abort:
+    /*
+     * We only abort if there is already a failure so ignore any error
+     * from ending the transaction.
+     */
+    xs_transaction_end(xenbus->xsh, tid, true);
+    error_propagate(errp, local_err);
+}
+
 static void xen_bus_print_dev(Monitor *mon, DeviceState *dev, int indent)
 {
     XenDevice *xendev = XEN_DEVICE(dev);
@@ -208,14 +256,26 @@  fail:
     xen_bus_unrealize(bus, &error_abort);
 }
 
+static void xen_bus_unplug_request(HotplugHandler *hotplug,
+                                   DeviceState *dev,
+                                   Error **errp)
+{
+    XenDevice *xendev = XEN_DEVICE(dev);
+
+    xen_device_unplug(xendev, errp);
+}
+
 static void xen_bus_class_init(ObjectClass *class, void *data)
 {
     BusClass *bus_class = BUS_CLASS(class);
+    HotplugHandlerClass *hotplug_class = HOTPLUG_HANDLER_CLASS(class);
 
     bus_class->print_dev = xen_bus_print_dev;
     bus_class->get_dev_path = xen_bus_get_dev_path;
     bus_class->realize = xen_bus_realize;
     bus_class->unrealize = xen_bus_unrealize;
+
+    hotplug_class->unplug_request = xen_bus_unplug_request;
 }
 
 static const TypeInfo xen_bus_type_info = {
@@ -230,8 +290,8 @@  static const TypeInfo xen_bus_type_info = {
     },
 };
 
-static void xen_device_backend_printf(XenDevice *xendev, const char *key,
-                                      const char *fmt, ...)
+void xen_device_backend_printf(XenDevice *xendev, const char *key,
+                               const char *fmt, ...)
 {
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     Error *local_err = NULL;
@@ -287,6 +347,70 @@  enum xenbus_state xen_device_backend_get_state(XenDevice *xendev)
     return xendev->backend_state;
 }
 
+static void xen_device_backend_set_online(XenDevice *xendev, bool online)
+{
+    const char *type = object_get_typename(OBJECT(xendev));
+
+    if (xendev->backend_online == online) {
+        return;
+    }
+
+    trace_xen_device_backend_online(type, xendev->name, online);
+
+    xendev->backend_online = online;
+    xen_device_backend_printf(xendev, "online", "%u", online);
+}
+
+static void xen_device_backend_changed(void *opaque)
+{
+    XenDevice *xendev = opaque;
+    const char *type = object_get_typename(OBJECT(xendev));
+    enum xenbus_state state;
+    unsigned int online;
+
+    trace_xen_device_backend_changed(type, xendev->name);
+
+    if (xen_device_backend_scanf(xendev, "state", "%u", &state) != 1) {
+        state = XenbusStateUnknown;
+    }
+
+    xen_device_backend_set_state(xendev, state);
+
+    if (xen_device_backend_scanf(xendev, "online", "%u", &online) != 1) {
+        online = 0;
+    }
+
+    xen_device_backend_set_online(xendev, !!online);
+
+    /*
+     * If the toolstack (or unplug request callback) has set the backend
+     * state to Closing, but there is no active frontend (i.e. the
+     * state is not Connected) then set the backend state to Closed.
+     */
+    if (xendev->backend_state == XenbusStateClosing &&
+        xendev->frontend_state != XenbusStateConnected) {
+        xen_device_backend_set_state(xendev, XenbusStateClosed);
+    }
+
+    /*
+     * If a backend is still 'online' then its state should be cycled
+     * back round to InitWait in order for a new frontend instance to
+     * connect. This may happen when, for example, a frontend driver is
+     * re-installed or updated.
+     * If a backend is not 'online' then the device should be destroyed.
+     */
+    if (xendev->backend_online &&
+        xendev->backend_state == XenbusStateClosed) {
+        xen_device_backend_set_state(xendev, XenbusStateInitWait);
+    } else if (!xendev->backend_online &&
+               (xendev->backend_state == XenbusStateClosed ||
+                xendev->backend_state == XenbusStateInitialising ||
+                xendev->backend_state == XenbusStateInitWait ||
+                xendev->backend_state == XenbusStateUnknown)) {
+        object_unparent(OBJECT(xendev));
+    }
+}
+
 static void xen_device_backend_create(XenDevice *xendev, Error **errp)
 {
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
@@ -307,6 +431,27 @@  static void xen_device_backend_create(XenDevice *xendev, Error **errp)
     if (local_err) {
         error_propagate_prepend(errp, local_err,
                                 "failed to create backend: ");
+        return;
+    }
+
+    xendev->backend_state_watch =
+        xen_bus_add_watch(xenbus, xendev->backend_path,
+                          "state", xen_device_backend_changed,
+                          xendev, &local_err);
+    if (local_err) {
+        error_propagate_prepend(errp, local_err,
+                                "failed to watch backend state: ");
+        return;
+    }
+
+    xendev->backend_online_watch =
+        xen_bus_add_watch(xenbus, xendev->backend_path,
+                          "online", xen_device_backend_changed,
+                          xendev, &local_err);
+    if (local_err) {
+        error_propagate_prepend(errp, local_err,
+                                "failed to watch backend online: ");
+        return;
     }
 }
 
@@ -315,6 +460,16 @@  static void xen_device_backend_destroy(XenDevice *xendev)
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     Error *local_err = NULL;
 
+    if (xendev->backend_online_watch) {
+        xen_bus_remove_watch(xenbus, xendev->backend_online_watch, NULL);
+        xendev->backend_online_watch = NULL;
+    }
+
+    if (xendev->backend_state_watch) {
+        xen_bus_remove_watch(xenbus, xendev->backend_state_watch, NULL);
+        xendev->backend_state_watch = NULL;
+    }
+
     if (!xendev->backend_path) {
         return;
     }
@@ -331,8 +486,8 @@  static void xen_device_backend_destroy(XenDevice *xendev)
     }
 }
 
-static void xen_device_frontend_printf(XenDevice *xendev, const char *key,
-                                       const char *fmt, ...)
+void xen_device_frontend_printf(XenDevice *xendev, const char *key,
+                                const char *fmt, ...)
 {
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     Error *local_err = NULL;
@@ -350,8 +505,8 @@  static void xen_device_frontend_printf(XenDevice *xendev, const char *key,
     }
 }
 
-static int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
-                                     const char *fmt, ...)
+int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
+                              const char *fmt, ...)
 {
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     va_list ap;
@@ -407,24 +562,6 @@  static void xen_device_frontend_changed(void *opaque)
             error_reportf_err(local_err, "frontend change error: ");
         }
     }
-
-    /*
-     * If a backend is still 'online' then its state should be cycled
-     * back round to InitWait in order for a new frontend instance to
-     * connect. This may happen when, for example, a frontend driver is
-     * re-installed or updated.
-     */
-    if (xendev->backend_state == XenbusStateClosed) {
-        unsigned int online;
-
-        if (xen_device_backend_scanf(xendev, "online", "%u", &online) != 1) {
-            online = 0;
-        }
-
-        if (online) {
-            xen_device_backend_set_state(xendev, XenbusStateInitWait);
-        }
-    }
 }
 
 static void xen_device_frontend_create(XenDevice *xendev, Error **errp)
@@ -822,9 +959,9 @@  static void xen_device_realize(DeviceState *dev, Error **errp)
                               xendev->frontend_path);
     xen_device_backend_printf(xendev, "frontend-id", "%u",
                               xendev->frontend_id);
-    xen_device_backend_printf(xendev, "online", "%u", 1);
     xen_device_backend_printf(xendev, "hotplug-status", "connected");
 
+    xen_device_backend_set_online(xendev, true);
     xen_device_backend_set_state(xendev, XenbusStateInitWait);
 
     xen_device_frontend_printf(xendev, "backend", "%s",
diff --git a/include/hw/xen/xen-block.h b/include/hw/xen/xen-block.h
index 29413256e9..c4223f9be1 100644
--- a/include/hw/xen/xen-block.h
+++ b/include/hw/xen/xen-block.h
@@ -9,6 +9,9 @@ 
 #define HW_XEN_BLOCK_H
 
 #include "hw/xen/xen-bus.h"
+#include "hw/block/block.h"
+#include "hw/block/dataplane/xen-block.h"
+#include "sysemu/iothread.h"
 
 typedef enum XenBlockVdevType {
     XEN_BLOCK_VDEV_TYPE_INVALID,
@@ -28,11 +31,17 @@  typedef struct XenBlockVdev {
 
 typedef struct XenBlockProperties {
     XenBlockVdev vdev;
+    BlockConf conf;
+    unsigned int max_ring_page_order;
+    IOThread *iothread;
 } XenBlockProperties;
 
 typedef struct XenBlockDevice {
     XenDevice xendev;
     XenBlockProperties props;
+    const char *device_type;
+    unsigned int info;
+    XenBlockDataPlane *dataplane;
 } XenBlockDevice;
 
 typedef void (*XenBlockDeviceRealize)(XenBlockDevice *blockdev, Error **errp);
diff --git a/include/hw/xen/xen-bus.h b/include/hw/xen/xen-bus.h
index f83a95cebd..0834cb3a7e 100644
--- a/include/hw/xen/xen-bus.h
+++ b/include/hw/xen/xen-bus.h
@@ -23,7 +23,9 @@  typedef struct XenDevice {
     char *backend_path, *frontend_path;
     enum xenbus_state backend_state, frontend_state;
     Notifier exit;
-    XenWatch *frontend_state_watch;
+    XenWatch *backend_state_watch, *frontend_state_watch;
+    bool backend_online;
+    XenWatch *backend_online_watch;
     xengnttab_handle *xgth;
     bool feature_grant_copy;
     xenevtchn_handle *xeh;
@@ -84,6 +86,16 @@  void xen_device_backend_set_state(XenDevice *xendev,
                                   enum xenbus_state state);
 enum xenbus_state xen_device_backend_get_state(XenDevice *xendev);
 
+void xen_device_backend_printf(XenDevice *xendev, const char *key,
+                               const char *fmt, ...)
+    GCC_FMT_ATTR(3, 4);
+void xen_device_frontend_printf(XenDevice *xendev, const char *key,
+                                const char *fmt, ...)
+    GCC_FMT_ATTR(3, 4);
+
+int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
+                              const char *fmt, ...);
+
 void xen_device_set_max_grant_refs(XenDevice *xendev, unsigned int nr_refs,
                                    Error **errp);
 void *xen_device_map_grant_refs(XenDevice *xendev, uint32_t *refs,