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 int do_syslog(int type, char __user *buf, int len, bool from_file)
260 unsigned i, j, limit, count;
265 error = security_syslog(type, from_file);
270 case SYSLOG_ACTION_CLOSE: /* Close log */
272 case SYSLOG_ACTION_OPEN: /* Open log */
274 case SYSLOG_ACTION_READ: /* Read from log */
281 if (!access_ok(VERIFY_WRITE, buf, len)) {
285 error = wait_event_interruptible(log_wait,
286 (log_start - log_end));
290 spin_lock_irq(&logbuf_lock);
291 while (!error && (log_start != log_end) && i < len) {
292 c = LOG_BUF(log_start);
294 spin_unlock_irq(&logbuf_lock);
295 error = __put_user(c,buf);
299 spin_lock_irq(&logbuf_lock);
301 spin_unlock_irq(&logbuf_lock);
305 /* Read/clear last kernel messages */
306 case SYSLOG_ACTION_READ_CLEAR:
309 /* Read last kernel messages */
310 case SYSLOG_ACTION_READ_ALL:
317 if (!access_ok(VERIFY_WRITE, buf, len)) {
322 if (count > log_buf_len)
324 spin_lock_irq(&logbuf_lock);
325 if (count > logged_chars)
326 count = logged_chars;
331 * __put_user() could sleep, and while we sleep
332 * printk() could overwrite the messages
333 * we try to copy to user space. Therefore
334 * the messages are copied in reverse. <manfreds>
336 for (i = 0; i < count && !error; i++) {
338 if (j + log_buf_len < log_end)
341 spin_unlock_irq(&logbuf_lock);
342 error = __put_user(c,&buf[count-1-i]);
344 spin_lock_irq(&logbuf_lock);
346 spin_unlock_irq(&logbuf_lock);
351 int offset = count-error;
352 /* buffer overflow during copy, correct user buffer. */
353 for (i = 0; i < error; i++) {
354 if (__get_user(c,&buf[i+offset]) ||
355 __put_user(c,&buf[i])) {
363 /* Clear ring buffer */
364 case SYSLOG_ACTION_CLEAR:
367 /* Disable logging to console */
368 case SYSLOG_ACTION_CONSOLE_OFF:
369 if (saved_console_loglevel == -1)
370 saved_console_loglevel = console_loglevel;
371 console_loglevel = minimum_console_loglevel;
373 /* Enable logging to console */
374 case SYSLOG_ACTION_CONSOLE_ON:
375 if (saved_console_loglevel != -1) {
376 console_loglevel = saved_console_loglevel;
377 saved_console_loglevel = -1;
380 /* Set level of messages printed to console */
381 case SYSLOG_ACTION_CONSOLE_LEVEL:
383 if (len < 1 || len > 8)
385 if (len < minimum_console_loglevel)
386 len = minimum_console_loglevel;
387 console_loglevel = len;
388 /* Implicitly re-enable logging to console */
389 saved_console_loglevel = -1;
392 /* Number of chars in the log buffer */
393 case SYSLOG_ACTION_SIZE_UNREAD:
394 error = log_end - log_start;
396 /* Size of the log buffer */
397 case SYSLOG_ACTION_SIZE_BUFFER:
408 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
410 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
413 #ifdef CONFIG_KGDB_KDB
414 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
415 * uses locks so it cannot be used during debugging. Just tell kdb
416 * where the start and end of the physical and logical logs are. This
417 * is equivalent to do_syslog(3).
419 void kdb_syslog_data(char *syslog_data[4])
421 syslog_data[0] = log_buf;
422 syslog_data[1] = log_buf + log_buf_len;
423 syslog_data[2] = log_buf + log_end -
424 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
425 syslog_data[3] = log_buf + log_end;
427 #endif /* CONFIG_KGDB_KDB */
430 * Call the console drivers on a range of log_buf
432 static void __call_console_drivers(unsigned start, unsigned end)
436 for_each_console(con) {
437 if ((con->flags & CON_ENABLED) && con->write &&
438 (cpu_online(smp_processor_id()) ||
439 (con->flags & CON_ANYTIME)))
440 con->write(con, &LOG_BUF(start), end - start);
444 static int __read_mostly ignore_loglevel;
446 static int __init ignore_loglevel_setup(char *str)
449 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
454 early_param("ignore_loglevel", ignore_loglevel_setup);
457 * Write out chars from start to end - 1 inclusive
459 static void _call_console_drivers(unsigned start,
460 unsigned end, int msg_log_level)
462 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
463 console_drivers && start != end) {
464 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
466 __call_console_drivers(start & LOG_BUF_MASK,
468 __call_console_drivers(0, end & LOG_BUF_MASK);
470 __call_console_drivers(start, end);
476 * Call the console drivers, asking them to write out
477 * log_buf[start] to log_buf[end - 1].
478 * The console_sem must be held.
480 static void call_console_drivers(unsigned start, unsigned end)
482 unsigned cur_index, start_print;
483 static int msg_level = -1;
485 BUG_ON(((int)(start - end)) > 0);
489 while (cur_index != end) {
490 if (msg_level < 0 && ((end - cur_index) > 2) &&
491 LOG_BUF(cur_index + 0) == '<' &&
492 LOG_BUF(cur_index + 1) >= '0' &&
493 LOG_BUF(cur_index + 1) <= '7' &&
494 LOG_BUF(cur_index + 2) == '>') {
495 msg_level = LOG_BUF(cur_index + 1) - '0';
497 start_print = cur_index;
499 while (cur_index != end) {
500 char c = LOG_BUF(cur_index);
506 * printk() has already given us loglevel tags in
507 * the buffer. This code is here in case the
508 * log buffer has wrapped right round and scribbled
511 msg_level = default_message_loglevel;
513 _call_console_drivers(start_print, cur_index, msg_level);
515 start_print = cur_index;
520 _call_console_drivers(start_print, end, msg_level);
523 static void emit_log_char(char c)
525 LOG_BUF(log_end) = c;
527 if (log_end - log_start > log_buf_len)
528 log_start = log_end - log_buf_len;
529 if (log_end - con_start > log_buf_len)
530 con_start = log_end - log_buf_len;
531 if (logged_chars < log_buf_len)
536 * Zap console related locks when oopsing. Only zap at most once
537 * every 10 seconds, to leave time for slow consoles to print a
540 static void zap_locks(void)
542 static unsigned long oops_timestamp;
544 if (time_after_eq(jiffies, oops_timestamp) &&
545 !time_after(jiffies, oops_timestamp + 30 * HZ))
548 oops_timestamp = jiffies;
550 /* If a crash is occurring, make sure we can't deadlock */
551 spin_lock_init(&logbuf_lock);
552 /* And make sure that we print immediately */
553 sema_init(&console_sem, 1);
556 #if defined(CONFIG_PRINTK_TIME)
557 static int printk_time = 1;
559 static int printk_time = 0;
561 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
563 /* Check if we have any console registered that can be called early in boot. */
564 static int have_callable_console(void)
568 for_each_console(con)
569 if (con->flags & CON_ANYTIME)
576 * printk - print a kernel message
577 * @fmt: format string
579 * This is printk(). It can be called from any context. We want it to work.
581 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
582 * call the console drivers. If we fail to get the semaphore we place the output
583 * into the log buffer and return. The current holder of the console_sem will
584 * notice the new output in release_console_sem() and will send it to the
585 * consoles before releasing the semaphore.
587 * One effect of this deferred printing is that code which calls printk() and
588 * then changes console_loglevel may break. This is because console_loglevel
589 * is inspected when the actual printing occurs.
594 * See the vsnprintf() documentation for format string extensions over C99.
597 asmlinkage int printk(const char *fmt, ...)
602 #ifdef CONFIG_KGDB_KDB
603 if (unlikely(kdb_trap_printk)) {
605 r = vkdb_printf(fmt, args);
611 r = vprintk(fmt, args);
617 /* cpu currently holding logbuf_lock */
618 static volatile unsigned int printk_cpu = UINT_MAX;
621 * Can we actually use the console at this time on this cpu?
623 * Console drivers may assume that per-cpu resources have
624 * been allocated. So unless they're explicitly marked as
625 * being able to cope (CON_ANYTIME) don't call them until
626 * this CPU is officially up.
628 static inline int can_use_console(unsigned int cpu)
630 return cpu_online(cpu) || have_callable_console();
634 * Try to get console ownership to actually show the kernel
635 * messages from a 'printk'. Return true (and with the
636 * console_semaphore held, and 'console_locked' set) if it
637 * is successful, false otherwise.
639 * This gets called with the 'logbuf_lock' spinlock held and
640 * interrupts disabled. It should return with 'lockbuf_lock'
641 * released but interrupts still disabled.
643 static int acquire_console_semaphore_for_printk(unsigned int cpu)
644 __releases(&logbuf_lock)
648 if (!try_acquire_console_sem()) {
652 * If we can't use the console, we need to release
653 * the console semaphore by hand to avoid flushing
654 * the buffer. We need to hold the console semaphore
655 * in order to do this test safely.
657 if (!can_use_console(cpu)) {
663 printk_cpu = UINT_MAX;
664 spin_unlock(&logbuf_lock);
667 static const char recursion_bug_msg [] =
668 KERN_CRIT "BUG: recent printk recursion!\n";
669 static int recursion_bug;
670 static int new_text_line = 1;
671 static char printk_buf[1024];
673 int printk_delay_msec __read_mostly;
675 static inline void printk_delay(void)
677 if (unlikely(printk_delay_msec)) {
678 int m = printk_delay_msec;
682 touch_nmi_watchdog();
687 asmlinkage int vprintk(const char *fmt, va_list args)
690 int current_log_level = default_message_loglevel;
699 /* This stops the holder of console_sem just where we want him */
700 raw_local_irq_save(flags);
701 this_cpu = smp_processor_id();
704 * Ouch, printk recursed into itself!
706 if (unlikely(printk_cpu == this_cpu)) {
708 * If a crash is occurring during printk() on this CPU,
709 * then try to get the crash message out but make sure
710 * we can't deadlock. Otherwise just return to avoid the
711 * recursion and return - but flag the recursion so that
712 * it can be printed at the next appropriate moment:
714 if (!oops_in_progress) {
716 goto out_restore_irqs;
722 spin_lock(&logbuf_lock);
723 printk_cpu = this_cpu;
727 strcpy(printk_buf, recursion_bug_msg);
728 printed_len = strlen(recursion_bug_msg);
730 /* Emit the output into the temporary buffer */
731 printed_len += vscnprintf(printk_buf + printed_len,
732 sizeof(printk_buf) - printed_len, fmt, args);
737 /* Do we have a loglevel in the string? */
739 unsigned char c = p[1];
740 if (c && p[2] == '>') {
742 case '0' ... '7': /* loglevel */
743 current_log_level = c - '0';
744 /* Fallthrough - make sure we're on a new line */
745 case 'd': /* KERN_DEFAULT */
746 if (!new_text_line) {
750 /* Fallthrough - skip the loglevel */
751 case 'c': /* KERN_CONT */
759 * Copy the output into log_buf. If the caller didn't provide
760 * appropriate log level tags, we insert them here
764 /* Always output the token */
766 emit_log_char(current_log_level + '0');
772 /* Follow the token with the time */
775 unsigned long long t;
776 unsigned long nanosec_rem;
778 t = cpu_clock(printk_cpu);
779 nanosec_rem = do_div(t, 1000000000);
780 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
784 for (tp = tbuf; tp < tbuf + tlen; tp++)
799 * Try to acquire and then immediately release the
800 * console semaphore. The release will do all the
801 * actual magic (print out buffers, wake up klogd,
804 * The acquire_console_semaphore_for_printk() function
805 * will release 'logbuf_lock' regardless of whether it
806 * actually gets the semaphore or not.
808 if (acquire_console_semaphore_for_printk(this_cpu))
809 release_console_sem();
813 raw_local_irq_restore(flags);
818 EXPORT_SYMBOL(printk);
819 EXPORT_SYMBOL(vprintk);
823 static void call_console_drivers(unsigned start, unsigned end)
829 static int __add_preferred_console(char *name, int idx, char *options,
832 struct console_cmdline *c;
836 * See if this tty is not yet registered, and
837 * if we have a slot free.
839 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
840 if (strcmp(console_cmdline[i].name, name) == 0 &&
841 console_cmdline[i].index == idx) {
843 selected_console = i;
846 if (i == MAX_CMDLINECONSOLES)
849 selected_console = i;
850 c = &console_cmdline[i];
851 strlcpy(c->name, name, sizeof(c->name));
852 c->options = options;
853 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
854 c->brl_options = brl_options;
860 * Set up a list of consoles. Called from init/main.c
862 static int __init console_setup(char *str)
864 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
865 char *s, *options, *brl_options = NULL;
868 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
869 if (!memcmp(str, "brl,", 4)) {
872 } else if (!memcmp(str, "brl=", 4)) {
873 brl_options = str + 4;
874 str = strchr(brl_options, ',');
876 printk(KERN_ERR "need port name after brl=\n");
884 * Decode str into name, index, options.
886 if (str[0] >= '0' && str[0] <= '9') {
888 strncpy(buf + 4, str, sizeof(buf) - 5);
890 strncpy(buf, str, sizeof(buf) - 1);
892 buf[sizeof(buf) - 1] = 0;
893 if ((options = strchr(str, ',')) != NULL)
896 if (!strcmp(str, "ttya"))
897 strcpy(buf, "ttyS0");
898 if (!strcmp(str, "ttyb"))
899 strcpy(buf, "ttyS1");
901 for (s = buf; *s; s++)
902 if ((*s >= '0' && *s <= '9') || *s == ',')
904 idx = simple_strtoul(s, NULL, 10);
907 __add_preferred_console(buf, idx, options, brl_options);
908 console_set_on_cmdline = 1;
911 __setup("console=", console_setup);
914 * add_preferred_console - add a device to the list of preferred consoles.
917 * @options: options for this console
919 * The last preferred console added will be used for kernel messages
920 * and stdin/out/err for init. Normally this is used by console_setup
921 * above to handle user-supplied console arguments; however it can also
922 * be used by arch-specific code either to override the user or more
923 * commonly to provide a default console (ie from PROM variables) when
924 * the user has not supplied one.
926 int add_preferred_console(char *name, int idx, char *options)
928 return __add_preferred_console(name, idx, options, NULL);
931 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
933 struct console_cmdline *c;
936 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
937 if (strcmp(console_cmdline[i].name, name) == 0 &&
938 console_cmdline[i].index == idx) {
939 c = &console_cmdline[i];
940 strlcpy(c->name, name_new, sizeof(c->name));
941 c->name[sizeof(c->name) - 1] = 0;
942 c->options = options;
950 int console_suspend_enabled = 1;
951 EXPORT_SYMBOL(console_suspend_enabled);
953 static int __init console_suspend_disable(char *str)
955 console_suspend_enabled = 0;
958 __setup("no_console_suspend", console_suspend_disable);
961 * suspend_console - suspend the console subsystem
963 * This disables printk() while we go into suspend states
965 void suspend_console(void)
967 if (!console_suspend_enabled)
969 printk("Suspending console(s) (use no_console_suspend to debug)\n");
970 acquire_console_sem();
971 console_suspended = 1;
975 void resume_console(void)
977 if (!console_suspend_enabled)
980 console_suspended = 0;
981 release_console_sem();
985 * console_cpu_notify - print deferred console messages after CPU hotplug
986 * @self: notifier struct
987 * @action: CPU hotplug event
990 * If printk() is called from a CPU that is not online yet, the messages
991 * will be spooled but will not show up on the console. This function is
992 * called when a new CPU comes online (or fails to come up), and ensures
993 * that any such output gets printed.
995 static int __cpuinit console_cpu_notify(struct notifier_block *self,
996 unsigned long action, void *hcpu)
1002 case CPU_DOWN_FAILED:
1003 case CPU_UP_CANCELED:
1004 acquire_console_sem();
1005 release_console_sem();
1011 * acquire_console_sem - lock the console system for exclusive use.
1013 * Acquires a semaphore which guarantees that the caller has
1014 * exclusive access to the console system and the console_drivers list.
1016 * Can sleep, returns nothing.
1018 void acquire_console_sem(void)
1020 BUG_ON(in_interrupt());
1022 if (console_suspended)
1025 console_may_schedule = 1;
1027 EXPORT_SYMBOL(acquire_console_sem);
1029 int try_acquire_console_sem(void)
1031 if (down_trylock(&console_sem))
1033 if (console_suspended) {
1038 console_may_schedule = 0;
1041 EXPORT_SYMBOL(try_acquire_console_sem);
1043 int is_console_locked(void)
1045 return console_locked;
1048 static DEFINE_PER_CPU(int, printk_pending);
1050 void printk_tick(void)
1052 if (__get_cpu_var(printk_pending)) {
1053 __get_cpu_var(printk_pending) = 0;
1054 wake_up_interruptible(&log_wait);
1058 int printk_needs_cpu(int cpu)
1060 return per_cpu(printk_pending, cpu);
1063 void wake_up_klogd(void)
1065 if (waitqueue_active(&log_wait))
1066 __raw_get_cpu_var(printk_pending) = 1;
1070 * release_console_sem - unlock the console system
1072 * Releases the semaphore which the caller holds on the console system
1073 * and the console driver list.
1075 * While the semaphore was held, console output may have been buffered
1076 * by printk(). If this is the case, release_console_sem() emits
1077 * the output prior to releasing the semaphore.
1079 * If there is output waiting for klogd, we wake it up.
1081 * release_console_sem() may be called from any context.
1083 void release_console_sem(void)
1085 unsigned long flags;
1086 unsigned _con_start, _log_end;
1087 unsigned wake_klogd = 0;
1089 if (console_suspended) {
1094 console_may_schedule = 0;
1097 spin_lock_irqsave(&logbuf_lock, flags);
1098 wake_klogd |= log_start - log_end;
1099 if (con_start == log_end)
1100 break; /* Nothing to print */
1101 _con_start = con_start;
1103 con_start = log_end; /* Flush */
1104 spin_unlock(&logbuf_lock);
1105 stop_critical_timings(); /* don't trace print latency */
1106 call_console_drivers(_con_start, _log_end);
1107 start_critical_timings();
1108 local_irq_restore(flags);
1112 spin_unlock_irqrestore(&logbuf_lock, flags);
1116 EXPORT_SYMBOL(release_console_sem);
1119 * console_conditional_schedule - yield the CPU if required
1121 * If the console code is currently allowed to sleep, and
1122 * if this CPU should yield the CPU to another task, do
1125 * Must be called within acquire_console_sem().
1127 void __sched console_conditional_schedule(void)
1129 if (console_may_schedule)
1132 EXPORT_SYMBOL(console_conditional_schedule);
1134 void console_unblank(void)
1139 * console_unblank can no longer be called in interrupt context unless
1140 * oops_in_progress is set to 1..
1142 if (oops_in_progress) {
1143 if (down_trylock(&console_sem) != 0)
1146 acquire_console_sem();
1149 console_may_schedule = 0;
1151 if ((c->flags & CON_ENABLED) && c->unblank)
1153 release_console_sem();
1157 * Return the console tty driver structure and its associated index
1159 struct tty_driver *console_device(int *index)
1162 struct tty_driver *driver = NULL;
1164 acquire_console_sem();
1165 for_each_console(c) {
1168 driver = c->device(c, index);
1172 release_console_sem();
1177 * Prevent further output on the passed console device so that (for example)
1178 * serial drivers can disable console output before suspending a port, and can
1179 * re-enable output afterwards.
1181 void console_stop(struct console *console)
1183 acquire_console_sem();
1184 console->flags &= ~CON_ENABLED;
1185 release_console_sem();
1187 EXPORT_SYMBOL(console_stop);
1189 void console_start(struct console *console)
1191 acquire_console_sem();
1192 console->flags |= CON_ENABLED;
1193 release_console_sem();
1195 EXPORT_SYMBOL(console_start);
1198 * The console driver calls this routine during kernel initialization
1199 * to register the console printing procedure with printk() and to
1200 * print any messages that were printed by the kernel before the
1201 * console driver was initialized.
1203 * This can happen pretty early during the boot process (because of
1204 * early_printk) - sometimes before setup_arch() completes - be careful
1205 * of what kernel features are used - they may not be initialised yet.
1207 * There are two types of consoles - bootconsoles (early_printk) and
1208 * "real" consoles (everything which is not a bootconsole) which are
1209 * handled differently.
1210 * - Any number of bootconsoles can be registered at any time.
1211 * - As soon as a "real" console is registered, all bootconsoles
1212 * will be unregistered automatically.
1213 * - Once a "real" console is registered, any attempt to register a
1214 * bootconsoles will be rejected
1216 void register_console(struct console *newcon)
1219 unsigned long flags;
1220 struct console *bcon = NULL;
1223 * before we register a new CON_BOOT console, make sure we don't
1224 * already have a valid console
1226 if (console_drivers && newcon->flags & CON_BOOT) {
1227 /* find the last or real console */
1228 for_each_console(bcon) {
1229 if (!(bcon->flags & CON_BOOT)) {
1230 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1231 newcon->name, newcon->index);
1237 if (console_drivers && console_drivers->flags & CON_BOOT)
1238 bcon = console_drivers;
1240 if (preferred_console < 0 || bcon || !console_drivers)
1241 preferred_console = selected_console;
1243 if (newcon->early_setup)
1244 newcon->early_setup();
1247 * See if we want to use this console driver. If we
1248 * didn't select a console we take the first one
1249 * that registers here.
1251 if (preferred_console < 0) {
1252 if (newcon->index < 0)
1254 if (newcon->setup == NULL ||
1255 newcon->setup(newcon, NULL) == 0) {
1256 newcon->flags |= CON_ENABLED;
1257 if (newcon->device) {
1258 newcon->flags |= CON_CONSDEV;
1259 preferred_console = 0;
1265 * See if this console matches one we selected on
1268 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1270 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1272 if (newcon->index >= 0 &&
1273 newcon->index != console_cmdline[i].index)
1275 if (newcon->index < 0)
1276 newcon->index = console_cmdline[i].index;
1277 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1278 if (console_cmdline[i].brl_options) {
1279 newcon->flags |= CON_BRL;
1280 braille_register_console(newcon,
1281 console_cmdline[i].index,
1282 console_cmdline[i].options,
1283 console_cmdline[i].brl_options);
1287 if (newcon->setup &&
1288 newcon->setup(newcon, console_cmdline[i].options) != 0)
1290 newcon->flags |= CON_ENABLED;
1291 newcon->index = console_cmdline[i].index;
1292 if (i == selected_console) {
1293 newcon->flags |= CON_CONSDEV;
1294 preferred_console = selected_console;
1299 if (!(newcon->flags & CON_ENABLED))
1303 * If we have a bootconsole, and are switching to a real console,
1304 * don't print everything out again, since when the boot console, and
1305 * the real console are the same physical device, it's annoying to
1306 * see the beginning boot messages twice
1308 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1309 newcon->flags &= ~CON_PRINTBUFFER;
1312 * Put this console in the list - keep the
1313 * preferred driver at the head of the list.
1315 acquire_console_sem();
1316 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1317 newcon->next = console_drivers;
1318 console_drivers = newcon;
1320 newcon->next->flags &= ~CON_CONSDEV;
1322 newcon->next = console_drivers->next;
1323 console_drivers->next = newcon;
1325 if (newcon->flags & CON_PRINTBUFFER) {
1327 * release_console_sem() will print out the buffered messages
1330 spin_lock_irqsave(&logbuf_lock, flags);
1331 con_start = log_start;
1332 spin_unlock_irqrestore(&logbuf_lock, flags);
1334 release_console_sem();
1335 console_sysfs_notify();
1338 * By unregistering the bootconsoles after we enable the real console
1339 * we get the "console xxx enabled" message on all the consoles -
1340 * boot consoles, real consoles, etc - this is to ensure that end
1341 * users know there might be something in the kernel's log buffer that
1342 * went to the bootconsole (that they do not see on the real console)
1344 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1345 /* we need to iterate through twice, to make sure we print
1346 * everything out, before we unregister the console(s)
1348 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1349 newcon->name, newcon->index);
1350 for_each_console(bcon)
1351 if (bcon->flags & CON_BOOT)
1352 unregister_console(bcon);
1354 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1355 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1356 newcon->name, newcon->index);
1359 EXPORT_SYMBOL(register_console);
1361 int unregister_console(struct console *console)
1363 struct console *a, *b;
1366 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1367 if (console->flags & CON_BRL)
1368 return braille_unregister_console(console);
1371 acquire_console_sem();
1372 if (console_drivers == console) {
1373 console_drivers=console->next;
1375 } else if (console_drivers) {
1376 for (a=console_drivers->next, b=console_drivers ;
1377 a; b=a, a=b->next) {
1387 * If this isn't the last console and it has CON_CONSDEV set, we
1388 * need to set it on the next preferred console.
1390 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1391 console_drivers->flags |= CON_CONSDEV;
1393 release_console_sem();
1394 console_sysfs_notify();
1397 EXPORT_SYMBOL(unregister_console);
1399 static int __init printk_late_init(void)
1401 struct console *con;
1403 for_each_console(con) {
1404 if (con->flags & CON_BOOT) {
1405 printk(KERN_INFO "turn off boot console %s%d\n",
1406 con->name, con->index);
1407 unregister_console(con);
1410 hotcpu_notifier(console_cpu_notify, 0);
1413 late_initcall(printk_late_init);
1415 #if defined CONFIG_PRINTK
1418 * printk rate limiting, lifted from the networking subsystem.
1420 * This enforces a rate limit: not more than 10 kernel messages
1421 * every 5s to make a denial-of-service attack impossible.
1423 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1425 int __printk_ratelimit(const char *func)
1427 return ___ratelimit(&printk_ratelimit_state, func);
1429 EXPORT_SYMBOL(__printk_ratelimit);
1432 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1433 * @caller_jiffies: pointer to caller's state
1434 * @interval_msecs: minimum interval between prints
1436 * printk_timed_ratelimit() returns true if more than @interval_msecs
1437 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1440 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1441 unsigned int interval_msecs)
1443 if (*caller_jiffies == 0
1444 || !time_in_range(jiffies, *caller_jiffies,
1446 + msecs_to_jiffies(interval_msecs))) {
1447 *caller_jiffies = jiffies;
1452 EXPORT_SYMBOL(printk_timed_ratelimit);
1454 static DEFINE_SPINLOCK(dump_list_lock);
1455 static LIST_HEAD(dump_list);
1458 * kmsg_dump_register - register a kernel log dumper.
1459 * @dumper: pointer to the kmsg_dumper structure
1461 * Adds a kernel log dumper to the system. The dump callback in the
1462 * structure will be called when the kernel oopses or panics and must be
1463 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1465 int kmsg_dump_register(struct kmsg_dumper *dumper)
1467 unsigned long flags;
1470 /* The dump callback needs to be set */
1474 spin_lock_irqsave(&dump_list_lock, flags);
1475 /* Don't allow registering multiple times */
1476 if (!dumper->registered) {
1477 dumper->registered = 1;
1478 list_add_tail(&dumper->list, &dump_list);
1481 spin_unlock_irqrestore(&dump_list_lock, flags);
1485 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1488 * kmsg_dump_unregister - unregister a kmsg dumper.
1489 * @dumper: pointer to the kmsg_dumper structure
1491 * Removes a dump device from the system. Returns zero on success and
1492 * %-EINVAL otherwise.
1494 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1496 unsigned long flags;
1499 spin_lock_irqsave(&dump_list_lock, flags);
1500 if (dumper->registered) {
1501 dumper->registered = 0;
1502 list_del(&dumper->list);
1505 spin_unlock_irqrestore(&dump_list_lock, flags);
1509 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1511 static const char * const kmsg_reasons[] = {
1512 [KMSG_DUMP_OOPS] = "oops",
1513 [KMSG_DUMP_PANIC] = "panic",
1514 [KMSG_DUMP_KEXEC] = "kexec",
1517 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1519 if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1522 return kmsg_reasons[reason];
1526 * kmsg_dump - dump kernel log to kernel message dumpers.
1527 * @reason: the reason (oops, panic etc) for dumping
1529 * Iterate through each of the dump devices and call the oops/panic
1530 * callbacks with the log buffer.
1532 void kmsg_dump(enum kmsg_dump_reason reason)
1536 struct kmsg_dumper *dumper;
1537 const char *s1, *s2;
1538 unsigned long l1, l2;
1539 unsigned long flags;
1541 /* Theoretically, the log could move on after we do this, but
1542 there's not a lot we can do about that. The new messages
1543 will overwrite the start of what we dump. */
1544 spin_lock_irqsave(&logbuf_lock, flags);
1545 end = log_end & LOG_BUF_MASK;
1546 chars = logged_chars;
1547 spin_unlock_irqrestore(&logbuf_lock, flags);
1550 s1 = log_buf + log_buf_len - chars + end;
1559 s2 = log_buf + end - chars;
1563 if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1564 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1565 kmsg_to_str(reason));
1568 list_for_each_entry(dumper, &dump_list, list)
1569 dumper->dump(dumper, reason, s1, l1, s2, l2);
1570 spin_unlock_irqrestore(&dump_list_lock, flags);