security: Define CAP_SYSLOG
[linux-2.6.git] / kernel / printk.c
1 /*
2  *  linux/kernel/printk.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *
6  * Modified to make sys_syslog() more flexible: added commands to
7  * return the last 4k of kernel messages, regardless of whether
8  * they've been read or not.  Added option to suppress kernel printk's
9  * to the console.  Added hook for sending the console messages
10  * elsewhere, in preparation for a serial line console (someday).
11  * Ted Ts'o, 2/11/93.
12  * Modified for sysctl support, 1/8/97, Chris Horn.
13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14  *     manfred@colorfullife.com
15  * Rewrote bits to get rid of console_lock
16  *      01Mar01 Andrew Morton
17  */
18
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/console.h>
24 #include <linux/init.h>
25 #include <linux/jiffies.h>
26 #include <linux/nmi.h>
27 #include <linux/module.h>
28 #include <linux/moduleparam.h>
29 #include <linux/interrupt.h>                    /* For in_interrupt() */
30 #include <linux/delay.h>
31 #include <linux/smp.h>
32 #include <linux/security.h>
33 #include <linux/bootmem.h>
34 #include <linux/syscalls.h>
35 #include <linux/kexec.h>
36 #include <linux/kdb.h>
37 #include <linux/ratelimit.h>
38 #include <linux/kmsg_dump.h>
39 #include <linux/syslog.h>
40 #include <linux/cpu.h>
41 #include <linux/notifier.h>
42
43 #include <asm/uaccess.h>
44
45 /*
46  * for_each_console() allows you to iterate on each console
47  */
48 #define for_each_console(con) \
49         for (con = console_drivers; con != NULL; con = con->next)
50
51 /*
52  * Architectures can override it:
53  */
54 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
55 {
56 }
57
58 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
59
60 /* printk's without a loglevel use this.. */
61 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
62
63 /* We show everything that is MORE important than this.. */
64 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
65 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
66
67 DECLARE_WAIT_QUEUE_HEAD(log_wait);
68
69 int console_printk[4] = {
70         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
71         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
72         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
73         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
74 };
75
76 /*
77  * Low level drivers may need that to know if they can schedule in
78  * their unblank() callback or not. So let's export it.
79  */
80 int oops_in_progress;
81 EXPORT_SYMBOL(oops_in_progress);
82
83 /*
84  * console_sem protects the console_drivers list, and also
85  * provides serialisation for access to the entire console
86  * driver system.
87  */
88 static DEFINE_SEMAPHORE(console_sem);
89 struct console *console_drivers;
90 EXPORT_SYMBOL_GPL(console_drivers);
91
92 /*
93  * This is used for debugging the mess that is the VT code by
94  * keeping track if we have the console semaphore held. It's
95  * definitely not the perfect debug tool (we don't know if _WE_
96  * hold it are racing, but it helps tracking those weird code
97  * path in the console code where we end up in places I want
98  * locked without the console sempahore held
99  */
100 static int console_locked, console_suspended;
101
102 /*
103  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
104  * It is also used in interesting ways to provide interlocking in
105  * release_console_sem().
106  */
107 static DEFINE_SPINLOCK(logbuf_lock);
108
109 #define LOG_BUF_MASK (log_buf_len-1)
110 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
111
112 /*
113  * The indices into log_buf are not constrained to log_buf_len - they
114  * must be masked before subscripting
115  */
116 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
117 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
118 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
119
120 /*
121  *      Array of consoles built from command line options (console=)
122  */
123 struct console_cmdline
124 {
125         char    name[8];                        /* Name of the driver       */
126         int     index;                          /* Minor dev. to use        */
127         char    *options;                       /* Options for the driver   */
128 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
129         char    *brl_options;                   /* Options for braille driver */
130 #endif
131 };
132
133 #define MAX_CMDLINECONSOLES 8
134
135 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
136 static int selected_console = -1;
137 static int preferred_console = -1;
138 int console_set_on_cmdline;
139 EXPORT_SYMBOL(console_set_on_cmdline);
140
141 /* Flag: console code may call schedule() */
142 static int console_may_schedule;
143
144 #ifdef CONFIG_PRINTK
145
146 static char __log_buf[__LOG_BUF_LEN];
147 static char *log_buf = __log_buf;
148 static int log_buf_len = __LOG_BUF_LEN;
149 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
150 static int saved_console_loglevel = -1;
151
152 #ifdef CONFIG_KEXEC
153 /*
154  * This appends the listed symbols to /proc/vmcoreinfo
155  *
156  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
157  * obtain access to symbols that are otherwise very difficult to locate.  These
158  * symbols are specifically used so that utilities can access and extract the
159  * dmesg log from a vmcore file after a crash.
160  */
161 void log_buf_kexec_setup(void)
162 {
163         VMCOREINFO_SYMBOL(log_buf);
164         VMCOREINFO_SYMBOL(log_end);
165         VMCOREINFO_SYMBOL(log_buf_len);
166         VMCOREINFO_SYMBOL(logged_chars);
167 }
168 #endif
169
170 static int __init log_buf_len_setup(char *str)
171 {
172         unsigned size = memparse(str, &str);
173         unsigned long flags;
174
175         if (size)
176                 size = roundup_pow_of_two(size);
177         if (size > log_buf_len) {
178                 unsigned start, dest_idx, offset;
179                 char *new_log_buf;
180
181                 new_log_buf = alloc_bootmem(size);
182                 if (!new_log_buf) {
183                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
184                         goto out;
185                 }
186
187                 spin_lock_irqsave(&logbuf_lock, flags);
188                 log_buf_len = size;
189                 log_buf = new_log_buf;
190
191                 offset = start = min(con_start, log_start);
192                 dest_idx = 0;
193                 while (start != log_end) {
194                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
195                         start++;
196                         dest_idx++;
197                 }
198                 log_start -= offset;
199                 con_start -= offset;
200                 log_end -= offset;
201                 spin_unlock_irqrestore(&logbuf_lock, flags);
202
203                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
204         }
205 out:
206         return 1;
207 }
208
209 __setup("log_buf_len=", log_buf_len_setup);
210
211 #ifdef CONFIG_BOOT_PRINTK_DELAY
212
213 static int boot_delay; /* msecs delay after each printk during bootup */
214 static unsigned long long loops_per_msec;       /* based on boot_delay */
215
216 static int __init boot_delay_setup(char *str)
217 {
218         unsigned long lpj;
219
220         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
221         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
222
223         get_option(&str, &boot_delay);
224         if (boot_delay > 10 * 1000)
225                 boot_delay = 0;
226
227         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
228                 "HZ: %d, loops_per_msec: %llu\n",
229                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
230         return 1;
231 }
232 __setup("boot_delay=", boot_delay_setup);
233
234 static void boot_delay_msec(void)
235 {
236         unsigned long long k;
237         unsigned long timeout;
238
239         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
240                 return;
241
242         k = (unsigned long long)loops_per_msec * boot_delay;
243
244         timeout = jiffies + msecs_to_jiffies(boot_delay);
245         while (k) {
246                 k--;
247                 cpu_relax();
248                 /*
249                  * use (volatile) jiffies to prevent
250                  * compiler reduction; loop termination via jiffies
251                  * is secondary and may or may not happen.
252                  */
253                 if (time_after(jiffies, timeout))
254                         break;
255                 touch_nmi_watchdog();
256         }
257 }
258 #else
259 static inline void boot_delay_msec(void)
260 {
261 }
262 #endif
263
264 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
265 int dmesg_restrict = 1;
266 #else
267 int dmesg_restrict;
268 #endif
269
270 int do_syslog(int type, char __user *buf, int len, bool from_file)
271 {
272         unsigned i, j, limit, count;
273         int do_clear = 0;
274         char c;
275         int error = 0;
276
277         /*
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_SYSLOG)) {
287                         /* remove after 2.6.38 */
288                         if (capable(CAP_SYS_ADMIN))
289                                 WARN_ONCE(1, "Attempt to access syslog with "
290                                   "CAP_SYS_ADMIN but no CAP_SYSLOG "
291                                   "(deprecated and denied).\n");
292                         return -EPERM;
293                 }
294         }
295
296         error = security_syslog(type);
297         if (error)
298                 return error;
299
300         switch (type) {
301         case SYSLOG_ACTION_CLOSE:       /* Close log */
302                 break;
303         case SYSLOG_ACTION_OPEN:        /* Open log */
304                 break;
305         case SYSLOG_ACTION_READ:        /* Read from log */
306                 error = -EINVAL;
307                 if (!buf || len < 0)
308                         goto out;
309                 error = 0;
310                 if (!len)
311                         goto out;
312                 if (!access_ok(VERIFY_WRITE, buf, len)) {
313                         error = -EFAULT;
314                         goto out;
315                 }
316                 error = wait_event_interruptible(log_wait,
317                                                         (log_start - log_end));
318                 if (error)
319                         goto out;
320                 i = 0;
321                 spin_lock_irq(&logbuf_lock);
322                 while (!error && (log_start != log_end) && i < len) {
323                         c = LOG_BUF(log_start);
324                         log_start++;
325                         spin_unlock_irq(&logbuf_lock);
326                         error = __put_user(c,buf);
327                         buf++;
328                         i++;
329                         cond_resched();
330                         spin_lock_irq(&logbuf_lock);
331                 }
332                 spin_unlock_irq(&logbuf_lock);
333                 if (!error)
334                         error = i;
335                 break;
336         /* Read/clear last kernel messages */
337         case SYSLOG_ACTION_READ_CLEAR:
338                 do_clear = 1;
339                 /* FALL THRU */
340         /* Read last kernel messages */
341         case SYSLOG_ACTION_READ_ALL:
342                 error = -EINVAL;
343                 if (!buf || len < 0)
344                         goto out;
345                 error = 0;
346                 if (!len)
347                         goto out;
348                 if (!access_ok(VERIFY_WRITE, buf, len)) {
349                         error = -EFAULT;
350                         goto out;
351                 }
352                 count = len;
353                 if (count > log_buf_len)
354                         count = log_buf_len;
355                 spin_lock_irq(&logbuf_lock);
356                 if (count > logged_chars)
357                         count = logged_chars;
358                 if (do_clear)
359                         logged_chars = 0;
360                 limit = log_end;
361                 /*
362                  * __put_user() could sleep, and while we sleep
363                  * printk() could overwrite the messages
364                  * we try to copy to user space. Therefore
365                  * the messages are copied in reverse. <manfreds>
366                  */
367                 for (i = 0; i < count && !error; i++) {
368                         j = limit-1-i;
369                         if (j + log_buf_len < log_end)
370                                 break;
371                         c = LOG_BUF(j);
372                         spin_unlock_irq(&logbuf_lock);
373                         error = __put_user(c,&buf[count-1-i]);
374                         cond_resched();
375                         spin_lock_irq(&logbuf_lock);
376                 }
377                 spin_unlock_irq(&logbuf_lock);
378                 if (error)
379                         break;
380                 error = i;
381                 if (i != count) {
382                         int offset = count-error;
383                         /* buffer overflow during copy, correct user buffer. */
384                         for (i = 0; i < error; i++) {
385                                 if (__get_user(c,&buf[i+offset]) ||
386                                     __put_user(c,&buf[i])) {
387                                         error = -EFAULT;
388                                         break;
389                                 }
390                                 cond_resched();
391                         }
392                 }
393                 break;
394         /* Clear ring buffer */
395         case SYSLOG_ACTION_CLEAR:
396                 logged_chars = 0;
397                 break;
398         /* Disable logging to console */
399         case SYSLOG_ACTION_CONSOLE_OFF:
400                 if (saved_console_loglevel == -1)
401                         saved_console_loglevel = console_loglevel;
402                 console_loglevel = minimum_console_loglevel;
403                 break;
404         /* Enable logging to console */
405         case SYSLOG_ACTION_CONSOLE_ON:
406                 if (saved_console_loglevel != -1) {
407                         console_loglevel = saved_console_loglevel;
408                         saved_console_loglevel = -1;
409                 }
410                 break;
411         /* Set level of messages printed to console */
412         case SYSLOG_ACTION_CONSOLE_LEVEL:
413                 error = -EINVAL;
414                 if (len < 1 || len > 8)
415                         goto out;
416                 if (len < minimum_console_loglevel)
417                         len = minimum_console_loglevel;
418                 console_loglevel = len;
419                 /* Implicitly re-enable logging to console */
420                 saved_console_loglevel = -1;
421                 error = 0;
422                 break;
423         /* Number of chars in the log buffer */
424         case SYSLOG_ACTION_SIZE_UNREAD:
425                 error = log_end - log_start;
426                 break;
427         /* Size of the log buffer */
428         case SYSLOG_ACTION_SIZE_BUFFER:
429                 error = log_buf_len;
430                 break;
431         default:
432                 error = -EINVAL;
433                 break;
434         }
435 out:
436         return error;
437 }
438
439 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
440 {
441         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
442 }
443
444 #ifdef  CONFIG_KGDB_KDB
445 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
446  * uses locks so it cannot be used during debugging.  Just tell kdb
447  * where the start and end of the physical and logical logs are.  This
448  * is equivalent to do_syslog(3).
449  */
450 void kdb_syslog_data(char *syslog_data[4])
451 {
452         syslog_data[0] = log_buf;
453         syslog_data[1] = log_buf + log_buf_len;
454         syslog_data[2] = log_buf + log_end -
455                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
456         syslog_data[3] = log_buf + log_end;
457 }
458 #endif  /* CONFIG_KGDB_KDB */
459
460 /*
461  * Call the console drivers on a range of log_buf
462  */
463 static void __call_console_drivers(unsigned start, unsigned end)
464 {
465         struct console *con;
466
467         for_each_console(con) {
468                 if ((con->flags & CON_ENABLED) && con->write &&
469                                 (cpu_online(smp_processor_id()) ||
470                                 (con->flags & CON_ANYTIME)))
471                         con->write(con, &LOG_BUF(start), end - start);
472         }
473 }
474
475 static int __read_mostly ignore_loglevel;
476
477 static int __init ignore_loglevel_setup(char *str)
478 {
479         ignore_loglevel = 1;
480         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
481
482         return 0;
483 }
484
485 early_param("ignore_loglevel", ignore_loglevel_setup);
486
487 /*
488  * Write out chars from start to end - 1 inclusive
489  */
490 static void _call_console_drivers(unsigned start,
491                                 unsigned end, int msg_log_level)
492 {
493         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
494                         console_drivers && start != end) {
495                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
496                         /* wrapped write */
497                         __call_console_drivers(start & LOG_BUF_MASK,
498                                                 log_buf_len);
499                         __call_console_drivers(0, end & LOG_BUF_MASK);
500                 } else {
501                         __call_console_drivers(start, end);
502                 }
503         }
504 }
505
506 /*
507  * Call the console drivers, asking them to write out
508  * log_buf[start] to log_buf[end - 1].
509  * The console_sem must be held.
510  */
511 static void call_console_drivers(unsigned start, unsigned end)
512 {
513         unsigned cur_index, start_print;
514         static int msg_level = -1;
515
516         BUG_ON(((int)(start - end)) > 0);
517
518         cur_index = start;
519         start_print = start;
520         while (cur_index != end) {
521                 if (msg_level < 0 && ((end - cur_index) > 2) &&
522                                 LOG_BUF(cur_index + 0) == '<' &&
523                                 LOG_BUF(cur_index + 1) >= '0' &&
524                                 LOG_BUF(cur_index + 1) <= '7' &&
525                                 LOG_BUF(cur_index + 2) == '>') {
526                         msg_level = LOG_BUF(cur_index + 1) - '0';
527                         cur_index += 3;
528                         start_print = cur_index;
529                 }
530                 while (cur_index != end) {
531                         char c = LOG_BUF(cur_index);
532
533                         cur_index++;
534                         if (c == '\n') {
535                                 if (msg_level < 0) {
536                                         /*
537                                          * printk() has already given us loglevel tags in
538                                          * the buffer.  This code is here in case the
539                                          * log buffer has wrapped right round and scribbled
540                                          * on those tags
541                                          */
542                                         msg_level = default_message_loglevel;
543                                 }
544                                 _call_console_drivers(start_print, cur_index, msg_level);
545                                 msg_level = -1;
546                                 start_print = cur_index;
547                                 break;
548                         }
549                 }
550         }
551         _call_console_drivers(start_print, end, msg_level);
552 }
553
554 static void emit_log_char(char c)
555 {
556         LOG_BUF(log_end) = c;
557         log_end++;
558         if (log_end - log_start > log_buf_len)
559                 log_start = log_end - log_buf_len;
560         if (log_end - con_start > log_buf_len)
561                 con_start = log_end - log_buf_len;
562         if (logged_chars < log_buf_len)
563                 logged_chars++;
564 }
565
566 /*
567  * Zap console related locks when oopsing. Only zap at most once
568  * every 10 seconds, to leave time for slow consoles to print a
569  * full oops.
570  */
571 static void zap_locks(void)
572 {
573         static unsigned long oops_timestamp;
574
575         if (time_after_eq(jiffies, oops_timestamp) &&
576                         !time_after(jiffies, oops_timestamp + 30 * HZ))
577                 return;
578
579         oops_timestamp = jiffies;
580
581         /* If a crash is occurring, make sure we can't deadlock */
582         spin_lock_init(&logbuf_lock);
583         /* And make sure that we print immediately */
584         sema_init(&console_sem, 1);
585 }
586
587 #if defined(CONFIG_PRINTK_TIME)
588 static int printk_time = 1;
589 #else
590 static int printk_time = 0;
591 #endif
592 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
593
594 /* Check if we have any console registered that can be called early in boot. */
595 static int have_callable_console(void)
596 {
597         struct console *con;
598
599         for_each_console(con)
600                 if (con->flags & CON_ANYTIME)
601                         return 1;
602
603         return 0;
604 }
605
606 /**
607  * printk - print a kernel message
608  * @fmt: format string
609  *
610  * This is printk().  It can be called from any context.  We want it to work.
611  *
612  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
613  * call the console drivers.  If we fail to get the semaphore we place the output
614  * into the log buffer and return.  The current holder of the console_sem will
615  * notice the new output in release_console_sem() and will send it to the
616  * consoles before releasing the semaphore.
617  *
618  * One effect of this deferred printing is that code which calls printk() and
619  * then changes console_loglevel may break. This is because console_loglevel
620  * is inspected when the actual printing occurs.
621  *
622  * See also:
623  * printf(3)
624  *
625  * See the vsnprintf() documentation for format string extensions over C99.
626  */
627
628 asmlinkage int printk(const char *fmt, ...)
629 {
630         va_list args;
631         int r;
632
633 #ifdef CONFIG_KGDB_KDB
634         if (unlikely(kdb_trap_printk)) {
635                 va_start(args, fmt);
636                 r = vkdb_printf(fmt, args);
637                 va_end(args);
638                 return r;
639         }
640 #endif
641         va_start(args, fmt);
642         r = vprintk(fmt, args);
643         va_end(args);
644
645         return r;
646 }
647
648 /* cpu currently holding logbuf_lock */
649 static volatile unsigned int printk_cpu = UINT_MAX;
650
651 /*
652  * Can we actually use the console at this time on this cpu?
653  *
654  * Console drivers may assume that per-cpu resources have
655  * been allocated. So unless they're explicitly marked as
656  * being able to cope (CON_ANYTIME) don't call them until
657  * this CPU is officially up.
658  */
659 static inline int can_use_console(unsigned int cpu)
660 {
661         return cpu_online(cpu) || have_callable_console();
662 }
663
664 /*
665  * Try to get console ownership to actually show the kernel
666  * messages from a 'printk'. Return true (and with the
667  * console_semaphore held, and 'console_locked' set) if it
668  * is successful, false otherwise.
669  *
670  * This gets called with the 'logbuf_lock' spinlock held and
671  * interrupts disabled. It should return with 'lockbuf_lock'
672  * released but interrupts still disabled.
673  */
674 static int acquire_console_semaphore_for_printk(unsigned int cpu)
675         __releases(&logbuf_lock)
676 {
677         int retval = 0;
678
679         if (!try_acquire_console_sem()) {
680                 retval = 1;
681
682                 /*
683                  * If we can't use the console, we need to release
684                  * the console semaphore by hand to avoid flushing
685                  * the buffer. We need to hold the console semaphore
686                  * in order to do this test safely.
687                  */
688                 if (!can_use_console(cpu)) {
689                         console_locked = 0;
690                         up(&console_sem);
691                         retval = 0;
692                 }
693         }
694         printk_cpu = UINT_MAX;
695         spin_unlock(&logbuf_lock);
696         return retval;
697 }
698 static const char recursion_bug_msg [] =
699                 KERN_CRIT "BUG: recent printk recursion!\n";
700 static int recursion_bug;
701 static int new_text_line = 1;
702 static char printk_buf[1024];
703
704 int printk_delay_msec __read_mostly;
705
706 static inline void printk_delay(void)
707 {
708         if (unlikely(printk_delay_msec)) {
709                 int m = printk_delay_msec;
710
711                 while (m--) {
712                         mdelay(1);
713                         touch_nmi_watchdog();
714                 }
715         }
716 }
717
718 asmlinkage int vprintk(const char *fmt, va_list args)
719 {
720         int printed_len = 0;
721         int current_log_level = default_message_loglevel;
722         unsigned long flags;
723         int this_cpu;
724         char *p;
725
726         boot_delay_msec();
727         printk_delay();
728
729         preempt_disable();
730         /* This stops the holder of console_sem just where we want him */
731         raw_local_irq_save(flags);
732         this_cpu = smp_processor_id();
733
734         /*
735          * Ouch, printk recursed into itself!
736          */
737         if (unlikely(printk_cpu == this_cpu)) {
738                 /*
739                  * If a crash is occurring during printk() on this CPU,
740                  * then try to get the crash message out but make sure
741                  * we can't deadlock. Otherwise just return to avoid the
742                  * recursion and return - but flag the recursion so that
743                  * it can be printed at the next appropriate moment:
744                  */
745                 if (!oops_in_progress) {
746                         recursion_bug = 1;
747                         goto out_restore_irqs;
748                 }
749                 zap_locks();
750         }
751
752         lockdep_off();
753         spin_lock(&logbuf_lock);
754         printk_cpu = this_cpu;
755
756         if (recursion_bug) {
757                 recursion_bug = 0;
758                 strcpy(printk_buf, recursion_bug_msg);
759                 printed_len = strlen(recursion_bug_msg);
760         }
761         /* Emit the output into the temporary buffer */
762         printed_len += vscnprintf(printk_buf + printed_len,
763                                   sizeof(printk_buf) - printed_len, fmt, args);
764
765
766         p = printk_buf;
767
768         /* Do we have a loglevel in the string? */
769         if (p[0] == '<') {
770                 unsigned char c = p[1];
771                 if (c && p[2] == '>') {
772                         switch (c) {
773                         case '0' ... '7': /* loglevel */
774                                 current_log_level = c - '0';
775                         /* Fallthrough - make sure we're on a new line */
776                         case 'd': /* KERN_DEFAULT */
777                                 if (!new_text_line) {
778                                         emit_log_char('\n');
779                                         new_text_line = 1;
780                                 }
781                         /* Fallthrough - skip the loglevel */
782                         case 'c': /* KERN_CONT */
783                                 p += 3;
784                                 break;
785                         }
786                 }
787         }
788
789         /*
790          * Copy the output into log_buf.  If the caller didn't provide
791          * appropriate log level tags, we insert them here
792          */
793         for ( ; *p; p++) {
794                 if (new_text_line) {
795                         /* Always output the token */
796                         emit_log_char('<');
797                         emit_log_char(current_log_level + '0');
798                         emit_log_char('>');
799                         printed_len += 3;
800                         new_text_line = 0;
801
802                         if (printk_time) {
803                                 /* Follow the token with the time */
804                                 char tbuf[50], *tp;
805                                 unsigned tlen;
806                                 unsigned long long t;
807                                 unsigned long nanosec_rem;
808
809                                 t = cpu_clock(printk_cpu);
810                                 nanosec_rem = do_div(t, 1000000000);
811                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
812                                                 (unsigned long) t,
813                                                 nanosec_rem / 1000);
814
815                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
816                                         emit_log_char(*tp);
817                                 printed_len += tlen;
818                         }
819
820                         if (!*p)
821                                 break;
822                 }
823
824                 emit_log_char(*p);
825                 if (*p == '\n')
826                         new_text_line = 1;
827         }
828
829         /*
830          * Try to acquire and then immediately release the
831          * console semaphore. The release will do all the
832          * actual magic (print out buffers, wake up klogd,
833          * etc). 
834          *
835          * The acquire_console_semaphore_for_printk() function
836          * will release 'logbuf_lock' regardless of whether it
837          * actually gets the semaphore or not.
838          */
839         if (acquire_console_semaphore_for_printk(this_cpu))
840                 release_console_sem();
841
842         lockdep_on();
843 out_restore_irqs:
844         raw_local_irq_restore(flags);
845
846         preempt_enable();
847         return printed_len;
848 }
849 EXPORT_SYMBOL(printk);
850 EXPORT_SYMBOL(vprintk);
851
852 #else
853
854 static void call_console_drivers(unsigned start, unsigned end)
855 {
856 }
857
858 #endif
859
860 static int __add_preferred_console(char *name, int idx, char *options,
861                                    char *brl_options)
862 {
863         struct console_cmdline *c;
864         int i;
865
866         /*
867          *      See if this tty is not yet registered, and
868          *      if we have a slot free.
869          */
870         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
871                 if (strcmp(console_cmdline[i].name, name) == 0 &&
872                           console_cmdline[i].index == idx) {
873                                 if (!brl_options)
874                                         selected_console = i;
875                                 return 0;
876                 }
877         if (i == MAX_CMDLINECONSOLES)
878                 return -E2BIG;
879         if (!brl_options)
880                 selected_console = i;
881         c = &console_cmdline[i];
882         strlcpy(c->name, name, sizeof(c->name));
883         c->options = options;
884 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
885         c->brl_options = brl_options;
886 #endif
887         c->index = idx;
888         return 0;
889 }
890 /*
891  * Set up a list of consoles.  Called from init/main.c
892  */
893 static int __init console_setup(char *str)
894 {
895         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
896         char *s, *options, *brl_options = NULL;
897         int idx;
898
899 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
900         if (!memcmp(str, "brl,", 4)) {
901                 brl_options = "";
902                 str += 4;
903         } else if (!memcmp(str, "brl=", 4)) {
904                 brl_options = str + 4;
905                 str = strchr(brl_options, ',');
906                 if (!str) {
907                         printk(KERN_ERR "need port name after brl=\n");
908                         return 1;
909                 }
910                 *(str++) = 0;
911         }
912 #endif
913
914         /*
915          * Decode str into name, index, options.
916          */
917         if (str[0] >= '0' && str[0] <= '9') {
918                 strcpy(buf, "ttyS");
919                 strncpy(buf + 4, str, sizeof(buf) - 5);
920         } else {
921                 strncpy(buf, str, sizeof(buf) - 1);
922         }
923         buf[sizeof(buf) - 1] = 0;
924         if ((options = strchr(str, ',')) != NULL)
925                 *(options++) = 0;
926 #ifdef __sparc__
927         if (!strcmp(str, "ttya"))
928                 strcpy(buf, "ttyS0");
929         if (!strcmp(str, "ttyb"))
930                 strcpy(buf, "ttyS1");
931 #endif
932         for (s = buf; *s; s++)
933                 if ((*s >= '0' && *s <= '9') || *s == ',')
934                         break;
935         idx = simple_strtoul(s, NULL, 10);
936         *s = 0;
937
938         __add_preferred_console(buf, idx, options, brl_options);
939         console_set_on_cmdline = 1;
940         return 1;
941 }
942 __setup("console=", console_setup);
943
944 /**
945  * add_preferred_console - add a device to the list of preferred consoles.
946  * @name: device name
947  * @idx: device index
948  * @options: options for this console
949  *
950  * The last preferred console added will be used for kernel messages
951  * and stdin/out/err for init.  Normally this is used by console_setup
952  * above to handle user-supplied console arguments; however it can also
953  * be used by arch-specific code either to override the user or more
954  * commonly to provide a default console (ie from PROM variables) when
955  * the user has not supplied one.
956  */
957 int add_preferred_console(char *name, int idx, char *options)
958 {
959         return __add_preferred_console(name, idx, options, NULL);
960 }
961
962 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
963 {
964         struct console_cmdline *c;
965         int i;
966
967         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
968                 if (strcmp(console_cmdline[i].name, name) == 0 &&
969                           console_cmdline[i].index == idx) {
970                                 c = &console_cmdline[i];
971                                 strlcpy(c->name, name_new, sizeof(c->name));
972                                 c->name[sizeof(c->name) - 1] = 0;
973                                 c->options = options;
974                                 c->index = idx_new;
975                                 return i;
976                 }
977         /* not found */
978         return -1;
979 }
980
981 int console_suspend_enabled = 1;
982 EXPORT_SYMBOL(console_suspend_enabled);
983
984 static int __init console_suspend_disable(char *str)
985 {
986         console_suspend_enabled = 0;
987         return 1;
988 }
989 __setup("no_console_suspend", console_suspend_disable);
990
991 /**
992  * suspend_console - suspend the console subsystem
993  *
994  * This disables printk() while we go into suspend states
995  */
996 void suspend_console(void)
997 {
998         if (!console_suspend_enabled)
999                 return;
1000         printk("Suspending console(s) (use no_console_suspend to debug)\n");
1001         acquire_console_sem();
1002         console_suspended = 1;
1003         up(&console_sem);
1004 }
1005
1006 void resume_console(void)
1007 {
1008         if (!console_suspend_enabled)
1009                 return;
1010         down(&console_sem);
1011         console_suspended = 0;
1012         release_console_sem();
1013 }
1014
1015 /**
1016  * console_cpu_notify - print deferred console messages after CPU hotplug
1017  * @self: notifier struct
1018  * @action: CPU hotplug event
1019  * @hcpu: unused
1020  *
1021  * If printk() is called from a CPU that is not online yet, the messages
1022  * will be spooled but will not show up on the console.  This function is
1023  * called when a new CPU comes online (or fails to come up), and ensures
1024  * that any such output gets printed.
1025  */
1026 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1027         unsigned long action, void *hcpu)
1028 {
1029         switch (action) {
1030         case CPU_ONLINE:
1031         case CPU_DEAD:
1032         case CPU_DYING:
1033         case CPU_DOWN_FAILED:
1034         case CPU_UP_CANCELED:
1035                 acquire_console_sem();
1036                 release_console_sem();
1037         }
1038         return NOTIFY_OK;
1039 }
1040
1041 /**
1042  * acquire_console_sem - lock the console system for exclusive use.
1043  *
1044  * Acquires a semaphore which guarantees that the caller has
1045  * exclusive access to the console system and the console_drivers list.
1046  *
1047  * Can sleep, returns nothing.
1048  */
1049 void acquire_console_sem(void)
1050 {
1051         BUG_ON(in_interrupt());
1052         down(&console_sem);
1053         if (console_suspended)
1054                 return;
1055         console_locked = 1;
1056         console_may_schedule = 1;
1057 }
1058 EXPORT_SYMBOL(acquire_console_sem);
1059
1060 int try_acquire_console_sem(void)
1061 {
1062         if (down_trylock(&console_sem))
1063                 return -1;
1064         if (console_suspended) {
1065                 up(&console_sem);
1066                 return -1;
1067         }
1068         console_locked = 1;
1069         console_may_schedule = 0;
1070         return 0;
1071 }
1072 EXPORT_SYMBOL(try_acquire_console_sem);
1073
1074 int is_console_locked(void)
1075 {
1076         return console_locked;
1077 }
1078
1079 static DEFINE_PER_CPU(int, printk_pending);
1080
1081 void printk_tick(void)
1082 {
1083         if (__get_cpu_var(printk_pending)) {
1084                 __get_cpu_var(printk_pending) = 0;
1085                 wake_up_interruptible(&log_wait);
1086         }
1087 }
1088
1089 int printk_needs_cpu(int cpu)
1090 {
1091         return per_cpu(printk_pending, cpu);
1092 }
1093
1094 void wake_up_klogd(void)
1095 {
1096         if (waitqueue_active(&log_wait))
1097                 __raw_get_cpu_var(printk_pending) = 1;
1098 }
1099
1100 /**
1101  * release_console_sem - unlock the console system
1102  *
1103  * Releases the semaphore which the caller holds on the console system
1104  * and the console driver list.
1105  *
1106  * While the semaphore was held, console output may have been buffered
1107  * by printk().  If this is the case, release_console_sem() emits
1108  * the output prior to releasing the semaphore.
1109  *
1110  * If there is output waiting for klogd, we wake it up.
1111  *
1112  * release_console_sem() may be called from any context.
1113  */
1114 void release_console_sem(void)
1115 {
1116         unsigned long flags;
1117         unsigned _con_start, _log_end;
1118         unsigned wake_klogd = 0;
1119
1120         if (console_suspended) {
1121                 up(&console_sem);
1122                 return;
1123         }
1124
1125         console_may_schedule = 0;
1126
1127         for ( ; ; ) {
1128                 spin_lock_irqsave(&logbuf_lock, flags);
1129                 wake_klogd |= log_start - log_end;
1130                 if (con_start == log_end)
1131                         break;                  /* Nothing to print */
1132                 _con_start = con_start;
1133                 _log_end = log_end;
1134                 con_start = log_end;            /* Flush */
1135                 spin_unlock(&logbuf_lock);
1136                 stop_critical_timings();        /* don't trace print latency */
1137                 call_console_drivers(_con_start, _log_end);
1138                 start_critical_timings();
1139                 local_irq_restore(flags);
1140         }
1141         console_locked = 0;
1142         up(&console_sem);
1143         spin_unlock_irqrestore(&logbuf_lock, flags);
1144         if (wake_klogd)
1145                 wake_up_klogd();
1146 }
1147 EXPORT_SYMBOL(release_console_sem);
1148
1149 /**
1150  * console_conditional_schedule - yield the CPU if required
1151  *
1152  * If the console code is currently allowed to sleep, and
1153  * if this CPU should yield the CPU to another task, do
1154  * so here.
1155  *
1156  * Must be called within acquire_console_sem().
1157  */
1158 void __sched console_conditional_schedule(void)
1159 {
1160         if (console_may_schedule)
1161                 cond_resched();
1162 }
1163 EXPORT_SYMBOL(console_conditional_schedule);
1164
1165 void console_unblank(void)
1166 {
1167         struct console *c;
1168
1169         /*
1170          * console_unblank can no longer be called in interrupt context unless
1171          * oops_in_progress is set to 1..
1172          */
1173         if (oops_in_progress) {
1174                 if (down_trylock(&console_sem) != 0)
1175                         return;
1176         } else
1177                 acquire_console_sem();
1178
1179         console_locked = 1;
1180         console_may_schedule = 0;
1181         for_each_console(c)
1182                 if ((c->flags & CON_ENABLED) && c->unblank)
1183                         c->unblank();
1184         release_console_sem();
1185 }
1186
1187 /*
1188  * Return the console tty driver structure and its associated index
1189  */
1190 struct tty_driver *console_device(int *index)
1191 {
1192         struct console *c;
1193         struct tty_driver *driver = NULL;
1194
1195         acquire_console_sem();
1196         for_each_console(c) {
1197                 if (!c->device)
1198                         continue;
1199                 driver = c->device(c, index);
1200                 if (driver)
1201                         break;
1202         }
1203         release_console_sem();
1204         return driver;
1205 }
1206
1207 /*
1208  * Prevent further output on the passed console device so that (for example)
1209  * serial drivers can disable console output before suspending a port, and can
1210  * re-enable output afterwards.
1211  */
1212 void console_stop(struct console *console)
1213 {
1214         acquire_console_sem();
1215         console->flags &= ~CON_ENABLED;
1216         release_console_sem();
1217 }
1218 EXPORT_SYMBOL(console_stop);
1219
1220 void console_start(struct console *console)
1221 {
1222         acquire_console_sem();
1223         console->flags |= CON_ENABLED;
1224         release_console_sem();
1225 }
1226 EXPORT_SYMBOL(console_start);
1227
1228 /*
1229  * The console driver calls this routine during kernel initialization
1230  * to register the console printing procedure with printk() and to
1231  * print any messages that were printed by the kernel before the
1232  * console driver was initialized.
1233  *
1234  * This can happen pretty early during the boot process (because of
1235  * early_printk) - sometimes before setup_arch() completes - be careful
1236  * of what kernel features are used - they may not be initialised yet.
1237  *
1238  * There are two types of consoles - bootconsoles (early_printk) and
1239  * "real" consoles (everything which is not a bootconsole) which are
1240  * handled differently.
1241  *  - Any number of bootconsoles can be registered at any time.
1242  *  - As soon as a "real" console is registered, all bootconsoles
1243  *    will be unregistered automatically.
1244  *  - Once a "real" console is registered, any attempt to register a
1245  *    bootconsoles will be rejected
1246  */
1247 void register_console(struct console *newcon)
1248 {
1249         int i;
1250         unsigned long flags;
1251         struct console *bcon = NULL;
1252
1253         /*
1254          * before we register a new CON_BOOT console, make sure we don't
1255          * already have a valid console
1256          */
1257         if (console_drivers && newcon->flags & CON_BOOT) {
1258                 /* find the last or real console */
1259                 for_each_console(bcon) {
1260                         if (!(bcon->flags & CON_BOOT)) {
1261                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1262                                         newcon->name, newcon->index);
1263                                 return;
1264                         }
1265                 }
1266         }
1267
1268         if (console_drivers && console_drivers->flags & CON_BOOT)
1269                 bcon = console_drivers;
1270
1271         if (preferred_console < 0 || bcon || !console_drivers)
1272                 preferred_console = selected_console;
1273
1274         if (newcon->early_setup)
1275                 newcon->early_setup();
1276
1277         /*
1278          *      See if we want to use this console driver. If we
1279          *      didn't select a console we take the first one
1280          *      that registers here.
1281          */
1282         if (preferred_console < 0) {
1283                 if (newcon->index < 0)
1284                         newcon->index = 0;
1285                 if (newcon->setup == NULL ||
1286                     newcon->setup(newcon, NULL) == 0) {
1287                         newcon->flags |= CON_ENABLED;
1288                         if (newcon->device) {
1289                                 newcon->flags |= CON_CONSDEV;
1290                                 preferred_console = 0;
1291                         }
1292                 }
1293         }
1294
1295         /*
1296          *      See if this console matches one we selected on
1297          *      the command line.
1298          */
1299         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1300                         i++) {
1301                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1302                         continue;
1303                 if (newcon->index >= 0 &&
1304                     newcon->index != console_cmdline[i].index)
1305                         continue;
1306                 if (newcon->index < 0)
1307                         newcon->index = console_cmdline[i].index;
1308 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1309                 if (console_cmdline[i].brl_options) {
1310                         newcon->flags |= CON_BRL;
1311                         braille_register_console(newcon,
1312                                         console_cmdline[i].index,
1313                                         console_cmdline[i].options,
1314                                         console_cmdline[i].brl_options);
1315                         return;
1316                 }
1317 #endif
1318                 if (newcon->setup &&
1319                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1320                         break;
1321                 newcon->flags |= CON_ENABLED;
1322                 newcon->index = console_cmdline[i].index;
1323                 if (i == selected_console) {
1324                         newcon->flags |= CON_CONSDEV;
1325                         preferred_console = selected_console;
1326                 }
1327                 break;
1328         }
1329
1330         if (!(newcon->flags & CON_ENABLED))
1331                 return;
1332
1333         /*
1334          * If we have a bootconsole, and are switching to a real console,
1335          * don't print everything out again, since when the boot console, and
1336          * the real console are the same physical device, it's annoying to
1337          * see the beginning boot messages twice
1338          */
1339         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1340                 newcon->flags &= ~CON_PRINTBUFFER;
1341
1342         /*
1343          *      Put this console in the list - keep the
1344          *      preferred driver at the head of the list.
1345          */
1346         acquire_console_sem();
1347         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1348                 newcon->next = console_drivers;
1349                 console_drivers = newcon;
1350                 if (newcon->next)
1351                         newcon->next->flags &= ~CON_CONSDEV;
1352         } else {
1353                 newcon->next = console_drivers->next;
1354                 console_drivers->next = newcon;
1355         }
1356         if (newcon->flags & CON_PRINTBUFFER) {
1357                 /*
1358                  * release_console_sem() will print out the buffered messages
1359                  * for us.
1360                  */
1361                 spin_lock_irqsave(&logbuf_lock, flags);
1362                 con_start = log_start;
1363                 spin_unlock_irqrestore(&logbuf_lock, flags);
1364         }
1365         release_console_sem();
1366
1367         /*
1368          * By unregistering the bootconsoles after we enable the real console
1369          * we get the "console xxx enabled" message on all the consoles -
1370          * boot consoles, real consoles, etc - this is to ensure that end
1371          * users know there might be something in the kernel's log buffer that
1372          * went to the bootconsole (that they do not see on the real console)
1373          */
1374         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1375                 /* we need to iterate through twice, to make sure we print
1376                  * everything out, before we unregister the console(s)
1377                  */
1378                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1379                         newcon->name, newcon->index);
1380                 for_each_console(bcon)
1381                         if (bcon->flags & CON_BOOT)
1382                                 unregister_console(bcon);
1383         } else {
1384                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1385                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1386                         newcon->name, newcon->index);
1387         }
1388 }
1389 EXPORT_SYMBOL(register_console);
1390
1391 int unregister_console(struct console *console)
1392 {
1393         struct console *a, *b;
1394         int res = 1;
1395
1396 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1397         if (console->flags & CON_BRL)
1398                 return braille_unregister_console(console);
1399 #endif
1400
1401         acquire_console_sem();
1402         if (console_drivers == console) {
1403                 console_drivers=console->next;
1404                 res = 0;
1405         } else if (console_drivers) {
1406                 for (a=console_drivers->next, b=console_drivers ;
1407                      a; b=a, a=b->next) {
1408                         if (a == console) {
1409                                 b->next = a->next;
1410                                 res = 0;
1411                                 break;
1412                         }
1413                 }
1414         }
1415
1416         /*
1417          * If this isn't the last console and it has CON_CONSDEV set, we
1418          * need to set it on the next preferred console.
1419          */
1420         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1421                 console_drivers->flags |= CON_CONSDEV;
1422
1423         release_console_sem();
1424         return res;
1425 }
1426 EXPORT_SYMBOL(unregister_console);
1427
1428 static int __init printk_late_init(void)
1429 {
1430         struct console *con;
1431
1432         for_each_console(con) {
1433                 if (con->flags & CON_BOOT) {
1434                         printk(KERN_INFO "turn off boot console %s%d\n",
1435                                 con->name, con->index);
1436                         unregister_console(con);
1437                 }
1438         }
1439         hotcpu_notifier(console_cpu_notify, 0);
1440         return 0;
1441 }
1442 late_initcall(printk_late_init);
1443
1444 #if defined CONFIG_PRINTK
1445
1446 /*
1447  * printk rate limiting, lifted from the networking subsystem.
1448  *
1449  * This enforces a rate limit: not more than 10 kernel messages
1450  * every 5s to make a denial-of-service attack impossible.
1451  */
1452 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1453
1454 int __printk_ratelimit(const char *func)
1455 {
1456         return ___ratelimit(&printk_ratelimit_state, func);
1457 }
1458 EXPORT_SYMBOL(__printk_ratelimit);
1459
1460 /**
1461  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1462  * @caller_jiffies: pointer to caller's state
1463  * @interval_msecs: minimum interval between prints
1464  *
1465  * printk_timed_ratelimit() returns true if more than @interval_msecs
1466  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1467  * returned true.
1468  */
1469 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1470                         unsigned int interval_msecs)
1471 {
1472         if (*caller_jiffies == 0
1473                         || !time_in_range(jiffies, *caller_jiffies,
1474                                         *caller_jiffies
1475                                         + msecs_to_jiffies(interval_msecs))) {
1476                 *caller_jiffies = jiffies;
1477                 return true;
1478         }
1479         return false;
1480 }
1481 EXPORT_SYMBOL(printk_timed_ratelimit);
1482
1483 static DEFINE_SPINLOCK(dump_list_lock);
1484 static LIST_HEAD(dump_list);
1485
1486 /**
1487  * kmsg_dump_register - register a kernel log dumper.
1488  * @dumper: pointer to the kmsg_dumper structure
1489  *
1490  * Adds a kernel log dumper to the system. The dump callback in the
1491  * structure will be called when the kernel oopses or panics and must be
1492  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1493  */
1494 int kmsg_dump_register(struct kmsg_dumper *dumper)
1495 {
1496         unsigned long flags;
1497         int err = -EBUSY;
1498
1499         /* The dump callback needs to be set */
1500         if (!dumper->dump)
1501                 return -EINVAL;
1502
1503         spin_lock_irqsave(&dump_list_lock, flags);
1504         /* Don't allow registering multiple times */
1505         if (!dumper->registered) {
1506                 dumper->registered = 1;
1507                 list_add_tail(&dumper->list, &dump_list);
1508                 err = 0;
1509         }
1510         spin_unlock_irqrestore(&dump_list_lock, flags);
1511
1512         return err;
1513 }
1514 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1515
1516 /**
1517  * kmsg_dump_unregister - unregister a kmsg dumper.
1518  * @dumper: pointer to the kmsg_dumper structure
1519  *
1520  * Removes a dump device from the system. Returns zero on success and
1521  * %-EINVAL otherwise.
1522  */
1523 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1524 {
1525         unsigned long flags;
1526         int err = -EINVAL;
1527
1528         spin_lock_irqsave(&dump_list_lock, flags);
1529         if (dumper->registered) {
1530                 dumper->registered = 0;
1531                 list_del(&dumper->list);
1532                 err = 0;
1533         }
1534         spin_unlock_irqrestore(&dump_list_lock, flags);
1535
1536         return err;
1537 }
1538 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1539
1540 static const char * const kmsg_reasons[] = {
1541         [KMSG_DUMP_OOPS]        = "oops",
1542         [KMSG_DUMP_PANIC]       = "panic",
1543         [KMSG_DUMP_KEXEC]       = "kexec",
1544 };
1545
1546 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1547 {
1548         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1549                 return "unknown";
1550
1551         return kmsg_reasons[reason];
1552 }
1553
1554 /**
1555  * kmsg_dump - dump kernel log to kernel message dumpers.
1556  * @reason: the reason (oops, panic etc) for dumping
1557  *
1558  * Iterate through each of the dump devices and call the oops/panic
1559  * callbacks with the log buffer.
1560  */
1561 void kmsg_dump(enum kmsg_dump_reason reason)
1562 {
1563         unsigned long end;
1564         unsigned chars;
1565         struct kmsg_dumper *dumper;
1566         const char *s1, *s2;
1567         unsigned long l1, l2;
1568         unsigned long flags;
1569
1570         /* Theoretically, the log could move on after we do this, but
1571            there's not a lot we can do about that. The new messages
1572            will overwrite the start of what we dump. */
1573         spin_lock_irqsave(&logbuf_lock, flags);
1574         end = log_end & LOG_BUF_MASK;
1575         chars = logged_chars;
1576         spin_unlock_irqrestore(&logbuf_lock, flags);
1577
1578         if (chars > end) {
1579                 s1 = log_buf + log_buf_len - chars + end;
1580                 l1 = chars - end;
1581
1582                 s2 = log_buf;
1583                 l2 = end;
1584         } else {
1585                 s1 = "";
1586                 l1 = 0;
1587
1588                 s2 = log_buf + end - chars;
1589                 l2 = chars;
1590         }
1591
1592         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1593                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1594                                 kmsg_to_str(reason));
1595                 return;
1596         }
1597         list_for_each_entry(dumper, &dump_list, list)
1598                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1599         spin_unlock_irqrestore(&dump_list_lock, flags);
1600 }
1601 #endif