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