Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  1 /*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
  2  * controls and communicates with the Guest.  For example, the first write will
  3  * tell us the Guest's memory layout, pagetable, entry point and kernel address
  4  * offset.  A read will run the Guest until something happens, such as a signal
  5  * or the Guest doing a NOTIFY out to the Launcher. :*/
  6 #include <linux/uaccess.h>
  7 #include <linux/miscdevice.h>
  8 #include <linux/fs.h>
  9 #include <linux/sched.h>
 10 #include "lg.h"
 11 
 12 /*L:055 When something happens, the Waker process needs a way to stop the
 13  * kernel running the Guest and return to the Launcher.  So the Waker writes
 14  * LHREQ_BREAK and the value "1" to /dev/lguest to do this.  Once the Launcher
 15  * has done whatever needs attention, it writes LHREQ_BREAK and "" to release
 16  * the Waker. */
 17 static int break_guest_out(struct lg_cpu *cpu, const unsigned long __user*input)
 18 {
 19         unsigned long on;
 20 
 21         /* Fetch whether they're turning break on or off. */
 22         if (get_user(on, input) != 0)
 23                 return -EFAULT;
 24 
 25         if (on) {
 26                 cpu->break_out = 1;
 27                 /* Pop it out of the Guest (may be running on different CPU) */
 28                 wake_up_process(cpu->tsk);
 29                 /* Wait for them to reset it */
 30                 return wait_event_interruptible(cpu->break_wq, !cpu->break_out);
 31         } else {
 32                 cpu->break_out = 0;
 33                 wake_up(&cpu->break_wq);
 34                 return 0;
 35         }
 36 }
 37 
 38 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
 39  * number to /dev/lguest. */
 40 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
 41 {
 42         unsigned long irq;
 43 
 44         if (get_user(irq, input) != 0)
 45                 return -EFAULT;
 46         if (irq >= LGUEST_IRQS)
 47                 return -EINVAL;
 48         /* Next time the Guest runs, the core code will see if it can deliver
 49          * this interrupt. */
 50         set_bit(irq, cpu->irqs_pending);
 51         return 0;
 52 }
 53 
 54 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
 55  * from /dev/lguest. */
 56 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
 57 {
 58         struct lguest *lg = file->private_data;
 59         struct lg_cpu *cpu;
 60         unsigned int cpu_id = *o;
 61 
 62         /* You must write LHREQ_INITIALIZE first! */
 63         if (!lg)
 64                 return -EINVAL;
 65 
 66         /* Watch out for arbitrary vcpu indexes! */
 67         if (cpu_id >= lg->nr_cpus)
 68                 return -EINVAL;
 69 
 70         cpu = &lg->cpus[cpu_id];
 71 
 72         /* If you're not the task which owns the Guest, go away. */
 73         if (current != cpu->tsk)
 74                 return -EPERM;
 75 
 76         /* If the Guest is already dead, we indicate why */
 77         if (lg->dead) {
 78                 size_t len;
 79 
 80                 /* lg->dead either contains an error code, or a string. */
 81                 if (IS_ERR(lg->dead))
 82                         return PTR_ERR(lg->dead);
 83 
 84                 /* We can only return as much as the buffer they read with. */
 85                 len = min(size, strlen(lg->dead)+1);
 86                 if (copy_to_user(user, lg->dead, len) != 0)
 87                         return -EFAULT;
 88                 return len;
 89         }
 90 
 91         /* If we returned from read() last time because the Guest sent I/O,
 92          * clear the flag. */
 93         if (cpu->pending_notify)
 94                 cpu->pending_notify = 0;
 95 
 96         /* Run the Guest until something interesting happens. */
 97         return run_guest(cpu, (unsigned long __user *)user);
 98 }
 99 
100 /*L:025 This actually initializes a CPU.  For the moment, a Guest is only
101  * uniprocessor, so "id" is always 0. */
102 static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
103 {
104         /* We have a limited number the number of CPUs in the lguest struct. */
105         if (id >= NR_CPUS)
106                 return -EINVAL;
107 
108         /* Set up this CPU's id, and pointer back to the lguest struct. */
109         cpu->id = id;
110         cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
111         cpu->lg->nr_cpus++;
112 
113         /* Each CPU has a timer it can set. */
114         init_clockdev(cpu);
115 
116         /* We need a complete page for the Guest registers: they are accessible
117          * to the Guest and we can only grant it access to whole pages. */
118         cpu->regs_page = get_zeroed_page(GFP_KERNEL);
119         if (!cpu->regs_page)
120                 return -ENOMEM;
121 
122         /* We actually put the registers at the bottom of the page. */
123         cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
124 
125         /* Now we initialize the Guest's registers, handing it the start
126          * address. */
127         lguest_arch_setup_regs(cpu, start_ip);
128 
129         /* Initialize the queue for the Waker to wait on */
130         init_waitqueue_head(&cpu->break_wq);
131 
132         /* We keep a pointer to the Launcher task (ie. current task) for when
133          * other Guests want to wake this one (eg. console input). */
134         cpu->tsk = current;
135 
136         /* We need to keep a pointer to the Launcher's memory map, because if
137          * the Launcher dies we need to clean it up.  If we don't keep a
138          * reference, it is destroyed before close() is called. */
139         cpu->mm = get_task_mm(cpu->tsk);
140 
141         /* We remember which CPU's pages this Guest used last, for optimization
142          * when the same Guest runs on the same CPU twice. */
143         cpu->last_pages = NULL;
144 
145         /* No error == success. */
146         return 0;
147 }
148 
149 /*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit)
150  * values (in addition to the LHREQ_INITIALIZE value).  These are:
151  *
152  * base: The start of the Guest-physical memory inside the Launcher memory.
153  *
154  * pfnlimit: The highest (Guest-physical) page number the Guest should be
155  * allowed to access.  The Guest memory lives inside the Launcher, so it sets
156  * this to ensure the Guest can only reach its own memory.
157  *
158  * pgdir: The (Guest-physical) address of the top of the initial Guest
159  * pagetables (which are set up by the Launcher).
160  *
161  * start: The first instruction to execute ("eip" in x86-speak).
162  */
163 static int initialize(struct file *file, const unsigned long __user *input)
164 {
165         /* "struct lguest" contains everything we (the Host) know about a
166          * Guest. */
167         struct lguest *lg;
168         int err;
169         unsigned long args[4];
170 
171         /* We grab the Big Lguest lock, which protects against multiple
172          * simultaneous initializations. */
173         mutex_lock(&lguest_lock);
174         /* You can't initialize twice!  Close the device and start again... */
175         if (file->private_data) {
176                 err = -EBUSY;
177                 goto unlock;
178         }
179 
180         if (copy_from_user(args, input, sizeof(args)) != 0) {
181                 err = -EFAULT;
182                 goto unlock;
183         }
184 
185         lg = kzalloc(sizeof(*lg), GFP_KERNEL);
186         if (!lg) {
187                 err = -ENOMEM;
188                 goto unlock;
189         }
190 
191         /* Populate the easy fields of our "struct lguest" */
192         lg->mem_base = (void __user *)args[0];
193         lg->pfn_limit = args[1];
194 
195         /* This is the first cpu (cpu 0) and it will start booting at args[3] */
196         err = lg_cpu_start(&lg->cpus[0], 0, args[3]);
197         if (err)
198                 goto release_guest;
199 
200         /* Initialize the Guest's shadow page tables, using the toplevel
201          * address the Launcher gave us.  This allocates memory, so can fail. */
202         err = init_guest_pagetable(lg, args[2]);
203         if (err)
204                 goto free_regs;
205 
206         /* We keep our "struct lguest" in the file's private_data. */
207         file->private_data = lg;
208 
209         mutex_unlock(&lguest_lock);
210 
211         /* And because this is a write() call, we return the length used. */
212         return sizeof(args);
213 
214 free_regs:
215         /* FIXME: This should be in free_vcpu */
216         free_page(lg->cpus[0].regs_page);
217 release_guest:
218         kfree(lg);
219 unlock:
220         mutex_unlock(&lguest_lock);
221         return err;
222 }
223 
224 /*L:010 The first operation the Launcher does must be a write.  All writes
225  * start with an unsigned long number: for the first write this must be
226  * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
227  * writes of other values to send interrupts.
228  *
229  * Note that we overload the "offset" in the /dev/lguest file to indicate what
230  * CPU number we're dealing with.  Currently this is always 0, since we only
231  * support uniprocessor Guests, but you can see the beginnings of SMP support
232  * here. */
233 static ssize_t write(struct file *file, const char __user *in,
234                      size_t size, loff_t *off)
235 {
236         /* Once the Guest is initialized, we hold the "struct lguest" in the
237          * file private data. */
238         struct lguest *lg = file->private_data;
239         const unsigned long __user *input = (const unsigned long __user *)in;
240         unsigned long req;
241         struct lg_cpu *uninitialized_var(cpu);
242         unsigned int cpu_id = *off;
243 
244         /* The first value tells us what this request is. */
245         if (get_user(req, input) != 0)
246                 return -EFAULT;
247         input++;
248 
249         /* If you haven't initialized, you must do that first. */
250         if (req != LHREQ_INITIALIZE) {
251                 if (!lg || (cpu_id >= lg->nr_cpus))
252                         return -EINVAL;
253                 cpu = &lg->cpus[cpu_id];
254                 if (!cpu)
255                         return -EINVAL;
256 
257                 /* Once the Guest is dead, you can only read() why it died. */
258                 if (lg->dead)
259                         return -ENOENT;
260 
261                 /* If you're not the task which owns the Guest, all you can do
262                  * is break the Launcher out of running the Guest. */
263                 if (current != cpu->tsk && req != LHREQ_BREAK)
264                         return -EPERM;
265         }
266 
267         switch (req) {
268         case LHREQ_INITIALIZE:
269                 return initialize(file, input);
270         case LHREQ_IRQ:
271                 return user_send_irq(cpu, input);
272         case LHREQ_BREAK:
273                 return break_guest_out(cpu, input);
274         default:
275                 return -EINVAL;
276         }
277 }
278 
279 /*L:060 The final piece of interface code is the close() routine.  It reverses
280  * everything done in initialize().  This is usually called because the
281  * Launcher exited.
282  *
283  * Note that the close routine returns 0 or a negative error number: it can't
284  * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
285  * letting them do it. :*/
286 static int close(struct inode *inode, struct file *file)
287 {
288         struct lguest *lg = file->private_data;
289         unsigned int i;
290 
291         /* If we never successfully initialized, there's nothing to clean up */
292         if (!lg)
293                 return 0;
294 
295         /* We need the big lock, to protect from inter-guest I/O and other
296          * Launchers initializing guests. */
297         mutex_lock(&lguest_lock);
298 
299         /* Free up the shadow page tables for the Guest. */
300         free_guest_pagetable(lg);
301 
302         for (i = 0; i < lg->nr_cpus; i++) {
303                 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
304                 hrtimer_cancel(&lg->cpus[i].hrt);
305                 /* We can free up the register page we allocated. */
306                 free_page(lg->cpus[i].regs_page);
307                 /* Now all the memory cleanups are done, it's safe to release
308                  * the Launcher's memory management structure. */
309                 mmput(lg->cpus[i].mm);
310         }
311         /* If lg->dead doesn't contain an error code it will be NULL or a
312          * kmalloc()ed string, either of which is ok to hand to kfree(). */
313         if (!IS_ERR(lg->dead))
314                 kfree(lg->dead);
315         /* We clear the entire structure, which also marks it as free for the
316          * next user. */
317         memset(lg, 0, sizeof(*lg));
318         /* Release lock and exit. */
319         mutex_unlock(&lguest_lock);
320 
321         return 0;
322 }
323 
324 /*L:000
325  * Welcome to our journey through the Launcher!
326  *
327  * The Launcher is the Host userspace program which sets up, runs and services
328  * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
329  * doing things are inaccurate: the Launcher does all the device handling for
330  * the Guest, but the Guest can't know that.
331  *
332  * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
333  * shall see more of that later.
334  *
335  * We begin our understanding with the Host kernel interface which the Launcher
336  * uses: reading and writing a character device called /dev/lguest.  All the
337  * work happens in the read(), write() and close() routines: */
338 static struct file_operations lguest_fops = {
339         .owner   = THIS_MODULE,
340         .release = close,
341         .write   = write,
342         .read    = read,
343 };
344 
345 /* This is a textbook example of a "misc" character device.  Populate a "struct
346  * miscdevice" and register it with misc_register(). */
347 static struct miscdevice lguest_dev = {
348         .minor  = MISC_DYNAMIC_MINOR,
349         .name   = "lguest",
350         .fops   = &lguest_fops,
351 };
352 
353 int __init lguest_device_init(void)
354 {
355         return misc_register(&lguest_dev);
356 }
357 
358 void __exit lguest_device_remove(void)
359 {
360         misc_deregister(&lguest_dev);
361 }
362 
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