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