Linux 2.6.19-rc6
[cris-mirror.git] / kernel / printk.c
blob66426552fbfef24e49442ed08f8d595930feca32
1 /*
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).
11 * Ted Ts'o, 2/11/93.
12 * Modified for sysctl support, 1/8/97, Chris Horn.
13 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
14 * manfred@colorfullife.com
15 * Rewrote bits to get rid of console_lock
16 * 01Mar01 Andrew Morton <andrewm@uow.edu.au>
19 #include <linux/kernel.h>
20 #include <linux/mm.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/module.h>
27 #include <linux/moduleparam.h>
28 #include <linux/interrupt.h> /* For in_interrupt() */
29 #include <linux/delay.h>
30 #include <linux/smp.h>
31 #include <linux/security.h>
32 #include <linux/bootmem.h>
33 #include <linux/syscalls.h>
34 #include <linux/jiffies.h>
36 #include <asm/uaccess.h>
38 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
40 /* printk's without a loglevel use this.. */
41 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
43 /* We show everything that is MORE important than this.. */
44 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
45 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
47 DECLARE_WAIT_QUEUE_HEAD(log_wait);
49 int console_printk[4] = {
50 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
51 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
52 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
53 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
56 EXPORT_UNUSED_SYMBOL(console_printk); /* June 2006 */
59 * Low lever drivers may need that to know if they can schedule in
60 * their unblank() callback or not. So let's export it.
62 int oops_in_progress;
63 EXPORT_SYMBOL(oops_in_progress);
66 * console_sem protects the console_drivers list, and also
67 * provides serialisation for access to the entire console
68 * driver system.
70 static DECLARE_MUTEX(console_sem);
71 static DECLARE_MUTEX(secondary_console_sem);
72 struct console *console_drivers;
74 * This is used for debugging the mess that is the VT code by
75 * keeping track if we have the console semaphore held. It's
76 * definitely not the perfect debug tool (we don't know if _WE_
77 * hold it are racing, but it helps tracking those weird code
78 * path in the console code where we end up in places I want
79 * locked without the console sempahore held
81 static int console_locked, console_suspended;
84 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
85 * It is also used in interesting ways to provide interlocking in
86 * release_console_sem().
88 static DEFINE_SPINLOCK(logbuf_lock);
90 #define LOG_BUF_MASK (log_buf_len-1)
91 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
94 * The indices into log_buf are not constrained to log_buf_len - they
95 * must be masked before subscripting
97 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
98 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
99 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
102 * Array of consoles built from command line options (console=)
104 struct console_cmdline
106 char name[8]; /* Name of the driver */
107 int index; /* Minor dev. to use */
108 char *options; /* Options for the driver */
111 #define MAX_CMDLINECONSOLES 8
113 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
114 static int selected_console = -1;
115 static int preferred_console = -1;
117 /* Flag: console code may call schedule() */
118 static int console_may_schedule;
120 #ifdef CONFIG_PRINTK
122 static char __log_buf[__LOG_BUF_LEN];
123 static char *log_buf = __log_buf;
124 static int log_buf_len = __LOG_BUF_LEN;
125 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
127 static int __init log_buf_len_setup(char *str)
129 unsigned long size = memparse(str, &str);
130 unsigned long flags;
132 if (size)
133 size = roundup_pow_of_two(size);
134 if (size > log_buf_len) {
135 unsigned long start, dest_idx, offset;
136 char *new_log_buf;
138 new_log_buf = alloc_bootmem(size);
139 if (!new_log_buf) {
140 printk(KERN_WARNING "log_buf_len: allocation failed\n");
141 goto out;
144 spin_lock_irqsave(&logbuf_lock, flags);
145 log_buf_len = size;
146 log_buf = new_log_buf;
148 offset = start = min(con_start, log_start);
149 dest_idx = 0;
150 while (start != log_end) {
151 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
152 start++;
153 dest_idx++;
155 log_start -= offset;
156 con_start -= offset;
157 log_end -= offset;
158 spin_unlock_irqrestore(&logbuf_lock, flags);
160 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
162 out:
163 return 1;
166 __setup("log_buf_len=", log_buf_len_setup);
169 * Commands to do_syslog:
171 * 0 -- Close the log. Currently a NOP.
172 * 1 -- Open the log. Currently a NOP.
173 * 2 -- Read from the log.
174 * 3 -- Read all messages remaining in the ring buffer.
175 * 4 -- Read and clear all messages remaining in the ring buffer
176 * 5 -- Clear ring buffer.
177 * 6 -- Disable printk's to console
178 * 7 -- Enable printk's to console
179 * 8 -- Set level of messages printed to console
180 * 9 -- Return number of unread characters in the log buffer
181 * 10 -- Return size of the log buffer
183 int do_syslog(int type, char __user *buf, int len)
185 unsigned long i, j, limit, count;
186 int do_clear = 0;
187 char c;
188 int error = 0;
190 error = security_syslog(type);
191 if (error)
192 return error;
194 switch (type) {
195 case 0: /* Close log */
196 break;
197 case 1: /* Open log */
198 break;
199 case 2: /* Read from log */
200 error = -EINVAL;
201 if (!buf || len < 0)
202 goto out;
203 error = 0;
204 if (!len)
205 goto out;
206 if (!access_ok(VERIFY_WRITE, buf, len)) {
207 error = -EFAULT;
208 goto out;
210 error = wait_event_interruptible(log_wait,
211 (log_start - log_end));
212 if (error)
213 goto out;
214 i = 0;
215 spin_lock_irq(&logbuf_lock);
216 while (!error && (log_start != log_end) && i < len) {
217 c = LOG_BUF(log_start);
218 log_start++;
219 spin_unlock_irq(&logbuf_lock);
220 error = __put_user(c,buf);
221 buf++;
222 i++;
223 cond_resched();
224 spin_lock_irq(&logbuf_lock);
226 spin_unlock_irq(&logbuf_lock);
227 if (!error)
228 error = i;
229 break;
230 case 4: /* Read/clear last kernel messages */
231 do_clear = 1;
232 /* FALL THRU */
233 case 3: /* Read last kernel messages */
234 error = -EINVAL;
235 if (!buf || len < 0)
236 goto out;
237 error = 0;
238 if (!len)
239 goto out;
240 if (!access_ok(VERIFY_WRITE, buf, len)) {
241 error = -EFAULT;
242 goto out;
244 count = len;
245 if (count > log_buf_len)
246 count = log_buf_len;
247 spin_lock_irq(&logbuf_lock);
248 if (count > logged_chars)
249 count = logged_chars;
250 if (do_clear)
251 logged_chars = 0;
252 limit = log_end;
254 * __put_user() could sleep, and while we sleep
255 * printk() could overwrite the messages
256 * we try to copy to user space. Therefore
257 * the messages are copied in reverse. <manfreds>
259 for (i = 0; i < count && !error; i++) {
260 j = limit-1-i;
261 if (j + log_buf_len < log_end)
262 break;
263 c = LOG_BUF(j);
264 spin_unlock_irq(&logbuf_lock);
265 error = __put_user(c,&buf[count-1-i]);
266 cond_resched();
267 spin_lock_irq(&logbuf_lock);
269 spin_unlock_irq(&logbuf_lock);
270 if (error)
271 break;
272 error = i;
273 if (i != count) {
274 int offset = count-error;
275 /* buffer overflow during copy, correct user buffer. */
276 for (i = 0; i < error; i++) {
277 if (__get_user(c,&buf[i+offset]) ||
278 __put_user(c,&buf[i])) {
279 error = -EFAULT;
280 break;
282 cond_resched();
285 break;
286 case 5: /* Clear ring buffer */
287 logged_chars = 0;
288 break;
289 case 6: /* Disable logging to console */
290 console_loglevel = minimum_console_loglevel;
291 break;
292 case 7: /* Enable logging to console */
293 console_loglevel = default_console_loglevel;
294 break;
295 case 8: /* Set level of messages printed to console */
296 error = -EINVAL;
297 if (len < 1 || len > 8)
298 goto out;
299 if (len < minimum_console_loglevel)
300 len = minimum_console_loglevel;
301 console_loglevel = len;
302 error = 0;
303 break;
304 case 9: /* Number of chars in the log buffer */
305 error = log_end - log_start;
306 break;
307 case 10: /* Size of the log buffer */
308 error = log_buf_len;
309 break;
310 default:
311 error = -EINVAL;
312 break;
314 out:
315 return error;
318 asmlinkage long sys_syslog(int type, char __user *buf, int len)
320 return do_syslog(type, buf, len);
324 * Call the console drivers on a range of log_buf
326 static void __call_console_drivers(unsigned long start, unsigned long end)
328 struct console *con;
330 for (con = console_drivers; con; con = con->next) {
331 if ((con->flags & CON_ENABLED) && con->write &&
332 (cpu_online(smp_processor_id()) ||
333 (con->flags & CON_ANYTIME)))
334 con->write(con, &LOG_BUF(start), end - start);
339 * Write out chars from start to end - 1 inclusive
341 static void _call_console_drivers(unsigned long start,
342 unsigned long end, int msg_log_level)
344 if (msg_log_level < console_loglevel &&
345 console_drivers && start != end) {
346 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
347 /* wrapped write */
348 __call_console_drivers(start & LOG_BUF_MASK,
349 log_buf_len);
350 __call_console_drivers(0, end & LOG_BUF_MASK);
351 } else {
352 __call_console_drivers(start, end);
358 * Call the console drivers, asking them to write out
359 * log_buf[start] to log_buf[end - 1].
360 * The console_sem must be held.
362 static void call_console_drivers(unsigned long start, unsigned long end)
364 unsigned long cur_index, start_print;
365 static int msg_level = -1;
367 BUG_ON(((long)(start - end)) > 0);
369 cur_index = start;
370 start_print = start;
371 while (cur_index != end) {
372 if (msg_level < 0 && ((end - cur_index) > 2) &&
373 LOG_BUF(cur_index + 0) == '<' &&
374 LOG_BUF(cur_index + 1) >= '0' &&
375 LOG_BUF(cur_index + 1) <= '7' &&
376 LOG_BUF(cur_index + 2) == '>') {
377 msg_level = LOG_BUF(cur_index + 1) - '0';
378 cur_index += 3;
379 start_print = cur_index;
381 while (cur_index != end) {
382 char c = LOG_BUF(cur_index);
384 cur_index++;
385 if (c == '\n') {
386 if (msg_level < 0) {
388 * printk() has already given us loglevel tags in
389 * the buffer. This code is here in case the
390 * log buffer has wrapped right round and scribbled
391 * on those tags
393 msg_level = default_message_loglevel;
395 _call_console_drivers(start_print, cur_index, msg_level);
396 msg_level = -1;
397 start_print = cur_index;
398 break;
402 _call_console_drivers(start_print, end, msg_level);
405 static void emit_log_char(char c)
407 LOG_BUF(log_end) = c;
408 log_end++;
409 if (log_end - log_start > log_buf_len)
410 log_start = log_end - log_buf_len;
411 if (log_end - con_start > log_buf_len)
412 con_start = log_end - log_buf_len;
413 if (logged_chars < log_buf_len)
414 logged_chars++;
418 * Zap console related locks when oopsing. Only zap at most once
419 * every 10 seconds, to leave time for slow consoles to print a
420 * full oops.
422 static void zap_locks(void)
424 static unsigned long oops_timestamp;
426 if (time_after_eq(jiffies, oops_timestamp) &&
427 !time_after(jiffies, oops_timestamp + 30 * HZ))
428 return;
430 oops_timestamp = jiffies;
432 /* If a crash is occurring, make sure we can't deadlock */
433 spin_lock_init(&logbuf_lock);
434 /* And make sure that we print immediately */
435 init_MUTEX(&console_sem);
438 #if defined(CONFIG_PRINTK_TIME)
439 static int printk_time = 1;
440 #else
441 static int printk_time = 0;
442 #endif
443 module_param(printk_time, int, S_IRUGO | S_IWUSR);
445 static int __init printk_time_setup(char *str)
447 if (*str)
448 return 0;
449 printk_time = 1;
450 return 1;
453 __setup("time", printk_time_setup);
455 __attribute__((weak)) unsigned long long printk_clock(void)
457 return sched_clock();
460 /* Check if we have any console registered that can be called early in boot. */
461 static int have_callable_console(void)
463 struct console *con;
465 for (con = console_drivers; con; con = con->next)
466 if (con->flags & CON_ANYTIME)
467 return 1;
469 return 0;
473 * printk - print a kernel message
474 * @fmt: format string
476 * This is printk. It can be called from any context. We want it to work.
478 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
479 * call the console drivers. If we fail to get the semaphore we place the output
480 * into the log buffer and return. The current holder of the console_sem will
481 * notice the new output in release_console_sem() and will send it to the
482 * consoles before releasing the semaphore.
484 * One effect of this deferred printing is that code which calls printk() and
485 * then changes console_loglevel may break. This is because console_loglevel
486 * is inspected when the actual printing occurs.
488 * See also:
489 * printf(3)
492 asmlinkage int printk(const char *fmt, ...)
494 va_list args;
495 int r;
497 va_start(args, fmt);
498 r = vprintk(fmt, args);
499 va_end(args);
501 return r;
504 /* cpu currently holding logbuf_lock */
505 static volatile unsigned int printk_cpu = UINT_MAX;
507 asmlinkage int vprintk(const char *fmt, va_list args)
509 unsigned long flags;
510 int printed_len;
511 char *p;
512 static char printk_buf[1024];
513 static int log_level_unknown = 1;
515 preempt_disable();
516 if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
517 /* If a crash is occurring during printk() on this CPU,
518 * make sure we can't deadlock */
519 zap_locks();
521 /* This stops the holder of console_sem just where we want him */
522 local_irq_save(flags);
523 lockdep_off();
524 spin_lock(&logbuf_lock);
525 printk_cpu = smp_processor_id();
527 /* Emit the output into the temporary buffer */
528 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
531 * Copy the output into log_buf. If the caller didn't provide
532 * appropriate log level tags, we insert them here
534 for (p = printk_buf; *p; p++) {
535 if (log_level_unknown) {
536 /* log_level_unknown signals the start of a new line */
537 if (printk_time) {
538 int loglev_char;
539 char tbuf[50], *tp;
540 unsigned tlen;
541 unsigned long long t;
542 unsigned long nanosec_rem;
545 * force the log level token to be
546 * before the time output.
548 if (p[0] == '<' && p[1] >='0' &&
549 p[1] <= '7' && p[2] == '>') {
550 loglev_char = p[1];
551 p += 3;
552 printed_len -= 3;
553 } else {
554 loglev_char = default_message_loglevel
555 + '0';
557 t = printk_clock();
558 nanosec_rem = do_div(t, 1000000000);
559 tlen = sprintf(tbuf,
560 "<%c>[%5lu.%06lu] ",
561 loglev_char,
562 (unsigned long)t,
563 nanosec_rem/1000);
565 for (tp = tbuf; tp < tbuf + tlen; tp++)
566 emit_log_char(*tp);
567 printed_len += tlen;
568 } else {
569 if (p[0] != '<' || p[1] < '0' ||
570 p[1] > '7' || p[2] != '>') {
571 emit_log_char('<');
572 emit_log_char(default_message_loglevel
573 + '0');
574 emit_log_char('>');
575 printed_len += 3;
578 log_level_unknown = 0;
579 if (!*p)
580 break;
582 emit_log_char(*p);
583 if (*p == '\n')
584 log_level_unknown = 1;
587 if (!down_trylock(&console_sem)) {
589 * We own the drivers. We can drop the spinlock and
590 * let release_console_sem() print the text, maybe ...
592 console_locked = 1;
593 printk_cpu = UINT_MAX;
594 spin_unlock(&logbuf_lock);
597 * Console drivers may assume that per-cpu resources have
598 * been allocated. So unless they're explicitly marked as
599 * being able to cope (CON_ANYTIME) don't call them until
600 * this CPU is officially up.
602 if (cpu_online(smp_processor_id()) || have_callable_console()) {
603 console_may_schedule = 0;
604 release_console_sem();
605 } else {
606 /* Release by hand to avoid flushing the buffer. */
607 console_locked = 0;
608 up(&console_sem);
610 lockdep_on();
611 local_irq_restore(flags);
612 } else {
614 * Someone else owns the drivers. We drop the spinlock, which
615 * allows the semaphore holder to proceed and to call the
616 * console drivers with the output which we just produced.
618 printk_cpu = UINT_MAX;
619 spin_unlock(&logbuf_lock);
620 lockdep_on();
621 local_irq_restore(flags);
624 preempt_enable();
625 return printed_len;
627 EXPORT_SYMBOL(printk);
628 EXPORT_SYMBOL(vprintk);
630 #else
632 asmlinkage long sys_syslog(int type, char __user *buf, int len)
634 return 0;
637 int do_syslog(int type, char __user *buf, int len)
639 return 0;
642 static void call_console_drivers(unsigned long start, unsigned long end)
646 #endif
649 * Set up a list of consoles. Called from init/main.c
651 static int __init console_setup(char *str)
653 char name[sizeof(console_cmdline[0].name)];
654 char *s, *options;
655 int idx;
658 * Decode str into name, index, options.
660 if (str[0] >= '0' && str[0] <= '9') {
661 strcpy(name, "ttyS");
662 strncpy(name + 4, str, sizeof(name) - 5);
663 } else {
664 strncpy(name, str, sizeof(name) - 1);
666 name[sizeof(name) - 1] = 0;
667 if ((options = strchr(str, ',')) != NULL)
668 *(options++) = 0;
669 #ifdef __sparc__
670 if (!strcmp(str, "ttya"))
671 strcpy(name, "ttyS0");
672 if (!strcmp(str, "ttyb"))
673 strcpy(name, "ttyS1");
674 #endif
675 for (s = name; *s; s++)
676 if ((*s >= '0' && *s <= '9') || *s == ',')
677 break;
678 idx = simple_strtoul(s, NULL, 10);
679 *s = 0;
681 add_preferred_console(name, idx, options);
682 return 1;
684 __setup("console=", console_setup);
687 * add_preferred_console - add a device to the list of preferred consoles.
688 * @name: device name
689 * @idx: device index
690 * @options: options for this console
692 * The last preferred console added will be used for kernel messages
693 * and stdin/out/err for init. Normally this is used by console_setup
694 * above to handle user-supplied console arguments; however it can also
695 * be used by arch-specific code either to override the user or more
696 * commonly to provide a default console (ie from PROM variables) when
697 * the user has not supplied one.
699 int __init add_preferred_console(char *name, int idx, char *options)
701 struct console_cmdline *c;
702 int i;
705 * See if this tty is not yet registered, and
706 * if we have a slot free.
708 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
709 if (strcmp(console_cmdline[i].name, name) == 0 &&
710 console_cmdline[i].index == idx) {
711 selected_console = i;
712 return 0;
714 if (i == MAX_CMDLINECONSOLES)
715 return -E2BIG;
716 selected_console = i;
717 c = &console_cmdline[i];
718 memcpy(c->name, name, sizeof(c->name));
719 c->name[sizeof(c->name) - 1] = 0;
720 c->options = options;
721 c->index = idx;
722 return 0;
725 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
727 * suspend_console - suspend the console subsystem
729 * This disables printk() while we go into suspend states
731 void suspend_console(void)
733 printk("Suspending console(s)\n");
734 acquire_console_sem();
735 console_suspended = 1;
738 void resume_console(void)
740 console_suspended = 0;
741 release_console_sem();
743 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
746 * acquire_console_sem - lock the console system for exclusive use.
748 * Acquires a semaphore which guarantees that the caller has
749 * exclusive access to the console system and the console_drivers list.
751 * Can sleep, returns nothing.
753 void acquire_console_sem(void)
755 BUG_ON(in_interrupt());
756 if (console_suspended) {
757 down(&secondary_console_sem);
758 return;
760 down(&console_sem);
761 console_locked = 1;
762 console_may_schedule = 1;
764 EXPORT_SYMBOL(acquire_console_sem);
766 int try_acquire_console_sem(void)
768 if (down_trylock(&console_sem))
769 return -1;
770 console_locked = 1;
771 console_may_schedule = 0;
772 return 0;
774 EXPORT_SYMBOL(try_acquire_console_sem);
776 int is_console_locked(void)
778 return console_locked;
780 EXPORT_UNUSED_SYMBOL(is_console_locked); /* June 2006 */
783 * release_console_sem - unlock the console system
785 * Releases the semaphore which the caller holds on the console system
786 * and the console driver list.
788 * While the semaphore was held, console output may have been buffered
789 * by printk(). If this is the case, release_console_sem() emits
790 * the output prior to releasing the semaphore.
792 * If there is output waiting for klogd, we wake it up.
794 * release_console_sem() may be called from any context.
796 void release_console_sem(void)
798 unsigned long flags;
799 unsigned long _con_start, _log_end;
800 unsigned long wake_klogd = 0;
802 if (console_suspended) {
803 up(&secondary_console_sem);
804 return;
807 console_may_schedule = 0;
809 for ( ; ; ) {
810 spin_lock_irqsave(&logbuf_lock, flags);
811 wake_klogd |= log_start - log_end;
812 if (con_start == log_end)
813 break; /* Nothing to print */
814 _con_start = con_start;
815 _log_end = log_end;
816 con_start = log_end; /* Flush */
817 spin_unlock(&logbuf_lock);
818 call_console_drivers(_con_start, _log_end);
819 local_irq_restore(flags);
821 console_locked = 0;
822 up(&console_sem);
823 spin_unlock_irqrestore(&logbuf_lock, flags);
824 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
825 wake_up_interruptible(&log_wait);
827 EXPORT_SYMBOL(release_console_sem);
830 * console_conditional_schedule - yield the CPU if required
832 * If the console code is currently allowed to sleep, and
833 * if this CPU should yield the CPU to another task, do
834 * so here.
836 * Must be called within acquire_console_sem().
838 void __sched console_conditional_schedule(void)
840 if (console_may_schedule)
841 cond_resched();
843 EXPORT_SYMBOL(console_conditional_schedule);
845 void console_print(const char *s)
847 printk(KERN_EMERG "%s", s);
849 EXPORT_SYMBOL(console_print);
851 void console_unblank(void)
853 struct console *c;
856 * console_unblank can no longer be called in interrupt context unless
857 * oops_in_progress is set to 1..
859 if (oops_in_progress) {
860 if (down_trylock(&console_sem) != 0)
861 return;
862 } else
863 acquire_console_sem();
865 console_locked = 1;
866 console_may_schedule = 0;
867 for (c = console_drivers; c != NULL; c = c->next)
868 if ((c->flags & CON_ENABLED) && c->unblank)
869 c->unblank();
870 release_console_sem();
874 * Return the console tty driver structure and its associated index
876 struct tty_driver *console_device(int *index)
878 struct console *c;
879 struct tty_driver *driver = NULL;
881 acquire_console_sem();
882 for (c = console_drivers; c != NULL; c = c->next) {
883 if (!c->device)
884 continue;
885 driver = c->device(c, index);
886 if (driver)
887 break;
889 release_console_sem();
890 return driver;
894 * Prevent further output on the passed console device so that (for example)
895 * serial drivers can disable console output before suspending a port, and can
896 * re-enable output afterwards.
898 void console_stop(struct console *console)
900 acquire_console_sem();
901 console->flags &= ~CON_ENABLED;
902 release_console_sem();
904 EXPORT_SYMBOL(console_stop);
906 void console_start(struct console *console)
908 acquire_console_sem();
909 console->flags |= CON_ENABLED;
910 release_console_sem();
912 EXPORT_SYMBOL(console_start);
915 * The console driver calls this routine during kernel initialization
916 * to register the console printing procedure with printk() and to
917 * print any messages that were printed by the kernel before the
918 * console driver was initialized.
920 void register_console(struct console *console)
922 int i;
923 unsigned long flags;
925 if (preferred_console < 0)
926 preferred_console = selected_console;
929 * See if we want to use this console driver. If we
930 * didn't select a console we take the first one
931 * that registers here.
933 if (preferred_console < 0) {
934 if (console->index < 0)
935 console->index = 0;
936 if (console->setup == NULL ||
937 console->setup(console, NULL) == 0) {
938 console->flags |= CON_ENABLED | CON_CONSDEV;
939 preferred_console = 0;
944 * See if this console matches one we selected on
945 * the command line.
947 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
948 i++) {
949 if (strcmp(console_cmdline[i].name, console->name) != 0)
950 continue;
951 if (console->index >= 0 &&
952 console->index != console_cmdline[i].index)
953 continue;
954 if (console->index < 0)
955 console->index = console_cmdline[i].index;
956 if (console->setup &&
957 console->setup(console, console_cmdline[i].options) != 0)
958 break;
959 console->flags |= CON_ENABLED;
960 console->index = console_cmdline[i].index;
961 if (i == selected_console) {
962 console->flags |= CON_CONSDEV;
963 preferred_console = selected_console;
965 break;
968 if (!(console->flags & CON_ENABLED))
969 return;
971 if (console_drivers && (console_drivers->flags & CON_BOOT)) {
972 unregister_console(console_drivers);
973 console->flags &= ~CON_PRINTBUFFER;
977 * Put this console in the list - keep the
978 * preferred driver at the head of the list.
980 acquire_console_sem();
981 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
982 console->next = console_drivers;
983 console_drivers = console;
984 if (console->next)
985 console->next->flags &= ~CON_CONSDEV;
986 } else {
987 console->next = console_drivers->next;
988 console_drivers->next = console;
990 if (console->flags & CON_PRINTBUFFER) {
992 * release_console_sem() will print out the buffered messages
993 * for us.
995 spin_lock_irqsave(&logbuf_lock, flags);
996 con_start = log_start;
997 spin_unlock_irqrestore(&logbuf_lock, flags);
999 release_console_sem();
1001 EXPORT_SYMBOL(register_console);
1003 int unregister_console(struct console *console)
1005 struct console *a, *b;
1006 int res = 1;
1008 acquire_console_sem();
1009 if (console_drivers == console) {
1010 console_drivers=console->next;
1011 res = 0;
1012 } else if (console_drivers) {
1013 for (a=console_drivers->next, b=console_drivers ;
1014 a; b=a, a=b->next) {
1015 if (a == console) {
1016 b->next = a->next;
1017 res = 0;
1018 break;
1023 /* If last console is removed, we re-enable picking the first
1024 * one that gets registered. Without that, pmac early boot console
1025 * would prevent fbcon from taking over.
1027 * If this isn't the last console and it has CON_CONSDEV set, we
1028 * need to set it on the next preferred console.
1030 if (console_drivers == NULL)
1031 preferred_console = selected_console;
1032 else if (console->flags & CON_CONSDEV)
1033 console_drivers->flags |= CON_CONSDEV;
1035 release_console_sem();
1036 return res;
1038 EXPORT_SYMBOL(unregister_console);
1041 * tty_write_message - write a message to a certain tty, not just the console.
1042 * @tty: the destination tty_struct
1043 * @msg: the message to write
1045 * This is used for messages that need to be redirected to a specific tty.
1046 * We don't put it into the syslog queue right now maybe in the future if
1047 * really needed.
1049 void tty_write_message(struct tty_struct *tty, char *msg)
1051 if (tty && tty->driver->write)
1052 tty->driver->write(tty, msg, strlen(msg));
1053 return;
1057 * printk rate limiting, lifted from the networking subsystem.
1059 * This enforces a rate limit: not more than one kernel message
1060 * every printk_ratelimit_jiffies to make a denial-of-service
1061 * attack impossible.
1063 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1065 static DEFINE_SPINLOCK(ratelimit_lock);
1066 static unsigned long toks = 10 * 5 * HZ;
1067 static unsigned long last_msg;
1068 static int missed;
1069 unsigned long flags;
1070 unsigned long now = jiffies;
1072 spin_lock_irqsave(&ratelimit_lock, flags);
1073 toks += now - last_msg;
1074 last_msg = now;
1075 if (toks > (ratelimit_burst * ratelimit_jiffies))
1076 toks = ratelimit_burst * ratelimit_jiffies;
1077 if (toks >= ratelimit_jiffies) {
1078 int lost = missed;
1080 missed = 0;
1081 toks -= ratelimit_jiffies;
1082 spin_unlock_irqrestore(&ratelimit_lock, flags);
1083 if (lost)
1084 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1085 return 1;
1087 missed++;
1088 spin_unlock_irqrestore(&ratelimit_lock, flags);
1089 return 0;
1091 EXPORT_SYMBOL(__printk_ratelimit);
1093 /* minimum time in jiffies between messages */
1094 int printk_ratelimit_jiffies = 5 * HZ;
1096 /* number of messages we send before ratelimiting */
1097 int printk_ratelimit_burst = 10;
1099 int printk_ratelimit(void)
1101 return __printk_ratelimit(printk_ratelimit_jiffies,
1102 printk_ratelimit_burst);
1104 EXPORT_SYMBOL(printk_ratelimit);
1107 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1108 * @caller_jiffies: pointer to caller's state
1109 * @interval_msecs: minimum interval between prints
1111 * printk_timed_ratelimit() returns true if more than @interval_msecs
1112 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1113 * returned true.
1115 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1116 unsigned int interval_msecs)
1118 if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1119 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1120 return true;
1122 return false;
1124 EXPORT_SYMBOL(printk_timed_ratelimit);