Restrict unprivileged access to kernel syslog
[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
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 #include <linux/kexec.h>
36 #include <linux/kdb.h>
37 #include <linux/ratelimit.h>
38 #include <linux/kmsg_dump.h>
39 #include <linux/syslog.h>
40 #include <linux/cpu.h>
41 #include <linux/notifier.h>
42
43 #include <asm/uaccess.h>
44
45 /*
46  * for_each_console() allows you to iterate on each console
47  */
48 #define for_each_console(con) \
49         for (con = console_drivers; con != NULL; con = con->next)
50
51 /*
52  * Architectures can override it:
53  */
54 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
55 {
56 }
57
58 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
59
60 /* printk's without a loglevel use this.. */
61 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
62
63 /* We show everything that is MORE important than this.. */
64 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
65 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
66
67 DECLARE_WAIT_QUEUE_HEAD(log_wait);
68
69 int console_printk[4] = {
70         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
71         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
72         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
73         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
74 };
75
76 /*
77  * Low level drivers may need that to know if they can schedule in
78  * their unblank() callback or not. So let's export it.
79  */
80 int oops_in_progress;
81 EXPORT_SYMBOL(oops_in_progress);
82
83 /*
84  * console_sem protects the console_drivers list, and also
85  * provides serialisation for access to the entire console
86  * driver system.
87  */
88 static DEFINE_SEMAPHORE(console_sem);
89 struct console *console_drivers;
90 EXPORT_SYMBOL_GPL(console_drivers);
91
92 /*
93  * This is used for debugging the mess that is the VT code by
94  * keeping track if we have the console semaphore held. It's
95  * definitely not the perfect debug tool (we don't know if _WE_
96  * hold it are racing, but it helps tracking those weird code
97  * path in the console code where we end up in places I want
98  * locked without the console sempahore held
99  */
100 static int console_locked, console_suspended;
101
102 /*
103  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
104  * It is also used in interesting ways to provide interlocking in
105  * release_console_sem().
106  */
107 static DEFINE_SPINLOCK(logbuf_lock);
108
109 #define LOG_BUF_MASK (log_buf_len-1)
110 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
111
112 /*
113  * The indices into log_buf are not constrained to log_buf_len - they
114  * must be masked before subscripting
115  */
116 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
117 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
118 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
119
120 /*
121  *      Array of consoles built from command line options (console=)
122  */
123 struct console_cmdline
124 {
125         char    name[8];                        /* Name of the driver       */
126         int     index;                          /* Minor dev. to use        */
127         char    *options;                       /* Options for the driver   */
128 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
129         char    *brl_options;                   /* Options for braille driver */
130 #endif
131 };
132
133 #define MAX_CMDLINECONSOLES 8
134
135 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
136 static int selected_console = -1;
137 static int preferred_console = -1;
138 int console_set_on_cmdline;
139 EXPORT_SYMBOL(console_set_on_cmdline);
140
141 /* Flag: console code may call schedule() */
142 static int console_may_schedule;
143
144 #ifdef CONFIG_PRINTK
145
146 static char __log_buf[__LOG_BUF_LEN];
147 static char *log_buf = __log_buf;
148 static int log_buf_len = __LOG_BUF_LEN;
149 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
150 static int saved_console_loglevel = -1;
151
152 #ifdef CONFIG_KEXEC
153 /*
154  * This appends the listed symbols to /proc/vmcoreinfo
155  *
156  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
157  * obtain access to symbols that are otherwise very difficult to locate.  These
158  * symbols are specifically used so that utilities can access and extract the
159  * dmesg log from a vmcore file after a crash.
160  */
161 void log_buf_kexec_setup(void)
162 {
163         VMCOREINFO_SYMBOL(log_buf);
164         VMCOREINFO_SYMBOL(log_end);
165         VMCOREINFO_SYMBOL(log_buf_len);
166         VMCOREINFO_SYMBOL(logged_chars);
167 }
168 #endif
169
170 static int __init log_buf_len_setup(char *str)
171 {
172         unsigned size = memparse(str, &str);
173         unsigned long flags;
174
175         if (size)
176                 size = roundup_pow_of_two(size);
177         if (size > log_buf_len) {
178                 unsigned start, dest_idx, offset;
179                 char *new_log_buf;
180
181                 new_log_buf = alloc_bootmem(size);
182                 if (!new_log_buf) {
183                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
184                         goto out;
185                 }
186
187                 spin_lock_irqsave(&logbuf_lock, flags);
188                 log_buf_len = size;
189                 log_buf = new_log_buf;
190
191                 offset = start = min(con_start, log_start);
192                 dest_idx = 0;
193                 while (start != log_end) {
194                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
195                         start++;
196                         dest_idx++;
197                 }
198                 log_start -= offset;
199                 con_start -= offset;
200                 log_end -= offset;
201                 spin_unlock_irqrestore(&logbuf_lock, flags);
202
203                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
204         }
205 out:
206         return 1;
207 }
208
209 __setup("log_buf_len=", log_buf_len_setup);
210
211 #ifdef CONFIG_BOOT_PRINTK_DELAY
212
213 static int boot_delay; /* msecs delay after each printk during bootup */
214 static unsigned long long loops_per_msec;       /* based on boot_delay */
215
216 static int __init boot_delay_setup(char *str)
217 {
218         unsigned long lpj;
219
220         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
221         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
222
223         get_option(&str, &boot_delay);
224         if (boot_delay > 10 * 1000)
225                 boot_delay = 0;
226
227         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
228                 "HZ: %d, loops_per_msec: %llu\n",
229                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
230         return 1;
231 }
232 __setup("boot_delay=", boot_delay_setup);
233
234 static void boot_delay_msec(void)
235 {
236         unsigned long long k;
237         unsigned long timeout;
238
239         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
240                 return;
241
242         k = (unsigned long long)loops_per_msec * boot_delay;
243
244         timeout = jiffies + msecs_to_jiffies(boot_delay);
245         while (k) {
246                 k--;
247                 cpu_relax();
248                 /*
249                  * use (volatile) jiffies to prevent
250                  * compiler reduction; loop termination via jiffies
251                  * is secondary and may or may not happen.
252                  */
253                 if (time_after(jiffies, timeout))
254                         break;
255                 touch_nmi_watchdog();
256         }
257 }
258 #else
259 static inline void boot_delay_msec(void)
260 {
261 }
262 #endif
263
264 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
265 int dmesg_restrict = 1;
266 #else
267 int dmesg_restrict;
268 #endif
269
270 int do_syslog(int type, char __user *buf, int len, bool from_file)
271 {
272         unsigned i, j, limit, count;
273         int do_clear = 0;
274         char c;
275         int error = 0;
276
277         error = security_syslog(type, from_file);
278         if (error)
279                 return error;
280
281         switch (type) {
282         case SYSLOG_ACTION_CLOSE:       /* Close log */
283                 break;
284         case SYSLOG_ACTION_OPEN:        /* Open log */
285                 break;
286         case SYSLOG_ACTION_READ:        /* Read from log */
287                 error = -EINVAL;
288                 if (!buf || len < 0)
289                         goto out;
290                 error = 0;
291                 if (!len)
292                         goto out;
293                 if (!access_ok(VERIFY_WRITE, buf, len)) {
294                         error = -EFAULT;
295                         goto out;
296                 }
297                 error = wait_event_interruptible(log_wait,
298                                                         (log_start - log_end));
299                 if (error)
300                         goto out;
301                 i = 0;
302                 spin_lock_irq(&logbuf_lock);
303                 while (!error && (log_start != log_end) && i < len) {
304                         c = LOG_BUF(log_start);
305                         log_start++;
306                         spin_unlock_irq(&logbuf_lock);
307                         error = __put_user(c,buf);
308                         buf++;
309                         i++;
310                         cond_resched();
311                         spin_lock_irq(&logbuf_lock);
312                 }
313                 spin_unlock_irq(&logbuf_lock);
314                 if (!error)
315                         error = i;
316                 break;
317         /* Read/clear last kernel messages */
318         case SYSLOG_ACTION_READ_CLEAR:
319                 do_clear = 1;
320                 /* FALL THRU */
321         /* Read last kernel messages */
322         case SYSLOG_ACTION_READ_ALL:
323                 error = -EINVAL;
324                 if (!buf || len < 0)
325                         goto out;
326                 error = 0;
327                 if (!len)
328                         goto out;
329                 if (!access_ok(VERIFY_WRITE, buf, len)) {
330                         error = -EFAULT;
331                         goto out;
332                 }
333                 count = len;
334                 if (count > log_buf_len)
335                         count = log_buf_len;
336                 spin_lock_irq(&logbuf_lock);
337                 if (count > logged_chars)
338                         count = logged_chars;
339                 if (do_clear)
340                         logged_chars = 0;
341                 limit = log_end;
342                 /*
343                  * __put_user() could sleep, and while we sleep
344                  * printk() could overwrite the messages
345                  * we try to copy to user space. Therefore
346                  * the messages are copied in reverse. <manfreds>
347                  */
348                 for (i = 0; i < count && !error; i++) {
349                         j = limit-1-i;
350                         if (j + log_buf_len < log_end)
351                                 break;
352                         c = LOG_BUF(j);
353                         spin_unlock_irq(&logbuf_lock);
354                         error = __put_user(c,&buf[count-1-i]);
355                         cond_resched();
356                         spin_lock_irq(&logbuf_lock);
357                 }
358                 spin_unlock_irq(&logbuf_lock);
359                 if (error)
360                         break;
361                 error = i;
362                 if (i != count) {
363                         int offset = count-error;
364                         /* buffer overflow during copy, correct user buffer. */
365                         for (i = 0; i < error; i++) {
366                                 if (__get_user(c,&buf[i+offset]) ||
367                                     __put_user(c,&buf[i])) {
368                                         error = -EFAULT;
369                                         break;
370                                 }
371                                 cond_resched();
372                         }
373                 }
374                 break;
375         /* Clear ring buffer */
376         case SYSLOG_ACTION_CLEAR:
377                 logged_chars = 0;
378                 break;
379         /* Disable logging to console */
380         case SYSLOG_ACTION_CONSOLE_OFF:
381                 if (saved_console_loglevel == -1)
382                         saved_console_loglevel = console_loglevel;
383                 console_loglevel = minimum_console_loglevel;
384                 break;
385         /* Enable logging to console */
386         case SYSLOG_ACTION_CONSOLE_ON:
387                 if (saved_console_loglevel != -1) {
388                         console_loglevel = saved_console_loglevel;
389                         saved_console_loglevel = -1;
390                 }
391                 break;
392         /* Set level of messages printed to console */
393         case SYSLOG_ACTION_CONSOLE_LEVEL:
394                 error = -EINVAL;
395                 if (len < 1 || len > 8)
396                         goto out;
397                 if (len < minimum_console_loglevel)
398                         len = minimum_console_loglevel;
399                 console_loglevel = len;
400                 /* Implicitly re-enable logging to console */
401                 saved_console_loglevel = -1;
402                 error = 0;
403                 break;
404         /* Number of chars in the log buffer */
405         case SYSLOG_ACTION_SIZE_UNREAD:
406                 error = log_end - log_start;
407                 break;
408         /* Size of the log buffer */
409         case SYSLOG_ACTION_SIZE_BUFFER:
410                 error = log_buf_len;
411                 break;
412         default:
413                 error = -EINVAL;
414                 break;
415         }
416 out:
417         return error;
418 }
419
420 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
421 {
422         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
423 }
424
425 #ifdef  CONFIG_KGDB_KDB
426 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
427  * uses locks so it cannot be used during debugging.  Just tell kdb
428  * where the start and end of the physical and logical logs are.  This
429  * is equivalent to do_syslog(3).
430  */
431 void kdb_syslog_data(char *syslog_data[4])
432 {
433         syslog_data[0] = log_buf;
434         syslog_data[1] = log_buf + log_buf_len;
435         syslog_data[2] = log_buf + log_end -
436                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
437         syslog_data[3] = log_buf + log_end;
438 }
439 #endif  /* CONFIG_KGDB_KDB */
440
441 /*
442  * Call the console drivers on a range of log_buf
443  */
444 static void __call_console_drivers(unsigned start, unsigned end)
445 {
446         struct console *con;
447
448         for_each_console(con) {
449                 if ((con->flags & CON_ENABLED) && con->write &&
450                                 (cpu_online(smp_processor_id()) ||
451                                 (con->flags & CON_ANYTIME)))
452                         con->write(con, &LOG_BUF(start), end - start);
453         }
454 }
455
456 static int __read_mostly ignore_loglevel;
457
458 static int __init ignore_loglevel_setup(char *str)
459 {
460         ignore_loglevel = 1;
461         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
462
463         return 0;
464 }
465
466 early_param("ignore_loglevel", ignore_loglevel_setup);
467
468 /*
469  * Write out chars from start to end - 1 inclusive
470  */
471 static void _call_console_drivers(unsigned start,
472                                 unsigned end, int msg_log_level)
473 {
474         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
475                         console_drivers && start != end) {
476                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
477                         /* wrapped write */
478                         __call_console_drivers(start & LOG_BUF_MASK,
479                                                 log_buf_len);
480                         __call_console_drivers(0, end & LOG_BUF_MASK);
481                 } else {
482                         __call_console_drivers(start, end);
483                 }
484         }
485 }
486
487 /*
488  * Call the console drivers, asking them to write out
489  * log_buf[start] to log_buf[end - 1].
490  * The console_sem must be held.
491  */
492 static void call_console_drivers(unsigned start, unsigned end)
493 {
494         unsigned cur_index, start_print;
495         static int msg_level = -1;
496
497         BUG_ON(((int)(start - end)) > 0);
498
499         cur_index = start;
500         start_print = start;
501         while (cur_index != end) {
502                 if (msg_level < 0 && ((end - cur_index) > 2) &&
503                                 LOG_BUF(cur_index + 0) == '<' &&
504                                 LOG_BUF(cur_index + 1) >= '0' &&
505                                 LOG_BUF(cur_index + 1) <= '7' &&
506                                 LOG_BUF(cur_index + 2) == '>') {
507                         msg_level = LOG_BUF(cur_index + 1) - '0';
508                         cur_index += 3;
509                         start_print = cur_index;
510                 }
511                 while (cur_index != end) {
512                         char c = LOG_BUF(cur_index);
513
514                         cur_index++;
515                         if (c == '\n') {
516                                 if (msg_level < 0) {
517                                         /*
518                                          * printk() has already given us loglevel tags in
519                                          * the buffer.  This code is here in case the
520                                          * log buffer has wrapped right round and scribbled
521                                          * on those tags
522                                          */
523                                         msg_level = default_message_loglevel;
524                                 }
525                                 _call_console_drivers(start_print, cur_index, msg_level);
526                                 msg_level = -1;
527                                 start_print = cur_index;
528                                 break;
529                         }
530                 }
531         }
532         _call_console_drivers(start_print, end, msg_level);
533 }
534
535 static void emit_log_char(char c)
536 {
537         LOG_BUF(log_end) = c;
538         log_end++;
539         if (log_end - log_start > log_buf_len)
540                 log_start = log_end - log_buf_len;
541         if (log_end - con_start > log_buf_len)
542                 con_start = log_end - log_buf_len;
543         if (logged_chars < log_buf_len)
544                 logged_chars++;
545 }
546
547 /*
548  * Zap console related locks when oopsing. Only zap at most once
549  * every 10 seconds, to leave time for slow consoles to print a
550  * full oops.
551  */
552 static void zap_locks(void)
553 {
554         static unsigned long oops_timestamp;
555
556         if (time_after_eq(jiffies, oops_timestamp) &&
557                         !time_after(jiffies, oops_timestamp + 30 * HZ))
558                 return;
559
560         oops_timestamp = jiffies;
561
562         /* If a crash is occurring, make sure we can't deadlock */
563         spin_lock_init(&logbuf_lock);
564         /* And make sure that we print immediately */
565         sema_init(&console_sem, 1);
566 }
567
568 #if defined(CONFIG_PRINTK_TIME)
569 static int printk_time = 1;
570 #else
571 static int printk_time = 0;
572 #endif
573 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
574
575 /* Check if we have any console registered that can be called early in boot. */
576 static int have_callable_console(void)
577 {
578         struct console *con;
579
580         for_each_console(con)
581                 if (con->flags & CON_ANYTIME)
582                         return 1;
583
584         return 0;
585 }
586
587 /**
588  * printk - print a kernel message
589  * @fmt: format string
590  *
591  * This is printk().  It can be called from any context.  We want it to work.
592  *
593  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
594  * call the console drivers.  If we fail to get the semaphore we place the output
595  * into the log buffer and return.  The current holder of the console_sem will
596  * notice the new output in release_console_sem() and will send it to the
597  * consoles before releasing the semaphore.
598  *
599  * One effect of this deferred printing is that code which calls printk() and
600  * then changes console_loglevel may break. This is because console_loglevel
601  * is inspected when the actual printing occurs.
602  *
603  * See also:
604  * printf(3)
605  *
606  * See the vsnprintf() documentation for format string extensions over C99.
607  */
608
609 asmlinkage int printk(const char *fmt, ...)
610 {
611         va_list args;
612         int r;
613
614 #ifdef CONFIG_KGDB_KDB
615         if (unlikely(kdb_trap_printk)) {
616                 va_start(args, fmt);
617                 r = vkdb_printf(fmt, args);
618                 va_end(args);
619                 return r;
620         }
621 #endif
622         va_start(args, fmt);
623         r = vprintk(fmt, args);
624         va_end(args);
625
626         return r;
627 }
628
629 /* cpu currently holding logbuf_lock */
630 static volatile unsigned int printk_cpu = UINT_MAX;
631
632 /*
633  * Can we actually use the console at this time on this cpu?
634  *
635  * Console drivers may assume that per-cpu resources have
636  * been allocated. So unless they're explicitly marked as
637  * being able to cope (CON_ANYTIME) don't call them until
638  * this CPU is officially up.
639  */
640 static inline int can_use_console(unsigned int cpu)
641 {
642         return cpu_online(cpu) || have_callable_console();
643 }
644
645 /*
646  * Try to get console ownership to actually show the kernel
647  * messages from a 'printk'. Return true (and with the
648  * console_semaphore held, and 'console_locked' set) if it
649  * is successful, false otherwise.
650  *
651  * This gets called with the 'logbuf_lock' spinlock held and
652  * interrupts disabled. It should return with 'lockbuf_lock'
653  * released but interrupts still disabled.
654  */
655 static int acquire_console_semaphore_for_printk(unsigned int cpu)
656         __releases(&logbuf_lock)
657 {
658         int retval = 0;
659
660         if (!try_acquire_console_sem()) {
661                 retval = 1;
662
663                 /*
664                  * If we can't use the console, we need to release
665                  * the console semaphore by hand to avoid flushing
666                  * the buffer. We need to hold the console semaphore
667                  * in order to do this test safely.
668                  */
669                 if (!can_use_console(cpu)) {
670                         console_locked = 0;
671                         up(&console_sem);
672                         retval = 0;
673                 }
674         }
675         printk_cpu = UINT_MAX;
676         spin_unlock(&logbuf_lock);
677         return retval;
678 }
679 static const char recursion_bug_msg [] =
680                 KERN_CRIT "BUG: recent printk recursion!\n";
681 static int recursion_bug;
682 static int new_text_line = 1;
683 static char printk_buf[1024];
684
685 int printk_delay_msec __read_mostly;
686
687 static inline void printk_delay(void)
688 {
689         if (unlikely(printk_delay_msec)) {
690                 int m = printk_delay_msec;
691
692                 while (m--) {
693                         mdelay(1);
694                         touch_nmi_watchdog();
695                 }
696         }
697 }
698
699 asmlinkage int vprintk(const char *fmt, va_list args)
700 {
701         int printed_len = 0;
702         int current_log_level = default_message_loglevel;
703         unsigned long flags;
704         int this_cpu;
705         char *p;
706
707         boot_delay_msec();
708         printk_delay();
709
710         preempt_disable();
711         /* This stops the holder of console_sem just where we want him */
712         raw_local_irq_save(flags);
713         this_cpu = smp_processor_id();
714
715         /*
716          * Ouch, printk recursed into itself!
717          */
718         if (unlikely(printk_cpu == this_cpu)) {
719                 /*
720                  * If a crash is occurring during printk() on this CPU,
721                  * then try to get the crash message out but make sure
722                  * we can't deadlock. Otherwise just return to avoid the
723                  * recursion and return - but flag the recursion so that
724                  * it can be printed at the next appropriate moment:
725                  */
726                 if (!oops_in_progress) {
727                         recursion_bug = 1;
728                         goto out_restore_irqs;
729                 }
730                 zap_locks();
731         }
732
733         lockdep_off();
734         spin_lock(&logbuf_lock);
735         printk_cpu = this_cpu;
736
737         if (recursion_bug) {
738                 recursion_bug = 0;
739                 strcpy(printk_buf, recursion_bug_msg);
740                 printed_len = strlen(recursion_bug_msg);
741         }
742         /* Emit the output into the temporary buffer */
743         printed_len += vscnprintf(printk_buf + printed_len,
744                                   sizeof(printk_buf) - printed_len, fmt, args);
745
746
747         p = printk_buf;
748
749         /* Do we have a loglevel in the string? */
750         if (p[0] == '<') {
751                 unsigned char c = p[1];
752                 if (c && p[2] == '>') {
753                         switch (c) {
754                         case '0' ... '7': /* loglevel */
755                                 current_log_level = c - '0';
756                         /* Fallthrough - make sure we're on a new line */
757                         case 'd': /* KERN_DEFAULT */
758                                 if (!new_text_line) {
759                                         emit_log_char('\n');
760                                         new_text_line = 1;
761                                 }
762                         /* Fallthrough - skip the loglevel */
763                         case 'c': /* KERN_CONT */
764                                 p += 3;
765                                 break;
766                         }
767                 }
768         }
769
770         /*
771          * Copy the output into log_buf.  If the caller didn't provide
772          * appropriate log level tags, we insert them here
773          */
774         for ( ; *p; p++) {
775                 if (new_text_line) {
776                         /* Always output the token */
777                         emit_log_char('<');
778                         emit_log_char(current_log_level + '0');
779                         emit_log_char('>');
780                         printed_len += 3;
781                         new_text_line = 0;
782
783                         if (printk_time) {
784                                 /* Follow the token with the time */
785                                 char tbuf[50], *tp;
786                                 unsigned tlen;
787                                 unsigned long long t;
788                                 unsigned long nanosec_rem;
789
790                                 t = cpu_clock(printk_cpu);
791                                 nanosec_rem = do_div(t, 1000000000);
792                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
793                                                 (unsigned long) t,
794                                                 nanosec_rem / 1000);
795
796                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
797                                         emit_log_char(*tp);
798                                 printed_len += tlen;
799                         }
800
801                         if (!*p)
802                                 break;
803                 }
804
805                 emit_log_char(*p);
806                 if (*p == '\n')
807                         new_text_line = 1;
808         }
809
810         /*
811          * Try to acquire and then immediately release the
812          * console semaphore. The release will do all the
813          * actual magic (print out buffers, wake up klogd,
814          * etc). 
815          *
816          * The acquire_console_semaphore_for_printk() function
817          * will release 'logbuf_lock' regardless of whether it
818          * actually gets the semaphore or not.
819          */
820         if (acquire_console_semaphore_for_printk(this_cpu))
821                 release_console_sem();
822
823         lockdep_on();
824 out_restore_irqs:
825         raw_local_irq_restore(flags);
826
827         preempt_enable();
828         return printed_len;
829 }
830 EXPORT_SYMBOL(printk);
831 EXPORT_SYMBOL(vprintk);
832
833 #else
834
835 static void call_console_drivers(unsigned start, unsigned end)
836 {
837 }
838
839 #endif
840
841 static int __add_preferred_console(char *name, int idx, char *options,
842                                    char *brl_options)
843 {
844         struct console_cmdline *c;
845         int i;
846
847         /*
848          *      See if this tty is not yet registered, and
849          *      if we have a slot free.
850          */
851         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
852                 if (strcmp(console_cmdline[i].name, name) == 0 &&
853                           console_cmdline[i].index == idx) {
854                                 if (!brl_options)
855                                         selected_console = i;
856                                 return 0;
857                 }
858         if (i == MAX_CMDLINECONSOLES)
859                 return -E2BIG;
860         if (!brl_options)
861                 selected_console = i;
862         c = &console_cmdline[i];
863         strlcpy(c->name, name, sizeof(c->name));
864         c->options = options;
865 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
866         c->brl_options = brl_options;
867 #endif
868         c->index = idx;
869         return 0;
870 }
871 /*
872  * Set up a list of consoles.  Called from init/main.c
873  */
874 static int __init console_setup(char *str)
875 {
876         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
877         char *s, *options, *brl_options = NULL;
878         int idx;
879
880 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
881         if (!memcmp(str, "brl,", 4)) {
882                 brl_options = "";
883                 str += 4;
884         } else if (!memcmp(str, "brl=", 4)) {
885                 brl_options = str + 4;
886                 str = strchr(brl_options, ',');
887                 if (!str) {
888                         printk(KERN_ERR "need port name after brl=\n");
889                         return 1;
890                 }
891                 *(str++) = 0;
892         }
893 #endif
894
895         /*
896          * Decode str into name, index, options.
897          */
898         if (str[0] >= '0' && str[0] <= '9') {
899                 strcpy(buf, "ttyS");
900                 strncpy(buf + 4, str, sizeof(buf) - 5);
901         } else {
902                 strncpy(buf, str, sizeof(buf) - 1);
903         }
904         buf[sizeof(buf) - 1] = 0;
905         if ((options = strchr(str, ',')) != NULL)
906                 *(options++) = 0;
907 #ifdef __sparc__
908         if (!strcmp(str, "ttya"))
909                 strcpy(buf, "ttyS0");
910         if (!strcmp(str, "ttyb"))
911                 strcpy(buf, "ttyS1");
912 #endif
913         for (s = buf; *s; s++)
914                 if ((*s >= '0' && *s <= '9') || *s == ',')
915                         break;
916         idx = simple_strtoul(s, NULL, 10);
917         *s = 0;
918
919         __add_preferred_console(buf, idx, options, brl_options);
920         console_set_on_cmdline = 1;
921         return 1;
922 }
923 __setup("console=", console_setup);
924
925 /**
926  * add_preferred_console - add a device to the list of preferred consoles.
927  * @name: device name
928  * @idx: device index
929  * @options: options for this console
930  *
931  * The last preferred console added will be used for kernel messages
932  * and stdin/out/err for init.  Normally this is used by console_setup
933  * above to handle user-supplied console arguments; however it can also
934  * be used by arch-specific code either to override the user or more
935  * commonly to provide a default console (ie from PROM variables) when
936  * the user has not supplied one.
937  */
938 int add_preferred_console(char *name, int idx, char *options)
939 {
940         return __add_preferred_console(name, idx, options, NULL);
941 }
942
943 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
944 {
945         struct console_cmdline *c;
946         int i;
947
948         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
949                 if (strcmp(console_cmdline[i].name, name) == 0 &&
950                           console_cmdline[i].index == idx) {
951                                 c = &console_cmdline[i];
952                                 strlcpy(c->name, name_new, sizeof(c->name));
953                                 c->name[sizeof(c->name) - 1] = 0;
954                                 c->options = options;
955                                 c->index = idx_new;
956                                 return i;
957                 }
958         /* not found */
959         return -1;
960 }
961
962 int console_suspend_enabled = 1;
963 EXPORT_SYMBOL(console_suspend_enabled);
964
965 static int __init console_suspend_disable(char *str)
966 {
967         console_suspend_enabled = 0;
968         return 1;
969 }
970 __setup("no_console_suspend", console_suspend_disable);
971
972 /**
973  * suspend_console - suspend the console subsystem
974  *
975  * This disables printk() while we go into suspend states
976  */
977 void suspend_console(void)
978 {
979         if (!console_suspend_enabled)
980                 return;
981         printk("Suspending console(s) (use no_console_suspend to debug)\n");
982         acquire_console_sem();
983         console_suspended = 1;
984         up(&console_sem);
985 }
986
987 void resume_console(void)
988 {
989         if (!console_suspend_enabled)
990                 return;
991         down(&console_sem);
992         console_suspended = 0;
993         release_console_sem();
994 }
995
996 /**
997  * console_cpu_notify - print deferred console messages after CPU hotplug
998  * @self: notifier struct
999  * @action: CPU hotplug event
1000  * @hcpu: unused
1001  *
1002  * If printk() is called from a CPU that is not online yet, the messages
1003  * will be spooled but will not show up on the console.  This function is
1004  * called when a new CPU comes online (or fails to come up), and ensures
1005  * that any such output gets printed.
1006  */
1007 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1008         unsigned long action, void *hcpu)
1009 {
1010         switch (action) {
1011         case CPU_ONLINE:
1012         case CPU_DEAD:
1013         case CPU_DYING:
1014         case CPU_DOWN_FAILED:
1015         case CPU_UP_CANCELED:
1016                 acquire_console_sem();
1017                 release_console_sem();
1018         }
1019         return NOTIFY_OK;
1020 }
1021
1022 /**
1023  * acquire_console_sem - lock the console system for exclusive use.
1024  *
1025  * Acquires a semaphore which guarantees that the caller has
1026  * exclusive access to the console system and the console_drivers list.
1027  *
1028  * Can sleep, returns nothing.
1029  */
1030 void acquire_console_sem(void)
1031 {
1032         BUG_ON(in_interrupt());
1033         down(&console_sem);
1034         if (console_suspended)
1035                 return;
1036         console_locked = 1;
1037         console_may_schedule = 1;
1038 }
1039 EXPORT_SYMBOL(acquire_console_sem);
1040
1041 int try_acquire_console_sem(void)
1042 {
1043         if (down_trylock(&console_sem))
1044                 return -1;
1045         if (console_suspended) {
1046                 up(&console_sem);
1047                 return -1;
1048         }
1049         console_locked = 1;
1050         console_may_schedule = 0;
1051         return 0;
1052 }
1053 EXPORT_SYMBOL(try_acquire_console_sem);
1054
1055 int is_console_locked(void)
1056 {
1057         return console_locked;
1058 }
1059
1060 static DEFINE_PER_CPU(int, printk_pending);
1061
1062 void printk_tick(void)
1063 {
1064         if (__get_cpu_var(printk_pending)) {
1065                 __get_cpu_var(printk_pending) = 0;
1066                 wake_up_interruptible(&log_wait);
1067         }
1068 }
1069
1070 int printk_needs_cpu(int cpu)
1071 {
1072         return per_cpu(printk_pending, cpu);
1073 }
1074
1075 void wake_up_klogd(void)
1076 {
1077         if (waitqueue_active(&log_wait))
1078                 __raw_get_cpu_var(printk_pending) = 1;
1079 }
1080
1081 /**
1082  * release_console_sem - unlock the console system
1083  *
1084  * Releases the semaphore which the caller holds on the console system
1085  * and the console driver list.
1086  *
1087  * While the semaphore was held, console output may have been buffered
1088  * by printk().  If this is the case, release_console_sem() emits
1089  * the output prior to releasing the semaphore.
1090  *
1091  * If there is output waiting for klogd, we wake it up.
1092  *
1093  * release_console_sem() may be called from any context.
1094  */
1095 void release_console_sem(void)
1096 {
1097         unsigned long flags;
1098         unsigned _con_start, _log_end;
1099         unsigned wake_klogd = 0;
1100
1101         if (console_suspended) {
1102                 up(&console_sem);
1103                 return;
1104         }
1105
1106         console_may_schedule = 0;
1107
1108         for ( ; ; ) {
1109                 spin_lock_irqsave(&logbuf_lock, flags);
1110                 wake_klogd |= log_start - log_end;
1111                 if (con_start == log_end)
1112                         break;                  /* Nothing to print */
1113                 _con_start = con_start;
1114                 _log_end = log_end;
1115                 con_start = log_end;            /* Flush */
1116                 spin_unlock(&logbuf_lock);
1117                 stop_critical_timings();        /* don't trace print latency */
1118                 call_console_drivers(_con_start, _log_end);
1119                 start_critical_timings();
1120                 local_irq_restore(flags);
1121         }
1122         console_locked = 0;
1123         up(&console_sem);
1124         spin_unlock_irqrestore(&logbuf_lock, flags);
1125         if (wake_klogd)
1126                 wake_up_klogd();
1127 }
1128 EXPORT_SYMBOL(release_console_sem);
1129
1130 /**
1131  * console_conditional_schedule - yield the CPU if required
1132  *
1133  * If the console code is currently allowed to sleep, and
1134  * if this CPU should yield the CPU to another task, do
1135  * so here.
1136  *
1137  * Must be called within acquire_console_sem().
1138  */
1139 void __sched console_conditional_schedule(void)
1140 {
1141         if (console_may_schedule)
1142                 cond_resched();
1143 }
1144 EXPORT_SYMBOL(console_conditional_schedule);
1145
1146 void console_unblank(void)
1147 {
1148         struct console *c;
1149
1150         /*
1151          * console_unblank can no longer be called in interrupt context unless
1152          * oops_in_progress is set to 1..
1153          */
1154         if (oops_in_progress) {
1155                 if (down_trylock(&console_sem) != 0)
1156                         return;
1157         } else
1158                 acquire_console_sem();
1159
1160         console_locked = 1;
1161         console_may_schedule = 0;
1162         for_each_console(c)
1163                 if ((c->flags & CON_ENABLED) && c->unblank)
1164                         c->unblank();
1165         release_console_sem();
1166 }
1167
1168 /*
1169  * Return the console tty driver structure and its associated index
1170  */
1171 struct tty_driver *console_device(int *index)
1172 {
1173         struct console *c;
1174         struct tty_driver *driver = NULL;
1175
1176         acquire_console_sem();
1177         for_each_console(c) {
1178                 if (!c->device)
1179                         continue;
1180                 driver = c->device(c, index);
1181                 if (driver)
1182                         break;
1183         }
1184         release_console_sem();
1185         return driver;
1186 }
1187
1188 /*
1189  * Prevent further output on the passed console device so that (for example)
1190  * serial drivers can disable console output before suspending a port, and can
1191  * re-enable output afterwards.
1192  */
1193 void console_stop(struct console *console)
1194 {
1195         acquire_console_sem();
1196         console->flags &= ~CON_ENABLED;
1197         release_console_sem();
1198 }
1199 EXPORT_SYMBOL(console_stop);
1200
1201 void console_start(struct console *console)
1202 {
1203         acquire_console_sem();
1204         console->flags |= CON_ENABLED;
1205         release_console_sem();
1206 }
1207 EXPORT_SYMBOL(console_start);
1208
1209 /*
1210  * The console driver calls this routine during kernel initialization
1211  * to register the console printing procedure with printk() and to
1212  * print any messages that were printed by the kernel before the
1213  * console driver was initialized.
1214  *
1215  * This can happen pretty early during the boot process (because of
1216  * early_printk) - sometimes before setup_arch() completes - be careful
1217  * of what kernel features are used - they may not be initialised yet.
1218  *
1219  * There are two types of consoles - bootconsoles (early_printk) and
1220  * "real" consoles (everything which is not a bootconsole) which are
1221  * handled differently.
1222  *  - Any number of bootconsoles can be registered at any time.
1223  *  - As soon as a "real" console is registered, all bootconsoles
1224  *    will be unregistered automatically.
1225  *  - Once a "real" console is registered, any attempt to register a
1226  *    bootconsoles will be rejected
1227  */
1228 void register_console(struct console *newcon)
1229 {
1230         int i;
1231         unsigned long flags;
1232         struct console *bcon = NULL;
1233
1234         /*
1235          * before we register a new CON_BOOT console, make sure we don't
1236          * already have a valid console
1237          */
1238         if (console_drivers && newcon->flags & CON_BOOT) {
1239                 /* find the last or real console */
1240                 for_each_console(bcon) {
1241                         if (!(bcon->flags & CON_BOOT)) {
1242                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1243                                         newcon->name, newcon->index);
1244                                 return;
1245                         }
1246                 }
1247         }
1248
1249         if (console_drivers && console_drivers->flags & CON_BOOT)
1250                 bcon = console_drivers;
1251
1252         if (preferred_console < 0 || bcon || !console_drivers)
1253                 preferred_console = selected_console;
1254
1255         if (newcon->early_setup)
1256                 newcon->early_setup();
1257
1258         /*
1259          *      See if we want to use this console driver. If we
1260          *      didn't select a console we take the first one
1261          *      that registers here.
1262          */
1263         if (preferred_console < 0) {
1264                 if (newcon->index < 0)
1265                         newcon->index = 0;
1266                 if (newcon->setup == NULL ||
1267                     newcon->setup(newcon, NULL) == 0) {
1268                         newcon->flags |= CON_ENABLED;
1269                         if (newcon->device) {
1270                                 newcon->flags |= CON_CONSDEV;
1271                                 preferred_console = 0;
1272                         }
1273                 }
1274         }
1275
1276         /*
1277          *      See if this console matches one we selected on
1278          *      the command line.
1279          */
1280         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1281                         i++) {
1282                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1283                         continue;
1284                 if (newcon->index >= 0 &&
1285                     newcon->index != console_cmdline[i].index)
1286                         continue;
1287                 if (newcon->index < 0)
1288                         newcon->index = console_cmdline[i].index;
1289 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1290                 if (console_cmdline[i].brl_options) {
1291                         newcon->flags |= CON_BRL;
1292                         braille_register_console(newcon,
1293                                         console_cmdline[i].index,
1294                                         console_cmdline[i].options,
1295                                         console_cmdline[i].brl_options);
1296                         return;
1297                 }
1298 #endif
1299                 if (newcon->setup &&
1300                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1301                         break;
1302                 newcon->flags |= CON_ENABLED;
1303                 newcon->index = console_cmdline[i].index;
1304                 if (i == selected_console) {
1305                         newcon->flags |= CON_CONSDEV;
1306                         preferred_console = selected_console;
1307                 }
1308                 break;
1309         }
1310
1311         if (!(newcon->flags & CON_ENABLED))
1312                 return;
1313
1314         /*
1315          * If we have a bootconsole, and are switching to a real console,
1316          * don't print everything out again, since when the boot console, and
1317          * the real console are the same physical device, it's annoying to
1318          * see the beginning boot messages twice
1319          */
1320         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1321                 newcon->flags &= ~CON_PRINTBUFFER;
1322
1323         /*
1324          *      Put this console in the list - keep the
1325          *      preferred driver at the head of the list.
1326          */
1327         acquire_console_sem();
1328         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1329                 newcon->next = console_drivers;
1330                 console_drivers = newcon;
1331                 if (newcon->next)
1332                         newcon->next->flags &= ~CON_CONSDEV;
1333         } else {
1334                 newcon->next = console_drivers->next;
1335                 console_drivers->next = newcon;
1336         }
1337         if (newcon->flags & CON_PRINTBUFFER) {
1338                 /*
1339                  * release_console_sem() will print out the buffered messages
1340                  * for us.
1341                  */
1342                 spin_lock_irqsave(&logbuf_lock, flags);
1343                 con_start = log_start;
1344                 spin_unlock_irqrestore(&logbuf_lock, flags);
1345         }
1346         release_console_sem();
1347
1348         /*
1349          * By unregistering the bootconsoles after we enable the real console
1350          * we get the "console xxx enabled" message on all the consoles -
1351          * boot consoles, real consoles, etc - this is to ensure that end
1352          * users know there might be something in the kernel's log buffer that
1353          * went to the bootconsole (that they do not see on the real console)
1354          */
1355         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1356                 /* we need to iterate through twice, to make sure we print
1357                  * everything out, before we unregister the console(s)
1358                  */
1359                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1360                         newcon->name, newcon->index);
1361                 for_each_console(bcon)
1362                         if (bcon->flags & CON_BOOT)
1363                                 unregister_console(bcon);
1364         } else {
1365                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1366                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1367                         newcon->name, newcon->index);
1368         }
1369 }
1370 EXPORT_SYMBOL(register_console);
1371
1372 int unregister_console(struct console *console)
1373 {
1374         struct console *a, *b;
1375         int res = 1;
1376
1377 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1378         if (console->flags & CON_BRL)
1379                 return braille_unregister_console(console);
1380 #endif
1381
1382         acquire_console_sem();
1383         if (console_drivers == console) {
1384                 console_drivers=console->next;
1385                 res = 0;
1386         } else if (console_drivers) {
1387                 for (a=console_drivers->next, b=console_drivers ;
1388                      a; b=a, a=b->next) {
1389                         if (a == console) {
1390                                 b->next = a->next;
1391                                 res = 0;
1392                                 break;
1393                         }
1394                 }
1395         }
1396
1397         /*
1398          * If this isn't the last console and it has CON_CONSDEV set, we
1399          * need to set it on the next preferred console.
1400          */
1401         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1402                 console_drivers->flags |= CON_CONSDEV;
1403
1404         release_console_sem();
1405         return res;
1406 }
1407 EXPORT_SYMBOL(unregister_console);
1408
1409 static int __init printk_late_init(void)
1410 {
1411         struct console *con;
1412
1413         for_each_console(con) {
1414                 if (con->flags & CON_BOOT) {
1415                         printk(KERN_INFO "turn off boot console %s%d\n",
1416                                 con->name, con->index);
1417                         unregister_console(con);
1418                 }
1419         }
1420         hotcpu_notifier(console_cpu_notify, 0);
1421         return 0;
1422 }
1423 late_initcall(printk_late_init);
1424
1425 #if defined CONFIG_PRINTK
1426
1427 /*
1428  * printk rate limiting, lifted from the networking subsystem.
1429  *
1430  * This enforces a rate limit: not more than 10 kernel messages
1431  * every 5s to make a denial-of-service attack impossible.
1432  */
1433 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1434
1435 int __printk_ratelimit(const char *func)
1436 {
1437         return ___ratelimit(&printk_ratelimit_state, func);
1438 }
1439 EXPORT_SYMBOL(__printk_ratelimit);
1440
1441 /**
1442  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1443  * @caller_jiffies: pointer to caller's state
1444  * @interval_msecs: minimum interval between prints
1445  *
1446  * printk_timed_ratelimit() returns true if more than @interval_msecs
1447  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1448  * returned true.
1449  */
1450 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1451                         unsigned int interval_msecs)
1452 {
1453         if (*caller_jiffies == 0
1454                         || !time_in_range(jiffies, *caller_jiffies,
1455                                         *caller_jiffies
1456                                         + msecs_to_jiffies(interval_msecs))) {
1457                 *caller_jiffies = jiffies;
1458                 return true;
1459         }
1460         return false;
1461 }
1462 EXPORT_SYMBOL(printk_timed_ratelimit);
1463
1464 static DEFINE_SPINLOCK(dump_list_lock);
1465 static LIST_HEAD(dump_list);
1466
1467 /**
1468  * kmsg_dump_register - register a kernel log dumper.
1469  * @dumper: pointer to the kmsg_dumper structure
1470  *
1471  * Adds a kernel log dumper to the system. The dump callback in the
1472  * structure will be called when the kernel oopses or panics and must be
1473  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1474  */
1475 int kmsg_dump_register(struct kmsg_dumper *dumper)
1476 {
1477         unsigned long flags;
1478         int err = -EBUSY;
1479
1480         /* The dump callback needs to be set */
1481         if (!dumper->dump)
1482                 return -EINVAL;
1483
1484         spin_lock_irqsave(&dump_list_lock, flags);
1485         /* Don't allow registering multiple times */
1486         if (!dumper->registered) {
1487                 dumper->registered = 1;
1488                 list_add_tail(&dumper->list, &dump_list);
1489                 err = 0;
1490         }
1491         spin_unlock_irqrestore(&dump_list_lock, flags);
1492
1493         return err;
1494 }
1495 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1496
1497 /**
1498  * kmsg_dump_unregister - unregister a kmsg dumper.
1499  * @dumper: pointer to the kmsg_dumper structure
1500  *
1501  * Removes a dump device from the system. Returns zero on success and
1502  * %-EINVAL otherwise.
1503  */
1504 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1505 {
1506         unsigned long flags;
1507         int err = -EINVAL;
1508
1509         spin_lock_irqsave(&dump_list_lock, flags);
1510         if (dumper->registered) {
1511                 dumper->registered = 0;
1512                 list_del(&dumper->list);
1513                 err = 0;
1514         }
1515         spin_unlock_irqrestore(&dump_list_lock, flags);
1516
1517         return err;
1518 }
1519 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1520
1521 static const char * const kmsg_reasons[] = {
1522         [KMSG_DUMP_OOPS]        = "oops",
1523         [KMSG_DUMP_PANIC]       = "panic",
1524         [KMSG_DUMP_KEXEC]       = "kexec",
1525 };
1526
1527 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1528 {
1529         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1530                 return "unknown";
1531
1532         return kmsg_reasons[reason];
1533 }
1534
1535 /**
1536  * kmsg_dump - dump kernel log to kernel message dumpers.
1537  * @reason: the reason (oops, panic etc) for dumping
1538  *
1539  * Iterate through each of the dump devices and call the oops/panic
1540  * callbacks with the log buffer.
1541  */
1542 void kmsg_dump(enum kmsg_dump_reason reason)
1543 {
1544         unsigned long end;
1545         unsigned chars;
1546         struct kmsg_dumper *dumper;
1547         const char *s1, *s2;
1548         unsigned long l1, l2;
1549         unsigned long flags;
1550
1551         /* Theoretically, the log could move on after we do this, but
1552            there's not a lot we can do about that. The new messages
1553            will overwrite the start of what we dump. */
1554         spin_lock_irqsave(&logbuf_lock, flags);
1555         end = log_end & LOG_BUF_MASK;
1556         chars = logged_chars;
1557         spin_unlock_irqrestore(&logbuf_lock, flags);
1558
1559         if (chars > end) {
1560                 s1 = log_buf + log_buf_len - chars + end;
1561                 l1 = chars - end;
1562
1563                 s2 = log_buf;
1564                 l2 = end;
1565         } else {
1566                 s1 = "";
1567                 l1 = 0;
1568
1569                 s2 = log_buf + end - chars;
1570                 l2 = chars;
1571         }
1572
1573         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1574                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1575                                 kmsg_to_str(reason));
1576                 return;
1577         }
1578         list_for_each_entry(dumper, &dump_list, list)
1579                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1580         spin_unlock_irqrestore(&dump_list_lock, flags);
1581 }
1582 #endif