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