header cleaning: don't include smp_lock.h when not used
[linux-2.6.git] / kernel / printk.c
1 /*
2  *  linux/kernel/printk.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *
6  * Modified to make sys_syslog() more flexible: added commands to
7  * return the last 4k of kernel messages, regardless of whether
8  * they've been read or not.  Added option to suppress kernel printk's
9  * to the console.  Added hook for sending the console messages
10  * elsewhere, in preparation for a serial line console (someday).
11  * Ted Ts'o, 2/11/93.
12  * Modified for sysctl support, 1/8/97, Chris Horn.
13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14  *     manfred@colorfullife.com
15  * Rewrote bits to get rid of console_lock
16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
17  */
18
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/console.h>
24 #include <linux/init.h>
25 #include <linux/module.h>
26 #include <linux/moduleparam.h>
27 #include <linux/interrupt.h>                    /* For in_interrupt() */
28 #include <linux/delay.h>
29 #include <linux/smp.h>
30 #include <linux/security.h>
31 #include <linux/bootmem.h>
32 #include <linux/syscalls.h>
33 #include <linux/jiffies.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 /*
56  * Low level drivers may need that to know if they can schedule in
57  * their unblank() callback or not. So let's export it.
58  */
59 int oops_in_progress;
60 EXPORT_SYMBOL(oops_in_progress);
61
62 /*
63  * console_sem protects the console_drivers list, and also
64  * provides serialisation for access to the entire console
65  * driver system.
66  */
67 static DECLARE_MUTEX(console_sem);
68 static DECLARE_MUTEX(secondary_console_sem);
69 struct console *console_drivers;
70 /*
71  * This is used for debugging the mess that is the VT code by
72  * keeping track if we have the console semaphore held. It's
73  * definitely not the perfect debug tool (we don't know if _WE_
74  * hold it are racing, but it helps tracking those weird code
75  * path in the console code where we end up in places I want
76  * locked without the console sempahore held
77  */
78 static int console_locked, console_suspended;
79
80 /*
81  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
82  * It is also used in interesting ways to provide interlocking in
83  * release_console_sem().
84  */
85 static DEFINE_SPINLOCK(logbuf_lock);
86
87 #define LOG_BUF_MASK    (log_buf_len-1)
88 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
89
90 /*
91  * The indices into log_buf are not constrained to log_buf_len - they
92  * must be masked before subscripting
93  */
94 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
95 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
96 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
97
98 /*
99  *      Array of consoles built from command line options (console=)
100  */
101 struct console_cmdline
102 {
103         char    name[8];                        /* Name of the driver       */
104         int     index;                          /* Minor dev. to use        */
105         char    *options;                       /* Options for the driver   */
106 };
107
108 #define MAX_CMDLINECONSOLES 8
109
110 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
111 static int selected_console = -1;
112 static int preferred_console = -1;
113
114 /* Flag: console code may call schedule() */
115 static int console_may_schedule;
116
117 #ifdef CONFIG_PRINTK
118
119 static char __log_buf[__LOG_BUF_LEN];
120 static char *log_buf = __log_buf;
121 static int log_buf_len = __LOG_BUF_LEN;
122 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
123
124 static int __init log_buf_len_setup(char *str)
125 {
126         unsigned long size = memparse(str, &str);
127         unsigned long flags;
128
129         if (size)
130                 size = roundup_pow_of_two(size);
131         if (size > log_buf_len) {
132                 unsigned long start, dest_idx, offset;
133                 char *new_log_buf;
134
135                 new_log_buf = alloc_bootmem(size);
136                 if (!new_log_buf) {
137                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
138                         goto out;
139                 }
140
141                 spin_lock_irqsave(&logbuf_lock, flags);
142                 log_buf_len = size;
143                 log_buf = new_log_buf;
144
145                 offset = start = min(con_start, log_start);
146                 dest_idx = 0;
147                 while (start != log_end) {
148                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
149                         start++;
150                         dest_idx++;
151                 }
152                 log_start -= offset;
153                 con_start -= offset;
154                 log_end -= offset;
155                 spin_unlock_irqrestore(&logbuf_lock, flags);
156
157                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
158         }
159 out:
160         return 1;
161 }
162
163 __setup("log_buf_len=", log_buf_len_setup);
164
165 /*
166  * Commands to do_syslog:
167  *
168  *      0 -- Close the log.  Currently a NOP.
169  *      1 -- Open the log. Currently a NOP.
170  *      2 -- Read from the log.
171  *      3 -- Read all messages remaining in the ring buffer.
172  *      4 -- Read and clear all messages remaining in the ring buffer
173  *      5 -- Clear ring buffer.
174  *      6 -- Disable printk's to console
175  *      7 -- Enable printk's to console
176  *      8 -- Set level of messages printed to console
177  *      9 -- Return number of unread characters in the log buffer
178  *     10 -- Return size of the log buffer
179  */
180 int do_syslog(int type, char __user *buf, int len)
181 {
182         unsigned long i, j, limit, count;
183         int do_clear = 0;
184         char c;
185         int error = 0;
186
187         error = security_syslog(type);
188         if (error)
189                 return error;
190
191         switch (type) {
192         case 0:         /* Close log */
193                 break;
194         case 1:         /* Open log */
195                 break;
196         case 2:         /* Read from log */
197                 error = -EINVAL;
198                 if (!buf || len < 0)
199                         goto out;
200                 error = 0;
201                 if (!len)
202                         goto out;
203                 if (!access_ok(VERIFY_WRITE, buf, len)) {
204                         error = -EFAULT;
205                         goto out;
206                 }
207                 error = wait_event_interruptible(log_wait,
208                                                         (log_start - log_end));
209                 if (error)
210                         goto out;
211                 i = 0;
212                 spin_lock_irq(&logbuf_lock);
213                 while (!error && (log_start != log_end) && i < len) {
214                         c = LOG_BUF(log_start);
215                         log_start++;
216                         spin_unlock_irq(&logbuf_lock);
217                         error = __put_user(c,buf);
218                         buf++;
219                         i++;
220                         cond_resched();
221                         spin_lock_irq(&logbuf_lock);
222                 }
223                 spin_unlock_irq(&logbuf_lock);
224                 if (!error)
225                         error = i;
226                 break;
227         case 4:         /* Read/clear last kernel messages */
228                 do_clear = 1;
229                 /* FALL THRU */
230         case 3:         /* Read last kernel messages */
231                 error = -EINVAL;
232                 if (!buf || len < 0)
233                         goto out;
234                 error = 0;
235                 if (!len)
236                         goto out;
237                 if (!access_ok(VERIFY_WRITE, buf, len)) {
238                         error = -EFAULT;
239                         goto out;
240                 }
241                 count = len;
242                 if (count > log_buf_len)
243                         count = log_buf_len;
244                 spin_lock_irq(&logbuf_lock);
245                 if (count > logged_chars)
246                         count = logged_chars;
247                 if (do_clear)
248                         logged_chars = 0;
249                 limit = log_end;
250                 /*
251                  * __put_user() could sleep, and while we sleep
252                  * printk() could overwrite the messages
253                  * we try to copy to user space. Therefore
254                  * the messages are copied in reverse. <manfreds>
255                  */
256                 for (i = 0; i < count && !error; i++) {
257                         j = limit-1-i;
258                         if (j + log_buf_len < log_end)
259                                 break;
260                         c = LOG_BUF(j);
261                         spin_unlock_irq(&logbuf_lock);
262                         error = __put_user(c,&buf[count-1-i]);
263                         cond_resched();
264                         spin_lock_irq(&logbuf_lock);
265                 }
266                 spin_unlock_irq(&logbuf_lock);
267                 if (error)
268                         break;
269                 error = i;
270                 if (i != count) {
271                         int offset = count-error;
272                         /* buffer overflow during copy, correct user buffer. */
273                         for (i = 0; i < error; i++) {
274                                 if (__get_user(c,&buf[i+offset]) ||
275                                     __put_user(c,&buf[i])) {
276                                         error = -EFAULT;
277                                         break;
278                                 }
279                                 cond_resched();
280                         }
281                 }
282                 break;
283         case 5:         /* Clear ring buffer */
284                 logged_chars = 0;
285                 break;
286         case 6:         /* Disable logging to console */
287                 console_loglevel = minimum_console_loglevel;
288                 break;
289         case 7:         /* Enable logging to console */
290                 console_loglevel = default_console_loglevel;
291                 break;
292         case 8:         /* Set level of messages printed to console */
293                 error = -EINVAL;
294                 if (len < 1 || len > 8)
295                         goto out;
296                 if (len < minimum_console_loglevel)
297                         len = minimum_console_loglevel;
298                 console_loglevel = len;
299                 error = 0;
300                 break;
301         case 9:         /* Number of chars in the log buffer */
302                 error = log_end - log_start;
303                 break;
304         case 10:        /* Size of the log buffer */
305                 error = log_buf_len;
306                 break;
307         default:
308                 error = -EINVAL;
309                 break;
310         }
311 out:
312         return error;
313 }
314
315 asmlinkage long sys_syslog(int type, char __user *buf, int len)
316 {
317         return do_syslog(type, buf, len);
318 }
319
320 /*
321  * Call the console drivers on a range of log_buf
322  */
323 static void __call_console_drivers(unsigned long start, unsigned long end)
324 {
325         struct console *con;
326
327         for (con = console_drivers; con; con = con->next) {
328                 if ((con->flags & CON_ENABLED) && con->write &&
329                                 (cpu_online(smp_processor_id()) ||
330                                 (con->flags & CON_ANYTIME)))
331                         con->write(con, &LOG_BUF(start), end - start);
332         }
333 }
334
335 static int __read_mostly ignore_loglevel;
336
337 static int __init ignore_loglevel_setup(char *str)
338 {
339         ignore_loglevel = 1;
340         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
341
342         return 1;
343 }
344
345 __setup("ignore_loglevel", ignore_loglevel_setup);
346
347 /*
348  * Write out chars from start to end - 1 inclusive
349  */
350 static void _call_console_drivers(unsigned long start,
351                                 unsigned long end, int msg_log_level)
352 {
353         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
354                         console_drivers && start != end) {
355                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
356                         /* wrapped write */
357                         __call_console_drivers(start & LOG_BUF_MASK,
358                                                 log_buf_len);
359                         __call_console_drivers(0, end & LOG_BUF_MASK);
360                 } else {
361                         __call_console_drivers(start, end);
362                 }
363         }
364 }
365
366 /*
367  * Call the console drivers, asking them to write out
368  * log_buf[start] to log_buf[end - 1].
369  * The console_sem must be held.
370  */
371 static void call_console_drivers(unsigned long start, unsigned long end)
372 {
373         unsigned long cur_index, start_print;
374         static int msg_level = -1;
375
376         BUG_ON(((long)(start - end)) > 0);
377
378         cur_index = start;
379         start_print = start;
380         while (cur_index != end) {
381                 if (msg_level < 0 && ((end - cur_index) > 2) &&
382                                 LOG_BUF(cur_index + 0) == '<' &&
383                                 LOG_BUF(cur_index + 1) >= '0' &&
384                                 LOG_BUF(cur_index + 1) <= '7' &&
385                                 LOG_BUF(cur_index + 2) == '>') {
386                         msg_level = LOG_BUF(cur_index + 1) - '0';
387                         cur_index += 3;
388                         start_print = cur_index;
389                 }
390                 while (cur_index != end) {
391                         char c = LOG_BUF(cur_index);
392
393                         cur_index++;
394                         if (c == '\n') {
395                                 if (msg_level < 0) {
396                                         /*
397                                          * printk() has already given us loglevel tags in
398                                          * the buffer.  This code is here in case the
399                                          * log buffer has wrapped right round and scribbled
400                                          * on those tags
401                                          */
402                                         msg_level = default_message_loglevel;
403                                 }
404                                 _call_console_drivers(start_print, cur_index, msg_level);
405                                 msg_level = -1;
406                                 start_print = cur_index;
407                                 break;
408                         }
409                 }
410         }
411         _call_console_drivers(start_print, end, msg_level);
412 }
413
414 static void emit_log_char(char c)
415 {
416         LOG_BUF(log_end) = c;
417         log_end++;
418         if (log_end - log_start > log_buf_len)
419                 log_start = log_end - log_buf_len;
420         if (log_end - con_start > log_buf_len)
421                 con_start = log_end - log_buf_len;
422         if (logged_chars < log_buf_len)
423                 logged_chars++;
424 }
425
426 /*
427  * Zap console related locks when oopsing. Only zap at most once
428  * every 10 seconds, to leave time for slow consoles to print a
429  * full oops.
430  */
431 static void zap_locks(void)
432 {
433         static unsigned long oops_timestamp;
434
435         if (time_after_eq(jiffies, oops_timestamp) &&
436                         !time_after(jiffies, oops_timestamp + 30 * HZ))
437                 return;
438
439         oops_timestamp = jiffies;
440
441         /* If a crash is occurring, make sure we can't deadlock */
442         spin_lock_init(&logbuf_lock);
443         /* And make sure that we print immediately */
444         init_MUTEX(&console_sem);
445 }
446
447 #if defined(CONFIG_PRINTK_TIME)
448 static int printk_time = 1;
449 #else
450 static int printk_time = 0;
451 #endif
452 module_param(printk_time, int, S_IRUGO | S_IWUSR);
453
454 static int __init printk_time_setup(char *str)
455 {
456         if (*str)
457                 return 0;
458         printk_time = 1;
459         return 1;
460 }
461
462 __setup("time", printk_time_setup);
463
464 __attribute__((weak)) unsigned long long printk_clock(void)
465 {
466         return sched_clock();
467 }
468
469 /* Check if we have any console registered that can be called early in boot. */
470 static int have_callable_console(void)
471 {
472         struct console *con;
473
474         for (con = console_drivers; con; con = con->next)
475                 if (con->flags & CON_ANYTIME)
476                         return 1;
477
478         return 0;
479 }
480
481 /**
482  * printk - print a kernel message
483  * @fmt: format string
484  *
485  * This is printk().  It can be called from any context.  We want it to work.
486  *
487  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
488  * call the console drivers.  If we fail to get the semaphore we place the output
489  * into the log buffer and return.  The current holder of the console_sem will
490  * notice the new output in release_console_sem() and will send it to the
491  * consoles before releasing the semaphore.
492  *
493  * One effect of this deferred printing is that code which calls printk() and
494  * then changes console_loglevel may break. This is because console_loglevel
495  * is inspected when the actual printing occurs.
496  *
497  * See also:
498  * printf(3)
499  */
500
501 asmlinkage int printk(const char *fmt, ...)
502 {
503         va_list args;
504         int r;
505
506         va_start(args, fmt);
507         r = vprintk(fmt, args);
508         va_end(args);
509
510         return r;
511 }
512
513 /* cpu currently holding logbuf_lock */
514 static volatile unsigned int printk_cpu = UINT_MAX;
515
516 asmlinkage int vprintk(const char *fmt, va_list args)
517 {
518         unsigned long flags;
519         int printed_len;
520         char *p;
521         static char printk_buf[1024];
522         static int log_level_unknown = 1;
523
524         preempt_disable();
525         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
526                 /* If a crash is occurring during printk() on this CPU,
527                  * make sure we can't deadlock */
528                 zap_locks();
529
530         /* This stops the holder of console_sem just where we want him */
531         raw_local_irq_save(flags);
532         lockdep_off();
533         spin_lock(&logbuf_lock);
534         printk_cpu = smp_processor_id();
535
536         /* Emit the output into the temporary buffer */
537         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
538
539         /*
540          * Copy the output into log_buf.  If the caller didn't provide
541          * appropriate log level tags, we insert them here
542          */
543         for (p = printk_buf; *p; p++) {
544                 if (log_level_unknown) {
545                         /* log_level_unknown signals the start of a new line */
546                         if (printk_time) {
547                                 int loglev_char;
548                                 char tbuf[50], *tp;
549                                 unsigned tlen;
550                                 unsigned long long t;
551                                 unsigned long nanosec_rem;
552
553                                 /*
554                                  * force the log level token to be
555                                  * before the time output.
556                                  */
557                                 if (p[0] == '<' && p[1] >='0' &&
558                                    p[1] <= '7' && p[2] == '>') {
559                                         loglev_char = p[1];
560                                         p += 3;
561                                         printed_len -= 3;
562                                 } else {
563                                         loglev_char = default_message_loglevel
564                                                 + '0';
565                                 }
566                                 t = printk_clock();
567                                 nanosec_rem = do_div(t, 1000000000);
568                                 tlen = sprintf(tbuf,
569                                                 "<%c>[%5lu.%06lu] ",
570                                                 loglev_char,
571                                                 (unsigned long)t,
572                                                 nanosec_rem/1000);
573
574                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
575                                         emit_log_char(*tp);
576                                 printed_len += tlen;
577                         } else {
578                                 if (p[0] != '<' || p[1] < '0' ||
579                                    p[1] > '7' || p[2] != '>') {
580                                         emit_log_char('<');
581                                         emit_log_char(default_message_loglevel
582                                                 + '0');
583                                         emit_log_char('>');
584                                         printed_len += 3;
585                                 }
586                         }
587                         log_level_unknown = 0;
588                         if (!*p)
589                                 break;
590                 }
591                 emit_log_char(*p);
592                 if (*p == '\n')
593                         log_level_unknown = 1;
594         }
595
596         if (!down_trylock(&console_sem)) {
597                 /*
598                  * We own the drivers.  We can drop the spinlock and
599                  * let release_console_sem() print the text, maybe ...
600                  */
601                 console_locked = 1;
602                 printk_cpu = UINT_MAX;
603                 spin_unlock(&logbuf_lock);
604
605                 /*
606                  * Console drivers may assume that per-cpu resources have
607                  * been allocated. So unless they're explicitly marked as
608                  * being able to cope (CON_ANYTIME) don't call them until
609                  * this CPU is officially up.
610                  */
611                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
612                         console_may_schedule = 0;
613                         release_console_sem();
614                 } else {
615                         /* Release by hand to avoid flushing the buffer. */
616                         console_locked = 0;
617                         up(&console_sem);
618                 }
619                 lockdep_on();
620                 raw_local_irq_restore(flags);
621         } else {
622                 /*
623                  * Someone else owns the drivers.  We drop the spinlock, which
624                  * allows the semaphore holder to proceed and to call the
625                  * console drivers with the output which we just produced.
626                  */
627                 printk_cpu = UINT_MAX;
628                 spin_unlock(&logbuf_lock);
629                 lockdep_on();
630                 raw_local_irq_restore(flags);
631         }
632
633         preempt_enable();
634         return printed_len;
635 }
636 EXPORT_SYMBOL(printk);
637 EXPORT_SYMBOL(vprintk);
638
639 #else
640
641 asmlinkage long sys_syslog(int type, char __user *buf, int len)
642 {
643         return -ENOSYS;
644 }
645
646 static void call_console_drivers(unsigned long start, unsigned long end)
647 {
648 }
649
650 #endif
651
652 /*
653  * Set up a list of consoles.  Called from init/main.c
654  */
655 static int __init console_setup(char *str)
656 {
657         char name[sizeof(console_cmdline[0].name)];
658         char *s, *options;
659         int idx;
660
661         /*
662          * Decode str into name, index, options.
663          */
664         if (str[0] >= '0' && str[0] <= '9') {
665                 strcpy(name, "ttyS");
666                 strncpy(name + 4, str, sizeof(name) - 5);
667         } else {
668                 strncpy(name, str, sizeof(name) - 1);
669         }
670         name[sizeof(name) - 1] = 0;
671         if ((options = strchr(str, ',')) != NULL)
672                 *(options++) = 0;
673 #ifdef __sparc__
674         if (!strcmp(str, "ttya"))
675                 strcpy(name, "ttyS0");
676         if (!strcmp(str, "ttyb"))
677                 strcpy(name, "ttyS1");
678 #endif
679         for (s = name; *s; s++)
680                 if ((*s >= '0' && *s <= '9') || *s == ',')
681                         break;
682         idx = simple_strtoul(s, NULL, 10);
683         *s = 0;
684
685         add_preferred_console(name, idx, options);
686         return 1;
687 }
688 __setup("console=", console_setup);
689
690 /**
691  * add_preferred_console - add a device to the list of preferred consoles.
692  * @name: device name
693  * @idx: device index
694  * @options: options for this console
695  *
696  * The last preferred console added will be used for kernel messages
697  * and stdin/out/err for init.  Normally this is used by console_setup
698  * above to handle user-supplied console arguments; however it can also
699  * be used by arch-specific code either to override the user or more
700  * commonly to provide a default console (ie from PROM variables) when
701  * the user has not supplied one.
702  */
703 int __init add_preferred_console(char *name, int idx, char *options)
704 {
705         struct console_cmdline *c;
706         int i;
707
708         /*
709          *      See if this tty is not yet registered, and
710          *      if we have a slot free.
711          */
712         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
713                 if (strcmp(console_cmdline[i].name, name) == 0 &&
714                           console_cmdline[i].index == idx) {
715                                 selected_console = i;
716                                 return 0;
717                 }
718         if (i == MAX_CMDLINECONSOLES)
719                 return -E2BIG;
720         selected_console = i;
721         c = &console_cmdline[i];
722         memcpy(c->name, name, sizeof(c->name));
723         c->name[sizeof(c->name) - 1] = 0;
724         c->options = options;
725         c->index = idx;
726         return 0;
727 }
728
729 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
730 /**
731  * suspend_console - suspend the console subsystem
732  *
733  * This disables printk() while we go into suspend states
734  */
735 void suspend_console(void)
736 {
737         printk("Suspending console(s)\n");
738         acquire_console_sem();
739         console_suspended = 1;
740 }
741
742 void resume_console(void)
743 {
744         console_suspended = 0;
745         release_console_sem();
746 }
747 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
748
749 /**
750  * acquire_console_sem - lock the console system for exclusive use.
751  *
752  * Acquires a semaphore which guarantees that the caller has
753  * exclusive access to the console system and the console_drivers list.
754  *
755  * Can sleep, returns nothing.
756  */
757 void acquire_console_sem(void)
758 {
759         BUG_ON(in_interrupt());
760         if (console_suspended) {
761                 down(&secondary_console_sem);
762                 return;
763         }
764         down(&console_sem);
765         console_locked = 1;
766         console_may_schedule = 1;
767 }
768 EXPORT_SYMBOL(acquire_console_sem);
769
770 int try_acquire_console_sem(void)
771 {
772         if (down_trylock(&console_sem))
773                 return -1;
774         console_locked = 1;
775         console_may_schedule = 0;
776         return 0;
777 }
778 EXPORT_SYMBOL(try_acquire_console_sem);
779
780 int is_console_locked(void)
781 {
782         return console_locked;
783 }
784
785 void wake_up_klogd(void)
786 {
787         if (!oops_in_progress && waitqueue_active(&log_wait))
788                 wake_up_interruptible(&log_wait);
789 }
790
791 /**
792  * release_console_sem - unlock the console system
793  *
794  * Releases the semaphore which the caller holds on the console system
795  * and the console driver list.
796  *
797  * While the semaphore was held, console output may have been buffered
798  * by printk().  If this is the case, release_console_sem() emits
799  * the output prior to releasing the semaphore.
800  *
801  * If there is output waiting for klogd, we wake it up.
802  *
803  * release_console_sem() may be called from any context.
804  */
805 void release_console_sem(void)
806 {
807         unsigned long flags;
808         unsigned long _con_start, _log_end;
809         unsigned long wake_klogd = 0;
810
811         if (console_suspended) {
812                 up(&secondary_console_sem);
813                 return;
814         }
815
816         console_may_schedule = 0;
817
818         for ( ; ; ) {
819                 spin_lock_irqsave(&logbuf_lock, flags);
820                 wake_klogd |= log_start - log_end;
821                 if (con_start == log_end)
822                         break;                  /* Nothing to print */
823                 _con_start = con_start;
824                 _log_end = log_end;
825                 con_start = log_end;            /* Flush */
826                 spin_unlock(&logbuf_lock);
827                 call_console_drivers(_con_start, _log_end);
828                 local_irq_restore(flags);
829         }
830         console_locked = 0;
831         up(&console_sem);
832         spin_unlock_irqrestore(&logbuf_lock, flags);
833         if (wake_klogd)
834                 wake_up_klogd();
835 }
836 EXPORT_SYMBOL(release_console_sem);
837
838 /**
839  * console_conditional_schedule - yield the CPU if required
840  *
841  * If the console code is currently allowed to sleep, and
842  * if this CPU should yield the CPU to another task, do
843  * so here.
844  *
845  * Must be called within acquire_console_sem().
846  */
847 void __sched console_conditional_schedule(void)
848 {
849         if (console_may_schedule)
850                 cond_resched();
851 }
852 EXPORT_SYMBOL(console_conditional_schedule);
853
854 void console_print(const char *s)
855 {
856         printk(KERN_EMERG "%s", s);
857 }
858 EXPORT_SYMBOL(console_print);
859
860 void console_unblank(void)
861 {
862         struct console *c;
863
864         /*
865          * console_unblank can no longer be called in interrupt context unless
866          * oops_in_progress is set to 1..
867          */
868         if (oops_in_progress) {
869                 if (down_trylock(&console_sem) != 0)
870                         return;
871         } else
872                 acquire_console_sem();
873
874         console_locked = 1;
875         console_may_schedule = 0;
876         for (c = console_drivers; c != NULL; c = c->next)
877                 if ((c->flags & CON_ENABLED) && c->unblank)
878                         c->unblank();
879         release_console_sem();
880 }
881
882 /*
883  * Return the console tty driver structure and its associated index
884  */
885 struct tty_driver *console_device(int *index)
886 {
887         struct console *c;
888         struct tty_driver *driver = NULL;
889
890         acquire_console_sem();
891         for (c = console_drivers; c != NULL; c = c->next) {
892                 if (!c->device)
893                         continue;
894                 driver = c->device(c, index);
895                 if (driver)
896                         break;
897         }
898         release_console_sem();
899         return driver;
900 }
901
902 /*
903  * Prevent further output on the passed console device so that (for example)
904  * serial drivers can disable console output before suspending a port, and can
905  * re-enable output afterwards.
906  */
907 void console_stop(struct console *console)
908 {
909         acquire_console_sem();
910         console->flags &= ~CON_ENABLED;
911         release_console_sem();
912 }
913 EXPORT_SYMBOL(console_stop);
914
915 void console_start(struct console *console)
916 {
917         acquire_console_sem();
918         console->flags |= CON_ENABLED;
919         release_console_sem();
920 }
921 EXPORT_SYMBOL(console_start);
922
923 /*
924  * The console driver calls this routine during kernel initialization
925  * to register the console printing procedure with printk() and to
926  * print any messages that were printed by the kernel before the
927  * console driver was initialized.
928  */
929 void register_console(struct console *console)
930 {
931         int i;
932         unsigned long flags;
933         struct console *bootconsole = NULL;
934
935         if (console_drivers) {
936                 if (console->flags & CON_BOOT)
937                         return;
938                 if (console_drivers->flags & CON_BOOT)
939                         bootconsole = console_drivers;
940         }
941
942         if (preferred_console < 0 || bootconsole || !console_drivers)
943                 preferred_console = selected_console;
944
945         /*
946          *      See if we want to use this console driver. If we
947          *      didn't select a console we take the first one
948          *      that registers here.
949          */
950         if (preferred_console < 0) {
951                 if (console->index < 0)
952                         console->index = 0;
953                 if (console->setup == NULL ||
954                     console->setup(console, NULL) == 0) {
955                         console->flags |= CON_ENABLED | CON_CONSDEV;
956                         preferred_console = 0;
957                 }
958         }
959
960         /*
961          *      See if this console matches one we selected on
962          *      the command line.
963          */
964         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
965                         i++) {
966                 if (strcmp(console_cmdline[i].name, console->name) != 0)
967                         continue;
968                 if (console->index >= 0 &&
969                     console->index != console_cmdline[i].index)
970                         continue;
971                 if (console->index < 0)
972                         console->index = console_cmdline[i].index;
973                 if (console->setup &&
974                     console->setup(console, console_cmdline[i].options) != 0)
975                         break;
976                 console->flags |= CON_ENABLED;
977                 console->index = console_cmdline[i].index;
978                 if (i == selected_console) {
979                         console->flags |= CON_CONSDEV;
980                         preferred_console = selected_console;
981                 }
982                 break;
983         }
984
985         if (!(console->flags & CON_ENABLED))
986                 return;
987
988         if (bootconsole) {
989                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
990                        bootconsole->name, bootconsole->index,
991                        console->name, console->index);
992                 unregister_console(bootconsole);
993                 console->flags &= ~CON_PRINTBUFFER;
994         }
995
996         /*
997          *      Put this console in the list - keep the
998          *      preferred driver at the head of the list.
999          */
1000         acquire_console_sem();
1001         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1002                 console->next = console_drivers;
1003                 console_drivers = console;
1004                 if (console->next)
1005                         console->next->flags &= ~CON_CONSDEV;
1006         } else {
1007                 console->next = console_drivers->next;
1008                 console_drivers->next = console;
1009         }
1010         if (console->flags & CON_PRINTBUFFER) {
1011                 /*
1012                  * release_console_sem() will print out the buffered messages
1013                  * for us.
1014                  */
1015                 spin_lock_irqsave(&logbuf_lock, flags);
1016                 con_start = log_start;
1017                 spin_unlock_irqrestore(&logbuf_lock, flags);
1018         }
1019         release_console_sem();
1020 }
1021 EXPORT_SYMBOL(register_console);
1022
1023 int unregister_console(struct console *console)
1024 {
1025         struct console *a, *b;
1026         int res = 1;
1027
1028         acquire_console_sem();
1029         if (console_drivers == console) {
1030                 console_drivers=console->next;
1031                 res = 0;
1032         } else if (console_drivers) {
1033                 for (a=console_drivers->next, b=console_drivers ;
1034                      a; b=a, a=b->next) {
1035                         if (a == console) {
1036                                 b->next = a->next;
1037                                 res = 0;
1038                                 break;
1039                         }
1040                 }
1041         }
1042
1043         /*
1044          * If this isn't the last console and it has CON_CONSDEV set, we
1045          * need to set it on the next preferred console.
1046          */
1047         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1048                 console_drivers->flags |= CON_CONSDEV;
1049
1050         release_console_sem();
1051         return res;
1052 }
1053 EXPORT_SYMBOL(unregister_console);
1054
1055 /**
1056  * tty_write_message - write a message to a certain tty, not just the console.
1057  * @tty: the destination tty_struct
1058  * @msg: the message to write
1059  *
1060  * This is used for messages that need to be redirected to a specific tty.
1061  * We don't put it into the syslog queue right now maybe in the future if
1062  * really needed.
1063  */
1064 void tty_write_message(struct tty_struct *tty, char *msg)
1065 {
1066         if (tty && tty->driver->write)
1067                 tty->driver->write(tty, msg, strlen(msg));
1068         return;
1069 }
1070
1071 /*
1072  * printk rate limiting, lifted from the networking subsystem.
1073  *
1074  * This enforces a rate limit: not more than one kernel message
1075  * every printk_ratelimit_jiffies to make a denial-of-service
1076  * attack impossible.
1077  */
1078 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1079 {
1080         static DEFINE_SPINLOCK(ratelimit_lock);
1081         static unsigned long toks = 10 * 5 * HZ;
1082         static unsigned long last_msg;
1083         static int missed;
1084         unsigned long flags;
1085         unsigned long now = jiffies;
1086
1087         spin_lock_irqsave(&ratelimit_lock, flags);
1088         toks += now - last_msg;
1089         last_msg = now;
1090         if (toks > (ratelimit_burst * ratelimit_jiffies))
1091                 toks = ratelimit_burst * ratelimit_jiffies;
1092         if (toks >= ratelimit_jiffies) {
1093                 int lost = missed;
1094
1095                 missed = 0;
1096                 toks -= ratelimit_jiffies;
1097                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1098                 if (lost)
1099                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1100                 return 1;
1101         }
1102         missed++;
1103         spin_unlock_irqrestore(&ratelimit_lock, flags);
1104         return 0;
1105 }
1106 EXPORT_SYMBOL(__printk_ratelimit);
1107
1108 /* minimum time in jiffies between messages */
1109 int printk_ratelimit_jiffies = 5 * HZ;
1110
1111 /* number of messages we send before ratelimiting */
1112 int printk_ratelimit_burst = 10;
1113
1114 int printk_ratelimit(void)
1115 {
1116         return __printk_ratelimit(printk_ratelimit_jiffies,
1117                                 printk_ratelimit_burst);
1118 }
1119 EXPORT_SYMBOL(printk_ratelimit);
1120
1121 /**
1122  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1123  * @caller_jiffies: pointer to caller's state
1124  * @interval_msecs: minimum interval between prints
1125  *
1126  * printk_timed_ratelimit() returns true if more than @interval_msecs
1127  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1128  * returned true.
1129  */
1130 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1131                         unsigned int interval_msecs)
1132 {
1133         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1134                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1135                 return true;
1136         }
1137         return false;
1138 }
1139 EXPORT_SYMBOL(printk_timed_ratelimit);