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 * manfred@colorfullife.com
15 * Rewrote bits to get rid of console_lock
16 * 01Mar01 Andrew Morton
19 #include <linux/kernel.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/console.h>
24 #include <linux/init.h>
25 #include <linux/jiffies.h>
26 #include <linux/nmi.h>
27 #include <linux/module.h>
28 #include <linux/moduleparam.h>
29 #include <linux/interrupt.h> /* For in_interrupt() */
30 #include <linux/delay.h>
31 #include <linux/smp.h>
32 #include <linux/security.h>
33 #include <linux/bootmem.h>
34 #include <linux/syscalls.h>
35 #include <linux/kexec.h>
36 #include <linux/kdb.h>
37 #include <linux/ratelimit.h>
38 #include <linux/kmsg_dump.h>
39 #include <linux/syslog.h>
40 #include <linux/cpu.h>
41 #include <linux/notifier.h>
43 #include <asm/uaccess.h>
46 * Architectures can override it:
48 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
52 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
54 /* printk's without a loglevel use this.. */
55 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
57 /* We show everything that is MORE important than this.. */
58 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
59 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
61 DECLARE_WAIT_QUEUE_HEAD(log_wait);
63 int console_printk[4] = {
64 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
65 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
66 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
67 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
71 * Low level drivers may need that to know if they can schedule in
72 * their unblank() callback or not. So let's export it.
75 EXPORT_SYMBOL(oops_in_progress);
78 * console_sem protects the console_drivers list, and also
79 * provides serialisation for access to the entire console
82 static DEFINE_SEMAPHORE(console_sem);
83 struct console *console_drivers;
84 EXPORT_SYMBOL_GPL(console_drivers);
87 * This is used for debugging the mess that is the VT code by
88 * keeping track if we have the console semaphore held. It's
89 * definitely not the perfect debug tool (we don't know if _WE_
90 * hold it are racing, but it helps tracking those weird code
91 * path in the console code where we end up in places I want
92 * locked without the console sempahore held
94 static int console_locked, console_suspended;
97 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
98 * It is also used in interesting ways to provide interlocking in
99 * release_console_sem().
101 static DEFINE_SPINLOCK(logbuf_lock);
103 #define LOG_BUF_MASK (log_buf_len-1)
104 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
107 * The indices into log_buf are not constrained to log_buf_len - they
108 * must be masked before subscripting
110 static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
111 static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
112 static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
115 * Array of consoles built from command line options (console=)
117 struct console_cmdline
119 char name[8]; /* Name of the driver */
120 int index; /* Minor dev. to use */
121 char *options; /* Options for the driver */
122 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
123 char *brl_options; /* Options for braille driver */
127 #define MAX_CMDLINECONSOLES 8
129 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
130 static int selected_console = -1;
131 static int preferred_console = -1;
132 int console_set_on_cmdline;
133 EXPORT_SYMBOL(console_set_on_cmdline);
135 /* Flag: console code may call schedule() */
136 static int console_may_schedule;
140 static char __log_buf[__LOG_BUF_LEN];
141 static char *log_buf = __log_buf;
142 static int log_buf_len = __LOG_BUF_LEN;
143 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
144 static int saved_console_loglevel = -1;
148 * This appends the listed symbols to /proc/vmcoreinfo
150 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
151 * obtain access to symbols that are otherwise very difficult to locate. These
152 * symbols are specifically used so that utilities can access and extract the
153 * dmesg log from a vmcore file after a crash.
155 void log_buf_kexec_setup(void)
157 VMCOREINFO_SYMBOL(log_buf);
158 VMCOREINFO_SYMBOL(log_end);
159 VMCOREINFO_SYMBOL(log_buf_len);
160 VMCOREINFO_SYMBOL(logged_chars);
164 static int __init log_buf_len_setup(char *str)
166 unsigned size = memparse(str, &str);
170 size = roundup_pow_of_two(size);
171 if (size > log_buf_len) {
172 unsigned start, dest_idx, offset;
175 new_log_buf = alloc_bootmem(size);
177 printk(KERN_WARNING "log_buf_len: allocation failed\n");
181 spin_lock_irqsave(&logbuf_lock, flags);
183 log_buf = new_log_buf;
185 offset = start = min(con_start, log_start);
187 while (start != log_end) {
188 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
195 spin_unlock_irqrestore(&logbuf_lock, flags);
197 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
203 __setup("log_buf_len=", log_buf_len_setup);
205 #ifdef CONFIG_BOOT_PRINTK_DELAY
207 static int boot_delay; /* msecs delay after each printk during bootup */
208 static unsigned long long loops_per_msec; /* based on boot_delay */
210 static int __init boot_delay_setup(char *str)
214 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
215 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
217 get_option(&str, &boot_delay);
218 if (boot_delay > 10 * 1000)
221 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
222 "HZ: %d, loops_per_msec: %llu\n",
223 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
226 __setup("boot_delay=", boot_delay_setup);
228 static void boot_delay_msec(void)
230 unsigned long long k;
231 unsigned long timeout;
233 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
236 k = (unsigned long long)loops_per_msec * boot_delay;
238 timeout = jiffies + msecs_to_jiffies(boot_delay);
243 * use (volatile) jiffies to prevent
244 * compiler reduction; loop termination via jiffies
245 * is secondary and may or may not happen.
247 if (time_after(jiffies, timeout))
249 touch_nmi_watchdog();
253 static inline void boot_delay_msec(void)
258 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
259 int dmesg_restrict = 1;
264 int do_syslog(int type, char __user *buf, int len, bool from_file)
266 unsigned i, j, limit, count;
272 * If this is from /proc/kmsg we only do the capabilities checks
275 if (type == SYSLOG_ACTION_OPEN || !from_file) {
276 if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
278 if ((type != SYSLOG_ACTION_READ_ALL &&
279 type != SYSLOG_ACTION_SIZE_BUFFER) &&
280 !capable(CAP_SYS_ADMIN))
284 error = security_syslog(type);
289 case SYSLOG_ACTION_CLOSE: /* Close log */
291 case SYSLOG_ACTION_OPEN: /* Open log */
293 case SYSLOG_ACTION_READ: /* Read from log */
300 if (!access_ok(VERIFY_WRITE, buf, len)) {
304 error = wait_event_interruptible(log_wait,
305 (log_start - log_end));
309 spin_lock_irq(&logbuf_lock);
310 while (!error && (log_start != log_end) && i < len) {
311 c = LOG_BUF(log_start);
313 spin_unlock_irq(&logbuf_lock);
314 error = __put_user(c,buf);
318 spin_lock_irq(&logbuf_lock);
320 spin_unlock_irq(&logbuf_lock);
324 /* Read/clear last kernel messages */
325 case SYSLOG_ACTION_READ_CLEAR:
328 /* Read last kernel messages */
329 case SYSLOG_ACTION_READ_ALL:
336 if (!access_ok(VERIFY_WRITE, buf, len)) {
341 if (count > log_buf_len)
343 spin_lock_irq(&logbuf_lock);
344 if (count > logged_chars)
345 count = logged_chars;
350 * __put_user() could sleep, and while we sleep
351 * printk() could overwrite the messages
352 * we try to copy to user space. Therefore
353 * the messages are copied in reverse. <manfreds>
355 for (i = 0; i < count && !error; i++) {
357 if (j + log_buf_len < log_end)
360 spin_unlock_irq(&logbuf_lock);
361 error = __put_user(c,&buf[count-1-i]);
363 spin_lock_irq(&logbuf_lock);
365 spin_unlock_irq(&logbuf_lock);
370 int offset = count-error;
371 /* buffer overflow during copy, correct user buffer. */
372 for (i = 0; i < error; i++) {
373 if (__get_user(c,&buf[i+offset]) ||
374 __put_user(c,&buf[i])) {
382 /* Clear ring buffer */
383 case SYSLOG_ACTION_CLEAR:
386 /* Disable logging to console */
387 case SYSLOG_ACTION_CONSOLE_OFF:
388 if (saved_console_loglevel == -1)
389 saved_console_loglevel = console_loglevel;
390 console_loglevel = minimum_console_loglevel;
392 /* Enable logging to console */
393 case SYSLOG_ACTION_CONSOLE_ON:
394 if (saved_console_loglevel != -1) {
395 console_loglevel = saved_console_loglevel;
396 saved_console_loglevel = -1;
399 /* Set level of messages printed to console */
400 case SYSLOG_ACTION_CONSOLE_LEVEL:
402 if (len < 1 || len > 8)
404 if (len < minimum_console_loglevel)
405 len = minimum_console_loglevel;
406 console_loglevel = len;
407 /* Implicitly re-enable logging to console */
408 saved_console_loglevel = -1;
411 /* Number of chars in the log buffer */
412 case SYSLOG_ACTION_SIZE_UNREAD:
413 error = log_end - log_start;
415 /* Size of the log buffer */
416 case SYSLOG_ACTION_SIZE_BUFFER:
427 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
429 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
432 #ifdef CONFIG_KGDB_KDB
433 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
434 * uses locks so it cannot be used during debugging. Just tell kdb
435 * where the start and end of the physical and logical logs are. This
436 * is equivalent to do_syslog(3).
438 void kdb_syslog_data(char *syslog_data[4])
440 syslog_data[0] = log_buf;
441 syslog_data[1] = log_buf + log_buf_len;
442 syslog_data[2] = log_buf + log_end -
443 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
444 syslog_data[3] = log_buf + log_end;
446 #endif /* CONFIG_KGDB_KDB */
449 * Call the console drivers on a range of log_buf
451 static void __call_console_drivers(unsigned start, unsigned end)
455 for_each_console(con) {
456 if ((con->flags & CON_ENABLED) && con->write &&
457 (cpu_online(smp_processor_id()) ||
458 (con->flags & CON_ANYTIME)))
459 con->write(con, &LOG_BUF(start), end - start);
463 static int __read_mostly ignore_loglevel;
465 static int __init ignore_loglevel_setup(char *str)
468 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
473 early_param("ignore_loglevel", ignore_loglevel_setup);
476 * Write out chars from start to end - 1 inclusive
478 static void _call_console_drivers(unsigned start,
479 unsigned end, int msg_log_level)
481 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
482 console_drivers && start != end) {
483 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
485 __call_console_drivers(start & LOG_BUF_MASK,
487 __call_console_drivers(0, end & LOG_BUF_MASK);
489 __call_console_drivers(start, end);
495 * Call the console drivers, asking them to write out
496 * log_buf[start] to log_buf[end - 1].
497 * The console_sem must be held.
499 static void call_console_drivers(unsigned start, unsigned end)
501 unsigned cur_index, start_print;
502 static int msg_level = -1;
504 BUG_ON(((int)(start - end)) > 0);
508 while (cur_index != end) {
509 if (msg_level < 0 && ((end - cur_index) > 2) &&
510 LOG_BUF(cur_index + 0) == '<' &&
511 LOG_BUF(cur_index + 1) >= '0' &&
512 LOG_BUF(cur_index + 1) <= '7' &&
513 LOG_BUF(cur_index + 2) == '>') {
514 msg_level = LOG_BUF(cur_index + 1) - '0';
516 start_print = cur_index;
518 while (cur_index != end) {
519 char c = LOG_BUF(cur_index);
525 * printk() has already given us loglevel tags in
526 * the buffer. This code is here in case the
527 * log buffer has wrapped right round and scribbled
530 msg_level = default_message_loglevel;
532 _call_console_drivers(start_print, cur_index, msg_level);
534 start_print = cur_index;
539 _call_console_drivers(start_print, end, msg_level);
542 static void emit_log_char(char c)
544 LOG_BUF(log_end) = c;
546 if (log_end - log_start > log_buf_len)
547 log_start = log_end - log_buf_len;
548 if (log_end - con_start > log_buf_len)
549 con_start = log_end - log_buf_len;
550 if (logged_chars < log_buf_len)
555 * Zap console related locks when oopsing. Only zap at most once
556 * every 10 seconds, to leave time for slow consoles to print a
559 static void zap_locks(void)
561 static unsigned long oops_timestamp;
563 if (time_after_eq(jiffies, oops_timestamp) &&
564 !time_after(jiffies, oops_timestamp + 30 * HZ))
567 oops_timestamp = jiffies;
569 /* If a crash is occurring, make sure we can't deadlock */
570 spin_lock_init(&logbuf_lock);
571 /* And make sure that we print immediately */
572 sema_init(&console_sem, 1);
575 #if defined(CONFIG_PRINTK_TIME)
576 static int printk_time = 1;
578 static int printk_time = 0;
580 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
582 /* Check if we have any console registered that can be called early in boot. */
583 static int have_callable_console(void)
587 for_each_console(con)
588 if (con->flags & CON_ANYTIME)
595 * printk - print a kernel message
596 * @fmt: format string
598 * This is printk(). It can be called from any context. We want it to work.
600 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
601 * call the console drivers. If we fail to get the semaphore we place the output
602 * into the log buffer and return. The current holder of the console_sem will
603 * notice the new output in release_console_sem() and will send it to the
604 * consoles before releasing the semaphore.
606 * One effect of this deferred printing is that code which calls printk() and
607 * then changes console_loglevel may break. This is because console_loglevel
608 * is inspected when the actual printing occurs.
613 * See the vsnprintf() documentation for format string extensions over C99.
616 asmlinkage int printk(const char *fmt, ...)
621 #ifdef CONFIG_KGDB_KDB
622 if (unlikely(kdb_trap_printk)) {
624 r = vkdb_printf(fmt, args);
630 r = vprintk(fmt, args);
636 /* cpu currently holding logbuf_lock */
637 static volatile unsigned int printk_cpu = UINT_MAX;
640 * Can we actually use the console at this time on this cpu?
642 * Console drivers may assume that per-cpu resources have
643 * been allocated. So unless they're explicitly marked as
644 * being able to cope (CON_ANYTIME) don't call them until
645 * this CPU is officially up.
647 static inline int can_use_console(unsigned int cpu)
649 return cpu_online(cpu) || have_callable_console();
653 * Try to get console ownership to actually show the kernel
654 * messages from a 'printk'. Return true (and with the
655 * console_semaphore held, and 'console_locked' set) if it
656 * is successful, false otherwise.
658 * This gets called with the 'logbuf_lock' spinlock held and
659 * interrupts disabled. It should return with 'lockbuf_lock'
660 * released but interrupts still disabled.
662 static int acquire_console_semaphore_for_printk(unsigned int cpu)
663 __releases(&logbuf_lock)
667 if (!try_acquire_console_sem()) {
671 * If we can't use the console, we need to release
672 * the console semaphore by hand to avoid flushing
673 * the buffer. We need to hold the console semaphore
674 * in order to do this test safely.
676 if (!can_use_console(cpu)) {
682 printk_cpu = UINT_MAX;
683 spin_unlock(&logbuf_lock);
686 static const char recursion_bug_msg [] =
687 KERN_CRIT "BUG: recent printk recursion!\n";
688 static int recursion_bug;
689 static int new_text_line = 1;
690 static char printk_buf[1024];
692 int printk_delay_msec __read_mostly;
694 static inline void printk_delay(void)
696 if (unlikely(printk_delay_msec)) {
697 int m = printk_delay_msec;
701 touch_nmi_watchdog();
706 asmlinkage int vprintk(const char *fmt, va_list args)
709 int current_log_level = default_message_loglevel;
718 /* This stops the holder of console_sem just where we want him */
719 raw_local_irq_save(flags);
720 this_cpu = smp_processor_id();
723 * Ouch, printk recursed into itself!
725 if (unlikely(printk_cpu == this_cpu)) {
727 * If a crash is occurring during printk() on this CPU,
728 * then try to get the crash message out but make sure
729 * we can't deadlock. Otherwise just return to avoid the
730 * recursion and return - but flag the recursion so that
731 * it can be printed at the next appropriate moment:
733 if (!oops_in_progress) {
735 goto out_restore_irqs;
741 spin_lock(&logbuf_lock);
742 printk_cpu = this_cpu;
746 strcpy(printk_buf, recursion_bug_msg);
747 printed_len = strlen(recursion_bug_msg);
749 /* Emit the output into the temporary buffer */
750 printed_len += vscnprintf(printk_buf + printed_len,
751 sizeof(printk_buf) - printed_len, fmt, args);
756 /* Do we have a loglevel in the string? */
758 unsigned char c = p[1];
759 if (c && p[2] == '>') {
761 case '0' ... '7': /* loglevel */
762 current_log_level = c - '0';
763 /* Fallthrough - make sure we're on a new line */
764 case 'd': /* KERN_DEFAULT */
765 if (!new_text_line) {
769 /* Fallthrough - skip the loglevel */
770 case 'c': /* KERN_CONT */
778 * Copy the output into log_buf. If the caller didn't provide
779 * appropriate log level tags, we insert them here
783 /* Always output the token */
785 emit_log_char(current_log_level + '0');
791 /* Follow the token with the time */
794 unsigned long long t;
795 unsigned long nanosec_rem;
797 t = cpu_clock(printk_cpu);
798 nanosec_rem = do_div(t, 1000000000);
799 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
803 for (tp = tbuf; tp < tbuf + tlen; tp++)
818 * Try to acquire and then immediately release the
819 * console semaphore. The release will do all the
820 * actual magic (print out buffers, wake up klogd,
823 * The acquire_console_semaphore_for_printk() function
824 * will release 'logbuf_lock' regardless of whether it
825 * actually gets the semaphore or not.
827 if (acquire_console_semaphore_for_printk(this_cpu))
828 release_console_sem();
832 raw_local_irq_restore(flags);
837 EXPORT_SYMBOL(printk);
838 EXPORT_SYMBOL(vprintk);
842 static void call_console_drivers(unsigned start, unsigned end)
848 static int __add_preferred_console(char *name, int idx, char *options,
851 struct console_cmdline *c;
855 * See if this tty is not yet registered, and
856 * if we have a slot free.
858 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
859 if (strcmp(console_cmdline[i].name, name) == 0 &&
860 console_cmdline[i].index == idx) {
862 selected_console = i;
865 if (i == MAX_CMDLINECONSOLES)
868 selected_console = i;
869 c = &console_cmdline[i];
870 strlcpy(c->name, name, sizeof(c->name));
871 c->options = options;
872 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
873 c->brl_options = brl_options;
879 * Set up a list of consoles. Called from init/main.c
881 static int __init console_setup(char *str)
883 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
884 char *s, *options, *brl_options = NULL;
887 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
888 if (!memcmp(str, "brl,", 4)) {
891 } else if (!memcmp(str, "brl=", 4)) {
892 brl_options = str + 4;
893 str = strchr(brl_options, ',');
895 printk(KERN_ERR "need port name after brl=\n");
903 * Decode str into name, index, options.
905 if (str[0] >= '0' && str[0] <= '9') {
907 strncpy(buf + 4, str, sizeof(buf) - 5);
909 strncpy(buf, str, sizeof(buf) - 1);
911 buf[sizeof(buf) - 1] = 0;
912 if ((options = strchr(str, ',')) != NULL)
915 if (!strcmp(str, "ttya"))
916 strcpy(buf, "ttyS0");
917 if (!strcmp(str, "ttyb"))
918 strcpy(buf, "ttyS1");
920 for (s = buf; *s; s++)
921 if ((*s >= '0' && *s <= '9') || *s == ',')
923 idx = simple_strtoul(s, NULL, 10);
926 __add_preferred_console(buf, idx, options, brl_options);
927 console_set_on_cmdline = 1;
930 __setup("console=", console_setup);
933 * add_preferred_console - add a device to the list of preferred consoles.
936 * @options: options for this console
938 * The last preferred console added will be used for kernel messages
939 * and stdin/out/err for init. Normally this is used by console_setup
940 * above to handle user-supplied console arguments; however it can also
941 * be used by arch-specific code either to override the user or more
942 * commonly to provide a default console (ie from PROM variables) when
943 * the user has not supplied one.
945 int add_preferred_console(char *name, int idx, char *options)
947 return __add_preferred_console(name, idx, options, NULL);
950 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
952 struct console_cmdline *c;
955 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
956 if (strcmp(console_cmdline[i].name, name) == 0 &&
957 console_cmdline[i].index == idx) {
958 c = &console_cmdline[i];
959 strlcpy(c->name, name_new, sizeof(c->name));
960 c->name[sizeof(c->name) - 1] = 0;
961 c->options = options;
969 int console_suspend_enabled = 1;
970 EXPORT_SYMBOL(console_suspend_enabled);
972 static int __init console_suspend_disable(char *str)
974 console_suspend_enabled = 0;
977 __setup("no_console_suspend", console_suspend_disable);
980 * suspend_console - suspend the console subsystem
982 * This disables printk() while we go into suspend states
984 void suspend_console(void)
986 if (!console_suspend_enabled)
988 printk("Suspending console(s) (use no_console_suspend to debug)\n");
989 acquire_console_sem();
990 console_suspended = 1;
994 void resume_console(void)
996 if (!console_suspend_enabled)
999 console_suspended = 0;
1000 release_console_sem();
1004 * console_cpu_notify - print deferred console messages after CPU hotplug
1005 * @self: notifier struct
1006 * @action: CPU hotplug event
1009 * If printk() is called from a CPU that is not online yet, the messages
1010 * will be spooled but will not show up on the console. This function is
1011 * called when a new CPU comes online (or fails to come up), and ensures
1012 * that any such output gets printed.
1014 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1015 unsigned long action, void *hcpu)
1021 case CPU_DOWN_FAILED:
1022 case CPU_UP_CANCELED:
1023 acquire_console_sem();
1024 release_console_sem();
1030 * acquire_console_sem - lock the console system for exclusive use.
1032 * Acquires a semaphore which guarantees that the caller has
1033 * exclusive access to the console system and the console_drivers list.
1035 * Can sleep, returns nothing.
1037 void acquire_console_sem(void)
1039 BUG_ON(in_interrupt());
1041 if (console_suspended)
1044 console_may_schedule = 1;
1046 EXPORT_SYMBOL(acquire_console_sem);
1048 int try_acquire_console_sem(void)
1050 if (down_trylock(&console_sem))
1052 if (console_suspended) {
1057 console_may_schedule = 0;
1060 EXPORT_SYMBOL(try_acquire_console_sem);
1062 int is_console_locked(void)
1064 return console_locked;
1067 static DEFINE_PER_CPU(int, printk_pending);
1069 void printk_tick(void)
1071 if (__this_cpu_read(printk_pending)) {
1072 __this_cpu_write(printk_pending, 0);
1073 wake_up_interruptible(&log_wait);
1077 int printk_needs_cpu(int cpu)
1079 if (cpu_is_offline(cpu))
1081 return __this_cpu_read(printk_pending);
1084 void wake_up_klogd(void)
1086 if (waitqueue_active(&log_wait))
1087 this_cpu_write(printk_pending, 1);
1091 * release_console_sem - unlock the console system
1093 * Releases the semaphore which the caller holds on the console system
1094 * and the console driver list.
1096 * While the semaphore was held, console output may have been buffered
1097 * by printk(). If this is the case, release_console_sem() emits
1098 * the output prior to releasing the semaphore.
1100 * If there is output waiting for klogd, we wake it up.
1102 * release_console_sem() may be called from any context.
1104 void release_console_sem(void)
1106 unsigned long flags;
1107 unsigned _con_start, _log_end;
1108 unsigned wake_klogd = 0;
1110 if (console_suspended) {
1115 console_may_schedule = 0;
1118 spin_lock_irqsave(&logbuf_lock, flags);
1119 wake_klogd |= log_start - log_end;
1120 if (con_start == log_end)
1121 break; /* Nothing to print */
1122 _con_start = con_start;
1124 con_start = log_end; /* Flush */
1125 spin_unlock(&logbuf_lock);
1126 stop_critical_timings(); /* don't trace print latency */
1127 call_console_drivers(_con_start, _log_end);
1128 start_critical_timings();
1129 local_irq_restore(flags);
1133 spin_unlock_irqrestore(&logbuf_lock, flags);
1137 EXPORT_SYMBOL(release_console_sem);
1140 * console_conditional_schedule - yield the CPU if required
1142 * If the console code is currently allowed to sleep, and
1143 * if this CPU should yield the CPU to another task, do
1146 * Must be called within acquire_console_sem().
1148 void __sched console_conditional_schedule(void)
1150 if (console_may_schedule)
1153 EXPORT_SYMBOL(console_conditional_schedule);
1155 void console_unblank(void)
1160 * console_unblank can no longer be called in interrupt context unless
1161 * oops_in_progress is set to 1..
1163 if (oops_in_progress) {
1164 if (down_trylock(&console_sem) != 0)
1167 acquire_console_sem();
1170 console_may_schedule = 0;
1172 if ((c->flags & CON_ENABLED) && c->unblank)
1174 release_console_sem();
1178 * Return the console tty driver structure and its associated index
1180 struct tty_driver *console_device(int *index)
1183 struct tty_driver *driver = NULL;
1185 acquire_console_sem();
1186 for_each_console(c) {
1189 driver = c->device(c, index);
1193 release_console_sem();
1198 * Prevent further output on the passed console device so that (for example)
1199 * serial drivers can disable console output before suspending a port, and can
1200 * re-enable output afterwards.
1202 void console_stop(struct console *console)
1204 acquire_console_sem();
1205 console->flags &= ~CON_ENABLED;
1206 release_console_sem();
1208 EXPORT_SYMBOL(console_stop);
1210 void console_start(struct console *console)
1212 acquire_console_sem();
1213 console->flags |= CON_ENABLED;
1214 release_console_sem();
1216 EXPORT_SYMBOL(console_start);
1219 * The console driver calls this routine during kernel initialization
1220 * to register the console printing procedure with printk() and to
1221 * print any messages that were printed by the kernel before the
1222 * console driver was initialized.
1224 * This can happen pretty early during the boot process (because of
1225 * early_printk) - sometimes before setup_arch() completes - be careful
1226 * of what kernel features are used - they may not be initialised yet.
1228 * There are two types of consoles - bootconsoles (early_printk) and
1229 * "real" consoles (everything which is not a bootconsole) which are
1230 * handled differently.
1231 * - Any number of bootconsoles can be registered at any time.
1232 * - As soon as a "real" console is registered, all bootconsoles
1233 * will be unregistered automatically.
1234 * - Once a "real" console is registered, any attempt to register a
1235 * bootconsoles will be rejected
1237 void register_console(struct console *newcon)
1240 unsigned long flags;
1241 struct console *bcon = NULL;
1244 * before we register a new CON_BOOT console, make sure we don't
1245 * already have a valid console
1247 if (console_drivers && newcon->flags & CON_BOOT) {
1248 /* find the last or real console */
1249 for_each_console(bcon) {
1250 if (!(bcon->flags & CON_BOOT)) {
1251 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1252 newcon->name, newcon->index);
1258 if (console_drivers && console_drivers->flags & CON_BOOT)
1259 bcon = console_drivers;
1261 if (preferred_console < 0 || bcon || !console_drivers)
1262 preferred_console = selected_console;
1264 if (newcon->early_setup)
1265 newcon->early_setup();
1268 * See if we want to use this console driver. If we
1269 * didn't select a console we take the first one
1270 * that registers here.
1272 if (preferred_console < 0) {
1273 if (newcon->index < 0)
1275 if (newcon->setup == NULL ||
1276 newcon->setup(newcon, NULL) == 0) {
1277 newcon->flags |= CON_ENABLED;
1278 if (newcon->device) {
1279 newcon->flags |= CON_CONSDEV;
1280 preferred_console = 0;
1286 * See if this console matches one we selected on
1289 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1291 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1293 if (newcon->index >= 0 &&
1294 newcon->index != console_cmdline[i].index)
1296 if (newcon->index < 0)
1297 newcon->index = console_cmdline[i].index;
1298 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1299 if (console_cmdline[i].brl_options) {
1300 newcon->flags |= CON_BRL;
1301 braille_register_console(newcon,
1302 console_cmdline[i].index,
1303 console_cmdline[i].options,
1304 console_cmdline[i].brl_options);
1308 if (newcon->setup &&
1309 newcon->setup(newcon, console_cmdline[i].options) != 0)
1311 newcon->flags |= CON_ENABLED;
1312 newcon->index = console_cmdline[i].index;
1313 if (i == selected_console) {
1314 newcon->flags |= CON_CONSDEV;
1315 preferred_console = selected_console;
1320 if (!(newcon->flags & CON_ENABLED))
1324 * If we have a bootconsole, and are switching to a real console,
1325 * don't print everything out again, since when the boot console, and
1326 * the real console are the same physical device, it's annoying to
1327 * see the beginning boot messages twice
1329 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1330 newcon->flags &= ~CON_PRINTBUFFER;
1333 * Put this console in the list - keep the
1334 * preferred driver at the head of the list.
1336 acquire_console_sem();
1337 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1338 newcon->next = console_drivers;
1339 console_drivers = newcon;
1341 newcon->next->flags &= ~CON_CONSDEV;
1343 newcon->next = console_drivers->next;
1344 console_drivers->next = newcon;
1346 if (newcon->flags & CON_PRINTBUFFER) {
1348 * release_console_sem() will print out the buffered messages
1351 spin_lock_irqsave(&logbuf_lock, flags);
1352 con_start = log_start;
1353 spin_unlock_irqrestore(&logbuf_lock, flags);
1355 release_console_sem();
1356 console_sysfs_notify();
1359 * By unregistering the bootconsoles after we enable the real console
1360 * we get the "console xxx enabled" message on all the consoles -
1361 * boot consoles, real consoles, etc - this is to ensure that end
1362 * users know there might be something in the kernel's log buffer that
1363 * went to the bootconsole (that they do not see on the real console)
1365 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1366 /* we need to iterate through twice, to make sure we print
1367 * everything out, before we unregister the console(s)
1369 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1370 newcon->name, newcon->index);
1371 for_each_console(bcon)
1372 if (bcon->flags & CON_BOOT)
1373 unregister_console(bcon);
1375 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1376 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1377 newcon->name, newcon->index);
1380 EXPORT_SYMBOL(register_console);
1382 int unregister_console(struct console *console)
1384 struct console *a, *b;
1387 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1388 if (console->flags & CON_BRL)
1389 return braille_unregister_console(console);
1392 acquire_console_sem();
1393 if (console_drivers == console) {
1394 console_drivers=console->next;
1396 } else if (console_drivers) {
1397 for (a=console_drivers->next, b=console_drivers ;
1398 a; b=a, a=b->next) {
1408 * If this isn't the last console and it has CON_CONSDEV set, we
1409 * need to set it on the next preferred console.
1411 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1412 console_drivers->flags |= CON_CONSDEV;
1414 release_console_sem();
1415 console_sysfs_notify();
1418 EXPORT_SYMBOL(unregister_console);
1420 static int __init printk_late_init(void)
1422 struct console *con;
1424 for_each_console(con) {
1425 if (con->flags & CON_BOOT) {
1426 printk(KERN_INFO "turn off boot console %s%d\n",
1427 con->name, con->index);
1428 unregister_console(con);
1431 hotcpu_notifier(console_cpu_notify, 0);
1434 late_initcall(printk_late_init);
1436 #if defined CONFIG_PRINTK
1439 * printk rate limiting, lifted from the networking subsystem.
1441 * This enforces a rate limit: not more than 10 kernel messages
1442 * every 5s to make a denial-of-service attack impossible.
1444 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1446 int __printk_ratelimit(const char *func)
1448 return ___ratelimit(&printk_ratelimit_state, func);
1450 EXPORT_SYMBOL(__printk_ratelimit);
1453 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1454 * @caller_jiffies: pointer to caller's state
1455 * @interval_msecs: minimum interval between prints
1457 * printk_timed_ratelimit() returns true if more than @interval_msecs
1458 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1461 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1462 unsigned int interval_msecs)
1464 if (*caller_jiffies == 0
1465 || !time_in_range(jiffies, *caller_jiffies,
1467 + msecs_to_jiffies(interval_msecs))) {
1468 *caller_jiffies = jiffies;
1473 EXPORT_SYMBOL(printk_timed_ratelimit);
1475 static DEFINE_SPINLOCK(dump_list_lock);
1476 static LIST_HEAD(dump_list);
1479 * kmsg_dump_register - register a kernel log dumper.
1480 * @dumper: pointer to the kmsg_dumper structure
1482 * Adds a kernel log dumper to the system. The dump callback in the
1483 * structure will be called when the kernel oopses or panics and must be
1484 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1486 int kmsg_dump_register(struct kmsg_dumper *dumper)
1488 unsigned long flags;
1491 /* The dump callback needs to be set */
1495 spin_lock_irqsave(&dump_list_lock, flags);
1496 /* Don't allow registering multiple times */
1497 if (!dumper->registered) {
1498 dumper->registered = 1;
1499 list_add_tail(&dumper->list, &dump_list);
1502 spin_unlock_irqrestore(&dump_list_lock, flags);
1506 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1509 * kmsg_dump_unregister - unregister a kmsg dumper.
1510 * @dumper: pointer to the kmsg_dumper structure
1512 * Removes a dump device from the system. Returns zero on success and
1513 * %-EINVAL otherwise.
1515 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1517 unsigned long flags;
1520 spin_lock_irqsave(&dump_list_lock, flags);
1521 if (dumper->registered) {
1522 dumper->registered = 0;
1523 list_del(&dumper->list);
1526 spin_unlock_irqrestore(&dump_list_lock, flags);
1530 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1532 static const char * const kmsg_reasons[] = {
1533 [KMSG_DUMP_OOPS] = "oops",
1534 [KMSG_DUMP_PANIC] = "panic",
1535 [KMSG_DUMP_KEXEC] = "kexec",
1538 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1540 if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1543 return kmsg_reasons[reason];
1547 * kmsg_dump - dump kernel log to kernel message dumpers.
1548 * @reason: the reason (oops, panic etc) for dumping
1550 * Iterate through each of the dump devices and call the oops/panic
1551 * callbacks with the log buffer.
1553 void kmsg_dump(enum kmsg_dump_reason reason)
1557 struct kmsg_dumper *dumper;
1558 const char *s1, *s2;
1559 unsigned long l1, l2;
1560 unsigned long flags;
1562 /* Theoretically, the log could move on after we do this, but
1563 there's not a lot we can do about that. The new messages
1564 will overwrite the start of what we dump. */
1565 spin_lock_irqsave(&logbuf_lock, flags);
1566 end = log_end & LOG_BUF_MASK;
1567 chars = logged_chars;
1568 spin_unlock_irqrestore(&logbuf_lock, flags);
1571 s1 = log_buf + log_buf_len - chars + end;
1580 s2 = log_buf + end - chars;
1584 if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1585 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1586 kmsg_to_str(reason));
1589 list_for_each_entry(dumper, &dump_list, list)
1590 dumper->dump(dumper, reason, s1, l1, s2, l2);
1591 spin_unlock_irqrestore(&dump_list_lock, flags);