Merge branch 'tty-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6
[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  * Architectures can override it:
47  */
48 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
49 {
50 }
51
52 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
53
54 /* printk's without a loglevel use this.. */
55 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
56
57 /* We show everything that is MORE important than this.. */
58 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
59 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
60
61 DECLARE_WAIT_QUEUE_HEAD(log_wait);
62
63 int console_printk[4] = {
64         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
65         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
66         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
67         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
68 };
69
70 /*
71  * Low level drivers may need that to know if they can schedule in
72  * their unblank() callback or not. So let's export it.
73  */
74 int oops_in_progress;
75 EXPORT_SYMBOL(oops_in_progress);
76
77 /*
78  * console_sem protects the console_drivers list, and also
79  * provides serialisation for access to the entire console
80  * driver system.
81  */
82 static DEFINE_SEMAPHORE(console_sem);
83 struct console *console_drivers;
84 EXPORT_SYMBOL_GPL(console_drivers);
85
86 /*
87  * This is used for debugging the mess that is the VT code by
88  * keeping track if we have the console semaphore held. It's
89  * definitely not the perfect debug tool (we don't know if _WE_
90  * hold it are racing, but it helps tracking those weird code
91  * path in the console code where we end up in places I want
92  * locked without the console sempahore held
93  */
94 static int console_locked, console_suspended;
95
96 /*
97  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
98  * It is also used in interesting ways to provide interlocking in
99  * release_console_sem().
100  */
101 static DEFINE_SPINLOCK(logbuf_lock);
102
103 #define LOG_BUF_MASK (log_buf_len-1)
104 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
105
106 /*
107  * The indices into log_buf are not constrained to log_buf_len - they
108  * must be masked before subscripting
109  */
110 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
111 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
112 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
113
114 /*
115  *      Array of consoles built from command line options (console=)
116  */
117 struct console_cmdline
118 {
119         char    name[8];                        /* Name of the driver       */
120         int     index;                          /* Minor dev. to use        */
121         char    *options;                       /* Options for the driver   */
122 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
123         char    *brl_options;                   /* Options for braille driver */
124 #endif
125 };
126
127 #define MAX_CMDLINECONSOLES 8
128
129 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
130 static int selected_console = -1;
131 static int preferred_console = -1;
132 int console_set_on_cmdline;
133 EXPORT_SYMBOL(console_set_on_cmdline);
134
135 /* Flag: console code may call schedule() */
136 static int console_may_schedule;
137
138 #ifdef CONFIG_PRINTK
139
140 static char __log_buf[__LOG_BUF_LEN];
141 static char *log_buf = __log_buf;
142 static int log_buf_len = __LOG_BUF_LEN;
143 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
144 static int saved_console_loglevel = -1;
145
146 #ifdef CONFIG_KEXEC
147 /*
148  * This appends the listed symbols to /proc/vmcoreinfo
149  *
150  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
151  * obtain access to symbols that are otherwise very difficult to locate.  These
152  * symbols are specifically used so that utilities can access and extract the
153  * dmesg log from a vmcore file after a crash.
154  */
155 void log_buf_kexec_setup(void)
156 {
157         VMCOREINFO_SYMBOL(log_buf);
158         VMCOREINFO_SYMBOL(log_end);
159         VMCOREINFO_SYMBOL(log_buf_len);
160         VMCOREINFO_SYMBOL(logged_chars);
161 }
162 #endif
163
164 static int __init log_buf_len_setup(char *str)
165 {
166         unsigned size = memparse(str, &str);
167         unsigned long flags;
168
169         if (size)
170                 size = roundup_pow_of_two(size);
171         if (size > log_buf_len) {
172                 unsigned start, dest_idx, offset;
173                 char *new_log_buf;
174
175                 new_log_buf = alloc_bootmem(size);
176                 if (!new_log_buf) {
177                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
178                         goto out;
179                 }
180
181                 spin_lock_irqsave(&logbuf_lock, flags);
182                 log_buf_len = size;
183                 log_buf = new_log_buf;
184
185                 offset = start = min(con_start, log_start);
186                 dest_idx = 0;
187                 while (start != log_end) {
188                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
189                         start++;
190                         dest_idx++;
191                 }
192                 log_start -= offset;
193                 con_start -= offset;
194                 log_end -= offset;
195                 spin_unlock_irqrestore(&logbuf_lock, flags);
196
197                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
198         }
199 out:
200         return 1;
201 }
202
203 __setup("log_buf_len=", log_buf_len_setup);
204
205 #ifdef CONFIG_BOOT_PRINTK_DELAY
206
207 static int boot_delay; /* msecs delay after each printk during bootup */
208 static unsigned long long loops_per_msec;       /* based on boot_delay */
209
210 static int __init boot_delay_setup(char *str)
211 {
212         unsigned long lpj;
213
214         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
215         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
216
217         get_option(&str, &boot_delay);
218         if (boot_delay > 10 * 1000)
219                 boot_delay = 0;
220
221         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
222                 "HZ: %d, loops_per_msec: %llu\n",
223                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
224         return 1;
225 }
226 __setup("boot_delay=", boot_delay_setup);
227
228 static void boot_delay_msec(void)
229 {
230         unsigned long long k;
231         unsigned long timeout;
232
233         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
234                 return;
235
236         k = (unsigned long long)loops_per_msec * boot_delay;
237
238         timeout = jiffies + msecs_to_jiffies(boot_delay);
239         while (k) {
240                 k--;
241                 cpu_relax();
242                 /*
243                  * use (volatile) jiffies to prevent
244                  * compiler reduction; loop termination via jiffies
245                  * is secondary and may or may not happen.
246                  */
247                 if (time_after(jiffies, timeout))
248                         break;
249                 touch_nmi_watchdog();
250         }
251 }
252 #else
253 static inline void boot_delay_msec(void)
254 {
255 }
256 #endif
257
258 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
259 int dmesg_restrict = 1;
260 #else
261 int dmesg_restrict;
262 #endif
263
264 int do_syslog(int type, char __user *buf, int len, bool from_file)
265 {
266         unsigned i, j, limit, count;
267         int do_clear = 0;
268         char c;
269         int error = 0;
270
271         /*
272          * If this is from /proc/kmsg we only do the capabilities checks
273          * at open time.
274          */
275         if (type == SYSLOG_ACTION_OPEN || !from_file) {
276                 if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
277                         return -EPERM;
278                 if ((type != SYSLOG_ACTION_READ_ALL &&
279                      type != SYSLOG_ACTION_SIZE_BUFFER) &&
280                     !capable(CAP_SYS_ADMIN))
281                         return -EPERM;
282         }
283
284         error = security_syslog(type);
285         if (error)
286                 return error;
287
288         switch (type) {
289         case SYSLOG_ACTION_CLOSE:       /* Close log */
290                 break;
291         case SYSLOG_ACTION_OPEN:        /* Open log */
292                 break;
293         case SYSLOG_ACTION_READ:        /* Read from log */
294                 error = -EINVAL;
295                 if (!buf || len < 0)
296                         goto out;
297                 error = 0;
298                 if (!len)
299                         goto out;
300                 if (!access_ok(VERIFY_WRITE, buf, len)) {
301                         error = -EFAULT;
302                         goto out;
303                 }
304                 error = wait_event_interruptible(log_wait,
305                                                         (log_start - log_end));
306                 if (error)
307                         goto out;
308                 i = 0;
309                 spin_lock_irq(&logbuf_lock);
310                 while (!error && (log_start != log_end) && i < len) {
311                         c = LOG_BUF(log_start);
312                         log_start++;
313                         spin_unlock_irq(&logbuf_lock);
314                         error = __put_user(c,buf);
315                         buf++;
316                         i++;
317                         cond_resched();
318                         spin_lock_irq(&logbuf_lock);
319                 }
320                 spin_unlock_irq(&logbuf_lock);
321                 if (!error)
322                         error = i;
323                 break;
324         /* Read/clear last kernel messages */
325         case SYSLOG_ACTION_READ_CLEAR:
326                 do_clear = 1;
327                 /* FALL THRU */
328         /* Read last kernel messages */
329         case SYSLOG_ACTION_READ_ALL:
330                 error = -EINVAL;
331                 if (!buf || len < 0)
332                         goto out;
333                 error = 0;
334                 if (!len)
335                         goto out;
336                 if (!access_ok(VERIFY_WRITE, buf, len)) {
337                         error = -EFAULT;
338                         goto out;
339                 }
340                 count = len;
341                 if (count > log_buf_len)
342                         count = log_buf_len;
343                 spin_lock_irq(&logbuf_lock);
344                 if (count > logged_chars)
345                         count = logged_chars;
346                 if (do_clear)
347                         logged_chars = 0;
348                 limit = log_end;
349                 /*
350                  * __put_user() could sleep, and while we sleep
351                  * printk() could overwrite the messages
352                  * we try to copy to user space. Therefore
353                  * the messages are copied in reverse. <manfreds>
354                  */
355                 for (i = 0; i < count && !error; i++) {
356                         j = limit-1-i;
357                         if (j + log_buf_len < log_end)
358                                 break;
359                         c = LOG_BUF(j);
360                         spin_unlock_irq(&logbuf_lock);
361                         error = __put_user(c,&buf[count-1-i]);
362                         cond_resched();
363                         spin_lock_irq(&logbuf_lock);
364                 }
365                 spin_unlock_irq(&logbuf_lock);
366                 if (error)
367                         break;
368                 error = i;
369                 if (i != count) {
370                         int offset = count-error;
371                         /* buffer overflow during copy, correct user buffer. */
372                         for (i = 0; i < error; i++) {
373                                 if (__get_user(c,&buf[i+offset]) ||
374                                     __put_user(c,&buf[i])) {
375                                         error = -EFAULT;
376                                         break;
377                                 }
378                                 cond_resched();
379                         }
380                 }
381                 break;
382         /* Clear ring buffer */
383         case SYSLOG_ACTION_CLEAR:
384                 logged_chars = 0;
385                 break;
386         /* Disable logging to console */
387         case SYSLOG_ACTION_CONSOLE_OFF:
388                 if (saved_console_loglevel == -1)
389                         saved_console_loglevel = console_loglevel;
390                 console_loglevel = minimum_console_loglevel;
391                 break;
392         /* Enable logging to console */
393         case SYSLOG_ACTION_CONSOLE_ON:
394                 if (saved_console_loglevel != -1) {
395                         console_loglevel = saved_console_loglevel;
396                         saved_console_loglevel = -1;
397                 }
398                 break;
399         /* Set level of messages printed to console */
400         case SYSLOG_ACTION_CONSOLE_LEVEL:
401                 error = -EINVAL;
402                 if (len < 1 || len > 8)
403                         goto out;
404                 if (len < minimum_console_loglevel)
405                         len = minimum_console_loglevel;
406                 console_loglevel = len;
407                 /* Implicitly re-enable logging to console */
408                 saved_console_loglevel = -1;
409                 error = 0;
410                 break;
411         /* Number of chars in the log buffer */
412         case SYSLOG_ACTION_SIZE_UNREAD:
413                 error = log_end - log_start;
414                 break;
415         /* Size of the log buffer */
416         case SYSLOG_ACTION_SIZE_BUFFER:
417                 error = log_buf_len;
418                 break;
419         default:
420                 error = -EINVAL;
421                 break;
422         }
423 out:
424         return error;
425 }
426
427 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
428 {
429         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
430 }
431
432 #ifdef  CONFIG_KGDB_KDB
433 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
434  * uses locks so it cannot be used during debugging.  Just tell kdb
435  * where the start and end of the physical and logical logs are.  This
436  * is equivalent to do_syslog(3).
437  */
438 void kdb_syslog_data(char *syslog_data[4])
439 {
440         syslog_data[0] = log_buf;
441         syslog_data[1] = log_buf + log_buf_len;
442         syslog_data[2] = log_buf + log_end -
443                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
444         syslog_data[3] = log_buf + log_end;
445 }
446 #endif  /* CONFIG_KGDB_KDB */
447
448 /*
449  * Call the console drivers on a range of log_buf
450  */
451 static void __call_console_drivers(unsigned start, unsigned end)
452 {
453         struct console *con;
454
455         for_each_console(con) {
456                 if ((con->flags & CON_ENABLED) && con->write &&
457                                 (cpu_online(smp_processor_id()) ||
458                                 (con->flags & CON_ANYTIME)))
459                         con->write(con, &LOG_BUF(start), end - start);
460         }
461 }
462
463 static int __read_mostly ignore_loglevel;
464
465 static int __init ignore_loglevel_setup(char *str)
466 {
467         ignore_loglevel = 1;
468         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
469
470         return 0;
471 }
472
473 early_param("ignore_loglevel", ignore_loglevel_setup);
474
475 /*
476  * Write out chars from start to end - 1 inclusive
477  */
478 static void _call_console_drivers(unsigned start,
479                                 unsigned end, int msg_log_level)
480 {
481         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
482                         console_drivers && start != end) {
483                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
484                         /* wrapped write */
485                         __call_console_drivers(start & LOG_BUF_MASK,
486                                                 log_buf_len);
487                         __call_console_drivers(0, end & LOG_BUF_MASK);
488                 } else {
489                         __call_console_drivers(start, end);
490                 }
491         }
492 }
493
494 /*
495  * Call the console drivers, asking them to write out
496  * log_buf[start] to log_buf[end - 1].
497  * The console_sem must be held.
498  */
499 static void call_console_drivers(unsigned start, unsigned end)
500 {
501         unsigned cur_index, start_print;
502         static int msg_level = -1;
503
504         BUG_ON(((int)(start - end)) > 0);
505
506         cur_index = start;
507         start_print = start;
508         while (cur_index != end) {
509                 if (msg_level < 0 && ((end - cur_index) > 2) &&
510                                 LOG_BUF(cur_index + 0) == '<' &&
511                                 LOG_BUF(cur_index + 1) >= '0' &&
512                                 LOG_BUF(cur_index + 1) <= '7' &&
513                                 LOG_BUF(cur_index + 2) == '>') {
514                         msg_level = LOG_BUF(cur_index + 1) - '0';
515                         cur_index += 3;
516                         start_print = cur_index;
517                 }
518                 while (cur_index != end) {
519                         char c = LOG_BUF(cur_index);
520
521                         cur_index++;
522                         if (c == '\n') {
523                                 if (msg_level < 0) {
524                                         /*
525                                          * printk() has already given us loglevel tags in
526                                          * the buffer.  This code is here in case the
527                                          * log buffer has wrapped right round and scribbled
528                                          * on those tags
529                                          */
530                                         msg_level = default_message_loglevel;
531                                 }
532                                 _call_console_drivers(start_print, cur_index, msg_level);
533                                 msg_level = -1;
534                                 start_print = cur_index;
535                                 break;
536                         }
537                 }
538         }
539         _call_console_drivers(start_print, end, msg_level);
540 }
541
542 static void emit_log_char(char c)
543 {
544         LOG_BUF(log_end) = c;
545         log_end++;
546         if (log_end - log_start > log_buf_len)
547                 log_start = log_end - log_buf_len;
548         if (log_end - con_start > log_buf_len)
549                 con_start = log_end - log_buf_len;
550         if (logged_chars < log_buf_len)
551                 logged_chars++;
552 }
553
554 /*
555  * Zap console related locks when oopsing. Only zap at most once
556  * every 10 seconds, to leave time for slow consoles to print a
557  * full oops.
558  */
559 static void zap_locks(void)
560 {
561         static unsigned long oops_timestamp;
562
563         if (time_after_eq(jiffies, oops_timestamp) &&
564                         !time_after(jiffies, oops_timestamp + 30 * HZ))
565                 return;
566
567         oops_timestamp = jiffies;
568
569         /* If a crash is occurring, make sure we can't deadlock */
570         spin_lock_init(&logbuf_lock);
571         /* And make sure that we print immediately */
572         sema_init(&console_sem, 1);
573 }
574
575 #if defined(CONFIG_PRINTK_TIME)
576 static int printk_time = 1;
577 #else
578 static int printk_time = 0;
579 #endif
580 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
581
582 /* Check if we have any console registered that can be called early in boot. */
583 static int have_callable_console(void)
584 {
585         struct console *con;
586
587         for_each_console(con)
588                 if (con->flags & CON_ANYTIME)
589                         return 1;
590
591         return 0;
592 }
593
594 /**
595  * printk - print a kernel message
596  * @fmt: format string
597  *
598  * This is printk().  It can be called from any context.  We want it to work.
599  *
600  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
601  * call the console drivers.  If we fail to get the semaphore we place the output
602  * into the log buffer and return.  The current holder of the console_sem will
603  * notice the new output in release_console_sem() and will send it to the
604  * consoles before releasing the semaphore.
605  *
606  * One effect of this deferred printing is that code which calls printk() and
607  * then changes console_loglevel may break. This is because console_loglevel
608  * is inspected when the actual printing occurs.
609  *
610  * See also:
611  * printf(3)
612  *
613  * See the vsnprintf() documentation for format string extensions over C99.
614  */
615
616 asmlinkage int printk(const char *fmt, ...)
617 {
618         va_list args;
619         int r;
620
621 #ifdef CONFIG_KGDB_KDB
622         if (unlikely(kdb_trap_printk)) {
623                 va_start(args, fmt);
624                 r = vkdb_printf(fmt, args);
625                 va_end(args);
626                 return r;
627         }
628 #endif
629         va_start(args, fmt);
630         r = vprintk(fmt, args);
631         va_end(args);
632
633         return r;
634 }
635
636 /* cpu currently holding logbuf_lock */
637 static volatile unsigned int printk_cpu = UINT_MAX;
638
639 /*
640  * Can we actually use the console at this time on this cpu?
641  *
642  * Console drivers may assume that per-cpu resources have
643  * been allocated. So unless they're explicitly marked as
644  * being able to cope (CON_ANYTIME) don't call them until
645  * this CPU is officially up.
646  */
647 static inline int can_use_console(unsigned int cpu)
648 {
649         return cpu_online(cpu) || have_callable_console();
650 }
651
652 /*
653  * Try to get console ownership to actually show the kernel
654  * messages from a 'printk'. Return true (and with the
655  * console_semaphore held, and 'console_locked' set) if it
656  * is successful, false otherwise.
657  *
658  * This gets called with the 'logbuf_lock' spinlock held and
659  * interrupts disabled. It should return with 'lockbuf_lock'
660  * released but interrupts still disabled.
661  */
662 static int acquire_console_semaphore_for_printk(unsigned int cpu)
663         __releases(&logbuf_lock)
664 {
665         int retval = 0;
666
667         if (!try_acquire_console_sem()) {
668                 retval = 1;
669
670                 /*
671                  * If we can't use the console, we need to release
672                  * the console semaphore by hand to avoid flushing
673                  * the buffer. We need to hold the console semaphore
674                  * in order to do this test safely.
675                  */
676                 if (!can_use_console(cpu)) {
677                         console_locked = 0;
678                         up(&console_sem);
679                         retval = 0;
680                 }
681         }
682         printk_cpu = UINT_MAX;
683         spin_unlock(&logbuf_lock);
684         return retval;
685 }
686 static const char recursion_bug_msg [] =
687                 KERN_CRIT "BUG: recent printk recursion!\n";
688 static int recursion_bug;
689 static int new_text_line = 1;
690 static char printk_buf[1024];
691
692 int printk_delay_msec __read_mostly;
693
694 static inline void printk_delay(void)
695 {
696         if (unlikely(printk_delay_msec)) {
697                 int m = printk_delay_msec;
698
699                 while (m--) {
700                         mdelay(1);
701                         touch_nmi_watchdog();
702                 }
703         }
704 }
705
706 asmlinkage int vprintk(const char *fmt, va_list args)
707 {
708         int printed_len = 0;
709         int current_log_level = default_message_loglevel;
710         unsigned long flags;
711         int this_cpu;
712         char *p;
713
714         boot_delay_msec();
715         printk_delay();
716
717         preempt_disable();
718         /* This stops the holder of console_sem just where we want him */
719         raw_local_irq_save(flags);
720         this_cpu = smp_processor_id();
721
722         /*
723          * Ouch, printk recursed into itself!
724          */
725         if (unlikely(printk_cpu == this_cpu)) {
726                 /*
727                  * If a crash is occurring during printk() on this CPU,
728                  * then try to get the crash message out but make sure
729                  * we can't deadlock. Otherwise just return to avoid the
730                  * recursion and return - but flag the recursion so that
731                  * it can be printed at the next appropriate moment:
732                  */
733                 if (!oops_in_progress) {
734                         recursion_bug = 1;
735                         goto out_restore_irqs;
736                 }
737                 zap_locks();
738         }
739
740         lockdep_off();
741         spin_lock(&logbuf_lock);
742         printk_cpu = this_cpu;
743
744         if (recursion_bug) {
745                 recursion_bug = 0;
746                 strcpy(printk_buf, recursion_bug_msg);
747                 printed_len = strlen(recursion_bug_msg);
748         }
749         /* Emit the output into the temporary buffer */
750         printed_len += vscnprintf(printk_buf + printed_len,
751                                   sizeof(printk_buf) - printed_len, fmt, args);
752
753
754         p = printk_buf;
755
756         /* Do we have a loglevel in the string? */
757         if (p[0] == '<') {
758                 unsigned char c = p[1];
759                 if (c && p[2] == '>') {
760                         switch (c) {
761                         case '0' ... '7': /* loglevel */
762                                 current_log_level = c - '0';
763                         /* Fallthrough - make sure we're on a new line */
764                         case 'd': /* KERN_DEFAULT */
765                                 if (!new_text_line) {
766                                         emit_log_char('\n');
767                                         new_text_line = 1;
768                                 }
769                         /* Fallthrough - skip the loglevel */
770                         case 'c': /* KERN_CONT */
771                                 p += 3;
772                                 break;
773                         }
774                 }
775         }
776
777         /*
778          * Copy the output into log_buf.  If the caller didn't provide
779          * appropriate log level tags, we insert them here
780          */
781         for ( ; *p; p++) {
782                 if (new_text_line) {
783                         /* Always output the token */
784                         emit_log_char('<');
785                         emit_log_char(current_log_level + '0');
786                         emit_log_char('>');
787                         printed_len += 3;
788                         new_text_line = 0;
789
790                         if (printk_time) {
791                                 /* Follow the token with the time */
792                                 char tbuf[50], *tp;
793                                 unsigned tlen;
794                                 unsigned long long t;
795                                 unsigned long nanosec_rem;
796
797                                 t = cpu_clock(printk_cpu);
798                                 nanosec_rem = do_div(t, 1000000000);
799                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
800                                                 (unsigned long) t,
801                                                 nanosec_rem / 1000);
802
803                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
804                                         emit_log_char(*tp);
805                                 printed_len += tlen;
806                         }
807
808                         if (!*p)
809                                 break;
810                 }
811
812                 emit_log_char(*p);
813                 if (*p == '\n')
814                         new_text_line = 1;
815         }
816
817         /*
818          * Try to acquire and then immediately release the
819          * console semaphore. The release will do all the
820          * actual magic (print out buffers, wake up klogd,
821          * etc). 
822          *
823          * The acquire_console_semaphore_for_printk() function
824          * will release 'logbuf_lock' regardless of whether it
825          * actually gets the semaphore or not.
826          */
827         if (acquire_console_semaphore_for_printk(this_cpu))
828                 release_console_sem();
829
830         lockdep_on();
831 out_restore_irqs:
832         raw_local_irq_restore(flags);
833
834         preempt_enable();
835         return printed_len;
836 }
837 EXPORT_SYMBOL(printk);
838 EXPORT_SYMBOL(vprintk);
839
840 #else
841
842 static void call_console_drivers(unsigned start, unsigned end)
843 {
844 }
845
846 #endif
847
848 static int __add_preferred_console(char *name, int idx, char *options,
849                                    char *brl_options)
850 {
851         struct console_cmdline *c;
852         int i;
853
854         /*
855          *      See if this tty is not yet registered, and
856          *      if we have a slot free.
857          */
858         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
859                 if (strcmp(console_cmdline[i].name, name) == 0 &&
860                           console_cmdline[i].index == idx) {
861                                 if (!brl_options)
862                                         selected_console = i;
863                                 return 0;
864                 }
865         if (i == MAX_CMDLINECONSOLES)
866                 return -E2BIG;
867         if (!brl_options)
868                 selected_console = i;
869         c = &console_cmdline[i];
870         strlcpy(c->name, name, sizeof(c->name));
871         c->options = options;
872 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
873         c->brl_options = brl_options;
874 #endif
875         c->index = idx;
876         return 0;
877 }
878 /*
879  * Set up a list of consoles.  Called from init/main.c
880  */
881 static int __init console_setup(char *str)
882 {
883         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
884         char *s, *options, *brl_options = NULL;
885         int idx;
886
887 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
888         if (!memcmp(str, "brl,", 4)) {
889                 brl_options = "";
890                 str += 4;
891         } else if (!memcmp(str, "brl=", 4)) {
892                 brl_options = str + 4;
893                 str = strchr(brl_options, ',');
894                 if (!str) {
895                         printk(KERN_ERR "need port name after brl=\n");
896                         return 1;
897                 }
898                 *(str++) = 0;
899         }
900 #endif
901
902         /*
903          * Decode str into name, index, options.
904          */
905         if (str[0] >= '0' && str[0] <= '9') {
906                 strcpy(buf, "ttyS");
907                 strncpy(buf + 4, str, sizeof(buf) - 5);
908         } else {
909                 strncpy(buf, str, sizeof(buf) - 1);
910         }
911         buf[sizeof(buf) - 1] = 0;
912         if ((options = strchr(str, ',')) != NULL)
913                 *(options++) = 0;
914 #ifdef __sparc__
915         if (!strcmp(str, "ttya"))
916                 strcpy(buf, "ttyS0");
917         if (!strcmp(str, "ttyb"))
918                 strcpy(buf, "ttyS1");
919 #endif
920         for (s = buf; *s; s++)
921                 if ((*s >= '0' && *s <= '9') || *s == ',')
922                         break;
923         idx = simple_strtoul(s, NULL, 10);
924         *s = 0;
925
926         __add_preferred_console(buf, idx, options, brl_options);
927         console_set_on_cmdline = 1;
928         return 1;
929 }
930 __setup("console=", console_setup);
931
932 /**
933  * add_preferred_console - add a device to the list of preferred consoles.
934  * @name: device name
935  * @idx: device index
936  * @options: options for this console
937  *
938  * The last preferred console added will be used for kernel messages
939  * and stdin/out/err for init.  Normally this is used by console_setup
940  * above to handle user-supplied console arguments; however it can also
941  * be used by arch-specific code either to override the user or more
942  * commonly to provide a default console (ie from PROM variables) when
943  * the user has not supplied one.
944  */
945 int add_preferred_console(char *name, int idx, char *options)
946 {
947         return __add_preferred_console(name, idx, options, NULL);
948 }
949
950 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
951 {
952         struct console_cmdline *c;
953         int i;
954
955         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
956                 if (strcmp(console_cmdline[i].name, name) == 0 &&
957                           console_cmdline[i].index == idx) {
958                                 c = &console_cmdline[i];
959                                 strlcpy(c->name, name_new, sizeof(c->name));
960                                 c->name[sizeof(c->name) - 1] = 0;
961                                 c->options = options;
962                                 c->index = idx_new;
963                                 return i;
964                 }
965         /* not found */
966         return -1;
967 }
968
969 int console_suspend_enabled = 1;
970 EXPORT_SYMBOL(console_suspend_enabled);
971
972 static int __init console_suspend_disable(char *str)
973 {
974         console_suspend_enabled = 0;
975         return 1;
976 }
977 __setup("no_console_suspend", console_suspend_disable);
978
979 /**
980  * suspend_console - suspend the console subsystem
981  *
982  * This disables printk() while we go into suspend states
983  */
984 void suspend_console(void)
985 {
986         if (!console_suspend_enabled)
987                 return;
988         printk("Suspending console(s) (use no_console_suspend to debug)\n");
989         acquire_console_sem();
990         console_suspended = 1;
991         up(&console_sem);
992 }
993
994 void resume_console(void)
995 {
996         if (!console_suspend_enabled)
997                 return;
998         down(&console_sem);
999         console_suspended = 0;
1000         release_console_sem();
1001 }
1002
1003 /**
1004  * console_cpu_notify - print deferred console messages after CPU hotplug
1005  * @self: notifier struct
1006  * @action: CPU hotplug event
1007  * @hcpu: unused
1008  *
1009  * If printk() is called from a CPU that is not online yet, the messages
1010  * will be spooled but will not show up on the console.  This function is
1011  * called when a new CPU comes online (or fails to come up), and ensures
1012  * that any such output gets printed.
1013  */
1014 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1015         unsigned long action, void *hcpu)
1016 {
1017         switch (action) {
1018         case CPU_ONLINE:
1019         case CPU_DEAD:
1020         case CPU_DYING:
1021         case CPU_DOWN_FAILED:
1022         case CPU_UP_CANCELED:
1023                 acquire_console_sem();
1024                 release_console_sem();
1025         }
1026         return NOTIFY_OK;
1027 }
1028
1029 /**
1030  * acquire_console_sem - lock the console system for exclusive use.
1031  *
1032  * Acquires a semaphore which guarantees that the caller has
1033  * exclusive access to the console system and the console_drivers list.
1034  *
1035  * Can sleep, returns nothing.
1036  */
1037 void acquire_console_sem(void)
1038 {
1039         BUG_ON(in_interrupt());
1040         down(&console_sem);
1041         if (console_suspended)
1042                 return;
1043         console_locked = 1;
1044         console_may_schedule = 1;
1045 }
1046 EXPORT_SYMBOL(acquire_console_sem);
1047
1048 int try_acquire_console_sem(void)
1049 {
1050         if (down_trylock(&console_sem))
1051                 return -1;
1052         if (console_suspended) {
1053                 up(&console_sem);
1054                 return -1;
1055         }
1056         console_locked = 1;
1057         console_may_schedule = 0;
1058         return 0;
1059 }
1060 EXPORT_SYMBOL(try_acquire_console_sem);
1061
1062 int is_console_locked(void)
1063 {
1064         return console_locked;
1065 }
1066
1067 static DEFINE_PER_CPU(int, printk_pending);
1068
1069 void printk_tick(void)
1070 {
1071         if (__this_cpu_read(printk_pending)) {
1072                 __this_cpu_write(printk_pending, 0);
1073                 wake_up_interruptible(&log_wait);
1074         }
1075 }
1076
1077 int printk_needs_cpu(int cpu)
1078 {
1079         if (cpu_is_offline(cpu))
1080                 printk_tick();
1081         return __this_cpu_read(printk_pending);
1082 }
1083
1084 void wake_up_klogd(void)
1085 {
1086         if (waitqueue_active(&log_wait))
1087                 this_cpu_write(printk_pending, 1);
1088 }
1089
1090 /**
1091  * release_console_sem - unlock the console system
1092  *
1093  * Releases the semaphore which the caller holds on the console system
1094  * and the console driver list.
1095  *
1096  * While the semaphore was held, console output may have been buffered
1097  * by printk().  If this is the case, release_console_sem() emits
1098  * the output prior to releasing the semaphore.
1099  *
1100  * If there is output waiting for klogd, we wake it up.
1101  *
1102  * release_console_sem() may be called from any context.
1103  */
1104 void release_console_sem(void)
1105 {
1106         unsigned long flags;
1107         unsigned _con_start, _log_end;
1108         unsigned wake_klogd = 0;
1109
1110         if (console_suspended) {
1111                 up(&console_sem);
1112                 return;
1113         }
1114
1115         console_may_schedule = 0;
1116
1117         for ( ; ; ) {
1118                 spin_lock_irqsave(&logbuf_lock, flags);
1119                 wake_klogd |= log_start - log_end;
1120                 if (con_start == log_end)
1121                         break;                  /* Nothing to print */
1122                 _con_start = con_start;
1123                 _log_end = log_end;
1124                 con_start = log_end;            /* Flush */
1125                 spin_unlock(&logbuf_lock);
1126                 stop_critical_timings();        /* don't trace print latency */
1127                 call_console_drivers(_con_start, _log_end);
1128                 start_critical_timings();
1129                 local_irq_restore(flags);
1130         }
1131         console_locked = 0;
1132         up(&console_sem);
1133         spin_unlock_irqrestore(&logbuf_lock, flags);
1134         if (wake_klogd)
1135                 wake_up_klogd();
1136 }
1137 EXPORT_SYMBOL(release_console_sem);
1138
1139 /**
1140  * console_conditional_schedule - yield the CPU if required
1141  *
1142  * If the console code is currently allowed to sleep, and
1143  * if this CPU should yield the CPU to another task, do
1144  * so here.
1145  *
1146  * Must be called within acquire_console_sem().
1147  */
1148 void __sched console_conditional_schedule(void)
1149 {
1150         if (console_may_schedule)
1151                 cond_resched();
1152 }
1153 EXPORT_SYMBOL(console_conditional_schedule);
1154
1155 void console_unblank(void)
1156 {
1157         struct console *c;
1158
1159         /*
1160          * console_unblank can no longer be called in interrupt context unless
1161          * oops_in_progress is set to 1..
1162          */
1163         if (oops_in_progress) {
1164                 if (down_trylock(&console_sem) != 0)
1165                         return;
1166         } else
1167                 acquire_console_sem();
1168
1169         console_locked = 1;
1170         console_may_schedule = 0;
1171         for_each_console(c)
1172                 if ((c->flags & CON_ENABLED) && c->unblank)
1173                         c->unblank();
1174         release_console_sem();
1175 }
1176
1177 /*
1178  * Return the console tty driver structure and its associated index
1179  */
1180 struct tty_driver *console_device(int *index)
1181 {
1182         struct console *c;
1183         struct tty_driver *driver = NULL;
1184
1185         acquire_console_sem();
1186         for_each_console(c) {
1187                 if (!c->device)
1188                         continue;
1189                 driver = c->device(c, index);
1190                 if (driver)
1191                         break;
1192         }
1193         release_console_sem();
1194         return driver;
1195 }
1196
1197 /*
1198  * Prevent further output on the passed console device so that (for example)
1199  * serial drivers can disable console output before suspending a port, and can
1200  * re-enable output afterwards.
1201  */
1202 void console_stop(struct console *console)
1203 {
1204         acquire_console_sem();
1205         console->flags &= ~CON_ENABLED;
1206         release_console_sem();
1207 }
1208 EXPORT_SYMBOL(console_stop);
1209
1210 void console_start(struct console *console)
1211 {
1212         acquire_console_sem();
1213         console->flags |= CON_ENABLED;
1214         release_console_sem();
1215 }
1216 EXPORT_SYMBOL(console_start);
1217
1218 /*
1219  * The console driver calls this routine during kernel initialization
1220  * to register the console printing procedure with printk() and to
1221  * print any messages that were printed by the kernel before the
1222  * console driver was initialized.
1223  *
1224  * This can happen pretty early during the boot process (because of
1225  * early_printk) - sometimes before setup_arch() completes - be careful
1226  * of what kernel features are used - they may not be initialised yet.
1227  *
1228  * There are two types of consoles - bootconsoles (early_printk) and
1229  * "real" consoles (everything which is not a bootconsole) which are
1230  * handled differently.
1231  *  - Any number of bootconsoles can be registered at any time.
1232  *  - As soon as a "real" console is registered, all bootconsoles
1233  *    will be unregistered automatically.
1234  *  - Once a "real" console is registered, any attempt to register a
1235  *    bootconsoles will be rejected
1236  */
1237 void register_console(struct console *newcon)
1238 {
1239         int i;
1240         unsigned long flags;
1241         struct console *bcon = NULL;
1242
1243         /*
1244          * before we register a new CON_BOOT console, make sure we don't
1245          * already have a valid console
1246          */
1247         if (console_drivers && newcon->flags & CON_BOOT) {
1248                 /* find the last or real console */
1249                 for_each_console(bcon) {
1250                         if (!(bcon->flags & CON_BOOT)) {
1251                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1252                                         newcon->name, newcon->index);
1253                                 return;
1254                         }
1255                 }
1256         }
1257
1258         if (console_drivers && console_drivers->flags & CON_BOOT)
1259                 bcon = console_drivers;
1260
1261         if (preferred_console < 0 || bcon || !console_drivers)
1262                 preferred_console = selected_console;
1263
1264         if (newcon->early_setup)
1265                 newcon->early_setup();
1266
1267         /*
1268          *      See if we want to use this console driver. If we
1269          *      didn't select a console we take the first one
1270          *      that registers here.
1271          */
1272         if (preferred_console < 0) {
1273                 if (newcon->index < 0)
1274                         newcon->index = 0;
1275                 if (newcon->setup == NULL ||
1276                     newcon->setup(newcon, NULL) == 0) {
1277                         newcon->flags |= CON_ENABLED;
1278                         if (newcon->device) {
1279                                 newcon->flags |= CON_CONSDEV;
1280                                 preferred_console = 0;
1281                         }
1282                 }
1283         }
1284
1285         /*
1286          *      See if this console matches one we selected on
1287          *      the command line.
1288          */
1289         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1290                         i++) {
1291                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1292                         continue;
1293                 if (newcon->index >= 0 &&
1294                     newcon->index != console_cmdline[i].index)
1295                         continue;
1296                 if (newcon->index < 0)
1297                         newcon->index = console_cmdline[i].index;
1298 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1299                 if (console_cmdline[i].brl_options) {
1300                         newcon->flags |= CON_BRL;
1301                         braille_register_console(newcon,
1302                                         console_cmdline[i].index,
1303                                         console_cmdline[i].options,
1304                                         console_cmdline[i].brl_options);
1305                         return;
1306                 }
1307 #endif
1308                 if (newcon->setup &&
1309                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1310                         break;
1311                 newcon->flags |= CON_ENABLED;
1312                 newcon->index = console_cmdline[i].index;
1313                 if (i == selected_console) {
1314                         newcon->flags |= CON_CONSDEV;
1315                         preferred_console = selected_console;
1316                 }
1317                 break;
1318         }
1319
1320         if (!(newcon->flags & CON_ENABLED))
1321                 return;
1322
1323         /*
1324          * If we have a bootconsole, and are switching to a real console,
1325          * don't print everything out again, since when the boot console, and
1326          * the real console are the same physical device, it's annoying to
1327          * see the beginning boot messages twice
1328          */
1329         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1330                 newcon->flags &= ~CON_PRINTBUFFER;
1331
1332         /*
1333          *      Put this console in the list - keep the
1334          *      preferred driver at the head of the list.
1335          */
1336         acquire_console_sem();
1337         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1338                 newcon->next = console_drivers;
1339                 console_drivers = newcon;
1340                 if (newcon->next)
1341                         newcon->next->flags &= ~CON_CONSDEV;
1342         } else {
1343                 newcon->next = console_drivers->next;
1344                 console_drivers->next = newcon;
1345         }
1346         if (newcon->flags & CON_PRINTBUFFER) {
1347                 /*
1348                  * release_console_sem() will print out the buffered messages
1349                  * for us.
1350                  */
1351                 spin_lock_irqsave(&logbuf_lock, flags);
1352                 con_start = log_start;
1353                 spin_unlock_irqrestore(&logbuf_lock, flags);
1354         }
1355         release_console_sem();
1356         console_sysfs_notify();
1357
1358         /*
1359          * By unregistering the bootconsoles after we enable the real console
1360          * we get the "console xxx enabled" message on all the consoles -
1361          * boot consoles, real consoles, etc - this is to ensure that end
1362          * users know there might be something in the kernel's log buffer that
1363          * went to the bootconsole (that they do not see on the real console)
1364          */
1365         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1366                 /* we need to iterate through twice, to make sure we print
1367                  * everything out, before we unregister the console(s)
1368                  */
1369                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1370                         newcon->name, newcon->index);
1371                 for_each_console(bcon)
1372                         if (bcon->flags & CON_BOOT)
1373                                 unregister_console(bcon);
1374         } else {
1375                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1376                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1377                         newcon->name, newcon->index);
1378         }
1379 }
1380 EXPORT_SYMBOL(register_console);
1381
1382 int unregister_console(struct console *console)
1383 {
1384         struct console *a, *b;
1385         int res = 1;
1386
1387 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1388         if (console->flags & CON_BRL)
1389                 return braille_unregister_console(console);
1390 #endif
1391
1392         acquire_console_sem();
1393         if (console_drivers == console) {
1394                 console_drivers=console->next;
1395                 res = 0;
1396         } else if (console_drivers) {
1397                 for (a=console_drivers->next, b=console_drivers ;
1398                      a; b=a, a=b->next) {
1399                         if (a == console) {
1400                                 b->next = a->next;
1401                                 res = 0;
1402                                 break;
1403                         }
1404                 }
1405         }
1406
1407         /*
1408          * If this isn't the last console and it has CON_CONSDEV set, we
1409          * need to set it on the next preferred console.
1410          */
1411         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1412                 console_drivers->flags |= CON_CONSDEV;
1413
1414         release_console_sem();
1415         console_sysfs_notify();
1416         return res;
1417 }
1418 EXPORT_SYMBOL(unregister_console);
1419
1420 static int __init printk_late_init(void)
1421 {
1422         struct console *con;
1423
1424         for_each_console(con) {
1425                 if (con->flags & CON_BOOT) {
1426                         printk(KERN_INFO "turn off boot console %s%d\n",
1427                                 con->name, con->index);
1428                         unregister_console(con);
1429                 }
1430         }
1431         hotcpu_notifier(console_cpu_notify, 0);
1432         return 0;
1433 }
1434 late_initcall(printk_late_init);
1435
1436 #if defined CONFIG_PRINTK
1437
1438 /*
1439  * printk rate limiting, lifted from the networking subsystem.
1440  *
1441  * This enforces a rate limit: not more than 10 kernel messages
1442  * every 5s to make a denial-of-service attack impossible.
1443  */
1444 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1445
1446 int __printk_ratelimit(const char *func)
1447 {
1448         return ___ratelimit(&printk_ratelimit_state, func);
1449 }
1450 EXPORT_SYMBOL(__printk_ratelimit);
1451
1452 /**
1453  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1454  * @caller_jiffies: pointer to caller's state
1455  * @interval_msecs: minimum interval between prints
1456  *
1457  * printk_timed_ratelimit() returns true if more than @interval_msecs
1458  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1459  * returned true.
1460  */
1461 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1462                         unsigned int interval_msecs)
1463 {
1464         if (*caller_jiffies == 0
1465                         || !time_in_range(jiffies, *caller_jiffies,
1466                                         *caller_jiffies
1467                                         + msecs_to_jiffies(interval_msecs))) {
1468                 *caller_jiffies = jiffies;
1469                 return true;
1470         }
1471         return false;
1472 }
1473 EXPORT_SYMBOL(printk_timed_ratelimit);
1474
1475 static DEFINE_SPINLOCK(dump_list_lock);
1476 static LIST_HEAD(dump_list);
1477
1478 /**
1479  * kmsg_dump_register - register a kernel log dumper.
1480  * @dumper: pointer to the kmsg_dumper structure
1481  *
1482  * Adds a kernel log dumper to the system. The dump callback in the
1483  * structure will be called when the kernel oopses or panics and must be
1484  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1485  */
1486 int kmsg_dump_register(struct kmsg_dumper *dumper)
1487 {
1488         unsigned long flags;
1489         int err = -EBUSY;
1490
1491         /* The dump callback needs to be set */
1492         if (!dumper->dump)
1493                 return -EINVAL;
1494
1495         spin_lock_irqsave(&dump_list_lock, flags);
1496         /* Don't allow registering multiple times */
1497         if (!dumper->registered) {
1498                 dumper->registered = 1;
1499                 list_add_tail(&dumper->list, &dump_list);
1500                 err = 0;
1501         }
1502         spin_unlock_irqrestore(&dump_list_lock, flags);
1503
1504         return err;
1505 }
1506 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1507
1508 /**
1509  * kmsg_dump_unregister - unregister a kmsg dumper.
1510  * @dumper: pointer to the kmsg_dumper structure
1511  *
1512  * Removes a dump device from the system. Returns zero on success and
1513  * %-EINVAL otherwise.
1514  */
1515 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1516 {
1517         unsigned long flags;
1518         int err = -EINVAL;
1519
1520         spin_lock_irqsave(&dump_list_lock, flags);
1521         if (dumper->registered) {
1522                 dumper->registered = 0;
1523                 list_del(&dumper->list);
1524                 err = 0;
1525         }
1526         spin_unlock_irqrestore(&dump_list_lock, flags);
1527
1528         return err;
1529 }
1530 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1531
1532 static const char * const kmsg_reasons[] = {
1533         [KMSG_DUMP_OOPS]        = "oops",
1534         [KMSG_DUMP_PANIC]       = "panic",
1535         [KMSG_DUMP_KEXEC]       = "kexec",
1536 };
1537
1538 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1539 {
1540         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1541                 return "unknown";
1542
1543         return kmsg_reasons[reason];
1544 }
1545
1546 /**
1547  * kmsg_dump - dump kernel log to kernel message dumpers.
1548  * @reason: the reason (oops, panic etc) for dumping
1549  *
1550  * Iterate through each of the dump devices and call the oops/panic
1551  * callbacks with the log buffer.
1552  */
1553 void kmsg_dump(enum kmsg_dump_reason reason)
1554 {
1555         unsigned long end;
1556         unsigned chars;
1557         struct kmsg_dumper *dumper;
1558         const char *s1, *s2;
1559         unsigned long l1, l2;
1560         unsigned long flags;
1561
1562         /* Theoretically, the log could move on after we do this, but
1563            there's not a lot we can do about that. The new messages
1564            will overwrite the start of what we dump. */
1565         spin_lock_irqsave(&logbuf_lock, flags);
1566         end = log_end & LOG_BUF_MASK;
1567         chars = logged_chars;
1568         spin_unlock_irqrestore(&logbuf_lock, flags);
1569
1570         if (chars > end) {
1571                 s1 = log_buf + log_buf_len - chars + end;
1572                 l1 = chars - end;
1573
1574                 s2 = log_buf;
1575                 l2 = end;
1576         } else {
1577                 s1 = "";
1578                 l1 = 0;
1579
1580                 s2 = log_buf + end - chars;
1581                 l2 = chars;
1582         }
1583
1584         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1585                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1586                                 kmsg_to_str(reason));
1587                 return;
1588         }
1589         list_for_each_entry(dumper, &dump_list, list)
1590                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1591         spin_unlock_irqrestore(&dump_list_lock, flags);
1592 }
1593 #endif