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/syscalls.h>
34 #include <linux/vserver/cvirt.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 DEFINE_SPINLOCK(logbuf_lock);
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 error = security_syslog(type);
261 if ((type >= 2) && (type <= 4)) {
268 error = verify_area(VERIFY_WRITE,buf,len);
272 if (!vx_check(0, VX_ADMIN|VX_WATCH))
273 return vx_do_syslog(type, buf, len);
276 case 0: /* Close log */
278 case 1: /* Open log */
280 case 2: /* Read from log */
281 error = wait_event_interruptible(log_wait, (log_start - log_end));
285 spin_lock_irq(&logbuf_lock);
286 while (!error && (log_start != log_end) && i < len) {
287 c = LOG_BUF(log_start);
289 spin_unlock_irq(&logbuf_lock);
290 error = __put_user(c,buf);
294 spin_lock_irq(&logbuf_lock);
296 spin_unlock_irq(&logbuf_lock);
300 case 4: /* Read/clear last kernel messages */
303 case 3: /* Read last kernel messages */
305 if (count > log_buf_len)
307 spin_lock_irq(&logbuf_lock);
308 if (count > logged_chars)
309 count = logged_chars;
314 * __put_user() could sleep, and while we sleep
315 * printk() could overwrite the messages
316 * we try to copy to user space. Therefore
317 * the messages are copied in reverse. <manfreds>
319 for(i = 0; i < count && !error; i++) {
321 if (j + log_buf_len < log_end)
324 spin_unlock_irq(&logbuf_lock);
325 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])) {
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 r = vprintk(fmt, args);
524 static volatile int printk_cpu = -1;
526 asmlinkage int vprintk(const char *fmt, va_list args)
531 static char printk_buf[1024];
532 static int log_level_unknown = 1;
534 if (unlikely(oops_in_progress && printk_cpu == smp_processor_id()))
537 /* This stops the holder of console_sem just where we want him */
538 spin_lock_irqsave(&logbuf_lock, flags);
539 printk_cpu = smp_processor_id();
541 /* Emit the output into the temporary buffer */
542 printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
545 * Copy the output into log_buf. If the caller didn't provide
546 * appropriate log level tags, we insert them here
548 for (p = printk_buf; *p; p++) {
549 if (log_level_unknown) {
550 if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
552 emit_log_char(default_message_loglevel + '0');
555 log_level_unknown = 0;
559 log_level_unknown = 1;
562 if (!cpu_online(smp_processor_id()) &&
563 system_state != SYSTEM_RUNNING) {
565 * Some console drivers may assume that per-cpu resources have
566 * been allocated. So don't allow them to be called by this
567 * CPU until it is officially up. We shouldn't be calling into
568 * random console drivers on a CPU which doesn't exist yet..
570 spin_unlock_irqrestore(&logbuf_lock, flags);
573 if (!down_trylock(&console_sem)) {
576 * We own the drivers. We can drop the spinlock and let
577 * release_console_sem() print the text
579 spin_unlock_irqrestore(&logbuf_lock, flags);
580 console_may_schedule = 0;
581 release_console_sem();
584 * Someone else owns the drivers. We drop the spinlock, which
585 * allows the semaphore holder to proceed and to call the
586 * console drivers with the output which we just produced.
588 spin_unlock_irqrestore(&logbuf_lock, flags);
593 EXPORT_SYMBOL(printk);
594 EXPORT_SYMBOL(vprintk);
597 * acquire_console_sem - lock the console system for exclusive use.
599 * Acquires a semaphore which guarantees that the caller has
600 * exclusive access to the console system and the console_drivers list.
602 * Can sleep, returns nothing.
604 void acquire_console_sem(void)
610 console_may_schedule = 1;
612 EXPORT_SYMBOL(acquire_console_sem);
614 int try_acquire_console_sem(void)
616 if (down_trylock(&console_sem))
619 console_may_schedule = 0;
622 EXPORT_SYMBOL(try_acquire_console_sem);
624 int is_console_locked(void)
626 return console_locked;
628 EXPORT_SYMBOL(is_console_locked);
631 * release_console_sem - unlock the console system
633 * Releases the semaphore which the caller holds on the console system
634 * and the console driver list.
636 * While the semaphore was held, console output may have been buffered
637 * by printk(). If this is the case, release_console_sem() emits
638 * the output prior to releasing the semaphore.
640 * If there is output waiting for klogd, we wake it up.
642 * release_console_sem() may be called from any context.
644 void release_console_sem(void)
647 unsigned long _con_start, _log_end;
648 unsigned long wake_klogd = 0;
651 spin_lock_irqsave(&logbuf_lock, flags);
652 wake_klogd |= log_start - log_end;
653 if (con_start == log_end)
654 break; /* Nothing to print */
655 _con_start = con_start;
657 con_start = log_end; /* Flush */
658 spin_unlock(&logbuf_lock);
659 call_console_drivers(_con_start, _log_end);
660 local_irq_restore(flags);
663 console_may_schedule = 0;
665 spin_unlock_irqrestore(&logbuf_lock, flags);
666 if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
667 wake_up_interruptible(&log_wait);
669 EXPORT_SYMBOL(release_console_sem);
671 /** console_conditional_schedule - yield the CPU if required
673 * If the console code is currently allowed to sleep, and
674 * if this CPU should yield the CPU to another task, do
677 * Must be called within acquire_console_sem().
679 void __sched console_conditional_schedule(void)
681 if (console_may_schedule)
684 EXPORT_SYMBOL(console_conditional_schedule);
686 void console_print(const char *s)
688 printk(KERN_EMERG "%s", s);
690 EXPORT_SYMBOL(console_print);
692 void console_unblank(void)
697 * Try to get the console semaphore. If someone else owns it
698 * we have to return without unblanking because console_unblank
699 * may be called in interrupt context.
701 if (down_trylock(&console_sem) != 0)
704 console_may_schedule = 0;
705 for (c = console_drivers; c != NULL; c = c->next)
706 if ((c->flags & CON_ENABLED) && c->unblank)
708 release_console_sem();
710 EXPORT_SYMBOL(console_unblank);
713 * Return the console tty driver structure and its associated index
715 struct tty_driver *console_device(int *index)
718 struct tty_driver *driver = NULL;
720 acquire_console_sem();
721 for (c = console_drivers; c != NULL; c = c->next) {
724 driver = c->device(c, index);
728 release_console_sem();
733 * Prevent further output on the passed console device so that (for example)
734 * serial drivers can disable console output before suspending a port, and can
735 * re-enable output afterwards.
737 void console_stop(struct console *console)
739 acquire_console_sem();
740 console->flags &= ~CON_ENABLED;
741 release_console_sem();
743 EXPORT_SYMBOL(console_stop);
745 void console_start(struct console *console)
747 acquire_console_sem();
748 console->flags |= CON_ENABLED;
749 release_console_sem();
751 EXPORT_SYMBOL(console_start);
754 * The console driver calls this routine during kernel initialization
755 * to register the console printing procedure with printk() and to
756 * print any messages that were printed by the kernel before the
757 * console driver was initialized.
759 void register_console(struct console * console)
764 if (preferred_console < 0)
765 preferred_console = selected_console;
768 * See if we want to use this console driver. If we
769 * didn't select a console we take the first one
770 * that registers here.
772 if (preferred_console < 0) {
773 if (console->index < 0)
775 if (console->setup == NULL ||
776 console->setup(console, NULL) == 0) {
777 console->flags |= CON_ENABLED | CON_CONSDEV;
778 preferred_console = 0;
783 * See if this console matches one we selected on
786 for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
787 if (strcmp(console_cmdline[i].name, console->name) != 0)
789 if (console->index >= 0 &&
790 console->index != console_cmdline[i].index)
792 if (console->index < 0)
793 console->index = console_cmdline[i].index;
794 if (console->setup &&
795 console->setup(console, console_cmdline[i].options) != 0)
797 console->flags |= CON_ENABLED;
798 console->index = console_cmdline[i].index;
799 if (i == preferred_console)
800 console->flags |= CON_CONSDEV;
804 if (!(console->flags & CON_ENABLED))
808 * Put this console in the list - keep the
809 * preferred driver at the head of the list.
811 acquire_console_sem();
812 if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
813 console->next = console_drivers;
814 console_drivers = console;
816 console->next = console_drivers->next;
817 console_drivers->next = console;
819 if (console->flags & CON_PRINTBUFFER) {
821 * release_console_sem() will print out the buffered messages
824 spin_lock_irqsave(&logbuf_lock, flags);
825 con_start = log_start;
826 spin_unlock_irqrestore(&logbuf_lock, flags);
828 release_console_sem();
830 EXPORT_SYMBOL(register_console);
832 int unregister_console(struct console * console)
834 struct console *a,*b;
837 acquire_console_sem();
838 if (console_drivers == console) {
839 console_drivers=console->next;
842 for (a=console_drivers->next, b=console_drivers ;
852 /* If last console is removed, we re-enable picking the first
853 * one that gets registered. Without that, pmac early boot console
854 * would prevent fbcon from taking over.
856 if (console_drivers == NULL)
857 preferred_console = selected_console;
860 release_console_sem();
863 EXPORT_SYMBOL(unregister_console);
866 * tty_write_message - write a message to a certain tty, not just the console.
868 * This is used for messages that need to be redirected to a specific tty.
869 * We don't put it into the syslog queue right now maybe in the future if
872 void tty_write_message(struct tty_struct *tty, char *msg)
874 if (tty && tty->driver->write)
875 tty->driver->write(tty, msg, strlen(msg));
880 * printk rate limiting, lifted from the networking subsystem.
882 * This enforces a rate limit: not more than one kernel message
883 * every printk_ratelimit_jiffies to make a denial-of-service
886 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
888 static DEFINE_SPINLOCK(ratelimit_lock);
889 static unsigned long toks = 10*5*HZ;
890 static unsigned long last_msg;
893 unsigned long now = jiffies;
895 spin_lock_irqsave(&ratelimit_lock, flags);
896 toks += now - last_msg;
898 if (toks > (ratelimit_burst * ratelimit_jiffies))
899 toks = ratelimit_burst * ratelimit_jiffies;
900 if (toks >= ratelimit_jiffies) {
903 toks -= ratelimit_jiffies;
904 spin_unlock_irqrestore(&ratelimit_lock, flags);
906 printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
910 spin_unlock_irqrestore(&ratelimit_lock, flags);
913 EXPORT_SYMBOL(__printk_ratelimit);
915 /* minimum time in jiffies between messages */
916 int printk_ratelimit_jiffies = 5*HZ;
918 /* number of messages we send before ratelimiting */
919 int printk_ratelimit_burst = 10;
921 int printk_ratelimit(void)
923 return __printk_ratelimit(printk_ratelimit_jiffies,
924 printk_ratelimit_burst);
926 EXPORT_SYMBOL(printk_ratelimit);