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/moduleparam.h>
30 #include <linux/interrupt.h> /* For in_interrupt() */
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/jiffies.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 */
60 * Low lever drivers may need that to know if they can schedule in
61 * their unblank() callback or not. So let's export it.
64 EXPORT_SYMBOL(oops_in_progress);
67 * console_sem protects the console_drivers list, and also
68 * provides serialisation for access to the entire console
71 static DECLARE_MUTEX(console_sem);
72 static DECLARE_MUTEX(secondary_console_sem);
73 struct console *console_drivers;
75 * This is used for debugging the mess that is the VT code by
76 * keeping track if we have the console semaphore held. It's
77 * definitely not the perfect debug tool (we don't know if _WE_
78 * hold it are racing, but it helps tracking those weird code
79 * path in the console code where we end up in places I want
80 * locked without the console sempahore held
82 static int console_locked, console_suspended;
85 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
86 * It is also used in interesting ways to provide interlocking in
87 * release_console_sem().
89 static DEFINE_SPINLOCK(logbuf_lock);
91 #define LOG_BUF_MASK (log_buf_len-1)
92 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
95 * The indices into log_buf are not constrained to log_buf_len - they
96 * must be masked before subscripting
98 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
99 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
100 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
103 * Array of consoles built from command line options (console=)
105 struct console_cmdline
107 char name[8]; /* Name of the driver */
108 int index; /* Minor dev. to use */
109 char *options; /* Options for the driver */
112 #define MAX_CMDLINECONSOLES 8
114 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
115 static int selected_console = -1;
116 static int preferred_console = -1;
118 /* Flag: console code may call schedule() */
119 static int console_may_schedule;
123 static char __log_buf[__LOG_BUF_LEN];
124 static char *log_buf = __log_buf;
125 static int log_buf_len = __LOG_BUF_LEN;
126 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
128 static int __init log_buf_len_setup(char *str)
130 unsigned long size = memparse(str, &str);
134 size = roundup_pow_of_two(size);
135 if (size > log_buf_len) {
136 unsigned long start, dest_idx, offset;
139 new_log_buf = alloc_bootmem(size);
141 printk(KERN_WARNING "log_buf_len: allocation failed\n");
145 spin_lock_irqsave(&logbuf_lock, flags);
147 log_buf = new_log_buf;
149 offset = start = min(con_start, log_start);
151 while (start != log_end) {
152 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
159 spin_unlock_irqrestore(&logbuf_lock, flags);
161 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
167 __setup("log_buf_len=", log_buf_len_setup);
169 #ifdef CONFIG_BOOT_DELAY
171 extern unsigned int boot_delay; /* msecs to delay after each printk during bootup */
172 extern long preset_lpj;
173 extern unsigned long long printk_delay_msec;
175 static void boot_delay_msec(int millisecs)
177 unsigned long long k = printk_delay_msec * millisecs;
178 unsigned long timeout;
180 timeout = jiffies + msecs_to_jiffies(millisecs);
185 * use (volatile) jiffies to prevent
186 * compiler reduction; loop termination via jiffies
187 * is secondary and may or may not happen.
189 if (time_after(jiffies, timeout))
191 touch_nmi_watchdog();
198 * Commands to do_syslog:
200 * 0 -- Close the log. Currently a NOP.
201 * 1 -- Open the log. Currently a NOP.
202 * 2 -- Read from the log.
203 * 3 -- Read all messages remaining in the ring buffer.
204 * 4 -- Read and clear all messages remaining in the ring buffer
205 * 5 -- Clear ring buffer.
206 * 6 -- Disable printk's to console
207 * 7 -- Enable printk's to console
208 * 8 -- Set level of messages printed to console
209 * 9 -- Return number of unread characters in the log buffer
210 * 10 -- Return size of the log buffer
212 int do_syslog(int type, char __user *buf, int len)
214 unsigned long i, j, limit, count;
219 error = security_syslog(type);
223 if ((type >= 2) && (type <= 4)) {
230 if (!access_ok(VERIFY_WRITE, buf, len)) {
235 if (!vx_check(0, VS_ADMIN|VS_WATCH))
236 return vx_do_syslog(type, buf, len);
239 case 0: /* Close log */
241 case 1: /* Open log */
243 case 2: /* Read from log */
244 error = wait_event_interruptible(log_wait,
245 (log_start - log_end));
249 spin_lock_irq(&logbuf_lock);
250 while (!error && (log_start != log_end) && i < len) {
251 c = LOG_BUF(log_start);
253 spin_unlock_irq(&logbuf_lock);
254 error = __put_user(c,buf);
258 spin_lock_irq(&logbuf_lock);
260 spin_unlock_irq(&logbuf_lock);
264 case 4: /* Read/clear last kernel messages */
267 case 3: /* Read last kernel messages */
269 if (count > log_buf_len)
271 spin_lock_irq(&logbuf_lock);
272 if (count > logged_chars)
273 count = logged_chars;
278 * __put_user() could sleep, and while we sleep
279 * printk() could overwrite the messages
280 * we try to copy to user space. Therefore
281 * the messages are copied in reverse. <manfreds>
283 for (i = 0; i < count && !error; i++) {
285 if (j + log_buf_len < log_end)
288 spin_unlock_irq(&logbuf_lock);
289 error = __put_user(c,&buf[count-1-i]);
291 spin_lock_irq(&logbuf_lock);
293 spin_unlock_irq(&logbuf_lock);
298 int offset = count-error;
299 /* buffer overflow during copy, correct user buffer. */
300 for (i = 0; i < error; i++) {
301 if (__get_user(c,&buf[i+offset]) ||
302 __put_user(c,&buf[i])) {
310 case 5: /* Clear ring buffer */
313 case 6: /* Disable logging to console */
314 console_loglevel = minimum_console_loglevel;
316 case 7: /* Enable logging to console */
317 console_loglevel = default_console_loglevel;
319 case 8: /* Set level of messages printed to console */
321 if (len < 1 || len > 8)
323 if (len < minimum_console_loglevel)
324 len = minimum_console_loglevel;
325 console_loglevel = len;
328 case 9: /* Number of chars in the log buffer */
329 error = log_end - log_start;
331 case 10: /* Size of the log buffer */
342 asmlinkage long sys_syslog(int type, char __user *buf, int len)
344 return do_syslog(type, buf, len);
348 * Call the console drivers on a range of log_buf
350 static void __call_console_drivers(unsigned long start, unsigned long end)
354 for (con = console_drivers; con; con = con->next) {
355 if ((con->flags & CON_ENABLED) && con->write &&
356 (cpu_online(smp_processor_id()) ||
357 (con->flags & CON_ANYTIME)))
358 con->write(con, &LOG_BUF(start), end - start);
362 static int __read_mostly ignore_loglevel;
364 static int __init ignore_loglevel_setup(char *str)
367 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
372 __setup("ignore_loglevel", ignore_loglevel_setup);
375 * Write out chars from start to end - 1 inclusive
377 static void _call_console_drivers(unsigned long start,
378 unsigned long end, int msg_log_level)
380 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
381 console_drivers && start != end) {
382 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
384 __call_console_drivers(start & LOG_BUF_MASK,
386 __call_console_drivers(0, end & LOG_BUF_MASK);
388 __call_console_drivers(start, end);
394 * Call the console drivers, asking them to write out
395 * log_buf[start] to log_buf[end - 1].
396 * The console_sem must be held.
398 static void call_console_drivers(unsigned long start, unsigned long end)
400 unsigned long cur_index, start_print;
401 static int msg_level = -1;
403 BUG_ON(((long)(start - end)) > 0);
407 while (cur_index != end) {
408 if (msg_level < 0 && ((end - cur_index) > 2) &&
409 LOG_BUF(cur_index + 0) == '<' &&
410 LOG_BUF(cur_index + 1) >= '0' &&
411 LOG_BUF(cur_index + 1) <= '7' &&
412 LOG_BUF(cur_index + 2) == '>') {
413 msg_level = LOG_BUF(cur_index + 1) - '0';
415 start_print = cur_index;
417 while (cur_index != end) {
418 char c = LOG_BUF(cur_index);
424 * printk() has already given us loglevel tags in
425 * the buffer. This code is here in case the
426 * log buffer has wrapped right round and scribbled
429 msg_level = default_message_loglevel;
431 _call_console_drivers(start_print, cur_index, msg_level);
433 start_print = cur_index;
438 _call_console_drivers(start_print, end, msg_level);
441 static void emit_log_char(char c)
443 LOG_BUF(log_end) = c;
445 if (log_end - log_start > log_buf_len)
446 log_start = log_end - log_buf_len;
447 if (log_end - con_start > log_buf_len)
448 con_start = log_end - log_buf_len;
449 if (logged_chars < log_buf_len)
454 * Zap console related locks when oopsing. Only zap at most once
455 * every 10 seconds, to leave time for slow consoles to print a
458 static void zap_locks(void)
460 static unsigned long oops_timestamp;
462 if (time_after_eq(jiffies, oops_timestamp) &&
463 !time_after(jiffies, oops_timestamp + 30 * HZ))
466 oops_timestamp = jiffies;
468 /* If a crash is occurring, make sure we can't deadlock */
469 spin_lock_init(&logbuf_lock);
470 /* And make sure that we print immediately */
471 init_MUTEX(&console_sem);
474 #if defined(CONFIG_PRINTK_TIME)
475 static int printk_time = 1;
477 static int printk_time = 0;
479 module_param(printk_time, int, S_IRUGO | S_IWUSR);
481 static int __init printk_time_setup(char *str)
489 __setup("time", printk_time_setup);
491 __attribute__((weak)) unsigned long long printk_clock(void)
493 return sched_clock();
496 /* Check if we have any console registered that can be called early in boot. */
497 static int have_callable_console(void)
501 for (con = console_drivers; con; con = con->next)
502 if (con->flags & CON_ANYTIME)
509 * printk - print a kernel message
510 * @fmt: format string
512 * This is printk. It can be called from any context. We want it to work.
514 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
515 * call the console drivers. If we fail to get the semaphore we place the output
516 * into the log buffer and return. The current holder of the console_sem will
517 * notice the new output in release_console_sem() and will send it to the
518 * consoles before releasing the semaphore.
520 * One effect of this deferred printing is that code which calls printk() and
521 * then changes console_loglevel may break. This is because console_loglevel
522 * is inspected when the actual printing occurs.
528 asmlinkage int printk(const char *fmt, ...)
534 r = vprintk(fmt, args);
537 #ifdef CONFIG_BOOT_DELAY
538 if (boot_delay && system_state == SYSTEM_BOOTING)
539 boot_delay_msec(boot_delay);
545 /* cpu currently holding logbuf_lock */
546 static volatile unsigned int printk_cpu = UINT_MAX;
548 asmlinkage int vprintk(const char *fmt, va_list args)
553 static char printk_buf[1024];
554 static int log_level_unknown = 1;
557 if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
558 /* If a crash is occurring during printk() on this CPU,
559 * make sure we can't deadlock */
562 /* This stops the holder of console_sem just where we want him */
563 local_irq_save(flags);
565 spin_lock(&logbuf_lock);
566 printk_cpu = smp_processor_id();
568 /* Emit the output into the temporary buffer */
569 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
572 * Copy the output into log_buf. If the caller didn't provide
573 * appropriate log level tags, we insert them here
575 for (p = printk_buf; *p; p++) {
576 if (log_level_unknown) {
577 /* log_level_unknown signals the start of a new line */
582 unsigned long long t;
583 unsigned long nanosec_rem;
586 * force the log level token to be
587 * before the time output.
589 if (p[0] == '<' && p[1] >='0' &&
590 p[1] <= '7' && p[2] == '>') {
595 loglev_char = default_message_loglevel
599 nanosec_rem = do_div(t, 1000000000);
606 for (tp = tbuf; tp < tbuf + tlen; tp++)
610 if (p[0] != '<' || p[1] < '0' ||
611 p[1] > '7' || p[2] != '>') {
613 emit_log_char(default_message_loglevel
619 log_level_unknown = 0;
625 log_level_unknown = 1;
628 if (!down_trylock(&console_sem)) {
630 * We own the drivers. We can drop the spinlock and
631 * let release_console_sem() print the text, maybe ...
634 printk_cpu = UINT_MAX;
635 spin_unlock(&logbuf_lock);
638 * Console drivers may assume that per-cpu resources have
639 * been allocated. So unless they're explicitly marked as
640 * being able to cope (CON_ANYTIME) don't call them until
641 * this CPU is officially up.
643 if (cpu_online(smp_processor_id()) || have_callable_console()) {
644 console_may_schedule = 0;
645 release_console_sem();
647 /* Release by hand to avoid flushing the buffer. */
652 local_irq_restore(flags);
655 * Someone else owns the drivers. We drop the spinlock, which
656 * allows the semaphore holder to proceed and to call the
657 * console drivers with the output which we just produced.
659 printk_cpu = UINT_MAX;
660 spin_unlock(&logbuf_lock);
662 local_irq_restore(flags);
668 EXPORT_SYMBOL(printk);
669 EXPORT_SYMBOL(vprintk);
673 asmlinkage long sys_syslog(int type, char __user *buf, int len)
678 static void call_console_drivers(unsigned long start, unsigned long end)
685 * Set up a list of consoles. Called from init/main.c
687 static int __init console_setup(char *str)
689 char name[sizeof(console_cmdline[0].name)];
694 * Decode str into name, index, options.
696 if (str[0] >= '0' && str[0] <= '9') {
697 strcpy(name, "ttyS");
698 strncpy(name + 4, str, sizeof(name) - 5);
700 strncpy(name, str, sizeof(name) - 1);
702 name[sizeof(name) - 1] = 0;
703 if ((options = strchr(str, ',')) != NULL)
706 if (!strcmp(str, "ttya"))
707 strcpy(name, "ttyS0");
708 if (!strcmp(str, "ttyb"))
709 strcpy(name, "ttyS1");
711 for (s = name; *s; s++)
712 if ((*s >= '0' && *s <= '9') || *s == ',')
714 idx = simple_strtoul(s, NULL, 10);
717 add_preferred_console(name, idx, options);
720 __setup("console=", console_setup);
723 * add_preferred_console - add a device to the list of preferred consoles.
726 * @options: options for this console
728 * The last preferred console added will be used for kernel messages
729 * and stdin/out/err for init. Normally this is used by console_setup
730 * above to handle user-supplied console arguments; however it can also
731 * be used by arch-specific code either to override the user or more
732 * commonly to provide a default console (ie from PROM variables) when
733 * the user has not supplied one.
735 int __init add_preferred_console(char *name, int idx, char *options)
737 struct console_cmdline *c;
741 * See if this tty is not yet registered, and
742 * if we have a slot free.
744 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
745 if (strcmp(console_cmdline[i].name, name) == 0 &&
746 console_cmdline[i].index == idx) {
747 selected_console = i;
750 if (i == MAX_CMDLINECONSOLES)
752 selected_console = i;
753 c = &console_cmdline[i];
754 memcpy(c->name, name, sizeof(c->name));
755 c->name[sizeof(c->name) - 1] = 0;
756 c->options = options;
761 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
763 * suspend_console - suspend the console subsystem
765 * This disables printk() while we go into suspend states
767 void suspend_console(void)
769 printk("Suspending console(s)\n");
770 acquire_console_sem();
771 console_suspended = 1;
774 void resume_console(void)
776 console_suspended = 0;
777 release_console_sem();
779 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
782 * acquire_console_sem - lock the console system for exclusive use.
784 * Acquires a semaphore which guarantees that the caller has
785 * exclusive access to the console system and the console_drivers list.
787 * Can sleep, returns nothing.
789 void acquire_console_sem(void)
791 BUG_ON(in_interrupt());
792 if (console_suspended) {
793 down(&secondary_console_sem);
798 console_may_schedule = 1;
800 EXPORT_SYMBOL(acquire_console_sem);
802 int try_acquire_console_sem(void)
804 if (down_trylock(&console_sem))
807 console_may_schedule = 0;
810 EXPORT_SYMBOL(try_acquire_console_sem);
812 int is_console_locked(void)
814 return console_locked;
818 * release_console_sem - unlock the console system
820 * Releases the semaphore which the caller holds on the console system
821 * and the console driver list.
823 * While the semaphore was held, console output may have been buffered
824 * by printk(). If this is the case, release_console_sem() emits
825 * the output prior to releasing the semaphore.
827 * If there is output waiting for klogd, we wake it up.
829 * release_console_sem() may be called from any context.
831 void release_console_sem(void)
834 unsigned long _con_start, _log_end;
835 unsigned long wake_klogd = 0;
837 if (console_suspended) {
838 up(&secondary_console_sem);
842 console_may_schedule = 0;
845 spin_lock_irqsave(&logbuf_lock, flags);
846 wake_klogd |= log_start - log_end;
847 if (con_start == log_end)
848 break; /* Nothing to print */
849 _con_start = con_start;
851 con_start = log_end; /* Flush */
852 spin_unlock(&logbuf_lock);
853 call_console_drivers(_con_start, _log_end);
854 local_irq_restore(flags);
858 spin_unlock_irqrestore(&logbuf_lock, flags);
859 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
860 wake_up_interruptible(&log_wait);
862 EXPORT_SYMBOL(release_console_sem);
865 * console_conditional_schedule - yield the CPU if required
867 * If the console code is currently allowed to sleep, and
868 * if this CPU should yield the CPU to another task, do
871 * Must be called within acquire_console_sem().
873 void __sched console_conditional_schedule(void)
875 if (console_may_schedule)
878 EXPORT_SYMBOL(console_conditional_schedule);
880 void console_print(const char *s)
882 printk(KERN_EMERG "%s", s);
884 EXPORT_SYMBOL(console_print);
886 void console_unblank(void)
891 * console_unblank can no longer be called in interrupt context unless
892 * oops_in_progress is set to 1..
894 if (oops_in_progress) {
895 if (down_trylock(&console_sem) != 0)
898 acquire_console_sem();
901 console_may_schedule = 0;
902 for (c = console_drivers; c != NULL; c = c->next)
903 if ((c->flags & CON_ENABLED) && c->unblank)
905 release_console_sem();
909 * Return the console tty driver structure and its associated index
911 struct tty_driver *console_device(int *index)
914 struct tty_driver *driver = NULL;
916 acquire_console_sem();
917 for (c = console_drivers; c != NULL; c = c->next) {
920 driver = c->device(c, index);
924 release_console_sem();
929 * Prevent further output on the passed console device so that (for example)
930 * serial drivers can disable console output before suspending a port, and can
931 * re-enable output afterwards.
933 void console_stop(struct console *console)
935 acquire_console_sem();
936 console->flags &= ~CON_ENABLED;
937 release_console_sem();
939 EXPORT_SYMBOL(console_stop);
941 void console_start(struct console *console)
943 acquire_console_sem();
944 console->flags |= CON_ENABLED;
945 release_console_sem();
947 EXPORT_SYMBOL(console_start);
950 * The console driver calls this routine during kernel initialization
951 * to register the console printing procedure with printk() and to
952 * print any messages that were printed by the kernel before the
953 * console driver was initialized.
955 void register_console(struct console *console)
960 if (preferred_console < 0)
961 preferred_console = selected_console;
964 * See if we want to use this console driver. If we
965 * didn't select a console we take the first one
966 * that registers here.
968 if (preferred_console < 0) {
969 if (console->index < 0)
971 if (console->setup == NULL ||
972 console->setup(console, NULL) == 0) {
973 console->flags |= CON_ENABLED | CON_CONSDEV;
974 preferred_console = 0;
979 * See if this console matches one we selected on
982 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
984 if (strcmp(console_cmdline[i].name, console->name) != 0)
986 if (console->index >= 0 &&
987 console->index != console_cmdline[i].index)
989 if (console->index < 0)
990 console->index = console_cmdline[i].index;
991 if (console->setup &&
992 console->setup(console, console_cmdline[i].options) != 0)
994 console->flags |= CON_ENABLED;
995 console->index = console_cmdline[i].index;
996 if (i == selected_console) {
997 console->flags |= CON_CONSDEV;
998 preferred_console = selected_console;
1003 if (!(console->flags & CON_ENABLED))
1006 if (console_drivers && (console_drivers->flags & CON_BOOT)) {
1007 unregister_console(console_drivers);
1008 console->flags &= ~CON_PRINTBUFFER;
1012 * Put this console in the list - keep the
1013 * preferred driver at the head of the list.
1015 acquire_console_sem();
1016 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1017 console->next = console_drivers;
1018 console_drivers = console;
1020 console->next->flags &= ~CON_CONSDEV;
1022 console->next = console_drivers->next;
1023 console_drivers->next = console;
1025 if (console->flags & CON_PRINTBUFFER) {
1027 * release_console_sem() will print out the buffered messages
1030 spin_lock_irqsave(&logbuf_lock, flags);
1031 con_start = log_start;
1032 spin_unlock_irqrestore(&logbuf_lock, flags);
1034 release_console_sem();
1036 EXPORT_SYMBOL(register_console);
1038 int unregister_console(struct console *console)
1040 struct console *a, *b;
1043 acquire_console_sem();
1044 if (console_drivers == console) {
1045 console_drivers=console->next;
1047 } else if (console_drivers) {
1048 for (a=console_drivers->next, b=console_drivers ;
1049 a; b=a, a=b->next) {
1058 /* If last console is removed, we re-enable picking the first
1059 * one that gets registered. Without that, pmac early boot console
1060 * would prevent fbcon from taking over.
1062 * If this isn't the last console and it has CON_CONSDEV set, we
1063 * need to set it on the next preferred console.
1065 if (console_drivers == NULL)
1066 preferred_console = selected_console;
1067 else if (console->flags & CON_CONSDEV)
1068 console_drivers->flags |= CON_CONSDEV;
1070 release_console_sem();
1073 EXPORT_SYMBOL(unregister_console);
1076 * tty_write_message - write a message to a certain tty, not just the console.
1077 * @tty: the destination tty_struct
1078 * @msg: the message to write
1080 * This is used for messages that need to be redirected to a specific tty.
1081 * We don't put it into the syslog queue right now maybe in the future if
1084 void tty_write_message(struct tty_struct *tty, char *msg)
1086 if (tty && tty->driver->write)
1087 tty->driver->write(tty, msg, strlen(msg));
1092 * printk rate limiting, lifted from the networking subsystem.
1094 * This enforces a rate limit: not more than one kernel message
1095 * every printk_ratelimit_jiffies to make a denial-of-service
1096 * attack impossible.
1098 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1100 static DEFINE_SPINLOCK(ratelimit_lock);
1101 static unsigned long toks = 10 * 5 * HZ;
1102 static unsigned long last_msg;
1104 unsigned long flags;
1105 unsigned long now = jiffies;
1107 spin_lock_irqsave(&ratelimit_lock, flags);
1108 toks += now - last_msg;
1110 if (toks > (ratelimit_burst * ratelimit_jiffies))
1111 toks = ratelimit_burst * ratelimit_jiffies;
1112 if (toks >= ratelimit_jiffies) {
1116 toks -= ratelimit_jiffies;
1117 spin_unlock_irqrestore(&ratelimit_lock, flags);
1119 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1123 spin_unlock_irqrestore(&ratelimit_lock, flags);
1126 EXPORT_SYMBOL(__printk_ratelimit);
1128 /* minimum time in jiffies between messages */
1129 int printk_ratelimit_jiffies = 5 * HZ;
1131 /* number of messages we send before ratelimiting */
1132 int printk_ratelimit_burst = 10;
1134 int printk_ratelimit(void)
1136 return __printk_ratelimit(printk_ratelimit_jiffies,
1137 printk_ratelimit_burst);
1139 EXPORT_SYMBOL(printk_ratelimit);
1142 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1143 * @caller_jiffies: pointer to caller's state
1144 * @interval_msecs: minimum interval between prints
1146 * printk_timed_ratelimit() returns true if more than @interval_msecs
1147 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1150 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1151 unsigned int interval_msecs)
1153 if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1154 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1159 EXPORT_SYMBOL(printk_timed_ratelimit);