1 /*P:050 Lguest guests use a very simple method to describe devices. It's a
2 * series of device descriptors contained just above the top of normal
5 * We use the standard "virtio" device infrastructure, which provides us with a
6 * console, a network and a block driver. Each one expects some configuration
7 * information and a "virtqueue" mechanism to send and receive data. :*/
8 #include <linux/init.h>
9 #include <linux/bootmem.h>
10 #include <linux/lguest_launcher.h>
11 #include <linux/virtio.h>
12 #include <linux/virtio_config.h>
13 #include <linux/interrupt.h>
14 #include <linux/virtio_ring.h>
15 #include <linux/err.h>
17 #include <asm/paravirt.h>
18 #include <asm/lguest_hcall.h>
20 /* The pointer to our (page) of device descriptions. */
21 static void *lguest_devices;
23 /* Unique numbering for lguest devices. */
24 static unsigned int dev_index;
26 /* For Guests, device memory can be used as normal memory, so we cast away the
27 * __iomem to quieten sparse. */
28 static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
30 return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
33 static inline void lguest_unmap(void *addr)
35 iounmap((__force void __iomem *)addr);
38 /*D:100 Each lguest device is just a virtio device plus a pointer to its entry
39 * in the lguest_devices page. */
40 struct lguest_device {
41 struct virtio_device vdev;
43 /* The entry in the lguest_devices page for this device. */
44 struct lguest_device_desc *desc;
47 /* Since the virtio infrastructure hands us a pointer to the virtio_device all
48 * the time, it helps to have a curt macro to get a pointer to the struct
49 * lguest_device it's enclosed in. */
50 #define to_lgdev(vdev) container_of(vdev, struct lguest_device, vdev)
53 * Device configurations
55 * The configuration information for a device consists of a series of fields.
56 * The device will look for these fields during setup.
58 * For us these fields come immediately after that device's descriptor in the
59 * lguest_devices page.
61 * Each field starts with a "type" byte, a "length" byte, then that number of
62 * bytes of configuration information. The device descriptor tells us the
63 * total configuration length so we know when we've reached the last field. */
65 /* type + length bytes */
68 /* This finds the first field of a given type for a device's configuration. */
69 static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len)
71 struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
74 for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) {
75 if (desc->config[i] == type) {
76 /* Mark it used, so Host can know we looked at it, and
77 * also so we won't find the same one twice. */
78 desc->config[i] |= 0x80;
79 /* Remember, the second byte is the length. */
80 *len = desc->config[i+1];
81 /* We return a pointer to the field header. */
82 return desc->config + i;
86 /* Not found: return NULL for failure. */
90 /* Once they've found a field, getting a copy of it is easy. */
91 static void lg_get(struct virtio_device *vdev, void *token,
92 void *buf, unsigned len)
94 /* Check they didn't ask for more than the length of the field! */
95 BUG_ON(len > ((u8 *)token)[1]);
96 memcpy(buf, token + FHDR_LEN, len);
99 /* Setting the contents is also trivial. */
100 static void lg_set(struct virtio_device *vdev, void *token,
101 const void *buf, unsigned len)
103 BUG_ON(len > ((u8 *)token)[1]);
104 memcpy(token + FHDR_LEN, buf, len);
107 /* The operations to get and set the status word just access the status field
108 * of the device descriptor. */
109 static u8 lg_get_status(struct virtio_device *vdev)
111 return to_lgdev(vdev)->desc->status;
114 static void lg_set_status(struct virtio_device *vdev, u8 status)
116 to_lgdev(vdev)->desc->status = status;
122 * The other piece of infrastructure virtio needs is a "virtqueue": a way of
123 * the Guest device registering buffers for the other side to read from or
124 * write into (ie. send and receive buffers). Each device can have multiple
125 * virtqueues: for example the console has one queue for sending and one for
128 * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
129 * already exists in virtio_ring.c. We just need to connect it up.
131 * We start with the information we need to keep about each virtqueue.
134 /*D:140 This is the information we remember about each virtqueue. */
135 struct lguest_vq_info
137 /* A copy of the information contained in the device config. */
138 struct lguest_vqconfig config;
140 /* The address where we mapped the virtio ring, so we can unmap it. */
144 /* When the virtio_ring code wants to prod the Host, it calls us here and we
145 * make a hypercall. We hand the page number of the virtqueue so the Host
146 * knows which virtqueue we're talking about. */
147 static void lg_notify(struct virtqueue *vq)
149 /* We store our virtqueue information in the "priv" pointer of the
150 * virtqueue structure. */
151 struct lguest_vq_info *lvq = vq->priv;
153 hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
156 /* This routine finds the first virtqueue described in the configuration of
157 * this device and sets it up.
159 * This is kind of an ugly duckling. It'd be nicer to have a standard
160 * representation of a virtqueue in the configuration space, but it seems that
161 * everyone wants to do it differently. The KVM guys want the Guest to
162 * allocate its own pages and tell the Host where they are, but for lguest it's
163 * simpler for the Host to simply tell us where the pages are.
165 * So we provide devices with a "find virtqueue and set it up" function. */
166 static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
167 bool (*callback)(struct virtqueue *vq))
169 struct lguest_vq_info *lvq;
170 struct virtqueue *vq;
175 /* Look for a field of the correct type to mark a virtqueue. Note that
176 * if this succeeds, then the type will be changed so it won't be found
177 * again, and future lg_find_vq() calls will find the next
178 * virtqueue (if any). */
179 token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len);
181 return ERR_PTR(-ENOENT);
183 lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
185 return ERR_PTR(-ENOMEM);
187 /* Note: we could use a configuration space inside here, just like we
188 * do for the device. This would allow expansion in future, because
189 * our configuration system is designed to be expansible. But this is
191 if (len != sizeof(lvq->config)) {
192 dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len);
196 /* Make a copy of the "struct lguest_vqconfig" field. We need a copy
197 * because the config space might not be aligned correctly. */
198 vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config));
200 /* Figure out how many pages the ring will take, and map that memory */
201 lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
202 DIV_ROUND_UP(vring_size(lvq->config.num),
209 /* OK, tell virtio_ring.c to set up a virtqueue now we know its size
210 * and we've got a pointer to its pages. */
211 vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages,
212 lg_notify, callback);
218 /* Tell the interrupt for this virtqueue to go to the virtio_ring
219 * interrupt handler. */
220 /* FIXME: We used to have a flag for the Host to tell us we could use
221 * the interrupt as a source of randomness: it'd be nice to have that
223 err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
224 vdev->dev.bus_id, vq);
228 /* Last of all we hook up our 'struct lguest_vq_info" to the
229 * virtqueue's priv pointer. */
234 vring_del_virtqueue(vq);
236 lguest_unmap(lvq->pages);
243 /* Cleaning up a virtqueue is easy */
244 static void lg_del_vq(struct virtqueue *vq)
246 struct lguest_vq_info *lvq = vq->priv;
248 /* Tell virtio_ring.c to free the virtqueue. */
249 vring_del_virtqueue(vq);
250 /* Unmap the pages containing the ring. */
251 lguest_unmap(lvq->pages);
252 /* Free our own queue information. */
256 /* The ops structure which hooks everything together. */
257 static struct virtio_config_ops lguest_config_ops = {
261 .get_status = lg_get_status,
262 .set_status = lg_set_status,
263 .find_vq = lg_find_vq,
267 /* The root device for the lguest virtio devices. This makes them appear as
268 * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
269 static struct device lguest_root = {
274 /*D:120 This is the core of the lguest bus: actually adding a new device.
275 * It's a separate function because it's neater that way, and because an
276 * earlier version of the code supported hotplug and unplug. They were removed
277 * early on because they were never used.
279 * As Andrew Tridgell says, "Untested code is buggy code".
281 * It's worth reading this carefully: we start with a pointer to the new device
282 * descriptor in the "lguest_devices" page. */
283 static void add_lguest_device(struct lguest_device_desc *d)
285 struct lguest_device *ldev;
287 ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
289 printk(KERN_EMERG "Cannot allocate lguest dev %u\n",
294 /* This devices' parent is the lguest/ dir. */
295 ldev->vdev.dev.parent = &lguest_root;
296 /* We have a unique device index thanks to the dev_index counter. */
297 ldev->vdev.index = dev_index++;
298 /* The device type comes straight from the descriptor. There's also a
299 * device vendor field in the virtio_device struct, which we leave as
301 ldev->vdev.id.device = d->type;
302 /* We have a simple set of routines for querying the device's
303 * configuration information and setting its status. */
304 ldev->vdev.config = &lguest_config_ops;
305 /* And we remember the device's descriptor for lguest_config_ops. */
308 /* register_virtio_device() sets up the generic fields for the struct
309 * virtio_device and calls device_register(). This makes the bus
310 * infrastructure look for a matching driver. */
311 if (register_virtio_device(&ldev->vdev) != 0) {
312 printk(KERN_ERR "Failed to register lguest device %u\n",
318 /*D:110 scan_devices() simply iterates through the device page. The type 0 is
319 * reserved to mean "end of devices". */
320 static void scan_devices(void)
323 struct lguest_device_desc *d;
325 /* We start at the page beginning, and skip over each entry. */
326 for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) {
327 d = lguest_devices + i;
329 /* Once we hit a zero, stop. */
333 add_lguest_device(d);
337 /*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
338 * lguest device infrastructure. We check that we are a Guest by checking
339 * pv_info.name: there are other ways of checking, but this seems most
342 * So we can access the "struct lguest_device_desc"s easily, we map that memory
343 * and store the pointer in the global "lguest_devices". Then we register a
344 * root device from which all our devices will hang (this seems to be the
345 * correct sysfs incantation).
347 * Finally we call scan_devices() which adds all the devices found in the
348 * lguest_devices page. */
349 static int __init lguest_devices_init(void)
351 if (strcmp(pv_info.name, "lguest") != 0)
354 if (device_register(&lguest_root) != 0)
355 panic("Could not register lguest root");
357 /* Devices are in a single page above top of "normal" mem */
358 lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
363 /* We do this after core stuff, but before the drivers. */
364 postcore_initcall(lguest_devices_init);
366 /*D:150 At this point in the journey we used to now wade through the lguest
367 * devices themselves: net, block and console. Since they're all now virtio
368 * devices rather than lguest-specific, I've decided to ignore them. Mostly,
369 * they're kind of boring. But this does mean you'll never experience the
370 * thrill of reading the forbidden love scene buried deep in the block driver.
372 * "make Launcher" beckons, where we answer questions like "Where do Guests
373 * come from?", and "What do you do when someone asks for optimization?". */