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;
114 extern int evl_kbufread(char *, size_t);
115 #ifdef CONFIG_EVLOG_FWPRINTK
116 extern int evl_fwd_printk(const char *fmt, va_list args, const char *msg);
120 /* Flag: console code may call schedule() */
121 static int console_may_schedule;
124 * Setup a list of consoles. Called from init/main.c
126 static int __init console_setup(char *str)
128 char name[sizeof(console_cmdline[0].name)];
133 * Decode str into name, index, options.
135 if (str[0] >= '0' && str[0] <= '9') {
136 strcpy(name, "ttyS");
137 strncpy(name + 4, str, sizeof(name) - 5);
139 strncpy(name, str, sizeof(name) - 1);
140 name[sizeof(name) - 1] = 0;
141 if ((options = strchr(str, ',')) != NULL)
144 if (!strcmp(str, "ttya"))
145 strcpy(name, "ttyS0");
146 if (!strcmp(str, "ttyb"))
147 strcpy(name, "ttyS1");
149 for(s = name; *s; s++)
150 if (*s >= '0' && *s <= '9')
152 idx = simple_strtoul(s, NULL, 10);
155 add_preferred_console(name, idx, options);
159 __setup("console=", console_setup);
162 * add_preferred_console - add a device to the list of preferred consoles.
164 * The last preferred console added will be used for kernel messages
165 * and stdin/out/err for init. Normally this is used by console_setup
166 * above to handle user-supplied console arguments; however it can also
167 * be used by arch-specific code either to override the user or more
168 * commonly to provide a default console (ie from PROM variables) when
169 * the user has not supplied one.
171 int __init add_preferred_console(char *name, int idx, char *options)
173 struct console_cmdline *c;
177 * See if this tty is not yet registered, and
178 * if we have a slot free.
180 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
181 if (strcmp(console_cmdline[i].name, name) == 0 &&
182 console_cmdline[i].index == idx) {
183 preferred_console = i;
186 if (i == MAX_CMDLINECONSOLES)
188 preferred_console = i;
189 c = &console_cmdline[i];
190 memcpy(c->name, name, sizeof(c->name));
191 c->name[sizeof(c->name) - 1] = 0;
192 c->options = options;
197 static int __init log_buf_len_setup(char *str)
199 unsigned long size = memparse(str, &str);
202 if (size > log_buf_len) {
203 unsigned long start, dest_idx, offset;
206 new_log_buf = alloc_bootmem(size);
208 printk("log_buf_len: allocation failed\n");
212 spin_lock_irqsave(&logbuf_lock, flags);
214 log_buf = new_log_buf;
216 offset = start = min(con_start, log_start);
218 while (start != log_end) {
219 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
226 spin_unlock_irqrestore(&logbuf_lock, flags);
228 printk("log_buf_len: %d\n", log_buf_len);
235 __setup("log_buf_len=", log_buf_len_setup);
238 * Commands to do_syslog:
240 * 0 -- Close the log. Currently a NOP.
241 * 1 -- Open the log. Currently a NOP.
242 * 2 -- Read from the log.
243 * 3 -- Read all messages remaining in the ring buffer.
244 * 4 -- Read and clear all messages remaining in the ring buffer
245 * 5 -- Clear ring buffer.
246 * 6 -- Disable printk's to console
247 * 7 -- Enable printk's to console
248 * 8 -- Set level of messages printed to console
249 * 9 -- Return number of unread characters in the log buffer
250 * 10 -- Return size of the log buffer
251 * 20 -- Read from event logging buffer
253 int do_syslog(int type, char __user * buf, int len)
255 unsigned long i, j, limit, count;
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 */
376 error = verify_area(VERIFY_WRITE, buf, len);
380 error = evl_kbufread(buf, len);
394 /* kdb dmesg command needs access to the syslog buffer. do_syslog() uses locks
395 * so it cannot be used during debugging. Just tell kdb where the start and
396 * end of the physical and logical logs are. This is equivalent to do_syslog(3).
398 void kdb_syslog_data(char *syslog_data[4])
400 syslog_data[0] = log_buf;
401 syslog_data[1] = log_buf + __LOG_BUF_LEN;
402 syslog_data[2] = log_buf + log_end - (logged_chars < __LOG_BUF_LEN ? logged_chars : __LOG_BUF_LEN);
403 syslog_data[3] = log_buf + log_end;
405 #endif /* CONFIG_KDB */
407 asmlinkage long sys_syslog(int type, char __user * buf, int len)
409 return do_syslog(type, buf, len);
413 * Call the console drivers on a range of log_buf
415 static void __call_console_drivers(unsigned long start, unsigned long end)
419 for (con = console_drivers; con; con = con->next) {
420 if ((con->flags & CON_ENABLED) && con->write)
421 con->write(con, &LOG_BUF(start), end - start);
426 * Write out chars from start to end - 1 inclusive
428 static void _call_console_drivers(unsigned long start,
429 unsigned long end, int msg_log_level)
431 if (msg_log_level < console_loglevel &&
432 console_drivers && start != end) {
433 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
435 __call_console_drivers(start & LOG_BUF_MASK,
437 __call_console_drivers(0, end & LOG_BUF_MASK);
439 __call_console_drivers(start, end);
445 * Call the console drivers, asking them to write out
446 * log_buf[start] to log_buf[end - 1].
447 * The console_sem must be held.
449 static void call_console_drivers(unsigned long start, unsigned long end)
451 unsigned long cur_index, start_print;
452 static int msg_level = -1;
454 if (((long)(start - end)) > 0)
459 while (cur_index != end) {
460 if ( msg_level < 0 &&
461 ((end - cur_index) > 2) &&
462 LOG_BUF(cur_index + 0) == '<' &&
463 LOG_BUF(cur_index + 1) >= '0' &&
464 LOG_BUF(cur_index + 1) <= '7' &&
465 LOG_BUF(cur_index + 2) == '>')
467 msg_level = LOG_BUF(cur_index + 1) - '0';
469 start_print = cur_index;
471 while (cur_index != end) {
472 char c = LOG_BUF(cur_index);
478 * printk() has already given us loglevel tags in
479 * the buffer. This code is here in case the
480 * log buffer has wrapped right round and scribbled
483 msg_level = default_message_loglevel;
485 _call_console_drivers(start_print, cur_index, msg_level);
487 start_print = cur_index;
492 _call_console_drivers(start_print, end, msg_level);
495 static void emit_log_char(char c)
497 LOG_BUF(log_end) = c;
499 if (log_end - log_start > log_buf_len)
500 log_start = log_end - log_buf_len;
501 if (log_end - con_start > log_buf_len)
502 con_start = log_end - log_buf_len;
503 if (logged_chars < log_buf_len)
508 * Zap console related locks when oopsing. Only zap at most once
509 * every 10 seconds, to leave time for slow consoles to print a
512 static void zap_locks(void)
514 static unsigned long oops_timestamp;
516 if (time_after_eq(jiffies, oops_timestamp) &&
517 !time_after(jiffies, oops_timestamp + 30*HZ))
520 oops_timestamp = jiffies;
522 /* If a crash is occurring, make sure we can't deadlock */
523 spin_lock_init(&logbuf_lock);
524 /* And make sure that we print immediately */
525 init_MUTEX(&console_sem);
529 * This is printk. It can be called from any context. We want it to work.
531 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
532 * call the console drivers. If we fail to get the semaphore we place the output
533 * into the log buffer and return. The current holder of the console_sem will
534 * notice the new output in release_console_sem() and will send it to the
535 * consoles before releasing the semaphore.
537 * One effect of this deferred printing is that code which calls printk() and
538 * then changes console_loglevel may break. This is because console_loglevel
539 * is inspected when the actual printing occurs.
541 asmlinkage int printk(const char *fmt, ...)
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 */
558 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
559 #ifdef CONFIG_EVLOG_FWPRINTK
560 (void) evl_fwd_printk(fmt, args, printk_buf);
565 * Copy the output into log_buf. If the caller didn't provide
566 * appropriate log level tags, we insert them here
568 for (p = printk_buf; *p; p++) {
569 if (log_level_unknown) {
570 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
572 emit_log_char(default_message_loglevel + '0');
575 log_level_unknown = 0;
579 log_level_unknown = 1;
582 if (!cpu_online(smp_processor_id()) &&
583 system_state != SYSTEM_RUNNING) {
585 * Some console drivers may assume that per-cpu resources have
586 * been allocated. So don't allow them to be called by this
587 * CPU until it is officially up. We shouldn't be calling into
588 * random console drivers on a CPU which doesn't exist yet..
590 spin_unlock_irqrestore(&logbuf_lock, flags);
593 if (!down_trylock(&console_sem)) {
596 * We own the drivers. We can drop the spinlock and let
597 * release_console_sem() print the text
599 spin_unlock_irqrestore(&logbuf_lock, flags);
600 console_may_schedule = 0;
601 release_console_sem();
604 * Someone else owns the drivers. We drop the spinlock, which
605 * allows the semaphore holder to proceed and to call the
606 * console drivers with the output which we just produced.
608 spin_unlock_irqrestore(&logbuf_lock, flags);
613 EXPORT_SYMBOL(printk);
616 * acquire_console_sem - lock the console system for exclusive use.
618 * Acquires a semaphore which guarantees that the caller has
619 * exclusive access to the console system and the console_drivers list.
621 * Can sleep, returns nothing.
623 void acquire_console_sem(void)
629 console_may_schedule = 1;
631 EXPORT_SYMBOL(acquire_console_sem);
633 int is_console_locked(void)
635 return console_locked;
637 EXPORT_SYMBOL(is_console_locked);
640 * release_console_sem - unlock the console system
642 * Releases the semaphore which the caller holds on the console system
643 * and the console driver list.
645 * While the semaphore was held, console output may have been buffered
646 * by printk(). If this is the case, release_console_sem() emits
647 * the output prior to releasing the semaphore.
649 * If there is output waiting for klogd, we wake it up.
651 * release_console_sem() may be called from any context.
653 void release_console_sem(void)
656 unsigned long _con_start, _log_end;
657 unsigned long wake_klogd = 0;
660 spin_lock_irqsave(&logbuf_lock, flags);
661 wake_klogd |= log_start - log_end;
662 if (con_start == log_end)
663 break; /* Nothing to print */
664 _con_start = con_start;
666 con_start = log_end; /* Flush */
667 spin_unlock_irqrestore(&logbuf_lock, flags);
668 call_console_drivers(_con_start, _log_end);
671 console_may_schedule = 0;
673 spin_unlock_irqrestore(&logbuf_lock, flags);
674 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
675 wake_up_interruptible(&log_wait);
677 EXPORT_SYMBOL(release_console_sem);
679 /** console_conditional_schedule - yield the CPU if required
681 * If the console code is currently allowed to sleep, and
682 * if this CPU should yield the CPU to another task, do
685 * Must be called within acquire_console_sem().
687 void console_conditional_schedule(void)
689 if (console_may_schedule && need_resched()) {
690 set_current_state(TASK_RUNNING);
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)
775 * See if we want to use this console driver. If we
776 * didn't select a console we take the first one
777 * that registers here.
779 if (preferred_console < 0) {
780 if (console->index < 0)
782 if (console->setup == NULL ||
783 console->setup(console, NULL) == 0) {
784 console->flags |= CON_ENABLED | CON_CONSDEV;
785 preferred_console = 0;
790 * See if this console matches one we selected on
793 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
794 if (strcmp(console_cmdline[i].name, console->name) != 0)
796 if (console->index >= 0 &&
797 console->index != console_cmdline[i].index)
799 if (console->index < 0)
800 console->index = console_cmdline[i].index;
801 if (console->setup &&
802 console->setup(console, console_cmdline[i].options) != 0)
804 console->flags |= CON_ENABLED;
805 console->index = console_cmdline[i].index;
806 if (i == preferred_console)
807 console->flags |= CON_CONSDEV;
811 if (!(console->flags & CON_ENABLED))
815 * Put this console in the list - keep the
816 * preferred driver at the head of the list.
818 acquire_console_sem();
819 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
820 console->next = console_drivers;
821 console_drivers = console;
823 console->next = console_drivers->next;
824 console_drivers->next = console;
826 if (console->flags & CON_PRINTBUFFER) {
828 * release_console_sem() will print out the buffered messages
831 spin_lock_irqsave(&logbuf_lock, flags);
832 con_start = log_start;
833 spin_unlock_irqrestore(&logbuf_lock, flags);
835 release_console_sem();
837 EXPORT_SYMBOL(register_console);
839 int unregister_console(struct console * console)
841 struct console *a,*b;
844 acquire_console_sem();
845 if (console_drivers == console) {
846 console_drivers=console->next;
849 for (a=console_drivers->next, b=console_drivers ;
859 /* If last console is removed, we re-enable picking the first
860 * one that gets registered. Without that, pmac early boot console
861 * would prevent fbcon from taking over.
863 if (console_drivers == NULL)
864 preferred_console = -1;
867 release_console_sem();
870 EXPORT_SYMBOL(unregister_console);
873 * tty_write_message - write a message to a certain tty, not just the console.
875 * This is used for messages that need to be redirected to a specific tty.
876 * We don't put it into the syslog queue right now maybe in the future if
879 void tty_write_message(struct tty_struct *tty, char *msg)
881 if (tty && tty->driver->write)
882 tty->driver->write(tty, 0, msg, strlen(msg));
887 * printk rate limiting, lifted from the networking subsystem.
889 * This enforces a rate limit: not more than one kernel message
890 * every printk_ratelimit_jiffies to make a denial-of-service
893 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
895 static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
896 static unsigned long toks = 10*5*HZ;
897 static unsigned long last_msg;
900 unsigned long now = jiffies;
902 spin_lock_irqsave(&ratelimit_lock, flags);
903 toks += now - last_msg;
905 if (toks > (ratelimit_burst * ratelimit_jiffies))
906 toks = ratelimit_burst * ratelimit_jiffies;
907 if (toks >= ratelimit_jiffies) {
910 toks -= ratelimit_jiffies;
911 spin_unlock_irqrestore(&ratelimit_lock, flags);
913 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
917 spin_unlock_irqrestore(&ratelimit_lock, flags);
920 EXPORT_SYMBOL(__printk_ratelimit);
922 /* minimum time in jiffies between messages */
923 int printk_ratelimit_jiffies = 5*HZ;
925 /* number of messages we send before ratelimiting */
926 int printk_ratelimit_burst = 10;
928 int printk_ratelimit(void)
930 return __printk_ratelimit(printk_ratelimit_jiffies,
931 printk_ratelimit_burst);
933 EXPORT_SYMBOL(printk_ratelimit);