xen/xenbus/xenbus_probe_backend.c

0001 /******************************************************************************
0002  * Talks to Xen Store to figure out what devices we have (backend half).
0003  *
0004  * Copyright (C) 2005 Rusty Russell, IBM Corporation
0005  * Copyright (C) 2005 Mike Wray, Hewlett-Packard
0006  * Copyright (C) 2005, 2006 XenSource Ltd
0007  * Copyright (C) 2007 Solarflare Communications, Inc.
0008  *
0009  * This program is free software; you can redistribute it and/or
0010  * modify it under the terms of the GNU General Public License version 2
0011  * as published by the Free Software Foundation; or, when distributed
0012  * separately from the Linux kernel or incorporated into other
0013  * software packages, subject to the following license:
0014  *
0015  * Permission is hereby granted, free of charge, to any person obtaining a copy
0016  * of this source file (the "Software"), to deal in the Software without
0017  * restriction, including without limitation the rights to use, copy, modify,
0018  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
0019  * and to permit persons to whom the Software is furnished to do so, subject to
0020  * the following conditions:
0021  *
0022  * The above copyright notice and this permission notice shall be included in
0023  * all copies or substantial portions of the Software.
0024  *
0025  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
0026  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
0027  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
0028  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
0029  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
0030  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
0031  * IN THE SOFTWARE.
0032  */
0033
0034 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0035
0036 #define DPRINTK(fmt, ...)               \
0037     pr_debug("(%s:%d) " fmt "\n",           \
0038          __func__, __LINE__, ##__VA_ARGS__)
0039
0040 #include <linux/kernel.h>
0041 #include <linux/err.h>
0042 #include <linux/string.h>
0043 #include <linux/ctype.h>
0044 #include <linux/fcntl.h>
0045 #include <linux/mm.h>
0046 #include <linux/notifier.h>
0047 #include <linux/export.h>
0048 #include <linux/semaphore.h>
0049
0050 #include <asm/page.h>
0051 #include <asm/xen/hypervisor.h>
0052 #include <asm/hypervisor.h>
0053 #include <xen/xenbus.h>
0054 #include <xen/features.h>
0055
0056 #include "xenbus.h"
0057
0058 /* backend/<type>/<fe-uuid>/<id> => <type>-<fe-domid>-<id> */
0059 static int backend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
0060 {
0061     int domid, err;
0062     const char *devid, *type, *frontend;
0063     unsigned int typelen;
0064
0065     type = strchr(nodename, '/');
0066     if (!type)
0067         return -EINVAL;
0068     type++;
0069     typelen = strcspn(type, "/");
0070     if (!typelen || type[typelen] != '/')
0071         return -EINVAL;
0072
0073     devid = strrchr(nodename, '/') + 1;
0074
0075     err = xenbus_gather(XBT_NIL, nodename, "frontend-id", "%i", &domid,
0076                 "frontend", NULL, &frontend,
0077                 NULL);
0078     if (err)
0079         return err;
0080     if (strlen(frontend) == 0)
0081         err = -ERANGE;
0082     if (!err && !xenbus_exists(XBT_NIL, frontend, ""))
0083         err = -ENOENT;
0084     kfree(frontend);
0085
0086     if (err)
0087         return err;
0088
0089     if (snprintf(bus_id, XEN_BUS_ID_SIZE, "%.*s-%i-%s",
0090              typelen, type, domid, devid) >= XEN_BUS_ID_SIZE)
0091         return -ENOSPC;
0092     return 0;
0093 }
0094
0095 static int xenbus_uevent_backend(struct device *dev,
0096                  struct kobj_uevent_env *env)
0097 {
0098     struct xenbus_device *xdev;
0099     struct xenbus_driver *drv;
0100     struct xen_bus_type *bus;
0101
0102     DPRINTK("");
0103
0104     if (dev == NULL)
0105         return -ENODEV;
0106
0107     xdev = to_xenbus_device(dev);
0108     bus = container_of(xdev->dev.bus, struct xen_bus_type, bus);
0109
0110     if (add_uevent_var(env, "MODALIAS=xen-backend:%s", xdev->devicetype))
0111         return -ENOMEM;
0112
0113     /* stuff we want to pass to /sbin/hotplug */
0114     if (add_uevent_var(env, "XENBUS_TYPE=%s", xdev->devicetype))
0115         return -ENOMEM;
0116
0117     if (add_uevent_var(env, "XENBUS_PATH=%s", xdev->nodename))
0118         return -ENOMEM;
0119
0120     if (add_uevent_var(env, "XENBUS_BASE_PATH=%s", bus->root))
0121         return -ENOMEM;
0122
0123     if (dev->driver) {
0124         drv = to_xenbus_driver(dev->driver);
0125         if (drv && drv->uevent)
0126             return drv->uevent(xdev, env);
0127     }
0128
0129     return 0;
0130 }
0131
0132 /* backend/<typename>/<frontend-uuid>/<name> */
0133 static int xenbus_probe_backend_unit(struct xen_bus_type *bus,
0134                      const char *dir,
0135                      const char *type,
0136                      const char *name)
0137 {
0138     char *nodename;
0139     int err;
0140
0141     nodename = kasprintf(GFP_KERNEL, "%s/%s", dir, name);
0142     if (!nodename)
0143         return -ENOMEM;
0144
0145     DPRINTK("%s\n", nodename);
0146
0147     err = xenbus_probe_node(bus, type, nodename);
0148     kfree(nodename);
0149     return err;
0150 }
0151
0152 /* backend/<typename>/<frontend-domid> */
0153 static int xenbus_probe_backend(struct xen_bus_type *bus, const char *type,
0154                 const char *domid)
0155 {
0156     char *nodename;
0157     int err = 0;
0158     char **dir;
0159     unsigned int i, dir_n = 0;
0160
0161     DPRINTK("");
0162
0163     nodename = kasprintf(GFP_KERNEL, "%s/%s/%s", bus->root, type, domid);
0164     if (!nodename)
0165         return -ENOMEM;
0166
0167     dir = xenbus_directory(XBT_NIL, nodename, "", &dir_n);
0168     if (IS_ERR(dir)) {
0169         kfree(nodename);
0170         return PTR_ERR(dir);
0171     }
0172
0173     for (i = 0; i < dir_n; i++) {
0174         err = xenbus_probe_backend_unit(bus, nodename, type, dir[i]);
0175         if (err)
0176             break;
0177     }
0178     kfree(dir);
0179     kfree(nodename);
0180     return err;
0181 }
0182
0183 static bool frontend_will_handle(struct xenbus_watch *watch,
0184                  const char *path, const char *token)
0185 {
0186     return watch->nr_pending == 0;
0187 }
0188
0189 static void frontend_changed(struct xenbus_watch *watch,
0190                  const char *path, const char *token)
0191 {
0192     xenbus_otherend_changed(watch, path, token, 0);
0193 }
0194
0195 static struct xen_bus_type xenbus_backend = {
0196     .root = "backend",
0197     .levels = 3,        /* backend/type/<frontend>/<id> */
0198     .get_bus_id = backend_bus_id,
0199     .probe = xenbus_probe_backend,
0200     .otherend_will_handle = frontend_will_handle,
0201     .otherend_changed = frontend_changed,
0202     .bus = {
0203         .name       = "xen-backend",
0204         .match      = xenbus_match,
0205         .uevent     = xenbus_uevent_backend,
0206         .probe      = xenbus_dev_probe,
0207         .remove     = xenbus_dev_remove,
0208         .dev_groups = xenbus_dev_groups,
0209     },
0210 };
0211
0212 static void backend_changed(struct xenbus_watch *watch,
0213                 const char *path, const char *token)
0214 {
0215     DPRINTK("");
0216
0217     xenbus_dev_changed(path, &xenbus_backend);
0218 }
0219
0220 static struct xenbus_watch be_watch = {
0221     .node = "backend",
0222     .callback = backend_changed,
0223 };
0224
0225 static int read_frontend_details(struct xenbus_device *xendev)
0226 {
0227     return xenbus_read_otherend_details(xendev, "frontend-id", "frontend");
0228 }
0229
0230 int xenbus_dev_is_online(struct xenbus_device *dev)
0231 {
0232     return !!xenbus_read_unsigned(dev->nodename, "online", 0);
0233 }
0234 EXPORT_SYMBOL_GPL(xenbus_dev_is_online);
0235
0236 int __xenbus_register_backend(struct xenbus_driver *drv, struct module *owner,
0237                   const char *mod_name)
0238 {
0239     drv->read_otherend_details = read_frontend_details;
0240
0241     return xenbus_register_driver_common(drv, &xenbus_backend,
0242                          owner, mod_name);
0243 }
0244 EXPORT_SYMBOL_GPL(__xenbus_register_backend);
0245
0246 static int backend_probe_and_watch(struct notifier_block *notifier,
0247                    unsigned long event,
0248                    void *data)
0249 {
0250     /* Enumerate devices in xenstore and watch for changes. */
0251     xenbus_probe_devices(&xenbus_backend);
0252     register_xenbus_watch(&be_watch);
0253
0254     return NOTIFY_DONE;
0255 }
0256
0257 static int backend_reclaim_memory(struct device *dev, void *data)
0258 {
0259     const struct xenbus_driver *drv;
0260     struct xenbus_device *xdev;
0261
0262     if (!dev->driver)
0263         return 0;
0264     drv = to_xenbus_driver(dev->driver);
0265     if (drv && drv->reclaim_memory) {
0266         xdev = to_xenbus_device(dev);
0267         if (down_trylock(&xdev->reclaim_sem))
0268             return 0;
0269         drv->reclaim_memory(xdev);
0270         up(&xdev->reclaim_sem);
0271     }
0272     return 0;
0273 }
0274
0275 /*
0276  * Returns 0 always because we are using shrinker to only detect memory
0277  * pressure.
0278  */
0279 static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
0280                 struct shrink_control *sc)
0281 {
0282     bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
0283             backend_reclaim_memory);
0284     return 0;
0285 }
0286
0287 static struct shrinker backend_memory_shrinker = {
0288     .count_objects = backend_shrink_memory_count,
0289     .seeks = DEFAULT_SEEKS,
0290 };
0291
0292 static int __init xenbus_probe_backend_init(void)
0293 {
0294     static struct notifier_block xenstore_notifier = {
0295         .notifier_call = backend_probe_and_watch
0296     };
0297     int err;
0298
0299     DPRINTK("");
0300
0301     /* Register ourselves with the kernel bus subsystem */
0302     err = bus_register(&xenbus_backend.bus);
0303     if (err)
0304         return err;
0305
0306     register_xenstore_notifier(&xenstore_notifier);
0307
0308     if (register_shrinker(&backend_memory_shrinker, "xen-backend"))
0309         pr_warn("shrinker registration failed\n");
0310
0311     return 0;
0312 }
0313 subsys_initcall(xenbus_probe_backend_init);