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 * manfreds@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/module.h>
27 #include <linux/interrupt.h> /* For in_interrupt() */
28 #include <linux/config.h>
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>
35 #include <asm/uaccess.h>
37 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
39 /* printk's without a loglevel use this.. */
40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
42 /* We show everything that is MORE important than this.. */
43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
48 int console_printk[4] = {
49 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
50 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
51 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
52 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
55 EXPORT_SYMBOL(console_printk);
60 * console_sem protects the console_drivers list, and also
61 * provides serialisation for access to the entire console
64 static DECLARE_MUTEX(console_sem);
65 struct console *console_drivers;
67 * This is used for debugging the mess that is the VT code by
68 * keeping track if we have the console semaphore held. It's
69 * definitely not the perfect debug tool (we don't know if _WE_
70 * hold it are racing, but it helps tracking those weird code
71 * path in the console code where we end up in places I want
72 * locked without the console sempahore held
74 static int console_locked;
77 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
78 * It is also used in interesting ways to provide interlocking in
79 * release_console_sem().
81 static DEFINE_SPINLOCK(logbuf_lock);
83 static char __log_buf[__LOG_BUF_LEN];
84 static char *log_buf = __log_buf;
85 static int log_buf_len = __LOG_BUF_LEN;
87 #define LOG_BUF_MASK (log_buf_len-1)
88 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
91 * The indices into log_buf are not constrained to log_buf_len - they
92 * must be masked before subscripting
94 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
95 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
96 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
97 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
100 * Array of consoles built from command line options (console=)
102 struct console_cmdline
104 char name[8]; /* Name of the driver */
105 int index; /* Minor dev. to use */
106 char *options; /* Options for the driver */
109 #define MAX_CMDLINECONSOLES 8
111 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
112 static int selected_console = -1;
113 static int preferred_console = -1;
115 /* Flag: console code may call schedule() */
116 static int console_may_schedule;
119 * Setup a list of consoles. Called from init/main.c
121 static int __init console_setup(char *str)
123 char name[sizeof(console_cmdline[0].name)];
128 * Decode str into name, index, options.
130 if (str[0] >= '0' && str[0] <= '9') {
131 strcpy(name, "ttyS");
132 strncpy(name + 4, str, sizeof(name) - 5);
134 strncpy(name, str, sizeof(name) - 1);
135 name[sizeof(name) - 1] = 0;
136 if ((options = strchr(str, ',')) != NULL)
139 if (!strcmp(str, "ttya"))
140 strcpy(name, "ttyS0");
141 if (!strcmp(str, "ttyb"))
142 strcpy(name, "ttyS1");
144 for(s = name; *s; s++)
145 if ((*s >= '0' && *s <= '9') || *s == ',')
147 idx = simple_strtoul(s, NULL, 10);
150 add_preferred_console(name, idx, options);
154 __setup("console=", console_setup);
157 * add_preferred_console - add a device to the list of preferred consoles.
159 * The last preferred console added will be used for kernel messages
160 * and stdin/out/err for init. Normally this is used by console_setup
161 * above to handle user-supplied console arguments; however it can also
162 * be used by arch-specific code either to override the user or more
163 * commonly to provide a default console (ie from PROM variables) when
164 * the user has not supplied one.
166 int __init add_preferred_console(char *name, int idx, char *options)
168 struct console_cmdline *c;
172 * See if this tty is not yet registered, and
173 * if we have a slot free.
175 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
176 if (strcmp(console_cmdline[i].name, name) == 0 &&
177 console_cmdline[i].index == idx) {
178 selected_console = i;
181 if (i == MAX_CMDLINECONSOLES)
183 selected_console = i;
184 c = &console_cmdline[i];
185 memcpy(c->name, name, sizeof(c->name));
186 c->name[sizeof(c->name) - 1] = 0;
187 c->options = options;
192 static int __init log_buf_len_setup(char *str)
194 unsigned long size = memparse(str, &str);
198 size = roundup_pow_of_two(size);
199 if (size > log_buf_len) {
200 unsigned long start, dest_idx, offset;
203 new_log_buf = alloc_bootmem(size);
205 printk("log_buf_len: allocation failed\n");
209 spin_lock_irqsave(&logbuf_lock, flags);
211 log_buf = new_log_buf;
213 offset = start = min(con_start, log_start);
215 while (start != log_end) {
216 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
223 spin_unlock_irqrestore(&logbuf_lock, flags);
225 printk("log_buf_len: %d\n", log_buf_len);
232 __setup("log_buf_len=", log_buf_len_setup);
235 * Commands to do_syslog:
237 * 0 -- Close the log. Currently a NOP.
238 * 1 -- Open the log. Currently a NOP.
239 * 2 -- Read from the log.
240 * 3 -- Read all messages remaining in the ring buffer.
241 * 4 -- Read and clear all messages remaining in the ring buffer
242 * 5 -- Clear ring buffer.
243 * 6 -- Disable printk's to console
244 * 7 -- Enable printk's to console
245 * 8 -- Set level of messages printed to console
246 * 9 -- Return number of unread characters in the log buffer
247 * 10 -- Return size of the log buffer
249 int do_syslog(int type, char __user * buf, int len)
251 unsigned long i, j, limit, count;
256 error = security_syslog(type);
261 case 0: /* Close log */
263 case 1: /* Open log */
265 case 2: /* Read from log */
272 error = verify_area(VERIFY_WRITE,buf,len);
275 error = wait_event_interruptible(log_wait, (log_start - log_end));
279 spin_lock_irq(&logbuf_lock);
280 while (!error && (log_start != log_end) && i < len) {
281 c = LOG_BUF(log_start);
283 spin_unlock_irq(&logbuf_lock);
284 error = __put_user(c,buf);
288 spin_lock_irq(&logbuf_lock);
290 spin_unlock_irq(&logbuf_lock);
294 case 4: /* Read/clear last kernel messages */
297 case 3: /* Read last kernel messages */
304 error = verify_area(VERIFY_WRITE,buf,len);
308 if (count > log_buf_len)
310 spin_lock_irq(&logbuf_lock);
311 if (count > logged_chars)
312 count = logged_chars;
317 * __put_user() could sleep, and while we sleep
318 * printk() could overwrite the messages
319 * we try to copy to user space. Therefore
320 * the messages are copied in reverse. <manfreds>
322 for(i = 0; i < count && !error; i++) {
324 if (j + log_buf_len < log_end)
327 spin_unlock_irq(&logbuf_lock);
328 error = __put_user(c,&buf[count-1-i]);
330 spin_lock_irq(&logbuf_lock);
332 spin_unlock_irq(&logbuf_lock);
337 int offset = count-error;
338 /* buffer overflow during copy, correct user buffer. */
339 for(i=0;i<error;i++) {
340 if (__get_user(c,&buf[i+offset]) ||
341 __put_user(c,&buf[i])) {
349 case 5: /* Clear ring buffer */
352 case 6: /* Disable logging to console */
353 console_loglevel = minimum_console_loglevel;
355 case 7: /* Enable logging to console */
356 console_loglevel = default_console_loglevel;
358 case 8: /* Set level of messages printed to console */
360 if (len < 1 || len > 8)
362 if (len < minimum_console_loglevel)
363 len = minimum_console_loglevel;
364 console_loglevel = len;
367 case 9: /* Number of chars in the log buffer */
368 error = log_end - log_start;
370 case 10: /* Size of the log buffer */
381 asmlinkage long sys_syslog(int type, char __user * buf, int len)
383 return do_syslog(type, buf, len);
387 * Call the console drivers on a range of log_buf
389 static void __call_console_drivers(unsigned long start, unsigned long end)
393 for (con = console_drivers; con; con = con->next) {
394 if ((con->flags & CON_ENABLED) && con->write)
395 con->write(con, &LOG_BUF(start), end - start);
400 * Write out chars from start to end - 1 inclusive
402 static void _call_console_drivers(unsigned long start,
403 unsigned long end, int msg_log_level)
405 if (msg_log_level < console_loglevel &&
406 console_drivers && start != end) {
407 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
409 __call_console_drivers(start & LOG_BUF_MASK,
411 __call_console_drivers(0, end & LOG_BUF_MASK);
413 __call_console_drivers(start, end);
419 * Call the console drivers, asking them to write out
420 * log_buf[start] to log_buf[end - 1].
421 * The console_sem must be held.
423 static void call_console_drivers(unsigned long start, unsigned long end)
425 unsigned long cur_index, start_print;
426 static int msg_level = -1;
428 if (((long)(start - end)) > 0)
433 while (cur_index != end) {
434 if ( msg_level < 0 &&
435 ((end - cur_index) > 2) &&
436 LOG_BUF(cur_index + 0) == '<' &&
437 LOG_BUF(cur_index + 1) >= '0' &&
438 LOG_BUF(cur_index + 1) <= '7' &&
439 LOG_BUF(cur_index + 2) == '>')
441 msg_level = LOG_BUF(cur_index + 1) - '0';
443 start_print = cur_index;
445 while (cur_index != end) {
446 char c = LOG_BUF(cur_index);
452 * printk() has already given us loglevel tags in
453 * the buffer. This code is here in case the
454 * log buffer has wrapped right round and scribbled
457 msg_level = default_message_loglevel;
459 _call_console_drivers(start_print, cur_index, msg_level);
461 start_print = cur_index;
466 _call_console_drivers(start_print, end, msg_level);
469 static void emit_log_char(char c)
471 LOG_BUF(log_end) = c;
473 if (log_end - log_start > log_buf_len)
474 log_start = log_end - log_buf_len;
475 if (log_end - con_start > log_buf_len)
476 con_start = log_end - log_buf_len;
477 if (logged_chars < log_buf_len)
482 * Zap console related locks when oopsing. Only zap at most once
483 * every 10 seconds, to leave time for slow consoles to print a
486 static void zap_locks(void)
488 static unsigned long oops_timestamp;
490 if (time_after_eq(jiffies, oops_timestamp) &&
491 !time_after(jiffies, oops_timestamp + 30*HZ))
494 oops_timestamp = jiffies;
496 /* If a crash is occurring, make sure we can't deadlock */
497 spin_lock_init(&logbuf_lock);
498 /* And make sure that we print immediately */
499 init_MUTEX(&console_sem);
503 * This is printk. It can be called from any context. We want it to work.
505 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
506 * call the console drivers. If we fail to get the semaphore we place the output
507 * into the log buffer and return. The current holder of the console_sem will
508 * notice the new output in release_console_sem() and will send it to the
509 * consoles before releasing the semaphore.
511 * One effect of this deferred printing is that code which calls printk() and
512 * then changes console_loglevel may break. This is because console_loglevel
513 * is inspected when the actual printing occurs.
515 asmlinkage int printk(const char *fmt, ...)
521 r = vprintk(fmt, args);
527 asmlinkage int vprintk(const char *fmt, va_list args)
532 static char printk_buf[1024];
533 static int log_level_unknown = 1;
535 if (unlikely(oops_in_progress))
538 /* This stops the holder of console_sem just where we want him */
539 spin_lock_irqsave(&logbuf_lock, flags);
541 /* Emit the output into the temporary buffer */
542 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
545 * Copy the output into log_buf. If the caller didn't provide
546 * appropriate log level tags, we insert them here
548 for (p = printk_buf; *p; p++) {
549 if (log_level_unknown) {
550 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
552 emit_log_char(default_message_loglevel + '0');
555 log_level_unknown = 0;
559 log_level_unknown = 1;
562 if (!cpu_online(smp_processor_id()) &&
563 system_state != SYSTEM_RUNNING) {
565 * Some console drivers may assume that per-cpu resources have
566 * been allocated. So don't allow them to be called by this
567 * CPU until it is officially up. We shouldn't be calling into
568 * random console drivers on a CPU which doesn't exist yet..
570 spin_unlock_irqrestore(&logbuf_lock, flags);
573 if (!down_trylock(&console_sem)) {
576 * We own the drivers. We can drop the spinlock and let
577 * release_console_sem() print the text
579 spin_unlock_irqrestore(&logbuf_lock, flags);
580 console_may_schedule = 0;
581 release_console_sem();
584 * Someone else owns the drivers. We drop the spinlock, which
585 * allows the semaphore holder to proceed and to call the
586 * console drivers with the output which we just produced.
588 spin_unlock_irqrestore(&logbuf_lock, flags);
593 EXPORT_SYMBOL(printk);
594 EXPORT_SYMBOL(vprintk);
597 * acquire_console_sem - lock the console system for exclusive use.
599 * Acquires a semaphore which guarantees that the caller has
600 * exclusive access to the console system and the console_drivers list.
602 * Can sleep, returns nothing.
604 void acquire_console_sem(void)
610 console_may_schedule = 1;
612 EXPORT_SYMBOL(acquire_console_sem);
614 int is_console_locked(void)
616 return console_locked;
618 EXPORT_SYMBOL(is_console_locked);
621 * release_console_sem - unlock the console system
623 * Releases the semaphore which the caller holds on the console system
624 * and the console driver list.
626 * While the semaphore was held, console output may have been buffered
627 * by printk(). If this is the case, release_console_sem() emits
628 * the output prior to releasing the semaphore.
630 * If there is output waiting for klogd, we wake it up.
632 * release_console_sem() may be called from any context.
634 void release_console_sem(void)
637 unsigned long _con_start, _log_end;
638 unsigned long wake_klogd = 0;
641 spin_lock_irqsave(&logbuf_lock, flags);
642 wake_klogd |= log_start - log_end;
643 if (con_start == log_end)
644 break; /* Nothing to print */
645 _con_start = con_start;
647 con_start = log_end; /* Flush */
648 spin_unlock(&logbuf_lock);
649 call_console_drivers(_con_start, _log_end);
650 local_irq_restore(flags);
653 console_may_schedule = 0;
655 spin_unlock_irqrestore(&logbuf_lock, flags);
656 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
657 wake_up_interruptible(&log_wait);
659 EXPORT_SYMBOL(release_console_sem);
661 /** console_conditional_schedule - yield the CPU if required
663 * If the console code is currently allowed to sleep, and
664 * if this CPU should yield the CPU to another task, do
667 * Must be called within acquire_console_sem().
669 void __sched console_conditional_schedule(void)
671 if (console_may_schedule)
674 EXPORT_SYMBOL(console_conditional_schedule);
676 void console_print(const char *s)
678 printk(KERN_EMERG "%s", s);
680 EXPORT_SYMBOL(console_print);
682 void console_unblank(void)
687 * Try to get the console semaphore. If someone else owns it
688 * we have to return without unblanking because console_unblank
689 * may be called in interrupt context.
691 if (down_trylock(&console_sem) != 0)
694 console_may_schedule = 0;
695 for (c = console_drivers; c != NULL; c = c->next)
696 if ((c->flags & CON_ENABLED) && c->unblank)
698 release_console_sem();
700 EXPORT_SYMBOL(console_unblank);
703 * Return the console tty driver structure and its associated index
705 struct tty_driver *console_device(int *index)
708 struct tty_driver *driver = NULL;
710 acquire_console_sem();
711 for (c = console_drivers; c != NULL; c = c->next) {
714 driver = c->device(c, index);
718 release_console_sem();
723 * Prevent further output on the passed console device so that (for example)
724 * serial drivers can disable console output before suspending a port, and can
725 * re-enable output afterwards.
727 void console_stop(struct console *console)
729 acquire_console_sem();
730 console->flags &= ~CON_ENABLED;
731 release_console_sem();
733 EXPORT_SYMBOL(console_stop);
735 void console_start(struct console *console)
737 acquire_console_sem();
738 console->flags |= CON_ENABLED;
739 release_console_sem();
741 EXPORT_SYMBOL(console_start);
744 * The console driver calls this routine during kernel initialization
745 * to register the console printing procedure with printk() and to
746 * print any messages that were printed by the kernel before the
747 * console driver was initialized.
749 void register_console(struct console * console)
754 if (preferred_console < 0)
755 preferred_console = selected_console;
758 * See if we want to use this console driver. If we
759 * didn't select a console we take the first one
760 * that registers here.
762 if (preferred_console < 0) {
763 if (console->index < 0)
765 if (console->setup == NULL ||
766 console->setup(console, NULL) == 0) {
767 console->flags |= CON_ENABLED | CON_CONSDEV;
768 preferred_console = 0;
773 * See if this console matches one we selected on
776 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
777 if (strcmp(console_cmdline[i].name, console->name) != 0)
779 if (console->index >= 0 &&
780 console->index != console_cmdline[i].index)
782 if (console->index < 0)
783 console->index = console_cmdline[i].index;
784 if (console->setup &&
785 console->setup(console, console_cmdline[i].options) != 0)
787 console->flags |= CON_ENABLED;
788 console->index = console_cmdline[i].index;
789 if (i == preferred_console)
790 console->flags |= CON_CONSDEV;
794 if (!(console->flags & CON_ENABLED))
798 * Put this console in the list - keep the
799 * preferred driver at the head of the list.
801 acquire_console_sem();
802 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
803 console->next = console_drivers;
804 console_drivers = console;
806 console->next = console_drivers->next;
807 console_drivers->next = console;
809 if (console->flags & CON_PRINTBUFFER) {
811 * release_console_sem() will print out the buffered messages
814 spin_lock_irqsave(&logbuf_lock, flags);
815 con_start = log_start;
816 spin_unlock_irqrestore(&logbuf_lock, flags);
818 release_console_sem();
820 EXPORT_SYMBOL(register_console);
822 int unregister_console(struct console * console)
824 struct console *a,*b;
827 acquire_console_sem();
828 if (console_drivers == console) {
829 console_drivers=console->next;
832 for (a=console_drivers->next, b=console_drivers ;
842 /* If last console is removed, we re-enable picking the first
843 * one that gets registered. Without that, pmac early boot console
844 * would prevent fbcon from taking over.
846 if (console_drivers == NULL)
847 preferred_console = selected_console;
850 release_console_sem();
853 EXPORT_SYMBOL(unregister_console);
856 * tty_write_message - write a message to a certain tty, not just the console.
858 * This is used for messages that need to be redirected to a specific tty.
859 * We don't put it into the syslog queue right now maybe in the future if
862 void tty_write_message(struct tty_struct *tty, char *msg)
864 if (tty && tty->driver->write)
865 tty->driver->write(tty, msg, strlen(msg));
870 * printk rate limiting, lifted from the networking subsystem.
872 * This enforces a rate limit: not more than one kernel message
873 * every printk_ratelimit_jiffies to make a denial-of-service
876 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
878 static DEFINE_SPINLOCK(ratelimit_lock);
879 static unsigned long toks = 10*5*HZ;
880 static unsigned long last_msg;
883 unsigned long now = jiffies;
885 spin_lock_irqsave(&ratelimit_lock, flags);
886 toks += now - last_msg;
888 if (toks > (ratelimit_burst * ratelimit_jiffies))
889 toks = ratelimit_burst * ratelimit_jiffies;
890 if (toks >= ratelimit_jiffies) {
893 toks -= ratelimit_jiffies;
894 spin_unlock_irqrestore(&ratelimit_lock, flags);
896 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
900 spin_unlock_irqrestore(&ratelimit_lock, flags);
903 EXPORT_SYMBOL(__printk_ratelimit);
905 /* minimum time in jiffies between messages */
906 int printk_ratelimit_jiffies = 5*HZ;
908 /* number of messages we send before ratelimiting */
909 int printk_ratelimit_burst = 10;
911 int printk_ratelimit(void)
913 return __printk_ratelimit(printk_ratelimit_jiffies,
914 printk_ratelimit_burst);
916 EXPORT_SYMBOL(printk_ratelimit);