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 <andrewm@uow.edu.au>
19 #include <linux/kernel.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/smp_lock.h>
24 #include <linux/console.h>
25 #include <linux/init.h>
26 #include <linux/jiffies.h>
27 #include <linux/nmi.h>
28 #include <linux/module.h>
29 #include <linux/interrupt.h> /* For in_interrupt() */
30 #include <linux/config.h>
31 #include <linux/delay.h>
32 #include <linux/smp.h>
33 #include <linux/security.h>
34 #include <linux/bootmem.h>
35 #include <linux/syscalls.h>
36 #include <linux/vs_base.h>
37 #include <linux/vs_cvirt.h>
39 #include <asm/uaccess.h>
41 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
43 /* printk's without a loglevel use this.. */
44 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
46 /* We show everything that is MORE important than this.. */
47 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
48 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
50 DECLARE_WAIT_QUEUE_HEAD(log_wait);
52 int console_printk[4] = {
53 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
54 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
55 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
56 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
59 EXPORT_SYMBOL(console_printk);
62 * Low lever drivers may need that to know if they can schedule in
63 * their unblank() callback or not. So let's export it.
66 EXPORT_SYMBOL(oops_in_progress);
69 * console_sem protects the console_drivers list, and also
70 * provides serialisation for access to the entire console
73 static DECLARE_MUTEX(console_sem);
74 static DECLARE_MUTEX(secondary_console_sem);
75 struct console *console_drivers;
77 * This is used for debugging the mess that is the VT code by
78 * keeping track if we have the console semaphore held. It's
79 * definitely not the perfect debug tool (we don't know if _WE_
80 * hold it are racing, but it helps tracking those weird code
81 * path in the console code where we end up in places I want
82 * locked without the console sempahore held
84 static int console_locked;
85 int console_suspended;
88 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
89 * It is also used in interesting ways to provide interlocking in
90 * release_console_sem().
92 static DEFINE_SPINLOCK(logbuf_lock);
94 #define LOG_BUF_MASK (log_buf_len-1)
95 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
98 * The indices into log_buf are not constrained to log_buf_len - they
99 * must be masked before subscripting
101 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
102 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
103 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
106 * Array of consoles built from command line options (console=)
108 struct console_cmdline
110 char name[8]; /* Name of the driver */
111 int index; /* Minor dev. to use */
112 char *options; /* Options for the driver */
115 #define MAX_CMDLINECONSOLES 8
117 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
118 static int selected_console = -1;
119 static int preferred_console = -1;
121 /* Flag: console code may call schedule() */
122 static int console_may_schedule;
126 static char __log_buf[__LOG_BUF_LEN];
127 static char *log_buf = __log_buf;
128 static int log_buf_len = __LOG_BUF_LEN;
129 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
131 static int __init log_buf_len_setup(char *str)
133 unsigned long size = memparse(str, &str);
137 size = roundup_pow_of_two(size);
138 if (size > log_buf_len) {
139 unsigned long start, dest_idx, offset;
142 new_log_buf = alloc_bootmem(size);
144 printk(KERN_WARNING "log_buf_len: allocation failed\n");
148 spin_lock_irqsave(&logbuf_lock, flags);
150 log_buf = new_log_buf;
152 offset = start = min(con_start, log_start);
154 while (start != log_end) {
155 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
162 spin_unlock_irqrestore(&logbuf_lock, flags);
164 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
170 __setup("log_buf_len=", log_buf_len_setup);
172 #ifdef CONFIG_BOOT_DELAY
174 extern unsigned int boot_delay; /* msecs to delay after each printk during bootup */
175 extern long preset_lpj;
176 extern unsigned long long printk_delay_msec;
178 static void boot_delay_msec(int millisecs)
180 unsigned long long k = printk_delay_msec * millisecs;
181 unsigned long timeout;
183 timeout = jiffies + msecs_to_jiffies(millisecs);
188 * use (volatile) jiffies to prevent
189 * compiler reduction; loop termination via jiffies
190 * is secondary and may or may not happen.
192 if (time_after(jiffies, timeout))
194 touch_nmi_watchdog();
201 * Commands to do_syslog:
203 * 0 -- Close the log. Currently a NOP.
204 * 1 -- Open the log. Currently a NOP.
205 * 2 -- Read from the log.
206 * 3 -- Read all messages remaining in the ring buffer.
207 * 4 -- Read and clear all messages remaining in the ring buffer
208 * 5 -- Clear ring buffer.
209 * 6 -- Disable printk's to console
210 * 7 -- Enable printk's to console
211 * 8 -- Set level of messages printed to console
212 * 9 -- Return number of unread characters in the log buffer
213 * 10 -- Return size of the log buffer
215 int do_syslog(int type, char __user *buf, int len)
217 unsigned long i, j, limit, count;
222 error = security_syslog(type);
226 if ((type >= 2) && (type <= 4)) {
233 if (!access_ok(VERIFY_WRITE, buf, len)) {
238 if (!vx_check(0, VX_ADMIN|VX_WATCH))
239 return vx_do_syslog(type, buf, len);
242 case 0: /* Close log */
244 case 1: /* Open log */
246 case 2: /* Read from log */
247 error = wait_event_interruptible(log_wait,
248 (log_start - log_end));
252 spin_lock_irq(&logbuf_lock);
253 while (!error && (log_start != log_end) && i < len) {
254 c = LOG_BUF(log_start);
256 spin_unlock_irq(&logbuf_lock);
257 error = __put_user(c,buf);
261 spin_lock_irq(&logbuf_lock);
263 spin_unlock_irq(&logbuf_lock);
267 case 4: /* Read/clear last kernel messages */
270 case 3: /* Read last kernel messages */
272 if (count > log_buf_len)
274 spin_lock_irq(&logbuf_lock);
275 if (count > logged_chars)
276 count = logged_chars;
281 * __put_user() could sleep, and while we sleep
282 * printk() could overwrite the messages
283 * we try to copy to user space. Therefore
284 * the messages are copied in reverse. <manfreds>
286 for (i = 0; i < count && !error; i++) {
288 if (j + log_buf_len < log_end)
291 spin_unlock_irq(&logbuf_lock);
292 error = __put_user(c,&buf[count-1-i]);
294 spin_lock_irq(&logbuf_lock);
296 spin_unlock_irq(&logbuf_lock);
301 int offset = count-error;
302 /* buffer overflow during copy, correct user buffer. */
303 for (i = 0; i < error; i++) {
304 if (__get_user(c,&buf[i+offset]) ||
305 __put_user(c,&buf[i])) {
313 case 5: /* Clear ring buffer */
316 case 6: /* Disable logging to console */
317 console_loglevel = minimum_console_loglevel;
319 case 7: /* Enable logging to console */
320 console_loglevel = default_console_loglevel;
322 case 8: /* Set level of messages printed to console */
324 if (len < 1 || len > 8)
326 if (len < minimum_console_loglevel)
327 len = minimum_console_loglevel;
328 console_loglevel = len;
331 case 9: /* Number of chars in the log buffer */
332 error = log_end - log_start;
334 case 10: /* Size of the log buffer */
345 asmlinkage long sys_syslog(int type, char __user *buf, int len)
347 return do_syslog(type, buf, len);
351 * Call the console drivers on a range of log_buf
353 static void __call_console_drivers(unsigned long start, unsigned long end)
357 for (con = console_drivers; con; con = con->next) {
358 if ((con->flags & CON_ENABLED) && con->write)
359 con->write(con, &LOG_BUF(start), end - start);
364 * Write out chars from start to end - 1 inclusive
366 static void _call_console_drivers(unsigned long start,
367 unsigned long end, int msg_log_level)
369 if (msg_log_level < console_loglevel &&
370 console_drivers && start != end) {
371 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
373 __call_console_drivers(start & LOG_BUF_MASK,
375 __call_console_drivers(0, end & LOG_BUF_MASK);
377 __call_console_drivers(start, end);
383 * Call the console drivers, asking them to write out
384 * log_buf[start] to log_buf[end - 1].
385 * The console_sem must be held.
387 static void call_console_drivers(unsigned long start, unsigned long end)
389 unsigned long cur_index, start_print;
390 static int msg_level = -1;
392 BUG_ON(((long)(start - end)) > 0);
396 while (cur_index != end) {
397 if (msg_level < 0 && ((end - cur_index) > 2) &&
398 LOG_BUF(cur_index + 0) == '<' &&
399 LOG_BUF(cur_index + 1) >= '0' &&
400 LOG_BUF(cur_index + 1) <= '7' &&
401 LOG_BUF(cur_index + 2) == '>') {
402 msg_level = LOG_BUF(cur_index + 1) - '0';
404 start_print = cur_index;
406 while (cur_index != end) {
407 char c = LOG_BUF(cur_index);
413 * printk() has already given us loglevel tags in
414 * the buffer. This code is here in case the
415 * log buffer has wrapped right round and scribbled
418 msg_level = default_message_loglevel;
420 _call_console_drivers(start_print, cur_index, msg_level);
422 start_print = cur_index;
427 _call_console_drivers(start_print, end, msg_level);
430 static void emit_log_char(char c)
432 LOG_BUF(log_end) = c;
434 if (log_end - log_start > log_buf_len)
435 log_start = log_end - log_buf_len;
436 if (log_end - con_start > log_buf_len)
437 con_start = log_end - log_buf_len;
438 if (logged_chars < log_buf_len)
443 * Zap console related locks when oopsing. Only zap at most once
444 * every 10 seconds, to leave time for slow consoles to print a
447 static void zap_locks(void)
449 static unsigned long oops_timestamp;
451 if (time_after_eq(jiffies, oops_timestamp) &&
452 !time_after(jiffies, oops_timestamp + 30 * HZ))
455 oops_timestamp = jiffies;
457 /* If a crash is occurring, make sure we can't deadlock */
458 spin_lock_init(&logbuf_lock);
459 /* And make sure that we print immediately */
460 init_MUTEX(&console_sem);
463 #if defined(CONFIG_PRINTK_TIME)
464 static int printk_time = 1;
466 static int printk_time = 0;
469 static int __init printk_time_setup(char *str)
477 __setup("time", printk_time_setup);
479 __attribute__((weak)) unsigned long long printk_clock(void)
481 return sched_clock();
485 * printk - print a kernel message
486 * @fmt: format string
488 * This is printk. It can be called from any context. We want it to work.
490 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
491 * call the console drivers. If we fail to get the semaphore we place the output
492 * into the log buffer and return. The current holder of the console_sem will
493 * notice the new output in release_console_sem() and will send it to the
494 * consoles before releasing the semaphore.
496 * One effect of this deferred printing is that code which calls printk() and
497 * then changes console_loglevel may break. This is because console_loglevel
498 * is inspected when the actual printing occurs.
504 asmlinkage int printk(const char *fmt, ...)
510 r = vprintk(fmt, args);
513 #ifdef CONFIG_BOOT_DELAY
514 if (boot_delay && system_state == SYSTEM_BOOTING)
515 boot_delay_msec(boot_delay);
521 /* cpu currently holding logbuf_lock */
522 static volatile unsigned int printk_cpu = UINT_MAX;
524 asmlinkage int vprintk(const char *fmt, va_list args)
529 static char printk_buf[1024];
530 static int log_level_unknown = 1;
533 if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
534 /* If a crash is occurring during printk() on this CPU,
535 * make sure we can't deadlock */
538 /* This stops the holder of console_sem just where we want him */
539 spin_lock_irqsave(&logbuf_lock, flags);
540 printk_cpu = smp_processor_id();
542 /* Emit the output into the temporary buffer */
543 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
546 * Copy the output into log_buf. If the caller didn't provide
547 * appropriate log level tags, we insert them here
549 for (p = printk_buf; *p; p++) {
550 if (log_level_unknown) {
551 /* log_level_unknown signals the start of a new line */
556 unsigned long long t;
557 unsigned long nanosec_rem;
560 * force the log level token to be
561 * before the time output.
563 if (p[0] == '<' && p[1] >='0' &&
564 p[1] <= '7' && p[2] == '>') {
569 loglev_char = default_message_loglevel
573 nanosec_rem = do_div(t, 1000000000);
580 for (tp = tbuf; tp < tbuf + tlen; tp++)
584 if (p[0] != '<' || p[1] < '0' ||
585 p[1] > '7' || p[2] != '>') {
587 emit_log_char(default_message_loglevel
593 log_level_unknown = 0;
599 log_level_unknown = 1;
602 if (!cpu_online(smp_processor_id())) {
604 * Some console drivers may assume that per-cpu resources have
605 * been allocated. So don't allow them to be called by this
606 * CPU until it is officially up. We shouldn't be calling into
607 * random console drivers on a CPU which doesn't exist yet..
609 printk_cpu = UINT_MAX;
610 spin_unlock_irqrestore(&logbuf_lock, flags);
613 if (!down_trylock(&console_sem)) {
616 * We own the drivers. We can drop the spinlock and let
617 * release_console_sem() print the text
619 printk_cpu = UINT_MAX;
620 spin_unlock_irqrestore(&logbuf_lock, flags);
621 console_may_schedule = 0;
622 release_console_sem();
625 * Someone else owns the drivers. We drop the spinlock, which
626 * allows the semaphore holder to proceed and to call the
627 * console drivers with the output which we just produced.
629 printk_cpu = UINT_MAX;
630 spin_unlock_irqrestore(&logbuf_lock, flags);
636 EXPORT_SYMBOL(printk);
637 EXPORT_SYMBOL(vprintk);
641 asmlinkage long sys_syslog(int type, char __user *buf, int len)
646 int do_syslog(int type, char __user *buf, int len)
651 static void call_console_drivers(unsigned long start, unsigned long end)
658 * Set up a list of consoles. Called from init/main.c
660 static int __init console_setup(char *str)
662 char name[sizeof(console_cmdline[0].name)];
667 * Decode str into name, index, options.
669 if (str[0] >= '0' && str[0] <= '9') {
670 strcpy(name, "ttyS");
671 strncpy(name + 4, str, sizeof(name) - 5);
673 strncpy(name, str, sizeof(name) - 1);
675 name[sizeof(name) - 1] = 0;
676 if ((options = strchr(str, ',')) != NULL)
679 if (!strcmp(str, "ttya"))
680 strcpy(name, "ttyS0");
681 if (!strcmp(str, "ttyb"))
682 strcpy(name, "ttyS1");
684 for (s = name; *s; s++)
685 if ((*s >= '0' && *s <= '9') || *s == ',')
687 idx = simple_strtoul(s, NULL, 10);
690 add_preferred_console(name, idx, options);
693 __setup("console=", console_setup);
696 * add_preferred_console - add a device to the list of preferred consoles.
699 * @options: options for this console
701 * The last preferred console added will be used for kernel messages
702 * and stdin/out/err for init. Normally this is used by console_setup
703 * above to handle user-supplied console arguments; however it can also
704 * be used by arch-specific code either to override the user or more
705 * commonly to provide a default console (ie from PROM variables) when
706 * the user has not supplied one.
708 int __init add_preferred_console(char *name, int idx, char *options)
710 struct console_cmdline *c;
714 * See if this tty is not yet registered, and
715 * if we have a slot free.
717 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
718 if (strcmp(console_cmdline[i].name, name) == 0 &&
719 console_cmdline[i].index == idx) {
720 selected_console = i;
723 if (i == MAX_CMDLINECONSOLES)
725 selected_console = i;
726 c = &console_cmdline[i];
727 memcpy(c->name, name, sizeof(c->name));
728 c->name[sizeof(c->name) - 1] = 0;
729 c->options = options;
735 * acquire_console_sem - lock the console system for exclusive use.
737 * Acquires a semaphore which guarantees that the caller has
738 * exclusive access to the console system and the console_drivers list.
740 * Can sleep, returns nothing.
742 void acquire_console_sem(void)
744 if (console_suspended) {
745 down(&secondary_console_sem);
749 BUG_ON(in_interrupt());
752 console_may_schedule = 1;
754 EXPORT_SYMBOL(acquire_console_sem);
756 int try_acquire_console_sem(void)
758 if (down_trylock(&console_sem))
761 console_may_schedule = 0;
764 EXPORT_SYMBOL(try_acquire_console_sem);
766 int is_console_locked(void)
768 return console_locked;
770 EXPORT_SYMBOL(is_console_locked);
773 * release_console_sem - unlock the console system
775 * Releases the semaphore which the caller holds on the console system
776 * and the console driver list.
778 * While the semaphore was held, console output may have been buffered
779 * by printk(). If this is the case, release_console_sem() emits
780 * the output prior to releasing the semaphore.
782 * If there is output waiting for klogd, we wake it up.
784 * release_console_sem() may be called from any context.
786 void release_console_sem(void)
789 unsigned long _con_start, _log_end;
790 unsigned long wake_klogd = 0;
792 if (console_suspended) {
793 up(&secondary_console_sem);
798 spin_lock_irqsave(&logbuf_lock, flags);
799 wake_klogd |= log_start - log_end;
800 if (con_start == log_end)
801 break; /* Nothing to print */
802 _con_start = con_start;
804 con_start = log_end; /* Flush */
805 spin_unlock(&logbuf_lock);
806 call_console_drivers(_con_start, _log_end);
807 local_irq_restore(flags);
810 console_may_schedule = 0;
812 spin_unlock_irqrestore(&logbuf_lock, flags);
813 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
814 wake_up_interruptible(&log_wait);
816 EXPORT_SYMBOL(release_console_sem);
819 * console_conditional_schedule - yield the CPU if required
821 * If the console code is currently allowed to sleep, and
822 * if this CPU should yield the CPU to another task, do
825 * Must be called within acquire_console_sem().
827 void __sched console_conditional_schedule(void)
829 if (console_may_schedule)
832 EXPORT_SYMBOL(console_conditional_schedule);
834 void console_print(const char *s)
836 printk(KERN_EMERG "%s", s);
838 EXPORT_SYMBOL(console_print);
840 void console_unblank(void)
845 * console_unblank can no longer be called in interrupt context unless
846 * oops_in_progress is set to 1..
848 if (oops_in_progress) {
849 if (down_trylock(&console_sem) != 0)
852 acquire_console_sem();
855 console_may_schedule = 0;
856 for (c = console_drivers; c != NULL; c = c->next)
857 if ((c->flags & CON_ENABLED) && c->unblank)
859 release_console_sem();
863 * Return the console tty driver structure and its associated index
865 struct tty_driver *console_device(int *index)
868 struct tty_driver *driver = NULL;
870 acquire_console_sem();
871 for (c = console_drivers; c != NULL; c = c->next) {
874 driver = c->device(c, index);
878 release_console_sem();
883 * Prevent further output on the passed console device so that (for example)
884 * serial drivers can disable console output before suspending a port, and can
885 * re-enable output afterwards.
887 void console_stop(struct console *console)
889 acquire_console_sem();
890 console->flags &= ~CON_ENABLED;
891 release_console_sem();
893 EXPORT_SYMBOL(console_stop);
895 void console_start(struct console *console)
897 acquire_console_sem();
898 console->flags |= CON_ENABLED;
899 release_console_sem();
901 EXPORT_SYMBOL(console_start);
904 * The console driver calls this routine during kernel initialization
905 * to register the console printing procedure with printk() and to
906 * print any messages that were printed by the kernel before the
907 * console driver was initialized.
909 void register_console(struct console *console)
914 if (preferred_console < 0)
915 preferred_console = selected_console;
918 * See if we want to use this console driver. If we
919 * didn't select a console we take the first one
920 * that registers here.
922 if (preferred_console < 0) {
923 if (console->index < 0)
925 if (console->setup == NULL ||
926 console->setup(console, NULL) == 0) {
927 console->flags |= CON_ENABLED | CON_CONSDEV;
928 preferred_console = 0;
933 * See if this console matches one we selected on
936 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
938 if (strcmp(console_cmdline[i].name, console->name) != 0)
940 if (console->index >= 0 &&
941 console->index != console_cmdline[i].index)
943 if (console->index < 0)
944 console->index = console_cmdline[i].index;
945 if (console->setup &&
946 console->setup(console, console_cmdline[i].options) != 0)
948 console->flags |= CON_ENABLED;
949 console->index = console_cmdline[i].index;
950 if (i == selected_console) {
951 console->flags |= CON_CONSDEV;
952 preferred_console = selected_console;
957 if (!(console->flags & CON_ENABLED))
960 if (console_drivers && (console_drivers->flags & CON_BOOT)) {
961 unregister_console(console_drivers);
962 console->flags &= ~CON_PRINTBUFFER;
966 * Put this console in the list - keep the
967 * preferred driver at the head of the list.
969 acquire_console_sem();
970 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
971 console->next = console_drivers;
972 console_drivers = console;
974 console->next->flags &= ~CON_CONSDEV;
976 console->next = console_drivers->next;
977 console_drivers->next = console;
979 if (console->flags & CON_PRINTBUFFER) {
981 * release_console_sem() will print out the buffered messages
984 spin_lock_irqsave(&logbuf_lock, flags);
985 con_start = log_start;
986 spin_unlock_irqrestore(&logbuf_lock, flags);
988 release_console_sem();
990 EXPORT_SYMBOL(register_console);
992 int unregister_console(struct console *console)
994 struct console *a, *b;
997 acquire_console_sem();
998 if (console_drivers == console) {
999 console_drivers=console->next;
1001 } else if (console_drivers) {
1002 for (a=console_drivers->next, b=console_drivers ;
1003 a; b=a, a=b->next) {
1012 /* If last console is removed, we re-enable picking the first
1013 * one that gets registered. Without that, pmac early boot console
1014 * would prevent fbcon from taking over.
1016 * If this isn't the last console and it has CON_CONSDEV set, we
1017 * need to set it on the next preferred console.
1019 if (console_drivers == NULL)
1020 preferred_console = selected_console;
1021 else if (console->flags & CON_CONSDEV)
1022 console_drivers->flags |= CON_CONSDEV;
1024 release_console_sem();
1027 EXPORT_SYMBOL(unregister_console);
1030 * tty_write_message - write a message to a certain tty, not just the console.
1031 * @tty: the destination tty_struct
1032 * @msg: the message to write
1034 * This is used for messages that need to be redirected to a specific tty.
1035 * We don't put it into the syslog queue right now maybe in the future if
1038 void tty_write_message(struct tty_struct *tty, char *msg)
1040 if (tty && tty->driver->write)
1041 tty->driver->write(tty, msg, strlen(msg));
1046 * printk rate limiting, lifted from the networking subsystem.
1048 * This enforces a rate limit: not more than one kernel message
1049 * every printk_ratelimit_jiffies to make a denial-of-service
1050 * attack impossible.
1052 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1054 static DEFINE_SPINLOCK(ratelimit_lock);
1055 static unsigned long toks = 10 * 5 * HZ;
1056 static unsigned long last_msg;
1058 unsigned long flags;
1059 unsigned long now = jiffies;
1061 spin_lock_irqsave(&ratelimit_lock, flags);
1062 toks += now - last_msg;
1064 if (toks > (ratelimit_burst * ratelimit_jiffies))
1065 toks = ratelimit_burst * ratelimit_jiffies;
1066 if (toks >= ratelimit_jiffies) {
1070 toks -= ratelimit_jiffies;
1071 spin_unlock_irqrestore(&ratelimit_lock, flags);
1073 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1077 spin_unlock_irqrestore(&ratelimit_lock, flags);
1080 EXPORT_SYMBOL(__printk_ratelimit);
1082 /* minimum time in jiffies between messages */
1083 int printk_ratelimit_jiffies = 5 * HZ;
1085 /* number of messages we send before ratelimiting */
1086 int printk_ratelimit_burst = 10;
1088 int printk_ratelimit(void)
1090 return __printk_ratelimit(printk_ratelimit_jiffies,
1091 printk_ratelimit_burst);
1093 EXPORT_SYMBOL(printk_ratelimit);