2 * linux/kernel/printk.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
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).
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
19 #include <linux/kernel.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/console.h>
24 #include <linux/init.h>
25 #include <linux/jiffies.h>
26 #include <linux/nmi.h>
27 #include <linux/module.h>
28 #include <linux/moduleparam.h>
29 #include <linux/interrupt.h> /* For in_interrupt() */
30 #include <linux/delay.h>
31 #include <linux/smp.h>
32 #include <linux/security.h>
33 #include <linux/bootmem.h>
34 #include <linux/syscalls.h>
35 #include <linux/kexec.h>
36 #include <linux/ratelimit.h>
37 #include <linux/kmsg_dump.h>
38 #include <linux/syslog.h>
40 #include <asm/uaccess.h>
43 * for_each_console() allows you to iterate on each console
45 #define for_each_console(con) \
46 for (con = console_drivers; con != NULL; con = con->next)
49 * Architectures can override it:
51 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
55 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
57 /* printk's without a loglevel use this.. */
58 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
60 /* We show everything that is MORE important than this.. */
61 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
62 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
64 DECLARE_WAIT_QUEUE_HEAD(log_wait);
66 int console_printk[4] = {
67 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
68 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
69 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
70 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
74 * Low level drivers may need that to know if they can schedule in
75 * their unblank() callback or not. So let's export it.
78 EXPORT_SYMBOL(oops_in_progress);
81 * console_sem protects the console_drivers list, and also
82 * provides serialisation for access to the entire console
85 static DECLARE_MUTEX(console_sem);
86 struct console *console_drivers;
87 EXPORT_SYMBOL_GPL(console_drivers);
90 * This is used for debugging the mess that is the VT code by
91 * keeping track if we have the console semaphore held. It's
92 * definitely not the perfect debug tool (we don't know if _WE_
93 * hold it are racing, but it helps tracking those weird code
94 * path in the console code where we end up in places I want
95 * locked without the console sempahore held
97 static int console_locked, console_suspended;
100 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
101 * It is also used in interesting ways to provide interlocking in
102 * release_console_sem().
104 static DEFINE_SPINLOCK(logbuf_lock);
106 #define LOG_BUF_MASK (log_buf_len-1)
107 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
110 * The indices into log_buf are not constrained to log_buf_len - they
111 * must be masked before subscripting
113 static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
114 static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
115 static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
118 * Array of consoles built from command line options (console=)
120 struct console_cmdline
122 char name[8]; /* Name of the driver */
123 int index; /* Minor dev. to use */
124 char *options; /* Options for the driver */
125 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
126 char *brl_options; /* Options for braille driver */
130 #define MAX_CMDLINECONSOLES 8
132 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
133 static int selected_console = -1;
134 static int preferred_console = -1;
135 int console_set_on_cmdline;
136 EXPORT_SYMBOL(console_set_on_cmdline);
138 /* Flag: console code may call schedule() */
139 static int console_may_schedule;
143 static char __log_buf[__LOG_BUF_LEN];
144 static char *log_buf = __log_buf;
145 static int log_buf_len = __LOG_BUF_LEN;
146 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
147 static int saved_console_loglevel = -1;
151 * This appends the listed symbols to /proc/vmcoreinfo
153 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
154 * obtain access to symbols that are otherwise very difficult to locate. These
155 * symbols are specifically used so that utilities can access and extract the
156 * dmesg log from a vmcore file after a crash.
158 void log_buf_kexec_setup(void)
160 VMCOREINFO_SYMBOL(log_buf);
161 VMCOREINFO_SYMBOL(log_end);
162 VMCOREINFO_SYMBOL(log_buf_len);
163 VMCOREINFO_SYMBOL(logged_chars);
167 static int __init log_buf_len_setup(char *str)
169 unsigned size = memparse(str, &str);
173 size = roundup_pow_of_two(size);
174 if (size > log_buf_len) {
175 unsigned start, dest_idx, offset;
178 new_log_buf = alloc_bootmem(size);
180 printk(KERN_WARNING "log_buf_len: allocation failed\n");
184 spin_lock_irqsave(&logbuf_lock, flags);
186 log_buf = new_log_buf;
188 offset = start = min(con_start, log_start);
190 while (start != log_end) {
191 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
198 spin_unlock_irqrestore(&logbuf_lock, flags);
200 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
206 __setup("log_buf_len=", log_buf_len_setup);
208 #ifdef CONFIG_BOOT_PRINTK_DELAY
210 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
211 static unsigned long long loops_per_msec; /* based on boot_delay */
213 static int __init boot_delay_setup(char *str)
217 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
218 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
220 get_option(&str, &boot_delay);
221 if (boot_delay > 10 * 1000)
224 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
225 "HZ: %d, loops_per_msec: %llu\n",
226 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
229 __setup("boot_delay=", boot_delay_setup);
231 static void boot_delay_msec(void)
233 unsigned long long k;
234 unsigned long timeout;
236 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
239 k = (unsigned long long)loops_per_msec * boot_delay;
241 timeout = jiffies + msecs_to_jiffies(boot_delay);
246 * use (volatile) jiffies to prevent
247 * compiler reduction; loop termination via jiffies
248 * is secondary and may or may not happen.
250 if (time_after(jiffies, timeout))
252 touch_nmi_watchdog();
256 static inline void boot_delay_msec(void)
261 int do_syslog(int type, char __user *buf, int len, bool from_file)
263 unsigned i, j, limit, count;
268 error = security_syslog(type, from_file);
273 case SYSLOG_ACTION_CLOSE: /* Close log */
275 case SYSLOG_ACTION_OPEN: /* Open log */
277 case SYSLOG_ACTION_READ: /* Read from log */
284 if (!access_ok(VERIFY_WRITE, buf, len)) {
288 error = wait_event_interruptible(log_wait,
289 (log_start - log_end));
293 spin_lock_irq(&logbuf_lock);
294 while (!error && (log_start != log_end) && i < len) {
295 c = LOG_BUF(log_start);
297 spin_unlock_irq(&logbuf_lock);
298 error = __put_user(c,buf);
302 spin_lock_irq(&logbuf_lock);
304 spin_unlock_irq(&logbuf_lock);
308 /* Read/clear last kernel messages */
309 case SYSLOG_ACTION_READ_CLEAR:
312 /* Read last kernel messages */
313 case SYSLOG_ACTION_READ_ALL:
320 if (!access_ok(VERIFY_WRITE, buf, len)) {
325 if (count > log_buf_len)
327 spin_lock_irq(&logbuf_lock);
328 if (count > logged_chars)
329 count = logged_chars;
334 * __put_user() could sleep, and while we sleep
335 * printk() could overwrite the messages
336 * we try to copy to user space. Therefore
337 * the messages are copied in reverse. <manfreds>
339 for (i = 0; i < count && !error; i++) {
341 if (j + log_buf_len < log_end)
344 spin_unlock_irq(&logbuf_lock);
345 error = __put_user(c,&buf[count-1-i]);
347 spin_lock_irq(&logbuf_lock);
349 spin_unlock_irq(&logbuf_lock);
354 int offset = count-error;
355 /* buffer overflow during copy, correct user buffer. */
356 for (i = 0; i < error; i++) {
357 if (__get_user(c,&buf[i+offset]) ||
358 __put_user(c,&buf[i])) {
366 /* Clear ring buffer */
367 case SYSLOG_ACTION_CLEAR:
370 /* Disable logging to console */
371 case SYSLOG_ACTION_CONSOLE_OFF:
372 if (saved_console_loglevel == -1)
373 saved_console_loglevel = console_loglevel;
374 console_loglevel = minimum_console_loglevel;
376 /* Enable logging to console */
377 case SYSLOG_ACTION_CONSOLE_ON:
378 if (saved_console_loglevel != -1) {
379 console_loglevel = saved_console_loglevel;
380 saved_console_loglevel = -1;
383 /* Set level of messages printed to console */
384 case SYSLOG_ACTION_CONSOLE_LEVEL:
386 if (len < 1 || len > 8)
388 if (len < minimum_console_loglevel)
389 len = minimum_console_loglevel;
390 console_loglevel = len;
391 /* Implicitly re-enable logging to console */
392 saved_console_loglevel = -1;
395 /* Number of chars in the log buffer */
396 case SYSLOG_ACTION_SIZE_UNREAD:
397 error = log_end - log_start;
399 /* Size of the log buffer */
400 case SYSLOG_ACTION_SIZE_BUFFER:
411 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
413 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
416 #ifdef CONFIG_KGDB_KDB
417 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
418 * uses locks so it cannot be used during debugging. Just tell kdb
419 * where the start and end of the physical and logical logs are. This
420 * is equivalent to do_syslog(3).
422 void kdb_syslog_data(char *syslog_data[4])
424 syslog_data[0] = log_buf;
425 syslog_data[1] = log_buf + log_buf_len;
426 syslog_data[2] = log_buf + log_end -
427 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
428 syslog_data[3] = log_buf + log_end;
430 #endif /* CONFIG_KGDB_KDB */
433 * Call the console drivers on a range of log_buf
435 static void __call_console_drivers(unsigned start, unsigned end)
439 for_each_console(con) {
440 if ((con->flags & CON_ENABLED) && con->write &&
441 (cpu_online(smp_processor_id()) ||
442 (con->flags & CON_ANYTIME)))
443 con->write(con, &LOG_BUF(start), end - start);
447 static int __read_mostly ignore_loglevel;
449 static int __init ignore_loglevel_setup(char *str)
452 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
457 early_param("ignore_loglevel", ignore_loglevel_setup);
460 * Write out chars from start to end - 1 inclusive
462 static void _call_console_drivers(unsigned start,
463 unsigned end, int msg_log_level)
465 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
466 console_drivers && start != end) {
467 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
469 __call_console_drivers(start & LOG_BUF_MASK,
471 __call_console_drivers(0, end & LOG_BUF_MASK);
473 __call_console_drivers(start, end);
479 * Call the console drivers, asking them to write out
480 * log_buf[start] to log_buf[end - 1].
481 * The console_sem must be held.
483 static void call_console_drivers(unsigned start, unsigned end)
485 unsigned cur_index, start_print;
486 static int msg_level = -1;
488 BUG_ON(((int)(start - end)) > 0);
492 while (cur_index != end) {
493 if (msg_level < 0 && ((end - cur_index) > 2) &&
494 LOG_BUF(cur_index + 0) == '<' &&
495 LOG_BUF(cur_index + 1) >= '0' &&
496 LOG_BUF(cur_index + 1) <= '7' &&
497 LOG_BUF(cur_index + 2) == '>') {
498 msg_level = LOG_BUF(cur_index + 1) - '0';
500 start_print = cur_index;
502 while (cur_index != end) {
503 char c = LOG_BUF(cur_index);
509 * printk() has already given us loglevel tags in
510 * the buffer. This code is here in case the
511 * log buffer has wrapped right round and scribbled
514 msg_level = default_message_loglevel;
516 _call_console_drivers(start_print, cur_index, msg_level);
518 start_print = cur_index;
523 _call_console_drivers(start_print, end, msg_level);
526 static void emit_log_char(char c)
528 LOG_BUF(log_end) = c;
530 if (log_end - log_start > log_buf_len)
531 log_start = log_end - log_buf_len;
532 if (log_end - con_start > log_buf_len)
533 con_start = log_end - log_buf_len;
534 if (logged_chars < log_buf_len)
539 * Zap console related locks when oopsing. Only zap at most once
540 * every 10 seconds, to leave time for slow consoles to print a
543 static void zap_locks(void)
545 static unsigned long oops_timestamp;
547 if (time_after_eq(jiffies, oops_timestamp) &&
548 !time_after(jiffies, oops_timestamp + 30 * HZ))
551 oops_timestamp = jiffies;
553 /* If a crash is occurring, make sure we can't deadlock */
554 spin_lock_init(&logbuf_lock);
555 /* And make sure that we print immediately */
556 init_MUTEX(&console_sem);
559 #if defined(CONFIG_PRINTK_TIME)
560 static int printk_time = 1;
562 static int printk_time = 0;
564 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
566 /* Check if we have any console registered that can be called early in boot. */
567 static int have_callable_console(void)
571 for_each_console(con)
572 if (con->flags & CON_ANYTIME)
579 * printk - print a kernel message
580 * @fmt: format string
582 * This is printk(). It can be called from any context. We want it to work.
584 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
585 * call the console drivers. If we fail to get the semaphore we place the output
586 * into the log buffer and return. The current holder of the console_sem will
587 * notice the new output in release_console_sem() and will send it to the
588 * consoles before releasing the semaphore.
590 * One effect of this deferred printing is that code which calls printk() and
591 * then changes console_loglevel may break. This is because console_loglevel
592 * is inspected when the actual printing occurs.
597 * See the vsnprintf() documentation for format string extensions over C99.
600 asmlinkage int printk(const char *fmt, ...)
606 r = vprintk(fmt, args);
612 /* cpu currently holding logbuf_lock */
613 static volatile unsigned int printk_cpu = UINT_MAX;
616 * Can we actually use the console at this time on this cpu?
618 * Console drivers may assume that per-cpu resources have
619 * been allocated. So unless they're explicitly marked as
620 * being able to cope (CON_ANYTIME) don't call them until
621 * this CPU is officially up.
623 static inline int can_use_console(unsigned int cpu)
625 return cpu_online(cpu) || have_callable_console();
629 * Try to get console ownership to actually show the kernel
630 * messages from a 'printk'. Return true (and with the
631 * console_semaphore held, and 'console_locked' set) if it
632 * is successful, false otherwise.
634 * This gets called with the 'logbuf_lock' spinlock held and
635 * interrupts disabled. It should return with 'lockbuf_lock'
636 * released but interrupts still disabled.
638 static int acquire_console_semaphore_for_printk(unsigned int cpu)
642 if (!try_acquire_console_sem()) {
646 * If we can't use the console, we need to release
647 * the console semaphore by hand to avoid flushing
648 * the buffer. We need to hold the console semaphore
649 * in order to do this test safely.
651 if (!can_use_console(cpu)) {
657 printk_cpu = UINT_MAX;
658 spin_unlock(&logbuf_lock);
661 static const char recursion_bug_msg [] =
662 KERN_CRIT "BUG: recent printk recursion!\n";
663 static int recursion_bug;
664 static int new_text_line = 1;
665 static char printk_buf[1024];
667 int printk_delay_msec __read_mostly;
669 static inline void printk_delay(void)
671 if (unlikely(printk_delay_msec)) {
672 int m = printk_delay_msec;
676 touch_nmi_watchdog();
681 asmlinkage int vprintk(const char *fmt, va_list args)
684 int current_log_level = default_message_loglevel;
693 /* This stops the holder of console_sem just where we want him */
694 raw_local_irq_save(flags);
695 this_cpu = smp_processor_id();
698 * Ouch, printk recursed into itself!
700 if (unlikely(printk_cpu == this_cpu)) {
702 * If a crash is occurring during printk() on this CPU,
703 * then try to get the crash message out but make sure
704 * we can't deadlock. Otherwise just return to avoid the
705 * recursion and return - but flag the recursion so that
706 * it can be printed at the next appropriate moment:
708 if (!oops_in_progress) {
710 goto out_restore_irqs;
716 spin_lock(&logbuf_lock);
717 printk_cpu = this_cpu;
721 strcpy(printk_buf, recursion_bug_msg);
722 printed_len = strlen(recursion_bug_msg);
724 /* Emit the output into the temporary buffer */
725 printed_len += vscnprintf(printk_buf + printed_len,
726 sizeof(printk_buf) - printed_len, fmt, args);
731 /* Do we have a loglevel in the string? */
733 unsigned char c = p[1];
734 if (c && p[2] == '>') {
736 case '0' ... '7': /* loglevel */
737 current_log_level = c - '0';
738 /* Fallthrough - make sure we're on a new line */
739 case 'd': /* KERN_DEFAULT */
740 if (!new_text_line) {
744 /* Fallthrough - skip the loglevel */
745 case 'c': /* KERN_CONT */
753 * Copy the output into log_buf. If the caller didn't provide
754 * appropriate log level tags, we insert them here
758 /* Always output the token */
760 emit_log_char(current_log_level + '0');
766 /* Follow the token with the time */
769 unsigned long long t;
770 unsigned long nanosec_rem;
772 t = cpu_clock(printk_cpu);
773 nanosec_rem = do_div(t, 1000000000);
774 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
778 for (tp = tbuf; tp < tbuf + tlen; tp++)
793 * Try to acquire and then immediately release the
794 * console semaphore. The release will do all the
795 * actual magic (print out buffers, wake up klogd,
798 * The acquire_console_semaphore_for_printk() function
799 * will release 'logbuf_lock' regardless of whether it
800 * actually gets the semaphore or not.
802 if (acquire_console_semaphore_for_printk(this_cpu))
803 release_console_sem();
807 raw_local_irq_restore(flags);
812 EXPORT_SYMBOL(printk);
813 EXPORT_SYMBOL(vprintk);
817 static void call_console_drivers(unsigned start, unsigned end)
823 static int __add_preferred_console(char *name, int idx, char *options,
826 struct console_cmdline *c;
830 * See if this tty is not yet registered, and
831 * if we have a slot free.
833 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
834 if (strcmp(console_cmdline[i].name, name) == 0 &&
835 console_cmdline[i].index == idx) {
837 selected_console = i;
840 if (i == MAX_CMDLINECONSOLES)
843 selected_console = i;
844 c = &console_cmdline[i];
845 strlcpy(c->name, name, sizeof(c->name));
846 c->options = options;
847 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
848 c->brl_options = brl_options;
854 * Set up a list of consoles. Called from init/main.c
856 static int __init console_setup(char *str)
858 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
859 char *s, *options, *brl_options = NULL;
862 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
863 if (!memcmp(str, "brl,", 4)) {
866 } else if (!memcmp(str, "brl=", 4)) {
867 brl_options = str + 4;
868 str = strchr(brl_options, ',');
870 printk(KERN_ERR "need port name after brl=\n");
878 * Decode str into name, index, options.
880 if (str[0] >= '0' && str[0] <= '9') {
882 strncpy(buf + 4, str, sizeof(buf) - 5);
884 strncpy(buf, str, sizeof(buf) - 1);
886 buf[sizeof(buf) - 1] = 0;
887 if ((options = strchr(str, ',')) != NULL)
890 if (!strcmp(str, "ttya"))
891 strcpy(buf, "ttyS0");
892 if (!strcmp(str, "ttyb"))
893 strcpy(buf, "ttyS1");
895 for (s = buf; *s; s++)
896 if ((*s >= '0' && *s <= '9') || *s == ',')
898 idx = simple_strtoul(s, NULL, 10);
901 __add_preferred_console(buf, idx, options, brl_options);
902 console_set_on_cmdline = 1;
905 __setup("console=", console_setup);
908 * add_preferred_console - add a device to the list of preferred consoles.
911 * @options: options for this console
913 * The last preferred console added will be used for kernel messages
914 * and stdin/out/err for init. Normally this is used by console_setup
915 * above to handle user-supplied console arguments; however it can also
916 * be used by arch-specific code either to override the user or more
917 * commonly to provide a default console (ie from PROM variables) when
918 * the user has not supplied one.
920 int add_preferred_console(char *name, int idx, char *options)
922 return __add_preferred_console(name, idx, options, NULL);
925 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
927 struct console_cmdline *c;
930 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
931 if (strcmp(console_cmdline[i].name, name) == 0 &&
932 console_cmdline[i].index == idx) {
933 c = &console_cmdline[i];
934 strlcpy(c->name, name_new, sizeof(c->name));
935 c->name[sizeof(c->name) - 1] = 0;
936 c->options = options;
944 int console_suspend_enabled = 1;
945 EXPORT_SYMBOL(console_suspend_enabled);
947 static int __init console_suspend_disable(char *str)
949 console_suspend_enabled = 0;
952 __setup("no_console_suspend", console_suspend_disable);
955 * suspend_console - suspend the console subsystem
957 * This disables printk() while we go into suspend states
959 void suspend_console(void)
961 if (!console_suspend_enabled)
963 printk("Suspending console(s) (use no_console_suspend to debug)\n");
964 acquire_console_sem();
965 console_suspended = 1;
969 void resume_console(void)
971 if (!console_suspend_enabled)
974 console_suspended = 0;
975 release_console_sem();
979 * acquire_console_sem - lock the console system for exclusive use.
981 * Acquires a semaphore which guarantees that the caller has
982 * exclusive access to the console system and the console_drivers list.
984 * Can sleep, returns nothing.
986 void acquire_console_sem(void)
988 BUG_ON(in_interrupt());
990 if (console_suspended)
993 console_may_schedule = 1;
995 EXPORT_SYMBOL(acquire_console_sem);
997 int try_acquire_console_sem(void)
999 if (down_trylock(&console_sem))
1001 if (console_suspended) {
1006 console_may_schedule = 0;
1009 EXPORT_SYMBOL(try_acquire_console_sem);
1011 int is_console_locked(void)
1013 return console_locked;
1016 static DEFINE_PER_CPU(int, printk_pending);
1018 void printk_tick(void)
1020 if (__get_cpu_var(printk_pending)) {
1021 __get_cpu_var(printk_pending) = 0;
1022 wake_up_interruptible(&log_wait);
1026 int printk_needs_cpu(int cpu)
1028 return per_cpu(printk_pending, cpu);
1031 void wake_up_klogd(void)
1033 if (waitqueue_active(&log_wait))
1034 __raw_get_cpu_var(printk_pending) = 1;
1038 * release_console_sem - unlock the console system
1040 * Releases the semaphore which the caller holds on the console system
1041 * and the console driver list.
1043 * While the semaphore was held, console output may have been buffered
1044 * by printk(). If this is the case, release_console_sem() emits
1045 * the output prior to releasing the semaphore.
1047 * If there is output waiting for klogd, we wake it up.
1049 * release_console_sem() may be called from any context.
1051 void release_console_sem(void)
1053 unsigned long flags;
1054 unsigned _con_start, _log_end;
1055 unsigned wake_klogd = 0;
1057 if (console_suspended) {
1062 console_may_schedule = 0;
1065 spin_lock_irqsave(&logbuf_lock, flags);
1066 wake_klogd |= log_start - log_end;
1067 if (con_start == log_end)
1068 break; /* Nothing to print */
1069 _con_start = con_start;
1071 con_start = log_end; /* Flush */
1072 spin_unlock(&logbuf_lock);
1073 stop_critical_timings(); /* don't trace print latency */
1074 call_console_drivers(_con_start, _log_end);
1075 start_critical_timings();
1076 local_irq_restore(flags);
1080 spin_unlock_irqrestore(&logbuf_lock, flags);
1084 EXPORT_SYMBOL(release_console_sem);
1087 * console_conditional_schedule - yield the CPU if required
1089 * If the console code is currently allowed to sleep, and
1090 * if this CPU should yield the CPU to another task, do
1093 * Must be called within acquire_console_sem().
1095 void __sched console_conditional_schedule(void)
1097 if (console_may_schedule)
1100 EXPORT_SYMBOL(console_conditional_schedule);
1102 void console_unblank(void)
1107 * console_unblank can no longer be called in interrupt context unless
1108 * oops_in_progress is set to 1..
1110 if (oops_in_progress) {
1111 if (down_trylock(&console_sem) != 0)
1114 acquire_console_sem();
1117 console_may_schedule = 0;
1119 if ((c->flags & CON_ENABLED) && c->unblank)
1121 release_console_sem();
1125 * Return the console tty driver structure and its associated index
1127 struct tty_driver *console_device(int *index)
1130 struct tty_driver *driver = NULL;
1132 acquire_console_sem();
1133 for_each_console(c) {
1136 driver = c->device(c, index);
1140 release_console_sem();
1145 * Prevent further output on the passed console device so that (for example)
1146 * serial drivers can disable console output before suspending a port, and can
1147 * re-enable output afterwards.
1149 void console_stop(struct console *console)
1151 acquire_console_sem();
1152 console->flags &= ~CON_ENABLED;
1153 release_console_sem();
1155 EXPORT_SYMBOL(console_stop);
1157 void console_start(struct console *console)
1159 acquire_console_sem();
1160 console->flags |= CON_ENABLED;
1161 release_console_sem();
1163 EXPORT_SYMBOL(console_start);
1166 * The console driver calls this routine during kernel initialization
1167 * to register the console printing procedure with printk() and to
1168 * print any messages that were printed by the kernel before the
1169 * console driver was initialized.
1171 * This can happen pretty early during the boot process (because of
1172 * early_printk) - sometimes before setup_arch() completes - be careful
1173 * of what kernel features are used - they may not be initialised yet.
1175 * There are two types of consoles - bootconsoles (early_printk) and
1176 * "real" consoles (everything which is not a bootconsole) which are
1177 * handled differently.
1178 * - Any number of bootconsoles can be registered at any time.
1179 * - As soon as a "real" console is registered, all bootconsoles
1180 * will be unregistered automatically.
1181 * - Once a "real" console is registered, any attempt to register a
1182 * bootconsoles will be rejected
1184 void register_console(struct console *newcon)
1187 unsigned long flags;
1188 struct console *bcon = NULL;
1191 * before we register a new CON_BOOT console, make sure we don't
1192 * already have a valid console
1194 if (console_drivers && newcon->flags & CON_BOOT) {
1195 /* find the last or real console */
1196 for_each_console(bcon) {
1197 if (!(bcon->flags & CON_BOOT)) {
1198 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1199 newcon->name, newcon->index);
1205 if (console_drivers && console_drivers->flags & CON_BOOT)
1206 bcon = console_drivers;
1208 if (preferred_console < 0 || bcon || !console_drivers)
1209 preferred_console = selected_console;
1211 if (newcon->early_setup)
1212 newcon->early_setup();
1215 * See if we want to use this console driver. If we
1216 * didn't select a console we take the first one
1217 * that registers here.
1219 if (preferred_console < 0) {
1220 if (newcon->index < 0)
1222 if (newcon->setup == NULL ||
1223 newcon->setup(newcon, NULL) == 0) {
1224 newcon->flags |= CON_ENABLED;
1225 if (newcon->device) {
1226 newcon->flags |= CON_CONSDEV;
1227 preferred_console = 0;
1233 * See if this console matches one we selected on
1236 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1238 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1240 if (newcon->index >= 0 &&
1241 newcon->index != console_cmdline[i].index)
1243 if (newcon->index < 0)
1244 newcon->index = console_cmdline[i].index;
1245 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1246 if (console_cmdline[i].brl_options) {
1247 newcon->flags |= CON_BRL;
1248 braille_register_console(newcon,
1249 console_cmdline[i].index,
1250 console_cmdline[i].options,
1251 console_cmdline[i].brl_options);
1255 if (newcon->setup &&
1256 newcon->setup(newcon, console_cmdline[i].options) != 0)
1258 newcon->flags |= CON_ENABLED;
1259 newcon->index = console_cmdline[i].index;
1260 if (i == selected_console) {
1261 newcon->flags |= CON_CONSDEV;
1262 preferred_console = selected_console;
1267 if (!(newcon->flags & CON_ENABLED))
1271 * If we have a bootconsole, and are switching to a real console,
1272 * don't print everything out again, since when the boot console, and
1273 * the real console are the same physical device, it's annoying to
1274 * see the beginning boot messages twice
1276 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1277 newcon->flags &= ~CON_PRINTBUFFER;
1280 * Put this console in the list - keep the
1281 * preferred driver at the head of the list.
1283 acquire_console_sem();
1284 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1285 newcon->next = console_drivers;
1286 console_drivers = newcon;
1288 newcon->next->flags &= ~CON_CONSDEV;
1290 newcon->next = console_drivers->next;
1291 console_drivers->next = newcon;
1293 if (newcon->flags & CON_PRINTBUFFER) {
1295 * release_console_sem() will print out the buffered messages
1298 spin_lock_irqsave(&logbuf_lock, flags);
1299 con_start = log_start;
1300 spin_unlock_irqrestore(&logbuf_lock, flags);
1302 release_console_sem();
1305 * By unregistering the bootconsoles after we enable the real console
1306 * we get the "console xxx enabled" message on all the consoles -
1307 * boot consoles, real consoles, etc - this is to ensure that end
1308 * users know there might be something in the kernel's log buffer that
1309 * went to the bootconsole (that they do not see on the real console)
1311 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1312 /* we need to iterate through twice, to make sure we print
1313 * everything out, before we unregister the console(s)
1315 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1316 newcon->name, newcon->index);
1317 for_each_console(bcon)
1318 if (bcon->flags & CON_BOOT)
1319 unregister_console(bcon);
1321 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1322 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1323 newcon->name, newcon->index);
1326 EXPORT_SYMBOL(register_console);
1328 int unregister_console(struct console *console)
1330 struct console *a, *b;
1333 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1334 if (console->flags & CON_BRL)
1335 return braille_unregister_console(console);
1338 acquire_console_sem();
1339 if (console_drivers == console) {
1340 console_drivers=console->next;
1342 } else if (console_drivers) {
1343 for (a=console_drivers->next, b=console_drivers ;
1344 a; b=a, a=b->next) {
1354 * If this isn't the last console and it has CON_CONSDEV set, we
1355 * need to set it on the next preferred console.
1357 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1358 console_drivers->flags |= CON_CONSDEV;
1360 release_console_sem();
1363 EXPORT_SYMBOL(unregister_console);
1365 static int __init disable_boot_consoles(void)
1367 struct console *con;
1369 for_each_console(con) {
1370 if (con->flags & CON_BOOT) {
1371 printk(KERN_INFO "turn off boot console %s%d\n",
1372 con->name, con->index);
1373 unregister_console(con);
1378 late_initcall(disable_boot_consoles);
1380 #if defined CONFIG_PRINTK
1383 * printk rate limiting, lifted from the networking subsystem.
1385 * This enforces a rate limit: not more than 10 kernel messages
1386 * every 5s to make a denial-of-service attack impossible.
1388 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1390 int __printk_ratelimit(const char *func)
1392 return ___ratelimit(&printk_ratelimit_state, func);
1394 EXPORT_SYMBOL(__printk_ratelimit);
1397 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1398 * @caller_jiffies: pointer to caller's state
1399 * @interval_msecs: minimum interval between prints
1401 * printk_timed_ratelimit() returns true if more than @interval_msecs
1402 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1405 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1406 unsigned int interval_msecs)
1408 if (*caller_jiffies == 0
1409 || !time_in_range(jiffies, *caller_jiffies,
1411 + msecs_to_jiffies(interval_msecs))) {
1412 *caller_jiffies = jiffies;
1417 EXPORT_SYMBOL(printk_timed_ratelimit);
1419 static DEFINE_SPINLOCK(dump_list_lock);
1420 static LIST_HEAD(dump_list);
1423 * kmsg_dump_register - register a kernel log dumper.
1424 * @dumper: pointer to the kmsg_dumper structure
1426 * Adds a kernel log dumper to the system. The dump callback in the
1427 * structure will be called when the kernel oopses or panics and must be
1428 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1430 int kmsg_dump_register(struct kmsg_dumper *dumper)
1432 unsigned long flags;
1435 /* The dump callback needs to be set */
1439 spin_lock_irqsave(&dump_list_lock, flags);
1440 /* Don't allow registering multiple times */
1441 if (!dumper->registered) {
1442 dumper->registered = 1;
1443 list_add_tail(&dumper->list, &dump_list);
1446 spin_unlock_irqrestore(&dump_list_lock, flags);
1450 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1453 * kmsg_dump_unregister - unregister a kmsg dumper.
1454 * @dumper: pointer to the kmsg_dumper structure
1456 * Removes a dump device from the system. Returns zero on success and
1457 * %-EINVAL otherwise.
1459 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1461 unsigned long flags;
1464 spin_lock_irqsave(&dump_list_lock, flags);
1465 if (dumper->registered) {
1466 dumper->registered = 0;
1467 list_del(&dumper->list);
1470 spin_unlock_irqrestore(&dump_list_lock, flags);
1474 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1476 static const char const *kmsg_reasons[] = {
1477 [KMSG_DUMP_OOPS] = "oops",
1478 [KMSG_DUMP_PANIC] = "panic",
1479 [KMSG_DUMP_KEXEC] = "kexec",
1482 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1484 if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1487 return kmsg_reasons[reason];
1491 * kmsg_dump - dump kernel log to kernel message dumpers.
1492 * @reason: the reason (oops, panic etc) for dumping
1494 * Iterate through each of the dump devices and call the oops/panic
1495 * callbacks with the log buffer.
1497 void kmsg_dump(enum kmsg_dump_reason reason)
1501 struct kmsg_dumper *dumper;
1502 const char *s1, *s2;
1503 unsigned long l1, l2;
1504 unsigned long flags;
1506 /* Theoretically, the log could move on after we do this, but
1507 there's not a lot we can do about that. The new messages
1508 will overwrite the start of what we dump. */
1509 spin_lock_irqsave(&logbuf_lock, flags);
1510 end = log_end & LOG_BUF_MASK;
1511 chars = logged_chars;
1512 spin_unlock_irqrestore(&logbuf_lock, flags);
1514 if (logged_chars > end) {
1515 s1 = log_buf + log_buf_len - logged_chars + end;
1516 l1 = logged_chars - end;
1524 s2 = log_buf + end - logged_chars;
1528 if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1529 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1530 kmsg_to_str(reason));
1533 list_for_each_entry(dumper, &dump_list, list)
1534 dumper->dump(dumper, reason, s1, l1, s2, l2);
1535 spin_unlock_irqrestore(&dump_list_lock, flags);