[PATCH] Make printk work for really early debugging
[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                                 (cpu_online(smp_processor_id()) ||
332                                 (con->flags & CON_ANYTIME)))
333                         con->write(con, &LOG_BUF(start), end - start);
334         }
335 }
336
337 /*
338  * Write out chars from start to end - 1 inclusive
339  */
340 static void _call_console_drivers(unsigned long start,
341                                 unsigned long end, int msg_log_level)
342 {
343         if (msg_log_level < console_loglevel &&
344                         console_drivers && start != end) {
345                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
346                         /* wrapped write */
347                         __call_console_drivers(start & LOG_BUF_MASK,
348                                                 log_buf_len);
349                         __call_console_drivers(0, end & LOG_BUF_MASK);
350                 } else {
351                         __call_console_drivers(start, end);
352                 }
353         }
354 }
355
356 /*
357  * Call the console drivers, asking them to write out
358  * log_buf[start] to log_buf[end - 1].
359  * The console_sem must be held.
360  */
361 static void call_console_drivers(unsigned long start, unsigned long end)
362 {
363         unsigned long cur_index, start_print;
364         static int msg_level = -1;
365
366         BUG_ON(((long)(start - end)) > 0);
367
368         cur_index = start;
369         start_print = start;
370         while (cur_index != end) {
371                 if (msg_level < 0 && ((end - cur_index) > 2) &&
372                                 LOG_BUF(cur_index + 0) == '<' &&
373                                 LOG_BUF(cur_index + 1) >= '0' &&
374                                 LOG_BUF(cur_index + 1) <= '7' &&
375                                 LOG_BUF(cur_index + 2) == '>') {
376                         msg_level = LOG_BUF(cur_index + 1) - '0';
377                         cur_index += 3;
378                         start_print = cur_index;
379                 }
380                 while (cur_index != end) {
381                         char c = LOG_BUF(cur_index);
382
383                         cur_index++;
384                         if (c == '\n') {
385                                 if (msg_level < 0) {
386                                         /*
387                                          * printk() has already given us loglevel tags in
388                                          * the buffer.  This code is here in case the
389                                          * log buffer has wrapped right round and scribbled
390                                          * on those tags
391                                          */
392                                         msg_level = default_message_loglevel;
393                                 }
394                                 _call_console_drivers(start_print, cur_index, msg_level);
395                                 msg_level = -1;
396                                 start_print = cur_index;
397                                 break;
398                         }
399                 }
400         }
401         _call_console_drivers(start_print, end, msg_level);
402 }
403
404 static void emit_log_char(char c)
405 {
406         LOG_BUF(log_end) = c;
407         log_end++;
408         if (log_end - log_start > log_buf_len)
409                 log_start = log_end - log_buf_len;
410         if (log_end - con_start > log_buf_len)
411                 con_start = log_end - log_buf_len;
412         if (logged_chars < log_buf_len)
413                 logged_chars++;
414 }
415
416 /*
417  * Zap console related locks when oopsing. Only zap at most once
418  * every 10 seconds, to leave time for slow consoles to print a
419  * full oops.
420  */
421 static void zap_locks(void)
422 {
423         static unsigned long oops_timestamp;
424
425         if (time_after_eq(jiffies, oops_timestamp) &&
426                         !time_after(jiffies, oops_timestamp + 30 * HZ))
427                 return;
428
429         oops_timestamp = jiffies;
430
431         /* If a crash is occurring, make sure we can't deadlock */
432         spin_lock_init(&logbuf_lock);
433         /* And make sure that we print immediately */
434         init_MUTEX(&console_sem);
435 }
436
437 #if defined(CONFIG_PRINTK_TIME)
438 static int printk_time = 1;
439 #else
440 static int printk_time = 0;
441 #endif
442
443 static int __init printk_time_setup(char *str)
444 {
445         if (*str)
446                 return 0;
447         printk_time = 1;
448         return 1;
449 }
450
451 __setup("time", printk_time_setup);
452
453 __attribute__((weak)) unsigned long long printk_clock(void)
454 {
455         return sched_clock();
456 }
457
458 /* Check if we have any console registered that can be called early in boot. */
459 static int have_callable_console(void)
460 {
461         struct console *con;
462
463         for (con = console_drivers; con; con = con->next)
464                 if (con->flags & CON_ANYTIME)
465                         return 1;
466
467         return 0;
468 }
469
470 /**
471  * printk - print a kernel message
472  * @fmt: format string
473  *
474  * This is printk.  It can be called from any context.  We want it to work.
475  *
476  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
477  * call the console drivers.  If we fail to get the semaphore we place the output
478  * into the log buffer and return.  The current holder of the console_sem will
479  * notice the new output in release_console_sem() and will send it to the
480  * consoles before releasing the semaphore.
481  *
482  * One effect of this deferred printing is that code which calls printk() and
483  * then changes console_loglevel may break. This is because console_loglevel
484  * is inspected when the actual printing occurs.
485  *
486  * See also:
487  * printf(3)
488  */
489
490 asmlinkage int printk(const char *fmt, ...)
491 {
492         va_list args;
493         int r;
494
495         va_start(args, fmt);
496         r = vprintk(fmt, args);
497         va_end(args);
498
499         return r;
500 }
501
502 /* cpu currently holding logbuf_lock */
503 static volatile unsigned int printk_cpu = UINT_MAX;
504
505 asmlinkage int vprintk(const char *fmt, va_list args)
506 {
507         unsigned long flags;
508         int printed_len;
509         char *p;
510         static char printk_buf[1024];
511         static int log_level_unknown = 1;
512
513         preempt_disable();
514         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
515                 /* If a crash is occurring during printk() on this CPU,
516                  * make sure we can't deadlock */
517                 zap_locks();
518
519         /* This stops the holder of console_sem just where we want him */
520         spin_lock_irqsave(&logbuf_lock, flags);
521         printk_cpu = smp_processor_id();
522
523         /* Emit the output into the temporary buffer */
524         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
525
526         /*
527          * Copy the output into log_buf.  If the caller didn't provide
528          * appropriate log level tags, we insert them here
529          */
530         for (p = printk_buf; *p; p++) {
531                 if (log_level_unknown) {
532                         /* log_level_unknown signals the start of a new line */
533                         if (printk_time) {
534                                 int loglev_char;
535                                 char tbuf[50], *tp;
536                                 unsigned tlen;
537                                 unsigned long long t;
538                                 unsigned long nanosec_rem;
539
540                                 /*
541                                  * force the log level token to be
542                                  * before the time output.
543                                  */
544                                 if (p[0] == '<' && p[1] >='0' &&
545                                    p[1] <= '7' && p[2] == '>') {
546                                         loglev_char = p[1];
547                                         p += 3;
548                                         printed_len -= 3;
549                                 } else {
550                                         loglev_char = default_message_loglevel
551                                                 + '0';
552                                 }
553                                 t = printk_clock();
554                                 nanosec_rem = do_div(t, 1000000000);
555                                 tlen = sprintf(tbuf,
556                                                 "<%c>[%5lu.%06lu] ",
557                                                 loglev_char,
558                                                 (unsigned long)t,
559                                                 nanosec_rem/1000);
560
561                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
562                                         emit_log_char(*tp);
563                                 printed_len += tlen;
564                         } else {
565                                 if (p[0] != '<' || p[1] < '0' ||
566                                    p[1] > '7' || p[2] != '>') {
567                                         emit_log_char('<');
568                                         emit_log_char(default_message_loglevel
569                                                 + '0');
570                                         emit_log_char('>');
571                                         printed_len += 3;
572                                 }
573                         }
574                         log_level_unknown = 0;
575                         if (!*p)
576                                 break;
577                 }
578                 emit_log_char(*p);
579                 if (*p == '\n')
580                         log_level_unknown = 1;
581         }
582
583         if (!down_trylock(&console_sem)) {
584                 /*
585                  * We own the drivers.  We can drop the spinlock and
586                  * let release_console_sem() print the text, maybe ...
587                  */
588                 console_locked = 1;
589                 printk_cpu = UINT_MAX;
590                 spin_unlock_irqrestore(&logbuf_lock, flags);
591
592                 /*
593                  * Console drivers may assume that per-cpu resources have
594                  * been allocated. So unless they're explicitly marked as
595                  * being able to cope (CON_ANYTIME) don't call them until
596                  * this CPU is officially up.
597                  */
598                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
599                         console_may_schedule = 0;
600                         release_console_sem();
601                 } else {
602                         /* Release by hand to avoid flushing the buffer. */
603                         console_locked = 0;
604                         up(&console_sem);
605                 }
606         } else {
607                 /*
608                  * Someone else owns the drivers.  We drop the spinlock, which
609                  * allows the semaphore holder to proceed and to call the
610                  * console drivers with the output which we just produced.
611                  */
612                 printk_cpu = UINT_MAX;
613                 spin_unlock_irqrestore(&logbuf_lock, flags);
614         }
615
616         preempt_enable();
617         return printed_len;
618 }
619 EXPORT_SYMBOL(printk);
620 EXPORT_SYMBOL(vprintk);
621
622 #else
623
624 asmlinkage long sys_syslog(int type, char __user *buf, int len)
625 {
626         return 0;
627 }
628
629 int do_syslog(int type, char __user *buf, int len)
630 {
631         return 0;
632 }
633
634 static void call_console_drivers(unsigned long start, unsigned long end)
635 {
636 }
637
638 #endif
639
640 /*
641  * Set up a list of consoles.  Called from init/main.c
642  */
643 static int __init console_setup(char *str)
644 {
645         char name[sizeof(console_cmdline[0].name)];
646         char *s, *options;
647         int idx;
648
649         /*
650          * Decode str into name, index, options.
651          */
652         if (str[0] >= '0' && str[0] <= '9') {
653                 strcpy(name, "ttyS");
654                 strncpy(name + 4, str, sizeof(name) - 5);
655         } else {
656                 strncpy(name, str, sizeof(name) - 1);
657         }
658         name[sizeof(name) - 1] = 0;
659         if ((options = strchr(str, ',')) != NULL)
660                 *(options++) = 0;
661 #ifdef __sparc__
662         if (!strcmp(str, "ttya"))
663                 strcpy(name, "ttyS0");
664         if (!strcmp(str, "ttyb"))
665                 strcpy(name, "ttyS1");
666 #endif
667         for (s = name; *s; s++)
668                 if ((*s >= '0' && *s <= '9') || *s == ',')
669                         break;
670         idx = simple_strtoul(s, NULL, 10);
671         *s = 0;
672
673         add_preferred_console(name, idx, options);
674         return 1;
675 }
676 __setup("console=", console_setup);
677
678 /**
679  * add_preferred_console - add a device to the list of preferred consoles.
680  * @name: device name
681  * @idx: device index
682  * @options: options for this console
683  *
684  * The last preferred console added will be used for kernel messages
685  * and stdin/out/err for init.  Normally this is used by console_setup
686  * above to handle user-supplied console arguments; however it can also
687  * be used by arch-specific code either to override the user or more
688  * commonly to provide a default console (ie from PROM variables) when
689  * the user has not supplied one.
690  */
691 int __init add_preferred_console(char *name, int idx, char *options)
692 {
693         struct console_cmdline *c;
694         int i;
695
696         /*
697          *      See if this tty is not yet registered, and
698          *      if we have a slot free.
699          */
700         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
701                 if (strcmp(console_cmdline[i].name, name) == 0 &&
702                           console_cmdline[i].index == idx) {
703                                 selected_console = i;
704                                 return 0;
705                 }
706         if (i == MAX_CMDLINECONSOLES)
707                 return -E2BIG;
708         selected_console = i;
709         c = &console_cmdline[i];
710         memcpy(c->name, name, sizeof(c->name));
711         c->name[sizeof(c->name) - 1] = 0;
712         c->options = options;
713         c->index = idx;
714         return 0;
715 }
716
717 /**
718  * suspend_console - suspend the console subsystem
719  *
720  * This disables printk() while we go into suspend states
721  */
722 void suspend_console(void)
723 {
724         acquire_console_sem();
725         console_suspended = 1;
726 }
727
728 void resume_console(void)
729 {
730         console_suspended = 0;
731         release_console_sem();
732 }
733
734 /**
735  * acquire_console_sem - lock the console system for exclusive use.
736  *
737  * Acquires a semaphore which guarantees that the caller has
738  * exclusive access to the console system and the console_drivers list.
739  *
740  * Can sleep, returns nothing.
741  */
742 void acquire_console_sem(void)
743 {
744         BUG_ON(in_interrupt());
745         if (console_suspended) {
746                 down(&secondary_console_sem);
747                 return;
748         }
749         down(&console_sem);
750         console_locked = 1;
751         console_may_schedule = 1;
752 }
753 EXPORT_SYMBOL(acquire_console_sem);
754
755 int try_acquire_console_sem(void)
756 {
757         if (down_trylock(&console_sem))
758                 return -1;
759         console_locked = 1;
760         console_may_schedule = 0;
761         return 0;
762 }
763 EXPORT_SYMBOL(try_acquire_console_sem);
764
765 int is_console_locked(void)
766 {
767         return console_locked;
768 }
769 EXPORT_SYMBOL(is_console_locked);
770
771 /**
772  * release_console_sem - unlock the console system
773  *
774  * Releases the semaphore which the caller holds on the console system
775  * and the console driver list.
776  *
777  * While the semaphore was held, console output may have been buffered
778  * by printk().  If this is the case, release_console_sem() emits
779  * the output prior to releasing the semaphore.
780  *
781  * If there is output waiting for klogd, we wake it up.
782  *
783  * release_console_sem() may be called from any context.
784  */
785 void release_console_sem(void)
786 {
787         unsigned long flags;
788         unsigned long _con_start, _log_end;
789         unsigned long wake_klogd = 0;
790
791         if (console_suspended) {
792                 up(&secondary_console_sem);
793                 return;
794         }
795         for ( ; ; ) {
796                 spin_lock_irqsave(&logbuf_lock, flags);
797                 wake_klogd |= log_start - log_end;
798                 if (con_start == log_end)
799                         break;                  /* Nothing to print */
800                 _con_start = con_start;
801                 _log_end = log_end;
802                 con_start = log_end;            /* Flush */
803                 spin_unlock(&logbuf_lock);
804                 call_console_drivers(_con_start, _log_end);
805                 local_irq_restore(flags);
806         }
807         console_locked = 0;
808         console_may_schedule = 0;
809         up(&console_sem);
810         spin_unlock_irqrestore(&logbuf_lock, flags);
811         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
812                 wake_up_interruptible(&log_wait);
813 }
814 EXPORT_SYMBOL(release_console_sem);
815
816 /**
817  * console_conditional_schedule - yield the CPU if required
818  *
819  * If the console code is currently allowed to sleep, and
820  * if this CPU should yield the CPU to another task, do
821  * so here.
822  *
823  * Must be called within acquire_console_sem().
824  */
825 void __sched console_conditional_schedule(void)
826 {
827         if (console_may_schedule)
828                 cond_resched();
829 }
830 EXPORT_SYMBOL(console_conditional_schedule);
831
832 void console_print(const char *s)
833 {
834         printk(KERN_EMERG "%s", s);
835 }
836 EXPORT_SYMBOL(console_print);
837
838 void console_unblank(void)
839 {
840         struct console *c;
841
842         /*
843          * console_unblank can no longer be called in interrupt context unless
844          * oops_in_progress is set to 1..
845          */
846         if (oops_in_progress) {
847                 if (down_trylock(&console_sem) != 0)
848                         return;
849         } else
850                 acquire_console_sem();
851
852         console_locked = 1;
853         console_may_schedule = 0;
854         for (c = console_drivers; c != NULL; c = c->next)
855                 if ((c->flags & CON_ENABLED) && c->unblank)
856                         c->unblank();
857         release_console_sem();
858 }
859
860 /*
861  * Return the console tty driver structure and its associated index
862  */
863 struct tty_driver *console_device(int *index)
864 {
865         struct console *c;
866         struct tty_driver *driver = NULL;
867
868         acquire_console_sem();
869         for (c = console_drivers; c != NULL; c = c->next) {
870                 if (!c->device)
871                         continue;
872                 driver = c->device(c, index);
873                 if (driver)
874                         break;
875         }
876         release_console_sem();
877         return driver;
878 }
879
880 /*
881  * Prevent further output on the passed console device so that (for example)
882  * serial drivers can disable console output before suspending a port, and can
883  * re-enable output afterwards.
884  */
885 void console_stop(struct console *console)
886 {
887         acquire_console_sem();
888         console->flags &= ~CON_ENABLED;
889         release_console_sem();
890 }
891 EXPORT_SYMBOL(console_stop);
892
893 void console_start(struct console *console)
894 {
895         acquire_console_sem();
896         console->flags |= CON_ENABLED;
897         release_console_sem();
898 }
899 EXPORT_SYMBOL(console_start);
900
901 /*
902  * The console driver calls this routine during kernel initialization
903  * to register the console printing procedure with printk() and to
904  * print any messages that were printed by the kernel before the
905  * console driver was initialized.
906  */
907 void register_console(struct console *console)
908 {
909         int i;
910         unsigned long flags;
911
912         if (preferred_console < 0)
913                 preferred_console = selected_console;
914
915         /*
916          *      See if we want to use this console driver. If we
917          *      didn't select a console we take the first one
918          *      that registers here.
919          */
920         if (preferred_console < 0) {
921                 if (console->index < 0)
922                         console->index = 0;
923                 if (console->setup == NULL ||
924                     console->setup(console, NULL) == 0) {
925                         console->flags |= CON_ENABLED | CON_CONSDEV;
926                         preferred_console = 0;
927                 }
928         }
929
930         /*
931          *      See if this console matches one we selected on
932          *      the command line.
933          */
934         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
935                         i++) {
936                 if (strcmp(console_cmdline[i].name, console->name) != 0)
937                         continue;
938                 if (console->index >= 0 &&
939                     console->index != console_cmdline[i].index)
940                         continue;
941                 if (console->index < 0)
942                         console->index = console_cmdline[i].index;
943                 if (console->setup &&
944                     console->setup(console, console_cmdline[i].options) != 0)
945                         break;
946                 console->flags |= CON_ENABLED;
947                 console->index = console_cmdline[i].index;
948                 if (i == selected_console) {
949                         console->flags |= CON_CONSDEV;
950                         preferred_console = selected_console;
951                 }
952                 break;
953         }
954
955         if (!(console->flags & CON_ENABLED))
956                 return;
957
958         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
959                 unregister_console(console_drivers);
960                 console->flags &= ~CON_PRINTBUFFER;
961         }
962
963         /*
964          *      Put this console in the list - keep the
965          *      preferred driver at the head of the list.
966          */
967         acquire_console_sem();
968         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
969                 console->next = console_drivers;
970                 console_drivers = console;
971                 if (console->next)
972                         console->next->flags &= ~CON_CONSDEV;
973         } else {
974                 console->next = console_drivers->next;
975                 console_drivers->next = console;
976         }
977         if (console->flags & CON_PRINTBUFFER) {
978                 /*
979                  * release_console_sem() will print out the buffered messages
980                  * for us.
981                  */
982                 spin_lock_irqsave(&logbuf_lock, flags);
983                 con_start = log_start;
984                 spin_unlock_irqrestore(&logbuf_lock, flags);
985         }
986         release_console_sem();
987 }
988 EXPORT_SYMBOL(register_console);
989
990 int unregister_console(struct console *console)
991 {
992         struct console *a, *b;
993         int res = 1;
994
995         acquire_console_sem();
996         if (console_drivers == console) {
997                 console_drivers=console->next;
998                 res = 0;
999         } else if (console_drivers) {
1000                 for (a=console_drivers->next, b=console_drivers ;
1001                      a; b=a, a=b->next) {
1002                         if (a == console) {
1003                                 b->next = a->next;
1004                                 res = 0;
1005                                 break;
1006                         }
1007                 }
1008         }
1009
1010         /* If last console is removed, we re-enable picking the first
1011          * one that gets registered. Without that, pmac early boot console
1012          * would prevent fbcon from taking over.
1013          *
1014          * If this isn't the last console and it has CON_CONSDEV set, we
1015          * need to set it on the next preferred console.
1016          */
1017         if (console_drivers == NULL)
1018                 preferred_console = selected_console;
1019         else if (console->flags & CON_CONSDEV)
1020                 console_drivers->flags |= CON_CONSDEV;
1021
1022         release_console_sem();
1023         return res;
1024 }
1025 EXPORT_SYMBOL(unregister_console);
1026
1027 /**
1028  * tty_write_message - write a message to a certain tty, not just the console.
1029  * @tty: the destination tty_struct
1030  * @msg: the message to write
1031  *
1032  * This is used for messages that need to be redirected to a specific tty.
1033  * We don't put it into the syslog queue right now maybe in the future if
1034  * really needed.
1035  */
1036 void tty_write_message(struct tty_struct *tty, char *msg)
1037 {
1038         if (tty && tty->driver->write)
1039                 tty->driver->write(tty, msg, strlen(msg));
1040         return;
1041 }
1042
1043 /*
1044  * printk rate limiting, lifted from the networking subsystem.
1045  *
1046  * This enforces a rate limit: not more than one kernel message
1047  * every printk_ratelimit_jiffies to make a denial-of-service
1048  * attack impossible.
1049  */
1050 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1051 {
1052         static DEFINE_SPINLOCK(ratelimit_lock);
1053         static unsigned long toks = 10 * 5 * HZ;
1054         static unsigned long last_msg;
1055         static int missed;
1056         unsigned long flags;
1057         unsigned long now = jiffies;
1058
1059         spin_lock_irqsave(&ratelimit_lock, flags);
1060         toks += now - last_msg;
1061         last_msg = now;
1062         if (toks > (ratelimit_burst * ratelimit_jiffies))
1063                 toks = ratelimit_burst * ratelimit_jiffies;
1064         if (toks >= ratelimit_jiffies) {
1065                 int lost = missed;
1066
1067                 missed = 0;
1068                 toks -= ratelimit_jiffies;
1069                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1070                 if (lost)
1071                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1072                 return 1;
1073         }
1074         missed++;
1075         spin_unlock_irqrestore(&ratelimit_lock, flags);
1076         return 0;
1077 }
1078 EXPORT_SYMBOL(__printk_ratelimit);
1079
1080 /* minimum time in jiffies between messages */
1081 int printk_ratelimit_jiffies = 5 * HZ;
1082
1083 /* number of messages we send before ratelimiting */
1084 int printk_ratelimit_burst = 10;
1085
1086 int printk_ratelimit(void)
1087 {
1088         return __printk_ratelimit(printk_ratelimit_jiffies,
1089                                 printk_ratelimit_burst);
1090 }
1091 EXPORT_SYMBOL(printk_ratelimit);