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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] skeleton frontend/backend examples and a deadlock
Here are example frontend and backend driver skeletons. They're
*designed* to handle driver restart and module unloading. However,
device_unregister deadlocks. I guess noone tried testing
unregister_xenbus_watch when not called from a watch callback.
The unregistration code in the skeleton driver calls
unregister_xenbus_watch, which deadlocks on the xenwatch_mutex (against
dev_changed->device_find->bus_for_each_dev). Bring up a skeleton
device, then modprobe -r skeleton_fe to see the deadlock.
Here is the helper script which creates the skeleton device:
#! /bin/sh
if [ $# -ne 2 ]; then
echo Usage: $0 frontend backend
exit 1
fi
xenstore-write /local/domain/$1/device/skeleton/100/backend
/local/domain/$2/backend/skeleton/$1/100
/local/domain/$1/device/skeleton/100/backend-id $2
/local/domain/$2/backend/skeleton/$1/100/frontend
/local/domain/$1/device/skeleton/100
/local/domain/$2/backend/skeleton/$1/100/frontend-id $1
# hotplug scripts in backend would normally do this
xenstore-write /local/domain/$2/backend/skeleton/$1/100/config 777
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff -r 20d1a79ebe31 linux-2.6-xen-sparse/arch/xen/Kconfig
--- a/linux-2.6-xen-sparse/arch/xen/Kconfig Wed Oct 26 15:59:13 2005
+++ b/linux-2.6-xen-sparse/arch/xen/Kconfig Wed Nov 2 15:24:59 2005
@@ -155,6 +155,22 @@
If security is not a concern then you may increase performance by
saying N.
+config XEN_SKELETON_FE
+ tristate "Compile Xen skeleton example frontend driver code"
+ default m
+ help
+ There is an example skeleton driver frontend in drivers/xen/skeleton
+ which you can use as a basis for your own xenbus-aware
+ drivers.
+
+config XEN_SKELETON_BE
+ tristate "Compile Xen skeleton example backend driver code"
+ default m
+ help
+ There is an example skeleton driver backend in drivers/xen/skeleton
+ which you can use as a basis for your own xenbus-aware
+ drivers.
+
choice
prompt "Processor Type"
default XEN_X86
diff -r 20d1a79ebe31 linux-2.6-xen-sparse/drivers/xen/Makefile
--- a/linux-2.6-xen-sparse/drivers/xen/Makefile Wed Oct 26 15:59:13 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/Makefile Wed Nov 2 15:24:59 2005
@@ -6,6 +6,7 @@
obj-y += balloon/
obj-y += privcmd/
obj-y += xenbus/
+obj-y += skeleton/
obj-$(CONFIG_XEN_BLKDEV_BACKEND) += blkback/
obj-$(CONFIG_XEN_NETDEV_BACKEND) += netback/
diff -r 20d1a79ebe31 linux-2.6-xen-sparse/drivers/xen/skeleton/Makefile
--- /dev/null Wed Oct 26 15:59:13 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/skeleton/Makefile Wed Nov 2
15:24:59 2005
@@ -0,0 +1,2 @@
+obj-$(CONFIG_XEN_SKELETON_FE) += skeleton_fe.o
+obj-$(CONFIG_XEN_SKELETON_BE) += skeleton_be.o
diff -r 20d1a79ebe31 linux-2.6-xen-sparse/drivers/xen/skeleton/skeleton_be.c
--- /dev/null Wed Oct 26 15:59:13 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/skeleton/skeleton_be.c Wed Nov 2
15:24:59 2005
@@ -0,0 +1,443 @@
+/* Example backend driver which simply shares a page with the front end.
+ Copyright (C) 2005 Rusty Russell, IBM Corporation
+
+ 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, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
+/* The "skeleton" device is an example. The store layout looks like:
+ * In the frontend directory:
+ * NAME CREATOR PURPOSE
+ * backend xend Path to backend to get backend data
+ * backend-id xend Domain ID to give evtchn/grantrefs
+ * ring-reference frontend Tells backend about shared page
+ * event-channel frontend Tells backend about event channel
+ *
+ * In the backend directory:
+ * NAME CREATOR PURPOSE
+ * frontend xend Path to frontend to get frontend data
+ * frontend-id xend ID to accept evtchn/grantrefs from
+ * config xend/hotplug Configuration info for backend.
+ * stuff backend Tells frontend about, um, useful stuff
+ *
+ * As the frontend can be saved/restored, it must handle the "backend" fields
+ * changing (after the ->resume callback). As either end's driver could go
+ * away (module unload), both frontend and backend must handle the dynamic
+ * fields (ring-reference & event-channel, or stuff) vanishing, and appearing.
+ */
+
+#include <linux/stringify.h>
+#include <linux/module.h>
+#include <linux/err.h>
+#include <asm-xen/xenbus.h>
+#include <asm-xen/evtchn.h>
+#include <asm-xen/driver_util.h>
+#include <asm-xen/gnttab.h>
+
+/* WAITING: our directory exists, fields aren't there yet.
+ * EXISTS: the tools/udev has written fields we need.
+ * READY: we have written our info into the store for the frontend to read.
+ * We can only enter this state once frontend is not "connected", to
+ * cover the case of module reload (frontend might not have noticed us
+ * going away yet).
+ * CONNECTED: we have read frontend information from the store. We create the
+ * "connected" node.
+ */
+enum state
+{
+ WAITING,
+ EXISTS,
+ READY,
+ CONNECTED,
+};
+
+/* Private information about this device */
+struct skeleton_be_info
+{
+ /* xenbus device we belong to */
+ struct xenbus_device *dev;
+
+ /* frontend path */
+ char *frontend;
+
+ /* frontend id */
+ int frontend_id;
+
+ /* Mapping for frontend page */
+ struct vm_struct *vm;
+ u16 shmem_handle;
+
+ /* grant table reference to page frontend offered */
+ int ring_ref;
+
+ /* event channel to send interrupts to frontend */
+ int evtchn;
+ int fe_evtchn;
+
+ /* Watch we place on frontend */
+ struct xenbus_watch watch;
+
+ /* Watch we place on ourselves. */
+ struct xenbus_watch be_watch;
+
+ /* If we are fully connected to backend. */
+ enum state state;
+
+ /* Device-specific (eg. net, block) stuff. */
+ struct device_specific_info *info;
+};
+
+static const char *state(struct skeleton_be_info *info)
+{
+ return info->state == WAITING ? "WAITING" :
+ info->state == EXISTS ? "EXISTS" :
+ info->state == READY ? "READY" :
+ info->state == CONNECTED ? "CONNECTED" : "UNKNOWN";
+}
+
+static inline int bind_event_channel(domid_t id, int evtchn)
+{
+ int err;
+ evtchn_op_t op = {
+ .cmd = EVTCHNOP_bind_interdomain,
+ .u.bind_interdomain.remote_dom = id,
+ .u.bind_interdomain.remote_port = evtchn };
+ err = HYPERVISOR_event_channel_op(&op);
+ if (err)
+ return err;
+ return op.u.bind_interdomain.local_port;
+}
+
+static struct device_specific_info *
+setup_device_specific_crap(struct xenbus_device *dev)
+{
+ int ret, dummy;
+
+ /* Read any local info set up by tools or hotplug/udev
+ * (eg. device to serve) */
+ ret = xenbus_scanf(NULL, dev->nodename, "config", "%i", &dummy);
+ if (ret != 1)
+ return NULL;
+
+ /* Request net/block/usb/etc device from kernel. */
+ return (void *)1;
+}
+
+static void free_device_specific_crap(struct device_specific_info *crap)
+{
+ /* Release net/block/usb/etc device from kernel. */
+}
+
+static void stop_device_replies(struct device_specific_info *crap)
+{
+ /* Frontend has gone away, we should drop outstanding replies. */
+}
+
+/* Write the information out to the store for the frontend to read, and
+ * know we're ready. */
+static int publish_info(struct skeleton_be_info *info)
+{
+ return xenbus_printf(NULL, info->dev->nodename, "stuff", "%u", 7);
+}
+
+/* Frontend gone/going away. Clean up. */
+static void skeleton_stop(struct skeleton_be_info *info)
+{
+ printk("%s: state %s\n", __func__, state(info));
+ stop_device_replies(info->info);
+
+ xenbus_rm(NULL, info->dev->nodename, "stuff");
+}
+
+static struct vm_struct *map_page(int ref, domid_t id, u16 *handle)
+{
+ struct gnttab_map_grant_ref op;
+ struct vm_struct *vm;
+
+ vm = alloc_vm_area(PAGE_SIZE);
+ if (!vm)
+ return ERR_PTR(-ENOMEM);
+
+ op.host_addr = (unsigned long)vm->addr;
+ op.flags = GNTMAP_host_map;
+ op.ref = ref;
+ op.dom = id;
+
+ lock_vm_area(vm);
+ BUG_ON(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1));
+ unlock_vm_area(vm);
+
+ if (op.handle < 0) {
+ free_vm_area(vm);
+ return ERR_PTR(op.handle);
+ }
+
+ *handle = op.handle;
+ return vm;
+}
+
+static void unmap_page(struct vm_struct *vm, u16 handle)
+{
+ struct gnttab_unmap_grant_ref op;
+
+ printk("%s enter\n", __func__);
+ op.host_addr = (unsigned long)vm->addr;
+ op.handle = handle;
+ op.dev_bus_addr = 0;
+
+ lock_vm_area(vm);
+ BUG_ON(HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1));
+ unlock_vm_area(vm);
+ printk("%s exit\n", __func__);
+}
+
+/* FIXME: This can be called before skeleton_probe() finished. */
+static void frontend_changed(struct xenbus_watch *watch,
+ const char **vec, unsigned int len)
+{
+ struct skeleton_be_info *info;
+ struct xenbus_transaction *trans;
+ int err;
+
+ info = container_of(watch, struct skeleton_be_info, watch);
+
+ /* If frontend has gone away, shut down. */
+ if (!xenbus_exists(NULL, info->frontend, "")) {
+ device_unregister(&info->dev->dev);
+ return;
+ }
+
+ switch (info->state) {
+ case WAITING:
+ break;
+
+ case EXISTS:
+ if (xenbus_exists(NULL, info->frontend, "connected")) {
+ xenbus_dev_error(info->dev, -EBUSY,
+ "frontend still connected");
+ return;
+ }
+
+ err = publish_info(info);
+ if (err) {
+ xenbus_dev_error(info->dev, err,
+ "writing information");
+ return;
+ }
+ info->state = READY;
+ /* fall thru */
+
+ case READY:
+ /* Try to read frontend stuff. */
+ again:
+ trans = xenbus_transaction_start();
+ if (IS_ERR(trans)) {
+ xenbus_dev_error(info->dev, PTR_ERR(trans),
+ "starting transaction");
+ return;
+ }
+ err = xenbus_gather(NULL, info->frontend,
+ "ring-reference", "%u", &info->ring_ref,
+ "event-channel", "%u", &info->fe_evtchn,
+ NULL);
+ if (!err) {
+ err = xenbus_transaction_end(trans, 0);
+ if (err == -EAGAIN)
+ goto again;
+ }
+ if (err) {
+ xenbus_dev_error(info->dev, err, "reading from %s",
+ info->frontend);
+ return;
+ }
+
+ err = bind_event_channel(info->frontend_id, info->fe_evtchn);
+ if (err < 0) {
+ xenbus_dev_error(info->dev, err,
+ "binding event channel");
+ return;
+ }
+ info->fe_evtchn = err;
+
+ info->vm = map_page(info->ring_ref, info->frontend_id,
+ &info->shmem_handle);
+ if (IS_ERR(info->vm)) {
+ xenbus_dev_error(info->dev, PTR_ERR(info->vm),
+ "mapping page");
+ return;
+ }
+ info->state = CONNECTED;
+ /* Clear any previous errors. */
+ xenbus_dev_ok(info->dev);
+ xenbus_printf(NULL, info->dev->nodename, "connected", "ok");
+ break;
+
+ case CONNECTED:
+ /* Did frontend driver shut down? */
+ if (!xenbus_exists(NULL, info->frontend, "ring-reference")) {
+ xenbus_dev_error(info->dev, -ENOENT,
+ "frontend disconnected");
+ xenbus_rm(NULL, info->dev->nodename, "connected");
+ unmap_page(info->vm, info->shmem_handle);
+ skeleton_stop(info);
+ info->state = EXISTS;
+ }
+ }
+}
+
+static int skeleton_watch_front(struct xenbus_device *dev,
+ struct skeleton_be_info *info)
+{
+ int err;
+
+ printk("%s: state %s\n", __func__, state(info));
+
+ /* We need frontend-id and path. */
+ err = xenbus_gather(NULL, dev->nodename,
+ "frontend-id", "%i", &info->frontend_id,
+ "frontend", NULL, &info->frontend,
+ NULL);
+ if (err) {
+ xenbus_dev_error(dev, err, "reading frontend or frontend-id");
+ goto out;
+ }
+
+ info->watch.node = info->frontend;
+ info->watch.callback = frontend_changed;
+ err = register_xenbus_watch(&info->watch);
+ if (err) {
+ xenbus_dev_error(dev, err, "placing watch on %s",
+ info->frontend);
+ goto free_frontend;
+ }
+ /* frontend_changed called immediately: stuff might be there already.*/
+ frontend_changed(&info->watch, NULL, 0);
+ return 0;
+
+free_frontend:
+ kfree(info->frontend);
+out:
+ return err;
+}
+
+static void self_changed(struct xenbus_watch *watch,
+ const char **vec, unsigned int len)
+{
+ struct skeleton_be_info *info;
+ int err;
+
+ info = container_of(watch, struct skeleton_be_info, be_watch);
+ printk("%s: state %s\n", __func__, state(info));
+
+ /* We only need this while we're waiting for config. */
+ if (info->state != WAITING)
+ return;
+
+ /* Not there yet? Keep waiting. */
+ info->info = setup_device_specific_crap(info->dev);
+ if (!info->info)
+ return;
+
+ info->state = EXISTS;
+ err = skeleton_watch_front(info->dev, info);
+ if (err) {
+ free_device_specific_crap(info->info);
+ return;
+ }
+}
+
+static int skeleton_probe(struct xenbus_device *dev,
+ const struct xenbus_device_id *id)
+{
+ int err;
+ struct skeleton_be_info *info;
+
+ printk("skeleton_probe_be: %s\n", dev->nodename);
+
+ dev->data = info = kmalloc(sizeof(*info), GFP_KERNEL);
+ if (!info) {
+ xenbus_dev_error(dev, -ENOMEM, "allocating info structure");
+ return -ENOMEM;
+ }
+ info->dev = dev;
+ info->state = WAITING;
+
+ /* Try for config (might need to wait for udev). */
+ info->be_watch.node = dev->nodename;
+ info->be_watch.callback = self_changed;
+ err = register_xenbus_watch(&info->be_watch);
+ if (err) {
+ xenbus_dev_error(dev, err, "placing watch on self %s",
+ dev->nodename);
+ kfree(info);
+ return err;
+ }
+ self_changed(&info->be_watch, NULL, 0);
+ return 0;
+}
+
+static int skeleton_remove(struct xenbus_device *dev)
+{
+ struct skeleton_be_info *info = dev->data;
+
+ switch (info->state) {
+ case CONNECTED:
+ unmap_page(info->vm, info->shmem_handle);
+ /* fall thru */
+ case READY:
+ skeleton_stop(info);
+ /* Must remove this after other fields. */
+ xenbus_rm(NULL, dev->nodename, "connected");
+ /* fall thru */
+ case EXISTS:
+ unregister_xenbus_watch(&info->watch);
+ free_device_specific_crap(info->info);
+ /* fall thru */
+ case WAITING:
+ unregister_xenbus_watch(&info->be_watch);
+ }
+
+ kfree(info);
+
+ return 0;
+}
+
+static struct xenbus_device_id skeleton_ids[] = {
+ { "skeleton" },
+ { { 0 } },
+};
+
+/* A xenbus backend driver. */
+static struct xenbus_driver driver = {
+ /* Makefile defines KBUILD_MODNAME (in this case, skeleton_be) */
+ .name = __stringify(KBUILD_MODNAME),
+ .owner = THIS_MODULE,
+ .ids = skeleton_ids,
+ .probe = skeleton_probe,
+ .remove = skeleton_remove,
+};
+
+static int init(void)
+{
+ return xenbus_register_backend(&driver);
+}
+
+static void fini(void)
+{
+ xenbus_unregister_driver(&driver);
+}
+
+module_init(init);
+module_exit(fini);
+MODULE_LICENSE("GPL");
diff -r 20d1a79ebe31 linux-2.6-xen-sparse/drivers/xen/skeleton/skeleton_fe.c
--- /dev/null Wed Oct 26 15:59:13 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/skeleton/skeleton_fe.c Wed Nov 2
15:24:59 2005
@@ -0,0 +1,407 @@
+/* Example frontend driver which simply shares a page with the back end.
+ Copyright (C) 2005 Rusty Russell, IBM Corporation
+
+ 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, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
+/* The "skeleton" device is an example. The store layout looks like:
+ * In the frontend directory:
+ * NAME CREATOR PURPOSE
+ * backend xend Path to backend to get backend data
+ * backend-id xend Domain ID to give evtchn/grantrefs
+ * ring-reference frontend Tells backend about shared page
+ * event-channel frontend Tells backend about event channel
+ *
+ * In the backend directory:
+ * NAME CREATOR PURPOSE
+ * frontend xend Path to frontend to get frontend data
+ * frontend-id xend ID to accept evtchn/grantrefs from
+ * config xend/hotplug Configuration info for backend.
+ * stuff backend Tells frontend about, um, useful stuff
+ *
+ * As the frontend can be saved/restored, it must handle the "backend" fields
+ * changing (after the ->resume callback). As either end's driver could go
+ * away (module unload), both frontend and backend must handle the dynamic
+ * fields (ring-reference & event-channel, or stuff) vanishing, and appearing.
+ */
+
+#include <linux/stringify.h>
+#include <linux/module.h>
+#include <linux/err.h>
+#include <asm-xen/xenbus.h>
+#include <asm-xen/evtchn.h>
+#include <asm-xen/gnttab.h>
+
+/* EXISTS: our directory exists, with the tool-written stuff in it.
+ * READY: we have written our info into the store for the backend to read.
+ * We can only enter this state once backend is not "connected", to
+ * cover the case of module reload (backend might not have noticed us
+ * going away yet!).
+ * CONNECTED: we have read backend information from the store. We create the
+ * "connected" node.
+ */
+enum state
+{
+ EXISTS,
+ READY,
+ CONNECTED,
+};
+
+/* Private information about this device */
+struct skeleton_info
+{
+ /* xenbus device we belong to */
+ struct xenbus_device *dev;
+
+ /* backend path */
+ char *backend;
+
+ /* backend id */
+ int backend_id;
+
+ /* page we offer to share */
+ void *page;
+
+ /* grant table reference to page we offer to backend */
+ int ring_ref;
+
+ /* event channel to send interrupts to backend */
+ int evtchn;
+
+ /* Watch we place on backend */
+ struct xenbus_watch watch;
+
+ /* If we are fully connected to backend. */
+ enum state state;
+
+ /* Information given by the backend */
+ int backend_stuff;
+
+ /* Device-specific (eg. net, block) stuff. */
+ struct device_specific_info *info;
+};
+
+static const char *state(struct skeleton_info *info)
+{
+ return info->state == EXISTS ? "EXISTS" :
+ info->state == READY ? "READY" :
+ info->state == CONNECTED ? "CONNECTED" : "UNKNOWN";
+}
+
+static inline int allocate_event_channel(domid_t id)
+{
+ int err;
+ evtchn_op_t op = {
+ .cmd = EVTCHNOP_alloc_unbound,
+ .u.alloc_unbound.dom = DOMID_SELF,
+ .u.alloc_unbound.remote_dom = id };
+
+ err = HYPERVISOR_event_channel_op(&op);
+ if (err)
+ return err;
+ return op.u.alloc_unbound.port;
+}
+
+static inline void free_event_channel(int evtchn)
+{
+ evtchn_op_t op = {
+ .cmd = EVTCHNOP_close,
+ .u.close.port = evtchn };
+ HYPERVISOR_event_channel_op(&op);
+}
+
+static struct device_specific_info *
+setup_device_specific_crap(struct xenbus_device *dev)
+{
+ /* Read any local info set up by tools (eg. mac address) on creation */
+
+ /* Register as a net/block/usb/etc device with kernel. */
+
+ return (void *)1;
+}
+
+static void free_device_specific_crap(struct device_specific_info *crap)
+{
+ /* Unregister as a net/block/usb/etc device with kernel. */
+}
+
+static void stop_device_requests(struct device_specific_info *crap)
+{
+ /* Backend has gone away, we should queue requests. */
+}
+
+/* Write the information out to the store for the backend to read, and
+ * know we're ready. */
+static int publish_info(struct skeleton_info *info)
+{
+ struct xenbus_transaction *trans;
+ int err;
+
+ printk("%s: state %s\n", __func__, state(info));
+ /* Transactions can fail spuriously, which means we loop. */
+again:
+ trans = xenbus_transaction_start();
+ if (IS_ERR(trans))
+ return PTR_ERR(trans);
+
+ err = xenbus_printf(trans, info->dev->nodename, "ring-reference", "%u",
+ info->ring_ref);
+ if (!err)
+ err = xenbus_printf(trans, info->dev->nodename,
+ "event-channel", "%u", info->evtchn);
+
+ if (err) {
+ xenbus_transaction_end(trans, 1);
+ return err;
+ }
+ err = xenbus_transaction_end(trans, 0);
+ if (err == -EAGAIN)
+ goto again;
+ return err;
+}
+
+/* Backend gone/going away. Clean up. */
+static void skeleton_stop(struct skeleton_info *info)
+{
+ printk("%s: state %s\n", __func__, state(info));
+ stop_device_requests(info->info);
+
+ /* FIXME: can't use transaction, it requires alloc. */
+ xenbus_rm(NULL, info->dev->nodename, "ring-reference");
+ xenbus_rm(NULL, info->dev->nodename, "event-channel");
+}
+
+/* FIXME: This can be called before skeleton_probe() finished. */
+static void backend_changed(struct xenbus_watch *watch,
+ const char **vec, unsigned int len)
+{
+ struct skeleton_info *info;
+ int err;
+
+ info = container_of(watch, struct skeleton_info, watch);
+
+ printk("%s: state %s\n", __func__, state(info));
+
+ switch (info->state) {
+ case EXISTS:
+ if (xenbus_exists(NULL, info->backend, "connected")) {
+ xenbus_dev_error(info->dev, -EBUSY,
+ "backend still connected");
+ return;
+ }
+
+ err = publish_info(info);
+ if (err) {
+ xenbus_dev_error(info->dev, err,
+ "writing information");
+ return;
+ }
+ info->state = READY;
+ /* fall thru */
+
+ case READY:
+ /* Try to read backend stuff. */
+ err = xenbus_scanf(NULL, info->backend, "stuff", "%u",
+ &info->backend_stuff);
+ if (err < 0) {
+ xenbus_dev_error(info->dev, err, "reading %s/stuff",
+ info->backend);
+ return;
+ }
+ info->state = CONNECTED;
+ /* Clear any previous errors. */
+ xenbus_dev_ok(info->dev);
+ xenbus_printf(NULL, info->dev->nodename, "connected", "ok");
+ break;
+
+ case CONNECTED:
+ /* Did backend driver shut down? */
+ if (!xenbus_exists(NULL, info->backend, "stuff")) {
+ xenbus_dev_error(info->dev, -ENOENT,
+ "backend disconnected");
+ xenbus_rm(NULL, info->dev->nodename, "connected");
+ skeleton_stop(info);
+ info->state = EXISTS;
+ }
+ }
+}
+
+static int skeleton_resume(struct xenbus_device *dev)
+{
+ int err;
+ struct skeleton_info *info = dev->data;
+
+ printk("%s: state %s\n", __func__, state(info));
+
+ /* We need backend-id and path. */
+ err = xenbus_gather(NULL, dev->nodename,
+ "backend-id", "%i", &info->backend_id,
+ "backend", NULL, &info->backend,
+ NULL);
+ if (err) {
+ xenbus_dev_error(dev, err, "reading backend or backend-id");
+ goto out;
+ }
+
+ /* We need to allocate a page and event channel. */
+ info->page = (void *)__get_free_page(GFP_KERNEL);
+ if (!info->page) {
+ err = -ENOMEM;
+ xenbus_dev_error(dev, err, "allocating shared page");
+ goto free_backend;
+ }
+
+ err = gnttab_grant_foreign_access(info->backend_id,
+ virt_to_mfn(info->page), 0);
+ if (err < 0) {
+ xenbus_dev_error(dev, err, "granting page");
+ goto free_page;
+ }
+ info->ring_ref = err;
+
+ err = allocate_event_channel(info->backend_id);
+ if (err < 0) {
+ xenbus_dev_error(dev, err, "allocating event channel");
+ goto ungrant_page;
+ }
+ info->evtchn = err;
+
+ info->watch.node = info->backend;
+ info->watch.callback = backend_changed;
+ err = register_xenbus_watch(&info->watch);
+ if (err) {
+ xenbus_dev_error(dev, err, "placing watch on %s",
info->backend);
+ goto free_event_channel;
+ }
+ /* backend_changed called immediately: stuff might be there already. */
+ backend_changed(&info->watch, NULL, 0);
+ return 0;
+
+free_event_channel:
+ free_event_channel(info->evtchn);
+ungrant_page:
+ /* FIXME: Need infrastructure to handle otherside holding onto page. */
+ gnttab_end_foreign_access(info->ring_ref, 0);
+free_page:
+ free_page((unsigned long)info->page);
+free_backend:
+ kfree(info->backend);
+out:
+ return err;
+}
+
+static int skeleton_probe(struct xenbus_device *dev,
+ const struct xenbus_device_id *id)
+{
+ int err;
+ struct skeleton_info *info;
+
+ printk("skeleton_probe for %s\n", dev->nodename);
+
+ dev->data = info = kmalloc(sizeof(*info), GFP_KERNEL);
+ if (!info) {
+ xenbus_dev_error(dev, -ENOMEM, "allocating info structure");
+ return -ENOMEM;
+ }
+ info->dev = dev;
+ info->state = EXISTS;
+
+ info->info = setup_device_specific_crap(dev);
+ if (IS_ERR(info->info)) {
+ err = PTR_ERR(info->info);
+ xenbus_dev_error(dev, err, "setting up device");
+ kfree(info);
+ return err;
+ }
+
+ err = skeleton_resume(dev);
+ if (err) {
+ free_device_specific_crap(info->info);
+ kfree(info);
+ }
+ return err;
+}
+
+/* Clean up: will re-init and connect to backend on resume. */
+static int skeleton_suspend(struct xenbus_device *dev)
+{
+ struct skeleton_info *info = dev->data;
+
+ printk("%s: state %s\n", __func__, state(info));
+ switch (info->state) {
+ case CONNECTED:
+ xenbus_rm(NULL, dev->nodename, "connected");
+ info->state = READY;
+ /* fall thru */
+ case READY:
+ skeleton_stop(info);
+ info->state = EXISTS;
+ case EXISTS:
+ ; /* Nothing to do */
+ }
+
+ /* FIXME: Need infrastructure to handle otherside holding onto page. */
+ gnttab_end_foreign_access(info->ring_ref, 0);
+ free_page((unsigned long)info->page);
+ kfree(info->backend);
+ printk("%s:%i\n", __func__, __LINE__);
+ unregister_xenbus_watch(&info->watch);
+ printk("%s:%i\n", __func__, __LINE__);
+ return 0;
+}
+
+static int skeleton_remove(struct xenbus_device *dev)
+{
+ struct skeleton_info *info = dev->data;
+
+ printk("%s: state %s\n", __func__, state(info));
+ skeleton_suspend(dev);
+ free_device_specific_crap(info->info);
+ kfree(info);
+ printk("%s exiting\n", __func__);
+
+ return 0;
+}
+
+static struct xenbus_device_id skeleton_ids[] = {
+ { "skeleton" },
+ { { 0 } },
+};
+
+/* A xenbus driver. */
+static struct xenbus_driver driver = {
+ /* Makefile defines KBUILD_MODNAME (in this case, skeleton_fe) */
+ .name = __stringify(KBUILD_MODNAME),
+ .owner = THIS_MODULE,
+ .ids = skeleton_ids,
+ .probe = skeleton_probe,
+ .remove = skeleton_remove,
+ .suspend = skeleton_suspend,
+ .resume = skeleton_resume,
+};
+
+static int init(void)
+{
+ return xenbus_register_driver(&driver);
+}
+
+static void fini(void)
+{
+ xenbus_unregister_driver(&driver);
+}
+
+module_init(init);
+module_exit(fini);
+MODULE_LICENSE("GPL");
--
A bad analogy is like a leaky screwdriver -- Richard Braakman
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