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>
42 #include <linux/rculist.h>
44 #include <asm/uaccess.h>
47 * Architectures can override it:
49 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
53 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
55 /* printk's without a loglevel use this.. */
56 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
58 /* We show everything that is MORE important than this.. */
59 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
60 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
62 DECLARE_WAIT_QUEUE_HEAD(log_wait);
64 int console_printk[4] = {
65 DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
66 DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
67 MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
68 DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
72 * Low level drivers may need that to know if they can schedule in
73 * their unblank() callback or not. So let's export it.
76 EXPORT_SYMBOL(oops_in_progress);
79 * console_sem protects the console_drivers list, and also
80 * provides serialisation for access to the entire console
83 static DEFINE_SEMAPHORE(console_sem);
84 struct console *console_drivers;
85 EXPORT_SYMBOL_GPL(console_drivers);
88 * This is used for debugging the mess that is the VT code by
89 * keeping track if we have the console semaphore held. It's
90 * definitely not the perfect debug tool (we don't know if _WE_
91 * hold it are racing, but it helps tracking those weird code
92 * path in the console code where we end up in places I want
93 * locked without the console sempahore held
95 static int console_locked, console_suspended;
98 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
99 * It is also used in interesting ways to provide interlocking in
102 static DEFINE_SPINLOCK(logbuf_lock);
104 #define LOG_BUF_MASK (log_buf_len-1)
105 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
108 * The indices into log_buf are not constrained to log_buf_len - they
109 * must be masked before subscripting
111 static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
112 static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
113 static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
116 * Array of consoles built from command line options (console=)
118 struct console_cmdline
120 char name[8]; /* Name of the driver */
121 int index; /* Minor dev. to use */
122 char *options; /* Options for the driver */
123 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
124 char *brl_options; /* Options for braille driver */
128 #define MAX_CMDLINECONSOLES 8
130 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
131 static int selected_console = -1;
132 static int preferred_console = -1;
133 int console_set_on_cmdline;
134 EXPORT_SYMBOL(console_set_on_cmdline);
136 /* Flag: console code may call schedule() */
137 static int console_may_schedule;
141 static char __log_buf[__LOG_BUF_LEN];
142 static char *log_buf = __log_buf;
143 static int log_buf_len = __LOG_BUF_LEN;
144 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
145 static int saved_console_loglevel = -1;
149 * This appends the listed symbols to /proc/vmcoreinfo
151 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
152 * obtain access to symbols that are otherwise very difficult to locate. These
153 * symbols are specifically used so that utilities can access and extract the
154 * dmesg log from a vmcore file after a crash.
156 void log_buf_kexec_setup(void)
158 VMCOREINFO_SYMBOL(log_buf);
159 VMCOREINFO_SYMBOL(log_end);
160 VMCOREINFO_SYMBOL(log_buf_len);
161 VMCOREINFO_SYMBOL(logged_chars);
165 static int __init log_buf_len_setup(char *str)
167 unsigned size = memparse(str, &str);
171 size = roundup_pow_of_two(size);
172 if (size > log_buf_len) {
173 unsigned start, dest_idx, offset;
176 new_log_buf = alloc_bootmem(size);
178 printk(KERN_WARNING "log_buf_len: allocation failed\n");
182 spin_lock_irqsave(&logbuf_lock, flags);
184 log_buf = new_log_buf;
186 offset = start = min(con_start, log_start);
188 while (start != log_end) {
189 log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
196 spin_unlock_irqrestore(&logbuf_lock, flags);
198 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
204 __setup("log_buf_len=", log_buf_len_setup);
206 #ifdef CONFIG_BOOT_PRINTK_DELAY
208 static int boot_delay; /* msecs delay after each printk during bootup */
209 static unsigned long long loops_per_msec; /* based on boot_delay */
211 static int __init boot_delay_setup(char *str)
215 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
216 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
218 get_option(&str, &boot_delay);
219 if (boot_delay > 10 * 1000)
222 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
223 "HZ: %d, loops_per_msec: %llu\n",
224 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
227 __setup("boot_delay=", boot_delay_setup);
229 static void boot_delay_msec(void)
231 unsigned long long k;
232 unsigned long timeout;
234 if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
237 k = (unsigned long long)loops_per_msec * boot_delay;
239 timeout = jiffies + msecs_to_jiffies(boot_delay);
244 * use (volatile) jiffies to prevent
245 * compiler reduction; loop termination via jiffies
246 * is secondary and may or may not happen.
248 if (time_after(jiffies, timeout))
250 touch_nmi_watchdog();
254 static inline void boot_delay_msec(void)
259 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
260 int dmesg_restrict = 1;
265 static int syslog_action_restricted(int type)
269 /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
270 return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
273 static int check_syslog_permissions(int type, bool from_file)
276 * If this is from /proc/kmsg and we've already opened it, then we've
277 * already done the capabilities checks at open time.
279 if (from_file && type != SYSLOG_ACTION_OPEN)
282 if (syslog_action_restricted(type)) {
283 if (capable(CAP_SYSLOG))
285 /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
286 if (capable(CAP_SYS_ADMIN)) {
287 WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
288 "but no CAP_SYSLOG (deprecated).\n");
296 int do_syslog(int type, char __user *buf, int len, bool from_file)
298 unsigned i, j, limit, count;
303 error = check_syslog_permissions(type, from_file);
307 error = security_syslog(type);
312 case SYSLOG_ACTION_CLOSE: /* Close log */
314 case SYSLOG_ACTION_OPEN: /* Open log */
316 case SYSLOG_ACTION_READ: /* Read from log */
323 if (!access_ok(VERIFY_WRITE, buf, len)) {
327 error = wait_event_interruptible(log_wait,
328 (log_start - log_end));
332 spin_lock_irq(&logbuf_lock);
333 while (!error && (log_start != log_end) && i < len) {
334 c = LOG_BUF(log_start);
336 spin_unlock_irq(&logbuf_lock);
337 error = __put_user(c,buf);
341 spin_lock_irq(&logbuf_lock);
343 spin_unlock_irq(&logbuf_lock);
347 /* Read/clear last kernel messages */
348 case SYSLOG_ACTION_READ_CLEAR:
351 /* Read last kernel messages */
352 case SYSLOG_ACTION_READ_ALL:
359 if (!access_ok(VERIFY_WRITE, buf, len)) {
364 if (count > log_buf_len)
366 spin_lock_irq(&logbuf_lock);
367 if (count > logged_chars)
368 count = logged_chars;
373 * __put_user() could sleep, and while we sleep
374 * printk() could overwrite the messages
375 * we try to copy to user space. Therefore
376 * the messages are copied in reverse. <manfreds>
378 for (i = 0; i < count && !error; i++) {
380 if (j + log_buf_len < log_end)
383 spin_unlock_irq(&logbuf_lock);
384 error = __put_user(c,&buf[count-1-i]);
386 spin_lock_irq(&logbuf_lock);
388 spin_unlock_irq(&logbuf_lock);
393 int offset = count-error;
394 /* buffer overflow during copy, correct user buffer. */
395 for (i = 0; i < error; i++) {
396 if (__get_user(c,&buf[i+offset]) ||
397 __put_user(c,&buf[i])) {
405 /* Clear ring buffer */
406 case SYSLOG_ACTION_CLEAR:
409 /* Disable logging to console */
410 case SYSLOG_ACTION_CONSOLE_OFF:
411 if (saved_console_loglevel == -1)
412 saved_console_loglevel = console_loglevel;
413 console_loglevel = minimum_console_loglevel;
415 /* Enable logging to console */
416 case SYSLOG_ACTION_CONSOLE_ON:
417 if (saved_console_loglevel != -1) {
418 console_loglevel = saved_console_loglevel;
419 saved_console_loglevel = -1;
422 /* Set level of messages printed to console */
423 case SYSLOG_ACTION_CONSOLE_LEVEL:
425 if (len < 1 || len > 8)
427 if (len < minimum_console_loglevel)
428 len = minimum_console_loglevel;
429 console_loglevel = len;
430 /* Implicitly re-enable logging to console */
431 saved_console_loglevel = -1;
434 /* Number of chars in the log buffer */
435 case SYSLOG_ACTION_SIZE_UNREAD:
436 error = log_end - log_start;
438 /* Size of the log buffer */
439 case SYSLOG_ACTION_SIZE_BUFFER:
450 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
452 return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
455 #ifdef CONFIG_KGDB_KDB
456 /* kdb dmesg command needs access to the syslog buffer. do_syslog()
457 * uses locks so it cannot be used during debugging. Just tell kdb
458 * where the start and end of the physical and logical logs are. This
459 * is equivalent to do_syslog(3).
461 void kdb_syslog_data(char *syslog_data[4])
463 syslog_data[0] = log_buf;
464 syslog_data[1] = log_buf + log_buf_len;
465 syslog_data[2] = log_buf + log_end -
466 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
467 syslog_data[3] = log_buf + log_end;
469 #endif /* CONFIG_KGDB_KDB */
472 * Call the console drivers on a range of log_buf
474 static void __call_console_drivers(unsigned start, unsigned end)
478 for_each_console(con) {
479 if ((con->flags & CON_ENABLED) && con->write &&
480 (cpu_online(smp_processor_id()) ||
481 (con->flags & CON_ANYTIME)))
482 con->write(con, &LOG_BUF(start), end - start);
486 static int __read_mostly ignore_loglevel;
488 static int __init ignore_loglevel_setup(char *str)
491 printk(KERN_INFO "debug: ignoring loglevel setting.\n");
496 early_param("ignore_loglevel", ignore_loglevel_setup);
499 * Write out chars from start to end - 1 inclusive
501 static void _call_console_drivers(unsigned start,
502 unsigned end, int msg_log_level)
504 if ((msg_log_level < console_loglevel || ignore_loglevel) &&
505 console_drivers && start != end) {
506 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
508 __call_console_drivers(start & LOG_BUF_MASK,
510 __call_console_drivers(0, end & LOG_BUF_MASK);
512 __call_console_drivers(start, end);
518 * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
519 * lower 3 bit are the log level, the rest are the log facility. In case
520 * userspace passes usual userspace syslog messages to /dev/kmsg or
521 * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
522 * to extract the correct log level for in-kernel processing, and not mangle
523 * the original value.
525 * If a prefix is found, the length of the prefix is returned. If 'level' is
526 * passed, it will be filled in with the log level without a possible facility
527 * value. If 'special' is passed, the special printk prefix chars are accepted
528 * and returned. If no valid header is found, 0 is returned and the passed
529 * variables are not touched.
531 static size_t log_prefix(const char *p, unsigned int *level, char *special)
533 unsigned int lev = 0;
537 if (p[0] != '<' || !p[1])
540 /* usual single digit level number or special char */
545 case 'c': /* KERN_CONT */
546 case 'd': /* KERN_DEFAULT */
554 /* multi digit including the level and facility number */
557 if (p[1] < '0' && p[1] > '9')
560 lev = (simple_strtoul(&p[1], &endp, 10) & 7);
561 if (endp == NULL || endp[0] != '>')
563 len = (endp + 1) - p;
566 /* do not accept special char if not asked for */
572 /* return special char, do not touch level */
583 * Call the console drivers, asking them to write out
584 * log_buf[start] to log_buf[end - 1].
585 * The console_lock must be held.
587 static void call_console_drivers(unsigned start, unsigned end)
589 unsigned cur_index, start_print;
590 static int msg_level = -1;
592 BUG_ON(((int)(start - end)) > 0);
596 while (cur_index != end) {
597 if (msg_level < 0 && ((end - cur_index) > 2)) {
598 /* strip log prefix */
599 cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
600 start_print = cur_index;
602 while (cur_index != end) {
603 char c = LOG_BUF(cur_index);
609 * printk() has already given us loglevel tags in
610 * the buffer. This code is here in case the
611 * log buffer has wrapped right round and scribbled
614 msg_level = default_message_loglevel;
616 _call_console_drivers(start_print, cur_index, msg_level);
618 start_print = cur_index;
623 _call_console_drivers(start_print, end, msg_level);
626 static void emit_log_char(char c)
628 LOG_BUF(log_end) = c;
630 if (log_end - log_start > log_buf_len)
631 log_start = log_end - log_buf_len;
632 if (log_end - con_start > log_buf_len)
633 con_start = log_end - log_buf_len;
634 if (logged_chars < log_buf_len)
639 * Zap console related locks when oopsing. Only zap at most once
640 * every 10 seconds, to leave time for slow consoles to print a
643 static void zap_locks(void)
645 static unsigned long oops_timestamp;
647 if (time_after_eq(jiffies, oops_timestamp) &&
648 !time_after(jiffies, oops_timestamp + 30 * HZ))
651 oops_timestamp = jiffies;
653 /* If a crash is occurring, make sure we can't deadlock */
654 spin_lock_init(&logbuf_lock);
655 /* And make sure that we print immediately */
656 sema_init(&console_sem, 1);
659 #if defined(CONFIG_PRINTK_TIME)
660 static int printk_time = 1;
662 static int printk_time = 0;
664 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
666 /* Check if we have any console registered that can be called early in boot. */
667 static int have_callable_console(void)
671 for_each_console(con)
672 if (con->flags & CON_ANYTIME)
679 * printk - print a kernel message
680 * @fmt: format string
682 * This is printk(). It can be called from any context. We want it to work.
684 * We try to grab the console_lock. If we succeed, it's easy - we log the output and
685 * call the console drivers. If we fail to get the semaphore we place the output
686 * into the log buffer and return. The current holder of the console_sem will
687 * notice the new output in console_unlock(); and will send it to the
688 * consoles before releasing the lock.
690 * One effect of this deferred printing is that code which calls printk() and
691 * then changes console_loglevel may break. This is because console_loglevel
692 * is inspected when the actual printing occurs.
697 * See the vsnprintf() documentation for format string extensions over C99.
700 asmlinkage int printk(const char *fmt, ...)
705 #ifdef CONFIG_KGDB_KDB
706 if (unlikely(kdb_trap_printk)) {
708 r = vkdb_printf(fmt, args);
714 r = vprintk(fmt, args);
720 /* cpu currently holding logbuf_lock */
721 static volatile unsigned int printk_cpu = UINT_MAX;
724 * Can we actually use the console at this time on this cpu?
726 * Console drivers may assume that per-cpu resources have
727 * been allocated. So unless they're explicitly marked as
728 * being able to cope (CON_ANYTIME) don't call them until
729 * this CPU is officially up.
731 static inline int can_use_console(unsigned int cpu)
733 return cpu_online(cpu) || have_callable_console();
737 * Try to get console ownership to actually show the kernel
738 * messages from a 'printk'. Return true (and with the
739 * console_lock held, and 'console_locked' set) if it
740 * is successful, false otherwise.
742 * This gets called with the 'logbuf_lock' spinlock held and
743 * interrupts disabled. It should return with 'lockbuf_lock'
744 * released but interrupts still disabled.
746 static int console_trylock_for_printk(unsigned int cpu)
747 __releases(&logbuf_lock)
751 if (console_trylock()) {
755 * If we can't use the console, we need to release
756 * the console semaphore by hand to avoid flushing
757 * the buffer. We need to hold the console semaphore
758 * in order to do this test safely.
760 if (!can_use_console(cpu)) {
766 printk_cpu = UINT_MAX;
767 spin_unlock(&logbuf_lock);
770 static const char recursion_bug_msg [] =
771 KERN_CRIT "BUG: recent printk recursion!\n";
772 static int recursion_bug;
773 static int new_text_line = 1;
774 static char printk_buf[1024];
776 int printk_delay_msec __read_mostly;
778 static inline void printk_delay(void)
780 if (unlikely(printk_delay_msec)) {
781 int m = printk_delay_msec;
785 touch_nmi_watchdog();
790 asmlinkage int vprintk(const char *fmt, va_list args)
793 int current_log_level = default_message_loglevel;
804 /* This stops the holder of console_sem just where we want him */
805 raw_local_irq_save(flags);
806 this_cpu = smp_processor_id();
809 * Ouch, printk recursed into itself!
811 if (unlikely(printk_cpu == this_cpu)) {
813 * If a crash is occurring during printk() on this CPU,
814 * then try to get the crash message out but make sure
815 * we can't deadlock. Otherwise just return to avoid the
816 * recursion and return - but flag the recursion so that
817 * it can be printed at the next appropriate moment:
819 if (!oops_in_progress) {
821 goto out_restore_irqs;
827 spin_lock(&logbuf_lock);
828 printk_cpu = this_cpu;
832 strcpy(printk_buf, recursion_bug_msg);
833 printed_len = strlen(recursion_bug_msg);
835 /* Emit the output into the temporary buffer */
836 printed_len += vscnprintf(printk_buf + printed_len,
837 sizeof(printk_buf) - printed_len, fmt, args);
841 /* Read log level and handle special printk prefix */
842 plen = log_prefix(p, ¤t_log_level, &special);
847 case 'c': /* Strip <c> KERN_CONT, continue line */
850 case 'd': /* Strip <d> KERN_DEFAULT, start new line */
853 if (!new_text_line) {
861 * Copy the output into log_buf. If the caller didn't provide
862 * the appropriate log prefix, we insert them here
869 /* Copy original log prefix */
872 for (i = 0; i < plen; i++)
873 emit_log_char(printk_buf[i]);
878 emit_log_char(current_log_level + '0');
884 /* Add the current time stamp */
887 unsigned long long t;
888 unsigned long nanosec_rem;
890 t = cpu_clock(printk_cpu);
891 nanosec_rem = do_div(t, 1000000000);
892 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
896 for (tp = tbuf; tp < tbuf + tlen; tp++)
911 * Try to acquire and then immediately release the
912 * console semaphore. The release will do all the
913 * actual magic (print out buffers, wake up klogd,
916 * The console_trylock_for_printk() function
917 * will release 'logbuf_lock' regardless of whether it
918 * actually gets the semaphore or not.
920 if (console_trylock_for_printk(this_cpu))
925 raw_local_irq_restore(flags);
930 EXPORT_SYMBOL(printk);
931 EXPORT_SYMBOL(vprintk);
935 static void call_console_drivers(unsigned start, unsigned end)
941 static int __add_preferred_console(char *name, int idx, char *options,
944 struct console_cmdline *c;
948 * See if this tty is not yet registered, and
949 * if we have a slot free.
951 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
952 if (strcmp(console_cmdline[i].name, name) == 0 &&
953 console_cmdline[i].index == idx) {
955 selected_console = i;
958 if (i == MAX_CMDLINECONSOLES)
961 selected_console = i;
962 c = &console_cmdline[i];
963 strlcpy(c->name, name, sizeof(c->name));
964 c->options = options;
965 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
966 c->brl_options = brl_options;
972 * Set up a list of consoles. Called from init/main.c
974 static int __init console_setup(char *str)
976 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
977 char *s, *options, *brl_options = NULL;
980 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
981 if (!memcmp(str, "brl,", 4)) {
984 } else if (!memcmp(str, "brl=", 4)) {
985 brl_options = str + 4;
986 str = strchr(brl_options, ',');
988 printk(KERN_ERR "need port name after brl=\n");
996 * Decode str into name, index, options.
998 if (str[0] >= '0' && str[0] <= '9') {
1000 strncpy(buf + 4, str, sizeof(buf) - 5);
1002 strncpy(buf, str, sizeof(buf) - 1);
1004 buf[sizeof(buf) - 1] = 0;
1005 if ((options = strchr(str, ',')) != NULL)
1008 if (!strcmp(str, "ttya"))
1009 strcpy(buf, "ttyS0");
1010 if (!strcmp(str, "ttyb"))
1011 strcpy(buf, "ttyS1");
1013 for (s = buf; *s; s++)
1014 if ((*s >= '0' && *s <= '9') || *s == ',')
1016 idx = simple_strtoul(s, NULL, 10);
1019 __add_preferred_console(buf, idx, options, brl_options);
1020 console_set_on_cmdline = 1;
1023 __setup("console=", console_setup);
1026 * add_preferred_console - add a device to the list of preferred consoles.
1027 * @name: device name
1028 * @idx: device index
1029 * @options: options for this console
1031 * The last preferred console added will be used for kernel messages
1032 * and stdin/out/err for init. Normally this is used by console_setup
1033 * above to handle user-supplied console arguments; however it can also
1034 * be used by arch-specific code either to override the user or more
1035 * commonly to provide a default console (ie from PROM variables) when
1036 * the user has not supplied one.
1038 int add_preferred_console(char *name, int idx, char *options)
1040 return __add_preferred_console(name, idx, options, NULL);
1043 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
1045 struct console_cmdline *c;
1048 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
1049 if (strcmp(console_cmdline[i].name, name) == 0 &&
1050 console_cmdline[i].index == idx) {
1051 c = &console_cmdline[i];
1052 strlcpy(c->name, name_new, sizeof(c->name));
1053 c->name[sizeof(c->name) - 1] = 0;
1054 c->options = options;
1062 int console_suspend_enabled = 1;
1063 EXPORT_SYMBOL(console_suspend_enabled);
1065 static int __init console_suspend_disable(char *str)
1067 console_suspend_enabled = 0;
1070 __setup("no_console_suspend", console_suspend_disable);
1073 * suspend_console - suspend the console subsystem
1075 * This disables printk() while we go into suspend states
1077 void suspend_console(void)
1079 if (!console_suspend_enabled)
1081 printk("Suspending console(s) (use no_console_suspend to debug)\n");
1083 console_suspended = 1;
1087 void resume_console(void)
1089 if (!console_suspend_enabled)
1092 console_suspended = 0;
1097 * console_cpu_notify - print deferred console messages after CPU hotplug
1098 * @self: notifier struct
1099 * @action: CPU hotplug event
1102 * If printk() is called from a CPU that is not online yet, the messages
1103 * will be spooled but will not show up on the console. This function is
1104 * called when a new CPU comes online (or fails to come up), and ensures
1105 * that any such output gets printed.
1107 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1108 unsigned long action, void *hcpu)
1114 case CPU_DOWN_FAILED:
1115 case CPU_UP_CANCELED:
1123 * console_lock - lock the console system for exclusive use.
1125 * Acquires a lock which guarantees that the caller has
1126 * exclusive access to the console system and the console_drivers list.
1128 * Can sleep, returns nothing.
1130 void console_lock(void)
1132 BUG_ON(in_interrupt());
1134 if (console_suspended)
1137 console_may_schedule = 1;
1139 EXPORT_SYMBOL(console_lock);
1142 * console_trylock - try to lock the console system for exclusive use.
1144 * Tried to acquire a lock which guarantees that the caller has
1145 * exclusive access to the console system and the console_drivers list.
1147 * returns 1 on success, and 0 on failure to acquire the lock.
1149 int console_trylock(void)
1151 if (down_trylock(&console_sem))
1153 if (console_suspended) {
1158 console_may_schedule = 0;
1161 EXPORT_SYMBOL(console_trylock);
1163 int is_console_locked(void)
1165 return console_locked;
1168 static DEFINE_PER_CPU(int, printk_pending);
1170 void printk_tick(void)
1172 if (__this_cpu_read(printk_pending)) {
1173 __this_cpu_write(printk_pending, 0);
1174 wake_up_interruptible(&log_wait);
1178 int printk_needs_cpu(int cpu)
1180 if (cpu_is_offline(cpu))
1182 return __this_cpu_read(printk_pending);
1185 void wake_up_klogd(void)
1187 if (waitqueue_active(&log_wait))
1188 this_cpu_write(printk_pending, 1);
1192 * console_unlock - unlock the console system
1194 * Releases the console_lock which the caller holds on the console system
1195 * and the console driver list.
1197 * While the console_lock was held, console output may have been buffered
1198 * by printk(). If this is the case, console_unlock(); emits
1199 * the output prior to releasing the lock.
1201 * If there is output waiting for klogd, we wake it up.
1203 * console_unlock(); may be called from any context.
1205 void console_unlock(void)
1207 unsigned long flags;
1208 unsigned _con_start, _log_end;
1209 unsigned wake_klogd = 0;
1211 if (console_suspended) {
1216 console_may_schedule = 0;
1219 spin_lock_irqsave(&logbuf_lock, flags);
1220 wake_klogd |= log_start - log_end;
1221 if (con_start == log_end)
1222 break; /* Nothing to print */
1223 _con_start = con_start;
1225 con_start = log_end; /* Flush */
1226 spin_unlock(&logbuf_lock);
1227 stop_critical_timings(); /* don't trace print latency */
1228 call_console_drivers(_con_start, _log_end);
1229 start_critical_timings();
1230 local_irq_restore(flags);
1234 spin_unlock_irqrestore(&logbuf_lock, flags);
1238 EXPORT_SYMBOL(console_unlock);
1241 * console_conditional_schedule - yield the CPU if required
1243 * If the console code is currently allowed to sleep, and
1244 * if this CPU should yield the CPU to another task, do
1247 * Must be called within console_lock();.
1249 void __sched console_conditional_schedule(void)
1251 if (console_may_schedule)
1254 EXPORT_SYMBOL(console_conditional_schedule);
1256 void console_unblank(void)
1261 * console_unblank can no longer be called in interrupt context unless
1262 * oops_in_progress is set to 1..
1264 if (oops_in_progress) {
1265 if (down_trylock(&console_sem) != 0)
1271 console_may_schedule = 0;
1273 if ((c->flags & CON_ENABLED) && c->unblank)
1279 * Return the console tty driver structure and its associated index
1281 struct tty_driver *console_device(int *index)
1284 struct tty_driver *driver = NULL;
1287 for_each_console(c) {
1290 driver = c->device(c, index);
1299 * Prevent further output on the passed console device so that (for example)
1300 * serial drivers can disable console output before suspending a port, and can
1301 * re-enable output afterwards.
1303 void console_stop(struct console *console)
1306 console->flags &= ~CON_ENABLED;
1309 EXPORT_SYMBOL(console_stop);
1311 void console_start(struct console *console)
1314 console->flags |= CON_ENABLED;
1317 EXPORT_SYMBOL(console_start);
1320 * The console driver calls this routine during kernel initialization
1321 * to register the console printing procedure with printk() and to
1322 * print any messages that were printed by the kernel before the
1323 * console driver was initialized.
1325 * This can happen pretty early during the boot process (because of
1326 * early_printk) - sometimes before setup_arch() completes - be careful
1327 * of what kernel features are used - they may not be initialised yet.
1329 * There are two types of consoles - bootconsoles (early_printk) and
1330 * "real" consoles (everything which is not a bootconsole) which are
1331 * handled differently.
1332 * - Any number of bootconsoles can be registered at any time.
1333 * - As soon as a "real" console is registered, all bootconsoles
1334 * will be unregistered automatically.
1335 * - Once a "real" console is registered, any attempt to register a
1336 * bootconsoles will be rejected
1338 void register_console(struct console *newcon)
1341 unsigned long flags;
1342 struct console *bcon = NULL;
1345 * before we register a new CON_BOOT console, make sure we don't
1346 * already have a valid console
1348 if (console_drivers && newcon->flags & CON_BOOT) {
1349 /* find the last or real console */
1350 for_each_console(bcon) {
1351 if (!(bcon->flags & CON_BOOT)) {
1352 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1353 newcon->name, newcon->index);
1359 if (console_drivers && console_drivers->flags & CON_BOOT)
1360 bcon = console_drivers;
1362 if (preferred_console < 0 || bcon || !console_drivers)
1363 preferred_console = selected_console;
1365 if (newcon->early_setup)
1366 newcon->early_setup();
1369 * See if we want to use this console driver. If we
1370 * didn't select a console we take the first one
1371 * that registers here.
1373 if (preferred_console < 0) {
1374 if (newcon->index < 0)
1376 if (newcon->setup == NULL ||
1377 newcon->setup(newcon, NULL) == 0) {
1378 newcon->flags |= CON_ENABLED;
1379 if (newcon->device) {
1380 newcon->flags |= CON_CONSDEV;
1381 preferred_console = 0;
1387 * See if this console matches one we selected on
1390 for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1392 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1394 if (newcon->index >= 0 &&
1395 newcon->index != console_cmdline[i].index)
1397 if (newcon->index < 0)
1398 newcon->index = console_cmdline[i].index;
1399 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1400 if (console_cmdline[i].brl_options) {
1401 newcon->flags |= CON_BRL;
1402 braille_register_console(newcon,
1403 console_cmdline[i].index,
1404 console_cmdline[i].options,
1405 console_cmdline[i].brl_options);
1409 if (newcon->setup &&
1410 newcon->setup(newcon, console_cmdline[i].options) != 0)
1412 newcon->flags |= CON_ENABLED;
1413 newcon->index = console_cmdline[i].index;
1414 if (i == selected_console) {
1415 newcon->flags |= CON_CONSDEV;
1416 preferred_console = selected_console;
1421 if (!(newcon->flags & CON_ENABLED))
1425 * If we have a bootconsole, and are switching to a real console,
1426 * don't print everything out again, since when the boot console, and
1427 * the real console are the same physical device, it's annoying to
1428 * see the beginning boot messages twice
1430 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1431 newcon->flags &= ~CON_PRINTBUFFER;
1434 * Put this console in the list - keep the
1435 * preferred driver at the head of the list.
1438 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1439 newcon->next = console_drivers;
1440 console_drivers = newcon;
1442 newcon->next->flags &= ~CON_CONSDEV;
1444 newcon->next = console_drivers->next;
1445 console_drivers->next = newcon;
1447 if (newcon->flags & CON_PRINTBUFFER) {
1449 * console_unlock(); will print out the buffered messages
1452 spin_lock_irqsave(&logbuf_lock, flags);
1453 con_start = log_start;
1454 spin_unlock_irqrestore(&logbuf_lock, flags);
1457 console_sysfs_notify();
1460 * By unregistering the bootconsoles after we enable the real console
1461 * we get the "console xxx enabled" message on all the consoles -
1462 * boot consoles, real consoles, etc - this is to ensure that end
1463 * users know there might be something in the kernel's log buffer that
1464 * went to the bootconsole (that they do not see on the real console)
1466 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1467 /* we need to iterate through twice, to make sure we print
1468 * everything out, before we unregister the console(s)
1470 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1471 newcon->name, newcon->index);
1472 for_each_console(bcon)
1473 if (bcon->flags & CON_BOOT)
1474 unregister_console(bcon);
1476 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1477 (newcon->flags & CON_BOOT) ? "boot" : "" ,
1478 newcon->name, newcon->index);
1481 EXPORT_SYMBOL(register_console);
1483 int unregister_console(struct console *console)
1485 struct console *a, *b;
1488 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1489 if (console->flags & CON_BRL)
1490 return braille_unregister_console(console);
1494 if (console_drivers == console) {
1495 console_drivers=console->next;
1497 } else if (console_drivers) {
1498 for (a=console_drivers->next, b=console_drivers ;
1499 a; b=a, a=b->next) {
1509 * If this isn't the last console and it has CON_CONSDEV set, we
1510 * need to set it on the next preferred console.
1512 if (console_drivers != NULL && console->flags & CON_CONSDEV)
1513 console_drivers->flags |= CON_CONSDEV;
1516 console_sysfs_notify();
1519 EXPORT_SYMBOL(unregister_console);
1521 static int __init printk_late_init(void)
1523 struct console *con;
1525 for_each_console(con) {
1526 if (con->flags & CON_BOOT) {
1527 printk(KERN_INFO "turn off boot console %s%d\n",
1528 con->name, con->index);
1529 unregister_console(con);
1532 hotcpu_notifier(console_cpu_notify, 0);
1535 late_initcall(printk_late_init);
1537 #if defined CONFIG_PRINTK
1540 * printk rate limiting, lifted from the networking subsystem.
1542 * This enforces a rate limit: not more than 10 kernel messages
1543 * every 5s to make a denial-of-service attack impossible.
1545 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1547 int __printk_ratelimit(const char *func)
1549 return ___ratelimit(&printk_ratelimit_state, func);
1551 EXPORT_SYMBOL(__printk_ratelimit);
1554 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1555 * @caller_jiffies: pointer to caller's state
1556 * @interval_msecs: minimum interval between prints
1558 * printk_timed_ratelimit() returns true if more than @interval_msecs
1559 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1562 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1563 unsigned int interval_msecs)
1565 if (*caller_jiffies == 0
1566 || !time_in_range(jiffies, *caller_jiffies,
1568 + msecs_to_jiffies(interval_msecs))) {
1569 *caller_jiffies = jiffies;
1574 EXPORT_SYMBOL(printk_timed_ratelimit);
1576 static DEFINE_SPINLOCK(dump_list_lock);
1577 static LIST_HEAD(dump_list);
1580 * kmsg_dump_register - register a kernel log dumper.
1581 * @dumper: pointer to the kmsg_dumper structure
1583 * Adds a kernel log dumper to the system. The dump callback in the
1584 * structure will be called when the kernel oopses or panics and must be
1585 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1587 int kmsg_dump_register(struct kmsg_dumper *dumper)
1589 unsigned long flags;
1592 /* The dump callback needs to be set */
1596 spin_lock_irqsave(&dump_list_lock, flags);
1597 /* Don't allow registering multiple times */
1598 if (!dumper->registered) {
1599 dumper->registered = 1;
1600 list_add_tail_rcu(&dumper->list, &dump_list);
1603 spin_unlock_irqrestore(&dump_list_lock, flags);
1607 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1610 * kmsg_dump_unregister - unregister a kmsg dumper.
1611 * @dumper: pointer to the kmsg_dumper structure
1613 * Removes a dump device from the system. Returns zero on success and
1614 * %-EINVAL otherwise.
1616 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1618 unsigned long flags;
1621 spin_lock_irqsave(&dump_list_lock, flags);
1622 if (dumper->registered) {
1623 dumper->registered = 0;
1624 list_del_rcu(&dumper->list);
1627 spin_unlock_irqrestore(&dump_list_lock, flags);
1632 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1635 * kmsg_dump - dump kernel log to kernel message dumpers.
1636 * @reason: the reason (oops, panic etc) for dumping
1638 * Iterate through each of the dump devices and call the oops/panic
1639 * callbacks with the log buffer.
1641 void kmsg_dump(enum kmsg_dump_reason reason)
1645 struct kmsg_dumper *dumper;
1646 const char *s1, *s2;
1647 unsigned long l1, l2;
1648 unsigned long flags;
1650 /* Theoretically, the log could move on after we do this, but
1651 there's not a lot we can do about that. The new messages
1652 will overwrite the start of what we dump. */
1653 spin_lock_irqsave(&logbuf_lock, flags);
1654 end = log_end & LOG_BUF_MASK;
1655 chars = logged_chars;
1656 spin_unlock_irqrestore(&logbuf_lock, flags);
1659 s1 = log_buf + log_buf_len - chars + end;
1668 s2 = log_buf + end - chars;
1673 list_for_each_entry_rcu(dumper, &dump_list, list)
1674 dumper->dump(dumper, reason, s1, l1, s2, l2);