drivers/lguest/lguest_bus.c

   1 /*P:050 Lguest guests use a very simple bus for devices.  It's a simple array
   2  * of device descriptors contained just above the top of normal memory.  The
   3  * lguest bus is 80% tedious boilerplate code. :*/
   4 #include <linux/init.h>
   5 #include <linux/bootmem.h>
   6 #include <linux/lguest_bus.h>
   7 #include <asm/io.h>
   8 #include <asm/paravirt.h>
   9
  10 static ssize_t type_show(struct device *_dev,
  11                          struct device_attribute *attr, char *buf)
  12 {
  13         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  14         return sprintf(buf, "%hu", lguest_devices[dev->index].type);
  15 }
  16 static ssize_t features_show(struct device *_dev,
  17                              struct device_attribute *attr, char *buf)
  18 {
  19         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  20         return sprintf(buf, "%hx", lguest_devices[dev->index].features);
  21 }
  22 static ssize_t pfn_show(struct device *_dev,
  23                          struct device_attribute *attr, char *buf)
  24 {
  25         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  26         return sprintf(buf, "%u", lguest_devices[dev->index].pfn);
  27 }
  28 static ssize_t status_show(struct device *_dev,
  29                            struct device_attribute *attr, char *buf)
  30 {
  31         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  32         return sprintf(buf, "%hx", lguest_devices[dev->index].status);
  33 }
  34 static ssize_t status_store(struct device *_dev, struct device_attribute *attr,
  35                             const char *buf, size_t count)
  36 {
  37         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  38         if (sscanf(buf, "%hi", &lguest_devices[dev->index].status) != 1)
  39                 return -EINVAL;
  40         return count;
  41 }
  42 static struct device_attribute lguest_dev_attrs[] = {
  43         __ATTR_RO(type),
  44         __ATTR_RO(features),
  45         __ATTR_RO(pfn),
  46         __ATTR(status, 0644, status_show, status_store),
  47         __ATTR_NULL
  48 };
  49
  50 /*D:130 The generic bus infrastructure requires a function which says whether a
  51  * device matches a driver.  For us, it is simple: "struct lguest_driver"
  52  * contains a "device_type" field which indicates what type of device it can
  53  * handle, so we just cast the args and compare: */
  54 static int lguest_dev_match(struct device *_dev, struct device_driver *_drv)
  55 {
  56         struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
  57         struct lguest_driver *drv = container_of(_drv,struct lguest_driver,drv);
  58
  59         return (drv->device_type == lguest_devices[dev->index].type);
  60 }
  61 /*:*/
  62
  63 struct lguest_bus {
  64         struct bus_type bus;
  65         struct device dev;
  66 };
  67
  68 static struct lguest_bus lguest_bus = {
  69         .bus = {
  70                 .name  = "lguest",
  71                 .match = lguest_dev_match,
  72                 .dev_attrs = lguest_dev_attrs,
  73         },
  74         .dev = {
  75                 .parent = NULL,
  76                 .bus_id = "lguest",
  77         }
  78 };
  79
  80 /*D:140 This is the callback which occurs once the bus infrastructure matches
  81  * up a device and driver, ie. in response to add_lguest_device() calling
  82  * device_register(), or register_lguest_driver() calling driver_register().
  83  *
  84  * At the moment it's always the latter: the devices are added first, since
  85  * scan_devices() is called from a "core_initcall", and the drivers themselves
  86  * called later as a normal "initcall".  But it would work the other way too.
  87  *
  88  * So now we have the happy couple, we add the status bit to indicate that we
  89  * found a driver.  If the driver truly loves the device, it will return
  90  * happiness from its probe function (ok, perhaps this wasn't my greatest
  91  * analogy), and we set the final "driver ok" bit so the Host sees it's all
  92  * green. */
  93 static int lguest_dev_probe(struct device *_dev)
  94 {
  95         int ret;
  96         struct lguest_device*dev = container_of(_dev,struct lguest_device,dev);
  97         struct lguest_driver*drv = container_of(dev->dev.driver,
  98                                                 struct lguest_driver, drv);
  99
 100         lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER;
 101         ret = drv->probe(dev);
 102         if (ret == 0)
 103                 lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER_OK;
 104         return ret;
 105 }
 106
 107 /* The last part of the bus infrastructure is the function lguest drivers use
 108  * to register themselves.  Firstly, we do nothing if there's no lguest bus
 109  * (ie. this is not a Guest), otherwise we fill in the embedded generic "struct
 110  * driver" fields and call the generic driver_register(). */
 111 int register_lguest_driver(struct lguest_driver *drv)
 112 {
 113         if (!lguest_devices)
 114                 return 0;
 115
 116         drv->drv.bus = &lguest_bus.bus;
 117         drv->drv.name = drv->name;
 118         drv->drv.owner = drv->owner;
 119         drv->drv.probe = lguest_dev_probe;
 120
 121         return driver_register(&drv->drv);
 122 }
 123
 124 /* At the moment we build all the drivers into the kernel because they're so
 125  * simple: 8144 bytes for all three of them as I type this.  And as the console
 126  * really needs to be built in, it's actually only 3527 bytes for the network
 127  * and block drivers.
 128  *
 129  * If they get complex it will make sense for them to be modularized, so we
 130  * need to explicitly export the symbol.
 131  *
 132  * I don't think non-GPL modules make sense, so it's a GPL-only export.
 133  */
 134 EXPORT_SYMBOL_GPL(register_lguest_driver);
 135
 136 /*D:120 This is the core of the lguest bus: actually adding a new device.
 137  * It's a separate function because it's neater that way, and because an
 138  * earlier version of the code supported hotplug and unplug.  They were removed
 139  * early on because they were never used.
 140  *
 141  * As Andrew Tridgell says, "Untested code is buggy code".
 142  *
 143  * It's worth reading this carefully: we start with an index into the array of
 144  * "struct lguest_device_desc"s indicating the device which is new: */
 145 static void add_lguest_device(unsigned int index)
 146 {
 147         struct lguest_device *new;
 148
 149         /* Each "struct lguest_device_desc" has a "status" field, which the
 150          * Guest updates as the device is probed.  In the worst case, the Host
 151          * can look at these bits to tell what part of device setup failed,
 152          * even if the console isn't available. */
 153         lguest_devices[index].status |= LGUEST_DEVICE_S_ACKNOWLEDGE;
 154         new = kmalloc(sizeof(struct lguest_device), GFP_KERNEL);
 155         if (!new) {
 156                 printk(KERN_EMERG "Cannot allocate lguest device %u\n", index);
 157                 lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED;
 158                 return;
 159         }
 160
 161         /* The "struct lguest_device" setup is pretty straight-forward example
 162          * code. */
 163         new->index = index;
 164         new->private = NULL;
 165         memset(&new->dev, 0, sizeof(new->dev));
 166         new->dev.parent = &lguest_bus.dev;
 167         new->dev.bus = &lguest_bus.bus;
 168         sprintf(new->dev.bus_id, "%u", index);
 169
 170         /* device_register() causes the bus infrastructure to look for a
 171          * matching driver. */
 172         if (device_register(&new->dev) != 0) {
 173                 printk(KERN_EMERG "Cannot register lguest device %u\n", index);
 174                 lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED;
 175                 kfree(new);
 176         }
 177 }
 178
 179 /*D:110 scan_devices() simply iterates through the device array.  The type 0
 180  * is reserved to mean "no device", and anything else means we have found a
 181  * device: add it. */
 182 static void scan_devices(void)
 183 {
 184         unsigned int i;
 185
 186         for (i = 0; i < LGUEST_MAX_DEVICES; i++)
 187                 if (lguest_devices[i].type)
 188                         add_lguest_device(i);
 189 }
 190
 191 /*D:100 Fairly early in boot, lguest_bus_init() is called to set up the lguest
 192  * bus.  We check that we are a Guest by checking paravirt_ops.name: there are
 193  * other ways of checking, but this seems most obvious to me.
 194  *
 195  * So we can access the array of "struct lguest_device_desc"s easily, we map
 196  * that memory and store the pointer in the global "lguest_devices".  Then we
 197  * register the bus with the core.  Doing two registrations seems clunky to me,
 198  * but it seems to be the correct sysfs incantation.
 199  *
 200  * Finally we call scan_devices() which adds all the devices found in the
 201  * "struct lguest_device_desc" array. */
 202 static int __init lguest_bus_init(void)
 203 {
 204         if (strcmp(paravirt_ops.name, "lguest") != 0)
 205                 return 0;
 206
 207         /* Devices are in a single page above top of "normal" mem */
 208         lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
 209
 210         if (bus_register(&lguest_bus.bus) != 0
 211             || device_register(&lguest_bus.dev) != 0)
 212                 panic("lguest bus registration failed");
 213
 214         scan_devices();
 215         return 0;
 216 }
 217 /* Do this after core stuff, before devices. */
 218 postcore_initcall(lguest_bus_init);