[PATCH] unexport console_unblank
[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(KERN_WARNING "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(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
197         }
198 out:
199         return 1;
200 }
201
202 __setup("log_buf_len=", log_buf_len_setup);
203
204 /*
205  * Commands to do_syslog:
206  *
207  *      0 -- Close the log.  Currently a NOP.
208  *      1 -- Open the log. Currently a NOP.
209  *      2 -- Read from the log.
210  *      3 -- Read all messages remaining in the ring buffer.
211  *      4 -- Read and clear all messages remaining in the ring buffer
212  *      5 -- Clear ring buffer.
213  *      6 -- Disable printk's to console
214  *      7 -- Enable printk's to console
215  *      8 -- Set level of messages printed to console
216  *      9 -- Return number of unread characters in the log buffer
217  *     10 -- Return size of the log buffer
218  */
219 int do_syslog(int type, char __user *buf, int len)
220 {
221         unsigned long i, j, limit, count;
222         int do_clear = 0;
223         char c;
224         int error = 0;
225
226         error = security_syslog(type);
227         if (error)
228                 return error;
229
230         switch (type) {
231         case 0:         /* Close log */
232                 break;
233         case 1:         /* Open log */
234                 break;
235         case 2:         /* Read from log */
236                 error = -EINVAL;
237                 if (!buf || len < 0)
238                         goto out;
239                 error = 0;
240                 if (!len)
241                         goto out;
242                 if (!access_ok(VERIFY_WRITE, buf, len)) {
243                         error = -EFAULT;
244                         goto out;
245                 }
246                 error = wait_event_interruptible(log_wait,
247                                                         (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 && ((end - cur_index) > 2) &&
408                                 LOG_BUF(cur_index + 0) == '<' &&
409                                 LOG_BUF(cur_index + 1) >= '0' &&
410                                 LOG_BUF(cur_index + 1) <= '7' &&
411                                 LOG_BUF(cur_index + 2) == '>') {
412                         msg_level = LOG_BUF(cur_index + 1) - '0';
413                         cur_index += 3;
414                         start_print = cur_index;
415                 }
416                 while (cur_index != end) {
417                         char c = LOG_BUF(cur_index);
418
419                         cur_index++;
420                         if (c == '\n') {
421                                 if (msg_level < 0) {
422                                         /*
423                                          * printk() has already given us loglevel tags in
424                                          * the buffer.  This code is here in case the
425                                          * log buffer has wrapped right round and scribbled
426                                          * on those tags
427                                          */
428                                         msg_level = default_message_loglevel;
429                                 }
430                                 _call_console_drivers(start_print, cur_index, msg_level);
431                                 msg_level = -1;
432                                 start_print = cur_index;
433                                 break;
434                         }
435                 }
436         }
437         _call_console_drivers(start_print, end, msg_level);
438 }
439
440 static void emit_log_char(char c)
441 {
442         LOG_BUF(log_end) = c;
443         log_end++;
444         if (log_end - log_start > log_buf_len)
445                 log_start = log_end - log_buf_len;
446         if (log_end - con_start > log_buf_len)
447                 con_start = log_end - log_buf_len;
448         if (logged_chars < log_buf_len)
449                 logged_chars++;
450 }
451
452 /*
453  * Zap console related locks when oopsing. Only zap at most once
454  * every 10 seconds, to leave time for slow consoles to print a
455  * full oops.
456  */
457 static void zap_locks(void)
458 {
459         static unsigned long oops_timestamp;
460
461         if (time_after_eq(jiffies, oops_timestamp) &&
462                         !time_after(jiffies, oops_timestamp + 30 * HZ))
463                 return;
464
465         oops_timestamp = jiffies;
466
467         /* If a crash is occurring, make sure we can't deadlock */
468         spin_lock_init(&logbuf_lock);
469         /* And make sure that we print immediately */
470         init_MUTEX(&console_sem);
471 }
472
473 #if defined(CONFIG_PRINTK_TIME)
474 static int printk_time = 1;
475 #else
476 static int printk_time = 0;
477 #endif
478
479 static int __init printk_time_setup(char *str)
480 {
481         if (*str)
482                 return 0;
483         printk_time = 1;
484         return 1;
485 }
486
487 __setup("time", printk_time_setup);
488
489 __attribute__((weak)) unsigned long long printk_clock(void)
490 {
491         return sched_clock();
492 }
493
494 /*
495  * This is printk.  It can be called from any context.  We want it to work.
496  *
497  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
498  * call the console drivers.  If we fail to get the semaphore we place the output
499  * into the log buffer and return.  The current holder of the console_sem will
500  * notice the new output in release_console_sem() and will send it to the
501  * consoles before releasing the semaphore.
502  *
503  * One effect of this deferred printing is that code which calls printk() and
504  * then changes console_loglevel may break. This is because console_loglevel
505  * is inspected when the actual printing occurs.
506  */
507
508 asmlinkage int printk(const char *fmt, ...)
509 {
510         va_list args;
511         int r;
512
513         va_start(args, fmt);
514         r = vprintk(fmt, args);
515         va_end(args);
516
517         return r;
518 }
519
520 /* cpu currently holding logbuf_lock */
521 static volatile unsigned int printk_cpu = UINT_MAX;
522
523 asmlinkage int vprintk(const char *fmt, va_list args)
524 {
525         unsigned long flags;
526         int printed_len;
527         char *p;
528         static char printk_buf[1024];
529         static int log_level_unknown = 1;
530
531         preempt_disable();
532         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
533                 /* If a crash is occurring during printk() on this CPU,
534                  * make sure we can't deadlock */
535                 zap_locks();
536
537         /* This stops the holder of console_sem just where we want him */
538         spin_lock_irqsave(&logbuf_lock, flags);
539         printk_cpu = smp_processor_id();
540
541         /* Emit the output into the temporary buffer */
542         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
543
544         /*
545          * Copy the output into log_buf.  If the caller didn't provide
546          * appropriate log level tags, we insert them here
547          */
548         for (p = printk_buf; *p; p++) {
549                 if (log_level_unknown) {
550                         /* log_level_unknown signals the start of a new line */
551                         if (printk_time) {
552                                 int loglev_char;
553                                 char tbuf[50], *tp;
554                                 unsigned tlen;
555                                 unsigned long long t;
556                                 unsigned long nanosec_rem;
557
558                                 /*
559                                  * force the log level token to be
560                                  * before the time output.
561                                  */
562                                 if (p[0] == '<' && p[1] >='0' &&
563                                    p[1] <= '7' && p[2] == '>') {
564                                         loglev_char = p[1];
565                                         p += 3;
566                                         printed_len += 3;
567                                 } else {
568                                         loglev_char = default_message_loglevel
569                                                 + '0';
570                                 }
571                                 t = printk_clock();
572                                 nanosec_rem = do_div(t, 1000000000);
573                                 tlen = sprintf(tbuf,
574                                                 "<%c>[%5lu.%06lu] ",
575                                                 loglev_char,
576                                                 (unsigned long)t,
577                                                 nanosec_rem/1000);
578
579                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
580                                         emit_log_char(*tp);
581                                 printed_len += tlen - 3;
582                         } else {
583                                 if (p[0] != '<' || p[1] < '0' ||
584                                    p[1] > '7' || p[2] != '>') {
585                                         emit_log_char('<');
586                                         emit_log_char(default_message_loglevel
587                                                 + '0');
588                                         emit_log_char('>');
589                                 }
590                                 printed_len += 3;
591                         }
592                         log_level_unknown = 0;
593                         if (!*p)
594                                 break;
595                 }
596                 emit_log_char(*p);
597                 if (*p == '\n')
598                         log_level_unknown = 1;
599         }
600
601         if (!cpu_online(smp_processor_id())) {
602                 /*
603                  * Some console drivers may assume that per-cpu resources have
604                  * been allocated.  So don't allow them to be called by this
605                  * CPU until it is officially up.  We shouldn't be calling into
606                  * random console drivers on a CPU which doesn't exist yet..
607                  */
608                 printk_cpu = UINT_MAX;
609                 spin_unlock_irqrestore(&logbuf_lock, flags);
610                 goto out;
611         }
612         if (!down_trylock(&console_sem)) {
613                 console_locked = 1;
614                 /*
615                  * We own the drivers.  We can drop the spinlock and let
616                  * release_console_sem() print the text
617                  */
618                 printk_cpu = UINT_MAX;
619                 spin_unlock_irqrestore(&logbuf_lock, flags);
620                 console_may_schedule = 0;
621                 release_console_sem();
622         } else {
623                 /*
624                  * Someone else owns the drivers.  We drop the spinlock, which
625                  * allows the semaphore holder to proceed and to call the
626                  * console drivers with the output which we just produced.
627                  */
628                 printk_cpu = UINT_MAX;
629                 spin_unlock_irqrestore(&logbuf_lock, flags);
630         }
631 out:
632         preempt_enable();
633         return printed_len;
634 }
635 EXPORT_SYMBOL(printk);
636 EXPORT_SYMBOL(vprintk);
637
638 #else
639
640 asmlinkage long sys_syslog(int type, char __user *buf, int len)
641 {
642         return 0;
643 }
644
645 int do_syslog(int type, char __user *buf, int len)
646 {
647         return 0;
648 }
649
650 static void call_console_drivers(unsigned long start, unsigned long end)
651 {
652 }
653
654 #endif
655
656 /**
657  * add_preferred_console - add a device to the list of preferred consoles.
658  *
659  * The last preferred console added will be used for kernel messages
660  * and stdin/out/err for init.  Normally this is used by console_setup
661  * above to handle user-supplied console arguments; however it can also
662  * be used by arch-specific code either to override the user or more
663  * commonly to provide a default console (ie from PROM variables) when
664  * the user has not supplied one.
665  */
666 int __init add_preferred_console(char *name, int idx, char *options)
667 {
668         struct console_cmdline *c;
669         int i;
670
671         /*
672          *      See if this tty is not yet registered, and
673          *      if we have a slot free.
674          */
675         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
676                 if (strcmp(console_cmdline[i].name, name) == 0 &&
677                           console_cmdline[i].index == idx) {
678                                 selected_console = i;
679                                 return 0;
680                 }
681         if (i == MAX_CMDLINECONSOLES)
682                 return -E2BIG;
683         selected_console = i;
684         c = &console_cmdline[i];
685         memcpy(c->name, name, sizeof(c->name));
686         c->name[sizeof(c->name) - 1] = 0;
687         c->options = options;
688         c->index = idx;
689         return 0;
690 }
691
692 /**
693  * acquire_console_sem - lock the console system for exclusive use.
694  *
695  * Acquires a semaphore which guarantees that the caller has
696  * exclusive access to the console system and the console_drivers list.
697  *
698  * Can sleep, returns nothing.
699  */
700 void acquire_console_sem(void)
701 {
702         if (in_interrupt())
703                 BUG();
704         down(&console_sem);
705         console_locked = 1;
706         console_may_schedule = 1;
707 }
708 EXPORT_SYMBOL(acquire_console_sem);
709
710 int try_acquire_console_sem(void)
711 {
712         if (down_trylock(&console_sem))
713                 return -1;
714         console_locked = 1;
715         console_may_schedule = 0;
716         return 0;
717 }
718 EXPORT_SYMBOL(try_acquire_console_sem);
719
720 int is_console_locked(void)
721 {
722         return console_locked;
723 }
724 EXPORT_SYMBOL(is_console_locked);
725
726 /**
727  * release_console_sem - unlock the console system
728  *
729  * Releases the semaphore which the caller holds on the console system
730  * and the console driver list.
731  *
732  * While the semaphore was held, console output may have been buffered
733  * by printk().  If this is the case, release_console_sem() emits
734  * the output prior to releasing the semaphore.
735  *
736  * If there is output waiting for klogd, we wake it up.
737  *
738  * release_console_sem() may be called from any context.
739  */
740 void release_console_sem(void)
741 {
742         unsigned long flags;
743         unsigned long _con_start, _log_end;
744         unsigned long wake_klogd = 0;
745
746         for ( ; ; ) {
747                 spin_lock_irqsave(&logbuf_lock, flags);
748                 wake_klogd |= log_start - log_end;
749                 if (con_start == log_end)
750                         break;                  /* Nothing to print */
751                 _con_start = con_start;
752                 _log_end = log_end;
753                 con_start = log_end;            /* Flush */
754                 spin_unlock(&logbuf_lock);
755                 call_console_drivers(_con_start, _log_end);
756                 local_irq_restore(flags);
757         }
758         console_locked = 0;
759         console_may_schedule = 0;
760         up(&console_sem);
761         spin_unlock_irqrestore(&logbuf_lock, flags);
762         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
763                 wake_up_interruptible(&log_wait);
764 }
765 EXPORT_SYMBOL(release_console_sem);
766
767 /** console_conditional_schedule - yield the CPU if required
768  *
769  * If the console code is currently allowed to sleep, and
770  * if this CPU should yield the CPU to another task, do
771  * so here.
772  *
773  * Must be called within acquire_console_sem().
774  */
775 void __sched console_conditional_schedule(void)
776 {
777         if (console_may_schedule)
778                 cond_resched();
779 }
780 EXPORT_SYMBOL(console_conditional_schedule);
781
782 void console_print(const char *s)
783 {
784         printk(KERN_EMERG "%s", s);
785 }
786 EXPORT_SYMBOL(console_print);
787
788 void console_unblank(void)
789 {
790         struct console *c;
791
792         /*
793          * console_unblank can no longer be called in interrupt context unless
794          * oops_in_progress is set to 1..
795          */
796         if (oops_in_progress) {
797                 if (down_trylock(&console_sem) != 0)
798                         return;
799         } else
800                 acquire_console_sem();
801
802         console_locked = 1;
803         console_may_schedule = 0;
804         for (c = console_drivers; c != NULL; c = c->next)
805                 if ((c->flags & CON_ENABLED) && c->unblank)
806                         c->unblank();
807         release_console_sem();
808 }
809
810 /*
811  * Return the console tty driver structure and its associated index
812  */
813 struct tty_driver *console_device(int *index)
814 {
815         struct console *c;
816         struct tty_driver *driver = NULL;
817
818         acquire_console_sem();
819         for (c = console_drivers; c != NULL; c = c->next) {
820                 if (!c->device)
821                         continue;
822                 driver = c->device(c, index);
823                 if (driver)
824                         break;
825         }
826         release_console_sem();
827         return driver;
828 }
829
830 /*
831  * Prevent further output on the passed console device so that (for example)
832  * serial drivers can disable console output before suspending a port, and can
833  * re-enable output afterwards.
834  */
835 void console_stop(struct console *console)
836 {
837         acquire_console_sem();
838         console->flags &= ~CON_ENABLED;
839         release_console_sem();
840 }
841 EXPORT_SYMBOL(console_stop);
842
843 void console_start(struct console *console)
844 {
845         acquire_console_sem();
846         console->flags |= CON_ENABLED;
847         release_console_sem();
848 }
849 EXPORT_SYMBOL(console_start);
850
851 /*
852  * The console driver calls this routine during kernel initialization
853  * to register the console printing procedure with printk() and to
854  * print any messages that were printed by the kernel before the
855  * console driver was initialized.
856  */
857 void register_console(struct console *console)
858 {
859         int i;
860         unsigned long flags;
861
862         if (preferred_console < 0)
863                 preferred_console = selected_console;
864
865         /*
866          *      See if we want to use this console driver. If we
867          *      didn't select a console we take the first one
868          *      that registers here.
869          */
870         if (preferred_console < 0) {
871                 if (console->index < 0)
872                         console->index = 0;
873                 if (console->setup == NULL ||
874                     console->setup(console, NULL) == 0) {
875                         console->flags |= CON_ENABLED | CON_CONSDEV;
876                         preferred_console = 0;
877                 }
878         }
879
880         /*
881          *      See if this console matches one we selected on
882          *      the command line.
883          */
884         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
885                         i++) {
886                 if (strcmp(console_cmdline[i].name, console->name) != 0)
887                         continue;
888                 if (console->index >= 0 &&
889                     console->index != console_cmdline[i].index)
890                         continue;
891                 if (console->index < 0)
892                         console->index = console_cmdline[i].index;
893                 if (console->setup &&
894                     console->setup(console, console_cmdline[i].options) != 0)
895                         break;
896                 console->flags |= CON_ENABLED;
897                 console->index = console_cmdline[i].index;
898                 if (i == selected_console) {
899                         console->flags |= CON_CONSDEV;
900                         preferred_console = selected_console;
901                 }
902                 break;
903         }
904
905         if (!(console->flags & CON_ENABLED))
906                 return;
907
908         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
909                 unregister_console(console_drivers);
910                 console->flags &= ~CON_PRINTBUFFER;
911         }
912
913         /*
914          *      Put this console in the list - keep the
915          *      preferred driver at the head of the list.
916          */
917         acquire_console_sem();
918         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
919                 console->next = console_drivers;
920                 console_drivers = console;
921                 if (console->next)
922                         console->next->flags &= ~CON_CONSDEV;
923         } else {
924                 console->next = console_drivers->next;
925                 console_drivers->next = console;
926         }
927         if (console->flags & CON_PRINTBUFFER) {
928                 /*
929                  * release_console_sem() will print out the buffered messages
930                  * for us.
931                  */
932                 spin_lock_irqsave(&logbuf_lock, flags);
933                 con_start = log_start;
934                 spin_unlock_irqrestore(&logbuf_lock, flags);
935         }
936         release_console_sem();
937 }
938 EXPORT_SYMBOL(register_console);
939
940 int unregister_console(struct console *console)
941 {
942         struct console *a, *b;
943         int res = 1;
944
945         acquire_console_sem();
946         if (console_drivers == console) {
947                 console_drivers=console->next;
948                 res = 0;
949         } else {
950                 for (a=console_drivers->next, b=console_drivers ;
951                      a; b=a, a=b->next) {
952                         if (a == console) {
953                                 b->next = a->next;
954                                 res = 0;
955                                 break;
956                         }
957                 }
958         }
959
960         /* If last console is removed, we re-enable picking the first
961          * one that gets registered. Without that, pmac early boot console
962          * would prevent fbcon from taking over.
963          *
964          * If this isn't the last console and it has CON_CONSDEV set, we
965          * need to set it on the next preferred console.
966          */
967         if (console_drivers == NULL)
968                 preferred_console = selected_console;
969         else if (console->flags & CON_CONSDEV)
970                 console_drivers->flags |= CON_CONSDEV;
971
972         release_console_sem();
973         return res;
974 }
975 EXPORT_SYMBOL(unregister_console);
976
977 /**
978  * tty_write_message - write a message to a certain tty, not just the console.
979  *
980  * This is used for messages that need to be redirected to a specific tty.
981  * We don't put it into the syslog queue right now maybe in the future if
982  * really needed.
983  */
984 void tty_write_message(struct tty_struct *tty, char *msg)
985 {
986         if (tty && tty->driver->write)
987                 tty->driver->write(tty, msg, strlen(msg));
988         return;
989 }
990
991 /*
992  * printk rate limiting, lifted from the networking subsystem.
993  *
994  * This enforces a rate limit: not more than one kernel message
995  * every printk_ratelimit_jiffies to make a denial-of-service
996  * attack impossible.
997  */
998 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
999 {
1000         static DEFINE_SPINLOCK(ratelimit_lock);
1001         static unsigned long toks = 10 * 5 * HZ;
1002         static unsigned long last_msg;
1003         static int missed;
1004         unsigned long flags;
1005         unsigned long now = jiffies;
1006
1007         spin_lock_irqsave(&ratelimit_lock, flags);
1008         toks += now - last_msg;
1009         last_msg = now;
1010         if (toks > (ratelimit_burst * ratelimit_jiffies))
1011                 toks = ratelimit_burst * ratelimit_jiffies;
1012         if (toks >= ratelimit_jiffies) {
1013                 int lost = missed;
1014
1015                 missed = 0;
1016                 toks -= ratelimit_jiffies;
1017                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1018                 if (lost)
1019                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1020                 return 1;
1021         }
1022         missed++;
1023         spin_unlock_irqrestore(&ratelimit_lock, flags);
1024         return 0;
1025 }
1026 EXPORT_SYMBOL(__printk_ratelimit);
1027
1028 /* minimum time in jiffies between messages */
1029 int printk_ratelimit_jiffies = 5 * HZ;
1030
1031 /* number of messages we send before ratelimiting */
1032 int printk_ratelimit_burst = 10;
1033
1034 int printk_ratelimit(void)
1035 {
1036         return __printk_ratelimit(printk_ratelimit_jiffies,
1037                                 printk_ratelimit_burst);
1038 }
1039 EXPORT_SYMBOL(printk_ratelimit);