diff options
Diffstat (limited to 'drivers/lguest/lguest_bus.c')
| -rw-r--r-- | drivers/lguest/lguest_bus.c | 75 |
1 files changed, 72 insertions, 3 deletions
diff --git a/drivers/lguest/lguest_bus.c b/drivers/lguest/lguest_bus.c index 18d6ab21a43..55a7940ca73 100644 --- a/drivers/lguest/lguest_bus.c +++ b/drivers/lguest/lguest_bus.c @@ -1,3 +1,6 @@ +/*P:050 Lguest guests use a very simple bus for devices. It's a simple array + * of device descriptors contained just above the top of normal memory. The + * lguest bus is 80% tedious boilerplate code. :*/ #include <linux/init.h> #include <linux/bootmem.h> #include <linux/lguest_bus.h> @@ -43,6 +46,10 @@ static struct device_attribute lguest_dev_attrs[] = { __ATTR_NULL }; +/*D:130 The generic bus infrastructure requires a function which says whether a + * device matches a driver. For us, it is simple: "struct lguest_driver" + * contains a "device_type" field which indicates what type of device it can + * handle, so we just cast the args and compare: */ static int lguest_dev_match(struct device *_dev, struct device_driver *_drv) { struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); @@ -50,6 +57,7 @@ static int lguest_dev_match(struct device *_dev, struct device_driver *_drv) return (drv->device_type == lguest_devices[dev->index].type); } +/*:*/ struct lguest_bus { struct bus_type bus; @@ -68,11 +76,24 @@ static struct lguest_bus lguest_bus = { } }; +/*D:140 This is the callback which occurs once the bus infrastructure matches + * up a device and driver, ie. in response to add_lguest_device() calling + * device_register(), or register_lguest_driver() calling driver_register(). + * + * At the moment it's always the latter: the devices are added first, since + * scan_devices() is called from a "core_initcall", and the drivers themselves + * called later as a normal "initcall". But it would work the other way too. + * + * So now we have the happy couple, we add the status bit to indicate that we + * found a driver. If the driver truly loves the device, it will return + * happiness from its probe function (ok, perhaps this wasn't my greatest + * analogy), and we set the final "driver ok" bit so the Host sees it's all + * green. */ static int lguest_dev_probe(struct device *_dev) { int ret; - struct lguest_device *dev = container_of(_dev,struct lguest_device,dev); - struct lguest_driver *drv = container_of(dev->dev.driver, + struct lguest_device*dev = container_of(_dev,struct lguest_device,dev); + struct lguest_driver*drv = container_of(dev->dev.driver, struct lguest_driver, drv); lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER; @@ -82,6 +103,10 @@ static int lguest_dev_probe(struct device *_dev) return ret; } +/* The last part of the bus infrastructure is the function lguest drivers use + * to register themselves. Firstly, we do nothing if there's no lguest bus + * (ie. this is not a Guest), otherwise we fill in the embedded generic "struct + * driver" fields and call the generic driver_register(). */ int register_lguest_driver(struct lguest_driver *drv) { if (!lguest_devices) @@ -94,12 +119,36 @@ int register_lguest_driver(struct lguest_driver *drv) return driver_register(&drv->drv); } + +/* At the moment we build all the drivers into the kernel because they're so + * simple: 8144 bytes for all three of them as I type this. And as the console + * really needs to be built in, it's actually only 3527 bytes for the network + * and block drivers. + * + * If they get complex it will make sense for them to be modularized, so we + * need to explicitly export the symbol. + * + * I don't think non-GPL modules make sense, so it's a GPL-only export. + */ EXPORT_SYMBOL_GPL(register_lguest_driver); +/*D:120 This is the core of the lguest bus: actually adding a new device. + * It's a separate function because it's neater that way, and because an + * earlier version of the code supported hotplug and unplug. They were removed + * early on because they were never used. + * + * As Andrew Tridgell says, "Untested code is buggy code". + * + * It's worth reading this carefully: we start with an index into the array of + * "struct lguest_device_desc"s indicating the device which is new: */ static void add_lguest_device(unsigned int index) { struct lguest_device *new; + /* Each "struct lguest_device_desc" has a "status" field, which the + * Guest updates as the device is probed. In the worst case, the Host + * can look at these bits to tell what part of device setup failed, + * even if the console isn't available. */ lguest_devices[index].status |= LGUEST_DEVICE_S_ACKNOWLEDGE; new = kmalloc(sizeof(struct lguest_device), GFP_KERNEL); if (!new) { @@ -108,12 +157,17 @@ static void add_lguest_device(unsigned int index) return; } + /* The "struct lguest_device" setup is pretty straight-forward example + * code. */ new->index = index; new->private = NULL; memset(&new->dev, 0, sizeof(new->dev)); new->dev.parent = &lguest_bus.dev; new->dev.bus = &lguest_bus.bus; sprintf(new->dev.bus_id, "%u", index); + + /* device_register() causes the bus infrastructure to look for a + * matching driver. */ if (device_register(&new->dev) != 0) { printk(KERN_EMERG "Cannot register lguest device %u\n", index); lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED; @@ -121,6 +175,9 @@ static void add_lguest_device(unsigned int index) } } +/*D:110 scan_devices() simply iterates through the device array. The type 0 + * is reserved to mean "no device", and anything else means we have found a + * device: add it. */ static void scan_devices(void) { unsigned int i; @@ -130,12 +187,23 @@ static void scan_devices(void) add_lguest_device(i); } +/*D:100 Fairly early in boot, lguest_bus_init() is called to set up the lguest + * bus. We check that we are a Guest by checking paravirt_ops.name: there are + * other ways of checking, but this seems most obvious to me. + * + * So we can access the array of "struct lguest_device_desc"s easily, we map + * that memory and store the pointer in the global "lguest_devices". Then we + * register the bus with the core. Doing two registrations seems clunky to me, + * but it seems to be the correct sysfs incantation. + * + * Finally we call scan_devices() which adds all the devices found in the + * "struct lguest_device_desc" array. */ static int __init lguest_bus_init(void) { if (strcmp(paravirt_ops.name, "lguest") != 0) return 0; - /* Devices are in page above top of "normal" mem. */ + /* Devices are in a single page above top of "normal" mem */ lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1); if (bus_register(&lguest_bus.bus) != 0 @@ -145,4 +213,5 @@ static int __init lguest_bus_init(void) scan_devices(); return 0; } +/* Do this after core stuff, before devices. */ postcore_initcall(lguest_bus_init); |