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 * for_each_console() allows you to iterate on each console
48 #define for_each_console(con) \
49 for (con = console_drivers; con != NULL; con = con->next)
52 * Architectures can override it:
54 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
58 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
60 /* printk's without a loglevel use this.. */
61 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
63 /* We show everything that is MORE important than this.. */
64 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
65 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
67 DECLARE_WAIT_QUEUE_HEAD(log_wait);
69 int console_printk[4] = {
70 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
71 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
72 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
73 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
77 * Low level drivers may need that to know if they can schedule in
78 * their unblank() callback or not. So let's export it.
81 EXPORT_SYMBOL(oops_in_progress);
84 * console_sem protects the console_drivers list, and also
85 * provides serialisation for access to the entire console
88 static DEFINE_SEMAPHORE(console_sem);
89 struct console *console_drivers;
90 EXPORT_SYMBOL_GPL(console_drivers);
93 * This is used for debugging the mess that is the VT code by
94 * keeping track if we have the console semaphore held. It's
95 * definitely not the perfect debug tool (we don't know if _WE_
96 * hold it are racing, but it helps tracking those weird code
97 * path in the console code where we end up in places I want
98 * locked without the console sempahore held
100 static int console_locked, console_suspended;
103 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
104 * It is also used in interesting ways to provide interlocking in
105 * release_console_sem().
107 static DEFINE_SPINLOCK(logbuf_lock);
109 #define LOG_BUF_MASK (log_buf_len-1)
110 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
113 * The indices into log_buf are not constrained to log_buf_len - they
114 * must be masked before subscripting
116 static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
117 static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
118 static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
121 * Array of consoles built from command line options (console=)
123 struct console_cmdline
125 char name[8]; /* Name of the driver */
126 int index; /* Minor dev. to use */
127 char *options; /* Options for the driver */
128 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
129 char *brl_options; /* Options for braille driver */
133 #define MAX_CMDLINECONSOLES 8
135 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
136 static int selected_console = -1;
137 static int preferred_console = -1;
138 int console_set_on_cmdline;
139 EXPORT_SYMBOL(console_set_on_cmdline);
141 /* Flag: console code may call schedule() */
142 static int console_may_schedule;
146 static char __log_buf[__LOG_BUF_LEN];
147 static char *log_buf = __log_buf;
148 static int log_buf_len = __LOG_BUF_LEN;
149 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
150 static int saved_console_loglevel = -1;
154 * This appends the listed symbols to /proc/vmcoreinfo
156 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
157 * obtain access to symbols that are otherwise very difficult to locate. These
158 * symbols are specifically used so that utilities can access and extract the
159 * dmesg log from a vmcore file after a crash.
161 void log_buf_kexec_setup(void)
163 VMCOREINFO_SYMBOL(log_buf);
164 VMCOREINFO_SYMBOL(log_end);
165 VMCOREINFO_SYMBOL(log_buf_len);
166 VMCOREINFO_SYMBOL(logged_chars);
170 static int __init log_buf_len_setup(char *str)
172 unsigned size = memparse(str, &str);
176 size = roundup_pow_of_two(size);
177 if (size > log_buf_len) {
178 unsigned start, dest_idx, offset;
181 new_log_buf = alloc_bootmem(size);
183 printk(KERN_WARNING "log_buf_len: allocation failed\n");
187 spin_lock_irqsave(&logbuf_lock, flags);
189 log_buf = new_log_buf;
191 offset = start = min(con_start, log_start);
193 while (start != log_end) {
194 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
201 spin_unlock_irqrestore(&logbuf_lock, flags);
203 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
209 __setup("log_buf_len=", log_buf_len_setup);
211 #ifdef CONFIG_BOOT_PRINTK_DELAY
213 static int boot_delay; /* msecs delay after each printk during bootup */
214 static unsigned long long loops_per_msec; /* based on boot_delay */
216 static int __init boot_delay_setup(char *str)
220 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
221 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
223 get_option(&str, &boot_delay);
224 if (boot_delay > 10 * 1000)
227 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
228 "HZ: %d, loops_per_msec: %llu\n",
229 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
232 __setup("boot_delay=", boot_delay_setup);
234 static void boot_delay_msec(void)
236 unsigned long long k;
237 unsigned long timeout;
239 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
242 k = (unsigned long long)loops_per_msec * boot_delay;
244 timeout = jiffies + msecs_to_jiffies(boot_delay);
249 * use (volatile) jiffies to prevent
250 * compiler reduction; loop termination via jiffies
251 * is secondary and may or may not happen.
253 if (time_after(jiffies, timeout))
255 touch_nmi_watchdog();
259 static inline void boot_delay_msec(void)
264 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
265 int dmesg_restrict = 1;
270 int do_syslog(int type, char __user *buf, int len, bool from_file)
272 unsigned i, j, limit, count;
278 * If this is from /proc/kmsg we only do the capabilities checks
281 if (type == SYSLOG_ACTION_OPEN || !from_file) {
282 if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
284 if ((type != SYSLOG_ACTION_READ_ALL &&
285 type != SYSLOG_ACTION_SIZE_BUFFER) &&
286 !capable(CAP_SYSLOG)) {
287 /* remove after 2.6.38 */
288 if (capable(CAP_SYS_ADMIN))
289 WARN_ONCE(1, "Attempt to access syslog with "
290 "CAP_SYS_ADMIN but no CAP_SYSLOG "
291 "(deprecated and denied).\n");
296 error = security_syslog(type);
301 case SYSLOG_ACTION_CLOSE: /* Close log */
303 case SYSLOG_ACTION_OPEN: /* Open log */
305 case SYSLOG_ACTION_READ: /* Read from log */
312 if (!access_ok(VERIFY_WRITE, buf, len)) {
316 error = wait_event_interruptible(log_wait,
317 (log_start - log_end));
321 spin_lock_irq(&logbuf_lock);
322 while (!error && (log_start != log_end) && i < len) {
323 c = LOG_BUF(log_start);
325 spin_unlock_irq(&logbuf_lock);
326 error = __put_user(c,buf);
330 spin_lock_irq(&logbuf_lock);
332 spin_unlock_irq(&logbuf_lock);
336 /* Read/clear last kernel messages */
337 case SYSLOG_ACTION_READ_CLEAR:
340 /* Read last kernel messages */
341 case SYSLOG_ACTION_READ_ALL:
348 if (!access_ok(VERIFY_WRITE, buf, len)) {
353 if (count > log_buf_len)
355 spin_lock_irq(&logbuf_lock);
356 if (count > logged_chars)
357 count = logged_chars;
362 * __put_user() could sleep, and while we sleep
363 * printk() could overwrite the messages
364 * we try to copy to user space. Therefore
365 * the messages are copied in reverse. <manfreds>
367 for (i = 0; i < count && !error; i++) {
369 if (j + log_buf_len < log_end)
372 spin_unlock_irq(&logbuf_lock);
373 error = __put_user(c,&buf[count-1-i]);
375 spin_lock_irq(&logbuf_lock);
377 spin_unlock_irq(&logbuf_lock);
382 int offset = count-error;
383 /* buffer overflow during copy, correct user buffer. */
384 for (i = 0; i < error; i++) {
385 if (__get_user(c,&buf[i+offset]) ||
386 __put_user(c,&buf[i])) {
394 /* Clear ring buffer */
395 case SYSLOG_ACTION_CLEAR:
398 /* Disable logging to console */
399 case SYSLOG_ACTION_CONSOLE_OFF:
400 if (saved_console_loglevel == -1)
401 saved_console_loglevel = console_loglevel;
402 console_loglevel = minimum_console_loglevel;
404 /* Enable logging to console */
405 case SYSLOG_ACTION_CONSOLE_ON:
406 if (saved_console_loglevel != -1) {
407 console_loglevel = saved_console_loglevel;
408 saved_console_loglevel = -1;
411 /* Set level of messages printed to console */
412 case SYSLOG_ACTION_CONSOLE_LEVEL:
414 if (len < 1 || len > 8)
416 if (len < minimum_console_loglevel)
417 len = minimum_console_loglevel;
418 console_loglevel = len;
419 /* Implicitly re-enable logging to console */
420 saved_console_loglevel = -1;
423 /* Number of chars in the log buffer */
424 case SYSLOG_ACTION_SIZE_UNREAD:
425 error = log_end - log_start;
427 /* Size of the log buffer */
428 case SYSLOG_ACTION_SIZE_BUFFER:
439 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
441 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
444 #ifdef CONFIG_KGDB_KDB
445 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
446 * uses locks so it cannot be used during debugging. Just tell kdb
447 * where the start and end of the physical and logical logs are. This
448 * is equivalent to do_syslog(3).
450 void kdb_syslog_data(char *syslog_data[4])
452 syslog_data[0] = log_buf;
453 syslog_data[1] = log_buf + log_buf_len;
454 syslog_data[2] = log_buf + log_end -
455 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
456 syslog_data[3] = log_buf + log_end;
458 #endif /* CONFIG_KGDB_KDB */
461 * Call the console drivers on a range of log_buf
463 static void __call_console_drivers(unsigned start, unsigned end)
467 for_each_console(con) {
468 if ((con->flags & CON_ENABLED) && con->write &&
469 (cpu_online(smp_processor_id()) ||
470 (con->flags & CON_ANYTIME)))
471 con->write(con, &LOG_BUF(start), end - start);
475 static int __read_mostly ignore_loglevel;
477 static int __init ignore_loglevel_setup(char *str)
480 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
485 early_param("ignore_loglevel", ignore_loglevel_setup);
488 * Write out chars from start to end - 1 inclusive
490 static void _call_console_drivers(unsigned start,
491 unsigned end, int msg_log_level)
493 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
494 console_drivers && start != end) {
495 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
497 __call_console_drivers(start & LOG_BUF_MASK,
499 __call_console_drivers(0, end & LOG_BUF_MASK);
501 __call_console_drivers(start, end);
507 * Call the console drivers, asking them to write out
508 * log_buf[start] to log_buf[end - 1].
509 * The console_sem must be held.
511 static void call_console_drivers(unsigned start, unsigned end)
513 unsigned cur_index, start_print;
514 static int msg_level = -1;
516 BUG_ON(((int)(start - end)) > 0);
520 while (cur_index != end) {
521 if (msg_level < 0 && ((end - cur_index) > 2) &&
522 LOG_BUF(cur_index + 0) == '<' &&
523 LOG_BUF(cur_index + 1) >= '0' &&
524 LOG_BUF(cur_index + 1) <= '7' &&
525 LOG_BUF(cur_index + 2) == '>') {
526 msg_level = LOG_BUF(cur_index + 1) - '0';
528 start_print = cur_index;
530 while (cur_index != end) {
531 char c = LOG_BUF(cur_index);
537 * printk() has already given us loglevel tags in
538 * the buffer. This code is here in case the
539 * log buffer has wrapped right round and scribbled
542 msg_level = default_message_loglevel;
544 _call_console_drivers(start_print, cur_index, msg_level);
546 start_print = cur_index;
551 _call_console_drivers(start_print, end, msg_level);
554 static void emit_log_char(char c)
556 LOG_BUF(log_end) = c;
558 if (log_end - log_start > log_buf_len)
559 log_start = log_end - log_buf_len;
560 if (log_end - con_start > log_buf_len)
561 con_start = log_end - log_buf_len;
562 if (logged_chars < log_buf_len)
567 * Zap console related locks when oopsing. Only zap at most once
568 * every 10 seconds, to leave time for slow consoles to print a
571 static void zap_locks(void)
573 static unsigned long oops_timestamp;
575 if (time_after_eq(jiffies, oops_timestamp) &&
576 !time_after(jiffies, oops_timestamp + 30 * HZ))
579 oops_timestamp = jiffies;
581 /* If a crash is occurring, make sure we can't deadlock */
582 spin_lock_init(&logbuf_lock);
583 /* And make sure that we print immediately */
584 sema_init(&console_sem, 1);
587 #if defined(CONFIG_PRINTK_TIME)
588 static int printk_time = 1;
590 static int printk_time = 0;
592 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
594 /* Check if we have any console registered that can be called early in boot. */
595 static int have_callable_console(void)
599 for_each_console(con)
600 if (con->flags & CON_ANYTIME)
607 * printk - print a kernel message
608 * @fmt: format string
610 * This is printk(). It can be called from any context. We want it to work.
612 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
613 * call the console drivers. If we fail to get the semaphore we place the output
614 * into the log buffer and return. The current holder of the console_sem will
615 * notice the new output in release_console_sem() and will send it to the
616 * consoles before releasing the semaphore.
618 * One effect of this deferred printing is that code which calls printk() and
619 * then changes console_loglevel may break. This is because console_loglevel
620 * is inspected when the actual printing occurs.
625 * See the vsnprintf() documentation for format string extensions over C99.
628 asmlinkage int printk(const char *fmt, ...)
633 #ifdef CONFIG_KGDB_KDB
634 if (unlikely(kdb_trap_printk)) {
636 r = vkdb_printf(fmt, args);
642 r = vprintk(fmt, args);
648 /* cpu currently holding logbuf_lock */
649 static volatile unsigned int printk_cpu = UINT_MAX;
652 * Can we actually use the console at this time on this cpu?
654 * Console drivers may assume that per-cpu resources have
655 * been allocated. So unless they're explicitly marked as
656 * being able to cope (CON_ANYTIME) don't call them until
657 * this CPU is officially up.
659 static inline int can_use_console(unsigned int cpu)
661 return cpu_online(cpu) || have_callable_console();
665 * Try to get console ownership to actually show the kernel
666 * messages from a 'printk'. Return true (and with the
667 * console_semaphore held, and 'console_locked' set) if it
668 * is successful, false otherwise.
670 * This gets called with the 'logbuf_lock' spinlock held and
671 * interrupts disabled. It should return with 'lockbuf_lock'
672 * released but interrupts still disabled.
674 static int acquire_console_semaphore_for_printk(unsigned int cpu)
675 __releases(&logbuf_lock)
679 if (!try_acquire_console_sem()) {
683 * If we can't use the console, we need to release
684 * the console semaphore by hand to avoid flushing
685 * the buffer. We need to hold the console semaphore
686 * in order to do this test safely.
688 if (!can_use_console(cpu)) {
694 printk_cpu = UINT_MAX;
695 spin_unlock(&logbuf_lock);
698 static const char recursion_bug_msg [] =
699 KERN_CRIT "BUG: recent printk recursion!\n";
700 static int recursion_bug;
701 static int new_text_line = 1;
702 static char printk_buf[1024];
704 int printk_delay_msec __read_mostly;
706 static inline void printk_delay(void)
708 if (unlikely(printk_delay_msec)) {
709 int m = printk_delay_msec;
713 touch_nmi_watchdog();
718 asmlinkage int vprintk(const char *fmt, va_list args)
721 int current_log_level = default_message_loglevel;
730 /* This stops the holder of console_sem just where we want him */
731 raw_local_irq_save(flags);
732 this_cpu = smp_processor_id();
735 * Ouch, printk recursed into itself!
737 if (unlikely(printk_cpu == this_cpu)) {
739 * If a crash is occurring during printk() on this CPU,
740 * then try to get the crash message out but make sure
741 * we can't deadlock. Otherwise just return to avoid the
742 * recursion and return - but flag the recursion so that
743 * it can be printed at the next appropriate moment:
745 if (!oops_in_progress) {
747 goto out_restore_irqs;
753 spin_lock(&logbuf_lock);
754 printk_cpu = this_cpu;
758 strcpy(printk_buf, recursion_bug_msg);
759 printed_len = strlen(recursion_bug_msg);
761 /* Emit the output into the temporary buffer */
762 printed_len += vscnprintf(printk_buf + printed_len,
763 sizeof(printk_buf) - printed_len, fmt, args);
768 /* Do we have a loglevel in the string? */
770 unsigned char c = p[1];
771 if (c && p[2] == '>') {
773 case '0' ... '7': /* loglevel */
774 current_log_level = c - '0';
775 /* Fallthrough - make sure we're on a new line */
776 case 'd': /* KERN_DEFAULT */
777 if (!new_text_line) {
781 /* Fallthrough - skip the loglevel */
782 case 'c': /* KERN_CONT */
790 * Copy the output into log_buf. If the caller didn't provide
791 * appropriate log level tags, we insert them here
795 /* Always output the token */
797 emit_log_char(current_log_level + '0');
803 /* Follow the token with the time */
806 unsigned long long t;
807 unsigned long nanosec_rem;
809 t = cpu_clock(printk_cpu);
810 nanosec_rem = do_div(t, 1000000000);
811 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
815 for (tp = tbuf; tp < tbuf + tlen; tp++)
830 * Try to acquire and then immediately release the
831 * console semaphore. The release will do all the
832 * actual magic (print out buffers, wake up klogd,
835 * The acquire_console_semaphore_for_printk() function
836 * will release 'logbuf_lock' regardless of whether it
837 * actually gets the semaphore or not.
839 if (acquire_console_semaphore_for_printk(this_cpu))
840 release_console_sem();
844 raw_local_irq_restore(flags);
849 EXPORT_SYMBOL(printk);
850 EXPORT_SYMBOL(vprintk);
854 static void call_console_drivers(unsigned start, unsigned end)
860 static int __add_preferred_console(char *name, int idx, char *options,
863 struct console_cmdline *c;
867 * See if this tty is not yet registered, and
868 * if we have a slot free.
870 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
871 if (strcmp(console_cmdline[i].name, name) == 0 &&
872 console_cmdline[i].index == idx) {
874 selected_console = i;
877 if (i == MAX_CMDLINECONSOLES)
880 selected_console = i;
881 c = &console_cmdline[i];
882 strlcpy(c->name, name, sizeof(c->name));
883 c->options = options;
884 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
885 c->brl_options = brl_options;
891 * Set up a list of consoles. Called from init/main.c
893 static int __init console_setup(char *str)
895 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
896 char *s, *options, *brl_options = NULL;
899 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
900 if (!memcmp(str, "brl,", 4)) {
903 } else if (!memcmp(str, "brl=", 4)) {
904 brl_options = str + 4;
905 str = strchr(brl_options, ',');
907 printk(KERN_ERR "need port name after brl=\n");
915 * Decode str into name, index, options.
917 if (str[0] >= '0' && str[0] <= '9') {
919 strncpy(buf + 4, str, sizeof(buf) - 5);
921 strncpy(buf, str, sizeof(buf) - 1);
923 buf[sizeof(buf) - 1] = 0;
924 if ((options = strchr(str, ',')) != NULL)
927 if (!strcmp(str, "ttya"))
928 strcpy(buf, "ttyS0");
929 if (!strcmp(str, "ttyb"))
930 strcpy(buf, "ttyS1");
932 for (s = buf; *s; s++)
933 if ((*s >= '0' && *s <= '9') || *s == ',')
935 idx = simple_strtoul(s, NULL, 10);
938 __add_preferred_console(buf, idx, options, brl_options);
939 console_set_on_cmdline = 1;
942 __setup("console=", console_setup);
945 * add_preferred_console - add a device to the list of preferred consoles.
948 * @options: options for this console
950 * The last preferred console added will be used for kernel messages
951 * and stdin/out/err for init. Normally this is used by console_setup
952 * above to handle user-supplied console arguments; however it can also
953 * be used by arch-specific code either to override the user or more
954 * commonly to provide a default console (ie from PROM variables) when
955 * the user has not supplied one.
957 int add_preferred_console(char *name, int idx, char *options)
959 return __add_preferred_console(name, idx, options, NULL);
962 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
964 struct console_cmdline *c;
967 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
968 if (strcmp(console_cmdline[i].name, name) == 0 &&
969 console_cmdline[i].index == idx) {
970 c = &console_cmdline[i];
971 strlcpy(c->name, name_new, sizeof(c->name));
972 c->name[sizeof(c->name) - 1] = 0;
973 c->options = options;
981 int console_suspend_enabled = 1;
982 EXPORT_SYMBOL(console_suspend_enabled);
984 static int __init console_suspend_disable(char *str)
986 console_suspend_enabled = 0;
989 __setup("no_console_suspend", console_suspend_disable);
992 * suspend_console - suspend the console subsystem
994 * This disables printk() while we go into suspend states
996 void suspend_console(void)
998 if (!console_suspend_enabled)
1000 printk("Suspending console(s) (use no_console_suspend to debug)\n");
1001 acquire_console_sem();
1002 console_suspended = 1;
1006 void resume_console(void)
1008 if (!console_suspend_enabled)
1011 console_suspended = 0;
1012 release_console_sem();
1016 * console_cpu_notify - print deferred console messages after CPU hotplug
1017 * @self: notifier struct
1018 * @action: CPU hotplug event
1021 * If printk() is called from a CPU that is not online yet, the messages
1022 * will be spooled but will not show up on the console. This function is
1023 * called when a new CPU comes online (or fails to come up), and ensures
1024 * that any such output gets printed.
1026 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1027 unsigned long action, void *hcpu)
1033 case CPU_DOWN_FAILED:
1034 case CPU_UP_CANCELED:
1035 acquire_console_sem();
1036 release_console_sem();
1042 * acquire_console_sem - lock the console system for exclusive use.
1044 * Acquires a semaphore which guarantees that the caller has
1045 * exclusive access to the console system and the console_drivers list.
1047 * Can sleep, returns nothing.
1049 void acquire_console_sem(void)
1051 BUG_ON(in_interrupt());
1053 if (console_suspended)
1056 console_may_schedule = 1;
1058 EXPORT_SYMBOL(acquire_console_sem);
1060 int try_acquire_console_sem(void)
1062 if (down_trylock(&console_sem))
1064 if (console_suspended) {
1069 console_may_schedule = 0;
1072 EXPORT_SYMBOL(try_acquire_console_sem);
1074 int is_console_locked(void)
1076 return console_locked;
1079 static DEFINE_PER_CPU(int, printk_pending);
1081 void printk_tick(void)
1083 if (__get_cpu_var(printk_pending)) {
1084 __get_cpu_var(printk_pending) = 0;
1085 wake_up_interruptible(&log_wait);
1089 int printk_needs_cpu(int cpu)
1091 return per_cpu(printk_pending, cpu);
1094 void wake_up_klogd(void)
1096 if (waitqueue_active(&log_wait))
1097 __raw_get_cpu_var(printk_pending) = 1;
1101 * release_console_sem - unlock the console system
1103 * Releases the semaphore which the caller holds on the console system
1104 * and the console driver list.
1106 * While the semaphore was held, console output may have been buffered
1107 * by printk(). If this is the case, release_console_sem() emits
1108 * the output prior to releasing the semaphore.
1110 * If there is output waiting for klogd, we wake it up.
1112 * release_console_sem() may be called from any context.
1114 void release_console_sem(void)
1116 unsigned long flags;
1117 unsigned _con_start, _log_end;
1118 unsigned wake_klogd = 0;
1120 if (console_suspended) {
1125 console_may_schedule = 0;
1128 spin_lock_irqsave(&logbuf_lock, flags);
1129 wake_klogd |= log_start - log_end;
1130 if (con_start == log_end)
1131 break; /* Nothing to print */
1132 _con_start = con_start;
1134 con_start = log_end; /* Flush */
1135 spin_unlock(&logbuf_lock);
1136 stop_critical_timings(); /* don't trace print latency */
1137 call_console_drivers(_con_start, _log_end);
1138 start_critical_timings();
1139 local_irq_restore(flags);
1143 spin_unlock_irqrestore(&logbuf_lock, flags);
1147 EXPORT_SYMBOL(release_console_sem);
1150 * console_conditional_schedule - yield the CPU if required
1152 * If the console code is currently allowed to sleep, and
1153 * if this CPU should yield the CPU to another task, do
1156 * Must be called within acquire_console_sem().
1158 void __sched console_conditional_schedule(void)
1160 if (console_may_schedule)
1163 EXPORT_SYMBOL(console_conditional_schedule);
1165 void console_unblank(void)
1170 * console_unblank can no longer be called in interrupt context unless
1171 * oops_in_progress is set to 1..
1173 if (oops_in_progress) {
1174 if (down_trylock(&console_sem) != 0)
1177 acquire_console_sem();
1180 console_may_schedule = 0;
1182 if ((c->flags & CON_ENABLED) && c->unblank)
1184 release_console_sem();
1188 * Return the console tty driver structure and its associated index
1190 struct tty_driver *console_device(int *index)
1193 struct tty_driver *driver = NULL;
1195 acquire_console_sem();
1196 for_each_console(c) {
1199 driver = c->device(c, index);
1203 release_console_sem();
1208 * Prevent further output on the passed console device so that (for example)
1209 * serial drivers can disable console output before suspending a port, and can
1210 * re-enable output afterwards.
1212 void console_stop(struct console *console)
1214 acquire_console_sem();
1215 console->flags &= ~CON_ENABLED;
1216 release_console_sem();
1218 EXPORT_SYMBOL(console_stop);
1220 void console_start(struct console *console)
1222 acquire_console_sem();
1223 console->flags |= CON_ENABLED;
1224 release_console_sem();
1226 EXPORT_SYMBOL(console_start);
1229 * The console driver calls this routine during kernel initialization
1230 * to register the console printing procedure with printk() and to
1231 * print any messages that were printed by the kernel before the
1232 * console driver was initialized.
1234 * This can happen pretty early during the boot process (because of
1235 * early_printk) - sometimes before setup_arch() completes - be careful
1236 * of what kernel features are used - they may not be initialised yet.
1238 * There are two types of consoles - bootconsoles (early_printk) and
1239 * "real" consoles (everything which is not a bootconsole) which are
1240 * handled differently.
1241 * - Any number of bootconsoles can be registered at any time.
1242 * - As soon as a "real" console is registered, all bootconsoles
1243 * will be unregistered automatically.
1244 * - Once a "real" console is registered, any attempt to register a
1245 * bootconsoles will be rejected
1247 void register_console(struct console *newcon)
1250 unsigned long flags;
1251 struct console *bcon = NULL;
1254 * before we register a new CON_BOOT console, make sure we don't
1255 * already have a valid console
1257 if (console_drivers && newcon->flags & CON_BOOT) {
1258 /* find the last or real console */
1259 for_each_console(bcon) {
1260 if (!(bcon->flags & CON_BOOT)) {
1261 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1262 newcon->name, newcon->index);
1268 if (console_drivers && console_drivers->flags & CON_BOOT)
1269 bcon = console_drivers;
1271 if (preferred_console < 0 || bcon || !console_drivers)
1272 preferred_console = selected_console;
1274 if (newcon->early_setup)
1275 newcon->early_setup();
1278 * See if we want to use this console driver. If we
1279 * didn't select a console we take the first one
1280 * that registers here.
1282 if (preferred_console < 0) {
1283 if (newcon->index < 0)
1285 if (newcon->setup == NULL ||
1286 newcon->setup(newcon, NULL) == 0) {
1287 newcon->flags |= CON_ENABLED;
1288 if (newcon->device) {
1289 newcon->flags |= CON_CONSDEV;
1290 preferred_console = 0;
1296 * See if this console matches one we selected on
1299 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1301 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1303 if (newcon->index >= 0 &&
1304 newcon->index != console_cmdline[i].index)
1306 if (newcon->index < 0)
1307 newcon->index = console_cmdline[i].index;
1308 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1309 if (console_cmdline[i].brl_options) {
1310 newcon->flags |= CON_BRL;
1311 braille_register_console(newcon,
1312 console_cmdline[i].index,
1313 console_cmdline[i].options,
1314 console_cmdline[i].brl_options);
1318 if (newcon->setup &&
1319 newcon->setup(newcon, console_cmdline[i].options) != 0)
1321 newcon->flags |= CON_ENABLED;
1322 newcon->index = console_cmdline[i].index;
1323 if (i == selected_console) {
1324 newcon->flags |= CON_CONSDEV;
1325 preferred_console = selected_console;
1330 if (!(newcon->flags & CON_ENABLED))
1334 * If we have a bootconsole, and are switching to a real console,
1335 * don't print everything out again, since when the boot console, and
1336 * the real console are the same physical device, it's annoying to
1337 * see the beginning boot messages twice
1339 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1340 newcon->flags &= ~CON_PRINTBUFFER;
1343 * Put this console in the list - keep the
1344 * preferred driver at the head of the list.
1346 acquire_console_sem();
1347 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1348 newcon->next = console_drivers;
1349 console_drivers = newcon;
1351 newcon->next->flags &= ~CON_CONSDEV;
1353 newcon->next = console_drivers->next;
1354 console_drivers->next = newcon;
1356 if (newcon->flags & CON_PRINTBUFFER) {
1358 * release_console_sem() will print out the buffered messages
1361 spin_lock_irqsave(&logbuf_lock, flags);
1362 con_start = log_start;
1363 spin_unlock_irqrestore(&logbuf_lock, flags);
1365 release_console_sem();
1368 * By unregistering the bootconsoles after we enable the real console
1369 * we get the "console xxx enabled" message on all the consoles -
1370 * boot consoles, real consoles, etc - this is to ensure that end
1371 * users know there might be something in the kernel's log buffer that
1372 * went to the bootconsole (that they do not see on the real console)
1374 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1375 /* we need to iterate through twice, to make sure we print
1376 * everything out, before we unregister the console(s)
1378 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1379 newcon->name, newcon->index);
1380 for_each_console(bcon)
1381 if (bcon->flags & CON_BOOT)
1382 unregister_console(bcon);
1384 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1385 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1386 newcon->name, newcon->index);
1389 EXPORT_SYMBOL(register_console);
1391 int unregister_console(struct console *console)
1393 struct console *a, *b;
1396 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1397 if (console->flags & CON_BRL)
1398 return braille_unregister_console(console);
1401 acquire_console_sem();
1402 if (console_drivers == console) {
1403 console_drivers=console->next;
1405 } else if (console_drivers) {
1406 for (a=console_drivers->next, b=console_drivers ;
1407 a; b=a, a=b->next) {
1417 * If this isn't the last console and it has CON_CONSDEV set, we
1418 * need to set it on the next preferred console.
1420 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1421 console_drivers->flags |= CON_CONSDEV;
1423 release_console_sem();
1426 EXPORT_SYMBOL(unregister_console);
1428 static int __init printk_late_init(void)
1430 struct console *con;
1432 for_each_console(con) {
1433 if (con->flags & CON_BOOT) {
1434 printk(KERN_INFO "turn off boot console %s%d\n",
1435 con->name, con->index);
1436 unregister_console(con);
1439 hotcpu_notifier(console_cpu_notify, 0);
1442 late_initcall(printk_late_init);
1444 #if defined CONFIG_PRINTK
1447 * printk rate limiting, lifted from the networking subsystem.
1449 * This enforces a rate limit: not more than 10 kernel messages
1450 * every 5s to make a denial-of-service attack impossible.
1452 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1454 int __printk_ratelimit(const char *func)
1456 return ___ratelimit(&printk_ratelimit_state, func);
1458 EXPORT_SYMBOL(__printk_ratelimit);
1461 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1462 * @caller_jiffies: pointer to caller's state
1463 * @interval_msecs: minimum interval between prints
1465 * printk_timed_ratelimit() returns true if more than @interval_msecs
1466 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1469 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1470 unsigned int interval_msecs)
1472 if (*caller_jiffies == 0
1473 || !time_in_range(jiffies, *caller_jiffies,
1475 + msecs_to_jiffies(interval_msecs))) {
1476 *caller_jiffies = jiffies;
1481 EXPORT_SYMBOL(printk_timed_ratelimit);
1483 static DEFINE_SPINLOCK(dump_list_lock);
1484 static LIST_HEAD(dump_list);
1487 * kmsg_dump_register - register a kernel log dumper.
1488 * @dumper: pointer to the kmsg_dumper structure
1490 * Adds a kernel log dumper to the system. The dump callback in the
1491 * structure will be called when the kernel oopses or panics and must be
1492 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1494 int kmsg_dump_register(struct kmsg_dumper *dumper)
1496 unsigned long flags;
1499 /* The dump callback needs to be set */
1503 spin_lock_irqsave(&dump_list_lock, flags);
1504 /* Don't allow registering multiple times */
1505 if (!dumper->registered) {
1506 dumper->registered = 1;
1507 list_add_tail(&dumper->list, &dump_list);
1510 spin_unlock_irqrestore(&dump_list_lock, flags);
1514 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1517 * kmsg_dump_unregister - unregister a kmsg dumper.
1518 * @dumper: pointer to the kmsg_dumper structure
1520 * Removes a dump device from the system. Returns zero on success and
1521 * %-EINVAL otherwise.
1523 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1525 unsigned long flags;
1528 spin_lock_irqsave(&dump_list_lock, flags);
1529 if (dumper->registered) {
1530 dumper->registered = 0;
1531 list_del(&dumper->list);
1534 spin_unlock_irqrestore(&dump_list_lock, flags);
1538 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1540 static const char * const kmsg_reasons[] = {
1541 [KMSG_DUMP_OOPS] = "oops",
1542 [KMSG_DUMP_PANIC] = "panic",
1543 [KMSG_DUMP_KEXEC] = "kexec",
1546 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1548 if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1551 return kmsg_reasons[reason];
1555 * kmsg_dump - dump kernel log to kernel message dumpers.
1556 * @reason: the reason (oops, panic etc) for dumping
1558 * Iterate through each of the dump devices and call the oops/panic
1559 * callbacks with the log buffer.
1561 void kmsg_dump(enum kmsg_dump_reason reason)
1565 struct kmsg_dumper *dumper;
1566 const char *s1, *s2;
1567 unsigned long l1, l2;
1568 unsigned long flags;
1570 /* Theoretically, the log could move on after we do this, but
1571 there's not a lot we can do about that. The new messages
1572 will overwrite the start of what we dump. */
1573 spin_lock_irqsave(&logbuf_lock, flags);
1574 end = log_end & LOG_BUF_MASK;
1575 chars = logged_chars;
1576 spin_unlock_irqrestore(&logbuf_lock, flags);
1579 s1 = log_buf + log_buf_len - chars + end;
1588 s2 = log_buf + end - chars;
1592 if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1593 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1594 kmsg_to_str(reason));
1597 list_for_each_entry(dumper, &dump_list, list)
1598 dumper->dump(dumper, reason, s1, l1, s2, l2);
1599 spin_unlock_irqrestore(&dump_list_lock, flags);