printk: robustify printk, update comment
[linux-2.6.git] / kernel / printk.c
1 /*
2  *  linux/kernel/printk.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *
6  * Modified to make sys_syslog() more flexible: added commands to
7  * return the last 4k of kernel messages, regardless of whether
8  * they've been read or not.  Added option to suppress kernel printk's
9  * to the console.  Added hook for sending the console messages
10  * elsewhere, in preparation for a serial line console (someday).
11  * Ted Ts'o, 2/11/93.
12  * Modified for sysctl support, 1/8/97, Chris Horn.
13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14  *     manfred@colorfullife.com
15  * Rewrote bits to get rid of console_lock
16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
17  */
18
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/console.h>
24 #include <linux/init.h>
25 #include <linux/jiffies.h>
26 #include <linux/nmi.h>
27 #include <linux/module.h>
28 #include <linux/moduleparam.h>
29 #include <linux/interrupt.h>                    /* For in_interrupt() */
30 #include <linux/delay.h>
31 #include <linux/smp.h>
32 #include <linux/security.h>
33 #include <linux/bootmem.h>
34 #include <linux/syscalls.h>
35
36 #include <asm/uaccess.h>
37
38 /*
39  * Architectures can override it:
40  */
41 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
42 {
43 }
44
45 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
46
47 /* printk's without a loglevel use this.. */
48 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
49
50 /* We show everything that is MORE important than this.. */
51 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
52 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
53
54 DECLARE_WAIT_QUEUE_HEAD(log_wait);
55
56 int console_printk[4] = {
57         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
58         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
59         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
60         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
61 };
62
63 /*
64  * Low level drivers may need that to know if they can schedule in
65  * their unblank() callback or not. So let's export it.
66  */
67 int oops_in_progress;
68 EXPORT_SYMBOL(oops_in_progress);
69
70 /*
71  * console_sem protects the console_drivers list, and also
72  * provides serialisation for access to the entire console
73  * driver system.
74  */
75 static DECLARE_MUTEX(console_sem);
76 static DECLARE_MUTEX(secondary_console_sem);
77 struct console *console_drivers;
78 EXPORT_SYMBOL_GPL(console_drivers);
79
80 /*
81  * This is used for debugging the mess that is the VT code by
82  * keeping track if we have the console semaphore held. It's
83  * definitely not the perfect debug tool (we don't know if _WE_
84  * hold it are racing, but it helps tracking those weird code
85  * path in the console code where we end up in places I want
86  * locked without the console sempahore held
87  */
88 static int console_locked, console_suspended;
89
90 /*
91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
92  * It is also used in interesting ways to provide interlocking in
93  * release_console_sem().
94  */
95 static DEFINE_SPINLOCK(logbuf_lock);
96
97 #define LOG_BUF_MASK (log_buf_len-1)
98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
99
100 /*
101  * The indices into log_buf are not constrained to log_buf_len - they
102  * must be masked before subscripting
103  */
104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
107
108 /*
109  *      Array of consoles built from command line options (console=)
110  */
111 struct console_cmdline
112 {
113         char    name[8];                        /* Name of the driver       */
114         int     index;                          /* Minor dev. to use        */
115         char    *options;                       /* Options for the driver   */
116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
117         char    *brl_options;                   /* Options for braille driver */
118 #endif
119 };
120
121 #define MAX_CMDLINECONSOLES 8
122
123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
124 static int selected_console = -1;
125 static int preferred_console = -1;
126 int console_set_on_cmdline;
127 EXPORT_SYMBOL(console_set_on_cmdline);
128
129 /* Flag: console code may call schedule() */
130 static int console_may_schedule;
131
132 #ifdef CONFIG_PRINTK
133
134 static char __log_buf[__LOG_BUF_LEN];
135 static char *log_buf = __log_buf;
136 static int log_buf_len = __LOG_BUF_LEN;
137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
138
139 static int __init log_buf_len_setup(char *str)
140 {
141         unsigned size = memparse(str, &str);
142         unsigned long flags;
143
144         if (size)
145                 size = roundup_pow_of_two(size);
146         if (size > log_buf_len) {
147                 unsigned start, dest_idx, offset;
148                 char *new_log_buf;
149
150                 new_log_buf = alloc_bootmem(size);
151                 if (!new_log_buf) {
152                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
153                         goto out;
154                 }
155
156                 spin_lock_irqsave(&logbuf_lock, flags);
157                 log_buf_len = size;
158                 log_buf = new_log_buf;
159
160                 offset = start = min(con_start, log_start);
161                 dest_idx = 0;
162                 while (start != log_end) {
163                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
164                         start++;
165                         dest_idx++;
166                 }
167                 log_start -= offset;
168                 con_start -= offset;
169                 log_end -= offset;
170                 spin_unlock_irqrestore(&logbuf_lock, flags);
171
172                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
173         }
174 out:
175         return 1;
176 }
177
178 __setup("log_buf_len=", log_buf_len_setup);
179
180 #ifdef CONFIG_BOOT_PRINTK_DELAY
181
182 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
183 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
184
185 static int __init boot_delay_setup(char *str)
186 {
187         unsigned long lpj;
188         unsigned long long loops_per_msec;
189
190         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
191         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
192
193         get_option(&str, &boot_delay);
194         if (boot_delay > 10 * 1000)
195                 boot_delay = 0;
196
197         printk_delay_msec = loops_per_msec;
198         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
199                 "HZ: %d, printk_delay_msec: %llu\n",
200                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
201         return 1;
202 }
203 __setup("boot_delay=", boot_delay_setup);
204
205 static void boot_delay_msec(void)
206 {
207         unsigned long long k;
208         unsigned long timeout;
209
210         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
211                 return;
212
213         k = (unsigned long long)printk_delay_msec * boot_delay;
214
215         timeout = jiffies + msecs_to_jiffies(boot_delay);
216         while (k) {
217                 k--;
218                 cpu_relax();
219                 /*
220                  * use (volatile) jiffies to prevent
221                  * compiler reduction; loop termination via jiffies
222                  * is secondary and may or may not happen.
223                  */
224                 if (time_after(jiffies, timeout))
225                         break;
226                 touch_nmi_watchdog();
227         }
228 }
229 #else
230 static inline void boot_delay_msec(void)
231 {
232 }
233 #endif
234
235 /*
236  * Return the number of unread characters in the log buffer.
237  */
238 static int log_buf_get_len(void)
239 {
240         return logged_chars;
241 }
242
243 /*
244  * Copy a range of characters from the log buffer.
245  */
246 int log_buf_copy(char *dest, int idx, int len)
247 {
248         int ret, max;
249         bool took_lock = false;
250
251         if (!oops_in_progress) {
252                 spin_lock_irq(&logbuf_lock);
253                 took_lock = true;
254         }
255
256         max = log_buf_get_len();
257         if (idx < 0 || idx >= max) {
258                 ret = -1;
259         } else {
260                 if (len > max)
261                         len = max;
262                 ret = len;
263                 idx += (log_end - max);
264                 while (len-- > 0)
265                         dest[len] = LOG_BUF(idx + len);
266         }
267
268         if (took_lock)
269                 spin_unlock_irq(&logbuf_lock);
270
271         return ret;
272 }
273
274 /*
275  * Commands to do_syslog:
276  *
277  *      0 -- Close the log.  Currently a NOP.
278  *      1 -- Open the log. Currently a NOP.
279  *      2 -- Read from the log.
280  *      3 -- Read all messages remaining in the ring buffer.
281  *      4 -- Read and clear all messages remaining in the ring buffer
282  *      5 -- Clear ring buffer.
283  *      6 -- Disable printk's to console
284  *      7 -- Enable printk's to console
285  *      8 -- Set level of messages printed to console
286  *      9 -- Return number of unread characters in the log buffer
287  *     10 -- Return size of the log buffer
288  */
289 int do_syslog(int type, char __user *buf, int len)
290 {
291         unsigned i, j, limit, count;
292         int do_clear = 0;
293         char c;
294         int error = 0;
295
296         error = security_syslog(type);
297         if (error)
298                 return error;
299
300         switch (type) {
301         case 0:         /* Close log */
302                 break;
303         case 1:         /* Open log */
304                 break;
305         case 2:         /* Read from log */
306                 error = -EINVAL;
307                 if (!buf || len < 0)
308                         goto out;
309                 error = 0;
310                 if (!len)
311                         goto out;
312                 if (!access_ok(VERIFY_WRITE, buf, len)) {
313                         error = -EFAULT;
314                         goto out;
315                 }
316                 error = wait_event_interruptible(log_wait,
317                                                         (log_start - log_end));
318                 if (error)
319                         goto out;
320                 i = 0;
321                 spin_lock_irq(&logbuf_lock);
322                 while (!error && (log_start != log_end) && i < len) {
323                         c = LOG_BUF(log_start);
324                         log_start++;
325                         spin_unlock_irq(&logbuf_lock);
326                         error = __put_user(c,buf);
327                         buf++;
328                         i++;
329                         cond_resched();
330                         spin_lock_irq(&logbuf_lock);
331                 }
332                 spin_unlock_irq(&logbuf_lock);
333                 if (!error)
334                         error = i;
335                 break;
336         case 4:         /* Read/clear last kernel messages */
337                 do_clear = 1;
338                 /* FALL THRU */
339         case 3:         /* Read last kernel messages */
340                 error = -EINVAL;
341                 if (!buf || len < 0)
342                         goto out;
343                 error = 0;
344                 if (!len)
345                         goto out;
346                 if (!access_ok(VERIFY_WRITE, buf, len)) {
347                         error = -EFAULT;
348                         goto out;
349                 }
350                 count = len;
351                 if (count > log_buf_len)
352                         count = log_buf_len;
353                 spin_lock_irq(&logbuf_lock);
354                 if (count > logged_chars)
355                         count = logged_chars;
356                 if (do_clear)
357                         logged_chars = 0;
358                 limit = log_end;
359                 /*
360                  * __put_user() could sleep, and while we sleep
361                  * printk() could overwrite the messages
362                  * we try to copy to user space. Therefore
363                  * the messages are copied in reverse. <manfreds>
364                  */
365                 for (i = 0; i < count && !error; i++) {
366                         j = limit-1-i;
367                         if (j + log_buf_len < log_end)
368                                 break;
369                         c = LOG_BUF(j);
370                         spin_unlock_irq(&logbuf_lock);
371                         error = __put_user(c,&buf[count-1-i]);
372                         cond_resched();
373                         spin_lock_irq(&logbuf_lock);
374                 }
375                 spin_unlock_irq(&logbuf_lock);
376                 if (error)
377                         break;
378                 error = i;
379                 if (i != count) {
380                         int offset = count-error;
381                         /* buffer overflow during copy, correct user buffer. */
382                         for (i = 0; i < error; i++) {
383                                 if (__get_user(c,&buf[i+offset]) ||
384                                     __put_user(c,&buf[i])) {
385                                         error = -EFAULT;
386                                         break;
387                                 }
388                                 cond_resched();
389                         }
390                 }
391                 break;
392         case 5:         /* Clear ring buffer */
393                 logged_chars = 0;
394                 break;
395         case 6:         /* Disable logging to console */
396                 console_loglevel = minimum_console_loglevel;
397                 break;
398         case 7:         /* Enable logging to console */
399                 console_loglevel = default_console_loglevel;
400                 break;
401         case 8:         /* Set level of messages printed to console */
402                 error = -EINVAL;
403                 if (len < 1 || len > 8)
404                         goto out;
405                 if (len < minimum_console_loglevel)
406                         len = minimum_console_loglevel;
407                 console_loglevel = len;
408                 error = 0;
409                 break;
410         case 9:         /* Number of chars in the log buffer */
411                 error = log_end - log_start;
412                 break;
413         case 10:        /* Size of the log buffer */
414                 error = log_buf_len;
415                 break;
416         default:
417                 error = -EINVAL;
418                 break;
419         }
420 out:
421         return error;
422 }
423
424 asmlinkage long sys_syslog(int type, char __user *buf, int len)
425 {
426         return do_syslog(type, buf, len);
427 }
428
429 /*
430  * Call the console drivers on a range of log_buf
431  */
432 static void __call_console_drivers(unsigned start, unsigned end)
433 {
434         struct console *con;
435
436         for (con = console_drivers; con; con = con->next) {
437                 if ((con->flags & CON_ENABLED) && con->write &&
438                                 (cpu_online(smp_processor_id()) ||
439                                 (con->flags & CON_ANYTIME)))
440                         con->write(con, &LOG_BUF(start), end - start);
441         }
442 }
443
444 static int __read_mostly ignore_loglevel;
445
446 static int __init ignore_loglevel_setup(char *str)
447 {
448         ignore_loglevel = 1;
449         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
450
451         return 0;
452 }
453
454 early_param("ignore_loglevel", ignore_loglevel_setup);
455
456 /*
457  * Write out chars from start to end - 1 inclusive
458  */
459 static void _call_console_drivers(unsigned start,
460                                 unsigned end, int msg_log_level)
461 {
462         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
463                         console_drivers && start != end) {
464                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
465                         /* wrapped write */
466                         __call_console_drivers(start & LOG_BUF_MASK,
467                                                 log_buf_len);
468                         __call_console_drivers(0, end & LOG_BUF_MASK);
469                 } else {
470                         __call_console_drivers(start, end);
471                 }
472         }
473 }
474
475 /*
476  * Call the console drivers, asking them to write out
477  * log_buf[start] to log_buf[end - 1].
478  * The console_sem must be held.
479  */
480 static void call_console_drivers(unsigned start, unsigned end)
481 {
482         unsigned cur_index, start_print;
483         static int msg_level = -1;
484
485         BUG_ON(((int)(start - end)) > 0);
486
487         cur_index = start;
488         start_print = start;
489         while (cur_index != end) {
490                 if (msg_level < 0 && ((end - cur_index) > 2) &&
491                                 LOG_BUF(cur_index + 0) == '<' &&
492                                 LOG_BUF(cur_index + 1) >= '0' &&
493                                 LOG_BUF(cur_index + 1) <= '7' &&
494                                 LOG_BUF(cur_index + 2) == '>') {
495                         msg_level = LOG_BUF(cur_index + 1) - '0';
496                         cur_index += 3;
497                         start_print = cur_index;
498                 }
499                 while (cur_index != end) {
500                         char c = LOG_BUF(cur_index);
501
502                         cur_index++;
503                         if (c == '\n') {
504                                 if (msg_level < 0) {
505                                         /*
506                                          * printk() has already given us loglevel tags in
507                                          * the buffer.  This code is here in case the
508                                          * log buffer has wrapped right round and scribbled
509                                          * on those tags
510                                          */
511                                         msg_level = default_message_loglevel;
512                                 }
513                                 _call_console_drivers(start_print, cur_index, msg_level);
514                                 msg_level = -1;
515                                 start_print = cur_index;
516                                 break;
517                         }
518                 }
519         }
520         _call_console_drivers(start_print, end, msg_level);
521 }
522
523 static void emit_log_char(char c)
524 {
525         LOG_BUF(log_end) = c;
526         log_end++;
527         if (log_end - log_start > log_buf_len)
528                 log_start = log_end - log_buf_len;
529         if (log_end - con_start > log_buf_len)
530                 con_start = log_end - log_buf_len;
531         if (logged_chars < log_buf_len)
532                 logged_chars++;
533 }
534
535 /*
536  * Zap console related locks when oopsing. Only zap at most once
537  * every 10 seconds, to leave time for slow consoles to print a
538  * full oops.
539  */
540 static void zap_locks(void)
541 {
542         static unsigned long oops_timestamp;
543
544         if (time_after_eq(jiffies, oops_timestamp) &&
545                         !time_after(jiffies, oops_timestamp + 30 * HZ))
546                 return;
547
548         oops_timestamp = jiffies;
549
550         /* If a crash is occurring, make sure we can't deadlock */
551         spin_lock_init(&logbuf_lock);
552         /* And make sure that we print immediately */
553         init_MUTEX(&console_sem);
554 }
555
556 #if defined(CONFIG_PRINTK_TIME)
557 static int printk_time = 1;
558 #else
559 static int printk_time = 0;
560 #endif
561 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
562
563 /* Check if we have any console registered that can be called early in boot. */
564 static int have_callable_console(void)
565 {
566         struct console *con;
567
568         for (con = console_drivers; con; con = con->next)
569                 if (con->flags & CON_ANYTIME)
570                         return 1;
571
572         return 0;
573 }
574
575 /**
576  * printk - print a kernel message
577  * @fmt: format string
578  *
579  * This is printk().  It can be called from any context.  We want it to work.
580  *
581  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
582  * call the console drivers.  If we fail to get the semaphore we place the output
583  * into the log buffer and return.  The current holder of the console_sem will
584  * notice the new output in release_console_sem() and will send it to the
585  * consoles before releasing the semaphore.
586  *
587  * One effect of this deferred printing is that code which calls printk() and
588  * then changes console_loglevel may break. This is because console_loglevel
589  * is inspected when the actual printing occurs.
590  *
591  * See also:
592  * printf(3)
593  */
594
595 asmlinkage int printk(const char *fmt, ...)
596 {
597         va_list args;
598         int r;
599
600         va_start(args, fmt);
601         r = vprintk(fmt, args);
602         va_end(args);
603
604         return r;
605 }
606
607 /* cpu currently holding logbuf_lock */
608 static volatile unsigned int printk_cpu = UINT_MAX;
609
610 /*
611  * Can we actually use the console at this time on this cpu?
612  *
613  * Console drivers may assume that per-cpu resources have
614  * been allocated. So unless they're explicitly marked as
615  * being able to cope (CON_ANYTIME) don't call them until
616  * this CPU is officially up.
617  */
618 static inline int can_use_console(unsigned int cpu)
619 {
620         return cpu_online(cpu) || have_callable_console();
621 }
622
623 /*
624  * Try to get console ownership to actually show the kernel
625  * messages from a 'printk'. Return true (and with the
626  * console_semaphore held, and 'console_locked' set) if it
627  * is successful, false otherwise.
628  *
629  * This gets called with the 'logbuf_lock' spinlock held and
630  * interrupts disabled. It should return with 'lockbuf_lock'
631  * released but interrupts still disabled.
632  */
633 static int acquire_console_semaphore_for_printk(unsigned int cpu)
634 {
635         int retval = 0;
636
637         if (!try_acquire_console_sem()) {
638                 retval = 1;
639
640                 /*
641                  * If we can't use the console, we need to release
642                  * the console semaphore by hand to avoid flushing
643                  * the buffer. We need to hold the console semaphore
644                  * in order to do this test safely.
645                  */
646                 if (!can_use_console(cpu)) {
647                         console_locked = 0;
648                         up(&console_sem);
649                         retval = 0;
650                 }
651         }
652         printk_cpu = UINT_MAX;
653         spin_unlock(&logbuf_lock);
654         return retval;
655 }
656 static const char recursion_bug_msg [] =
657                 KERN_CRIT "BUG: recent printk recursion!\n";
658 static int recursion_bug;
659         static int new_text_line = 1;
660 static char printk_buf[1024];
661
662 asmlinkage int vprintk(const char *fmt, va_list args)
663 {
664         int printed_len = 0;
665         int current_log_level = default_message_loglevel;
666         unsigned long flags;
667         int this_cpu;
668         char *p;
669
670         boot_delay_msec();
671
672         preempt_disable();
673         /* This stops the holder of console_sem just where we want him */
674         raw_local_irq_save(flags);
675         this_cpu = smp_processor_id();
676
677         /*
678          * Ouch, printk recursed into itself!
679          */
680         if (unlikely(printk_cpu == this_cpu)) {
681                 /*
682                  * If a crash is occurring during printk() on this CPU,
683                  * then try to get the crash message out but make sure
684                  * we can't deadlock. Otherwise just return to avoid the
685                  * recursion and return - but flag the recursion so that
686                  * it can be printed at the next appropriate moment:
687                  */
688                 if (!oops_in_progress) {
689                         recursion_bug = 1;
690                         goto out_restore_irqs;
691                 }
692                 zap_locks();
693         }
694
695         lockdep_off();
696         spin_lock(&logbuf_lock);
697         printk_cpu = this_cpu;
698
699         if (recursion_bug) {
700                 recursion_bug = 0;
701                 strcpy(printk_buf, recursion_bug_msg);
702                 printed_len = sizeof(recursion_bug_msg);
703         }
704         /* Emit the output into the temporary buffer */
705         printed_len += vscnprintf(printk_buf + printed_len,
706                                   sizeof(printk_buf) - printed_len, fmt, args);
707
708
709         /*
710          * Copy the output into log_buf.  If the caller didn't provide
711          * appropriate log level tags, we insert them here
712          */
713         for (p = printk_buf; *p; p++) {
714                 if (new_text_line) {
715                         /* If a token, set current_log_level and skip over */
716                         if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
717                             p[2] == '>') {
718                                 current_log_level = p[1] - '0';
719                                 p += 3;
720                                 printed_len -= 3;
721                         }
722
723                         /* Always output the token */
724                         emit_log_char('<');
725                         emit_log_char(current_log_level + '0');
726                         emit_log_char('>');
727                         printed_len += 3;
728                         new_text_line = 0;
729
730                         if (printk_time) {
731                                 /* Follow the token with the time */
732                                 char tbuf[50], *tp;
733                                 unsigned tlen;
734                                 unsigned long long t;
735                                 unsigned long nanosec_rem;
736
737                                 t = cpu_clock(printk_cpu);
738                                 nanosec_rem = do_div(t, 1000000000);
739                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
740                                                 (unsigned long) t,
741                                                 nanosec_rem / 1000);
742
743                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
744                                         emit_log_char(*tp);
745                                 printed_len += tlen;
746                         }
747
748                         if (!*p)
749                                 break;
750                 }
751
752                 emit_log_char(*p);
753                 if (*p == '\n')
754                         new_text_line = 1;
755         }
756
757         /*
758          * Try to acquire and then immediately release the
759          * console semaphore. The release will do all the
760          * actual magic (print out buffers, wake up klogd,
761          * etc). 
762          *
763          * The acquire_console_semaphore_for_printk() function
764          * will release 'logbuf_lock' regardless of whether it
765          * actually gets the semaphore or not.
766          */
767         if (acquire_console_semaphore_for_printk(this_cpu))
768                 release_console_sem();
769
770         lockdep_on();
771 out_restore_irqs:
772         raw_local_irq_restore(flags);
773
774         preempt_enable();
775         return printed_len;
776 }
777 EXPORT_SYMBOL(printk);
778 EXPORT_SYMBOL(vprintk);
779
780 #else
781
782 asmlinkage long sys_syslog(int type, char __user *buf, int len)
783 {
784         return -ENOSYS;
785 }
786
787 static void call_console_drivers(unsigned start, unsigned end)
788 {
789 }
790
791 #endif
792
793 static int __add_preferred_console(char *name, int idx, char *options,
794                                    char *brl_options)
795 {
796         struct console_cmdline *c;
797         int i;
798
799         /*
800          *      See if this tty is not yet registered, and
801          *      if we have a slot free.
802          */
803         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
804                 if (strcmp(console_cmdline[i].name, name) == 0 &&
805                           console_cmdline[i].index == idx) {
806                                 if (!brl_options)
807                                         selected_console = i;
808                                 return 0;
809                 }
810         if (i == MAX_CMDLINECONSOLES)
811                 return -E2BIG;
812         if (!brl_options)
813                 selected_console = i;
814         c = &console_cmdline[i];
815         strlcpy(c->name, name, sizeof(c->name));
816         c->options = options;
817 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
818         c->brl_options = brl_options;
819 #endif
820         c->index = idx;
821         return 0;
822 }
823 /*
824  * Set up a list of consoles.  Called from init/main.c
825  */
826 static int __init console_setup(char *str)
827 {
828         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
829         char *s, *options, *brl_options = NULL;
830         int idx;
831
832 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
833         if (!memcmp(str, "brl,", 4)) {
834                 brl_options = "";
835                 str += 4;
836         } else if (!memcmp(str, "brl=", 4)) {
837                 brl_options = str + 4;
838                 str = strchr(brl_options, ',');
839                 if (!str) {
840                         printk(KERN_ERR "need port name after brl=\n");
841                         return 1;
842                 }
843                 *(str++) = 0;
844         }
845 #endif
846
847         /*
848          * Decode str into name, index, options.
849          */
850         if (str[0] >= '0' && str[0] <= '9') {
851                 strcpy(buf, "ttyS");
852                 strncpy(buf + 4, str, sizeof(buf) - 5);
853         } else {
854                 strncpy(buf, str, sizeof(buf) - 1);
855         }
856         buf[sizeof(buf) - 1] = 0;
857         if ((options = strchr(str, ',')) != NULL)
858                 *(options++) = 0;
859 #ifdef __sparc__
860         if (!strcmp(str, "ttya"))
861                 strcpy(buf, "ttyS0");
862         if (!strcmp(str, "ttyb"))
863                 strcpy(buf, "ttyS1");
864 #endif
865         for (s = buf; *s; s++)
866                 if ((*s >= '0' && *s <= '9') || *s == ',')
867                         break;
868         idx = simple_strtoul(s, NULL, 10);
869         *s = 0;
870
871         __add_preferred_console(buf, idx, options, brl_options);
872         console_set_on_cmdline = 1;
873         return 1;
874 }
875 __setup("console=", console_setup);
876
877 /**
878  * add_preferred_console - add a device to the list of preferred consoles.
879  * @name: device name
880  * @idx: device index
881  * @options: options for this console
882  *
883  * The last preferred console added will be used for kernel messages
884  * and stdin/out/err for init.  Normally this is used by console_setup
885  * above to handle user-supplied console arguments; however it can also
886  * be used by arch-specific code either to override the user or more
887  * commonly to provide a default console (ie from PROM variables) when
888  * the user has not supplied one.
889  */
890 int add_preferred_console(char *name, int idx, char *options)
891 {
892         return __add_preferred_console(name, idx, options, NULL);
893 }
894
895 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
896 {
897         struct console_cmdline *c;
898         int i;
899
900         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
901                 if (strcmp(console_cmdline[i].name, name) == 0 &&
902                           console_cmdline[i].index == idx) {
903                                 c = &console_cmdline[i];
904                                 strlcpy(c->name, name_new, sizeof(c->name));
905                                 c->name[sizeof(c->name) - 1] = 0;
906                                 c->options = options;
907                                 c->index = idx_new;
908                                 return i;
909                 }
910         /* not found */
911         return -1;
912 }
913
914 int console_suspend_enabled = 1;
915 EXPORT_SYMBOL(console_suspend_enabled);
916
917 static int __init console_suspend_disable(char *str)
918 {
919         console_suspend_enabled = 0;
920         return 1;
921 }
922 __setup("no_console_suspend", console_suspend_disable);
923
924 /**
925  * suspend_console - suspend the console subsystem
926  *
927  * This disables printk() while we go into suspend states
928  */
929 void suspend_console(void)
930 {
931         if (!console_suspend_enabled)
932                 return;
933         printk("Suspending console(s) (use no_console_suspend to debug)\n");
934         acquire_console_sem();
935         console_suspended = 1;
936 }
937
938 void resume_console(void)
939 {
940         if (!console_suspend_enabled)
941                 return;
942         console_suspended = 0;
943         release_console_sem();
944 }
945
946 /**
947  * acquire_console_sem - lock the console system for exclusive use.
948  *
949  * Acquires a semaphore which guarantees that the caller has
950  * exclusive access to the console system and the console_drivers list.
951  *
952  * Can sleep, returns nothing.
953  */
954 void acquire_console_sem(void)
955 {
956         BUG_ON(in_interrupt());
957         if (console_suspended) {
958                 down(&secondary_console_sem);
959                 return;
960         }
961         down(&console_sem);
962         console_locked = 1;
963         console_may_schedule = 1;
964 }
965 EXPORT_SYMBOL(acquire_console_sem);
966
967 int try_acquire_console_sem(void)
968 {
969         if (down_trylock(&console_sem))
970                 return -1;
971         console_locked = 1;
972         console_may_schedule = 0;
973         return 0;
974 }
975 EXPORT_SYMBOL(try_acquire_console_sem);
976
977 int is_console_locked(void)
978 {
979         return console_locked;
980 }
981
982 static DEFINE_PER_CPU(int, printk_pending);
983
984 void printk_tick(void)
985 {
986         if (__get_cpu_var(printk_pending)) {
987                 __get_cpu_var(printk_pending) = 0;
988                 wake_up_interruptible(&log_wait);
989         }
990 }
991
992 int printk_needs_cpu(int cpu)
993 {
994         return per_cpu(printk_pending, cpu);
995 }
996
997 void wake_up_klogd(void)
998 {
999         if (waitqueue_active(&log_wait))
1000                 __raw_get_cpu_var(printk_pending) = 1;
1001 }
1002
1003 /**
1004  * release_console_sem - unlock the console system
1005  *
1006  * Releases the semaphore which the caller holds on the console system
1007  * and the console driver list.
1008  *
1009  * While the semaphore was held, console output may have been buffered
1010  * by printk().  If this is the case, release_console_sem() emits
1011  * the output prior to releasing the semaphore.
1012  *
1013  * If there is output waiting for klogd, we wake it up.
1014  *
1015  * release_console_sem() may be called from any context.
1016  */
1017 void release_console_sem(void)
1018 {
1019         unsigned long flags;
1020         unsigned _con_start, _log_end;
1021         unsigned wake_klogd = 0;
1022
1023         if (console_suspended) {
1024                 up(&secondary_console_sem);
1025                 return;
1026         }
1027
1028         console_may_schedule = 0;
1029
1030         for ( ; ; ) {
1031                 spin_lock_irqsave(&logbuf_lock, flags);
1032                 wake_klogd |= log_start - log_end;
1033                 if (con_start == log_end)
1034                         break;                  /* Nothing to print */
1035                 _con_start = con_start;
1036                 _log_end = log_end;
1037                 con_start = log_end;            /* Flush */
1038                 spin_unlock(&logbuf_lock);
1039                 stop_critical_timings();        /* don't trace print latency */
1040                 call_console_drivers(_con_start, _log_end);
1041                 start_critical_timings();
1042                 local_irq_restore(flags);
1043         }
1044         console_locked = 0;
1045         up(&console_sem);
1046         spin_unlock_irqrestore(&logbuf_lock, flags);
1047         if (wake_klogd)
1048                 wake_up_klogd();
1049 }
1050 EXPORT_SYMBOL(release_console_sem);
1051
1052 /**
1053  * console_conditional_schedule - yield the CPU if required
1054  *
1055  * If the console code is currently allowed to sleep, and
1056  * if this CPU should yield the CPU to another task, do
1057  * so here.
1058  *
1059  * Must be called within acquire_console_sem().
1060  */
1061 void __sched console_conditional_schedule(void)
1062 {
1063         if (console_may_schedule)
1064                 cond_resched();
1065 }
1066 EXPORT_SYMBOL(console_conditional_schedule);
1067
1068 void console_print(const char *s)
1069 {
1070         printk(KERN_EMERG "%s", s);
1071 }
1072 EXPORT_SYMBOL(console_print);
1073
1074 void console_unblank(void)
1075 {
1076         struct console *c;
1077
1078         /*
1079          * console_unblank can no longer be called in interrupt context unless
1080          * oops_in_progress is set to 1..
1081          */
1082         if (oops_in_progress) {
1083                 if (down_trylock(&console_sem) != 0)
1084                         return;
1085         } else
1086                 acquire_console_sem();
1087
1088         console_locked = 1;
1089         console_may_schedule = 0;
1090         for (c = console_drivers; c != NULL; c = c->next)
1091                 if ((c->flags & CON_ENABLED) && c->unblank)
1092                         c->unblank();
1093         release_console_sem();
1094 }
1095
1096 /*
1097  * Return the console tty driver structure and its associated index
1098  */
1099 struct tty_driver *console_device(int *index)
1100 {
1101         struct console *c;
1102         struct tty_driver *driver = NULL;
1103
1104         acquire_console_sem();
1105         for (c = console_drivers; c != NULL; c = c->next) {
1106                 if (!c->device)
1107                         continue;
1108                 driver = c->device(c, index);
1109                 if (driver)
1110                         break;
1111         }
1112         release_console_sem();
1113         return driver;
1114 }
1115
1116 /*
1117  * Prevent further output on the passed console device so that (for example)
1118  * serial drivers can disable console output before suspending a port, and can
1119  * re-enable output afterwards.
1120  */
1121 void console_stop(struct console *console)
1122 {
1123         acquire_console_sem();
1124         console->flags &= ~CON_ENABLED;
1125         release_console_sem();
1126 }
1127 EXPORT_SYMBOL(console_stop);
1128
1129 void console_start(struct console *console)
1130 {
1131         acquire_console_sem();
1132         console->flags |= CON_ENABLED;
1133         release_console_sem();
1134 }
1135 EXPORT_SYMBOL(console_start);
1136
1137 /*
1138  * The console driver calls this routine during kernel initialization
1139  * to register the console printing procedure with printk() and to
1140  * print any messages that were printed by the kernel before the
1141  * console driver was initialized.
1142  */
1143 void register_console(struct console *console)
1144 {
1145         int i;
1146         unsigned long flags;
1147         struct console *bootconsole = NULL;
1148
1149         if (console_drivers) {
1150                 if (console->flags & CON_BOOT)
1151                         return;
1152                 if (console_drivers->flags & CON_BOOT)
1153                         bootconsole = console_drivers;
1154         }
1155
1156         if (preferred_console < 0 || bootconsole || !console_drivers)
1157                 preferred_console = selected_console;
1158
1159         if (console->early_setup)
1160                 console->early_setup();
1161
1162         /*
1163          *      See if we want to use this console driver. If we
1164          *      didn't select a console we take the first one
1165          *      that registers here.
1166          */
1167         if (preferred_console < 0) {
1168                 if (console->index < 0)
1169                         console->index = 0;
1170                 if (console->setup == NULL ||
1171                     console->setup(console, NULL) == 0) {
1172                         console->flags |= CON_ENABLED;
1173                         if (console->device) {
1174                                 console->flags |= CON_CONSDEV;
1175                                 preferred_console = 0;
1176                         }
1177                 }
1178         }
1179
1180         /*
1181          *      See if this console matches one we selected on
1182          *      the command line.
1183          */
1184         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1185                         i++) {
1186                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1187                         continue;
1188                 if (console->index >= 0 &&
1189                     console->index != console_cmdline[i].index)
1190                         continue;
1191                 if (console->index < 0)
1192                         console->index = console_cmdline[i].index;
1193 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1194                 if (console_cmdline[i].brl_options) {
1195                         console->flags |= CON_BRL;
1196                         braille_register_console(console,
1197                                         console_cmdline[i].index,
1198                                         console_cmdline[i].options,
1199                                         console_cmdline[i].brl_options);
1200                         return;
1201                 }
1202 #endif
1203                 if (console->setup &&
1204                     console->setup(console, console_cmdline[i].options) != 0)
1205                         break;
1206                 console->flags |= CON_ENABLED;
1207                 console->index = console_cmdline[i].index;
1208                 if (i == selected_console) {
1209                         console->flags |= CON_CONSDEV;
1210                         preferred_console = selected_console;
1211                 }
1212                 break;
1213         }
1214
1215         if (!(console->flags & CON_ENABLED))
1216                 return;
1217
1218         if (bootconsole && (console->flags & CON_CONSDEV)) {
1219                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1220                        bootconsole->name, bootconsole->index,
1221                        console->name, console->index);
1222                 unregister_console(bootconsole);
1223                 console->flags &= ~CON_PRINTBUFFER;
1224         } else {
1225                 printk(KERN_INFO "console [%s%d] enabled\n",
1226                        console->name, console->index);
1227         }
1228
1229         /*
1230          *      Put this console in the list - keep the
1231          *      preferred driver at the head of the list.
1232          */
1233         acquire_console_sem();
1234         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1235                 console->next = console_drivers;
1236                 console_drivers = console;
1237                 if (console->next)
1238                         console->next->flags &= ~CON_CONSDEV;
1239         } else {
1240                 console->next = console_drivers->next;
1241                 console_drivers->next = console;
1242         }
1243         if (console->flags & CON_PRINTBUFFER) {
1244                 /*
1245                  * release_console_sem() will print out the buffered messages
1246                  * for us.
1247                  */
1248                 spin_lock_irqsave(&logbuf_lock, flags);
1249                 con_start = log_start;
1250                 spin_unlock_irqrestore(&logbuf_lock, flags);
1251         }
1252         release_console_sem();
1253 }
1254 EXPORT_SYMBOL(register_console);
1255
1256 int unregister_console(struct console *console)
1257 {
1258         struct console *a, *b;
1259         int res = 1;
1260
1261 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1262         if (console->flags & CON_BRL)
1263                 return braille_unregister_console(console);
1264 #endif
1265
1266         acquire_console_sem();
1267         if (console_drivers == console) {
1268                 console_drivers=console->next;
1269                 res = 0;
1270         } else if (console_drivers) {
1271                 for (a=console_drivers->next, b=console_drivers ;
1272                      a; b=a, a=b->next) {
1273                         if (a == console) {
1274                                 b->next = a->next;
1275                                 res = 0;
1276                                 break;
1277                         }
1278                 }
1279         }
1280
1281         /*
1282          * If this isn't the last console and it has CON_CONSDEV set, we
1283          * need to set it on the next preferred console.
1284          */
1285         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1286                 console_drivers->flags |= CON_CONSDEV;
1287
1288         release_console_sem();
1289         return res;
1290 }
1291 EXPORT_SYMBOL(unregister_console);
1292
1293 static int __init disable_boot_consoles(void)
1294 {
1295         if (console_drivers != NULL) {
1296                 if (console_drivers->flags & CON_BOOT) {
1297                         printk(KERN_INFO "turn off boot console %s%d\n",
1298                                 console_drivers->name, console_drivers->index);
1299                         return unregister_console(console_drivers);
1300                 }
1301         }
1302         return 0;
1303 }
1304 late_initcall(disable_boot_consoles);
1305
1306 /**
1307  * tty_write_message - write a message to a certain tty, not just the console.
1308  * @tty: the destination tty_struct
1309  * @msg: the message to write
1310  *
1311  * This is used for messages that need to be redirected to a specific tty.
1312  * We don't put it into the syslog queue right now maybe in the future if
1313  * really needed.
1314  */
1315 void tty_write_message(struct tty_struct *tty, char *msg)
1316 {
1317         if (tty && tty->ops->write)
1318                 tty->ops->write(tty, msg, strlen(msg));
1319         return;
1320 }
1321
1322 #if defined CONFIG_PRINTK
1323
1324 /*
1325  * printk rate limiting, lifted from the networking subsystem.
1326  *
1327  * This enforces a rate limit: not more than 10 kernel messages
1328  * every 5s to make a denial-of-service attack impossible.
1329  */
1330 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1331
1332 int printk_ratelimit(void)
1333 {
1334         return __ratelimit(&printk_ratelimit_state);
1335 }
1336 EXPORT_SYMBOL(printk_ratelimit);
1337
1338 /**
1339  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1340  * @caller_jiffies: pointer to caller's state
1341  * @interval_msecs: minimum interval between prints
1342  *
1343  * printk_timed_ratelimit() returns true if more than @interval_msecs
1344  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1345  * returned true.
1346  */
1347 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1348                         unsigned int interval_msecs)
1349 {
1350         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1351                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1352                 return true;
1353         }
1354         return false;
1355 }
1356 EXPORT_SYMBOL(printk_timed_ratelimit);
1357 #endif