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/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>
36 #include <asm/uaccess.h>
39 * Architectures can override it:
41 void __attribute__((weak)) early_printk(const char *fmt, ...)
45 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
47 /* printk's without a loglevel use this.. */
48 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
50 /* We show everything that is MORE important than this.. */
51 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
52 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
54 DECLARE_WAIT_QUEUE_HEAD(log_wait);
56 int console_printk[4] = {
57 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
58 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
59 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
60 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
64 * Low level drivers may need that to know if they can schedule in
65 * their unblank() callback or not. So let's export it.
68 EXPORT_SYMBOL(oops_in_progress);
71 * console_sem protects the console_drivers list, and also
72 * provides serialisation for access to the entire console
75 static DECLARE_MUTEX(console_sem);
76 static DECLARE_MUTEX(secondary_console_sem);
77 struct console *console_drivers;
79 * This is used for debugging the mess that is the VT code by
80 * keeping track if we have the console semaphore held. It's
81 * definitely not the perfect debug tool (we don't know if _WE_
82 * hold it are racing, but it helps tracking those weird code
83 * path in the console code where we end up in places I want
84 * locked without the console sempahore held
86 static int console_locked, console_suspended;
89 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
90 * It is also used in interesting ways to provide interlocking in
91 * release_console_sem().
93 static DEFINE_SPINLOCK(logbuf_lock);
95 #define LOG_BUF_MASK (log_buf_len-1)
96 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
99 * The indices into log_buf are not constrained to log_buf_len - they
100 * must be masked before subscripting
102 static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
103 static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
104 static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
107 * Array of consoles built from command line options (console=)
109 struct console_cmdline
111 char name[8]; /* Name of the driver */
112 int index; /* Minor dev. to use */
113 char *options; /* Options for the driver */
114 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
115 char *brl_options; /* Options for braille driver */
119 #define MAX_CMDLINECONSOLES 8
121 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
122 static int selected_console = -1;
123 static int preferred_console = -1;
125 /* Flag: console code may call schedule() */
126 static int console_may_schedule;
130 static char __log_buf[__LOG_BUF_LEN];
131 static char *log_buf = __log_buf;
132 static int log_buf_len = __LOG_BUF_LEN;
133 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
135 static int __init log_buf_len_setup(char *str)
137 unsigned size = memparse(str, &str);
141 size = roundup_pow_of_two(size);
142 if (size > log_buf_len) {
143 unsigned start, dest_idx, offset;
146 new_log_buf = alloc_bootmem(size);
148 printk(KERN_WARNING "log_buf_len: allocation failed\n");
152 spin_lock_irqsave(&logbuf_lock, flags);
154 log_buf = new_log_buf;
156 offset = start = min(con_start, log_start);
158 while (start != log_end) {
159 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
166 spin_unlock_irqrestore(&logbuf_lock, flags);
168 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
174 __setup("log_buf_len=", log_buf_len_setup);
176 #ifdef CONFIG_BOOT_PRINTK_DELAY
178 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
179 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
181 static int __init boot_delay_setup(char *str)
184 unsigned long long loops_per_msec;
186 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
187 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
189 get_option(&str, &boot_delay);
190 if (boot_delay > 10 * 1000)
193 printk_delay_msec = loops_per_msec;
194 printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
195 "HZ: %d, printk_delay_msec: %llu\n",
196 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
199 __setup("boot_delay=", boot_delay_setup);
201 static void boot_delay_msec(void)
203 unsigned long long k;
204 unsigned long timeout;
206 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
209 k = (unsigned long long)printk_delay_msec * boot_delay;
211 timeout = jiffies + msecs_to_jiffies(boot_delay);
216 * use (volatile) jiffies to prevent
217 * compiler reduction; loop termination via jiffies
218 * is secondary and may or may not happen.
220 if (time_after(jiffies, timeout))
222 touch_nmi_watchdog();
226 static inline void boot_delay_msec(void)
232 * Return the number of unread characters in the log buffer.
234 static int log_buf_get_len(void)
240 * Copy a range of characters from the log buffer.
242 int log_buf_copy(char *dest, int idx, int len)
245 bool took_lock = false;
247 if (!oops_in_progress) {
248 spin_lock_irq(&logbuf_lock);
252 max = log_buf_get_len();
253 if (idx < 0 || idx >= max) {
259 idx += (log_end - max);
261 dest[len] = LOG_BUF(idx + len);
265 spin_unlock_irq(&logbuf_lock);
271 * Commands to do_syslog:
273 * 0 -- Close the log. Currently a NOP.
274 * 1 -- Open the log. Currently a NOP.
275 * 2 -- Read from the log.
276 * 3 -- Read all messages remaining in the ring buffer.
277 * 4 -- Read and clear all messages remaining in the ring buffer
278 * 5 -- Clear ring buffer.
279 * 6 -- Disable printk's to console
280 * 7 -- Enable printk's to console
281 * 8 -- Set level of messages printed to console
282 * 9 -- Return number of unread characters in the log buffer
283 * 10 -- Return size of the log buffer
285 int do_syslog(int type, char __user *buf, int len)
287 unsigned i, j, limit, count;
292 error = security_syslog(type);
297 case 0: /* Close log */
299 case 1: /* Open log */
301 case 2: /* Read from log */
308 if (!access_ok(VERIFY_WRITE, buf, len)) {
312 error = wait_event_interruptible(log_wait,
313 (log_start - log_end));
317 spin_lock_irq(&logbuf_lock);
318 while (!error && (log_start != log_end) && i < len) {
319 c = LOG_BUF(log_start);
321 spin_unlock_irq(&logbuf_lock);
322 error = __put_user(c,buf);
326 spin_lock_irq(&logbuf_lock);
328 spin_unlock_irq(&logbuf_lock);
332 case 4: /* Read/clear last kernel messages */
335 case 3: /* Read last kernel messages */
342 if (!access_ok(VERIFY_WRITE, buf, len)) {
347 if (count > log_buf_len)
349 spin_lock_irq(&logbuf_lock);
350 if (count > logged_chars)
351 count = logged_chars;
356 * __put_user() could sleep, and while we sleep
357 * printk() could overwrite the messages
358 * we try to copy to user space. Therefore
359 * the messages are copied in reverse. <manfreds>
361 for (i = 0; i < count && !error; i++) {
363 if (j + log_buf_len < log_end)
366 spin_unlock_irq(&logbuf_lock);
367 error = __put_user(c,&buf[count-1-i]);
369 spin_lock_irq(&logbuf_lock);
371 spin_unlock_irq(&logbuf_lock);
376 int offset = count-error;
377 /* buffer overflow during copy, correct user buffer. */
378 for (i = 0; i < error; i++) {
379 if (__get_user(c,&buf[i+offset]) ||
380 __put_user(c,&buf[i])) {
388 case 5: /* Clear ring buffer */
391 case 6: /* Disable logging to console */
392 console_loglevel = minimum_console_loglevel;
394 case 7: /* Enable logging to console */
395 console_loglevel = default_console_loglevel;
397 case 8: /* Set level of messages printed to console */
399 if (len < 1 || len > 8)
401 if (len < minimum_console_loglevel)
402 len = minimum_console_loglevel;
403 console_loglevel = len;
406 case 9: /* Number of chars in the log buffer */
407 error = log_end - log_start;
409 case 10: /* Size of the log buffer */
420 asmlinkage long sys_syslog(int type, char __user *buf, int len)
422 return do_syslog(type, buf, len);
426 * Call the console drivers on a range of log_buf
428 static void __call_console_drivers(unsigned start, unsigned end)
432 for (con = console_drivers; con; con = con->next) {
433 if ((con->flags & CON_ENABLED) && con->write &&
434 (cpu_online(smp_processor_id()) ||
435 (con->flags & CON_ANYTIME)))
436 con->write(con, &LOG_BUF(start), end - start);
440 static int __read_mostly ignore_loglevel;
442 static int __init ignore_loglevel_setup(char *str)
445 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
450 early_param("ignore_loglevel", ignore_loglevel_setup);
453 * Write out chars from start to end - 1 inclusive
455 static void _call_console_drivers(unsigned start,
456 unsigned end, int msg_log_level)
458 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
459 console_drivers && start != end) {
460 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
462 __call_console_drivers(start & LOG_BUF_MASK,
464 __call_console_drivers(0, end & LOG_BUF_MASK);
466 __call_console_drivers(start, end);
472 * Call the console drivers, asking them to write out
473 * log_buf[start] to log_buf[end - 1].
474 * The console_sem must be held.
476 static void call_console_drivers(unsigned start, unsigned end)
478 unsigned cur_index, start_print;
479 static int msg_level = -1;
481 BUG_ON(((int)(start - end)) > 0);
485 while (cur_index != end) {
486 if (msg_level < 0 && ((end - cur_index) > 2) &&
487 LOG_BUF(cur_index + 0) == '<' &&
488 LOG_BUF(cur_index + 1) >= '0' &&
489 LOG_BUF(cur_index + 1) <= '7' &&
490 LOG_BUF(cur_index + 2) == '>') {
491 msg_level = LOG_BUF(cur_index + 1) - '0';
493 start_print = cur_index;
495 while (cur_index != end) {
496 char c = LOG_BUF(cur_index);
502 * printk() has already given us loglevel tags in
503 * the buffer. This code is here in case the
504 * log buffer has wrapped right round and scribbled
507 msg_level = default_message_loglevel;
509 _call_console_drivers(start_print, cur_index, msg_level);
511 start_print = cur_index;
516 _call_console_drivers(start_print, end, msg_level);
519 static void emit_log_char(char c)
521 LOG_BUF(log_end) = c;
523 if (log_end - log_start > log_buf_len)
524 log_start = log_end - log_buf_len;
525 if (log_end - con_start > log_buf_len)
526 con_start = log_end - log_buf_len;
527 if (logged_chars < log_buf_len)
532 * Zap console related locks when oopsing. Only zap at most once
533 * every 10 seconds, to leave time for slow consoles to print a
536 static void zap_locks(void)
538 static unsigned long oops_timestamp;
540 if (time_after_eq(jiffies, oops_timestamp) &&
541 !time_after(jiffies, oops_timestamp + 30 * HZ))
544 oops_timestamp = jiffies;
546 /* If a crash is occurring, make sure we can't deadlock */
547 spin_lock_init(&logbuf_lock);
548 /* And make sure that we print immediately */
549 init_MUTEX(&console_sem);
552 #if defined(CONFIG_PRINTK_TIME)
553 static int printk_time = 1;
555 static int printk_time = 0;
557 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
559 /* Check if we have any console registered that can be called early in boot. */
560 static int have_callable_console(void)
564 for (con = console_drivers; con; con = con->next)
565 if (con->flags & CON_ANYTIME)
572 * printk - print a kernel message
573 * @fmt: format string
575 * This is printk(). It can be called from any context. We want it to work.
576 * Be aware of the fact that if oops_in_progress is not set, we might try to
577 * wake klogd up which could deadlock on runqueue lock if printk() is called
578 * from scheduler code.
580 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
581 * call the console drivers. If we fail to get the semaphore we place the output
582 * into the log buffer and return. The current holder of the console_sem will
583 * notice the new output in release_console_sem() and will send it to the
584 * consoles before releasing the semaphore.
586 * One effect of this deferred printing is that code which calls printk() and
587 * then changes console_loglevel may break. This is because console_loglevel
588 * is inspected when the actual printing occurs.
594 asmlinkage int printk(const char *fmt, ...)
600 r = vprintk(fmt, args);
606 /* cpu currently holding logbuf_lock */
607 static volatile unsigned int printk_cpu = UINT_MAX;
610 * Can we actually use the console at this time on this cpu?
612 * Console drivers may assume that per-cpu resources have
613 * been allocated. So unless they're explicitly marked as
614 * being able to cope (CON_ANYTIME) don't call them until
615 * this CPU is officially up.
617 static inline int can_use_console(unsigned int cpu)
619 return cpu_online(cpu) || have_callable_console();
623 * Try to get console ownership to actually show the kernel
624 * messages from a 'printk'. Return true (and with the
625 * console_semaphore held, and 'console_locked' set) if it
626 * is successful, false otherwise.
628 * This gets called with the 'logbuf_lock' spinlock held and
629 * interrupts disabled. It should return with 'lockbuf_lock'
630 * released but interrupts still disabled.
632 static int acquire_console_semaphore_for_printk(unsigned int cpu)
636 if (!try_acquire_console_sem()) {
640 * If we can't use the console, we need to release
641 * the console semaphore by hand to avoid flushing
642 * the buffer. We need to hold the console semaphore
643 * in order to do this test safely.
645 if (!can_use_console(cpu)) {
651 printk_cpu = UINT_MAX;
652 spin_unlock(&logbuf_lock);
656 const char printk_recursion_bug_msg [] =
657 KERN_CRIT "BUG: recent printk recursion!\n";
658 static int printk_recursion_bug;
660 asmlinkage int vprintk(const char *fmt, va_list args)
662 static int log_level_unknown = 1;
663 static char printk_buf[1024];
673 /* This stops the holder of console_sem just where we want him */
674 raw_local_irq_save(flags);
675 this_cpu = smp_processor_id();
678 * Ouch, printk recursed into itself!
680 if (unlikely(printk_cpu == this_cpu)) {
682 * If a crash is occurring during printk() on this CPU,
683 * then try to get the crash message out but make sure
684 * we can't deadlock. Otherwise just return to avoid the
685 * recursion and return - but flag the recursion so that
686 * it can be printed at the next appropriate moment:
688 if (!oops_in_progress) {
689 printk_recursion_bug = 1;
690 goto out_restore_irqs;
696 spin_lock(&logbuf_lock);
697 printk_cpu = this_cpu;
699 if (printk_recursion_bug) {
700 printk_recursion_bug = 0;
701 strcpy(printk_buf, printk_recursion_bug_msg);
702 printed_len = sizeof(printk_recursion_bug_msg);
704 /* Emit the output into the temporary buffer */
705 printed_len += vscnprintf(printk_buf + printed_len,
706 sizeof(printk_buf) - printed_len, fmt, args);
709 * Copy the output into log_buf. If the caller didn't provide
710 * appropriate log level tags, we insert them here
712 for (p = printk_buf; *p; p++) {
713 if (log_level_unknown) {
714 /* log_level_unknown signals the start of a new line */
719 unsigned long long t;
720 unsigned long nanosec_rem;
723 * force the log level token to be
724 * before the time output.
726 if (p[0] == '<' && p[1] >='0' &&
727 p[1] <= '7' && p[2] == '>') {
732 loglev_char = default_message_loglevel
735 t = cpu_clock(printk_cpu);
736 nanosec_rem = do_div(t, 1000000000);
743 for (tp = tbuf; tp < tbuf + tlen; tp++)
747 if (p[0] != '<' || p[1] < '0' ||
748 p[1] > '7' || p[2] != '>') {
750 emit_log_char(default_message_loglevel
756 log_level_unknown = 0;
762 log_level_unknown = 1;
766 * Try to acquire and then immediately release the
767 * console semaphore. The release will do all the
768 * actual magic (print out buffers, wake up klogd,
771 * The acquire_console_semaphore_for_printk() function
772 * will release 'logbuf_lock' regardless of whether it
773 * actually gets the semaphore or not.
775 if (acquire_console_semaphore_for_printk(this_cpu))
776 release_console_sem();
780 raw_local_irq_restore(flags);
785 EXPORT_SYMBOL(printk);
786 EXPORT_SYMBOL(vprintk);
790 asmlinkage long sys_syslog(int type, char __user *buf, int len)
795 static void call_console_drivers(unsigned start, unsigned end)
801 static int __add_preferred_console(char *name, int idx, char *options,
804 struct console_cmdline *c;
808 * See if this tty is not yet registered, and
809 * if we have a slot free.
811 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
812 if (strcmp(console_cmdline[i].name, name) == 0 &&
813 console_cmdline[i].index == idx) {
815 selected_console = i;
818 if (i == MAX_CMDLINECONSOLES)
821 selected_console = i;
822 c = &console_cmdline[i];
823 strlcpy(c->name, name, sizeof(c->name));
824 c->options = options;
825 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
826 c->brl_options = brl_options;
832 * Set up a list of consoles. Called from init/main.c
834 static int __init console_setup(char *str)
836 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
837 char *s, *options, *brl_options = NULL;
840 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
841 if (!memcmp(str, "brl,", 4)) {
844 } else if (!memcmp(str, "brl=", 4)) {
845 brl_options = str + 4;
846 str = strchr(brl_options, ',');
848 printk(KERN_ERR "need port name after brl=\n");
856 * Decode str into name, index, options.
858 if (str[0] >= '0' && str[0] <= '9') {
860 strncpy(buf + 4, str, sizeof(buf) - 5);
862 strncpy(buf, str, sizeof(buf) - 1);
864 buf[sizeof(buf) - 1] = 0;
865 if ((options = strchr(str, ',')) != NULL)
868 if (!strcmp(str, "ttya"))
869 strcpy(buf, "ttyS0");
870 if (!strcmp(str, "ttyb"))
871 strcpy(buf, "ttyS1");
873 for (s = buf; *s; s++)
874 if ((*s >= '0' && *s <= '9') || *s == ',')
876 idx = simple_strtoul(s, NULL, 10);
879 __add_preferred_console(buf, idx, options, brl_options);
882 __setup("console=", console_setup);
885 * add_preferred_console - add a device to the list of preferred consoles.
888 * @options: options for this console
890 * The last preferred console added will be used for kernel messages
891 * and stdin/out/err for init. Normally this is used by console_setup
892 * above to handle user-supplied console arguments; however it can also
893 * be used by arch-specific code either to override the user or more
894 * commonly to provide a default console (ie from PROM variables) when
895 * the user has not supplied one.
897 int add_preferred_console(char *name, int idx, char *options)
899 return __add_preferred_console(name, idx, options, NULL);
902 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
904 struct console_cmdline *c;
907 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
908 if (strcmp(console_cmdline[i].name, name) == 0 &&
909 console_cmdline[i].index == idx) {
910 c = &console_cmdline[i];
911 strlcpy(c->name, name_new, sizeof(c->name));
912 c->name[sizeof(c->name) - 1] = 0;
913 c->options = options;
921 int console_suspend_enabled = 1;
922 EXPORT_SYMBOL(console_suspend_enabled);
924 static int __init console_suspend_disable(char *str)
926 console_suspend_enabled = 0;
929 __setup("no_console_suspend", console_suspend_disable);
932 * suspend_console - suspend the console subsystem
934 * This disables printk() while we go into suspend states
936 void suspend_console(void)
938 if (!console_suspend_enabled)
940 printk("Suspending console(s)\n");
941 acquire_console_sem();
942 console_suspended = 1;
945 void resume_console(void)
947 if (!console_suspend_enabled)
949 console_suspended = 0;
950 release_console_sem();
954 * acquire_console_sem - lock the console system for exclusive use.
956 * Acquires a semaphore which guarantees that the caller has
957 * exclusive access to the console system and the console_drivers list.
959 * Can sleep, returns nothing.
961 void acquire_console_sem(void)
963 BUG_ON(in_interrupt());
964 if (console_suspended) {
965 down(&secondary_console_sem);
970 console_may_schedule = 1;
972 EXPORT_SYMBOL(acquire_console_sem);
974 int try_acquire_console_sem(void)
976 if (down_trylock(&console_sem))
979 console_may_schedule = 0;
982 EXPORT_SYMBOL(try_acquire_console_sem);
984 int is_console_locked(void)
986 return console_locked;
989 void wake_up_klogd(void)
991 if (!oops_in_progress && waitqueue_active(&log_wait))
992 wake_up_interruptible(&log_wait);
996 * release_console_sem - unlock the console system
998 * Releases the semaphore which the caller holds on the console system
999 * and the console driver list.
1001 * While the semaphore was held, console output may have been buffered
1002 * by printk(). If this is the case, release_console_sem() emits
1003 * the output prior to releasing the semaphore.
1005 * If there is output waiting for klogd, we wake it up.
1007 * release_console_sem() may be called from any context.
1009 void release_console_sem(void)
1011 unsigned long flags;
1012 unsigned _con_start, _log_end;
1013 unsigned wake_klogd = 0;
1015 if (console_suspended) {
1016 up(&secondary_console_sem);
1020 console_may_schedule = 0;
1023 spin_lock_irqsave(&logbuf_lock, flags);
1024 wake_klogd |= log_start - log_end;
1025 if (con_start == log_end)
1026 break; /* Nothing to print */
1027 _con_start = con_start;
1029 con_start = log_end; /* Flush */
1030 spin_unlock(&logbuf_lock);
1031 call_console_drivers(_con_start, _log_end);
1032 local_irq_restore(flags);
1036 spin_unlock_irqrestore(&logbuf_lock, flags);
1040 EXPORT_SYMBOL(release_console_sem);
1043 * console_conditional_schedule - yield the CPU if required
1045 * If the console code is currently allowed to sleep, and
1046 * if this CPU should yield the CPU to another task, do
1049 * Must be called within acquire_console_sem().
1051 void __sched console_conditional_schedule(void)
1053 if (console_may_schedule)
1056 EXPORT_SYMBOL(console_conditional_schedule);
1058 void console_print(const char *s)
1060 printk(KERN_EMERG "%s", s);
1062 EXPORT_SYMBOL(console_print);
1064 void console_unblank(void)
1069 * console_unblank can no longer be called in interrupt context unless
1070 * oops_in_progress is set to 1..
1072 if (oops_in_progress) {
1073 if (down_trylock(&console_sem) != 0)
1076 acquire_console_sem();
1079 console_may_schedule = 0;
1080 for (c = console_drivers; c != NULL; c = c->next)
1081 if ((c->flags & CON_ENABLED) && c->unblank)
1083 release_console_sem();
1087 * Return the console tty driver structure and its associated index
1089 struct tty_driver *console_device(int *index)
1092 struct tty_driver *driver = NULL;
1094 acquire_console_sem();
1095 for (c = console_drivers; c != NULL; c = c->next) {
1098 driver = c->device(c, index);
1102 release_console_sem();
1107 * Prevent further output on the passed console device so that (for example)
1108 * serial drivers can disable console output before suspending a port, and can
1109 * re-enable output afterwards.
1111 void console_stop(struct console *console)
1113 acquire_console_sem();
1114 console->flags &= ~CON_ENABLED;
1115 release_console_sem();
1117 EXPORT_SYMBOL(console_stop);
1119 void console_start(struct console *console)
1121 acquire_console_sem();
1122 console->flags |= CON_ENABLED;
1123 release_console_sem();
1125 EXPORT_SYMBOL(console_start);
1128 * The console driver calls this routine during kernel initialization
1129 * to register the console printing procedure with printk() and to
1130 * print any messages that were printed by the kernel before the
1131 * console driver was initialized.
1133 void register_console(struct console *console)
1136 unsigned long flags;
1137 struct console *bootconsole = NULL;
1139 if (console_drivers) {
1140 if (console->flags & CON_BOOT)
1142 if (console_drivers->flags & CON_BOOT)
1143 bootconsole = console_drivers;
1146 if (preferred_console < 0 || bootconsole || !console_drivers)
1147 preferred_console = selected_console;
1149 if (console->early_setup)
1150 console->early_setup();
1153 * See if we want to use this console driver. If we
1154 * didn't select a console we take the first one
1155 * that registers here.
1157 if (preferred_console < 0) {
1158 if (console->index < 0)
1160 if (console->setup == NULL ||
1161 console->setup(console, NULL) == 0) {
1162 console->flags |= CON_ENABLED | CON_CONSDEV;
1163 preferred_console = 0;
1168 * See if this console matches one we selected on
1171 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1173 if (strcmp(console_cmdline[i].name, console->name) != 0)
1175 if (console->index >= 0 &&
1176 console->index != console_cmdline[i].index)
1178 if (console->index < 0)
1179 console->index = console_cmdline[i].index;
1180 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1181 if (console_cmdline[i].brl_options) {
1182 console->flags |= CON_BRL;
1183 braille_register_console(console,
1184 console_cmdline[i].index,
1185 console_cmdline[i].options,
1186 console_cmdline[i].brl_options);
1190 if (console->setup &&
1191 console->setup(console, console_cmdline[i].options) != 0)
1193 console->flags |= CON_ENABLED;
1194 console->index = console_cmdline[i].index;
1195 if (i == selected_console) {
1196 console->flags |= CON_CONSDEV;
1197 preferred_console = selected_console;
1202 if (!(console->flags & CON_ENABLED))
1205 if (bootconsole && (console->flags & CON_CONSDEV)) {
1206 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1207 bootconsole->name, bootconsole->index,
1208 console->name, console->index);
1209 unregister_console(bootconsole);
1210 console->flags &= ~CON_PRINTBUFFER;
1212 printk(KERN_INFO "console [%s%d] enabled\n",
1213 console->name, console->index);
1217 * Put this console in the list - keep the
1218 * preferred driver at the head of the list.
1220 acquire_console_sem();
1221 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1222 console->next = console_drivers;
1223 console_drivers = console;
1225 console->next->flags &= ~CON_CONSDEV;
1227 console->next = console_drivers->next;
1228 console_drivers->next = console;
1230 if (console->flags & CON_PRINTBUFFER) {
1232 * release_console_sem() will print out the buffered messages
1235 spin_lock_irqsave(&logbuf_lock, flags);
1236 con_start = log_start;
1237 spin_unlock_irqrestore(&logbuf_lock, flags);
1239 release_console_sem();
1241 EXPORT_SYMBOL(register_console);
1243 int unregister_console(struct console *console)
1245 struct console *a, *b;
1248 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1249 if (console->flags & CON_BRL)
1250 return braille_unregister_console(console);
1253 acquire_console_sem();
1254 if (console_drivers == console) {
1255 console_drivers=console->next;
1257 } else if (console_drivers) {
1258 for (a=console_drivers->next, b=console_drivers ;
1259 a; b=a, a=b->next) {
1269 * If this isn't the last console and it has CON_CONSDEV set, we
1270 * need to set it on the next preferred console.
1272 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1273 console_drivers->flags |= CON_CONSDEV;
1275 release_console_sem();
1278 EXPORT_SYMBOL(unregister_console);
1280 static int __init disable_boot_consoles(void)
1282 if (console_drivers != NULL) {
1283 if (console_drivers->flags & CON_BOOT) {
1284 printk(KERN_INFO "turn off boot console %s%d\n",
1285 console_drivers->name, console_drivers->index);
1286 return unregister_console(console_drivers);
1291 late_initcall(disable_boot_consoles);
1294 * tty_write_message - write a message to a certain tty, not just the console.
1295 * @tty: the destination tty_struct
1296 * @msg: the message to write
1298 * This is used for messages that need to be redirected to a specific tty.
1299 * We don't put it into the syslog queue right now maybe in the future if
1302 void tty_write_message(struct tty_struct *tty, char *msg)
1304 if (tty && tty->ops->write)
1305 tty->ops->write(tty, msg, strlen(msg));
1309 #if defined CONFIG_PRINTK
1311 * printk rate limiting, lifted from the networking subsystem.
1313 * This enforces a rate limit: not more than one kernel message
1314 * every printk_ratelimit_jiffies to make a denial-of-service
1315 * attack impossible.
1317 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1319 return __ratelimit(ratelimit_jiffies, ratelimit_burst);
1321 EXPORT_SYMBOL(__printk_ratelimit);
1323 /* minimum time in jiffies between messages */
1324 int printk_ratelimit_jiffies = 5 * HZ;
1326 /* number of messages we send before ratelimiting */
1327 int printk_ratelimit_burst = 10;
1329 int printk_ratelimit(void)
1331 return __printk_ratelimit(printk_ratelimit_jiffies,
1332 printk_ratelimit_burst);
1334 EXPORT_SYMBOL(printk_ratelimit);
1337 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1338 * @caller_jiffies: pointer to caller's state
1339 * @interval_msecs: minimum interval between prints
1341 * printk_timed_ratelimit() returns true if more than @interval_msecs
1342 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1345 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1346 unsigned int interval_msecs)
1348 if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1349 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1354 EXPORT_SYMBOL(printk_timed_ratelimit);