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>
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 spinlock_t logbuf_lock = SPIN_LOCK_UNLOCKED;
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 preferred_console = -1;
114 /* Flag: console code may call schedule() */
115 static int console_may_schedule;
118 * Setup a list of consoles. Called from init/main.c
120 static int __init console_setup(char *str)
122 char name[sizeof(console_cmdline[0].name)];
127 * Decode str into name, index, options.
129 if (str[0] >= '0' && str[0] <= '9') {
130 strcpy(name, "ttyS");
131 strncpy(name + 4, str, sizeof(name) - 5);
133 strncpy(name, str, sizeof(name) - 1);
134 name[sizeof(name) - 1] = 0;
135 if ((options = strchr(str, ',')) != NULL)
138 if (!strcmp(str, "ttya"))
139 strcpy(name, "ttyS0");
140 if (!strcmp(str, "ttyb"))
141 strcpy(name, "ttyS1");
143 for(s = name; *s; s++)
144 if (*s >= '0' && *s <= '9')
146 idx = simple_strtoul(s, NULL, 10);
149 add_preferred_console(name, idx, options);
153 __setup("console=", console_setup);
156 * add_preferred_console - add a device to the list of preferred consoles.
158 * The last preferred console added will be used for kernel messages
159 * and stdin/out/err for init. Normally this is used by console_setup
160 * above to handle user-supplied console arguments; however it can also
161 * be used by arch-specific code either to override the user or more
162 * commonly to provide a default console (ie from PROM variables) when
163 * the user has not supplied one.
165 int __init add_preferred_console(char *name, int idx, char *options)
167 struct console_cmdline *c;
171 * See if this tty is not yet registered, and
172 * if we have a slot free.
174 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
175 if (strcmp(console_cmdline[i].name, name) == 0 &&
176 console_cmdline[i].index == idx) {
177 preferred_console = i;
180 if (i == MAX_CMDLINECONSOLES)
182 preferred_console = i;
183 c = &console_cmdline[i];
184 memcpy(c->name, name, sizeof(c->name));
185 c->name[sizeof(c->name) - 1] = 0;
186 c->options = options;
191 static int __init log_buf_len_setup(char *str)
193 unsigned long size = memparse(str, &str);
197 size = roundup_pow_of_two(size);
198 if (size > log_buf_len) {
199 unsigned long start, dest_idx, offset;
202 new_log_buf = alloc_bootmem(size);
204 printk("log_buf_len: allocation failed\n");
208 spin_lock_irqsave(&logbuf_lock, flags);
210 log_buf = new_log_buf;
212 offset = start = min(con_start, log_start);
214 while (start != log_end) {
215 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
222 spin_unlock_irqrestore(&logbuf_lock, flags);
224 printk("log_buf_len: %d\n", log_buf_len);
231 __setup("log_buf_len=", log_buf_len_setup);
234 * Commands to do_syslog:
236 * 0 -- Close the log. Currently a NOP.
237 * 1 -- Open the log. Currently a NOP.
238 * 2 -- Read from the log.
239 * 3 -- Read all messages remaining in the ring buffer.
240 * 4 -- Read and clear all messages remaining in the ring buffer
241 * 5 -- Clear ring buffer.
242 * 6 -- Disable printk's to console
243 * 7 -- Enable printk's to console
244 * 8 -- Set level of messages printed to console
245 * 9 -- Return number of unread characters in the log buffer
246 * 10 -- Return size of the log buffer
248 int do_syslog(int type, char __user * buf, int len)
250 unsigned long i, j, limit, count;
255 if (!vx_check(0, VX_ADMIN|VX_WATCH))
258 error = security_syslog(type);
263 case 0: /* Close log */
265 case 1: /* Open log */
267 case 2: /* Read from log */
274 error = verify_area(VERIFY_WRITE,buf,len);
277 error = wait_event_interruptible(log_wait, (log_start - log_end));
281 spin_lock_irq(&logbuf_lock);
282 while (!error && (log_start != log_end) && i < len) {
283 c = LOG_BUF(log_start);
285 spin_unlock_irq(&logbuf_lock);
286 error = __put_user(c,buf);
289 spin_lock_irq(&logbuf_lock);
291 spin_unlock_irq(&logbuf_lock);
295 case 4: /* Read/clear last kernel messages */
298 case 3: /* Read last kernel messages */
305 error = verify_area(VERIFY_WRITE,buf,len);
309 if (count > log_buf_len)
311 spin_lock_irq(&logbuf_lock);
312 if (count > logged_chars)
313 count = logged_chars;
318 * __put_user() could sleep, and while we sleep
319 * printk() could overwrite the messages
320 * we try to copy to user space. Therefore
321 * the messages are copied in reverse. <manfreds>
323 for(i = 0; i < count && !error; i++) {
325 if (j + log_buf_len < log_end)
328 spin_unlock_irq(&logbuf_lock);
329 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])) {
348 case 5: /* Clear ring buffer */
351 case 6: /* Disable logging to console */
352 console_loglevel = minimum_console_loglevel;
354 case 7: /* Enable logging to console */
355 console_loglevel = default_console_loglevel;
357 case 8: /* Set level of messages printed to console */
359 if (len < 1 || len > 8)
361 if (len < minimum_console_loglevel)
362 len = minimum_console_loglevel;
363 console_loglevel = len;
366 case 9: /* Number of chars in the log buffer */
367 error = log_end - log_start;
369 case 10: /* Size of the log buffer */
380 asmlinkage long sys_syslog(int type, char __user * buf, int len)
382 return do_syslog(type, buf, len);
386 * Call the console drivers on a range of log_buf
388 static void __call_console_drivers(unsigned long start, unsigned long end)
392 for (con = console_drivers; con; con = con->next) {
393 if ((con->flags & CON_ENABLED) && con->write)
394 con->write(con, &LOG_BUF(start), end - start);
399 * Write out chars from start to end - 1 inclusive
401 static void _call_console_drivers(unsigned long start,
402 unsigned long end, int msg_log_level)
404 if (msg_log_level < console_loglevel &&
405 console_drivers && start != end) {
406 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
408 __call_console_drivers(start & LOG_BUF_MASK,
410 __call_console_drivers(0, end & LOG_BUF_MASK);
412 __call_console_drivers(start, end);
418 * Call the console drivers, asking them to write out
419 * log_buf[start] to log_buf[end - 1].
420 * The console_sem must be held.
422 static void call_console_drivers(unsigned long start, unsigned long end)
424 unsigned long cur_index, start_print;
425 static int msg_level = -1;
427 if (((long)(start - end)) > 0)
432 while (cur_index != end) {
433 if ( msg_level < 0 &&
434 ((end - cur_index) > 2) &&
435 LOG_BUF(cur_index + 0) == '<' &&
436 LOG_BUF(cur_index + 1) >= '0' &&
437 LOG_BUF(cur_index + 1) <= '7' &&
438 LOG_BUF(cur_index + 2) == '>')
440 msg_level = LOG_BUF(cur_index + 1) - '0';
442 start_print = cur_index;
444 while (cur_index != end) {
445 char c = LOG_BUF(cur_index);
451 * printk() has already given us loglevel tags in
452 * the buffer. This code is here in case the
453 * log buffer has wrapped right round and scribbled
456 msg_level = default_message_loglevel;
458 _call_console_drivers(start_print, cur_index, msg_level);
460 start_print = cur_index;
465 _call_console_drivers(start_print, end, msg_level);
468 static void emit_log_char(char c)
470 LOG_BUF(log_end) = c;
472 if (log_end - log_start > log_buf_len)
473 log_start = log_end - log_buf_len;
474 if (log_end - con_start > log_buf_len)
475 con_start = log_end - log_buf_len;
476 if (logged_chars < log_buf_len)
481 * Zap console related locks when oopsing. Only zap at most once
482 * every 10 seconds, to leave time for slow consoles to print a
485 static void zap_locks(void)
487 static unsigned long oops_timestamp;
489 if (time_after_eq(jiffies, oops_timestamp) &&
490 !time_after(jiffies, oops_timestamp + 30*HZ))
493 oops_timestamp = jiffies;
495 /* If a crash is occurring, make sure we can't deadlock */
496 spin_lock_init(&logbuf_lock);
497 /* And make sure that we print immediately */
498 init_MUTEX(&console_sem);
502 * This is printk. It can be called from any context. We want it to work.
504 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
505 * call the console drivers. If we fail to get the semaphore we place the output
506 * into the log buffer and return. The current holder of the console_sem will
507 * notice the new output in release_console_sem() and will send it to the
508 * consoles before releasing the semaphore.
510 * One effect of this deferred printing is that code which calls printk() and
511 * then changes console_loglevel may break. This is because console_loglevel
512 * is inspected when the actual printing occurs.
514 asmlinkage int printk(const char *fmt, ...)
520 r = vprintk(fmt, args);
526 static volatile int printk_cpu = -1;
528 asmlinkage int vprintk(const char *fmt, va_list args)
533 static char printk_buf[1024];
534 static int log_level_unknown = 1;
536 if (unlikely(oops_in_progress && printk_cpu == smp_processor_id()))
539 /* This stops the holder of console_sem just where we want him */
540 spin_lock_irqsave(&logbuf_lock, flags);
541 printk_cpu = smp_processor_id();
543 /* Emit the output into the temporary buffer */
544 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
547 * Copy the output into log_buf. If the caller didn't provide
548 * appropriate log level tags, we insert them here
550 for (p = printk_buf; *p; p++) {
551 if (log_level_unknown) {
552 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
554 emit_log_char(default_message_loglevel + '0');
557 log_level_unknown = 0;
561 log_level_unknown = 1;
564 if (!cpu_online(smp_processor_id()) &&
565 system_state != SYSTEM_RUNNING) {
567 * Some console drivers may assume that per-cpu resources have
568 * been allocated. So don't allow them to be called by this
569 * CPU until it is officially up. We shouldn't be calling into
570 * random console drivers on a CPU which doesn't exist yet..
572 spin_unlock_irqrestore(&logbuf_lock, flags);
575 if (!down_trylock(&console_sem)) {
578 * We own the drivers. We can drop the spinlock and let
579 * release_console_sem() print the text
581 spin_unlock_irqrestore(&logbuf_lock, flags);
582 console_may_schedule = 0;
583 release_console_sem();
586 * Someone else owns the drivers. We drop the spinlock, which
587 * allows the semaphore holder to proceed and to call the
588 * console drivers with the output which we just produced.
590 spin_unlock_irqrestore(&logbuf_lock, flags);
595 EXPORT_SYMBOL(printk);
596 EXPORT_SYMBOL(vprintk);
599 * acquire_console_sem - lock the console system for exclusive use.
601 * Acquires a semaphore which guarantees that the caller has
602 * exclusive access to the console system and the console_drivers list.
604 * Can sleep, returns nothing.
606 void acquire_console_sem(void)
612 console_may_schedule = 1;
614 EXPORT_SYMBOL(acquire_console_sem);
616 int is_console_locked(void)
618 return console_locked;
620 EXPORT_SYMBOL(is_console_locked);
623 * release_console_sem - unlock the console system
625 * Releases the semaphore which the caller holds on the console system
626 * and the console driver list.
628 * While the semaphore was held, console output may have been buffered
629 * by printk(). If this is the case, release_console_sem() emits
630 * the output prior to releasing the semaphore.
632 * If there is output waiting for klogd, we wake it up.
634 * release_console_sem() may be called from any context.
636 void release_console_sem(void)
639 unsigned long _con_start, _log_end;
640 unsigned long wake_klogd = 0;
643 spin_lock_irqsave(&logbuf_lock, flags);
644 wake_klogd |= log_start - log_end;
645 if (con_start == log_end)
646 break; /* Nothing to print */
647 _con_start = con_start;
649 con_start = log_end; /* Flush */
650 spin_unlock_irqrestore(&logbuf_lock, flags);
651 call_console_drivers(_con_start, _log_end);
654 console_may_schedule = 0;
656 spin_unlock_irqrestore(&logbuf_lock, flags);
657 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
658 wake_up_interruptible(&log_wait);
660 EXPORT_SYMBOL(release_console_sem);
662 /** console_conditional_schedule - yield the CPU if required
664 * If the console code is currently allowed to sleep, and
665 * if this CPU should yield the CPU to another task, do
668 * Must be called within acquire_console_sem().
670 void console_conditional_schedule(void)
672 if (console_may_schedule && need_resched()) {
673 set_current_state(TASK_RUNNING);
677 EXPORT_SYMBOL(console_conditional_schedule);
679 void console_print(const char *s)
681 printk(KERN_EMERG "%s", s);
683 EXPORT_SYMBOL(console_print);
685 void console_unblank(void)
690 * Try to get the console semaphore. If someone else owns it
691 * we have to return without unblanking because console_unblank
692 * may be called in interrupt context.
694 if (down_trylock(&console_sem) != 0)
697 console_may_schedule = 0;
698 for (c = console_drivers; c != NULL; c = c->next)
699 if ((c->flags & CON_ENABLED) && c->unblank)
701 release_console_sem();
703 EXPORT_SYMBOL(console_unblank);
706 * Return the console tty driver structure and its associated index
708 struct tty_driver *console_device(int *index)
711 struct tty_driver *driver = NULL;
713 acquire_console_sem();
714 for (c = console_drivers; c != NULL; c = c->next) {
717 driver = c->device(c, index);
721 release_console_sem();
726 * Prevent further output on the passed console device so that (for example)
727 * serial drivers can disable console output before suspending a port, and can
728 * re-enable output afterwards.
730 void console_stop(struct console *console)
732 acquire_console_sem();
733 console->flags &= ~CON_ENABLED;
734 release_console_sem();
736 EXPORT_SYMBOL(console_stop);
738 void console_start(struct console *console)
740 acquire_console_sem();
741 console->flags |= CON_ENABLED;
742 release_console_sem();
744 EXPORT_SYMBOL(console_start);
747 * The console driver calls this routine during kernel initialization
748 * to register the console printing procedure with printk() and to
749 * print any messages that were printed by the kernel before the
750 * console driver was initialized.
752 void register_console(struct console * 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 = -1;
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, 0, 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 spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
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);