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);
196 if (size > log_buf_len) {
197 unsigned long start, dest_idx, offset;
200 new_log_buf = alloc_bootmem(size);
202 printk("log_buf_len: allocation failed\n");
206 spin_lock_irqsave(&logbuf_lock, flags);
208 log_buf = new_log_buf;
210 offset = start = min(con_start, log_start);
212 while (start != log_end) {
213 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
220 spin_unlock_irqrestore(&logbuf_lock, flags);
222 printk("log_buf_len: %d\n", log_buf_len);
229 __setup("log_buf_len=", log_buf_len_setup);
232 * Commands to do_syslog:
234 * 0 -- Close the log. Currently a NOP.
235 * 1 -- Open the log. Currently a NOP.
236 * 2 -- Read from the log.
237 * 3 -- Read all messages remaining in the ring buffer.
238 * 4 -- Read and clear all messages remaining in the ring buffer
239 * 5 -- Clear ring buffer.
240 * 6 -- Disable printk's to console
241 * 7 -- Enable printk's to console
242 * 8 -- Set level of messages printed to console
243 * 9 -- Return number of unread characters in the log buffer
244 * 10 -- Return size of the log buffer
246 int do_syslog(int type, char __user * buf, int len)
248 unsigned long i, j, limit, count;
253 if (!vx_check(0, VX_ADMIN|VX_WATCH))
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);
287 spin_lock_irq(&logbuf_lock);
289 spin_unlock_irq(&logbuf_lock);
293 case 4: /* Read/clear last kernel messages */
296 case 3: /* Read last kernel messages */
303 error = verify_area(VERIFY_WRITE,buf,len);
307 if (count > log_buf_len)
309 spin_lock_irq(&logbuf_lock);
310 if (count > logged_chars)
311 count = logged_chars;
316 * __put_user() could sleep, and while we sleep
317 * printk() could overwrite the messages
318 * we try to copy to user space. Therefore
319 * the messages are copied in reverse. <manfreds>
321 for(i = 0; i < count && !error; i++) {
323 if (j + log_buf_len < log_end)
326 spin_unlock_irq(&logbuf_lock);
327 error = __put_user(c,&buf[count-1-i]);
328 spin_lock_irq(&logbuf_lock);
330 spin_unlock_irq(&logbuf_lock);
335 int offset = count-error;
336 /* buffer overflow during copy, correct user buffer. */
337 for(i=0;i<error;i++) {
338 if (__get_user(c,&buf[i+offset]) ||
339 __put_user(c,&buf[i])) {
346 case 5: /* Clear ring buffer */
349 case 6: /* Disable logging to console */
350 console_loglevel = minimum_console_loglevel;
352 case 7: /* Enable logging to console */
353 console_loglevel = default_console_loglevel;
355 case 8: /* Set level of messages printed to console */
357 if (len < 1 || len > 8)
359 if (len < minimum_console_loglevel)
360 len = minimum_console_loglevel;
361 console_loglevel = len;
364 case 9: /* Number of chars in the log buffer */
365 error = log_end - log_start;
367 case 10: /* Size of the log buffer */
378 asmlinkage long sys_syslog(int type, char __user * buf, int len)
380 return do_syslog(type, buf, len);
384 * Call the console drivers on a range of log_buf
386 static void __call_console_drivers(unsigned long start, unsigned long end)
390 for (con = console_drivers; con; con = con->next) {
391 if ((con->flags & CON_ENABLED) && con->write)
392 con->write(con, &LOG_BUF(start), end - start);
397 * Write out chars from start to end - 1 inclusive
399 static void _call_console_drivers(unsigned long start,
400 unsigned long end, int msg_log_level)
402 if (msg_log_level < console_loglevel &&
403 console_drivers && start != end) {
404 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
406 __call_console_drivers(start & LOG_BUF_MASK,
408 __call_console_drivers(0, end & LOG_BUF_MASK);
410 __call_console_drivers(start, end);
416 * Call the console drivers, asking them to write out
417 * log_buf[start] to log_buf[end - 1].
418 * The console_sem must be held.
420 static void call_console_drivers(unsigned long start, unsigned long end)
422 unsigned long cur_index, start_print;
423 static int msg_level = -1;
425 if (((long)(start - end)) > 0)
430 while (cur_index != end) {
431 if ( msg_level < 0 &&
432 ((end - cur_index) > 2) &&
433 LOG_BUF(cur_index + 0) == '<' &&
434 LOG_BUF(cur_index + 1) >= '0' &&
435 LOG_BUF(cur_index + 1) <= '7' &&
436 LOG_BUF(cur_index + 2) == '>')
438 msg_level = LOG_BUF(cur_index + 1) - '0';
440 start_print = cur_index;
442 while (cur_index != end) {
443 char c = LOG_BUF(cur_index);
449 * printk() has already given us loglevel tags in
450 * the buffer. This code is here in case the
451 * log buffer has wrapped right round and scribbled
454 msg_level = default_message_loglevel;
456 _call_console_drivers(start_print, cur_index, msg_level);
458 start_print = cur_index;
463 _call_console_drivers(start_print, end, msg_level);
466 static void emit_log_char(char c)
468 LOG_BUF(log_end) = c;
470 if (log_end - log_start > log_buf_len)
471 log_start = log_end - log_buf_len;
472 if (log_end - con_start > log_buf_len)
473 con_start = log_end - log_buf_len;
474 if (logged_chars < log_buf_len)
479 * Zap console related locks when oopsing. Only zap at most once
480 * every 10 seconds, to leave time for slow consoles to print a
483 static void zap_locks(void)
485 static unsigned long oops_timestamp;
487 if (time_after_eq(jiffies, oops_timestamp) &&
488 !time_after(jiffies, oops_timestamp + 30*HZ))
491 oops_timestamp = jiffies;
493 /* If a crash is occurring, make sure we can't deadlock */
494 spin_lock_init(&logbuf_lock);
495 /* And make sure that we print immediately */
496 init_MUTEX(&console_sem);
500 * This is printk. It can be called from any context. We want it to work.
502 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
503 * call the console drivers. If we fail to get the semaphore we place the output
504 * into the log buffer and return. The current holder of the console_sem will
505 * notice the new output in release_console_sem() and will send it to the
506 * consoles before releasing the semaphore.
508 * One effect of this deferred printing is that code which calls printk() and
509 * then changes console_loglevel may break. This is because console_loglevel
510 * is inspected when the actual printing occurs.
512 asmlinkage int printk(const char *fmt, ...)
518 static char printk_buf[1024];
519 static int log_level_unknown = 1;
521 if (unlikely(oops_in_progress))
524 /* This stops the holder of console_sem just where we want him */
525 spin_lock_irqsave(&logbuf_lock, flags);
527 /* Emit the output into the temporary buffer */
529 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
533 * Copy the output into log_buf. If the caller didn't provide
534 * appropriate log level tags, we insert them here
536 for (p = printk_buf; *p; p++) {
537 if (log_level_unknown) {
538 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
540 emit_log_char(default_message_loglevel + '0');
543 log_level_unknown = 0;
547 log_level_unknown = 1;
550 if (!cpu_online(smp_processor_id()) &&
551 system_state != SYSTEM_RUNNING) {
553 * Some console drivers may assume that per-cpu resources have
554 * been allocated. So don't allow them to be called by this
555 * CPU until it is officially up. We shouldn't be calling into
556 * random console drivers on a CPU which doesn't exist yet..
558 spin_unlock_irqrestore(&logbuf_lock, flags);
561 if (!down_trylock(&console_sem)) {
564 * We own the drivers. We can drop the spinlock and let
565 * release_console_sem() print the text
567 spin_unlock_irqrestore(&logbuf_lock, flags);
568 console_may_schedule = 0;
569 release_console_sem();
572 * Someone else owns the drivers. We drop the spinlock, which
573 * allows the semaphore holder to proceed and to call the
574 * console drivers with the output which we just produced.
576 spin_unlock_irqrestore(&logbuf_lock, flags);
581 EXPORT_SYMBOL(printk);
584 * acquire_console_sem - lock the console system for exclusive use.
586 * Acquires a semaphore which guarantees that the caller has
587 * exclusive access to the console system and the console_drivers list.
589 * Can sleep, returns nothing.
591 void acquire_console_sem(void)
597 console_may_schedule = 1;
599 EXPORT_SYMBOL(acquire_console_sem);
601 int is_console_locked(void)
603 return console_locked;
605 EXPORT_SYMBOL(is_console_locked);
608 * release_console_sem - unlock the console system
610 * Releases the semaphore which the caller holds on the console system
611 * and the console driver list.
613 * While the semaphore was held, console output may have been buffered
614 * by printk(). If this is the case, release_console_sem() emits
615 * the output prior to releasing the semaphore.
617 * If there is output waiting for klogd, we wake it up.
619 * release_console_sem() may be called from any context.
621 void release_console_sem(void)
624 unsigned long _con_start, _log_end;
625 unsigned long wake_klogd = 0;
628 spin_lock_irqsave(&logbuf_lock, flags);
629 wake_klogd |= log_start - log_end;
630 if (con_start == log_end)
631 break; /* Nothing to print */
632 _con_start = con_start;
634 con_start = log_end; /* Flush */
635 spin_unlock_irqrestore(&logbuf_lock, flags);
636 call_console_drivers(_con_start, _log_end);
639 console_may_schedule = 0;
641 spin_unlock_irqrestore(&logbuf_lock, flags);
642 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
643 wake_up_interruptible(&log_wait);
645 EXPORT_SYMBOL(release_console_sem);
647 /** console_conditional_schedule - yield the CPU if required
649 * If the console code is currently allowed to sleep, and
650 * if this CPU should yield the CPU to another task, do
653 * Must be called within acquire_console_sem().
655 void console_conditional_schedule(void)
657 if (console_may_schedule && need_resched()) {
658 set_current_state(TASK_RUNNING);
662 EXPORT_SYMBOL(console_conditional_schedule);
664 void console_print(const char *s)
666 printk(KERN_EMERG "%s", s);
668 EXPORT_SYMBOL(console_print);
670 void console_unblank(void)
675 * Try to get the console semaphore. If someone else owns it
676 * we have to return without unblanking because console_unblank
677 * may be called in interrupt context.
679 if (down_trylock(&console_sem) != 0)
682 console_may_schedule = 0;
683 for (c = console_drivers; c != NULL; c = c->next)
684 if ((c->flags & CON_ENABLED) && c->unblank)
686 release_console_sem();
688 EXPORT_SYMBOL(console_unblank);
691 * Return the console tty driver structure and its associated index
693 struct tty_driver *console_device(int *index)
696 struct tty_driver *driver = NULL;
698 acquire_console_sem();
699 for (c = console_drivers; c != NULL; c = c->next) {
702 driver = c->device(c, index);
706 release_console_sem();
711 * Prevent further output on the passed console device so that (for example)
712 * serial drivers can disable console output before suspending a port, and can
713 * re-enable output afterwards.
715 void console_stop(struct console *console)
717 acquire_console_sem();
718 console->flags &= ~CON_ENABLED;
719 release_console_sem();
721 EXPORT_SYMBOL(console_stop);
723 void console_start(struct console *console)
725 acquire_console_sem();
726 console->flags |= CON_ENABLED;
727 release_console_sem();
729 EXPORT_SYMBOL(console_start);
732 * The console driver calls this routine during kernel initialization
733 * to register the console printing procedure with printk() and to
734 * print any messages that were printed by the kernel before the
735 * console driver was initialized.
737 void register_console(struct console * console)
743 * See if we want to use this console driver. If we
744 * didn't select a console we take the first one
745 * that registers here.
747 if (preferred_console < 0) {
748 if (console->index < 0)
750 if (console->setup == NULL ||
751 console->setup(console, NULL) == 0) {
752 console->flags |= CON_ENABLED | CON_CONSDEV;
753 preferred_console = 0;
758 * See if this console matches one we selected on
761 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
762 if (strcmp(console_cmdline[i].name, console->name) != 0)
764 if (console->index >= 0 &&
765 console->index != console_cmdline[i].index)
767 if (console->index < 0)
768 console->index = console_cmdline[i].index;
769 if (console->setup &&
770 console->setup(console, console_cmdline[i].options) != 0)
772 console->flags |= CON_ENABLED;
773 console->index = console_cmdline[i].index;
774 if (i == preferred_console)
775 console->flags |= CON_CONSDEV;
779 if (!(console->flags & CON_ENABLED))
783 * Put this console in the list - keep the
784 * preferred driver at the head of the list.
786 acquire_console_sem();
787 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
788 console->next = console_drivers;
789 console_drivers = console;
791 console->next = console_drivers->next;
792 console_drivers->next = console;
794 if (console->flags & CON_PRINTBUFFER) {
796 * release_console_sem() will print out the buffered messages
799 spin_lock_irqsave(&logbuf_lock, flags);
800 con_start = log_start;
801 spin_unlock_irqrestore(&logbuf_lock, flags);
803 release_console_sem();
805 EXPORT_SYMBOL(register_console);
807 int unregister_console(struct console * console)
809 struct console *a,*b;
812 acquire_console_sem();
813 if (console_drivers == console) {
814 console_drivers=console->next;
817 for (a=console_drivers->next, b=console_drivers ;
827 /* If last console is removed, we re-enable picking the first
828 * one that gets registered. Without that, pmac early boot console
829 * would prevent fbcon from taking over.
831 if (console_drivers == NULL)
832 preferred_console = -1;
835 release_console_sem();
838 EXPORT_SYMBOL(unregister_console);
841 * tty_write_message - write a message to a certain tty, not just the console.
843 * This is used for messages that need to be redirected to a specific tty.
844 * We don't put it into the syslog queue right now maybe in the future if
847 void tty_write_message(struct tty_struct *tty, char *msg)
849 if (tty && tty->driver->write)
850 tty->driver->write(tty, 0, msg, strlen(msg));
855 * printk rate limiting, lifted from the networking subsystem.
857 * This enforces a rate limit: not more than one kernel message
858 * every printk_ratelimit_jiffies to make a denial-of-service
861 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
863 static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
864 static unsigned long toks = 10*5*HZ;
865 static unsigned long last_msg;
868 unsigned long now = jiffies;
870 spin_lock_irqsave(&ratelimit_lock, flags);
871 toks += now - last_msg;
873 if (toks > (ratelimit_burst * ratelimit_jiffies))
874 toks = ratelimit_burst * ratelimit_jiffies;
875 if (toks >= ratelimit_jiffies) {
878 toks -= ratelimit_jiffies;
879 spin_unlock_irqrestore(&ratelimit_lock, flags);
881 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
885 spin_unlock_irqrestore(&ratelimit_lock, flags);
888 EXPORT_SYMBOL(__printk_ratelimit);
890 /* minimum time in jiffies between messages */
891 int printk_ratelimit_jiffies = 5*HZ;
893 /* number of messages we send before ratelimiting */
894 int printk_ratelimit_burst = 10;
896 int printk_ratelimit(void)
898 return __printk_ratelimit(printk_ratelimit_jiffies,
899 printk_ratelimit_burst);
901 EXPORT_SYMBOL(printk_ratelimit);