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/memblock.h>
35 #include <linux/syscalls.h>
36 #include <linux/kexec.h>
37 #include <linux/kdb.h>
38 #include <linux/ratelimit.h>
39 #include <linux/kmsg_dump.h>
40 #include <linux/syslog.h>
41 #include <linux/cpu.h>
42 #include <linux/notifier.h>
43 #include <linux/rculist.h>
45 #include <asm/uaccess.h>
48 * Architectures can override it:
50 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
54 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
56 #ifdef CONFIG_DEBUG_LL
57 extern void printascii(char *);
60 /* printk's without a loglevel use this.. */
61 #define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL
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
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 * If exclusive_console is non-NULL then only this console is to be printed to.
123 static struct console *exclusive_console;
126 * Array of consoles built from command line options (console=)
128 struct console_cmdline
130 char name[8]; /* Name of the driver */
131 int index; /* Minor dev. to use */
132 char *options; /* Options for the driver */
133 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
134 char *brl_options; /* Options for braille driver */
138 #define MAX_CMDLINECONSOLES 8
140 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
141 static int selected_console = -1;
142 static int preferred_console = -1;
143 int console_set_on_cmdline;
144 EXPORT_SYMBOL(console_set_on_cmdline);
146 /* Flag: console code may call schedule() */
147 static int console_may_schedule;
151 static char __log_buf[__LOG_BUF_LEN];
152 static char *log_buf = __log_buf;
153 static int log_buf_len = __LOG_BUF_LEN;
154 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
155 static int saved_console_loglevel = -1;
159 * This appends the listed symbols to /proc/vmcoreinfo
161 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
162 * obtain access to symbols that are otherwise very difficult to locate. These
163 * symbols are specifically used so that utilities can access and extract the
164 * dmesg log from a vmcore file after a crash.
166 void log_buf_kexec_setup(void)
168 VMCOREINFO_SYMBOL(log_buf);
169 VMCOREINFO_SYMBOL(log_end);
170 VMCOREINFO_SYMBOL(log_buf_len);
171 VMCOREINFO_SYMBOL(logged_chars);
175 /* requested log_buf_len from kernel cmdline */
176 static unsigned long __initdata new_log_buf_len;
178 /* save requested log_buf_len since it's too early to process it */
179 static int __init log_buf_len_setup(char *str)
181 unsigned size = memparse(str, &str);
184 size = roundup_pow_of_two(size);
185 if (size > log_buf_len)
186 new_log_buf_len = size;
190 early_param("log_buf_len", log_buf_len_setup);
192 void __init setup_log_buf(int early)
195 unsigned start, dest_idx, offset;
199 if (!new_log_buf_len)
205 mem = memblock_alloc(new_log_buf_len, PAGE_SIZE);
206 if (mem == MEMBLOCK_ERROR)
208 new_log_buf = __va(mem);
210 new_log_buf = alloc_bootmem_nopanic(new_log_buf_len);
213 if (unlikely(!new_log_buf)) {
214 pr_err("log_buf_len: %ld bytes not available\n",
219 spin_lock_irqsave(&logbuf_lock, flags);
220 log_buf_len = new_log_buf_len;
221 log_buf = new_log_buf;
223 free = __LOG_BUF_LEN - log_end;
225 offset = start = min(con_start, log_start);
227 while (start != log_end) {
228 unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);
230 log_buf[dest_idx] = __log_buf[log_idx_mask];
237 spin_unlock_irqrestore(&logbuf_lock, flags);
239 pr_info("log_buf_len: %d\n", log_buf_len);
240 pr_info("early log buf free: %d(%d%%)\n",
241 free, (free * 100) / __LOG_BUF_LEN);
244 #ifdef CONFIG_BOOT_PRINTK_DELAY
246 static int boot_delay; /* msecs delay after each printk during bootup */
247 static unsigned long long loops_per_msec; /* based on boot_delay */
249 static int __init boot_delay_setup(char *str)
253 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
254 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
256 get_option(&str, &boot_delay);
257 if (boot_delay > 10 * 1000)
260 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
261 "HZ: %d, loops_per_msec: %llu\n",
262 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
265 __setup("boot_delay=", boot_delay_setup);
267 static void boot_delay_msec(void)
269 unsigned long long k;
270 unsigned long timeout;
272 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
275 k = (unsigned long long)loops_per_msec * boot_delay;
277 timeout = jiffies + msecs_to_jiffies(boot_delay);
282 * use (volatile) jiffies to prevent
283 * compiler reduction; loop termination via jiffies
284 * is secondary and may or may not happen.
286 if (time_after(jiffies, timeout))
288 touch_nmi_watchdog();
292 static inline void boot_delay_msec(void)
298 * Return the number of unread characters in the log buffer.
300 static int log_buf_get_len(void)
306 * Clears the ring-buffer
308 void log_buf_clear(void)
314 * Copy a range of characters from the log buffer.
316 int log_buf_copy(char *dest, int idx, int len)
319 bool took_lock = false;
321 if (!oops_in_progress) {
322 spin_lock_irq(&logbuf_lock);
326 max = log_buf_get_len();
327 if (idx < 0 || idx >= max) {
333 idx += (log_end - max);
335 dest[len] = LOG_BUF(idx + len);
339 spin_unlock_irq(&logbuf_lock);
344 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
345 int dmesg_restrict = 1;
350 static int syslog_action_restricted(int type)
354 /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
355 return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
358 static int check_syslog_permissions(int type, bool from_file)
361 * If this is from /proc/kmsg and we've already opened it, then we've
362 * already done the capabilities checks at open time.
364 if (from_file && type != SYSLOG_ACTION_OPEN)
367 if (syslog_action_restricted(type)) {
368 if (capable(CAP_SYSLOG))
370 /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
371 if (capable(CAP_SYS_ADMIN)) {
372 WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
373 "but no CAP_SYSLOG (deprecated).\n");
381 int do_syslog(int type, char __user *buf, int len, bool from_file)
383 unsigned i, j, limit, count;
388 error = check_syslog_permissions(type, from_file);
392 error = security_syslog(type);
397 case SYSLOG_ACTION_CLOSE: /* Close log */
399 case SYSLOG_ACTION_OPEN: /* Open log */
401 case SYSLOG_ACTION_READ: /* Read from log */
408 if (!access_ok(VERIFY_WRITE, buf, len)) {
412 error = wait_event_interruptible(log_wait,
413 (log_start - log_end));
417 spin_lock_irq(&logbuf_lock);
418 while (!error && (log_start != log_end) && i < len) {
419 c = LOG_BUF(log_start);
421 spin_unlock_irq(&logbuf_lock);
422 error = __put_user(c,buf);
426 spin_lock_irq(&logbuf_lock);
428 spin_unlock_irq(&logbuf_lock);
432 /* Read/clear last kernel messages */
433 case SYSLOG_ACTION_READ_CLEAR:
436 /* Read last kernel messages */
437 case SYSLOG_ACTION_READ_ALL:
444 if (!access_ok(VERIFY_WRITE, buf, len)) {
449 if (count > log_buf_len)
451 spin_lock_irq(&logbuf_lock);
452 if (count > logged_chars)
453 count = logged_chars;
458 * __put_user() could sleep, and while we sleep
459 * printk() could overwrite the messages
460 * we try to copy to user space. Therefore
461 * the messages are copied in reverse. <manfreds>
463 for (i = 0; i < count && !error; i++) {
465 if (j + log_buf_len < log_end)
468 spin_unlock_irq(&logbuf_lock);
469 error = __put_user(c,&buf[count-1-i]);
471 spin_lock_irq(&logbuf_lock);
473 spin_unlock_irq(&logbuf_lock);
478 int offset = count-error;
479 /* buffer overflow during copy, correct user buffer. */
480 for (i = 0; i < error; i++) {
481 if (__get_user(c,&buf[i+offset]) ||
482 __put_user(c,&buf[i])) {
490 /* Clear ring buffer */
491 case SYSLOG_ACTION_CLEAR:
494 /* Disable logging to console */
495 case SYSLOG_ACTION_CONSOLE_OFF:
496 if (saved_console_loglevel == -1)
497 saved_console_loglevel = console_loglevel;
498 console_loglevel = minimum_console_loglevel;
500 /* Enable logging to console */
501 case SYSLOG_ACTION_CONSOLE_ON:
502 if (saved_console_loglevel != -1) {
503 console_loglevel = saved_console_loglevel;
504 saved_console_loglevel = -1;
507 /* Set level of messages printed to console */
508 case SYSLOG_ACTION_CONSOLE_LEVEL:
510 if (len < 1 || len > 8)
512 if (len < minimum_console_loglevel)
513 len = minimum_console_loglevel;
514 console_loglevel = len;
515 /* Implicitly re-enable logging to console */
516 saved_console_loglevel = -1;
519 /* Number of chars in the log buffer */
520 case SYSLOG_ACTION_SIZE_UNREAD:
521 error = log_end - log_start;
523 /* Size of the log buffer */
524 case SYSLOG_ACTION_SIZE_BUFFER:
535 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
537 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
540 #ifdef CONFIG_KGDB_KDB
541 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
542 * uses locks so it cannot be used during debugging. Just tell kdb
543 * where the start and end of the physical and logical logs are. This
544 * is equivalent to do_syslog(3).
546 void kdb_syslog_data(char *syslog_data[4])
548 syslog_data[0] = log_buf;
549 syslog_data[1] = log_buf + log_buf_len;
550 syslog_data[2] = log_buf + log_end -
551 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
552 syslog_data[3] = log_buf + log_end;
554 #endif /* CONFIG_KGDB_KDB */
557 * Call the console drivers on a range of log_buf
559 static void __call_console_drivers(unsigned start, unsigned end)
563 for_each_console(con) {
564 if (exclusive_console && con != exclusive_console)
566 if ((con->flags & CON_ENABLED) && con->write &&
567 (cpu_online(smp_processor_id()) ||
568 (con->flags & CON_ANYTIME)))
569 con->write(con, &LOG_BUF(start), end - start);
573 static int __read_mostly ignore_loglevel;
575 static int __init ignore_loglevel_setup(char *str)
578 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
583 early_param("ignore_loglevel", ignore_loglevel_setup);
586 * Write out chars from start to end - 1 inclusive
588 static void _call_console_drivers(unsigned start,
589 unsigned end, int msg_log_level)
591 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
592 console_drivers && start != end) {
593 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
595 __call_console_drivers(start & LOG_BUF_MASK,
597 __call_console_drivers(0, end & LOG_BUF_MASK);
599 __call_console_drivers(start, end);
605 * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
606 * lower 3 bit are the log level, the rest are the log facility. In case
607 * userspace passes usual userspace syslog messages to /dev/kmsg or
608 * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
609 * to extract the correct log level for in-kernel processing, and not mangle
610 * the original value.
612 * If a prefix is found, the length of the prefix is returned. If 'level' is
613 * passed, it will be filled in with the log level without a possible facility
614 * value. If 'special' is passed, the special printk prefix chars are accepted
615 * and returned. If no valid header is found, 0 is returned and the passed
616 * variables are not touched.
618 static size_t log_prefix(const char *p, unsigned int *level, char *special)
620 unsigned int lev = 0;
624 if (p[0] != '<' || !p[1])
627 /* usual single digit level number or special char */
632 case 'c': /* KERN_CONT */
633 case 'd': /* KERN_DEFAULT */
641 /* multi digit including the level and facility number */
644 if (p[1] < '0' && p[1] > '9')
647 lev = (simple_strtoul(&p[1], &endp, 10) & 7);
648 if (endp == NULL || endp[0] != '>')
650 len = (endp + 1) - p;
653 /* do not accept special char if not asked for */
659 /* return special char, do not touch level */
670 * Call the console drivers, asking them to write out
671 * log_buf[start] to log_buf[end - 1].
672 * The console_lock must be held.
674 static void call_console_drivers(unsigned start, unsigned end)
676 unsigned cur_index, start_print;
677 static int msg_level = -1;
679 BUG_ON(((int)(start - end)) > 0);
683 while (cur_index != end) {
684 if (msg_level < 0 && ((end - cur_index) > 2)) {
685 /* strip log prefix */
686 cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
687 start_print = cur_index;
689 while (cur_index != end) {
690 char c = LOG_BUF(cur_index);
696 * printk() has already given us loglevel tags in
697 * the buffer. This code is here in case the
698 * log buffer has wrapped right round and scribbled
701 msg_level = default_message_loglevel;
703 _call_console_drivers(start_print, cur_index, msg_level);
705 start_print = cur_index;
710 _call_console_drivers(start_print, end, msg_level);
713 static void emit_log_char(char c)
715 LOG_BUF(log_end) = c;
717 if (log_end - log_start > log_buf_len)
718 log_start = log_end - log_buf_len;
719 if (log_end - con_start > log_buf_len)
720 con_start = log_end - log_buf_len;
721 if (logged_chars < log_buf_len)
726 * Zap console related locks when oopsing. Only zap at most once
727 * every 10 seconds, to leave time for slow consoles to print a
730 static void zap_locks(void)
732 static unsigned long oops_timestamp;
734 if (time_after_eq(jiffies, oops_timestamp) &&
735 !time_after(jiffies, oops_timestamp + 30 * HZ))
738 oops_timestamp = jiffies;
740 /* If a crash is occurring, make sure we can't deadlock */
741 spin_lock_init(&logbuf_lock);
742 /* And make sure that we print immediately */
743 sema_init(&console_sem, 1);
746 #if defined(CONFIG_PRINTK_TIME)
747 static int printk_time = 1;
749 static int printk_time = 0;
751 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
753 /* Check if we have any console registered that can be called early in boot. */
754 static int have_callable_console(void)
758 for_each_console(con)
759 if (con->flags & CON_ANYTIME)
766 * printk - print a kernel message
767 * @fmt: format string
769 * This is printk(). It can be called from any context. We want it to work.
771 * We try to grab the console_lock. If we succeed, it's easy - we log the output and
772 * call the console drivers. If we fail to get the semaphore we place the output
773 * into the log buffer and return. The current holder of the console_sem will
774 * notice the new output in console_unlock(); and will send it to the
775 * consoles before releasing the lock.
777 * One effect of this deferred printing is that code which calls printk() and
778 * then changes console_loglevel may break. This is because console_loglevel
779 * is inspected when the actual printing occurs.
784 * See the vsnprintf() documentation for format string extensions over C99.
787 asmlinkage int printk(const char *fmt, ...)
792 #ifdef CONFIG_KGDB_KDB
793 if (unlikely(kdb_trap_printk)) {
795 r = vkdb_printf(fmt, args);
801 r = vprintk(fmt, args);
807 /* cpu currently holding logbuf_lock */
808 static volatile unsigned int printk_cpu = UINT_MAX;
811 * Can we actually use the console at this time on this cpu?
813 * Console drivers may assume that per-cpu resources have
814 * been allocated. So unless they're explicitly marked as
815 * being able to cope (CON_ANYTIME) don't call them until
816 * this CPU is officially up.
818 static inline int can_use_console(unsigned int cpu)
820 return cpu_online(cpu) || have_callable_console();
824 * Try to get console ownership to actually show the kernel
825 * messages from a 'printk'. Return true (and with the
826 * console_lock held, and 'console_locked' set) if it
827 * is successful, false otherwise.
829 * This gets called with the 'logbuf_lock' spinlock held and
830 * interrupts disabled. It should return with 'lockbuf_lock'
831 * released but interrupts still disabled.
833 static int console_trylock_for_printk(unsigned int cpu)
834 __releases(&logbuf_lock)
838 if (console_trylock()) {
842 * If we can't use the console, we need to release
843 * the console semaphore by hand to avoid flushing
844 * the buffer. We need to hold the console semaphore
845 * in order to do this test safely.
847 if (!can_use_console(cpu)) {
853 printk_cpu = UINT_MAX;
854 spin_unlock(&logbuf_lock);
857 static const char recursion_bug_msg [] =
858 KERN_CRIT "BUG: recent printk recursion!\n";
859 static int recursion_bug;
860 static int new_text_line = 1;
861 static char printk_buf[1024];
863 int printk_delay_msec __read_mostly;
865 static inline void printk_delay(void)
867 if (unlikely(printk_delay_msec)) {
868 int m = printk_delay_msec;
872 touch_nmi_watchdog();
877 asmlinkage int vprintk(const char *fmt, va_list args)
880 int current_log_level = default_message_loglevel;
891 /* This stops the holder of console_sem just where we want him */
892 raw_local_irq_save(flags);
893 this_cpu = smp_processor_id();
896 * Ouch, printk recursed into itself!
898 if (unlikely(printk_cpu == this_cpu)) {
900 * If a crash is occurring during printk() on this CPU,
901 * then try to get the crash message out but make sure
902 * we can't deadlock. Otherwise just return to avoid the
903 * recursion and return - but flag the recursion so that
904 * it can be printed at the next appropriate moment:
906 if (!oops_in_progress) {
908 goto out_restore_irqs;
914 spin_lock(&logbuf_lock);
915 printk_cpu = this_cpu;
919 strcpy(printk_buf, recursion_bug_msg);
920 printed_len = strlen(recursion_bug_msg);
922 /* Emit the output into the temporary buffer */
923 printed_len += vscnprintf(printk_buf + printed_len,
924 sizeof(printk_buf) - printed_len, fmt, args);
926 #ifdef CONFIG_DEBUG_LL
927 printascii(printk_buf);
932 /* Read log level and handle special printk prefix */
933 plen = log_prefix(p, ¤t_log_level, &special);
938 case 'c': /* Strip <c> KERN_CONT, continue line */
941 case 'd': /* Strip <d> KERN_DEFAULT, start new line */
944 if (!new_text_line) {
952 * Copy the output into log_buf. If the caller didn't provide
953 * the appropriate log prefix, we insert them here
960 /* Copy original log prefix */
963 for (i = 0; i < plen; i++)
964 emit_log_char(printk_buf[i]);
969 emit_log_char(current_log_level + '0');
975 /* Add the current time stamp */
978 unsigned long long t;
979 unsigned long nanosec_rem;
981 t = cpu_clock(printk_cpu);
982 nanosec_rem = do_div(t, 1000000000);
983 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
987 for (tp = tbuf; tp < tbuf + tlen; tp++)
1002 * Try to acquire and then immediately release the
1003 * console semaphore. The release will do all the
1004 * actual magic (print out buffers, wake up klogd,
1007 * The console_trylock_for_printk() function
1008 * will release 'logbuf_lock' regardless of whether it
1009 * actually gets the semaphore or not.
1011 if (console_trylock_for_printk(this_cpu))
1016 raw_local_irq_restore(flags);
1021 EXPORT_SYMBOL(printk);
1022 EXPORT_SYMBOL(vprintk);
1024 #ifdef CONFIG_RK29_LAST_LOG
1025 void switch_log_buf(char *new_log_buf, int size)
1027 unsigned long flags;
1029 if (!new_log_buf || log_buf_len > size)
1032 spin_lock_irqsave(&logbuf_lock, flags);
1033 memcpy(new_log_buf, log_buf, min(log_buf_len, size));
1034 log_buf = new_log_buf;
1036 spin_unlock_irqrestore(&logbuf_lock, flags);
1038 #endif /* CONFIG_RK29_LAST_LOG */
1041 static void call_console_drivers(unsigned start, unsigned end)
1047 static int __add_preferred_console(char *name, int idx, char *options,
1050 struct console_cmdline *c;
1054 * See if this tty is not yet registered, and
1055 * if we have a slot free.
1057 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
1058 if (strcmp(console_cmdline[i].name, name) == 0 &&
1059 console_cmdline[i].index == idx) {
1061 selected_console = i;
1064 if (i == MAX_CMDLINECONSOLES)
1067 selected_console = i;
1068 c = &console_cmdline[i];
1069 strlcpy(c->name, name, sizeof(c->name));
1070 c->options = options;
1071 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1072 c->brl_options = brl_options;
1078 * Set up a list of consoles. Called from init/main.c
1080 static int __init console_setup(char *str)
1082 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
1083 char *s, *options, *brl_options = NULL;
1086 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1087 if (!memcmp(str, "brl,", 4)) {
1090 } else if (!memcmp(str, "brl=", 4)) {
1091 brl_options = str + 4;
1092 str = strchr(brl_options, ',');
1094 printk(KERN_ERR "need port name after brl=\n");
1102 * Decode str into name, index, options.
1104 if (str[0] >= '0' && str[0] <= '9') {
1105 strcpy(buf, "ttyS");
1106 strncpy(buf + 4, str, sizeof(buf) - 5);
1108 strncpy(buf, str, sizeof(buf) - 1);
1110 buf[sizeof(buf) - 1] = 0;
1111 if ((options = strchr(str, ',')) != NULL)
1114 if (!strcmp(str, "ttya"))
1115 strcpy(buf, "ttyS0");
1116 if (!strcmp(str, "ttyb"))
1117 strcpy(buf, "ttyS1");
1119 for (s = buf; *s; s++)
1120 if ((*s >= '0' && *s <= '9') || *s == ',')
1122 idx = simple_strtoul(s, NULL, 10);
1125 __add_preferred_console(buf, idx, options, brl_options);
1126 console_set_on_cmdline = 1;
1129 __setup("console=", console_setup);
1132 * add_preferred_console - add a device to the list of preferred consoles.
1133 * @name: device name
1134 * @idx: device index
1135 * @options: options for this console
1137 * The last preferred console added will be used for kernel messages
1138 * and stdin/out/err for init. Normally this is used by console_setup
1139 * above to handle user-supplied console arguments; however it can also
1140 * be used by arch-specific code either to override the user or more
1141 * commonly to provide a default console (ie from PROM variables) when
1142 * the user has not supplied one.
1144 int add_preferred_console(char *name, int idx, char *options)
1146 return __add_preferred_console(name, idx, options, NULL);
1149 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
1151 struct console_cmdline *c;
1154 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
1155 if (strcmp(console_cmdline[i].name, name) == 0 &&
1156 console_cmdline[i].index == idx) {
1157 c = &console_cmdline[i];
1158 strlcpy(c->name, name_new, sizeof(c->name));
1159 c->name[sizeof(c->name) - 1] = 0;
1160 c->options = options;
1168 int console_suspend_enabled = 1;
1169 EXPORT_SYMBOL(console_suspend_enabled);
1171 static int __init console_suspend_disable(char *str)
1173 console_suspend_enabled = 0;
1176 __setup("no_console_suspend", console_suspend_disable);
1179 * suspend_console - suspend the console subsystem
1181 * This disables printk() while we go into suspend states
1183 void suspend_console(void)
1185 if (!console_suspend_enabled)
1187 printk("Suspending console(s) (use no_console_suspend to debug)\n");
1189 console_suspended = 1;
1193 void resume_console(void)
1195 if (!console_suspend_enabled)
1198 console_suspended = 0;
1203 * console_cpu_notify - print deferred console messages after CPU hotplug
1204 * @self: notifier struct
1205 * @action: CPU hotplug event
1208 * If printk() is called from a CPU that is not online yet, the messages
1209 * will be spooled but will not show up on the console. This function is
1210 * called when a new CPU comes online (or fails to come up), and ensures
1211 * that any such output gets printed.
1213 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1214 unsigned long action, void *hcpu)
1219 case CPU_DOWN_FAILED:
1220 case CPU_UP_CANCELED:
1228 * console_lock - lock the console system for exclusive use.
1230 * Acquires a lock which guarantees that the caller has
1231 * exclusive access to the console system and the console_drivers list.
1233 * Can sleep, returns nothing.
1235 void console_lock(void)
1237 BUG_ON(in_interrupt());
1239 if (console_suspended)
1242 console_may_schedule = 1;
1244 EXPORT_SYMBOL(console_lock);
1247 * console_trylock - try to lock the console system for exclusive use.
1249 * Tried to acquire a lock which guarantees that the caller has
1250 * exclusive access to the console system and the console_drivers list.
1252 * returns 1 on success, and 0 on failure to acquire the lock.
1254 int console_trylock(void)
1256 if (down_trylock(&console_sem))
1258 if (console_suspended) {
1263 console_may_schedule = 0;
1266 EXPORT_SYMBOL(console_trylock);
1268 int is_console_locked(void)
1270 return console_locked;
1273 static DEFINE_PER_CPU(int, printk_pending);
1275 void printk_tick(void)
1277 if (__this_cpu_read(printk_pending)) {
1278 __this_cpu_write(printk_pending, 0);
1279 wake_up_interruptible(&log_wait);
1283 int printk_needs_cpu(int cpu)
1285 if (cpu_is_offline(cpu))
1287 return __this_cpu_read(printk_pending);
1290 void wake_up_klogd(void)
1292 if (waitqueue_active(&log_wait))
1293 this_cpu_write(printk_pending, 1);
1297 * console_unlock - unlock the console system
1299 * Releases the console_lock which the caller holds on the console system
1300 * and the console driver list.
1302 * While the console_lock was held, console output may have been buffered
1303 * by printk(). If this is the case, console_unlock(); emits
1304 * the output prior to releasing the lock.
1306 * If there is output waiting for klogd, we wake it up.
1308 * console_unlock(); may be called from any context.
1310 void console_unlock(void)
1312 unsigned long flags;
1313 unsigned _con_start, _log_end;
1314 unsigned wake_klogd = 0;
1316 if (console_suspended) {
1321 console_may_schedule = 0;
1324 spin_lock_irqsave(&logbuf_lock, flags);
1325 wake_klogd |= log_start - log_end;
1326 if (con_start == log_end)
1327 break; /* Nothing to print */
1328 _con_start = con_start;
1330 con_start = log_end; /* Flush */
1331 spin_unlock(&logbuf_lock);
1332 stop_critical_timings(); /* don't trace print latency */
1333 call_console_drivers(_con_start, _log_end);
1334 start_critical_timings();
1335 local_irq_restore(flags);
1339 /* Release the exclusive_console once it is used */
1340 if (unlikely(exclusive_console))
1341 exclusive_console = NULL;
1344 spin_unlock_irqrestore(&logbuf_lock, flags);
1348 EXPORT_SYMBOL(console_unlock);
1351 * console_conditional_schedule - yield the CPU if required
1353 * If the console code is currently allowed to sleep, and
1354 * if this CPU should yield the CPU to another task, do
1357 * Must be called within console_lock();.
1359 void __sched console_conditional_schedule(void)
1361 if (console_may_schedule)
1364 EXPORT_SYMBOL(console_conditional_schedule);
1366 void console_unblank(void)
1371 * console_unblank can no longer be called in interrupt context unless
1372 * oops_in_progress is set to 1..
1374 if (oops_in_progress) {
1375 if (down_trylock(&console_sem) != 0)
1381 console_may_schedule = 0;
1383 if ((c->flags & CON_ENABLED) && c->unblank)
1389 * Return the console tty driver structure and its associated index
1391 struct tty_driver *console_device(int *index)
1394 struct tty_driver *driver = NULL;
1397 for_each_console(c) {
1400 driver = c->device(c, index);
1409 * Prevent further output on the passed console device so that (for example)
1410 * serial drivers can disable console output before suspending a port, and can
1411 * re-enable output afterwards.
1413 void console_stop(struct console *console)
1416 console->flags &= ~CON_ENABLED;
1419 EXPORT_SYMBOL(console_stop);
1421 void console_start(struct console *console)
1424 console->flags |= CON_ENABLED;
1427 EXPORT_SYMBOL(console_start);
1429 static int __read_mostly keep_bootcon;
1431 static int __init keep_bootcon_setup(char *str)
1434 printk(KERN_INFO "debug: skip boot console de-registration.\n");
1439 early_param("keep_bootcon", keep_bootcon_setup);
1442 * The console driver calls this routine during kernel initialization
1443 * to register the console printing procedure with printk() and to
1444 * print any messages that were printed by the kernel before the
1445 * console driver was initialized.
1447 * This can happen pretty early during the boot process (because of
1448 * early_printk) - sometimes before setup_arch() completes - be careful
1449 * of what kernel features are used - they may not be initialised yet.
1451 * There are two types of consoles - bootconsoles (early_printk) and
1452 * "real" consoles (everything which is not a bootconsole) which are
1453 * handled differently.
1454 * - Any number of bootconsoles can be registered at any time.
1455 * - As soon as a "real" console is registered, all bootconsoles
1456 * will be unregistered automatically.
1457 * - Once a "real" console is registered, any attempt to register a
1458 * bootconsoles will be rejected
1460 void register_console(struct console *newcon)
1463 unsigned long flags;
1464 struct console *bcon = NULL;
1467 * before we register a new CON_BOOT console, make sure we don't
1468 * already have a valid console
1470 if (console_drivers && newcon->flags & CON_BOOT) {
1471 /* find the last or real console */
1472 for_each_console(bcon) {
1473 if (!(bcon->flags & CON_BOOT)) {
1474 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1475 newcon->name, newcon->index);
1481 if (console_drivers && console_drivers->flags & CON_BOOT)
1482 bcon = console_drivers;
1484 if (preferred_console < 0 || bcon || !console_drivers)
1485 preferred_console = selected_console;
1487 if (newcon->early_setup)
1488 newcon->early_setup();
1491 * See if we want to use this console driver. If we
1492 * didn't select a console we take the first one
1493 * that registers here.
1495 if (preferred_console < 0) {
1496 if (newcon->index < 0)
1498 if (newcon->setup == NULL ||
1499 newcon->setup(newcon, NULL) == 0) {
1500 newcon->flags |= CON_ENABLED;
1501 if (newcon->device) {
1502 newcon->flags |= CON_CONSDEV;
1503 preferred_console = 0;
1509 * See if this console matches one we selected on
1512 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1514 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1516 if (newcon->index >= 0 &&
1517 newcon->index != console_cmdline[i].index)
1519 if (newcon->index < 0)
1520 newcon->index = console_cmdline[i].index;
1521 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1522 if (console_cmdline[i].brl_options) {
1523 newcon->flags |= CON_BRL;
1524 braille_register_console(newcon,
1525 console_cmdline[i].index,
1526 console_cmdline[i].options,
1527 console_cmdline[i].brl_options);
1531 if (newcon->setup &&
1532 newcon->setup(newcon, console_cmdline[i].options) != 0)
1534 newcon->flags |= CON_ENABLED;
1535 newcon->index = console_cmdline[i].index;
1536 if (i == selected_console) {
1537 newcon->flags |= CON_CONSDEV;
1538 preferred_console = selected_console;
1543 if (!(newcon->flags & CON_ENABLED))
1547 * If we have a bootconsole, and are switching to a real console,
1548 * don't print everything out again, since when the boot console, and
1549 * the real console are the same physical device, it's annoying to
1550 * see the beginning boot messages twice
1552 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1553 newcon->flags &= ~CON_PRINTBUFFER;
1556 * Put this console in the list - keep the
1557 * preferred driver at the head of the list.
1560 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1561 newcon->next = console_drivers;
1562 console_drivers = newcon;
1564 newcon->next->flags &= ~CON_CONSDEV;
1566 newcon->next = console_drivers->next;
1567 console_drivers->next = newcon;
1569 if (newcon->flags & CON_PRINTBUFFER) {
1571 * console_unlock(); will print out the buffered messages
1574 spin_lock_irqsave(&logbuf_lock, flags);
1575 con_start = log_start;
1576 spin_unlock_irqrestore(&logbuf_lock, flags);
1578 * We're about to replay the log buffer. Only do this to the
1579 * just-registered console to avoid excessive message spam to
1580 * the already-registered consoles.
1582 exclusive_console = newcon;
1585 console_sysfs_notify();
1588 * By unregistering the bootconsoles after we enable the real console
1589 * we get the "console xxx enabled" message on all the consoles -
1590 * boot consoles, real consoles, etc - this is to ensure that end
1591 * users know there might be something in the kernel's log buffer that
1592 * went to the bootconsole (that they do not see on the real console)
1595 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
1597 /* we need to iterate through twice, to make sure we print
1598 * everything out, before we unregister the console(s)
1600 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1601 newcon->name, newcon->index);
1602 for_each_console(bcon)
1603 if (bcon->flags & CON_BOOT)
1604 unregister_console(bcon);
1606 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1607 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1608 newcon->name, newcon->index);
1611 EXPORT_SYMBOL(register_console);
1613 int unregister_console(struct console *console)
1615 struct console *a, *b;
1618 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1619 if (console->flags & CON_BRL)
1620 return braille_unregister_console(console);
1624 if (console_drivers == console) {
1625 console_drivers=console->next;
1627 } else if (console_drivers) {
1628 for (a=console_drivers->next, b=console_drivers ;
1629 a; b=a, a=b->next) {
1639 * If this isn't the last console and it has CON_CONSDEV set, we
1640 * need to set it on the next preferred console.
1642 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1643 console_drivers->flags |= CON_CONSDEV;
1646 console_sysfs_notify();
1649 EXPORT_SYMBOL(unregister_console);
1651 static int __init printk_late_init(void)
1653 struct console *con;
1655 for_each_console(con) {
1656 if (!keep_bootcon && con->flags & CON_BOOT) {
1657 printk(KERN_INFO "turn off boot console %s%d\n",
1658 con->name, con->index);
1659 unregister_console(con);
1662 hotcpu_notifier(console_cpu_notify, 0);
1665 late_initcall(printk_late_init);
1667 #if defined CONFIG_PRINTK
1670 * printk rate limiting, lifted from the networking subsystem.
1672 * This enforces a rate limit: not more than 10 kernel messages
1673 * every 5s to make a denial-of-service attack impossible.
1675 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1677 int __printk_ratelimit(const char *func)
1679 return ___ratelimit(&printk_ratelimit_state, func);
1681 EXPORT_SYMBOL(__printk_ratelimit);
1684 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1685 * @caller_jiffies: pointer to caller's state
1686 * @interval_msecs: minimum interval between prints
1688 * printk_timed_ratelimit() returns true if more than @interval_msecs
1689 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1692 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1693 unsigned int interval_msecs)
1695 if (*caller_jiffies == 0
1696 || !time_in_range(jiffies, *caller_jiffies,
1698 + msecs_to_jiffies(interval_msecs))) {
1699 *caller_jiffies = jiffies;
1704 EXPORT_SYMBOL(printk_timed_ratelimit);
1706 static DEFINE_SPINLOCK(dump_list_lock);
1707 static LIST_HEAD(dump_list);
1710 * kmsg_dump_register - register a kernel log dumper.
1711 * @dumper: pointer to the kmsg_dumper structure
1713 * Adds a kernel log dumper to the system. The dump callback in the
1714 * structure will be called when the kernel oopses or panics and must be
1715 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1717 int kmsg_dump_register(struct kmsg_dumper *dumper)
1719 unsigned long flags;
1722 /* The dump callback needs to be set */
1726 spin_lock_irqsave(&dump_list_lock, flags);
1727 /* Don't allow registering multiple times */
1728 if (!dumper->registered) {
1729 dumper->registered = 1;
1730 list_add_tail_rcu(&dumper->list, &dump_list);
1733 spin_unlock_irqrestore(&dump_list_lock, flags);
1737 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1740 * kmsg_dump_unregister - unregister a kmsg dumper.
1741 * @dumper: pointer to the kmsg_dumper structure
1743 * Removes a dump device from the system. Returns zero on success and
1744 * %-EINVAL otherwise.
1746 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1748 unsigned long flags;
1751 spin_lock_irqsave(&dump_list_lock, flags);
1752 if (dumper->registered) {
1753 dumper->registered = 0;
1754 list_del_rcu(&dumper->list);
1757 spin_unlock_irqrestore(&dump_list_lock, flags);
1762 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1765 * kmsg_dump - dump kernel log to kernel message dumpers.
1766 * @reason: the reason (oops, panic etc) for dumping
1768 * Iterate through each of the dump devices and call the oops/panic
1769 * callbacks with the log buffer.
1771 void kmsg_dump(enum kmsg_dump_reason reason)
1775 struct kmsg_dumper *dumper;
1776 const char *s1, *s2;
1777 unsigned long l1, l2;
1778 unsigned long flags;
1780 /* Theoretically, the log could move on after we do this, but
1781 there's not a lot we can do about that. The new messages
1782 will overwrite the start of what we dump. */
1783 spin_lock_irqsave(&logbuf_lock, flags);
1784 end = log_end & LOG_BUF_MASK;
1785 chars = logged_chars;
1786 spin_unlock_irqrestore(&logbuf_lock, flags);
1789 s1 = log_buf + log_buf_len - chars + end;
1798 s2 = log_buf + end - chars;
1803 list_for_each_entry_rcu(dumper, &dump_list, list)
1804 dumper->dump(dumper, reason, s1, l1, s2, l2);