BUG_ON() Conversion in kernel/printk.c
[linux-2.6.git] / kernel / printk.c
1 /*
2  *  linux/kernel/printk.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *
6  * Modified to make sys_syslog() more flexible: added commands to
7  * return the last 4k of kernel messages, regardless of whether
8  * they've been read or not.  Added option to suppress kernel printk's
9  * to the console.  Added hook for sending the console messages
10  * elsewhere, in preparation for a serial line console (someday).
11  * Ted Ts'o, 2/11/93.
12  * Modified for sysctl support, 1/8/97, Chris Horn.
13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14  *     manfred@colorfullife.com
15  * Rewrote bits to get rid of console_lock
16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
17  */
18
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/smp_lock.h>
24 #include <linux/console.h>
25 #include <linux/init.h>
26 #include <linux/module.h>
27 #include <linux/interrupt.h>                    /* For in_interrupt() */
28 #include <linux/config.h>
29 #include <linux/delay.h>
30 #include <linux/smp.h>
31 #include <linux/security.h>
32 #include <linux/bootmem.h>
33 #include <linux/syscalls.h>
34
35 #include <asm/uaccess.h>
36
37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
38
39 /* printk's without a loglevel use this.. */
40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
41
42 /* We show everything that is MORE important than this.. */
43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
45
46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
47
48 int console_printk[4] = {
49         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
50         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
51         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
52         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
53 };
54
55 EXPORT_SYMBOL(console_printk);
56
57 /*
58  * Low lever drivers may need that to know if they can schedule in
59  * their unblank() callback or not. So let's export it.
60  */
61 int oops_in_progress;
62 EXPORT_SYMBOL(oops_in_progress);
63
64 /*
65  * console_sem protects the console_drivers list, and also
66  * provides serialisation for access to the entire console
67  * driver system.
68  */
69 static DECLARE_MUTEX(console_sem);
70 struct console *console_drivers;
71 /*
72  * This is used for debugging the mess that is the VT code by
73  * keeping track if we have the console semaphore held. It's
74  * definitely not the perfect debug tool (we don't know if _WE_
75  * hold it are racing, but it helps tracking those weird code
76  * path in the console code where we end up in places I want
77  * locked without the console sempahore held
78  */
79 static int console_locked;
80
81 /*
82  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
83  * It is also used in interesting ways to provide interlocking in
84  * release_console_sem().
85  */
86 static DEFINE_SPINLOCK(logbuf_lock);
87
88 #define LOG_BUF_MASK    (log_buf_len-1)
89 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
90
91 /*
92  * The indices into log_buf are not constrained to log_buf_len - they
93  * must be masked before subscripting
94  */
95 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
96 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
97 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
98
99 /*
100  *      Array of consoles built from command line options (console=)
101  */
102 struct console_cmdline
103 {
104         char    name[8];                        /* Name of the driver       */
105         int     index;                          /* Minor dev. to use        */
106         char    *options;                       /* Options for the driver   */
107 };
108
109 #define MAX_CMDLINECONSOLES 8
110
111 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
112 static int selected_console = -1;
113 static int preferred_console = -1;
114
115 /* Flag: console code may call schedule() */
116 static int console_may_schedule;
117
118 #ifdef CONFIG_PRINTK
119
120 static char __log_buf[__LOG_BUF_LEN];
121 static char *log_buf = __log_buf;
122 static int log_buf_len = __LOG_BUF_LEN;
123 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
124
125 static int __init log_buf_len_setup(char *str)
126 {
127         unsigned long size = memparse(str, &str);
128         unsigned long flags;
129
130         if (size)
131                 size = roundup_pow_of_two(size);
132         if (size > log_buf_len) {
133                 unsigned long start, dest_idx, offset;
134                 char *new_log_buf;
135
136                 new_log_buf = alloc_bootmem(size);
137                 if (!new_log_buf) {
138                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
139                         goto out;
140                 }
141
142                 spin_lock_irqsave(&logbuf_lock, flags);
143                 log_buf_len = size;
144                 log_buf = new_log_buf;
145
146                 offset = start = min(con_start, log_start);
147                 dest_idx = 0;
148                 while (start != log_end) {
149                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
150                         start++;
151                         dest_idx++;
152                 }
153                 log_start -= offset;
154                 con_start -= offset;
155                 log_end -= offset;
156                 spin_unlock_irqrestore(&logbuf_lock, flags);
157
158                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
159         }
160 out:
161         return 1;
162 }
163
164 __setup("log_buf_len=", log_buf_len_setup);
165
166 /*
167  * Commands to do_syslog:
168  *
169  *      0 -- Close the log.  Currently a NOP.
170  *      1 -- Open the log. Currently a NOP.
171  *      2 -- Read from the log.
172  *      3 -- Read all messages remaining in the ring buffer.
173  *      4 -- Read and clear all messages remaining in the ring buffer
174  *      5 -- Clear ring buffer.
175  *      6 -- Disable printk's to console
176  *      7 -- Enable printk's to console
177  *      8 -- Set level of messages printed to console
178  *      9 -- Return number of unread characters in the log buffer
179  *     10 -- Return size of the log buffer
180  */
181 int do_syslog(int type, char __user *buf, int len)
182 {
183         unsigned long i, j, limit, count;
184         int do_clear = 0;
185         char c;
186         int error = 0;
187
188         error = security_syslog(type);
189         if (error)
190                 return error;
191
192         switch (type) {
193         case 0:         /* Close log */
194                 break;
195         case 1:         /* Open log */
196                 break;
197         case 2:         /* Read from log */
198                 error = -EINVAL;
199                 if (!buf || len < 0)
200                         goto out;
201                 error = 0;
202                 if (!len)
203                         goto out;
204                 if (!access_ok(VERIFY_WRITE, buf, len)) {
205                         error = -EFAULT;
206                         goto out;
207                 }
208                 error = wait_event_interruptible(log_wait,
209                                                         (log_start - log_end));
210                 if (error)
211                         goto out;
212                 i = 0;
213                 spin_lock_irq(&logbuf_lock);
214                 while (!error && (log_start != log_end) && i < len) {
215                         c = LOG_BUF(log_start);
216                         log_start++;
217                         spin_unlock_irq(&logbuf_lock);
218                         error = __put_user(c,buf);
219                         buf++;
220                         i++;
221                         cond_resched();
222                         spin_lock_irq(&logbuf_lock);
223                 }
224                 spin_unlock_irq(&logbuf_lock);
225                 if (!error)
226                         error = i;
227                 break;
228         case 4:         /* Read/clear last kernel messages */
229                 do_clear = 1;
230                 /* FALL THRU */
231         case 3:         /* Read last kernel messages */
232                 error = -EINVAL;
233                 if (!buf || len < 0)
234                         goto out;
235                 error = 0;
236                 if (!len)
237                         goto out;
238                 if (!access_ok(VERIFY_WRITE, buf, len)) {
239                         error = -EFAULT;
240                         goto out;
241                 }
242                 count = len;
243                 if (count > log_buf_len)
244                         count = log_buf_len;
245                 spin_lock_irq(&logbuf_lock);
246                 if (count > logged_chars)
247                         count = logged_chars;
248                 if (do_clear)
249                         logged_chars = 0;
250                 limit = log_end;
251                 /*
252                  * __put_user() could sleep, and while we sleep
253                  * printk() could overwrite the messages
254                  * we try to copy to user space. Therefore
255                  * the messages are copied in reverse. <manfreds>
256                  */
257                 for (i = 0; i < count && !error; i++) {
258                         j = limit-1-i;
259                         if (j + log_buf_len < log_end)
260                                 break;
261                         c = LOG_BUF(j);
262                         spin_unlock_irq(&logbuf_lock);
263                         error = __put_user(c,&buf[count-1-i]);
264                         cond_resched();
265                         spin_lock_irq(&logbuf_lock);
266                 }
267                 spin_unlock_irq(&logbuf_lock);
268                 if (error)
269                         break;
270                 error = i;
271                 if (i != count) {
272                         int offset = count-error;
273                         /* buffer overflow during copy, correct user buffer. */
274                         for (i = 0; i < error; i++) {
275                                 if (__get_user(c,&buf[i+offset]) ||
276                                     __put_user(c,&buf[i])) {
277                                         error = -EFAULT;
278                                         break;
279                                 }
280                                 cond_resched();
281                         }
282                 }
283                 break;
284         case 5:         /* Clear ring buffer */
285                 logged_chars = 0;
286                 break;
287         case 6:         /* Disable logging to console */
288                 console_loglevel = minimum_console_loglevel;
289                 break;
290         case 7:         /* Enable logging to console */
291                 console_loglevel = default_console_loglevel;
292                 break;
293         case 8:         /* Set level of messages printed to console */
294                 error = -EINVAL;
295                 if (len < 1 || len > 8)
296                         goto out;
297                 if (len < minimum_console_loglevel)
298                         len = minimum_console_loglevel;
299                 console_loglevel = len;
300                 error = 0;
301                 break;
302         case 9:         /* Number of chars in the log buffer */
303                 error = log_end - log_start;
304                 break;
305         case 10:        /* Size of the log buffer */
306                 error = log_buf_len;
307                 break;
308         default:
309                 error = -EINVAL;
310                 break;
311         }
312 out:
313         return error;
314 }
315
316 asmlinkage long sys_syslog(int type, char __user *buf, int len)
317 {
318         return do_syslog(type, buf, len);
319 }
320
321 /*
322  * Call the console drivers on a range of log_buf
323  */
324 static void __call_console_drivers(unsigned long start, unsigned long end)
325 {
326         struct console *con;
327
328         for (con = console_drivers; con; con = con->next) {
329                 if ((con->flags & CON_ENABLED) && con->write)
330                         con->write(con, &LOG_BUF(start), end - start);
331         }
332 }
333
334 /*
335  * Write out chars from start to end - 1 inclusive
336  */
337 static void _call_console_drivers(unsigned long start,
338                                 unsigned long end, int msg_log_level)
339 {
340         if (msg_log_level < console_loglevel &&
341                         console_drivers && start != end) {
342                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
343                         /* wrapped write */
344                         __call_console_drivers(start & LOG_BUF_MASK,
345                                                 log_buf_len);
346                         __call_console_drivers(0, end & LOG_BUF_MASK);
347                 } else {
348                         __call_console_drivers(start, end);
349                 }
350         }
351 }
352
353 /*
354  * Call the console drivers, asking them to write out
355  * log_buf[start] to log_buf[end - 1].
356  * The console_sem must be held.
357  */
358 static void call_console_drivers(unsigned long start, unsigned long end)
359 {
360         unsigned long cur_index, start_print;
361         static int msg_level = -1;
362
363         BUG_ON(((long)(start - end)) > 0);
364
365         cur_index = start;
366         start_print = start;
367         while (cur_index != end) {
368                 if (msg_level < 0 && ((end - cur_index) > 2) &&
369                                 LOG_BUF(cur_index + 0) == '<' &&
370                                 LOG_BUF(cur_index + 1) >= '0' &&
371                                 LOG_BUF(cur_index + 1) <= '7' &&
372                                 LOG_BUF(cur_index + 2) == '>') {
373                         msg_level = LOG_BUF(cur_index + 1) - '0';
374                         cur_index += 3;
375                         start_print = cur_index;
376                 }
377                 while (cur_index != end) {
378                         char c = LOG_BUF(cur_index);
379
380                         cur_index++;
381                         if (c == '\n') {
382                                 if (msg_level < 0) {
383                                         /*
384                                          * printk() has already given us loglevel tags in
385                                          * the buffer.  This code is here in case the
386                                          * log buffer has wrapped right round and scribbled
387                                          * on those tags
388                                          */
389                                         msg_level = default_message_loglevel;
390                                 }
391                                 _call_console_drivers(start_print, cur_index, msg_level);
392                                 msg_level = -1;
393                                 start_print = cur_index;
394                                 break;
395                         }
396                 }
397         }
398         _call_console_drivers(start_print, end, msg_level);
399 }
400
401 static void emit_log_char(char c)
402 {
403         LOG_BUF(log_end) = c;
404         log_end++;
405         if (log_end - log_start > log_buf_len)
406                 log_start = log_end - log_buf_len;
407         if (log_end - con_start > log_buf_len)
408                 con_start = log_end - log_buf_len;
409         if (logged_chars < log_buf_len)
410                 logged_chars++;
411 }
412
413 /*
414  * Zap console related locks when oopsing. Only zap at most once
415  * every 10 seconds, to leave time for slow consoles to print a
416  * full oops.
417  */
418 static void zap_locks(void)
419 {
420         static unsigned long oops_timestamp;
421
422         if (time_after_eq(jiffies, oops_timestamp) &&
423                         !time_after(jiffies, oops_timestamp + 30 * HZ))
424                 return;
425
426         oops_timestamp = jiffies;
427
428         /* If a crash is occurring, make sure we can't deadlock */
429         spin_lock_init(&logbuf_lock);
430         /* And make sure that we print immediately */
431         init_MUTEX(&console_sem);
432 }
433
434 #if defined(CONFIG_PRINTK_TIME)
435 static int printk_time = 1;
436 #else
437 static int printk_time = 0;
438 #endif
439
440 static int __init printk_time_setup(char *str)
441 {
442         if (*str)
443                 return 0;
444         printk_time = 1;
445         return 1;
446 }
447
448 __setup("time", printk_time_setup);
449
450 __attribute__((weak)) unsigned long long printk_clock(void)
451 {
452         return sched_clock();
453 }
454
455 /**
456  * printk - print a kernel message
457  * @fmt: format string
458  *
459  * This is printk.  It can be called from any context.  We want it to work.
460  *
461  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
462  * call the console drivers.  If we fail to get the semaphore we place the output
463  * into the log buffer and return.  The current holder of the console_sem will
464  * notice the new output in release_console_sem() and will send it to the
465  * consoles before releasing the semaphore.
466  *
467  * One effect of this deferred printing is that code which calls printk() and
468  * then changes console_loglevel may break. This is because console_loglevel
469  * is inspected when the actual printing occurs.
470  *
471  * See also:
472  * printf(3)
473  */
474
475 asmlinkage int printk(const char *fmt, ...)
476 {
477         va_list args;
478         int r;
479
480         va_start(args, fmt);
481         r = vprintk(fmt, args);
482         va_end(args);
483
484         return r;
485 }
486
487 /* cpu currently holding logbuf_lock */
488 static volatile unsigned int printk_cpu = UINT_MAX;
489
490 asmlinkage int vprintk(const char *fmt, va_list args)
491 {
492         unsigned long flags;
493         int printed_len;
494         char *p;
495         static char printk_buf[1024];
496         static int log_level_unknown = 1;
497
498         preempt_disable();
499         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
500                 /* If a crash is occurring during printk() on this CPU,
501                  * make sure we can't deadlock */
502                 zap_locks();
503
504         /* This stops the holder of console_sem just where we want him */
505         spin_lock_irqsave(&logbuf_lock, flags);
506         printk_cpu = smp_processor_id();
507
508         /* Emit the output into the temporary buffer */
509         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
510
511         /*
512          * Copy the output into log_buf.  If the caller didn't provide
513          * appropriate log level tags, we insert them here
514          */
515         for (p = printk_buf; *p; p++) {
516                 if (log_level_unknown) {
517                         /* log_level_unknown signals the start of a new line */
518                         if (printk_time) {
519                                 int loglev_char;
520                                 char tbuf[50], *tp;
521                                 unsigned tlen;
522                                 unsigned long long t;
523                                 unsigned long nanosec_rem;
524
525                                 /*
526                                  * force the log level token to be
527                                  * before the time output.
528                                  */
529                                 if (p[0] == '<' && p[1] >='0' &&
530                                    p[1] <= '7' && p[2] == '>') {
531                                         loglev_char = p[1];
532                                         p += 3;
533                                         printed_len -= 3;
534                                 } else {
535                                         loglev_char = default_message_loglevel
536                                                 + '0';
537                                 }
538                                 t = printk_clock();
539                                 nanosec_rem = do_div(t, 1000000000);
540                                 tlen = sprintf(tbuf,
541                                                 "<%c>[%5lu.%06lu] ",
542                                                 loglev_char,
543                                                 (unsigned long)t,
544                                                 nanosec_rem/1000);
545
546                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
547                                         emit_log_char(*tp);
548                                 printed_len += tlen;
549                         } else {
550                                 if (p[0] != '<' || p[1] < '0' ||
551                                    p[1] > '7' || p[2] != '>') {
552                                         emit_log_char('<');
553                                         emit_log_char(default_message_loglevel
554                                                 + '0');
555                                         emit_log_char('>');
556                                         printed_len += 3;
557                                 }
558                         }
559                         log_level_unknown = 0;
560                         if (!*p)
561                                 break;
562                 }
563                 emit_log_char(*p);
564                 if (*p == '\n')
565                         log_level_unknown = 1;
566         }
567
568         if (!cpu_online(smp_processor_id())) {
569                 /*
570                  * Some console drivers may assume that per-cpu resources have
571                  * been allocated.  So don't allow them to be called by this
572                  * CPU until it is officially up.  We shouldn't be calling into
573                  * random console drivers on a CPU which doesn't exist yet..
574                  */
575                 printk_cpu = UINT_MAX;
576                 spin_unlock_irqrestore(&logbuf_lock, flags);
577                 goto out;
578         }
579         if (!down_trylock(&console_sem)) {
580                 console_locked = 1;
581                 /*
582                  * We own the drivers.  We can drop the spinlock and let
583                  * release_console_sem() print the text
584                  */
585                 printk_cpu = UINT_MAX;
586                 spin_unlock_irqrestore(&logbuf_lock, flags);
587                 console_may_schedule = 0;
588                 release_console_sem();
589         } else {
590                 /*
591                  * Someone else owns the drivers.  We drop the spinlock, which
592                  * allows the semaphore holder to proceed and to call the
593                  * console drivers with the output which we just produced.
594                  */
595                 printk_cpu = UINT_MAX;
596                 spin_unlock_irqrestore(&logbuf_lock, flags);
597         }
598 out:
599         preempt_enable();
600         return printed_len;
601 }
602 EXPORT_SYMBOL(printk);
603 EXPORT_SYMBOL(vprintk);
604
605 #else
606
607 asmlinkage long sys_syslog(int type, char __user *buf, int len)
608 {
609         return 0;
610 }
611
612 int do_syslog(int type, char __user *buf, int len)
613 {
614         return 0;
615 }
616
617 static void call_console_drivers(unsigned long start, unsigned long end)
618 {
619 }
620
621 #endif
622
623 /*
624  * Set up a list of consoles.  Called from init/main.c
625  */
626 static int __init console_setup(char *str)
627 {
628         char name[sizeof(console_cmdline[0].name)];
629         char *s, *options;
630         int idx;
631
632         /*
633          * Decode str into name, index, options.
634          */
635         if (str[0] >= '0' && str[0] <= '9') {
636                 strcpy(name, "ttyS");
637                 strncpy(name + 4, str, sizeof(name) - 5);
638         } else {
639                 strncpy(name, str, sizeof(name) - 1);
640         }
641         name[sizeof(name) - 1] = 0;
642         if ((options = strchr(str, ',')) != NULL)
643                 *(options++) = 0;
644 #ifdef __sparc__
645         if (!strcmp(str, "ttya"))
646                 strcpy(name, "ttyS0");
647         if (!strcmp(str, "ttyb"))
648                 strcpy(name, "ttyS1");
649 #endif
650         for (s = name; *s; s++)
651                 if ((*s >= '0' && *s <= '9') || *s == ',')
652                         break;
653         idx = simple_strtoul(s, NULL, 10);
654         *s = 0;
655
656         add_preferred_console(name, idx, options);
657         return 1;
658 }
659 __setup("console=", console_setup);
660
661 /**
662  * add_preferred_console - add a device to the list of preferred consoles.
663  * @name: device name
664  * @idx: device index
665  * @options: options for this console
666  *
667  * The last preferred console added will be used for kernel messages
668  * and stdin/out/err for init.  Normally this is used by console_setup
669  * above to handle user-supplied console arguments; however it can also
670  * be used by arch-specific code either to override the user or more
671  * commonly to provide a default console (ie from PROM variables) when
672  * the user has not supplied one.
673  */
674 int __init add_preferred_console(char *name, int idx, char *options)
675 {
676         struct console_cmdline *c;
677         int i;
678
679         /*
680          *      See if this tty is not yet registered, and
681          *      if we have a slot free.
682          */
683         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
684                 if (strcmp(console_cmdline[i].name, name) == 0 &&
685                           console_cmdline[i].index == idx) {
686                                 selected_console = i;
687                                 return 0;
688                 }
689         if (i == MAX_CMDLINECONSOLES)
690                 return -E2BIG;
691         selected_console = i;
692         c = &console_cmdline[i];
693         memcpy(c->name, name, sizeof(c->name));
694         c->name[sizeof(c->name) - 1] = 0;
695         c->options = options;
696         c->index = idx;
697         return 0;
698 }
699
700 /**
701  * acquire_console_sem - lock the console system for exclusive use.
702  *
703  * Acquires a semaphore which guarantees that the caller has
704  * exclusive access to the console system and the console_drivers list.
705  *
706  * Can sleep, returns nothing.
707  */
708 void acquire_console_sem(void)
709 {
710         BUG_ON(in_interrupt());
711         down(&console_sem);
712         console_locked = 1;
713         console_may_schedule = 1;
714 }
715 EXPORT_SYMBOL(acquire_console_sem);
716
717 int try_acquire_console_sem(void)
718 {
719         if (down_trylock(&console_sem))
720                 return -1;
721         console_locked = 1;
722         console_may_schedule = 0;
723         return 0;
724 }
725 EXPORT_SYMBOL(try_acquire_console_sem);
726
727 int is_console_locked(void)
728 {
729         return console_locked;
730 }
731 EXPORT_SYMBOL(is_console_locked);
732
733 /**
734  * release_console_sem - unlock the console system
735  *
736  * Releases the semaphore which the caller holds on the console system
737  * and the console driver list.
738  *
739  * While the semaphore was held, console output may have been buffered
740  * by printk().  If this is the case, release_console_sem() emits
741  * the output prior to releasing the semaphore.
742  *
743  * If there is output waiting for klogd, we wake it up.
744  *
745  * release_console_sem() may be called from any context.
746  */
747 void release_console_sem(void)
748 {
749         unsigned long flags;
750         unsigned long _con_start, _log_end;
751         unsigned long wake_klogd = 0;
752
753         for ( ; ; ) {
754                 spin_lock_irqsave(&logbuf_lock, flags);
755                 wake_klogd |= log_start - log_end;
756                 if (con_start == log_end)
757                         break;                  /* Nothing to print */
758                 _con_start = con_start;
759                 _log_end = log_end;
760                 con_start = log_end;            /* Flush */
761                 spin_unlock(&logbuf_lock);
762                 call_console_drivers(_con_start, _log_end);
763                 local_irq_restore(flags);
764         }
765         console_locked = 0;
766         console_may_schedule = 0;
767         up(&console_sem);
768         spin_unlock_irqrestore(&logbuf_lock, flags);
769         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
770                 wake_up_interruptible(&log_wait);
771 }
772 EXPORT_SYMBOL(release_console_sem);
773
774 /**
775  * console_conditional_schedule - yield the CPU if required
776  *
777  * If the console code is currently allowed to sleep, and
778  * if this CPU should yield the CPU to another task, do
779  * so here.
780  *
781  * Must be called within acquire_console_sem().
782  */
783 void __sched console_conditional_schedule(void)
784 {
785         if (console_may_schedule)
786                 cond_resched();
787 }
788 EXPORT_SYMBOL(console_conditional_schedule);
789
790 void console_print(const char *s)
791 {
792         printk(KERN_EMERG "%s", s);
793 }
794 EXPORT_SYMBOL(console_print);
795
796 void console_unblank(void)
797 {
798         struct console *c;
799
800         /*
801          * console_unblank can no longer be called in interrupt context unless
802          * oops_in_progress is set to 1..
803          */
804         if (oops_in_progress) {
805                 if (down_trylock(&console_sem) != 0)
806                         return;
807         } else
808                 acquire_console_sem();
809
810         console_locked = 1;
811         console_may_schedule = 0;
812         for (c = console_drivers; c != NULL; c = c->next)
813                 if ((c->flags & CON_ENABLED) && c->unblank)
814                         c->unblank();
815         release_console_sem();
816 }
817
818 /*
819  * Return the console tty driver structure and its associated index
820  */
821 struct tty_driver *console_device(int *index)
822 {
823         struct console *c;
824         struct tty_driver *driver = NULL;
825
826         acquire_console_sem();
827         for (c = console_drivers; c != NULL; c = c->next) {
828                 if (!c->device)
829                         continue;
830                 driver = c->device(c, index);
831                 if (driver)
832                         break;
833         }
834         release_console_sem();
835         return driver;
836 }
837
838 /*
839  * Prevent further output on the passed console device so that (for example)
840  * serial drivers can disable console output before suspending a port, and can
841  * re-enable output afterwards.
842  */
843 void console_stop(struct console *console)
844 {
845         acquire_console_sem();
846         console->flags &= ~CON_ENABLED;
847         release_console_sem();
848 }
849 EXPORT_SYMBOL(console_stop);
850
851 void console_start(struct console *console)
852 {
853         acquire_console_sem();
854         console->flags |= CON_ENABLED;
855         release_console_sem();
856 }
857 EXPORT_SYMBOL(console_start);
858
859 /*
860  * The console driver calls this routine during kernel initialization
861  * to register the console printing procedure with printk() and to
862  * print any messages that were printed by the kernel before the
863  * console driver was initialized.
864  */
865 void register_console(struct console *console)
866 {
867         int i;
868         unsigned long flags;
869
870         if (preferred_console < 0)
871                 preferred_console = selected_console;
872
873         /*
874          *      See if we want to use this console driver. If we
875          *      didn't select a console we take the first one
876          *      that registers here.
877          */
878         if (preferred_console < 0) {
879                 if (console->index < 0)
880                         console->index = 0;
881                 if (console->setup == NULL ||
882                     console->setup(console, NULL) == 0) {
883                         console->flags |= CON_ENABLED | CON_CONSDEV;
884                         preferred_console = 0;
885                 }
886         }
887
888         /*
889          *      See if this console matches one we selected on
890          *      the command line.
891          */
892         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
893                         i++) {
894                 if (strcmp(console_cmdline[i].name, console->name) != 0)
895                         continue;
896                 if (console->index >= 0 &&
897                     console->index != console_cmdline[i].index)
898                         continue;
899                 if (console->index < 0)
900                         console->index = console_cmdline[i].index;
901                 if (console->setup &&
902                     console->setup(console, console_cmdline[i].options) != 0)
903                         break;
904                 console->flags |= CON_ENABLED;
905                 console->index = console_cmdline[i].index;
906                 if (i == selected_console) {
907                         console->flags |= CON_CONSDEV;
908                         preferred_console = selected_console;
909                 }
910                 break;
911         }
912
913         if (!(console->flags & CON_ENABLED))
914                 return;
915
916         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
917                 unregister_console(console_drivers);
918                 console->flags &= ~CON_PRINTBUFFER;
919         }
920
921         /*
922          *      Put this console in the list - keep the
923          *      preferred driver at the head of the list.
924          */
925         acquire_console_sem();
926         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
927                 console->next = console_drivers;
928                 console_drivers = console;
929                 if (console->next)
930                         console->next->flags &= ~CON_CONSDEV;
931         } else {
932                 console->next = console_drivers->next;
933                 console_drivers->next = console;
934         }
935         if (console->flags & CON_PRINTBUFFER) {
936                 /*
937                  * release_console_sem() will print out the buffered messages
938                  * for us.
939                  */
940                 spin_lock_irqsave(&logbuf_lock, flags);
941                 con_start = log_start;
942                 spin_unlock_irqrestore(&logbuf_lock, flags);
943         }
944         release_console_sem();
945 }
946 EXPORT_SYMBOL(register_console);
947
948 int unregister_console(struct console *console)
949 {
950         struct console *a, *b;
951         int res = 1;
952
953         acquire_console_sem();
954         if (console_drivers == console) {
955                 console_drivers=console->next;
956                 res = 0;
957         } else if (console_drivers) {
958                 for (a=console_drivers->next, b=console_drivers ;
959                      a; b=a, a=b->next) {
960                         if (a == console) {
961                                 b->next = a->next;
962                                 res = 0;
963                                 break;
964                         }
965                 }
966         }
967
968         /* If last console is removed, we re-enable picking the first
969          * one that gets registered. Without that, pmac early boot console
970          * would prevent fbcon from taking over.
971          *
972          * If this isn't the last console and it has CON_CONSDEV set, we
973          * need to set it on the next preferred console.
974          */
975         if (console_drivers == NULL)
976                 preferred_console = selected_console;
977         else if (console->flags & CON_CONSDEV)
978                 console_drivers->flags |= CON_CONSDEV;
979
980         release_console_sem();
981         return res;
982 }
983 EXPORT_SYMBOL(unregister_console);
984
985 /**
986  * tty_write_message - write a message to a certain tty, not just the console.
987  * @tty: the destination tty_struct
988  * @msg: the message to write
989  *
990  * This is used for messages that need to be redirected to a specific tty.
991  * We don't put it into the syslog queue right now maybe in the future if
992  * really needed.
993  */
994 void tty_write_message(struct tty_struct *tty, char *msg)
995 {
996         if (tty && tty->driver->write)
997                 tty->driver->write(tty, msg, strlen(msg));
998         return;
999 }
1000
1001 /*
1002  * printk rate limiting, lifted from the networking subsystem.
1003  *
1004  * This enforces a rate limit: not more than one kernel message
1005  * every printk_ratelimit_jiffies to make a denial-of-service
1006  * attack impossible.
1007  */
1008 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1009 {
1010         static DEFINE_SPINLOCK(ratelimit_lock);
1011         static unsigned long toks = 10 * 5 * HZ;
1012         static unsigned long last_msg;
1013         static int missed;
1014         unsigned long flags;
1015         unsigned long now = jiffies;
1016
1017         spin_lock_irqsave(&ratelimit_lock, flags);
1018         toks += now - last_msg;
1019         last_msg = now;
1020         if (toks > (ratelimit_burst * ratelimit_jiffies))
1021                 toks = ratelimit_burst * ratelimit_jiffies;
1022         if (toks >= ratelimit_jiffies) {
1023                 int lost = missed;
1024
1025                 missed = 0;
1026                 toks -= ratelimit_jiffies;
1027                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1028                 if (lost)
1029                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1030                 return 1;
1031         }
1032         missed++;
1033         spin_unlock_irqrestore(&ratelimit_lock, flags);
1034         return 0;
1035 }
1036 EXPORT_SYMBOL(__printk_ratelimit);
1037
1038 /* minimum time in jiffies between messages */
1039 int printk_ratelimit_jiffies = 5 * HZ;
1040
1041 /* number of messages we send before ratelimiting */
1042 int printk_ratelimit_burst = 10;
1043
1044 int printk_ratelimit(void)
1045 {
1046         return __printk_ratelimit(printk_ratelimit_jiffies,
1047                                 printk_ratelimit_burst);
1048 }
1049 EXPORT_SYMBOL(printk_ratelimit);