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>
34 #include <asm/uaccess.h>
36 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
38 /* printk's without a loglevel use this.. */
39 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
41 /* We show everything that is MORE important than this.. */
42 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
43 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
45 DECLARE_WAIT_QUEUE_HEAD(log_wait);
47 int console_printk[4] = {
48 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
49 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
50 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
51 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
54 EXPORT_SYMBOL(console_printk);
59 * console_sem protects the console_drivers list, and also
60 * provides serialisation for access to the entire console
63 static DECLARE_MUTEX(console_sem);
64 struct console *console_drivers;
66 * This is used for debugging the mess that is the VT code by
67 * keeping track if we have the console semaphore held. It's
68 * definitely not the perfect debug tool (we don't know if _WE_
69 * hold it are racing, but it helps tracking those weird code
70 * path in the console code where we end up in places I want
71 * locked without the console sempahore held
73 static int console_locked;
76 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
77 * It is also used in interesting ways to provide interlocking in
78 * release_console_sem().
80 static spinlock_t logbuf_lock = SPIN_LOCK_UNLOCKED;
82 static char __log_buf[__LOG_BUF_LEN];
83 static char *log_buf = __log_buf;
84 static int log_buf_len = __LOG_BUF_LEN;
86 #define LOG_BUF_MASK (log_buf_len-1)
87 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
90 * The indices into log_buf are not constrained to log_buf_len - they
91 * must be masked before subscripting
93 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
94 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
95 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
96 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
99 * Array of consoles built from command line options (console=)
101 struct console_cmdline
103 char name[8]; /* Name of the driver */
104 int index; /* Minor dev. to use */
105 char *options; /* Options for the driver */
108 #define MAX_CMDLINECONSOLES 8
110 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
111 static int preferred_console = -1;
113 /* Flag: console code may call schedule() */
114 static int console_may_schedule;
117 * Setup a list of consoles. Called from init/main.c
119 static int __init console_setup(char *str)
121 char name[sizeof(console_cmdline[0].name)];
126 * Decode str into name, index, options.
128 if (str[0] >= '0' && str[0] <= '9') {
129 strcpy(name, "ttyS");
130 strncpy(name + 4, str, sizeof(name) - 5);
132 strncpy(name, str, sizeof(name) - 1);
133 name[sizeof(name) - 1] = 0;
134 if ((options = strchr(str, ',')) != NULL)
137 if (!strcmp(str, "ttya"))
138 strcpy(name, "ttyS0");
139 if (!strcmp(str, "ttyb"))
140 strcpy(name, "ttyS1");
142 for(s = name; *s; s++)
143 if (*s >= '0' && *s <= '9')
145 idx = simple_strtoul(s, NULL, 10);
148 add_preferred_console(name, idx, options);
152 __setup("console=", console_setup);
155 * add_preferred_console - add a device to the list of preferred consoles.
157 * The last preferred console added will be used for kernel messages
158 * and stdin/out/err for init. Normally this is used by console_setup
159 * above to handle user-supplied console arguments; however it can also
160 * be used by arch-specific code either to override the user or more
161 * commonly to provide a default console (ie from PROM variables) when
162 * the user has not supplied one.
164 int __init add_preferred_console(char *name, int idx, char *options)
166 struct console_cmdline *c;
170 * See if this tty is not yet registered, and
171 * if we have a slot free.
173 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
174 if (strcmp(console_cmdline[i].name, name) == 0 &&
175 console_cmdline[i].index == idx) {
176 preferred_console = i;
179 if (i == MAX_CMDLINECONSOLES)
181 preferred_console = i;
182 c = &console_cmdline[i];
183 memcpy(c->name, name, sizeof(c->name));
184 c->name[sizeof(c->name) - 1] = 0;
185 c->options = options;
190 static int __init log_buf_len_setup(char *str)
192 unsigned long size = memparse(str, &str);
195 if (size > log_buf_len) {
196 unsigned long start, dest_idx, offset;
199 new_log_buf = alloc_bootmem(size);
201 printk("log_buf_len: allocation failed\n");
205 spin_lock_irqsave(&logbuf_lock, flags);
207 log_buf = new_log_buf;
209 offset = start = min(con_start, log_start);
211 while (start != log_end) {
212 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
219 spin_unlock_irqrestore(&logbuf_lock, flags);
221 printk("log_buf_len: %d\n", log_buf_len);
228 __setup("log_buf_len=", log_buf_len_setup);
231 * Commands to do_syslog:
233 * 0 -- Close the log. Currently a NOP.
234 * 1 -- Open the log. Currently a NOP.
235 * 2 -- Read from the log.
236 * 3 -- Read all messages remaining in the ring buffer.
237 * 4 -- Read and clear all messages remaining in the ring buffer
238 * 5 -- Clear ring buffer.
239 * 6 -- Disable printk's to console
240 * 7 -- Enable printk's to console
241 * 8 -- Set level of messages printed to console
242 * 9 -- Return number of unread characters in the log buffer
243 * 10 -- Return size of the log buffer
245 int do_syslog(int type, char __user * buf, int len)
247 unsigned long i, j, limit, count;
252 if (!vx_check(0, VX_ADMIN|VX_WATCH))
255 error = security_syslog(type);
260 case 0: /* Close log */
262 case 1: /* Open log */
264 case 2: /* Read from log */
271 error = verify_area(VERIFY_WRITE,buf,len);
274 error = wait_event_interruptible(log_wait, (log_start - log_end));
278 spin_lock_irq(&logbuf_lock);
279 while (!error && (log_start != log_end) && i < len) {
280 c = LOG_BUF(log_start);
282 spin_unlock_irq(&logbuf_lock);
283 error = __put_user(c,buf);
286 spin_lock_irq(&logbuf_lock);
288 spin_unlock_irq(&logbuf_lock);
292 case 4: /* Read/clear last kernel messages */
295 case 3: /* Read last kernel messages */
302 error = verify_area(VERIFY_WRITE,buf,len);
306 if (count > log_buf_len)
308 spin_lock_irq(&logbuf_lock);
309 if (count > logged_chars)
310 count = logged_chars;
315 * __put_user() could sleep, and while we sleep
316 * printk() could overwrite the messages
317 * we try to copy to user space. Therefore
318 * the messages are copied in reverse. <manfreds>
320 for(i = 0; i < count && !error; i++) {
322 if (j + log_buf_len < log_end)
325 spin_unlock_irq(&logbuf_lock);
326 error = __put_user(c,&buf[count-1-i]);
327 spin_lock_irq(&logbuf_lock);
329 spin_unlock_irq(&logbuf_lock);
334 int offset = count-error;
335 /* buffer overflow during copy, correct user buffer. */
336 for(i=0;i<error;i++) {
337 if (__get_user(c,&buf[i+offset]) ||
338 __put_user(c,&buf[i])) {
345 case 5: /* Clear ring buffer */
348 case 6: /* Disable logging to console */
349 console_loglevel = minimum_console_loglevel;
351 case 7: /* Enable logging to console */
352 console_loglevel = default_console_loglevel;
354 case 8: /* Set level of messages printed to console */
356 if (len < 1 || len > 8)
358 if (len < minimum_console_loglevel)
359 len = minimum_console_loglevel;
360 console_loglevel = len;
363 case 9: /* Number of chars in the log buffer */
364 error = log_end - log_start;
366 case 10: /* Size of the log buffer */
377 asmlinkage long sys_syslog(int type, char __user * buf, int len)
379 return do_syslog(type, buf, len);
383 * Call the console drivers on a range of log_buf
385 static void __call_console_drivers(unsigned long start, unsigned long end)
389 for (con = console_drivers; con; con = con->next) {
390 if ((con->flags & CON_ENABLED) && con->write)
391 con->write(con, &LOG_BUF(start), end - start);
396 * Write out chars from start to end - 1 inclusive
398 static void _call_console_drivers(unsigned long start,
399 unsigned long end, int msg_log_level)
401 if (msg_log_level < console_loglevel &&
402 console_drivers && start != end) {
403 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
405 __call_console_drivers(start & LOG_BUF_MASK,
407 __call_console_drivers(0, end & LOG_BUF_MASK);
409 __call_console_drivers(start, end);
415 * Call the console drivers, asking them to write out
416 * log_buf[start] to log_buf[end - 1].
417 * The console_sem must be held.
419 static void call_console_drivers(unsigned long start, unsigned long end)
421 unsigned long cur_index, start_print;
422 static int msg_level = -1;
424 if (((long)(start - end)) > 0)
429 while (cur_index != end) {
430 if ( msg_level < 0 &&
431 ((end - cur_index) > 2) &&
432 LOG_BUF(cur_index + 0) == '<' &&
433 LOG_BUF(cur_index + 1) >= '0' &&
434 LOG_BUF(cur_index + 1) <= '7' &&
435 LOG_BUF(cur_index + 2) == '>')
437 msg_level = LOG_BUF(cur_index + 1) - '0';
439 start_print = cur_index;
441 while (cur_index != end) {
442 char c = LOG_BUF(cur_index);
448 * printk() has already given us loglevel tags in
449 * the buffer. This code is here in case the
450 * log buffer has wrapped right round and scribbled
453 msg_level = default_message_loglevel;
455 _call_console_drivers(start_print, cur_index, msg_level);
457 start_print = cur_index;
462 _call_console_drivers(start_print, end, msg_level);
465 static void emit_log_char(char c)
467 LOG_BUF(log_end) = c;
469 if (log_end - log_start > log_buf_len)
470 log_start = log_end - log_buf_len;
471 if (log_end - con_start > log_buf_len)
472 con_start = log_end - log_buf_len;
473 if (logged_chars < log_buf_len)
478 * Zap console related locks when oopsing. Only zap at most once
479 * every 10 seconds, to leave time for slow consoles to print a
482 static void zap_locks(void)
484 static unsigned long oops_timestamp;
486 if (time_after_eq(jiffies, oops_timestamp) &&
487 !time_after(jiffies, oops_timestamp + 30*HZ))
490 oops_timestamp = jiffies;
492 /* If a crash is occurring, make sure we can't deadlock */
493 spin_lock_init(&logbuf_lock);
494 /* And make sure that we print immediately */
495 init_MUTEX(&console_sem);
499 * This is printk. It can be called from any context. We want it to work.
501 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
502 * call the console drivers. If we fail to get the semaphore we place the output
503 * into the log buffer and return. The current holder of the console_sem will
504 * notice the new output in release_console_sem() and will send it to the
505 * consoles before releasing the semaphore.
507 * One effect of this deferred printing is that code which calls printk() and
508 * then changes console_loglevel may break. This is because console_loglevel
509 * is inspected when the actual printing occurs.
511 asmlinkage int printk(const char *fmt, ...)
517 static char printk_buf[1024];
518 static int log_level_unknown = 1;
520 if (unlikely(oops_in_progress))
523 /* This stops the holder of console_sem just where we want him */
524 spin_lock_irqsave(&logbuf_lock, flags);
526 /* Emit the output into the temporary buffer */
528 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
532 * Copy the output into log_buf. If the caller didn't provide
533 * appropriate log level tags, we insert them here
535 for (p = printk_buf; *p; p++) {
536 if (log_level_unknown) {
537 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
539 emit_log_char(default_message_loglevel + '0');
542 log_level_unknown = 0;
546 log_level_unknown = 1;
549 if (!cpu_online(smp_processor_id()) &&
550 system_state != SYSTEM_RUNNING) {
552 * Some console drivers may assume that per-cpu resources have
553 * been allocated. So don't allow them to be called by this
554 * CPU until it is officially up. We shouldn't be calling into
555 * random console drivers on a CPU which doesn't exist yet..
557 spin_unlock_irqrestore(&logbuf_lock, flags);
560 if (!down_trylock(&console_sem)) {
563 * We own the drivers. We can drop the spinlock and let
564 * release_console_sem() print the text
566 spin_unlock_irqrestore(&logbuf_lock, flags);
567 console_may_schedule = 0;
568 release_console_sem();
571 * Someone else owns the drivers. We drop the spinlock, which
572 * allows the semaphore holder to proceed and to call the
573 * console drivers with the output which we just produced.
575 spin_unlock_irqrestore(&logbuf_lock, flags);
580 EXPORT_SYMBOL(printk);
583 * acquire_console_sem - lock the console system for exclusive use.
585 * Acquires a semaphore which guarantees that the caller has
586 * exclusive access to the console system and the console_drivers list.
588 * Can sleep, returns nothing.
590 void acquire_console_sem(void)
596 console_may_schedule = 1;
598 EXPORT_SYMBOL(acquire_console_sem);
600 int is_console_locked(void)
602 return console_locked;
604 EXPORT_SYMBOL(is_console_locked);
607 * release_console_sem - unlock the console system
609 * Releases the semaphore which the caller holds on the console system
610 * and the console driver list.
612 * While the semaphore was held, console output may have been buffered
613 * by printk(). If this is the case, release_console_sem() emits
614 * the output prior to releasing the semaphore.
616 * If there is output waiting for klogd, we wake it up.
618 * release_console_sem() may be called from any context.
620 void release_console_sem(void)
623 unsigned long _con_start, _log_end;
624 unsigned long wake_klogd = 0;
627 spin_lock_irqsave(&logbuf_lock, flags);
628 wake_klogd |= log_start - log_end;
629 if (con_start == log_end)
630 break; /* Nothing to print */
631 _con_start = con_start;
633 con_start = log_end; /* Flush */
634 spin_unlock_irqrestore(&logbuf_lock, flags);
635 call_console_drivers(_con_start, _log_end);
638 console_may_schedule = 0;
640 spin_unlock_irqrestore(&logbuf_lock, flags);
641 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
642 wake_up_interruptible(&log_wait);
644 EXPORT_SYMBOL(release_console_sem);
646 /** console_conditional_schedule - yield the CPU if required
648 * If the console code is currently allowed to sleep, and
649 * if this CPU should yield the CPU to another task, do
652 * Must be called within acquire_console_sem().
654 void console_conditional_schedule(void)
656 if (console_may_schedule && need_resched()) {
657 set_current_state(TASK_RUNNING);
661 EXPORT_SYMBOL(console_conditional_schedule);
663 void console_print(const char *s)
665 printk(KERN_EMERG "%s", s);
667 EXPORT_SYMBOL(console_print);
669 void console_unblank(void)
674 * Try to get the console semaphore. If someone else owns it
675 * we have to return without unblanking because console_unblank
676 * may be called in interrupt context.
678 if (down_trylock(&console_sem) != 0)
681 console_may_schedule = 0;
682 for (c = console_drivers; c != NULL; c = c->next)
683 if ((c->flags & CON_ENABLED) && c->unblank)
685 release_console_sem();
687 EXPORT_SYMBOL(console_unblank);
690 * The console driver calls this routine during kernel initialization
691 * to register the console printing procedure with printk() and to
692 * print any messages that were printed by the kernel before the
693 * console driver was initialized.
695 void register_console(struct console * console)
701 * See if we want to use this console driver. If we
702 * didn't select a console we take the first one
703 * that registers here.
705 if (preferred_console < 0) {
706 if (console->index < 0)
708 if (console->setup == NULL ||
709 console->setup(console, NULL) == 0) {
710 console->flags |= CON_ENABLED | CON_CONSDEV;
711 preferred_console = 0;
716 * See if this console matches one we selected on
719 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
720 if (strcmp(console_cmdline[i].name, console->name) != 0)
722 if (console->index >= 0 &&
723 console->index != console_cmdline[i].index)
725 if (console->index < 0)
726 console->index = console_cmdline[i].index;
727 if (console->setup &&
728 console->setup(console, console_cmdline[i].options) != 0)
730 console->flags |= CON_ENABLED;
731 console->index = console_cmdline[i].index;
732 if (i == preferred_console)
733 console->flags |= CON_CONSDEV;
737 if (!(console->flags & CON_ENABLED))
741 * Put this console in the list - keep the
742 * preferred driver at the head of the list.
744 acquire_console_sem();
745 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
746 console->next = console_drivers;
747 console_drivers = console;
749 console->next = console_drivers->next;
750 console_drivers->next = console;
752 if (console->flags & CON_PRINTBUFFER) {
754 * release_console_sem() will print out the buffered messages
757 spin_lock_irqsave(&logbuf_lock, flags);
758 con_start = log_start;
759 spin_unlock_irqrestore(&logbuf_lock, flags);
761 release_console_sem();
763 EXPORT_SYMBOL(register_console);
765 int unregister_console(struct console * console)
767 struct console *a,*b;
770 acquire_console_sem();
771 if (console_drivers == console) {
772 console_drivers=console->next;
775 for (a=console_drivers->next, b=console_drivers ;
785 /* If last console is removed, we re-enable picking the first
786 * one that gets registered. Without that, pmac early boot console
787 * would prevent fbcon from taking over.
789 if (console_drivers == NULL)
790 preferred_console = -1;
793 release_console_sem();
796 EXPORT_SYMBOL(unregister_console);
799 * tty_write_message - write a message to a certain tty, not just the console.
801 * This is used for messages that need to be redirected to a specific tty.
802 * We don't put it into the syslog queue right now maybe in the future if
805 void tty_write_message(struct tty_struct *tty, char *msg)
807 if (tty && tty->driver->write)
808 tty->driver->write(tty, 0, msg, strlen(msg));
813 * printk rate limiting, lifted from the networking subsystem.
815 * This enforces a rate limit: not more than one kernel message
816 * every printk_ratelimit_jiffies to make a denial-of-service
819 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
821 static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
822 static unsigned long toks = 10*5*HZ;
823 static unsigned long last_msg;
826 unsigned long now = jiffies;
828 spin_lock_irqsave(&ratelimit_lock, flags);
829 toks += now - last_msg;
831 if (toks > (ratelimit_burst * ratelimit_jiffies))
832 toks = ratelimit_burst * ratelimit_jiffies;
833 if (toks >= ratelimit_jiffies) {
836 toks -= ratelimit_jiffies;
837 spin_unlock_irqrestore(&ratelimit_lock, flags);
839 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
843 spin_unlock_irqrestore(&ratelimit_lock, flags);
846 EXPORT_SYMBOL(__printk_ratelimit);
848 /* minimum time in jiffies between messages */
849 int printk_ratelimit_jiffies = 5*HZ;
851 /* number of messages we send before ratelimiting */
852 int printk_ratelimit_burst = 10;
854 int printk_ratelimit(void)
856 return __printk_ratelimit(printk_ratelimit_jiffies,
857 printk_ratelimit_burst);
859 EXPORT_SYMBOL(printk_ratelimit);