rtmutex: Fix comment about why new_owner can be NULL in wake_futex_pi()
[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         /*
278          * If this is from /proc/kmsg we only do the capabilities checks
279          * at open time.
280          */
281         if (type == SYSLOG_ACTION_OPEN || !from_file) {
282                 if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
283                         return -EPERM;
284                 if ((type != SYSLOG_ACTION_READ_ALL &&
285                      type != SYSLOG_ACTION_SIZE_BUFFER) &&
286                     !capable(CAP_SYS_ADMIN))
287                         return -EPERM;
288         }
289
290         error = security_syslog(type);
291         if (error)
292                 return error;
293
294         switch (type) {
295         case SYSLOG_ACTION_CLOSE:       /* Close log */
296                 break;
297         case SYSLOG_ACTION_OPEN:        /* Open log */
298                 break;
299         case SYSLOG_ACTION_READ:        /* Read from log */
300                 error = -EINVAL;
301                 if (!buf || len < 0)
302                         goto out;
303                 error = 0;
304                 if (!len)
305                         goto out;
306                 if (!access_ok(VERIFY_WRITE, buf, len)) {
307                         error = -EFAULT;
308                         goto out;
309                 }
310                 error = wait_event_interruptible(log_wait,
311                                                         (log_start - log_end));
312                 if (error)
313                         goto out;
314                 i = 0;
315                 spin_lock_irq(&logbuf_lock);
316                 while (!error && (log_start != log_end) && i < len) {
317                         c = LOG_BUF(log_start);
318                         log_start++;
319                         spin_unlock_irq(&logbuf_lock);
320                         error = __put_user(c,buf);
321                         buf++;
322                         i++;
323                         cond_resched();
324                         spin_lock_irq(&logbuf_lock);
325                 }
326                 spin_unlock_irq(&logbuf_lock);
327                 if (!error)
328                         error = i;
329                 break;
330         /* Read/clear last kernel messages */
331         case SYSLOG_ACTION_READ_CLEAR:
332                 do_clear = 1;
333                 /* FALL THRU */
334         /* Read last kernel messages */
335         case SYSLOG_ACTION_READ_ALL:
336                 error = -EINVAL;
337                 if (!buf || len < 0)
338                         goto out;
339                 error = 0;
340                 if (!len)
341                         goto out;
342                 if (!access_ok(VERIFY_WRITE, buf, len)) {
343                         error = -EFAULT;
344                         goto out;
345                 }
346                 count = len;
347                 if (count > log_buf_len)
348                         count = log_buf_len;
349                 spin_lock_irq(&logbuf_lock);
350                 if (count > logged_chars)
351                         count = logged_chars;
352                 if (do_clear)
353                         logged_chars = 0;
354                 limit = log_end;
355                 /*
356                  * __put_user() could sleep, and while we sleep
357                  * printk() could overwrite the messages
358                  * we try to copy to user space. Therefore
359                  * the messages are copied in reverse. <manfreds>
360                  */
361                 for (i = 0; i < count && !error; i++) {
362                         j = limit-1-i;
363                         if (j + log_buf_len < log_end)
364                                 break;
365                         c = LOG_BUF(j);
366                         spin_unlock_irq(&logbuf_lock);
367                         error = __put_user(c,&buf[count-1-i]);
368                         cond_resched();
369                         spin_lock_irq(&logbuf_lock);
370                 }
371                 spin_unlock_irq(&logbuf_lock);
372                 if (error)
373                         break;
374                 error = i;
375                 if (i != count) {
376                         int offset = count-error;
377                         /* buffer overflow during copy, correct user buffer. */
378                         for (i = 0; i < error; i++) {
379                                 if (__get_user(c,&buf[i+offset]) ||
380                                     __put_user(c,&buf[i])) {
381                                         error = -EFAULT;
382                                         break;
383                                 }
384                                 cond_resched();
385                         }
386                 }
387                 break;
388         /* Clear ring buffer */
389         case SYSLOG_ACTION_CLEAR:
390                 logged_chars = 0;
391                 break;
392         /* Disable logging to console */
393         case SYSLOG_ACTION_CONSOLE_OFF:
394                 if (saved_console_loglevel == -1)
395                         saved_console_loglevel = console_loglevel;
396                 console_loglevel = minimum_console_loglevel;
397                 break;
398         /* Enable logging to console */
399         case SYSLOG_ACTION_CONSOLE_ON:
400                 if (saved_console_loglevel != -1) {
401                         console_loglevel = saved_console_loglevel;
402                         saved_console_loglevel = -1;
403                 }
404                 break;
405         /* Set level of messages printed to console */
406         case SYSLOG_ACTION_CONSOLE_LEVEL:
407                 error = -EINVAL;
408                 if (len < 1 || len > 8)
409                         goto out;
410                 if (len < minimum_console_loglevel)
411                         len = minimum_console_loglevel;
412                 console_loglevel = len;
413                 /* Implicitly re-enable logging to console */
414                 saved_console_loglevel = -1;
415                 error = 0;
416                 break;
417         /* Number of chars in the log buffer */
418         case SYSLOG_ACTION_SIZE_UNREAD:
419                 error = log_end - log_start;
420                 break;
421         /* Size of the log buffer */
422         case SYSLOG_ACTION_SIZE_BUFFER:
423                 error = log_buf_len;
424                 break;
425         default:
426                 error = -EINVAL;
427                 break;
428         }
429 out:
430         return error;
431 }
432
433 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
434 {
435         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
436 }
437
438 #ifdef  CONFIG_KGDB_KDB
439 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
440  * uses locks so it cannot be used during debugging.  Just tell kdb
441  * where the start and end of the physical and logical logs are.  This
442  * is equivalent to do_syslog(3).
443  */
444 void kdb_syslog_data(char *syslog_data[4])
445 {
446         syslog_data[0] = log_buf;
447         syslog_data[1] = log_buf + log_buf_len;
448         syslog_data[2] = log_buf + log_end -
449                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
450         syslog_data[3] = log_buf + log_end;
451 }
452 #endif  /* CONFIG_KGDB_KDB */
453
454 /*
455  * Call the console drivers on a range of log_buf
456  */
457 static void __call_console_drivers(unsigned start, unsigned end)
458 {
459         struct console *con;
460
461         for_each_console(con) {
462                 if ((con->flags & CON_ENABLED) && con->write &&
463                                 (cpu_online(smp_processor_id()) ||
464                                 (con->flags & CON_ANYTIME)))
465                         con->write(con, &LOG_BUF(start), end - start);
466         }
467 }
468
469 static int __read_mostly ignore_loglevel;
470
471 static int __init ignore_loglevel_setup(char *str)
472 {
473         ignore_loglevel = 1;
474         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
475
476         return 0;
477 }
478
479 early_param("ignore_loglevel", ignore_loglevel_setup);
480
481 /*
482  * Write out chars from start to end - 1 inclusive
483  */
484 static void _call_console_drivers(unsigned start,
485                                 unsigned end, int msg_log_level)
486 {
487         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
488                         console_drivers && start != end) {
489                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
490                         /* wrapped write */
491                         __call_console_drivers(start & LOG_BUF_MASK,
492                                                 log_buf_len);
493                         __call_console_drivers(0, end & LOG_BUF_MASK);
494                 } else {
495                         __call_console_drivers(start, end);
496                 }
497         }
498 }
499
500 /*
501  * Call the console drivers, asking them to write out
502  * log_buf[start] to log_buf[end - 1].
503  * The console_sem must be held.
504  */
505 static void call_console_drivers(unsigned start, unsigned end)
506 {
507         unsigned cur_index, start_print;
508         static int msg_level = -1;
509
510         BUG_ON(((int)(start - end)) > 0);
511
512         cur_index = start;
513         start_print = start;
514         while (cur_index != end) {
515                 if (msg_level < 0 && ((end - cur_index) > 2) &&
516                                 LOG_BUF(cur_index + 0) == '<' &&
517                                 LOG_BUF(cur_index + 1) >= '0' &&
518                                 LOG_BUF(cur_index + 1) <= '7' &&
519                                 LOG_BUF(cur_index + 2) == '>') {
520                         msg_level = LOG_BUF(cur_index + 1) - '0';
521                         cur_index += 3;
522                         start_print = cur_index;
523                 }
524                 while (cur_index != end) {
525                         char c = LOG_BUF(cur_index);
526
527                         cur_index++;
528                         if (c == '\n') {
529                                 if (msg_level < 0) {
530                                         /*
531                                          * printk() has already given us loglevel tags in
532                                          * the buffer.  This code is here in case the
533                                          * log buffer has wrapped right round and scribbled
534                                          * on those tags
535                                          */
536                                         msg_level = default_message_loglevel;
537                                 }
538                                 _call_console_drivers(start_print, cur_index, msg_level);
539                                 msg_level = -1;
540                                 start_print = cur_index;
541                                 break;
542                         }
543                 }
544         }
545         _call_console_drivers(start_print, end, msg_level);
546 }
547
548 static void emit_log_char(char c)
549 {
550         LOG_BUF(log_end) = c;
551         log_end++;
552         if (log_end - log_start > log_buf_len)
553                 log_start = log_end - log_buf_len;
554         if (log_end - con_start > log_buf_len)
555                 con_start = log_end - log_buf_len;
556         if (logged_chars < log_buf_len)
557                 logged_chars++;
558 }
559
560 /*
561  * Zap console related locks when oopsing. Only zap at most once
562  * every 10 seconds, to leave time for slow consoles to print a
563  * full oops.
564  */
565 static void zap_locks(void)
566 {
567         static unsigned long oops_timestamp;
568
569         if (time_after_eq(jiffies, oops_timestamp) &&
570                         !time_after(jiffies, oops_timestamp + 30 * HZ))
571                 return;
572
573         oops_timestamp = jiffies;
574
575         /* If a crash is occurring, make sure we can't deadlock */
576         spin_lock_init(&logbuf_lock);
577         /* And make sure that we print immediately */
578         sema_init(&console_sem, 1);
579 }
580
581 #if defined(CONFIG_PRINTK_TIME)
582 static int printk_time = 1;
583 #else
584 static int printk_time = 0;
585 #endif
586 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
587
588 /* Check if we have any console registered that can be called early in boot. */
589 static int have_callable_console(void)
590 {
591         struct console *con;
592
593         for_each_console(con)
594                 if (con->flags & CON_ANYTIME)
595                         return 1;
596
597         return 0;
598 }
599
600 /**
601  * printk - print a kernel message
602  * @fmt: format string
603  *
604  * This is printk().  It can be called from any context.  We want it to work.
605  *
606  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
607  * call the console drivers.  If we fail to get the semaphore we place the output
608  * into the log buffer and return.  The current holder of the console_sem will
609  * notice the new output in release_console_sem() and will send it to the
610  * consoles before releasing the semaphore.
611  *
612  * One effect of this deferred printing is that code which calls printk() and
613  * then changes console_loglevel may break. This is because console_loglevel
614  * is inspected when the actual printing occurs.
615  *
616  * See also:
617  * printf(3)
618  *
619  * See the vsnprintf() documentation for format string extensions over C99.
620  */
621
622 asmlinkage int printk(const char *fmt, ...)
623 {
624         va_list args;
625         int r;
626
627 #ifdef CONFIG_KGDB_KDB
628         if (unlikely(kdb_trap_printk)) {
629                 va_start(args, fmt);
630                 r = vkdb_printf(fmt, args);
631                 va_end(args);
632                 return r;
633         }
634 #endif
635         va_start(args, fmt);
636         r = vprintk(fmt, args);
637         va_end(args);
638
639         return r;
640 }
641
642 /* cpu currently holding logbuf_lock */
643 static volatile unsigned int printk_cpu = UINT_MAX;
644
645 /*
646  * Can we actually use the console at this time on this cpu?
647  *
648  * Console drivers may assume that per-cpu resources have
649  * been allocated. So unless they're explicitly marked as
650  * being able to cope (CON_ANYTIME) don't call them until
651  * this CPU is officially up.
652  */
653 static inline int can_use_console(unsigned int cpu)
654 {
655         return cpu_online(cpu) || have_callable_console();
656 }
657
658 /*
659  * Try to get console ownership to actually show the kernel
660  * messages from a 'printk'. Return true (and with the
661  * console_semaphore held, and 'console_locked' set) if it
662  * is successful, false otherwise.
663  *
664  * This gets called with the 'logbuf_lock' spinlock held and
665  * interrupts disabled. It should return with 'lockbuf_lock'
666  * released but interrupts still disabled.
667  */
668 static int acquire_console_semaphore_for_printk(unsigned int cpu)
669         __releases(&logbuf_lock)
670 {
671         int retval = 0;
672
673         if (!try_acquire_console_sem()) {
674                 retval = 1;
675
676                 /*
677                  * If we can't use the console, we need to release
678                  * the console semaphore by hand to avoid flushing
679                  * the buffer. We need to hold the console semaphore
680                  * in order to do this test safely.
681                  */
682                 if (!can_use_console(cpu)) {
683                         console_locked = 0;
684                         up(&console_sem);
685                         retval = 0;
686                 }
687         }
688         printk_cpu = UINT_MAX;
689         spin_unlock(&logbuf_lock);
690         return retval;
691 }
692 static const char recursion_bug_msg [] =
693                 KERN_CRIT "BUG: recent printk recursion!\n";
694 static int recursion_bug;
695 static int new_text_line = 1;
696 static char printk_buf[1024];
697
698 int printk_delay_msec __read_mostly;
699
700 static inline void printk_delay(void)
701 {
702         if (unlikely(printk_delay_msec)) {
703                 int m = printk_delay_msec;
704
705                 while (m--) {
706                         mdelay(1);
707                         touch_nmi_watchdog();
708                 }
709         }
710 }
711
712 asmlinkage int vprintk(const char *fmt, va_list args)
713 {
714         int printed_len = 0;
715         int current_log_level = default_message_loglevel;
716         unsigned long flags;
717         int this_cpu;
718         char *p;
719
720         boot_delay_msec();
721         printk_delay();
722
723         preempt_disable();
724         /* This stops the holder of console_sem just where we want him */
725         raw_local_irq_save(flags);
726         this_cpu = smp_processor_id();
727
728         /*
729          * Ouch, printk recursed into itself!
730          */
731         if (unlikely(printk_cpu == this_cpu)) {
732                 /*
733                  * If a crash is occurring during printk() on this CPU,
734                  * then try to get the crash message out but make sure
735                  * we can't deadlock. Otherwise just return to avoid the
736                  * recursion and return - but flag the recursion so that
737                  * it can be printed at the next appropriate moment:
738                  */
739                 if (!oops_in_progress) {
740                         recursion_bug = 1;
741                         goto out_restore_irqs;
742                 }
743                 zap_locks();
744         }
745
746         lockdep_off();
747         spin_lock(&logbuf_lock);
748         printk_cpu = this_cpu;
749
750         if (recursion_bug) {
751                 recursion_bug = 0;
752                 strcpy(printk_buf, recursion_bug_msg);
753                 printed_len = strlen(recursion_bug_msg);
754         }
755         /* Emit the output into the temporary buffer */
756         printed_len += vscnprintf(printk_buf + printed_len,
757                                   sizeof(printk_buf) - printed_len, fmt, args);
758
759
760         p = printk_buf;
761
762         /* Do we have a loglevel in the string? */
763         if (p[0] == '<') {
764                 unsigned char c = p[1];
765                 if (c && p[2] == '>') {
766                         switch (c) {
767                         case '0' ... '7': /* loglevel */
768                                 current_log_level = c - '0';
769                         /* Fallthrough - make sure we're on a new line */
770                         case 'd': /* KERN_DEFAULT */
771                                 if (!new_text_line) {
772                                         emit_log_char('\n');
773                                         new_text_line = 1;
774                                 }
775                         /* Fallthrough - skip the loglevel */
776                         case 'c': /* KERN_CONT */
777                                 p += 3;
778                                 break;
779                         }
780                 }
781         }
782
783         /*
784          * Copy the output into log_buf.  If the caller didn't provide
785          * appropriate log level tags, we insert them here
786          */
787         for ( ; *p; p++) {
788                 if (new_text_line) {
789                         /* Always output the token */
790                         emit_log_char('<');
791                         emit_log_char(current_log_level + '0');
792                         emit_log_char('>');
793                         printed_len += 3;
794                         new_text_line = 0;
795
796                         if (printk_time) {
797                                 /* Follow the token with the time */
798                                 char tbuf[50], *tp;
799                                 unsigned tlen;
800                                 unsigned long long t;
801                                 unsigned long nanosec_rem;
802
803                                 t = cpu_clock(printk_cpu);
804                                 nanosec_rem = do_div(t, 1000000000);
805                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
806                                                 (unsigned long) t,
807                                                 nanosec_rem / 1000);
808
809                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
810                                         emit_log_char(*tp);
811                                 printed_len += tlen;
812                         }
813
814                         if (!*p)
815                                 break;
816                 }
817
818                 emit_log_char(*p);
819                 if (*p == '\n')
820                         new_text_line = 1;
821         }
822
823         /*
824          * Try to acquire and then immediately release the
825          * console semaphore. The release will do all the
826          * actual magic (print out buffers, wake up klogd,
827          * etc). 
828          *
829          * The acquire_console_semaphore_for_printk() function
830          * will release 'logbuf_lock' regardless of whether it
831          * actually gets the semaphore or not.
832          */
833         if (acquire_console_semaphore_for_printk(this_cpu))
834                 release_console_sem();
835
836         lockdep_on();
837 out_restore_irqs:
838         raw_local_irq_restore(flags);
839
840         preempt_enable();
841         return printed_len;
842 }
843 EXPORT_SYMBOL(printk);
844 EXPORT_SYMBOL(vprintk);
845
846 #else
847
848 static void call_console_drivers(unsigned start, unsigned end)
849 {
850 }
851
852 #endif
853
854 static int __add_preferred_console(char *name, int idx, char *options,
855                                    char *brl_options)
856 {
857         struct console_cmdline *c;
858         int i;
859
860         /*
861          *      See if this tty is not yet registered, and
862          *      if we have a slot free.
863          */
864         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
865                 if (strcmp(console_cmdline[i].name, name) == 0 &&
866                           console_cmdline[i].index == idx) {
867                                 if (!brl_options)
868                                         selected_console = i;
869                                 return 0;
870                 }
871         if (i == MAX_CMDLINECONSOLES)
872                 return -E2BIG;
873         if (!brl_options)
874                 selected_console = i;
875         c = &console_cmdline[i];
876         strlcpy(c->name, name, sizeof(c->name));
877         c->options = options;
878 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
879         c->brl_options = brl_options;
880 #endif
881         c->index = idx;
882         return 0;
883 }
884 /*
885  * Set up a list of consoles.  Called from init/main.c
886  */
887 static int __init console_setup(char *str)
888 {
889         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
890         char *s, *options, *brl_options = NULL;
891         int idx;
892
893 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
894         if (!memcmp(str, "brl,", 4)) {
895                 brl_options = "";
896                 str += 4;
897         } else if (!memcmp(str, "brl=", 4)) {
898                 brl_options = str + 4;
899                 str = strchr(brl_options, ',');
900                 if (!str) {
901                         printk(KERN_ERR "need port name after brl=\n");
902                         return 1;
903                 }
904                 *(str++) = 0;
905         }
906 #endif
907
908         /*
909          * Decode str into name, index, options.
910          */
911         if (str[0] >= '0' && str[0] <= '9') {
912                 strcpy(buf, "ttyS");
913                 strncpy(buf + 4, str, sizeof(buf) - 5);
914         } else {
915                 strncpy(buf, str, sizeof(buf) - 1);
916         }
917         buf[sizeof(buf) - 1] = 0;
918         if ((options = strchr(str, ',')) != NULL)
919                 *(options++) = 0;
920 #ifdef __sparc__
921         if (!strcmp(str, "ttya"))
922                 strcpy(buf, "ttyS0");
923         if (!strcmp(str, "ttyb"))
924                 strcpy(buf, "ttyS1");
925 #endif
926         for (s = buf; *s; s++)
927                 if ((*s >= '0' && *s <= '9') || *s == ',')
928                         break;
929         idx = simple_strtoul(s, NULL, 10);
930         *s = 0;
931
932         __add_preferred_console(buf, idx, options, brl_options);
933         console_set_on_cmdline = 1;
934         return 1;
935 }
936 __setup("console=", console_setup);
937
938 /**
939  * add_preferred_console - add a device to the list of preferred consoles.
940  * @name: device name
941  * @idx: device index
942  * @options: options for this console
943  *
944  * The last preferred console added will be used for kernel messages
945  * and stdin/out/err for init.  Normally this is used by console_setup
946  * above to handle user-supplied console arguments; however it can also
947  * be used by arch-specific code either to override the user or more
948  * commonly to provide a default console (ie from PROM variables) when
949  * the user has not supplied one.
950  */
951 int add_preferred_console(char *name, int idx, char *options)
952 {
953         return __add_preferred_console(name, idx, options, NULL);
954 }
955
956 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
957 {
958         struct console_cmdline *c;
959         int i;
960
961         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
962                 if (strcmp(console_cmdline[i].name, name) == 0 &&
963                           console_cmdline[i].index == idx) {
964                                 c = &console_cmdline[i];
965                                 strlcpy(c->name, name_new, sizeof(c->name));
966                                 c->name[sizeof(c->name) - 1] = 0;
967                                 c->options = options;
968                                 c->index = idx_new;
969                                 return i;
970                 }
971         /* not found */
972         return -1;
973 }
974
975 int console_suspend_enabled = 1;
976 EXPORT_SYMBOL(console_suspend_enabled);
977
978 static int __init console_suspend_disable(char *str)
979 {
980         console_suspend_enabled = 0;
981         return 1;
982 }
983 __setup("no_console_suspend", console_suspend_disable);
984
985 /**
986  * suspend_console - suspend the console subsystem
987  *
988  * This disables printk() while we go into suspend states
989  */
990 void suspend_console(void)
991 {
992         if (!console_suspend_enabled)
993                 return;
994         printk("Suspending console(s) (use no_console_suspend to debug)\n");
995         acquire_console_sem();
996         console_suspended = 1;
997         up(&console_sem);
998 }
999
1000 void resume_console(void)
1001 {
1002         if (!console_suspend_enabled)
1003                 return;
1004         down(&console_sem);
1005         console_suspended = 0;
1006         release_console_sem();
1007 }
1008
1009 /**
1010  * console_cpu_notify - print deferred console messages after CPU hotplug
1011  * @self: notifier struct
1012  * @action: CPU hotplug event
1013  * @hcpu: unused
1014  *
1015  * If printk() is called from a CPU that is not online yet, the messages
1016  * will be spooled but will not show up on the console.  This function is
1017  * called when a new CPU comes online (or fails to come up), and ensures
1018  * that any such output gets printed.
1019  */
1020 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1021         unsigned long action, void *hcpu)
1022 {
1023         switch (action) {
1024         case CPU_ONLINE:
1025         case CPU_DEAD:
1026         case CPU_DYING:
1027         case CPU_DOWN_FAILED:
1028         case CPU_UP_CANCELED:
1029                 acquire_console_sem();
1030                 release_console_sem();
1031         }
1032         return NOTIFY_OK;
1033 }
1034
1035 /**
1036  * acquire_console_sem - lock the console system for exclusive use.
1037  *
1038  * Acquires a semaphore which guarantees that the caller has
1039  * exclusive access to the console system and the console_drivers list.
1040  *
1041  * Can sleep, returns nothing.
1042  */
1043 void acquire_console_sem(void)
1044 {
1045         BUG_ON(in_interrupt());
1046         down(&console_sem);
1047         if (console_suspended)
1048                 return;
1049         console_locked = 1;
1050         console_may_schedule = 1;
1051 }
1052 EXPORT_SYMBOL(acquire_console_sem);
1053
1054 int try_acquire_console_sem(void)
1055 {
1056         if (down_trylock(&console_sem))
1057                 return -1;
1058         if (console_suspended) {
1059                 up(&console_sem);
1060                 return -1;
1061         }
1062         console_locked = 1;
1063         console_may_schedule = 0;
1064         return 0;
1065 }
1066 EXPORT_SYMBOL(try_acquire_console_sem);
1067
1068 int is_console_locked(void)
1069 {
1070         return console_locked;
1071 }
1072
1073 static DEFINE_PER_CPU(int, printk_pending);
1074
1075 void printk_tick(void)
1076 {
1077         if (__this_cpu_read(printk_pending)) {
1078                 __this_cpu_write(printk_pending, 0);
1079                 wake_up_interruptible(&log_wait);
1080         }
1081 }
1082
1083 int printk_needs_cpu(int cpu)
1084 {
1085         if (cpu_is_offline(cpu))
1086                 printk_tick();
1087         return __this_cpu_read(printk_pending);
1088 }
1089
1090 void wake_up_klogd(void)
1091 {
1092         if (waitqueue_active(&log_wait))
1093                 this_cpu_write(printk_pending, 1);
1094 }
1095
1096 /**
1097  * release_console_sem - unlock the console system
1098  *
1099  * Releases the semaphore which the caller holds on the console system
1100  * and the console driver list.
1101  *
1102  * While the semaphore was held, console output may have been buffered
1103  * by printk().  If this is the case, release_console_sem() emits
1104  * the output prior to releasing the semaphore.
1105  *
1106  * If there is output waiting for klogd, we wake it up.
1107  *
1108  * release_console_sem() may be called from any context.
1109  */
1110 void release_console_sem(void)
1111 {
1112         unsigned long flags;
1113         unsigned _con_start, _log_end;
1114         unsigned wake_klogd = 0;
1115
1116         if (console_suspended) {
1117                 up(&console_sem);
1118                 return;
1119         }
1120
1121         console_may_schedule = 0;
1122
1123         for ( ; ; ) {
1124                 spin_lock_irqsave(&logbuf_lock, flags);
1125                 wake_klogd |= log_start - log_end;
1126                 if (con_start == log_end)
1127                         break;                  /* Nothing to print */
1128                 _con_start = con_start;
1129                 _log_end = log_end;
1130                 con_start = log_end;            /* Flush */
1131                 spin_unlock(&logbuf_lock);
1132                 stop_critical_timings();        /* don't trace print latency */
1133                 call_console_drivers(_con_start, _log_end);
1134                 start_critical_timings();
1135                 local_irq_restore(flags);
1136         }
1137         console_locked = 0;
1138         up(&console_sem);
1139         spin_unlock_irqrestore(&logbuf_lock, flags);
1140         if (wake_klogd)
1141                 wake_up_klogd();
1142 }
1143 EXPORT_SYMBOL(release_console_sem);
1144
1145 /**
1146  * console_conditional_schedule - yield the CPU if required
1147  *
1148  * If the console code is currently allowed to sleep, and
1149  * if this CPU should yield the CPU to another task, do
1150  * so here.
1151  *
1152  * Must be called within acquire_console_sem().
1153  */
1154 void __sched console_conditional_schedule(void)
1155 {
1156         if (console_may_schedule)
1157                 cond_resched();
1158 }
1159 EXPORT_SYMBOL(console_conditional_schedule);
1160
1161 void console_unblank(void)
1162 {
1163         struct console *c;
1164
1165         /*
1166          * console_unblank can no longer be called in interrupt context unless
1167          * oops_in_progress is set to 1..
1168          */
1169         if (oops_in_progress) {
1170                 if (down_trylock(&console_sem) != 0)
1171                         return;
1172         } else
1173                 acquire_console_sem();
1174
1175         console_locked = 1;
1176         console_may_schedule = 0;
1177         for_each_console(c)
1178                 if ((c->flags & CON_ENABLED) && c->unblank)
1179                         c->unblank();
1180         release_console_sem();
1181 }
1182
1183 /*
1184  * Return the console tty driver structure and its associated index
1185  */
1186 struct tty_driver *console_device(int *index)
1187 {
1188         struct console *c;
1189         struct tty_driver *driver = NULL;
1190
1191         acquire_console_sem();
1192         for_each_console(c) {
1193                 if (!c->device)
1194                         continue;
1195                 driver = c->device(c, index);
1196                 if (driver)
1197                         break;
1198         }
1199         release_console_sem();
1200         return driver;
1201 }
1202
1203 /*
1204  * Prevent further output on the passed console device so that (for example)
1205  * serial drivers can disable console output before suspending a port, and can
1206  * re-enable output afterwards.
1207  */
1208 void console_stop(struct console *console)
1209 {
1210         acquire_console_sem();
1211         console->flags &= ~CON_ENABLED;
1212         release_console_sem();
1213 }
1214 EXPORT_SYMBOL(console_stop);
1215
1216 void console_start(struct console *console)
1217 {
1218         acquire_console_sem();
1219         console->flags |= CON_ENABLED;
1220         release_console_sem();
1221 }
1222 EXPORT_SYMBOL(console_start);
1223
1224 /*
1225  * The console driver calls this routine during kernel initialization
1226  * to register the console printing procedure with printk() and to
1227  * print any messages that were printed by the kernel before the
1228  * console driver was initialized.
1229  *
1230  * This can happen pretty early during the boot process (because of
1231  * early_printk) - sometimes before setup_arch() completes - be careful
1232  * of what kernel features are used - they may not be initialised yet.
1233  *
1234  * There are two types of consoles - bootconsoles (early_printk) and
1235  * "real" consoles (everything which is not a bootconsole) which are
1236  * handled differently.
1237  *  - Any number of bootconsoles can be registered at any time.
1238  *  - As soon as a "real" console is registered, all bootconsoles
1239  *    will be unregistered automatically.
1240  *  - Once a "real" console is registered, any attempt to register a
1241  *    bootconsoles will be rejected
1242  */
1243 void register_console(struct console *newcon)
1244 {
1245         int i;
1246         unsigned long flags;
1247         struct console *bcon = NULL;
1248
1249         /*
1250          * before we register a new CON_BOOT console, make sure we don't
1251          * already have a valid console
1252          */
1253         if (console_drivers && newcon->flags & CON_BOOT) {
1254                 /* find the last or real console */
1255                 for_each_console(bcon) {
1256                         if (!(bcon->flags & CON_BOOT)) {
1257                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1258                                         newcon->name, newcon->index);
1259                                 return;
1260                         }
1261                 }
1262         }
1263
1264         if (console_drivers && console_drivers->flags & CON_BOOT)
1265                 bcon = console_drivers;
1266
1267         if (preferred_console < 0 || bcon || !console_drivers)
1268                 preferred_console = selected_console;
1269
1270         if (newcon->early_setup)
1271                 newcon->early_setup();
1272
1273         /*
1274          *      See if we want to use this console driver. If we
1275          *      didn't select a console we take the first one
1276          *      that registers here.
1277          */
1278         if (preferred_console < 0) {
1279                 if (newcon->index < 0)
1280                         newcon->index = 0;
1281                 if (newcon->setup == NULL ||
1282                     newcon->setup(newcon, NULL) == 0) {
1283                         newcon->flags |= CON_ENABLED;
1284                         if (newcon->device) {
1285                                 newcon->flags |= CON_CONSDEV;
1286                                 preferred_console = 0;
1287                         }
1288                 }
1289         }
1290
1291         /*
1292          *      See if this console matches one we selected on
1293          *      the command line.
1294          */
1295         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1296                         i++) {
1297                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1298                         continue;
1299                 if (newcon->index >= 0 &&
1300                     newcon->index != console_cmdline[i].index)
1301                         continue;
1302                 if (newcon->index < 0)
1303                         newcon->index = console_cmdline[i].index;
1304 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1305                 if (console_cmdline[i].brl_options) {
1306                         newcon->flags |= CON_BRL;
1307                         braille_register_console(newcon,
1308                                         console_cmdline[i].index,
1309                                         console_cmdline[i].options,
1310                                         console_cmdline[i].brl_options);
1311                         return;
1312                 }
1313 #endif
1314                 if (newcon->setup &&
1315                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1316                         break;
1317                 newcon->flags |= CON_ENABLED;
1318                 newcon->index = console_cmdline[i].index;
1319                 if (i == selected_console) {
1320                         newcon->flags |= CON_CONSDEV;
1321                         preferred_console = selected_console;
1322                 }
1323                 break;
1324         }
1325
1326         if (!(newcon->flags & CON_ENABLED))
1327                 return;
1328
1329         /*
1330          * If we have a bootconsole, and are switching to a real console,
1331          * don't print everything out again, since when the boot console, and
1332          * the real console are the same physical device, it's annoying to
1333          * see the beginning boot messages twice
1334          */
1335         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1336                 newcon->flags &= ~CON_PRINTBUFFER;
1337
1338         /*
1339          *      Put this console in the list - keep the
1340          *      preferred driver at the head of the list.
1341          */
1342         acquire_console_sem();
1343         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1344                 newcon->next = console_drivers;
1345                 console_drivers = newcon;
1346                 if (newcon->next)
1347                         newcon->next->flags &= ~CON_CONSDEV;
1348         } else {
1349                 newcon->next = console_drivers->next;
1350                 console_drivers->next = newcon;
1351         }
1352         if (newcon->flags & CON_PRINTBUFFER) {
1353                 /*
1354                  * release_console_sem() will print out the buffered messages
1355                  * for us.
1356                  */
1357                 spin_lock_irqsave(&logbuf_lock, flags);
1358                 con_start = log_start;
1359                 spin_unlock_irqrestore(&logbuf_lock, flags);
1360         }
1361         release_console_sem();
1362
1363         /*
1364          * By unregistering the bootconsoles after we enable the real console
1365          * we get the "console xxx enabled" message on all the consoles -
1366          * boot consoles, real consoles, etc - this is to ensure that end
1367          * users know there might be something in the kernel's log buffer that
1368          * went to the bootconsole (that they do not see on the real console)
1369          */
1370         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1371                 /* we need to iterate through twice, to make sure we print
1372                  * everything out, before we unregister the console(s)
1373                  */
1374                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1375                         newcon->name, newcon->index);
1376                 for_each_console(bcon)
1377                         if (bcon->flags & CON_BOOT)
1378                                 unregister_console(bcon);
1379         } else {
1380                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1381                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1382                         newcon->name, newcon->index);
1383         }
1384 }
1385 EXPORT_SYMBOL(register_console);
1386
1387 int unregister_console(struct console *console)
1388 {
1389         struct console *a, *b;
1390         int res = 1;
1391
1392 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1393         if (console->flags & CON_BRL)
1394                 return braille_unregister_console(console);
1395 #endif
1396
1397         acquire_console_sem();
1398         if (console_drivers == console) {
1399                 console_drivers=console->next;
1400                 res = 0;
1401         } else if (console_drivers) {
1402                 for (a=console_drivers->next, b=console_drivers ;
1403                      a; b=a, a=b->next) {
1404                         if (a == console) {
1405                                 b->next = a->next;
1406                                 res = 0;
1407                                 break;
1408                         }
1409                 }
1410         }
1411
1412         /*
1413          * If this isn't the last console and it has CON_CONSDEV set, we
1414          * need to set it on the next preferred console.
1415          */
1416         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1417                 console_drivers->flags |= CON_CONSDEV;
1418
1419         release_console_sem();
1420         return res;
1421 }
1422 EXPORT_SYMBOL(unregister_console);
1423
1424 static int __init printk_late_init(void)
1425 {
1426         struct console *con;
1427
1428         for_each_console(con) {
1429                 if (con->flags & CON_BOOT) {
1430                         printk(KERN_INFO "turn off boot console %s%d\n",
1431                                 con->name, con->index);
1432                         unregister_console(con);
1433                 }
1434         }
1435         hotcpu_notifier(console_cpu_notify, 0);
1436         return 0;
1437 }
1438 late_initcall(printk_late_init);
1439
1440 #if defined CONFIG_PRINTK
1441
1442 /*
1443  * printk rate limiting, lifted from the networking subsystem.
1444  *
1445  * This enforces a rate limit: not more than 10 kernel messages
1446  * every 5s to make a denial-of-service attack impossible.
1447  */
1448 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1449
1450 int __printk_ratelimit(const char *func)
1451 {
1452         return ___ratelimit(&printk_ratelimit_state, func);
1453 }
1454 EXPORT_SYMBOL(__printk_ratelimit);
1455
1456 /**
1457  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1458  * @caller_jiffies: pointer to caller's state
1459  * @interval_msecs: minimum interval between prints
1460  *
1461  * printk_timed_ratelimit() returns true if more than @interval_msecs
1462  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1463  * returned true.
1464  */
1465 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1466                         unsigned int interval_msecs)
1467 {
1468         if (*caller_jiffies == 0
1469                         || !time_in_range(jiffies, *caller_jiffies,
1470                                         *caller_jiffies
1471                                         + msecs_to_jiffies(interval_msecs))) {
1472                 *caller_jiffies = jiffies;
1473                 return true;
1474         }
1475         return false;
1476 }
1477 EXPORT_SYMBOL(printk_timed_ratelimit);
1478
1479 static DEFINE_SPINLOCK(dump_list_lock);
1480 static LIST_HEAD(dump_list);
1481
1482 /**
1483  * kmsg_dump_register - register a kernel log dumper.
1484  * @dumper: pointer to the kmsg_dumper structure
1485  *
1486  * Adds a kernel log dumper to the system. The dump callback in the
1487  * structure will be called when the kernel oopses or panics and must be
1488  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1489  */
1490 int kmsg_dump_register(struct kmsg_dumper *dumper)
1491 {
1492         unsigned long flags;
1493         int err = -EBUSY;
1494
1495         /* The dump callback needs to be set */
1496         if (!dumper->dump)
1497                 return -EINVAL;
1498
1499         spin_lock_irqsave(&dump_list_lock, flags);
1500         /* Don't allow registering multiple times */
1501         if (!dumper->registered) {
1502                 dumper->registered = 1;
1503                 list_add_tail(&dumper->list, &dump_list);
1504                 err = 0;
1505         }
1506         spin_unlock_irqrestore(&dump_list_lock, flags);
1507
1508         return err;
1509 }
1510 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1511
1512 /**
1513  * kmsg_dump_unregister - unregister a kmsg dumper.
1514  * @dumper: pointer to the kmsg_dumper structure
1515  *
1516  * Removes a dump device from the system. Returns zero on success and
1517  * %-EINVAL otherwise.
1518  */
1519 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1520 {
1521         unsigned long flags;
1522         int err = -EINVAL;
1523
1524         spin_lock_irqsave(&dump_list_lock, flags);
1525         if (dumper->registered) {
1526                 dumper->registered = 0;
1527                 list_del(&dumper->list);
1528                 err = 0;
1529         }
1530         spin_unlock_irqrestore(&dump_list_lock, flags);
1531
1532         return err;
1533 }
1534 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1535
1536 static const char * const kmsg_reasons[] = {
1537         [KMSG_DUMP_OOPS]        = "oops",
1538         [KMSG_DUMP_PANIC]       = "panic",
1539         [KMSG_DUMP_KEXEC]       = "kexec",
1540 };
1541
1542 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1543 {
1544         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1545                 return "unknown";
1546
1547         return kmsg_reasons[reason];
1548 }
1549
1550 /**
1551  * kmsg_dump - dump kernel log to kernel message dumpers.
1552  * @reason: the reason (oops, panic etc) for dumping
1553  *
1554  * Iterate through each of the dump devices and call the oops/panic
1555  * callbacks with the log buffer.
1556  */
1557 void kmsg_dump(enum kmsg_dump_reason reason)
1558 {
1559         unsigned long end;
1560         unsigned chars;
1561         struct kmsg_dumper *dumper;
1562         const char *s1, *s2;
1563         unsigned long l1, l2;
1564         unsigned long flags;
1565
1566         /* Theoretically, the log could move on after we do this, but
1567            there's not a lot we can do about that. The new messages
1568            will overwrite the start of what we dump. */
1569         spin_lock_irqsave(&logbuf_lock, flags);
1570         end = log_end & LOG_BUF_MASK;
1571         chars = logged_chars;
1572         spin_unlock_irqrestore(&logbuf_lock, flags);
1573
1574         if (chars > end) {
1575                 s1 = log_buf + log_buf_len - chars + end;
1576                 l1 = chars - end;
1577
1578                 s2 = log_buf;
1579                 l2 = end;
1580         } else {
1581                 s1 = "";
1582                 l1 = 0;
1583
1584                 s2 = log_buf + end - chars;
1585                 l2 = chars;
1586         }
1587
1588         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1589                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1590                                 kmsg_to_str(reason));
1591                 return;
1592         }
1593         list_for_each_entry(dumper, &dump_list, list)
1594                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1595         spin_unlock_irqrestore(&dump_list_lock, flags);
1596 }
1597 #endif