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/vs_base.h>
34 #include <linux/syscalls.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_SYMBOL(console_printk);
61 * console_sem protects the console_drivers list, and also
62 * provides serialisation for access to the entire console
65 static DECLARE_MUTEX(console_sem);
66 struct console *console_drivers;
68 * This is used for debugging the mess that is the VT code by
69 * keeping track if we have the console semaphore held. It's
70 * definitely not the perfect debug tool (we don't know if _WE_
71 * hold it are racing, but it helps tracking those weird code
72 * path in the console code where we end up in places I want
73 * locked without the console sempahore held
75 static int console_locked;
78 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
79 * It is also used in interesting ways to provide interlocking in
80 * release_console_sem().
82 static spinlock_t logbuf_lock = SPIN_LOCK_UNLOCKED;
84 static char __log_buf[__LOG_BUF_LEN];
85 static char *log_buf = __log_buf;
86 static int log_buf_len = __LOG_BUF_LEN;
88 #define LOG_BUF_MASK (log_buf_len-1)
89 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
92 * The indices into log_buf are not constrained to log_buf_len - they
93 * must be masked before subscripting
95 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
96 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
97 static unsigned long log_end; /* Index into log_buf: most-recently-written-char + 1 */
98 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
101 * Array of consoles built from command line options (console=)
103 struct console_cmdline
105 char name[8]; /* Name of the driver */
106 int index; /* Minor dev. to use */
107 char *options; /* Options for the driver */
110 #define MAX_CMDLINECONSOLES 8
112 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
113 static int selected_console = -1;
114 static int preferred_console = -1;
116 /* Flag: console code may call schedule() */
117 static int console_may_schedule;
120 * Setup a list of consoles. Called from init/main.c
122 static int __init console_setup(char *str)
124 char name[sizeof(console_cmdline[0].name)];
129 * Decode str into name, index, options.
131 if (str[0] >= '0' && str[0] <= '9') {
132 strcpy(name, "ttyS");
133 strncpy(name + 4, str, sizeof(name) - 5);
135 strncpy(name, str, sizeof(name) - 1);
136 name[sizeof(name) - 1] = 0;
137 if ((options = strchr(str, ',')) != NULL)
140 if (!strcmp(str, "ttya"))
141 strcpy(name, "ttyS0");
142 if (!strcmp(str, "ttyb"))
143 strcpy(name, "ttyS1");
145 for(s = name; *s; s++)
146 if ((*s >= '0' && *s <= '9') || *s == ',')
148 idx = simple_strtoul(s, NULL, 10);
151 add_preferred_console(name, idx, options);
155 __setup("console=", console_setup);
158 * add_preferred_console - add a device to the list of preferred consoles.
160 * The last preferred console added will be used for kernel messages
161 * and stdin/out/err for init. Normally this is used by console_setup
162 * above to handle user-supplied console arguments; however it can also
163 * be used by arch-specific code either to override the user or more
164 * commonly to provide a default console (ie from PROM variables) when
165 * the user has not supplied one.
167 int __init add_preferred_console(char *name, int idx, char *options)
169 struct console_cmdline *c;
173 * See if this tty is not yet registered, and
174 * if we have a slot free.
176 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
177 if (strcmp(console_cmdline[i].name, name) == 0 &&
178 console_cmdline[i].index == idx) {
179 selected_console = i;
182 if (i == MAX_CMDLINECONSOLES)
184 selected_console = i;
185 c = &console_cmdline[i];
186 memcpy(c->name, name, sizeof(c->name));
187 c->name[sizeof(c->name) - 1] = 0;
188 c->options = options;
193 static int __init log_buf_len_setup(char *str)
195 unsigned long size = memparse(str, &str);
199 size = roundup_pow_of_two(size);
200 if (size > log_buf_len) {
201 unsigned long start, dest_idx, offset;
204 new_log_buf = alloc_bootmem(size);
206 printk("log_buf_len: allocation failed\n");
210 spin_lock_irqsave(&logbuf_lock, flags);
212 log_buf = new_log_buf;
214 offset = start = min(con_start, log_start);
216 while (start != log_end) {
217 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
224 spin_unlock_irqrestore(&logbuf_lock, flags);
226 printk("log_buf_len: %d\n", log_buf_len);
233 __setup("log_buf_len=", log_buf_len_setup);
236 * Commands to do_syslog:
238 * 0 -- Close the log. Currently a NOP.
239 * 1 -- Open the log. Currently a NOP.
240 * 2 -- Read from the log.
241 * 3 -- Read all messages remaining in the ring buffer.
242 * 4 -- Read and clear all messages remaining in the ring buffer
243 * 5 -- Clear ring buffer.
244 * 6 -- Disable printk's to console
245 * 7 -- Enable printk's to console
246 * 8 -- Set level of messages printed to console
247 * 9 -- Return number of unread characters in the log buffer
248 * 10 -- Return size of the log buffer
250 int do_syslog(int type, char __user * buf, int len)
252 unsigned long i, j, limit, count;
257 if (!vx_check(0, VX_ADMIN|VX_WATCH))
260 error = security_syslog(type);
265 case 0: /* Close log */
267 case 1: /* Open log */
269 case 2: /* Read from log */
276 error = verify_area(VERIFY_WRITE,buf,len);
279 error = wait_event_interruptible(log_wait, (log_start - log_end));
283 spin_lock_irq(&logbuf_lock);
284 while (!error && (log_start != log_end) && i < len) {
285 c = LOG_BUF(log_start);
287 spin_unlock_irq(&logbuf_lock);
288 error = __put_user(c,buf);
291 spin_lock_irq(&logbuf_lock);
293 spin_unlock_irq(&logbuf_lock);
297 case 4: /* Read/clear last kernel messages */
300 case 3: /* Read last kernel messages */
307 error = verify_area(VERIFY_WRITE,buf,len);
311 if (count > log_buf_len)
313 spin_lock_irq(&logbuf_lock);
314 if (count > logged_chars)
315 count = logged_chars;
320 * __put_user() could sleep, and while we sleep
321 * printk() could overwrite the messages
322 * we try to copy to user space. Therefore
323 * the messages are copied in reverse. <manfreds>
325 for(i = 0; i < count && !error; i++) {
327 if (j + log_buf_len < log_end)
330 spin_unlock_irq(&logbuf_lock);
331 error = __put_user(c,&buf[count-1-i]);
332 spin_lock_irq(&logbuf_lock);
334 spin_unlock_irq(&logbuf_lock);
339 int offset = count-error;
340 /* buffer overflow during copy, correct user buffer. */
341 for(i=0;i<error;i++) {
342 if (__get_user(c,&buf[i+offset]) ||
343 __put_user(c,&buf[i])) {
350 case 5: /* Clear ring buffer */
353 case 6: /* Disable logging to console */
354 console_loglevel = minimum_console_loglevel;
356 case 7: /* Enable logging to console */
357 console_loglevel = default_console_loglevel;
359 case 8: /* Set level of messages printed to console */
361 if (len < 1 || len > 8)
363 if (len < minimum_console_loglevel)
364 len = minimum_console_loglevel;
365 console_loglevel = len;
368 case 9: /* Number of chars in the log buffer */
369 error = log_end - log_start;
371 case 10: /* Size of the log buffer */
382 asmlinkage long sys_syslog(int type, char __user * buf, int len)
384 return do_syslog(type, buf, len);
388 * Crashdump special routine. Don't print to global log_buf, just to the
389 * actual console device(s).
391 static void crashdump_call_console_drivers(const char *buf, unsigned long len)
395 for (con = console_drivers; con; con = con->next) {
396 if ((con->flags & CON_ENABLED) && con->write)
397 con->write(con, buf, len);
402 * Call the console drivers on a range of log_buf
404 static void __call_console_drivers(unsigned long start, unsigned long end)
408 for (con = console_drivers; con; con = con->next) {
409 if ((con->flags & CON_ENABLED) && con->write)
410 con->write(con, &LOG_BUF(start), end - start);
415 * Write out chars from start to end - 1 inclusive
417 static void _call_console_drivers(unsigned long start,
418 unsigned long end, int msg_log_level)
420 if (msg_log_level < console_loglevel &&
421 console_drivers && start != end) {
422 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
424 __call_console_drivers(start & LOG_BUF_MASK,
426 __call_console_drivers(0, end & LOG_BUF_MASK);
428 __call_console_drivers(start, end);
434 * Call the console drivers, asking them to write out
435 * log_buf[start] to log_buf[end - 1].
436 * The console_sem must be held.
438 static void call_console_drivers(unsigned long start, unsigned long end)
440 unsigned long cur_index, start_print;
441 static int msg_level = -1;
443 if (((long)(start - end)) > 0)
448 while (cur_index != end) {
449 if ( msg_level < 0 &&
450 ((end - cur_index) > 2) &&
451 LOG_BUF(cur_index + 0) == '<' &&
452 LOG_BUF(cur_index + 1) >= '0' &&
453 LOG_BUF(cur_index + 1) <= '7' &&
454 LOG_BUF(cur_index + 2) == '>')
456 msg_level = LOG_BUF(cur_index + 1) - '0';
458 start_print = cur_index;
460 while (cur_index != end) {
461 char c = LOG_BUF(cur_index);
467 * printk() has already given us loglevel tags in
468 * the buffer. This code is here in case the
469 * log buffer has wrapped right round and scribbled
472 msg_level = default_message_loglevel;
474 _call_console_drivers(start_print, cur_index, msg_level);
476 start_print = cur_index;
481 _call_console_drivers(start_print, end, msg_level);
484 static void emit_log_char(char c)
486 LOG_BUF(log_end) = c;
488 if (log_end - log_start > log_buf_len)
489 log_start = log_end - log_buf_len;
490 if (log_end - con_start > log_buf_len)
491 con_start = log_end - log_buf_len;
492 if (logged_chars < log_buf_len)
497 * Zap console related locks when oopsing. Only zap at most once
498 * every 10 seconds, to leave time for slow consoles to print a
501 static void zap_locks(void)
503 static unsigned long oops_timestamp;
505 if (time_after_eq(jiffies, oops_timestamp) &&
506 !time_after(jiffies, oops_timestamp + 30*HZ))
509 oops_timestamp = jiffies;
511 /* If a crash is occurring, make sure we can't deadlock */
512 spin_lock_init(&logbuf_lock);
513 /* And make sure that we print immediately */
514 init_MUTEX(&console_sem);
518 * This is printk. It can be called from any context. We want it to work.
520 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
521 * call the console drivers. If we fail to get the semaphore we place the output
522 * into the log buffer and return. The current holder of the console_sem will
523 * notice the new output in release_console_sem() and will send it to the
524 * consoles before releasing the semaphore.
526 * One effect of this deferred printing is that code which calls printk() and
527 * then changes console_loglevel may break. This is because console_loglevel
528 * is inspected when the actual printing occurs.
530 asmlinkage int printk(const char *fmt, ...)
536 r = vprintk(fmt, args);
542 asmlinkage int vprintk(const char *fmt, va_list args)
547 static char printk_buf[1024];
548 static int log_level_unknown = 1;
550 if (unlikely(oops_in_progress))
553 /* This stops the holder of console_sem just where we want him */
554 spin_lock_irqsave(&logbuf_lock, flags);
556 /* Emit the output into the temporary buffer */
557 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
559 if (unlikely(crashdump_mode())) {
560 crashdump_call_console_drivers(printk_buf, printed_len);
561 spin_unlock_irqrestore(&logbuf_lock, flags);
566 * Copy the output into log_buf. If the caller didn't provide
567 * appropriate log level tags, we insert them here
569 for (p = printk_buf; *p; p++) {
570 if (log_level_unknown) {
571 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
573 emit_log_char(default_message_loglevel + '0');
576 log_level_unknown = 0;
580 log_level_unknown = 1;
583 if (!cpu_online(smp_processor_id()) &&
584 system_state != SYSTEM_RUNNING) {
586 * Some console drivers may assume that per-cpu resources have
587 * been allocated. So don't allow them to be called by this
588 * CPU until it is officially up. We shouldn't be calling into
589 * random console drivers on a CPU which doesn't exist yet..
591 spin_unlock_irqrestore(&logbuf_lock, flags);
594 if (!down_trylock(&console_sem)) {
597 * We own the drivers. We can drop the spinlock and let
598 * release_console_sem() print the text
600 spin_unlock_irqrestore(&logbuf_lock, flags);
601 console_may_schedule = 0;
602 release_console_sem();
605 * Someone else owns the drivers. We drop the spinlock, which
606 * allows the semaphore holder to proceed and to call the
607 * console drivers with the output which we just produced.
609 spin_unlock_irqrestore(&logbuf_lock, flags);
614 EXPORT_SYMBOL(printk);
615 EXPORT_SYMBOL(vprintk);
618 * acquire_console_sem - lock the console system for exclusive use.
620 * Acquires a semaphore which guarantees that the caller has
621 * exclusive access to the console system and the console_drivers list.
623 * Can sleep, returns nothing.
625 void acquire_console_sem(void)
631 console_may_schedule = 1;
633 EXPORT_SYMBOL(acquire_console_sem);
635 int is_console_locked(void)
637 return console_locked;
639 EXPORT_SYMBOL(is_console_locked);
642 * release_console_sem - unlock the console system
644 * Releases the semaphore which the caller holds on the console system
645 * and the console driver list.
647 * While the semaphore was held, console output may have been buffered
648 * by printk(). If this is the case, release_console_sem() emits
649 * the output prior to releasing the semaphore.
651 * If there is output waiting for klogd, we wake it up.
653 * release_console_sem() may be called from any context.
655 void release_console_sem(void)
658 unsigned long _con_start, _log_end;
659 unsigned long wake_klogd = 0;
662 spin_lock_irqsave(&logbuf_lock, flags);
663 wake_klogd |= log_start - log_end;
664 if (con_start == log_end)
665 break; /* Nothing to print */
666 _con_start = con_start;
668 con_start = log_end; /* Flush */
669 spin_unlock_irqrestore(&logbuf_lock, flags);
670 call_console_drivers(_con_start, _log_end);
673 console_may_schedule = 0;
675 spin_unlock_irqrestore(&logbuf_lock, flags);
676 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
677 wake_up_interruptible(&log_wait);
679 EXPORT_SYMBOL(release_console_sem);
681 /** console_conditional_schedule - yield the CPU if required
683 * If the console code is currently allowed to sleep, and
684 * if this CPU should yield the CPU to another task, do
687 * Must be called within acquire_console_sem().
689 void __sched console_conditional_schedule(void)
691 if (console_may_schedule)
694 EXPORT_SYMBOL(console_conditional_schedule);
696 void console_print(const char *s)
698 printk(KERN_EMERG "%s", s);
700 EXPORT_SYMBOL(console_print);
702 void console_unblank(void)
707 * Try to get the console semaphore. If someone else owns it
708 * we have to return without unblanking because console_unblank
709 * may be called in interrupt context.
711 if (down_trylock(&console_sem) != 0)
714 console_may_schedule = 0;
715 for (c = console_drivers; c != NULL; c = c->next)
716 if ((c->flags & CON_ENABLED) && c->unblank)
718 release_console_sem();
720 EXPORT_SYMBOL(console_unblank);
723 * Return the console tty driver structure and its associated index
725 struct tty_driver *console_device(int *index)
728 struct tty_driver *driver = NULL;
730 acquire_console_sem();
731 for (c = console_drivers; c != NULL; c = c->next) {
734 driver = c->device(c, index);
738 release_console_sem();
743 * Prevent further output on the passed console device so that (for example)
744 * serial drivers can disable console output before suspending a port, and can
745 * re-enable output afterwards.
747 void console_stop(struct console *console)
749 acquire_console_sem();
750 console->flags &= ~CON_ENABLED;
751 release_console_sem();
753 EXPORT_SYMBOL(console_stop);
755 void console_start(struct console *console)
757 acquire_console_sem();
758 console->flags |= CON_ENABLED;
759 release_console_sem();
761 EXPORT_SYMBOL(console_start);
764 * The console driver calls this routine during kernel initialization
765 * to register the console printing procedure with printk() and to
766 * print any messages that were printed by the kernel before the
767 * console driver was initialized.
769 void register_console(struct console * console)
774 if (preferred_console < 0)
775 preferred_console = selected_console;
778 * See if we want to use this console driver. If we
779 * didn't select a console we take the first one
780 * that registers here.
782 if (preferred_console < 0) {
783 if (console->index < 0)
785 if (console->setup == NULL ||
786 console->setup(console, NULL) == 0) {
787 console->flags |= CON_ENABLED | CON_CONSDEV;
788 preferred_console = 0;
793 * See if this console matches one we selected on
796 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
797 if (strcmp(console_cmdline[i].name, console->name) != 0)
799 if (console->index >= 0 &&
800 console->index != console_cmdline[i].index)
802 if (console->index < 0)
803 console->index = console_cmdline[i].index;
804 if (console->setup &&
805 console->setup(console, console_cmdline[i].options) != 0)
807 console->flags |= CON_ENABLED;
808 console->index = console_cmdline[i].index;
809 if (i == preferred_console)
810 console->flags |= CON_CONSDEV;
814 if (!(console->flags & CON_ENABLED))
818 * Put this console in the list - keep the
819 * preferred driver at the head of the list.
821 acquire_console_sem();
822 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
823 console->next = console_drivers;
824 console_drivers = console;
826 console->next = console_drivers->next;
827 console_drivers->next = console;
829 if (console->flags & CON_PRINTBUFFER) {
831 * release_console_sem() will print out the buffered messages
834 spin_lock_irqsave(&logbuf_lock, flags);
835 con_start = log_start;
836 spin_unlock_irqrestore(&logbuf_lock, flags);
838 release_console_sem();
840 EXPORT_SYMBOL(register_console);
842 int unregister_console(struct console * console)
844 struct console *a,*b;
847 acquire_console_sem();
848 if (console_drivers == console) {
849 console_drivers=console->next;
852 for (a=console_drivers->next, b=console_drivers ;
862 /* If last console is removed, we re-enable picking the first
863 * one that gets registered. Without that, pmac early boot console
864 * would prevent fbcon from taking over.
866 if (console_drivers == NULL)
867 preferred_console = selected_console;
870 release_console_sem();
873 EXPORT_SYMBOL(unregister_console);
876 * tty_write_message - write a message to a certain tty, not just the console.
878 * This is used for messages that need to be redirected to a specific tty.
879 * We don't put it into the syslog queue right now maybe in the future if
882 void tty_write_message(struct tty_struct *tty, char *msg)
884 if (tty && tty->driver->write)
885 tty->driver->write(tty, msg, strlen(msg));
890 * printk rate limiting, lifted from the networking subsystem.
892 * This enforces a rate limit: not more than one kernel message
893 * every printk_ratelimit_jiffies to make a denial-of-service
896 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
898 static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
899 static unsigned long toks = 10*5*HZ;
900 static unsigned long last_msg;
903 unsigned long now = jiffies;
905 spin_lock_irqsave(&ratelimit_lock, flags);
906 toks += now - last_msg;
908 if (toks > (ratelimit_burst * ratelimit_jiffies))
909 toks = ratelimit_burst * ratelimit_jiffies;
910 if (toks >= ratelimit_jiffies) {
913 toks -= ratelimit_jiffies;
914 spin_unlock_irqrestore(&ratelimit_lock, flags);
916 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
920 spin_unlock_irqrestore(&ratelimit_lock, flags);
923 EXPORT_SYMBOL(__printk_ratelimit);
925 /* minimum time in jiffies between messages */
926 int printk_ratelimit_jiffies = 5*HZ;
928 /* number of messages we send before ratelimiting */
929 int printk_ratelimit_burst = 10;
931 int printk_ratelimit(void)
933 return __printk_ratelimit(printk_ratelimit_jiffies,
934 printk_ratelimit_burst);
936 EXPORT_SYMBOL(printk_ratelimit);