1 /******************************************************************************
2  * Talks to Xen Store to figure out what devices we have (backend half).
3  *
4  * Copyright (C) 2005 Rusty Russell, IBM Corporation
5  * Copyright (C) 2005 Mike Wray, Hewlett-Packard
6  * Copyright (C) 2005, 2006 XenSource Ltd
7  * Copyright (C) 2007 Solarflare Communications, Inc.
8  *
9  * This program is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU General Public License version 2
11  * as published by the Free Software Foundation; or, when distributed
12  * separately from the Linux kernel or incorporated into other
13  * software packages, subject to the following license:
14  *
15  * Permission is hereby granted, free of charge, to any person obtaining a copy
16  * of this source file (the "Software"), to deal in the Software without
17  * restriction, including without limitation the rights to use, copy, modify,
18  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
19  * and to permit persons to whom the Software is furnished to do so, subject to
20  * the following conditions:
21  *
22  * The above copyright notice and this permission notice shall be included in
23  * all copies or substantial portions of the Software.
24  *
25  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
26  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
27  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
28  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
29  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
30  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
31  * IN THE SOFTWARE.
32  */
33 
34 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
35 
36 #define DPRINTK(fmt, ...)				\
37 	pr_debug("(%s:%d) " fmt "\n",			\
38 		 __func__, __LINE__, ##__VA_ARGS__)
39 
40 #include <linux/kernel.h>
41 #include <linux/err.h>
42 #include <linux/string.h>
43 #include <linux/ctype.h>
44 #include <linux/fcntl.h>
45 #include <linux/mm.h>
46 #include <linux/notifier.h>
47 #include <linux/export.h>
48 #include <linux/semaphore.h>
49 
50 #include <asm/page.h>
51 #include <asm/xen/hypervisor.h>
52 #include <asm/hypervisor.h>
53 #include <xen/xenbus.h>
54 #include <xen/features.h>
55 
56 #include "xenbus.h"
57 
58 /* backend/<type>/<fe-uuid>/<id> => <type>-<fe-domid>-<id> */
59 static int backend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
60 {
61 	int domid, err;
62 	const char *devid, *type, *frontend;
63 	unsigned int typelen;
64 
65 	type = strchr(nodename, '/');
66 	if (!type)
67 		return -EINVAL;
68 	type++;
69 	typelen = strcspn(type, "/");
70 	if (!typelen || type[typelen] != '/')
71 		return -EINVAL;
72 
73 	devid = strrchr(nodename, '/') + 1;
74 
75 	err = xenbus_gather(XBT_NIL, nodename, "frontend-id", "%i", &domid,
76 			    "frontend", NULL, &frontend,
77 			    NULL);
78 	if (err)
79 		return err;
80 	if (strlen(frontend) == 0)
81 		err = -ERANGE;
82 	if (!err && !xenbus_exists(XBT_NIL, frontend, ""))
83 		err = -ENOENT;
84 	kfree(frontend);
85 
86 	if (err)
87 		return err;
88 
89 	if (snprintf(bus_id, XEN_BUS_ID_SIZE, "%.*s-%i-%s",
90 		     typelen, type, domid, devid) >= XEN_BUS_ID_SIZE)
91 		return -ENOSPC;
92 	return 0;
93 }
94 
95 static int xenbus_uevent_backend(struct device *dev,
96 				 struct kobj_uevent_env *env)
97 {
98 	struct xenbus_device *xdev;
99 	struct xenbus_driver *drv;
100 	struct xen_bus_type *bus;
101 
102 	DPRINTK("");
103 
104 	if (dev == NULL)
105 		return -ENODEV;
106 
107 	xdev = to_xenbus_device(dev);
108 	bus = container_of(xdev->dev.bus, struct xen_bus_type, bus);
109 
110 	if (add_uevent_var(env, "MODALIAS=xen-backend:%s", xdev->devicetype))
111 		return -ENOMEM;
112 
113 	/* stuff we want to pass to /sbin/hotplug */
114 	if (add_uevent_var(env, "XENBUS_TYPE=%s", xdev->devicetype))
115 		return -ENOMEM;
116 
117 	if (add_uevent_var(env, "XENBUS_PATH=%s", xdev->nodename))
118 		return -ENOMEM;
119 
120 	if (add_uevent_var(env, "XENBUS_BASE_PATH=%s", bus->root))
121 		return -ENOMEM;
122 
123 	if (dev->driver) {
124 		drv = to_xenbus_driver(dev->driver);
125 		if (drv && drv->uevent)
126 			return drv->uevent(xdev, env);
127 	}
128 
129 	return 0;
130 }
131 
132 /* backend/<typename>/<frontend-uuid>/<name> */
133 static int xenbus_probe_backend_unit(struct xen_bus_type *bus,
134 				     const char *dir,
135 				     const char *type,
136 				     const char *name)
137 {
138 	char *nodename;
139 	int err;
140 
141 	nodename = kasprintf(GFP_KERNEL, "%s/%s", dir, name);
142 	if (!nodename)
143 		return -ENOMEM;
144 
145 	DPRINTK("%s\n", nodename);
146 
147 	err = xenbus_probe_node(bus, type, nodename);
148 	kfree(nodename);
149 	return err;
150 }
151 
152 /* backend/<typename>/<frontend-domid> */
153 static int xenbus_probe_backend(struct xen_bus_type *bus, const char *type,
154 				const char *domid)
155 {
156 	char *nodename;
157 	int err = 0;
158 	char **dir;
159 	unsigned int i, dir_n = 0;
160 
161 	DPRINTK("");
162 
163 	nodename = kasprintf(GFP_KERNEL, "%s/%s/%s", bus->root, type, domid);
164 	if (!nodename)
165 		return -ENOMEM;
166 
167 	dir = xenbus_directory(XBT_NIL, nodename, "", &dir_n);
168 	if (IS_ERR(dir)) {
169 		kfree(nodename);
170 		return PTR_ERR(dir);
171 	}
172 
173 	for (i = 0; i < dir_n; i++) {
174 		err = xenbus_probe_backend_unit(bus, nodename, type, dir[i]);
175 		if (err)
176 			break;
177 	}
178 	kfree(dir);
179 	kfree(nodename);
180 	return err;
181 }
182 
183 static bool frontend_will_handle(struct xenbus_watch *watch,
184 				 const char *path, const char *token)
185 {
186 	return watch->nr_pending == 0;
187 }
188 
189 static void frontend_changed(struct xenbus_watch *watch,
190 			     const char *path, const char *token)
191 {
192 	xenbus_otherend_changed(watch, path, token, 0);
193 }
194 
195 static struct xen_bus_type xenbus_backend = {
196 	.root = "backend",
197 	.levels = 3,		/* backend/type/<frontend>/<id> */
198 	.get_bus_id = backend_bus_id,
199 	.probe = xenbus_probe_backend,
200 	.otherend_will_handle = frontend_will_handle,
201 	.otherend_changed = frontend_changed,
202 	.bus = {
203 		.name		= "xen-backend",
204 		.match		= xenbus_match,
205 		.uevent		= xenbus_uevent_backend,
206 		.probe		= xenbus_dev_probe,
207 		.remove		= xenbus_dev_remove,
208 		.dev_groups	= xenbus_dev_groups,
209 	},
210 };
211 
212 static void backend_changed(struct xenbus_watch *watch,
213 			    const char *path, const char *token)
214 {
215 	DPRINTK("");
216 
217 	xenbus_dev_changed(path, &xenbus_backend);
218 }
219 
220 static struct xenbus_watch be_watch = {
221 	.node = "backend",
222 	.callback = backend_changed,
223 };
224 
225 static int read_frontend_details(struct xenbus_device *xendev)
226 {
227 	return xenbus_read_otherend_details(xendev, "frontend-id", "frontend");
228 }
229 
230 int xenbus_dev_is_online(struct xenbus_device *dev)
231 {
232 	return !!xenbus_read_unsigned(dev->nodename, "online", 0);
233 }
234 EXPORT_SYMBOL_GPL(xenbus_dev_is_online);
235 
236 int __xenbus_register_backend(struct xenbus_driver *drv, struct module *owner,
237 			      const char *mod_name)
238 {
239 	drv->read_otherend_details = read_frontend_details;
240 
241 	return xenbus_register_driver_common(drv, &xenbus_backend,
242 					     owner, mod_name);
243 }
244 EXPORT_SYMBOL_GPL(__xenbus_register_backend);
245 
246 static int backend_probe_and_watch(struct notifier_block *notifier,
247 				   unsigned long event,
248 				   void *data)
249 {
250 	/* Enumerate devices in xenstore and watch for changes. */
251 	xenbus_probe_devices(&xenbus_backend);
252 	register_xenbus_watch(&be_watch);
253 
254 	return NOTIFY_DONE;
255 }
256 
257 static int backend_reclaim_memory(struct device *dev, void *data)
258 {
259 	const struct xenbus_driver *drv;
260 	struct xenbus_device *xdev;
261 
262 	if (!dev->driver)
263 		return 0;
264 	drv = to_xenbus_driver(dev->driver);
265 	if (drv && drv->reclaim_memory) {
266 		xdev = to_xenbus_device(dev);
267 		if (down_trylock(&xdev->reclaim_sem))
268 			return 0;
269 		drv->reclaim_memory(xdev);
270 		up(&xdev->reclaim_sem);
271 	}
272 	return 0;
273 }
274 
275 /*
276  * Returns 0 always because we are using shrinker to only detect memory
277  * pressure.
278  */
279 static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
280 				struct shrink_control *sc)
281 {
282 	bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
283 			backend_reclaim_memory);
284 	return 0;
285 }
286 
287 static struct shrinker backend_memory_shrinker = {
288 	.count_objects = backend_shrink_memory_count,
289 	.seeks = DEFAULT_SEEKS,
290 };
291 
292 static int __init xenbus_probe_backend_init(void)
293 {
294 	static struct notifier_block xenstore_notifier = {
295 		.notifier_call = backend_probe_and_watch
296 	};
297 	int err;
298 
299 	DPRINTK("");
300 
301 	/* Register ourselves with the kernel bus subsystem */
302 	err = bus_register(&xenbus_backend.bus);
303 	if (err)
304 		return err;
305 
306 	register_xenstore_notifier(&xenstore_notifier);
307 
308 	if (register_shrinker(&backend_memory_shrinker, "xen-backend"))
309 		pr_warn("shrinker registration failed\n");
310 
311 	return 0;
312 }
313 subsys_initcall(xenbus_probe_backend_init);
314