MIPS: N32: Use compat version for sys_ppoll.
[kernel.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/ratelimit.h>
37 #include <linux/kmsg_dump.h>
38 #include <linux/syslog.h>
39
40 #include <asm/uaccess.h>
41
42 /*
43  * for_each_console() allows you to iterate on each console
44  */
45 #define for_each_console(con) \
46         for (con = console_drivers; con != NULL; con = con->next)
47
48 /*
49  * Architectures can override it:
50  */
51 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
52 {
53 }
54
55 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
56
57 /* printk's without a loglevel use this.. */
58 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
59
60 /* We show everything that is MORE important than this.. */
61 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
62 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
63
64 DECLARE_WAIT_QUEUE_HEAD(log_wait);
65
66 int console_printk[4] = {
67         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
68         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
69         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
70         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
71 };
72
73 /*
74  * Low level drivers may need that to know if they can schedule in
75  * their unblank() callback or not. So let's export it.
76  */
77 int oops_in_progress;
78 EXPORT_SYMBOL(oops_in_progress);
79
80 /*
81  * console_sem protects the console_drivers list, and also
82  * provides serialisation for access to the entire console
83  * driver system.
84  */
85 static DECLARE_MUTEX(console_sem);
86 struct console *console_drivers;
87 EXPORT_SYMBOL_GPL(console_drivers);
88
89 /*
90  * This is used for debugging the mess that is the VT code by
91  * keeping track if we have the console semaphore held. It's
92  * definitely not the perfect debug tool (we don't know if _WE_
93  * hold it are racing, but it helps tracking those weird code
94  * path in the console code where we end up in places I want
95  * locked without the console sempahore held
96  */
97 static int console_locked, console_suspended;
98
99 /*
100  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
101  * It is also used in interesting ways to provide interlocking in
102  * release_console_sem().
103  */
104 static DEFINE_SPINLOCK(logbuf_lock);
105
106 #define LOG_BUF_MASK (log_buf_len-1)
107 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
108
109 /*
110  * The indices into log_buf are not constrained to log_buf_len - they
111  * must be masked before subscripting
112  */
113 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
114 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
115 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
116
117 /*
118  *      Array of consoles built from command line options (console=)
119  */
120 struct console_cmdline
121 {
122         char    name[8];                        /* Name of the driver       */
123         int     index;                          /* Minor dev. to use        */
124         char    *options;                       /* Options for the driver   */
125 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
126         char    *brl_options;                   /* Options for braille driver */
127 #endif
128 };
129
130 #define MAX_CMDLINECONSOLES 8
131
132 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
133 static int selected_console = -1;
134 static int preferred_console = -1;
135 int console_set_on_cmdline;
136 EXPORT_SYMBOL(console_set_on_cmdline);
137
138 /* Flag: console code may call schedule() */
139 static int console_may_schedule;
140
141 #ifdef CONFIG_PRINTK
142
143 static char __log_buf[__LOG_BUF_LEN];
144 static char *log_buf = __log_buf;
145 static int log_buf_len = __LOG_BUF_LEN;
146 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
147 static int saved_console_loglevel = -1;
148
149 #ifdef CONFIG_KEXEC
150 /*
151  * This appends the listed symbols to /proc/vmcoreinfo
152  *
153  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
154  * obtain access to symbols that are otherwise very difficult to locate.  These
155  * symbols are specifically used so that utilities can access and extract the
156  * dmesg log from a vmcore file after a crash.
157  */
158 void log_buf_kexec_setup(void)
159 {
160         VMCOREINFO_SYMBOL(log_buf);
161         VMCOREINFO_SYMBOL(log_end);
162         VMCOREINFO_SYMBOL(log_buf_len);
163         VMCOREINFO_SYMBOL(logged_chars);
164 }
165 #endif
166
167 static int __init log_buf_len_setup(char *str)
168 {
169         unsigned size = memparse(str, &str);
170         unsigned long flags;
171
172         if (size)
173                 size = roundup_pow_of_two(size);
174         if (size > log_buf_len) {
175                 unsigned start, dest_idx, offset;
176                 char *new_log_buf;
177
178                 new_log_buf = alloc_bootmem(size);
179                 if (!new_log_buf) {
180                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
181                         goto out;
182                 }
183
184                 spin_lock_irqsave(&logbuf_lock, flags);
185                 log_buf_len = size;
186                 log_buf = new_log_buf;
187
188                 offset = start = min(con_start, log_start);
189                 dest_idx = 0;
190                 while (start != log_end) {
191                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
192                         start++;
193                         dest_idx++;
194                 }
195                 log_start -= offset;
196                 con_start -= offset;
197                 log_end -= offset;
198                 spin_unlock_irqrestore(&logbuf_lock, flags);
199
200                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
201         }
202 out:
203         return 1;
204 }
205
206 __setup("log_buf_len=", log_buf_len_setup);
207
208 #ifdef CONFIG_BOOT_PRINTK_DELAY
209
210 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
211 static unsigned long long loops_per_msec;       /* based on boot_delay */
212
213 static int __init boot_delay_setup(char *str)
214 {
215         unsigned long lpj;
216
217         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
218         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
219
220         get_option(&str, &boot_delay);
221         if (boot_delay > 10 * 1000)
222                 boot_delay = 0;
223
224         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
225                 "HZ: %d, loops_per_msec: %llu\n",
226                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
227         return 1;
228 }
229 __setup("boot_delay=", boot_delay_setup);
230
231 static void boot_delay_msec(void)
232 {
233         unsigned long long k;
234         unsigned long timeout;
235
236         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
237                 return;
238
239         k = (unsigned long long)loops_per_msec * boot_delay;
240
241         timeout = jiffies + msecs_to_jiffies(boot_delay);
242         while (k) {
243                 k--;
244                 cpu_relax();
245                 /*
246                  * use (volatile) jiffies to prevent
247                  * compiler reduction; loop termination via jiffies
248                  * is secondary and may or may not happen.
249                  */
250                 if (time_after(jiffies, timeout))
251                         break;
252                 touch_nmi_watchdog();
253         }
254 }
255 #else
256 static inline void boot_delay_msec(void)
257 {
258 }
259 #endif
260
261 int do_syslog(int type, char __user *buf, int len, bool from_file)
262 {
263         unsigned i, j, limit, count;
264         int do_clear = 0;
265         char c;
266         int error = 0;
267
268         error = security_syslog(type, from_file);
269         if (error)
270                 return error;
271
272         switch (type) {
273         case SYSLOG_ACTION_CLOSE:       /* Close log */
274                 break;
275         case SYSLOG_ACTION_OPEN:        /* Open log */
276                 break;
277         case SYSLOG_ACTION_READ:        /* Read from log */
278                 error = -EINVAL;
279                 if (!buf || len < 0)
280                         goto out;
281                 error = 0;
282                 if (!len)
283                         goto out;
284                 if (!access_ok(VERIFY_WRITE, buf, len)) {
285                         error = -EFAULT;
286                         goto out;
287                 }
288                 error = wait_event_interruptible(log_wait,
289                                                         (log_start - log_end));
290                 if (error)
291                         goto out;
292                 i = 0;
293                 spin_lock_irq(&logbuf_lock);
294                 while (!error && (log_start != log_end) && i < len) {
295                         c = LOG_BUF(log_start);
296                         log_start++;
297                         spin_unlock_irq(&logbuf_lock);
298                         error = __put_user(c,buf);
299                         buf++;
300                         i++;
301                         cond_resched();
302                         spin_lock_irq(&logbuf_lock);
303                 }
304                 spin_unlock_irq(&logbuf_lock);
305                 if (!error)
306                         error = i;
307                 break;
308         /* Read/clear last kernel messages */
309         case SYSLOG_ACTION_READ_CLEAR:
310                 do_clear = 1;
311                 /* FALL THRU */
312         /* Read last kernel messages */
313         case SYSLOG_ACTION_READ_ALL:
314                 error = -EINVAL;
315                 if (!buf || len < 0)
316                         goto out;
317                 error = 0;
318                 if (!len)
319                         goto out;
320                 if (!access_ok(VERIFY_WRITE, buf, len)) {
321                         error = -EFAULT;
322                         goto out;
323                 }
324                 count = len;
325                 if (count > log_buf_len)
326                         count = log_buf_len;
327                 spin_lock_irq(&logbuf_lock);
328                 if (count > logged_chars)
329                         count = logged_chars;
330                 if (do_clear)
331                         logged_chars = 0;
332                 limit = log_end;
333                 /*
334                  * __put_user() could sleep, and while we sleep
335                  * printk() could overwrite the messages
336                  * we try to copy to user space. Therefore
337                  * the messages are copied in reverse. <manfreds>
338                  */
339                 for (i = 0; i < count && !error; i++) {
340                         j = limit-1-i;
341                         if (j + log_buf_len < log_end)
342                                 break;
343                         c = LOG_BUF(j);
344                         spin_unlock_irq(&logbuf_lock);
345                         error = __put_user(c,&buf[count-1-i]);
346                         cond_resched();
347                         spin_lock_irq(&logbuf_lock);
348                 }
349                 spin_unlock_irq(&logbuf_lock);
350                 if (error)
351                         break;
352                 error = i;
353                 if (i != count) {
354                         int offset = count-error;
355                         /* buffer overflow during copy, correct user buffer. */
356                         for (i = 0; i < error; i++) {
357                                 if (__get_user(c,&buf[i+offset]) ||
358                                     __put_user(c,&buf[i])) {
359                                         error = -EFAULT;
360                                         break;
361                                 }
362                                 cond_resched();
363                         }
364                 }
365                 break;
366         /* Clear ring buffer */
367         case SYSLOG_ACTION_CLEAR:
368                 logged_chars = 0;
369                 break;
370         /* Disable logging to console */
371         case SYSLOG_ACTION_CONSOLE_OFF:
372                 if (saved_console_loglevel == -1)
373                         saved_console_loglevel = console_loglevel;
374                 console_loglevel = minimum_console_loglevel;
375                 break;
376         /* Enable logging to console */
377         case SYSLOG_ACTION_CONSOLE_ON:
378                 if (saved_console_loglevel != -1) {
379                         console_loglevel = saved_console_loglevel;
380                         saved_console_loglevel = -1;
381                 }
382                 break;
383         /* Set level of messages printed to console */
384         case SYSLOG_ACTION_CONSOLE_LEVEL:
385                 error = -EINVAL;
386                 if (len < 1 || len > 8)
387                         goto out;
388                 if (len < minimum_console_loglevel)
389                         len = minimum_console_loglevel;
390                 console_loglevel = len;
391                 /* Implicitly re-enable logging to console */
392                 saved_console_loglevel = -1;
393                 error = 0;
394                 break;
395         /* Number of chars in the log buffer */
396         case SYSLOG_ACTION_SIZE_UNREAD:
397                 error = log_end - log_start;
398                 break;
399         /* Size of the log buffer */
400         case SYSLOG_ACTION_SIZE_BUFFER:
401                 error = log_buf_len;
402                 break;
403         default:
404                 error = -EINVAL;
405                 break;
406         }
407 out:
408         return error;
409 }
410
411 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
412 {
413         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
414 }
415
416 /*
417  * Call the console drivers on a range of log_buf
418  */
419 static void __call_console_drivers(unsigned start, unsigned end)
420 {
421         struct console *con;
422
423         for_each_console(con) {
424                 if ((con->flags & CON_ENABLED) && con->write &&
425                                 (cpu_online(smp_processor_id()) ||
426                                 (con->flags & CON_ANYTIME)))
427                         con->write(con, &LOG_BUF(start), end - start);
428         }
429 }
430
431 static int __read_mostly ignore_loglevel;
432
433 static int __init ignore_loglevel_setup(char *str)
434 {
435         ignore_loglevel = 1;
436         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
437
438         return 0;
439 }
440
441 early_param("ignore_loglevel", ignore_loglevel_setup);
442
443 /*
444  * Write out chars from start to end - 1 inclusive
445  */
446 static void _call_console_drivers(unsigned start,
447                                 unsigned end, int msg_log_level)
448 {
449         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
450                         console_drivers && start != end) {
451                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
452                         /* wrapped write */
453                         __call_console_drivers(start & LOG_BUF_MASK,
454                                                 log_buf_len);
455                         __call_console_drivers(0, end & LOG_BUF_MASK);
456                 } else {
457                         __call_console_drivers(start, end);
458                 }
459         }
460 }
461
462 /*
463  * Call the console drivers, asking them to write out
464  * log_buf[start] to log_buf[end - 1].
465  * The console_sem must be held.
466  */
467 static void call_console_drivers(unsigned start, unsigned end)
468 {
469         unsigned cur_index, start_print;
470         static int msg_level = -1;
471
472         BUG_ON(((int)(start - end)) > 0);
473
474         cur_index = start;
475         start_print = start;
476         while (cur_index != end) {
477                 if (msg_level < 0 && ((end - cur_index) > 2) &&
478                                 LOG_BUF(cur_index + 0) == '<' &&
479                                 LOG_BUF(cur_index + 1) >= '0' &&
480                                 LOG_BUF(cur_index + 1) <= '7' &&
481                                 LOG_BUF(cur_index + 2) == '>') {
482                         msg_level = LOG_BUF(cur_index + 1) - '0';
483                         cur_index += 3;
484                         start_print = cur_index;
485                 }
486                 while (cur_index != end) {
487                         char c = LOG_BUF(cur_index);
488
489                         cur_index++;
490                         if (c == '\n') {
491                                 if (msg_level < 0) {
492                                         /*
493                                          * printk() has already given us loglevel tags in
494                                          * the buffer.  This code is here in case the
495                                          * log buffer has wrapped right round and scribbled
496                                          * on those tags
497                                          */
498                                         msg_level = default_message_loglevel;
499                                 }
500                                 _call_console_drivers(start_print, cur_index, msg_level);
501                                 msg_level = -1;
502                                 start_print = cur_index;
503                                 break;
504                         }
505                 }
506         }
507         _call_console_drivers(start_print, end, msg_level);
508 }
509
510 static void emit_log_char(char c)
511 {
512         LOG_BUF(log_end) = c;
513         log_end++;
514         if (log_end - log_start > log_buf_len)
515                 log_start = log_end - log_buf_len;
516         if (log_end - con_start > log_buf_len)
517                 con_start = log_end - log_buf_len;
518         if (logged_chars < log_buf_len)
519                 logged_chars++;
520 }
521
522 /*
523  * Zap console related locks when oopsing. Only zap at most once
524  * every 10 seconds, to leave time for slow consoles to print a
525  * full oops.
526  */
527 static void zap_locks(void)
528 {
529         static unsigned long oops_timestamp;
530
531         if (time_after_eq(jiffies, oops_timestamp) &&
532                         !time_after(jiffies, oops_timestamp + 30 * HZ))
533                 return;
534
535         oops_timestamp = jiffies;
536
537         /* If a crash is occurring, make sure we can't deadlock */
538         spin_lock_init(&logbuf_lock);
539         /* And make sure that we print immediately */
540         init_MUTEX(&console_sem);
541 }
542
543 #if defined(CONFIG_PRINTK_TIME)
544 static int printk_time = 1;
545 #else
546 static int printk_time = 0;
547 #endif
548 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
549
550 /* Check if we have any console registered that can be called early in boot. */
551 static int have_callable_console(void)
552 {
553         struct console *con;
554
555         for_each_console(con)
556                 if (con->flags & CON_ANYTIME)
557                         return 1;
558
559         return 0;
560 }
561
562 /**
563  * printk - print a kernel message
564  * @fmt: format string
565  *
566  * This is printk().  It can be called from any context.  We want it to work.
567  *
568  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
569  * call the console drivers.  If we fail to get the semaphore we place the output
570  * into the log buffer and return.  The current holder of the console_sem will
571  * notice the new output in release_console_sem() and will send it to the
572  * consoles before releasing the semaphore.
573  *
574  * One effect of this deferred printing is that code which calls printk() and
575  * then changes console_loglevel may break. This is because console_loglevel
576  * is inspected when the actual printing occurs.
577  *
578  * See also:
579  * printf(3)
580  *
581  * See the vsnprintf() documentation for format string extensions over C99.
582  */
583
584 asmlinkage int printk(const char *fmt, ...)
585 {
586         va_list args;
587         int r;
588
589         va_start(args, fmt);
590         r = vprintk(fmt, args);
591         va_end(args);
592
593         return r;
594 }
595
596 /* cpu currently holding logbuf_lock */
597 static volatile unsigned int printk_cpu = UINT_MAX;
598
599 /*
600  * Can we actually use the console at this time on this cpu?
601  *
602  * Console drivers may assume that per-cpu resources have
603  * been allocated. So unless they're explicitly marked as
604  * being able to cope (CON_ANYTIME) don't call them until
605  * this CPU is officially up.
606  */
607 static inline int can_use_console(unsigned int cpu)
608 {
609         return cpu_online(cpu) || have_callable_console();
610 }
611
612 /*
613  * Try to get console ownership to actually show the kernel
614  * messages from a 'printk'. Return true (and with the
615  * console_semaphore held, and 'console_locked' set) if it
616  * is successful, false otherwise.
617  *
618  * This gets called with the 'logbuf_lock' spinlock held and
619  * interrupts disabled. It should return with 'lockbuf_lock'
620  * released but interrupts still disabled.
621  */
622 static int acquire_console_semaphore_for_printk(unsigned int cpu)
623 {
624         int retval = 0;
625
626         if (!try_acquire_console_sem()) {
627                 retval = 1;
628
629                 /*
630                  * If we can't use the console, we need to release
631                  * the console semaphore by hand to avoid flushing
632                  * the buffer. We need to hold the console semaphore
633                  * in order to do this test safely.
634                  */
635                 if (!can_use_console(cpu)) {
636                         console_locked = 0;
637                         up(&console_sem);
638                         retval = 0;
639                 }
640         }
641         printk_cpu = UINT_MAX;
642         spin_unlock(&logbuf_lock);
643         return retval;
644 }
645 static const char recursion_bug_msg [] =
646                 KERN_CRIT "BUG: recent printk recursion!\n";
647 static int recursion_bug;
648 static int new_text_line = 1;
649 static char printk_buf[1024];
650
651 int printk_delay_msec __read_mostly;
652
653 static inline void printk_delay(void)
654 {
655         if (unlikely(printk_delay_msec)) {
656                 int m = printk_delay_msec;
657
658                 while (m--) {
659                         mdelay(1);
660                         touch_nmi_watchdog();
661                 }
662         }
663 }
664
665 asmlinkage int vprintk(const char *fmt, va_list args)
666 {
667         int printed_len = 0;
668         int current_log_level = default_message_loglevel;
669         unsigned long flags;
670         int this_cpu;
671         char *p;
672
673         boot_delay_msec();
674         printk_delay();
675
676         preempt_disable();
677         /* This stops the holder of console_sem just where we want him */
678         raw_local_irq_save(flags);
679         this_cpu = smp_processor_id();
680
681         /*
682          * Ouch, printk recursed into itself!
683          */
684         if (unlikely(printk_cpu == this_cpu)) {
685                 /*
686                  * If a crash is occurring during printk() on this CPU,
687                  * then try to get the crash message out but make sure
688                  * we can't deadlock. Otherwise just return to avoid the
689                  * recursion and return - but flag the recursion so that
690                  * it can be printed at the next appropriate moment:
691                  */
692                 if (!oops_in_progress) {
693                         recursion_bug = 1;
694                         goto out_restore_irqs;
695                 }
696                 zap_locks();
697         }
698
699         lockdep_off();
700         spin_lock(&logbuf_lock);
701         printk_cpu = this_cpu;
702
703         if (recursion_bug) {
704                 recursion_bug = 0;
705                 strcpy(printk_buf, recursion_bug_msg);
706                 printed_len = strlen(recursion_bug_msg);
707         }
708         /* Emit the output into the temporary buffer */
709         printed_len += vscnprintf(printk_buf + printed_len,
710                                   sizeof(printk_buf) - printed_len, fmt, args);
711
712
713         p = printk_buf;
714
715         /* Do we have a loglevel in the string? */
716         if (p[0] == '<') {
717                 unsigned char c = p[1];
718                 if (c && p[2] == '>') {
719                         switch (c) {
720                         case '0' ... '7': /* loglevel */
721                                 current_log_level = c - '0';
722                         /* Fallthrough - make sure we're on a new line */
723                         case 'd': /* KERN_DEFAULT */
724                                 if (!new_text_line) {
725                                         emit_log_char('\n');
726                                         new_text_line = 1;
727                                 }
728                         /* Fallthrough - skip the loglevel */
729                         case 'c': /* KERN_CONT */
730                                 p += 3;
731                                 break;
732                         }
733                 }
734         }
735
736         /*
737          * Copy the output into log_buf.  If the caller didn't provide
738          * appropriate log level tags, we insert them here
739          */
740         for ( ; *p; p++) {
741                 if (new_text_line) {
742                         /* Always output the token */
743                         emit_log_char('<');
744                         emit_log_char(current_log_level + '0');
745                         emit_log_char('>');
746                         printed_len += 3;
747                         new_text_line = 0;
748
749                         if (printk_time) {
750                                 /* Follow the token with the time */
751                                 char tbuf[50], *tp;
752                                 unsigned tlen;
753                                 unsigned long long t;
754                                 unsigned long nanosec_rem;
755
756                                 t = cpu_clock(printk_cpu);
757                                 nanosec_rem = do_div(t, 1000000000);
758                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
759                                                 (unsigned long) t,
760                                                 nanosec_rem / 1000);
761
762                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
763                                         emit_log_char(*tp);
764                                 printed_len += tlen;
765                         }
766
767                         if (!*p)
768                                 break;
769                 }
770
771                 emit_log_char(*p);
772                 if (*p == '\n')
773                         new_text_line = 1;
774         }
775
776         /*
777          * Try to acquire and then immediately release the
778          * console semaphore. The release will do all the
779          * actual magic (print out buffers, wake up klogd,
780          * etc). 
781          *
782          * The acquire_console_semaphore_for_printk() function
783          * will release 'logbuf_lock' regardless of whether it
784          * actually gets the semaphore or not.
785          */
786         if (acquire_console_semaphore_for_printk(this_cpu))
787                 release_console_sem();
788
789         lockdep_on();
790 out_restore_irqs:
791         raw_local_irq_restore(flags);
792
793         preempt_enable();
794         return printed_len;
795 }
796 EXPORT_SYMBOL(printk);
797 EXPORT_SYMBOL(vprintk);
798
799 #else
800
801 static void call_console_drivers(unsigned start, unsigned end)
802 {
803 }
804
805 #endif
806
807 static int __add_preferred_console(char *name, int idx, char *options,
808                                    char *brl_options)
809 {
810         struct console_cmdline *c;
811         int i;
812
813         /*
814          *      See if this tty is not yet registered, and
815          *      if we have a slot free.
816          */
817         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
818                 if (strcmp(console_cmdline[i].name, name) == 0 &&
819                           console_cmdline[i].index == idx) {
820                                 if (!brl_options)
821                                         selected_console = i;
822                                 return 0;
823                 }
824         if (i == MAX_CMDLINECONSOLES)
825                 return -E2BIG;
826         if (!brl_options)
827                 selected_console = i;
828         c = &console_cmdline[i];
829         strlcpy(c->name, name, sizeof(c->name));
830         c->options = options;
831 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
832         c->brl_options = brl_options;
833 #endif
834         c->index = idx;
835         return 0;
836 }
837 /*
838  * Set up a list of consoles.  Called from init/main.c
839  */
840 static int __init console_setup(char *str)
841 {
842         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
843         char *s, *options, *brl_options = NULL;
844         int idx;
845
846 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
847         if (!memcmp(str, "brl,", 4)) {
848                 brl_options = "";
849                 str += 4;
850         } else if (!memcmp(str, "brl=", 4)) {
851                 brl_options = str + 4;
852                 str = strchr(brl_options, ',');
853                 if (!str) {
854                         printk(KERN_ERR "need port name after brl=\n");
855                         return 1;
856                 }
857                 *(str++) = 0;
858         }
859 #endif
860
861         /*
862          * Decode str into name, index, options.
863          */
864         if (str[0] >= '0' && str[0] <= '9') {
865                 strcpy(buf, "ttyS");
866                 strncpy(buf + 4, str, sizeof(buf) - 5);
867         } else {
868                 strncpy(buf, str, sizeof(buf) - 1);
869         }
870         buf[sizeof(buf) - 1] = 0;
871         if ((options = strchr(str, ',')) != NULL)
872                 *(options++) = 0;
873 #ifdef __sparc__
874         if (!strcmp(str, "ttya"))
875                 strcpy(buf, "ttyS0");
876         if (!strcmp(str, "ttyb"))
877                 strcpy(buf, "ttyS1");
878 #endif
879         for (s = buf; *s; s++)
880                 if ((*s >= '0' && *s <= '9') || *s == ',')
881                         break;
882         idx = simple_strtoul(s, NULL, 10);
883         *s = 0;
884
885         __add_preferred_console(buf, idx, options, brl_options);
886         console_set_on_cmdline = 1;
887         return 1;
888 }
889 __setup("console=", console_setup);
890
891 /**
892  * add_preferred_console - add a device to the list of preferred consoles.
893  * @name: device name
894  * @idx: device index
895  * @options: options for this console
896  *
897  * The last preferred console added will be used for kernel messages
898  * and stdin/out/err for init.  Normally this is used by console_setup
899  * above to handle user-supplied console arguments; however it can also
900  * be used by arch-specific code either to override the user or more
901  * commonly to provide a default console (ie from PROM variables) when
902  * the user has not supplied one.
903  */
904 int add_preferred_console(char *name, int idx, char *options)
905 {
906         return __add_preferred_console(name, idx, options, NULL);
907 }
908
909 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
910 {
911         struct console_cmdline *c;
912         int i;
913
914         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
915                 if (strcmp(console_cmdline[i].name, name) == 0 &&
916                           console_cmdline[i].index == idx) {
917                                 c = &console_cmdline[i];
918                                 strlcpy(c->name, name_new, sizeof(c->name));
919                                 c->name[sizeof(c->name) - 1] = 0;
920                                 c->options = options;
921                                 c->index = idx_new;
922                                 return i;
923                 }
924         /* not found */
925         return -1;
926 }
927
928 int console_suspend_enabled = 1;
929 EXPORT_SYMBOL(console_suspend_enabled);
930
931 static int __init console_suspend_disable(char *str)
932 {
933         console_suspend_enabled = 0;
934         return 1;
935 }
936 __setup("no_console_suspend", console_suspend_disable);
937
938 /**
939  * suspend_console - suspend the console subsystem
940  *
941  * This disables printk() while we go into suspend states
942  */
943 void suspend_console(void)
944 {
945         if (!console_suspend_enabled)
946                 return;
947         printk("Suspending console(s) (use no_console_suspend to debug)\n");
948         acquire_console_sem();
949         console_suspended = 1;
950         up(&console_sem);
951 }
952
953 void resume_console(void)
954 {
955         if (!console_suspend_enabled)
956                 return;
957         down(&console_sem);
958         console_suspended = 0;
959         release_console_sem();
960 }
961
962 /**
963  * acquire_console_sem - lock the console system for exclusive use.
964  *
965  * Acquires a semaphore which guarantees that the caller has
966  * exclusive access to the console system and the console_drivers list.
967  *
968  * Can sleep, returns nothing.
969  */
970 void acquire_console_sem(void)
971 {
972         BUG_ON(in_interrupt());
973         down(&console_sem);
974         if (console_suspended)
975                 return;
976         console_locked = 1;
977         console_may_schedule = 1;
978 }
979 EXPORT_SYMBOL(acquire_console_sem);
980
981 int try_acquire_console_sem(void)
982 {
983         if (down_trylock(&console_sem))
984                 return -1;
985         if (console_suspended) {
986                 up(&console_sem);
987                 return -1;
988         }
989         console_locked = 1;
990         console_may_schedule = 0;
991         return 0;
992 }
993 EXPORT_SYMBOL(try_acquire_console_sem);
994
995 int is_console_locked(void)
996 {
997         return console_locked;
998 }
999
1000 static DEFINE_PER_CPU(int, printk_pending);
1001
1002 void printk_tick(void)
1003 {
1004         if (__get_cpu_var(printk_pending)) {
1005                 __get_cpu_var(printk_pending) = 0;
1006                 wake_up_interruptible(&log_wait);
1007         }
1008 }
1009
1010 int printk_needs_cpu(int cpu)
1011 {
1012         return per_cpu(printk_pending, cpu);
1013 }
1014
1015 void wake_up_klogd(void)
1016 {
1017         if (waitqueue_active(&log_wait))
1018                 __raw_get_cpu_var(printk_pending) = 1;
1019 }
1020
1021 /**
1022  * release_console_sem - unlock the console system
1023  *
1024  * Releases the semaphore which the caller holds on the console system
1025  * and the console driver list.
1026  *
1027  * While the semaphore was held, console output may have been buffered
1028  * by printk().  If this is the case, release_console_sem() emits
1029  * the output prior to releasing the semaphore.
1030  *
1031  * If there is output waiting for klogd, we wake it up.
1032  *
1033  * release_console_sem() may be called from any context.
1034  */
1035 void release_console_sem(void)
1036 {
1037         unsigned long flags;
1038         unsigned _con_start, _log_end;
1039         unsigned wake_klogd = 0;
1040
1041         if (console_suspended) {
1042                 up(&console_sem);
1043                 return;
1044         }
1045
1046         console_may_schedule = 0;
1047
1048         for ( ; ; ) {
1049                 spin_lock_irqsave(&logbuf_lock, flags);
1050                 wake_klogd |= log_start - log_end;
1051                 if (con_start == log_end)
1052                         break;                  /* Nothing to print */
1053                 _con_start = con_start;
1054                 _log_end = log_end;
1055                 con_start = log_end;            /* Flush */
1056                 spin_unlock(&logbuf_lock);
1057                 stop_critical_timings();        /* don't trace print latency */
1058                 call_console_drivers(_con_start, _log_end);
1059                 start_critical_timings();
1060                 local_irq_restore(flags);
1061         }
1062         console_locked = 0;
1063         up(&console_sem);
1064         spin_unlock_irqrestore(&logbuf_lock, flags);
1065         if (wake_klogd)
1066                 wake_up_klogd();
1067 }
1068 EXPORT_SYMBOL(release_console_sem);
1069
1070 /**
1071  * console_conditional_schedule - yield the CPU if required
1072  *
1073  * If the console code is currently allowed to sleep, and
1074  * if this CPU should yield the CPU to another task, do
1075  * so here.
1076  *
1077  * Must be called within acquire_console_sem().
1078  */
1079 void __sched console_conditional_schedule(void)
1080 {
1081         if (console_may_schedule)
1082                 cond_resched();
1083 }
1084 EXPORT_SYMBOL(console_conditional_schedule);
1085
1086 void console_unblank(void)
1087 {
1088         struct console *c;
1089
1090         /*
1091          * console_unblank can no longer be called in interrupt context unless
1092          * oops_in_progress is set to 1..
1093          */
1094         if (oops_in_progress) {
1095                 if (down_trylock(&console_sem) != 0)
1096                         return;
1097         } else
1098                 acquire_console_sem();
1099
1100         console_locked = 1;
1101         console_may_schedule = 0;
1102         for_each_console(c)
1103                 if ((c->flags & CON_ENABLED) && c->unblank)
1104                         c->unblank();
1105         release_console_sem();
1106 }
1107
1108 /*
1109  * Return the console tty driver structure and its associated index
1110  */
1111 struct tty_driver *console_device(int *index)
1112 {
1113         struct console *c;
1114         struct tty_driver *driver = NULL;
1115
1116         acquire_console_sem();
1117         for_each_console(c) {
1118                 if (!c->device)
1119                         continue;
1120                 driver = c->device(c, index);
1121                 if (driver)
1122                         break;
1123         }
1124         release_console_sem();
1125         return driver;
1126 }
1127
1128 /*
1129  * Prevent further output on the passed console device so that (for example)
1130  * serial drivers can disable console output before suspending a port, and can
1131  * re-enable output afterwards.
1132  */
1133 void console_stop(struct console *console)
1134 {
1135         acquire_console_sem();
1136         console->flags &= ~CON_ENABLED;
1137         release_console_sem();
1138 }
1139 EXPORT_SYMBOL(console_stop);
1140
1141 void console_start(struct console *console)
1142 {
1143         acquire_console_sem();
1144         console->flags |= CON_ENABLED;
1145         release_console_sem();
1146 }
1147 EXPORT_SYMBOL(console_start);
1148
1149 /*
1150  * The console driver calls this routine during kernel initialization
1151  * to register the console printing procedure with printk() and to
1152  * print any messages that were printed by the kernel before the
1153  * console driver was initialized.
1154  *
1155  * This can happen pretty early during the boot process (because of
1156  * early_printk) - sometimes before setup_arch() completes - be careful
1157  * of what kernel features are used - they may not be initialised yet.
1158  *
1159  * There are two types of consoles - bootconsoles (early_printk) and
1160  * "real" consoles (everything which is not a bootconsole) which are
1161  * handled differently.
1162  *  - Any number of bootconsoles can be registered at any time.
1163  *  - As soon as a "real" console is registered, all bootconsoles
1164  *    will be unregistered automatically.
1165  *  - Once a "real" console is registered, any attempt to register a
1166  *    bootconsoles will be rejected
1167  */
1168 void register_console(struct console *newcon)
1169 {
1170         int i;
1171         unsigned long flags;
1172         struct console *bcon = NULL;
1173
1174         /*
1175          * before we register a new CON_BOOT console, make sure we don't
1176          * already have a valid console
1177          */
1178         if (console_drivers && newcon->flags & CON_BOOT) {
1179                 /* find the last or real console */
1180                 for_each_console(bcon) {
1181                         if (!(bcon->flags & CON_BOOT)) {
1182                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1183                                         newcon->name, newcon->index);
1184                                 return;
1185                         }
1186                 }
1187         }
1188
1189         if (console_drivers && console_drivers->flags & CON_BOOT)
1190                 bcon = console_drivers;
1191
1192         if (preferred_console < 0 || bcon || !console_drivers)
1193                 preferred_console = selected_console;
1194
1195         if (newcon->early_setup)
1196                 newcon->early_setup();
1197
1198         /*
1199          *      See if we want to use this console driver. If we
1200          *      didn't select a console we take the first one
1201          *      that registers here.
1202          */
1203         if (preferred_console < 0) {
1204                 if (newcon->index < 0)
1205                         newcon->index = 0;
1206                 if (newcon->setup == NULL ||
1207                     newcon->setup(newcon, NULL) == 0) {
1208                         newcon->flags |= CON_ENABLED;
1209                         if (newcon->device) {
1210                                 newcon->flags |= CON_CONSDEV;
1211                                 preferred_console = 0;
1212                         }
1213                 }
1214         }
1215
1216         /*
1217          *      See if this console matches one we selected on
1218          *      the command line.
1219          */
1220         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1221                         i++) {
1222                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1223                         continue;
1224                 if (newcon->index >= 0 &&
1225                     newcon->index != console_cmdline[i].index)
1226                         continue;
1227                 if (newcon->index < 0)
1228                         newcon->index = console_cmdline[i].index;
1229 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1230                 if (console_cmdline[i].brl_options) {
1231                         newcon->flags |= CON_BRL;
1232                         braille_register_console(newcon,
1233                                         console_cmdline[i].index,
1234                                         console_cmdline[i].options,
1235                                         console_cmdline[i].brl_options);
1236                         return;
1237                 }
1238 #endif
1239                 if (newcon->setup &&
1240                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1241                         break;
1242                 newcon->flags |= CON_ENABLED;
1243                 newcon->index = console_cmdline[i].index;
1244                 if (i == selected_console) {
1245                         newcon->flags |= CON_CONSDEV;
1246                         preferred_console = selected_console;
1247                 }
1248                 break;
1249         }
1250
1251         if (!(newcon->flags & CON_ENABLED))
1252                 return;
1253
1254         /*
1255          * If we have a bootconsole, and are switching to a real console,
1256          * don't print everything out again, since when the boot console, and
1257          * the real console are the same physical device, it's annoying to
1258          * see the beginning boot messages twice
1259          */
1260         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1261                 newcon->flags &= ~CON_PRINTBUFFER;
1262
1263         /*
1264          *      Put this console in the list - keep the
1265          *      preferred driver at the head of the list.
1266          */
1267         acquire_console_sem();
1268         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1269                 newcon->next = console_drivers;
1270                 console_drivers = newcon;
1271                 if (newcon->next)
1272                         newcon->next->flags &= ~CON_CONSDEV;
1273         } else {
1274                 newcon->next = console_drivers->next;
1275                 console_drivers->next = newcon;
1276         }
1277         if (newcon->flags & CON_PRINTBUFFER) {
1278                 /*
1279                  * release_console_sem() will print out the buffered messages
1280                  * for us.
1281                  */
1282                 spin_lock_irqsave(&logbuf_lock, flags);
1283                 con_start = log_start;
1284                 spin_unlock_irqrestore(&logbuf_lock, flags);
1285         }
1286         release_console_sem();
1287
1288         /*
1289          * By unregistering the bootconsoles after we enable the real console
1290          * we get the "console xxx enabled" message on all the consoles -
1291          * boot consoles, real consoles, etc - this is to ensure that end
1292          * users know there might be something in the kernel's log buffer that
1293          * went to the bootconsole (that they do not see on the real console)
1294          */
1295         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1296                 /* we need to iterate through twice, to make sure we print
1297                  * everything out, before we unregister the console(s)
1298                  */
1299                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1300                         newcon->name, newcon->index);
1301                 for_each_console(bcon)
1302                         if (bcon->flags & CON_BOOT)
1303                                 unregister_console(bcon);
1304         } else {
1305                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1306                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1307                         newcon->name, newcon->index);
1308         }
1309 }
1310 EXPORT_SYMBOL(register_console);
1311
1312 int unregister_console(struct console *console)
1313 {
1314         struct console *a, *b;
1315         int res = 1;
1316
1317 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1318         if (console->flags & CON_BRL)
1319                 return braille_unregister_console(console);
1320 #endif
1321
1322         acquire_console_sem();
1323         if (console_drivers == console) {
1324                 console_drivers=console->next;
1325                 res = 0;
1326         } else if (console_drivers) {
1327                 for (a=console_drivers->next, b=console_drivers ;
1328                      a; b=a, a=b->next) {
1329                         if (a == console) {
1330                                 b->next = a->next;
1331                                 res = 0;
1332                                 break;
1333                         }
1334                 }
1335         }
1336
1337         /*
1338          * If this isn't the last console and it has CON_CONSDEV set, we
1339          * need to set it on the next preferred console.
1340          */
1341         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1342                 console_drivers->flags |= CON_CONSDEV;
1343
1344         release_console_sem();
1345         return res;
1346 }
1347 EXPORT_SYMBOL(unregister_console);
1348
1349 static int __init disable_boot_consoles(void)
1350 {
1351         struct console *con;
1352
1353         for_each_console(con) {
1354                 if (con->flags & CON_BOOT) {
1355                         printk(KERN_INFO "turn off boot console %s%d\n",
1356                                 con->name, con->index);
1357                         unregister_console(con);
1358                 }
1359         }
1360         return 0;
1361 }
1362 late_initcall(disable_boot_consoles);
1363
1364 #if defined CONFIG_PRINTK
1365
1366 /*
1367  * printk rate limiting, lifted from the networking subsystem.
1368  *
1369  * This enforces a rate limit: not more than 10 kernel messages
1370  * every 5s to make a denial-of-service attack impossible.
1371  */
1372 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1373
1374 int __printk_ratelimit(const char *func)
1375 {
1376         return ___ratelimit(&printk_ratelimit_state, func);
1377 }
1378 EXPORT_SYMBOL(__printk_ratelimit);
1379
1380 /**
1381  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1382  * @caller_jiffies: pointer to caller's state
1383  * @interval_msecs: minimum interval between prints
1384  *
1385  * printk_timed_ratelimit() returns true if more than @interval_msecs
1386  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1387  * returned true.
1388  */
1389 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1390                         unsigned int interval_msecs)
1391 {
1392         if (*caller_jiffies == 0
1393                         || !time_in_range(jiffies, *caller_jiffies,
1394                                         *caller_jiffies
1395                                         + msecs_to_jiffies(interval_msecs))) {
1396                 *caller_jiffies = jiffies;
1397                 return true;
1398         }
1399         return false;
1400 }
1401 EXPORT_SYMBOL(printk_timed_ratelimit);
1402
1403 static DEFINE_SPINLOCK(dump_list_lock);
1404 static LIST_HEAD(dump_list);
1405
1406 /**
1407  * kmsg_dump_register - register a kernel log dumper.
1408  * @dumper: pointer to the kmsg_dumper structure
1409  *
1410  * Adds a kernel log dumper to the system. The dump callback in the
1411  * structure will be called when the kernel oopses or panics and must be
1412  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1413  */
1414 int kmsg_dump_register(struct kmsg_dumper *dumper)
1415 {
1416         unsigned long flags;
1417         int err = -EBUSY;
1418
1419         /* The dump callback needs to be set */
1420         if (!dumper->dump)
1421                 return -EINVAL;
1422
1423         spin_lock_irqsave(&dump_list_lock, flags);
1424         /* Don't allow registering multiple times */
1425         if (!dumper->registered) {
1426                 dumper->registered = 1;
1427                 list_add_tail(&dumper->list, &dump_list);
1428                 err = 0;
1429         }
1430         spin_unlock_irqrestore(&dump_list_lock, flags);
1431
1432         return err;
1433 }
1434 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1435
1436 /**
1437  * kmsg_dump_unregister - unregister a kmsg dumper.
1438  * @dumper: pointer to the kmsg_dumper structure
1439  *
1440  * Removes a dump device from the system. Returns zero on success and
1441  * %-EINVAL otherwise.
1442  */
1443 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1444 {
1445         unsigned long flags;
1446         int err = -EINVAL;
1447
1448         spin_lock_irqsave(&dump_list_lock, flags);
1449         if (dumper->registered) {
1450                 dumper->registered = 0;
1451                 list_del(&dumper->list);
1452                 err = 0;
1453         }
1454         spin_unlock_irqrestore(&dump_list_lock, flags);
1455
1456         return err;
1457 }
1458 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1459
1460 static const char const *kmsg_reasons[] = {
1461         [KMSG_DUMP_OOPS]        = "oops",
1462         [KMSG_DUMP_PANIC]       = "panic",
1463         [KMSG_DUMP_KEXEC]       = "kexec",
1464 };
1465
1466 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1467 {
1468         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1469                 return "unknown";
1470
1471         return kmsg_reasons[reason];
1472 }
1473
1474 /**
1475  * kmsg_dump - dump kernel log to kernel message dumpers.
1476  * @reason: the reason (oops, panic etc) for dumping
1477  *
1478  * Iterate through each of the dump devices and call the oops/panic
1479  * callbacks with the log buffer.
1480  */
1481 void kmsg_dump(enum kmsg_dump_reason reason)
1482 {
1483         unsigned long end;
1484         unsigned chars;
1485         struct kmsg_dumper *dumper;
1486         const char *s1, *s2;
1487         unsigned long l1, l2;
1488         unsigned long flags;
1489
1490         /* Theoretically, the log could move on after we do this, but
1491            there's not a lot we can do about that. The new messages
1492            will overwrite the start of what we dump. */
1493         spin_lock_irqsave(&logbuf_lock, flags);
1494         end = log_end & LOG_BUF_MASK;
1495         chars = logged_chars;
1496         spin_unlock_irqrestore(&logbuf_lock, flags);
1497
1498         if (logged_chars > end) {
1499                 s1 = log_buf + log_buf_len - logged_chars + end;
1500                 l1 = logged_chars - end;
1501
1502                 s2 = log_buf;
1503                 l2 = end;
1504         } else {
1505                 s1 = "";
1506                 l1 = 0;
1507
1508                 s2 = log_buf + end - logged_chars;
1509                 l2 = logged_chars;
1510         }
1511
1512         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1513                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1514                                 kmsg_to_str(reason));
1515                 return;
1516         }
1517         list_for_each_entry(dumper, &dump_list, list)
1518                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1519         spin_unlock_irqrestore(&dump_list_lock, flags);
1520 }
1521 #endif