[PATCH] lockdep: do not recurse in printk
[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/moduleparam.h>
28 #include <linux/interrupt.h>                    /* For in_interrupt() */
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 module_param(printk_time, int, S_IRUGO | S_IWUSR);
443
444 static int __init printk_time_setup(char *str)
445 {
446         if (*str)
447                 return 0;
448         printk_time = 1;
449         return 1;
450 }
451
452 __setup("time", printk_time_setup);
453
454 __attribute__((weak)) unsigned long long printk_clock(void)
455 {
456         return sched_clock();
457 }
458
459 /* Check if we have any console registered that can be called early in boot. */
460 static int have_callable_console(void)
461 {
462         struct console *con;
463
464         for (con = console_drivers; con; con = con->next)
465                 if (con->flags & CON_ANYTIME)
466                         return 1;
467
468         return 0;
469 }
470
471 /**
472  * printk - print a kernel message
473  * @fmt: format string
474  *
475  * This is printk.  It can be called from any context.  We want it to work.
476  *
477  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
478  * call the console drivers.  If we fail to get the semaphore we place the output
479  * into the log buffer and return.  The current holder of the console_sem will
480  * notice the new output in release_console_sem() and will send it to the
481  * consoles before releasing the semaphore.
482  *
483  * One effect of this deferred printing is that code which calls printk() and
484  * then changes console_loglevel may break. This is because console_loglevel
485  * is inspected when the actual printing occurs.
486  *
487  * See also:
488  * printf(3)
489  */
490
491 asmlinkage int printk(const char *fmt, ...)
492 {
493         va_list args;
494         int r;
495
496         va_start(args, fmt);
497         r = vprintk(fmt, args);
498         va_end(args);
499
500         return r;
501 }
502
503 /* cpu currently holding logbuf_lock */
504 static volatile unsigned int printk_cpu = UINT_MAX;
505
506 asmlinkage int vprintk(const char *fmt, va_list args)
507 {
508         unsigned long flags;
509         int printed_len;
510         char *p;
511         static char printk_buf[1024];
512         static int log_level_unknown = 1;
513
514         preempt_disable();
515         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
516                 /* If a crash is occurring during printk() on this CPU,
517                  * make sure we can't deadlock */
518                 zap_locks();
519
520         /* This stops the holder of console_sem just where we want him */
521         local_irq_save(flags);
522         lockdep_off();
523         spin_lock(&logbuf_lock);
524         printk_cpu = smp_processor_id();
525
526         /* Emit the output into the temporary buffer */
527         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
528
529         /*
530          * Copy the output into log_buf.  If the caller didn't provide
531          * appropriate log level tags, we insert them here
532          */
533         for (p = printk_buf; *p; p++) {
534                 if (log_level_unknown) {
535                         /* log_level_unknown signals the start of a new line */
536                         if (printk_time) {
537                                 int loglev_char;
538                                 char tbuf[50], *tp;
539                                 unsigned tlen;
540                                 unsigned long long t;
541                                 unsigned long nanosec_rem;
542
543                                 /*
544                                  * force the log level token to be
545                                  * before the time output.
546                                  */
547                                 if (p[0] == '<' && p[1] >='0' &&
548                                    p[1] <= '7' && p[2] == '>') {
549                                         loglev_char = p[1];
550                                         p += 3;
551                                         printed_len -= 3;
552                                 } else {
553                                         loglev_char = default_message_loglevel
554                                                 + '0';
555                                 }
556                                 t = printk_clock();
557                                 nanosec_rem = do_div(t, 1000000000);
558                                 tlen = sprintf(tbuf,
559                                                 "<%c>[%5lu.%06lu] ",
560                                                 loglev_char,
561                                                 (unsigned long)t,
562                                                 nanosec_rem/1000);
563
564                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
565                                         emit_log_char(*tp);
566                                 printed_len += tlen;
567                         } else {
568                                 if (p[0] != '<' || p[1] < '0' ||
569                                    p[1] > '7' || p[2] != '>') {
570                                         emit_log_char('<');
571                                         emit_log_char(default_message_loglevel
572                                                 + '0');
573                                         emit_log_char('>');
574                                         printed_len += 3;
575                                 }
576                         }
577                         log_level_unknown = 0;
578                         if (!*p)
579                                 break;
580                 }
581                 emit_log_char(*p);
582                 if (*p == '\n')
583                         log_level_unknown = 1;
584         }
585
586         if (!down_trylock(&console_sem)) {
587                 /*
588                  * We own the drivers.  We can drop the spinlock and
589                  * let release_console_sem() print the text, maybe ...
590                  */
591                 console_locked = 1;
592                 printk_cpu = UINT_MAX;
593                 spin_unlock(&logbuf_lock);
594
595                 /*
596                  * Console drivers may assume that per-cpu resources have
597                  * been allocated. So unless they're explicitly marked as
598                  * being able to cope (CON_ANYTIME) don't call them until
599                  * this CPU is officially up.
600                  */
601                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
602                         console_may_schedule = 0;
603                         release_console_sem();
604                 } else {
605                         /* Release by hand to avoid flushing the buffer. */
606                         console_locked = 0;
607                         up(&console_sem);
608                 }
609                 lockdep_on();
610                 local_irq_restore(flags);
611         } else {
612                 /*
613                  * Someone else owns the drivers.  We drop the spinlock, which
614                  * allows the semaphore holder to proceed and to call the
615                  * console drivers with the output which we just produced.
616                  */
617                 printk_cpu = UINT_MAX;
618                 spin_unlock(&logbuf_lock);
619                 lockdep_on();
620                 local_irq_restore(flags);
621         }
622
623         preempt_enable();
624         return printed_len;
625 }
626 EXPORT_SYMBOL(printk);
627 EXPORT_SYMBOL(vprintk);
628
629 #else
630
631 asmlinkage long sys_syslog(int type, char __user *buf, int len)
632 {
633         return 0;
634 }
635
636 int do_syslog(int type, char __user *buf, int len)
637 {
638         return 0;
639 }
640
641 static void call_console_drivers(unsigned long start, unsigned long end)
642 {
643 }
644
645 #endif
646
647 /*
648  * Set up a list of consoles.  Called from init/main.c
649  */
650 static int __init console_setup(char *str)
651 {
652         char name[sizeof(console_cmdline[0].name)];
653         char *s, *options;
654         int idx;
655
656         /*
657          * Decode str into name, index, options.
658          */
659         if (str[0] >= '0' && str[0] <= '9') {
660                 strcpy(name, "ttyS");
661                 strncpy(name + 4, str, sizeof(name) - 5);
662         } else {
663                 strncpy(name, str, sizeof(name) - 1);
664         }
665         name[sizeof(name) - 1] = 0;
666         if ((options = strchr(str, ',')) != NULL)
667                 *(options++) = 0;
668 #ifdef __sparc__
669         if (!strcmp(str, "ttya"))
670                 strcpy(name, "ttyS0");
671         if (!strcmp(str, "ttyb"))
672                 strcpy(name, "ttyS1");
673 #endif
674         for (s = name; *s; s++)
675                 if ((*s >= '0' && *s <= '9') || *s == ',')
676                         break;
677         idx = simple_strtoul(s, NULL, 10);
678         *s = 0;
679
680         add_preferred_console(name, idx, options);
681         return 1;
682 }
683 __setup("console=", console_setup);
684
685 /**
686  * add_preferred_console - add a device to the list of preferred consoles.
687  * @name: device name
688  * @idx: device index
689  * @options: options for this console
690  *
691  * The last preferred console added will be used for kernel messages
692  * and stdin/out/err for init.  Normally this is used by console_setup
693  * above to handle user-supplied console arguments; however it can also
694  * be used by arch-specific code either to override the user or more
695  * commonly to provide a default console (ie from PROM variables) when
696  * the user has not supplied one.
697  */
698 int __init add_preferred_console(char *name, int idx, char *options)
699 {
700         struct console_cmdline *c;
701         int i;
702
703         /*
704          *      See if this tty is not yet registered, and
705          *      if we have a slot free.
706          */
707         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
708                 if (strcmp(console_cmdline[i].name, name) == 0 &&
709                           console_cmdline[i].index == idx) {
710                                 selected_console = i;
711                                 return 0;
712                 }
713         if (i == MAX_CMDLINECONSOLES)
714                 return -E2BIG;
715         selected_console = i;
716         c = &console_cmdline[i];
717         memcpy(c->name, name, sizeof(c->name));
718         c->name[sizeof(c->name) - 1] = 0;
719         c->options = options;
720         c->index = idx;
721         return 0;
722 }
723
724 /**
725  * suspend_console - suspend the console subsystem
726  *
727  * This disables printk() while we go into suspend states
728  */
729 void suspend_console(void)
730 {
731         acquire_console_sem();
732         console_suspended = 1;
733 }
734
735 void resume_console(void)
736 {
737         console_suspended = 0;
738         release_console_sem();
739 }
740
741 /**
742  * acquire_console_sem - lock the console system for exclusive use.
743  *
744  * Acquires a semaphore which guarantees that the caller has
745  * exclusive access to the console system and the console_drivers list.
746  *
747  * Can sleep, returns nothing.
748  */
749 void acquire_console_sem(void)
750 {
751         BUG_ON(in_interrupt());
752         if (console_suspended) {
753                 down(&secondary_console_sem);
754                 return;
755         }
756         down(&console_sem);
757         console_locked = 1;
758         console_may_schedule = 1;
759 }
760 EXPORT_SYMBOL(acquire_console_sem);
761
762 int try_acquire_console_sem(void)
763 {
764         if (down_trylock(&console_sem))
765                 return -1;
766         console_locked = 1;
767         console_may_schedule = 0;
768         return 0;
769 }
770 EXPORT_SYMBOL(try_acquire_console_sem);
771
772 int is_console_locked(void)
773 {
774         return console_locked;
775 }
776 EXPORT_SYMBOL(is_console_locked);
777
778 /**
779  * release_console_sem - unlock the console system
780  *
781  * Releases the semaphore which the caller holds on the console system
782  * and the console driver list.
783  *
784  * While the semaphore was held, console output may have been buffered
785  * by printk().  If this is the case, release_console_sem() emits
786  * the output prior to releasing the semaphore.
787  *
788  * If there is output waiting for klogd, we wake it up.
789  *
790  * release_console_sem() may be called from any context.
791  */
792 void release_console_sem(void)
793 {
794         unsigned long flags;
795         unsigned long _con_start, _log_end;
796         unsigned long wake_klogd = 0;
797
798         if (console_suspended) {
799                 up(&secondary_console_sem);
800                 return;
801         }
802         for ( ; ; ) {
803                 spin_lock_irqsave(&logbuf_lock, flags);
804                 wake_klogd |= log_start - log_end;
805                 if (con_start == log_end)
806                         break;                  /* Nothing to print */
807                 _con_start = con_start;
808                 _log_end = log_end;
809                 con_start = log_end;            /* Flush */
810                 spin_unlock(&logbuf_lock);
811                 call_console_drivers(_con_start, _log_end);
812                 local_irq_restore(flags);
813         }
814         console_locked = 0;
815         console_may_schedule = 0;
816         up(&console_sem);
817         spin_unlock_irqrestore(&logbuf_lock, flags);
818         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) {
819                 /*
820                  * If we printk from within the lock dependency code,
821                  * from within the scheduler code, then do not lock
822                  * up due to self-recursion:
823                  */
824                 if (!lockdep_internal())
825                         wake_up_interruptible(&log_wait);
826         }
827 }
828 EXPORT_SYMBOL(release_console_sem);
829
830 /**
831  * console_conditional_schedule - yield the CPU if required
832  *
833  * If the console code is currently allowed to sleep, and
834  * if this CPU should yield the CPU to another task, do
835  * so here.
836  *
837  * Must be called within acquire_console_sem().
838  */
839 void __sched console_conditional_schedule(void)
840 {
841         if (console_may_schedule)
842                 cond_resched();
843 }
844 EXPORT_SYMBOL(console_conditional_schedule);
845
846 void console_print(const char *s)
847 {
848         printk(KERN_EMERG "%s", s);
849 }
850 EXPORT_SYMBOL(console_print);
851
852 void console_unblank(void)
853 {
854         struct console *c;
855
856         /*
857          * console_unblank can no longer be called in interrupt context unless
858          * oops_in_progress is set to 1..
859          */
860         if (oops_in_progress) {
861                 if (down_trylock(&console_sem) != 0)
862                         return;
863         } else
864                 acquire_console_sem();
865
866         console_locked = 1;
867         console_may_schedule = 0;
868         for (c = console_drivers; c != NULL; c = c->next)
869                 if ((c->flags & CON_ENABLED) && c->unblank)
870                         c->unblank();
871         release_console_sem();
872 }
873
874 /*
875  * Return the console tty driver structure and its associated index
876  */
877 struct tty_driver *console_device(int *index)
878 {
879         struct console *c;
880         struct tty_driver *driver = NULL;
881
882         acquire_console_sem();
883         for (c = console_drivers; c != NULL; c = c->next) {
884                 if (!c->device)
885                         continue;
886                 driver = c->device(c, index);
887                 if (driver)
888                         break;
889         }
890         release_console_sem();
891         return driver;
892 }
893
894 /*
895  * Prevent further output on the passed console device so that (for example)
896  * serial drivers can disable console output before suspending a port, and can
897  * re-enable output afterwards.
898  */
899 void console_stop(struct console *console)
900 {
901         acquire_console_sem();
902         console->flags &= ~CON_ENABLED;
903         release_console_sem();
904 }
905 EXPORT_SYMBOL(console_stop);
906
907 void console_start(struct console *console)
908 {
909         acquire_console_sem();
910         console->flags |= CON_ENABLED;
911         release_console_sem();
912 }
913 EXPORT_SYMBOL(console_start);
914
915 /*
916  * The console driver calls this routine during kernel initialization
917  * to register the console printing procedure with printk() and to
918  * print any messages that were printed by the kernel before the
919  * console driver was initialized.
920  */
921 void register_console(struct console *console)
922 {
923         int i;
924         unsigned long flags;
925
926         if (preferred_console < 0)
927                 preferred_console = selected_console;
928
929         /*
930          *      See if we want to use this console driver. If we
931          *      didn't select a console we take the first one
932          *      that registers here.
933          */
934         if (preferred_console < 0) {
935                 if (console->index < 0)
936                         console->index = 0;
937                 if (console->setup == NULL ||
938                     console->setup(console, NULL) == 0) {
939                         console->flags |= CON_ENABLED | CON_CONSDEV;
940                         preferred_console = 0;
941                 }
942         }
943
944         /*
945          *      See if this console matches one we selected on
946          *      the command line.
947          */
948         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
949                         i++) {
950                 if (strcmp(console_cmdline[i].name, console->name) != 0)
951                         continue;
952                 if (console->index >= 0 &&
953                     console->index != console_cmdline[i].index)
954                         continue;
955                 if (console->index < 0)
956                         console->index = console_cmdline[i].index;
957                 if (console->setup &&
958                     console->setup(console, console_cmdline[i].options) != 0)
959                         break;
960                 console->flags |= CON_ENABLED;
961                 console->index = console_cmdline[i].index;
962                 if (i == selected_console) {
963                         console->flags |= CON_CONSDEV;
964                         preferred_console = selected_console;
965                 }
966                 break;
967         }
968
969         if (!(console->flags & CON_ENABLED))
970                 return;
971
972         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
973                 unregister_console(console_drivers);
974                 console->flags &= ~CON_PRINTBUFFER;
975         }
976
977         /*
978          *      Put this console in the list - keep the
979          *      preferred driver at the head of the list.
980          */
981         acquire_console_sem();
982         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
983                 console->next = console_drivers;
984                 console_drivers = console;
985                 if (console->next)
986                         console->next->flags &= ~CON_CONSDEV;
987         } else {
988                 console->next = console_drivers->next;
989                 console_drivers->next = console;
990         }
991         if (console->flags & CON_PRINTBUFFER) {
992                 /*
993                  * release_console_sem() will print out the buffered messages
994                  * for us.
995                  */
996                 spin_lock_irqsave(&logbuf_lock, flags);
997                 con_start = log_start;
998                 spin_unlock_irqrestore(&logbuf_lock, flags);
999         }
1000         release_console_sem();
1001 }
1002 EXPORT_SYMBOL(register_console);
1003
1004 int unregister_console(struct console *console)
1005 {
1006         struct console *a, *b;
1007         int res = 1;
1008
1009         acquire_console_sem();
1010         if (console_drivers == console) {
1011                 console_drivers=console->next;
1012                 res = 0;
1013         } else if (console_drivers) {
1014                 for (a=console_drivers->next, b=console_drivers ;
1015                      a; b=a, a=b->next) {
1016                         if (a == console) {
1017                                 b->next = a->next;
1018                                 res = 0;
1019                                 break;
1020                         }
1021                 }
1022         }
1023
1024         /* If last console is removed, we re-enable picking the first
1025          * one that gets registered. Without that, pmac early boot console
1026          * would prevent fbcon from taking over.
1027          *
1028          * If this isn't the last console and it has CON_CONSDEV set, we
1029          * need to set it on the next preferred console.
1030          */
1031         if (console_drivers == NULL)
1032                 preferred_console = selected_console;
1033         else if (console->flags & CON_CONSDEV)
1034                 console_drivers->flags |= CON_CONSDEV;
1035
1036         release_console_sem();
1037         return res;
1038 }
1039 EXPORT_SYMBOL(unregister_console);
1040
1041 /**
1042  * tty_write_message - write a message to a certain tty, not just the console.
1043  * @tty: the destination tty_struct
1044  * @msg: the message to write
1045  *
1046  * This is used for messages that need to be redirected to a specific tty.
1047  * We don't put it into the syslog queue right now maybe in the future if
1048  * really needed.
1049  */
1050 void tty_write_message(struct tty_struct *tty, char *msg)
1051 {
1052         if (tty && tty->driver->write)
1053                 tty->driver->write(tty, msg, strlen(msg));
1054         return;
1055 }
1056
1057 /*
1058  * printk rate limiting, lifted from the networking subsystem.
1059  *
1060  * This enforces a rate limit: not more than one kernel message
1061  * every printk_ratelimit_jiffies to make a denial-of-service
1062  * attack impossible.
1063  */
1064 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1065 {
1066         static DEFINE_SPINLOCK(ratelimit_lock);
1067         static unsigned long toks = 10 * 5 * HZ;
1068         static unsigned long last_msg;
1069         static int missed;
1070         unsigned long flags;
1071         unsigned long now = jiffies;
1072
1073         spin_lock_irqsave(&ratelimit_lock, flags);
1074         toks += now - last_msg;
1075         last_msg = now;
1076         if (toks > (ratelimit_burst * ratelimit_jiffies))
1077                 toks = ratelimit_burst * ratelimit_jiffies;
1078         if (toks >= ratelimit_jiffies) {
1079                 int lost = missed;
1080
1081                 missed = 0;
1082                 toks -= ratelimit_jiffies;
1083                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1084                 if (lost)
1085                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1086                 return 1;
1087         }
1088         missed++;
1089         spin_unlock_irqrestore(&ratelimit_lock, flags);
1090         return 0;
1091 }
1092 EXPORT_SYMBOL(__printk_ratelimit);
1093
1094 /* minimum time in jiffies between messages */
1095 int printk_ratelimit_jiffies = 5 * HZ;
1096
1097 /* number of messages we send before ratelimiting */
1098 int printk_ratelimit_burst = 10;
1099
1100 int printk_ratelimit(void)
1101 {
1102         return __printk_ratelimit(printk_ratelimit_jiffies,
1103                                 printk_ratelimit_burst);
1104 }
1105 EXPORT_SYMBOL(printk_ratelimit);