Merge branch 'master'
[linux-2.6.git] / kernel / printk.c
1 /*
2  *  linux/kernel/printk.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *
6  * Modified to make sys_syslog() more flexible: added commands to
7  * return the last 4k of kernel messages, regardless of whether
8  * they've been read or not.  Added option to suppress kernel printk's
9  * to the console.  Added hook for sending the console messages
10  * elsewhere, in preparation for a serial line console (someday).
11  * Ted Ts'o, 2/11/93.
12  * Modified for sysctl support, 1/8/97, Chris Horn.
13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14  *     manfred@colorfullife.com
15  * Rewrote bits to get rid of console_lock
16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
17  */
18
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/smp_lock.h>
24 #include <linux/console.h>
25 #include <linux/init.h>
26 #include <linux/module.h>
27 #include <linux/interrupt.h>                    /* For in_interrupt() */
28 #include <linux/config.h>
29 #include <linux/delay.h>
30 #include <linux/smp.h>
31 #include <linux/security.h>
32 #include <linux/bootmem.h>
33 #include <linux/syscalls.h>
34
35 #include <asm/uaccess.h>
36
37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
38
39 /* printk's without a loglevel use this.. */
40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
41
42 /* We show everything that is MORE important than this.. */
43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
45
46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
47
48 int console_printk[4] = {
49         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
50         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
51         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
52         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
53 };
54
55 EXPORT_SYMBOL(console_printk);
56
57 /*
58  * Low lever drivers may need that to know if they can schedule in
59  * their unblank() callback or not. So let's export it.
60  */
61 int oops_in_progress;
62 EXPORT_SYMBOL(oops_in_progress);
63
64 /*
65  * console_sem protects the console_drivers list, and also
66  * provides serialisation for access to the entire console
67  * driver system.
68  */
69 static DECLARE_MUTEX(console_sem);
70 static DECLARE_MUTEX(secondary_console_sem);
71 struct console *console_drivers;
72 /*
73  * This is used for debugging the mess that is the VT code by
74  * keeping track if we have the console semaphore held. It's
75  * definitely not the perfect debug tool (we don't know if _WE_
76  * hold it are racing, but it helps tracking those weird code
77  * path in the console code where we end up in places I want
78  * locked without the console sempahore held
79  */
80 static int console_locked, console_suspended;
81
82 /*
83  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
84  * It is also used in interesting ways to provide interlocking in
85  * release_console_sem().
86  */
87 static DEFINE_SPINLOCK(logbuf_lock);
88
89 #define LOG_BUF_MASK    (log_buf_len-1)
90 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
91
92 /*
93  * The indices into log_buf are not constrained to log_buf_len - they
94  * must be masked before subscripting
95  */
96 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
97 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
98 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
99
100 /*
101  *      Array of consoles built from command line options (console=)
102  */
103 struct console_cmdline
104 {
105         char    name[8];                        /* Name of the driver       */
106         int     index;                          /* Minor dev. to use        */
107         char    *options;                       /* Options for the driver   */
108 };
109
110 #define MAX_CMDLINECONSOLES 8
111
112 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
113 static int selected_console = -1;
114 static int preferred_console = -1;
115
116 /* Flag: console code may call schedule() */
117 static int console_may_schedule;
118
119 #ifdef CONFIG_PRINTK
120
121 static char __log_buf[__LOG_BUF_LEN];
122 static char *log_buf = __log_buf;
123 static int log_buf_len = __LOG_BUF_LEN;
124 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
125
126 static int __init log_buf_len_setup(char *str)
127 {
128         unsigned long size = memparse(str, &str);
129         unsigned long flags;
130
131         if (size)
132                 size = roundup_pow_of_two(size);
133         if (size > log_buf_len) {
134                 unsigned long start, dest_idx, offset;
135                 char *new_log_buf;
136
137                 new_log_buf = alloc_bootmem(size);
138                 if (!new_log_buf) {
139                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
140                         goto out;
141                 }
142
143                 spin_lock_irqsave(&logbuf_lock, flags);
144                 log_buf_len = size;
145                 log_buf = new_log_buf;
146
147                 offset = start = min(con_start, log_start);
148                 dest_idx = 0;
149                 while (start != log_end) {
150                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
151                         start++;
152                         dest_idx++;
153                 }
154                 log_start -= offset;
155                 con_start -= offset;
156                 log_end -= offset;
157                 spin_unlock_irqrestore(&logbuf_lock, flags);
158
159                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
160         }
161 out:
162         return 1;
163 }
164
165 __setup("log_buf_len=", log_buf_len_setup);
166
167 /*
168  * Commands to do_syslog:
169  *
170  *      0 -- Close the log.  Currently a NOP.
171  *      1 -- Open the log. Currently a NOP.
172  *      2 -- Read from the log.
173  *      3 -- Read all messages remaining in the ring buffer.
174  *      4 -- Read and clear all messages remaining in the ring buffer
175  *      5 -- Clear ring buffer.
176  *      6 -- Disable printk's to console
177  *      7 -- Enable printk's to console
178  *      8 -- Set level of messages printed to console
179  *      9 -- Return number of unread characters in the log buffer
180  *     10 -- Return size of the log buffer
181  */
182 int do_syslog(int type, char __user *buf, int len)
183 {
184         unsigned long i, j, limit, count;
185         int do_clear = 0;
186         char c;
187         int error = 0;
188
189         error = security_syslog(type);
190         if (error)
191                 return error;
192
193         switch (type) {
194         case 0:         /* Close log */
195                 break;
196         case 1:         /* Open log */
197                 break;
198         case 2:         /* Read from log */
199                 error = -EINVAL;
200                 if (!buf || len < 0)
201                         goto out;
202                 error = 0;
203                 if (!len)
204                         goto out;
205                 if (!access_ok(VERIFY_WRITE, buf, len)) {
206                         error = -EFAULT;
207                         goto out;
208                 }
209                 error = wait_event_interruptible(log_wait,
210                                                         (log_start - log_end));
211                 if (error)
212                         goto out;
213                 i = 0;
214                 spin_lock_irq(&logbuf_lock);
215                 while (!error && (log_start != log_end) && i < len) {
216                         c = LOG_BUF(log_start);
217                         log_start++;
218                         spin_unlock_irq(&logbuf_lock);
219                         error = __put_user(c,buf);
220                         buf++;
221                         i++;
222                         cond_resched();
223                         spin_lock_irq(&logbuf_lock);
224                 }
225                 spin_unlock_irq(&logbuf_lock);
226                 if (!error)
227                         error = i;
228                 break;
229         case 4:         /* Read/clear last kernel messages */
230                 do_clear = 1;
231                 /* FALL THRU */
232         case 3:         /* Read last kernel messages */
233                 error = -EINVAL;
234                 if (!buf || len < 0)
235                         goto out;
236                 error = 0;
237                 if (!len)
238                         goto out;
239                 if (!access_ok(VERIFY_WRITE, buf, len)) {
240                         error = -EFAULT;
241                         goto out;
242                 }
243                 count = len;
244                 if (count > log_buf_len)
245                         count = log_buf_len;
246                 spin_lock_irq(&logbuf_lock);
247                 if (count > logged_chars)
248                         count = logged_chars;
249                 if (do_clear)
250                         logged_chars = 0;
251                 limit = log_end;
252                 /*
253                  * __put_user() could sleep, and while we sleep
254                  * printk() could overwrite the messages
255                  * we try to copy to user space. Therefore
256                  * the messages are copied in reverse. <manfreds>
257                  */
258                 for (i = 0; i < count && !error; i++) {
259                         j = limit-1-i;
260                         if (j + log_buf_len < log_end)
261                                 break;
262                         c = LOG_BUF(j);
263                         spin_unlock_irq(&logbuf_lock);
264                         error = __put_user(c,&buf[count-1-i]);
265                         cond_resched();
266                         spin_lock_irq(&logbuf_lock);
267                 }
268                 spin_unlock_irq(&logbuf_lock);
269                 if (error)
270                         break;
271                 error = i;
272                 if (i != count) {
273                         int offset = count-error;
274                         /* buffer overflow during copy, correct user buffer. */
275                         for (i = 0; i < error; i++) {
276                                 if (__get_user(c,&buf[i+offset]) ||
277                                     __put_user(c,&buf[i])) {
278                                         error = -EFAULT;
279                                         break;
280                                 }
281                                 cond_resched();
282                         }
283                 }
284                 break;
285         case 5:         /* Clear ring buffer */
286                 logged_chars = 0;
287                 break;
288         case 6:         /* Disable logging to console */
289                 console_loglevel = minimum_console_loglevel;
290                 break;
291         case 7:         /* Enable logging to console */
292                 console_loglevel = default_console_loglevel;
293                 break;
294         case 8:         /* Set level of messages printed to console */
295                 error = -EINVAL;
296                 if (len < 1 || len > 8)
297                         goto out;
298                 if (len < minimum_console_loglevel)
299                         len = minimum_console_loglevel;
300                 console_loglevel = len;
301                 error = 0;
302                 break;
303         case 9:         /* Number of chars in the log buffer */
304                 error = log_end - log_start;
305                 break;
306         case 10:        /* Size of the log buffer */
307                 error = log_buf_len;
308                 break;
309         default:
310                 error = -EINVAL;
311                 break;
312         }
313 out:
314         return error;
315 }
316
317 asmlinkage long sys_syslog(int type, char __user *buf, int len)
318 {
319         return do_syslog(type, buf, len);
320 }
321
322 /*
323  * Call the console drivers on a range of log_buf
324  */
325 static void __call_console_drivers(unsigned long start, unsigned long end)
326 {
327         struct console *con;
328
329         for (con = console_drivers; con; con = con->next) {
330                 if ((con->flags & CON_ENABLED) && con->write)
331                         con->write(con, &LOG_BUF(start), end - start);
332         }
333 }
334
335 /*
336  * Write out chars from start to end - 1 inclusive
337  */
338 static void _call_console_drivers(unsigned long start,
339                                 unsigned long end, int msg_log_level)
340 {
341         if (msg_log_level < console_loglevel &&
342                         console_drivers && start != end) {
343                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
344                         /* wrapped write */
345                         __call_console_drivers(start & LOG_BUF_MASK,
346                                                 log_buf_len);
347                         __call_console_drivers(0, end & LOG_BUF_MASK);
348                 } else {
349                         __call_console_drivers(start, end);
350                 }
351         }
352 }
353
354 /*
355  * Call the console drivers, asking them to write out
356  * log_buf[start] to log_buf[end - 1].
357  * The console_sem must be held.
358  */
359 static void call_console_drivers(unsigned long start, unsigned long end)
360 {
361         unsigned long cur_index, start_print;
362         static int msg_level = -1;
363
364         BUG_ON(((long)(start - end)) > 0);
365
366         cur_index = start;
367         start_print = start;
368         while (cur_index != end) {
369                 if (msg_level < 0 && ((end - cur_index) > 2) &&
370                                 LOG_BUF(cur_index + 0) == '<' &&
371                                 LOG_BUF(cur_index + 1) >= '0' &&
372                                 LOG_BUF(cur_index + 1) <= '7' &&
373                                 LOG_BUF(cur_index + 2) == '>') {
374                         msg_level = LOG_BUF(cur_index + 1) - '0';
375                         cur_index += 3;
376                         start_print = cur_index;
377                 }
378                 while (cur_index != end) {
379                         char c = LOG_BUF(cur_index);
380
381                         cur_index++;
382                         if (c == '\n') {
383                                 if (msg_level < 0) {
384                                         /*
385                                          * printk() has already given us loglevel tags in
386                                          * the buffer.  This code is here in case the
387                                          * log buffer has wrapped right round and scribbled
388                                          * on those tags
389                                          */
390                                         msg_level = default_message_loglevel;
391                                 }
392                                 _call_console_drivers(start_print, cur_index, msg_level);
393                                 msg_level = -1;
394                                 start_print = cur_index;
395                                 break;
396                         }
397                 }
398         }
399         _call_console_drivers(start_print, end, msg_level);
400 }
401
402 static void emit_log_char(char c)
403 {
404         LOG_BUF(log_end) = c;
405         log_end++;
406         if (log_end - log_start > log_buf_len)
407                 log_start = log_end - log_buf_len;
408         if (log_end - con_start > log_buf_len)
409                 con_start = log_end - log_buf_len;
410         if (logged_chars < log_buf_len)
411                 logged_chars++;
412 }
413
414 /*
415  * Zap console related locks when oopsing. Only zap at most once
416  * every 10 seconds, to leave time for slow consoles to print a
417  * full oops.
418  */
419 static void zap_locks(void)
420 {
421         static unsigned long oops_timestamp;
422
423         if (time_after_eq(jiffies, oops_timestamp) &&
424                         !time_after(jiffies, oops_timestamp + 30 * HZ))
425                 return;
426
427         oops_timestamp = jiffies;
428
429         /* If a crash is occurring, make sure we can't deadlock */
430         spin_lock_init(&logbuf_lock);
431         /* And make sure that we print immediately */
432         init_MUTEX(&console_sem);
433 }
434
435 #if defined(CONFIG_PRINTK_TIME)
436 static int printk_time = 1;
437 #else
438 static int printk_time = 0;
439 #endif
440
441 static int __init printk_time_setup(char *str)
442 {
443         if (*str)
444                 return 0;
445         printk_time = 1;
446         return 1;
447 }
448
449 __setup("time", printk_time_setup);
450
451 __attribute__((weak)) unsigned long long printk_clock(void)
452 {
453         return sched_clock();
454 }
455
456 /**
457  * printk - print a kernel message
458  * @fmt: format string
459  *
460  * This is printk.  It can be called from any context.  We want it to work.
461  *
462  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
463  * call the console drivers.  If we fail to get the semaphore we place the output
464  * into the log buffer and return.  The current holder of the console_sem will
465  * notice the new output in release_console_sem() and will send it to the
466  * consoles before releasing the semaphore.
467  *
468  * One effect of this deferred printing is that code which calls printk() and
469  * then changes console_loglevel may break. This is because console_loglevel
470  * is inspected when the actual printing occurs.
471  *
472  * See also:
473  * printf(3)
474  */
475
476 asmlinkage int printk(const char *fmt, ...)
477 {
478         va_list args;
479         int r;
480
481         va_start(args, fmt);
482         r = vprintk(fmt, args);
483         va_end(args);
484
485         return r;
486 }
487
488 /* cpu currently holding logbuf_lock */
489 static volatile unsigned int printk_cpu = UINT_MAX;
490
491 asmlinkage int vprintk(const char *fmt, va_list args)
492 {
493         unsigned long flags;
494         int printed_len;
495         char *p;
496         static char printk_buf[1024];
497         static int log_level_unknown = 1;
498
499         preempt_disable();
500         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
501                 /* If a crash is occurring during printk() on this CPU,
502                  * make sure we can't deadlock */
503                 zap_locks();
504
505         /* This stops the holder of console_sem just where we want him */
506         spin_lock_irqsave(&logbuf_lock, flags);
507         printk_cpu = smp_processor_id();
508
509         /* Emit the output into the temporary buffer */
510         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
511
512         /*
513          * Copy the output into log_buf.  If the caller didn't provide
514          * appropriate log level tags, we insert them here
515          */
516         for (p = printk_buf; *p; p++) {
517                 if (log_level_unknown) {
518                         /* log_level_unknown signals the start of a new line */
519                         if (printk_time) {
520                                 int loglev_char;
521                                 char tbuf[50], *tp;
522                                 unsigned tlen;
523                                 unsigned long long t;
524                                 unsigned long nanosec_rem;
525
526                                 /*
527                                  * force the log level token to be
528                                  * before the time output.
529                                  */
530                                 if (p[0] == '<' && p[1] >='0' &&
531                                    p[1] <= '7' && p[2] == '>') {
532                                         loglev_char = p[1];
533                                         p += 3;
534                                         printed_len -= 3;
535                                 } else {
536                                         loglev_char = default_message_loglevel
537                                                 + '0';
538                                 }
539                                 t = printk_clock();
540                                 nanosec_rem = do_div(t, 1000000000);
541                                 tlen = sprintf(tbuf,
542                                                 "<%c>[%5lu.%06lu] ",
543                                                 loglev_char,
544                                                 (unsigned long)t,
545                                                 nanosec_rem/1000);
546
547                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
548                                         emit_log_char(*tp);
549                                 printed_len += tlen;
550                         } else {
551                                 if (p[0] != '<' || p[1] < '0' ||
552                                    p[1] > '7' || p[2] != '>') {
553                                         emit_log_char('<');
554                                         emit_log_char(default_message_loglevel
555                                                 + '0');
556                                         emit_log_char('>');
557                                         printed_len += 3;
558                                 }
559                         }
560                         log_level_unknown = 0;
561                         if (!*p)
562                                 break;
563                 }
564                 emit_log_char(*p);
565                 if (*p == '\n')
566                         log_level_unknown = 1;
567         }
568
569         if (!cpu_online(smp_processor_id())) {
570                 /*
571                  * Some console drivers may assume that per-cpu resources have
572                  * been allocated.  So don't allow them to be called by this
573                  * CPU until it is officially up.  We shouldn't be calling into
574                  * random console drivers on a CPU which doesn't exist yet..
575                  */
576                 printk_cpu = UINT_MAX;
577                 spin_unlock_irqrestore(&logbuf_lock, flags);
578                 goto out;
579         }
580         if (!down_trylock(&console_sem)) {
581                 console_locked = 1;
582                 /*
583                  * We own the drivers.  We can drop the spinlock and let
584                  * release_console_sem() print the text
585                  */
586                 printk_cpu = UINT_MAX;
587                 spin_unlock_irqrestore(&logbuf_lock, flags);
588                 console_may_schedule = 0;
589                 release_console_sem();
590         } else {
591                 /*
592                  * Someone else owns the drivers.  We drop the spinlock, which
593                  * allows the semaphore holder to proceed and to call the
594                  * console drivers with the output which we just produced.
595                  */
596                 printk_cpu = UINT_MAX;
597                 spin_unlock_irqrestore(&logbuf_lock, flags);
598         }
599 out:
600         preempt_enable();
601         return printed_len;
602 }
603 EXPORT_SYMBOL(printk);
604 EXPORT_SYMBOL(vprintk);
605
606 #else
607
608 asmlinkage long sys_syslog(int type, char __user *buf, int len)
609 {
610         return 0;
611 }
612
613 int do_syslog(int type, char __user *buf, int len)
614 {
615         return 0;
616 }
617
618 static void call_console_drivers(unsigned long start, unsigned long end)
619 {
620 }
621
622 #endif
623
624 /*
625  * Set up a list of consoles.  Called from init/main.c
626  */
627 static int __init console_setup(char *str)
628 {
629         char name[sizeof(console_cmdline[0].name)];
630         char *s, *options;
631         int idx;
632
633         /*
634          * Decode str into name, index, options.
635          */
636         if (str[0] >= '0' && str[0] <= '9') {
637                 strcpy(name, "ttyS");
638                 strncpy(name + 4, str, sizeof(name) - 5);
639         } else {
640                 strncpy(name, str, sizeof(name) - 1);
641         }
642         name[sizeof(name) - 1] = 0;
643         if ((options = strchr(str, ',')) != NULL)
644                 *(options++) = 0;
645 #ifdef __sparc__
646         if (!strcmp(str, "ttya"))
647                 strcpy(name, "ttyS0");
648         if (!strcmp(str, "ttyb"))
649                 strcpy(name, "ttyS1");
650 #endif
651         for (s = name; *s; s++)
652                 if ((*s >= '0' && *s <= '9') || *s == ',')
653                         break;
654         idx = simple_strtoul(s, NULL, 10);
655         *s = 0;
656
657         add_preferred_console(name, idx, options);
658         return 1;
659 }
660 __setup("console=", console_setup);
661
662 /**
663  * add_preferred_console - add a device to the list of preferred consoles.
664  * @name: device name
665  * @idx: device index
666  * @options: options for this console
667  *
668  * The last preferred console added will be used for kernel messages
669  * and stdin/out/err for init.  Normally this is used by console_setup
670  * above to handle user-supplied console arguments; however it can also
671  * be used by arch-specific code either to override the user or more
672  * commonly to provide a default console (ie from PROM variables) when
673  * the user has not supplied one.
674  */
675 int __init add_preferred_console(char *name, int idx, char *options)
676 {
677         struct console_cmdline *c;
678         int i;
679
680         /*
681          *      See if this tty is not yet registered, and
682          *      if we have a slot free.
683          */
684         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
685                 if (strcmp(console_cmdline[i].name, name) == 0 &&
686                           console_cmdline[i].index == idx) {
687                                 selected_console = i;
688                                 return 0;
689                 }
690         if (i == MAX_CMDLINECONSOLES)
691                 return -E2BIG;
692         selected_console = i;
693         c = &console_cmdline[i];
694         memcpy(c->name, name, sizeof(c->name));
695         c->name[sizeof(c->name) - 1] = 0;
696         c->options = options;
697         c->index = idx;
698         return 0;
699 }
700
701 /**
702  * suspend_console - suspend the console subsystem
703  *
704  * This disables printk() while we go into suspend states
705  */
706 void suspend_console(void)
707 {
708         acquire_console_sem();
709         console_suspended = 1;
710 }
711
712 void resume_console(void)
713 {
714         console_suspended = 0;
715         release_console_sem();
716 }
717
718 /**
719  * acquire_console_sem - lock the console system for exclusive use.
720  *
721  * Acquires a semaphore which guarantees that the caller has
722  * exclusive access to the console system and the console_drivers list.
723  *
724  * Can sleep, returns nothing.
725  */
726 void acquire_console_sem(void)
727 {
728         BUG_ON(in_interrupt());
729         if (console_suspended) {
730                 down(&secondary_console_sem);
731                 return;
732         }
733         down(&console_sem);
734         console_locked = 1;
735         console_may_schedule = 1;
736 }
737 EXPORT_SYMBOL(acquire_console_sem);
738
739 int try_acquire_console_sem(void)
740 {
741         if (down_trylock(&console_sem))
742                 return -1;
743         console_locked = 1;
744         console_may_schedule = 0;
745         return 0;
746 }
747 EXPORT_SYMBOL(try_acquire_console_sem);
748
749 int is_console_locked(void)
750 {
751         return console_locked;
752 }
753 EXPORT_SYMBOL(is_console_locked);
754
755 /**
756  * release_console_sem - unlock the console system
757  *
758  * Releases the semaphore which the caller holds on the console system
759  * and the console driver list.
760  *
761  * While the semaphore was held, console output may have been buffered
762  * by printk().  If this is the case, release_console_sem() emits
763  * the output prior to releasing the semaphore.
764  *
765  * If there is output waiting for klogd, we wake it up.
766  *
767  * release_console_sem() may be called from any context.
768  */
769 void release_console_sem(void)
770 {
771         unsigned long flags;
772         unsigned long _con_start, _log_end;
773         unsigned long wake_klogd = 0;
774
775         if (console_suspended) {
776                 up(&secondary_console_sem);
777                 return;
778         }
779         for ( ; ; ) {
780                 spin_lock_irqsave(&logbuf_lock, flags);
781                 wake_klogd |= log_start - log_end;
782                 if (con_start == log_end)
783                         break;                  /* Nothing to print */
784                 _con_start = con_start;
785                 _log_end = log_end;
786                 con_start = log_end;            /* Flush */
787                 spin_unlock(&logbuf_lock);
788                 call_console_drivers(_con_start, _log_end);
789                 local_irq_restore(flags);
790         }
791         console_locked = 0;
792         console_may_schedule = 0;
793         up(&console_sem);
794         spin_unlock_irqrestore(&logbuf_lock, flags);
795         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
796                 wake_up_interruptible(&log_wait);
797 }
798 EXPORT_SYMBOL(release_console_sem);
799
800 /**
801  * console_conditional_schedule - yield the CPU if required
802  *
803  * If the console code is currently allowed to sleep, and
804  * if this CPU should yield the CPU to another task, do
805  * so here.
806  *
807  * Must be called within acquire_console_sem().
808  */
809 void __sched console_conditional_schedule(void)
810 {
811         if (console_may_schedule)
812                 cond_resched();
813 }
814 EXPORT_SYMBOL(console_conditional_schedule);
815
816 void console_print(const char *s)
817 {
818         printk(KERN_EMERG "%s", s);
819 }
820 EXPORT_SYMBOL(console_print);
821
822 void console_unblank(void)
823 {
824         struct console *c;
825
826         /*
827          * console_unblank can no longer be called in interrupt context unless
828          * oops_in_progress is set to 1..
829          */
830         if (oops_in_progress) {
831                 if (down_trylock(&console_sem) != 0)
832                         return;
833         } else
834                 acquire_console_sem();
835
836         console_locked = 1;
837         console_may_schedule = 0;
838         for (c = console_drivers; c != NULL; c = c->next)
839                 if ((c->flags & CON_ENABLED) && c->unblank)
840                         c->unblank();
841         release_console_sem();
842 }
843
844 /*
845  * Return the console tty driver structure and its associated index
846  */
847 struct tty_driver *console_device(int *index)
848 {
849         struct console *c;
850         struct tty_driver *driver = NULL;
851
852         acquire_console_sem();
853         for (c = console_drivers; c != NULL; c = c->next) {
854                 if (!c->device)
855                         continue;
856                 driver = c->device(c, index);
857                 if (driver)
858                         break;
859         }
860         release_console_sem();
861         return driver;
862 }
863
864 /*
865  * Prevent further output on the passed console device so that (for example)
866  * serial drivers can disable console output before suspending a port, and can
867  * re-enable output afterwards.
868  */
869 void console_stop(struct console *console)
870 {
871         acquire_console_sem();
872         console->flags &= ~CON_ENABLED;
873         release_console_sem();
874 }
875 EXPORT_SYMBOL(console_stop);
876
877 void console_start(struct console *console)
878 {
879         acquire_console_sem();
880         console->flags |= CON_ENABLED;
881         release_console_sem();
882 }
883 EXPORT_SYMBOL(console_start);
884
885 /*
886  * The console driver calls this routine during kernel initialization
887  * to register the console printing procedure with printk() and to
888  * print any messages that were printed by the kernel before the
889  * console driver was initialized.
890  */
891 void register_console(struct console *console)
892 {
893         int i;
894         unsigned long flags;
895
896         if (preferred_console < 0)
897                 preferred_console = selected_console;
898
899         /*
900          *      See if we want to use this console driver. If we
901          *      didn't select a console we take the first one
902          *      that registers here.
903          */
904         if (preferred_console < 0) {
905                 if (console->index < 0)
906                         console->index = 0;
907                 if (console->setup == NULL ||
908                     console->setup(console, NULL) == 0) {
909                         console->flags |= CON_ENABLED | CON_CONSDEV;
910                         preferred_console = 0;
911                 }
912         }
913
914         /*
915          *      See if this console matches one we selected on
916          *      the command line.
917          */
918         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
919                         i++) {
920                 if (strcmp(console_cmdline[i].name, console->name) != 0)
921                         continue;
922                 if (console->index >= 0 &&
923                     console->index != console_cmdline[i].index)
924                         continue;
925                 if (console->index < 0)
926                         console->index = console_cmdline[i].index;
927                 if (console->setup &&
928                     console->setup(console, console_cmdline[i].options) != 0)
929                         break;
930                 console->flags |= CON_ENABLED;
931                 console->index = console_cmdline[i].index;
932                 if (i == selected_console) {
933                         console->flags |= CON_CONSDEV;
934                         preferred_console = selected_console;
935                 }
936                 break;
937         }
938
939         if (!(console->flags & CON_ENABLED))
940                 return;
941
942         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
943                 unregister_console(console_drivers);
944                 console->flags &= ~CON_PRINTBUFFER;
945         }
946
947         /*
948          *      Put this console in the list - keep the
949          *      preferred driver at the head of the list.
950          */
951         acquire_console_sem();
952         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
953                 console->next = console_drivers;
954                 console_drivers = console;
955                 if (console->next)
956                         console->next->flags &= ~CON_CONSDEV;
957         } else {
958                 console->next = console_drivers->next;
959                 console_drivers->next = console;
960         }
961         if (console->flags & CON_PRINTBUFFER) {
962                 /*
963                  * release_console_sem() will print out the buffered messages
964                  * for us.
965                  */
966                 spin_lock_irqsave(&logbuf_lock, flags);
967                 con_start = log_start;
968                 spin_unlock_irqrestore(&logbuf_lock, flags);
969         }
970         release_console_sem();
971 }
972 EXPORT_SYMBOL(register_console);
973
974 int unregister_console(struct console *console)
975 {
976         struct console *a, *b;
977         int res = 1;
978
979         acquire_console_sem();
980         if (console_drivers == console) {
981                 console_drivers=console->next;
982                 res = 0;
983         } else if (console_drivers) {
984                 for (a=console_drivers->next, b=console_drivers ;
985                      a; b=a, a=b->next) {
986                         if (a == console) {
987                                 b->next = a->next;
988                                 res = 0;
989                                 break;
990                         }
991                 }
992         }
993
994         /* If last console is removed, we re-enable picking the first
995          * one that gets registered. Without that, pmac early boot console
996          * would prevent fbcon from taking over.
997          *
998          * If this isn't the last console and it has CON_CONSDEV set, we
999          * need to set it on the next preferred console.
1000          */
1001         if (console_drivers == NULL)
1002                 preferred_console = selected_console;
1003         else if (console->flags & CON_CONSDEV)
1004                 console_drivers->flags |= CON_CONSDEV;
1005
1006         release_console_sem();
1007         return res;
1008 }
1009 EXPORT_SYMBOL(unregister_console);
1010
1011 /**
1012  * tty_write_message - write a message to a certain tty, not just the console.
1013  * @tty: the destination tty_struct
1014  * @msg: the message to write
1015  *
1016  * This is used for messages that need to be redirected to a specific tty.
1017  * We don't put it into the syslog queue right now maybe in the future if
1018  * really needed.
1019  */
1020 void tty_write_message(struct tty_struct *tty, char *msg)
1021 {
1022         if (tty && tty->driver->write)
1023                 tty->driver->write(tty, msg, strlen(msg));
1024         return;
1025 }
1026 EXPORT_SYMBOL_GPL(tty_write_message);
1027
1028 /*
1029  * printk rate limiting, lifted from the networking subsystem.
1030  *
1031  * This enforces a rate limit: not more than one kernel message
1032  * every printk_ratelimit_jiffies to make a denial-of-service
1033  * attack impossible.
1034  */
1035 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1036 {
1037         static DEFINE_SPINLOCK(ratelimit_lock);
1038         static unsigned long toks = 10 * 5 * HZ;
1039         static unsigned long last_msg;
1040         static int missed;
1041         unsigned long flags;
1042         unsigned long now = jiffies;
1043
1044         spin_lock_irqsave(&ratelimit_lock, flags);
1045         toks += now - last_msg;
1046         last_msg = now;
1047         if (toks > (ratelimit_burst * ratelimit_jiffies))
1048                 toks = ratelimit_burst * ratelimit_jiffies;
1049         if (toks >= ratelimit_jiffies) {
1050                 int lost = missed;
1051
1052                 missed = 0;
1053                 toks -= ratelimit_jiffies;
1054                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1055                 if (lost)
1056                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1057                 return 1;
1058         }
1059         missed++;
1060         spin_unlock_irqrestore(&ratelimit_lock, flags);
1061         return 0;
1062 }
1063 EXPORT_SYMBOL(__printk_ratelimit);
1064
1065 /* minimum time in jiffies between messages */
1066 int printk_ratelimit_jiffies = 5 * HZ;
1067
1068 /* number of messages we send before ratelimiting */
1069 int printk_ratelimit_burst = 10;
1070
1071 int printk_ratelimit(void)
1072 {
1073         return __printk_ratelimit(printk_ratelimit_jiffies,
1074                                 printk_ratelimit_burst);
1075 }
1076 EXPORT_SYMBOL(printk_ratelimit);