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/ratelimit.h>
38 #include <asm/uaccess.h>
41 * for_each_console() allows you to iterate on each console
43 #define for_each_console(con) \
44 for (con = console_drivers; con != NULL; con = con->next)
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 */
71 static int saved_console_loglevel
= -1;
74 * Low level drivers may need that to know if they can schedule in
75 * their unblank() callback or not. So let's export it.
78 EXPORT_SYMBOL(oops_in_progress
);
81 * console_sem protects the console_drivers list, and also
82 * provides serialisation for access to the entire console
85 static DECLARE_MUTEX(console_sem
);
86 struct console
*console_drivers
;
87 EXPORT_SYMBOL_GPL(console_drivers
);
90 * This is used for debugging the mess that is the VT code by
91 * keeping track if we have the console semaphore held. It's
92 * definitely not the perfect debug tool (we don't know if _WE_
93 * hold it are racing, but it helps tracking those weird code
94 * path in the console code where we end up in places I want
95 * locked without the console sempahore held
97 static int console_locked
, console_suspended
;
100 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
101 * It is also used in interesting ways to provide interlocking in
102 * release_console_sem().
104 static DEFINE_SPINLOCK(logbuf_lock
);
106 #define LOG_BUF_MASK (log_buf_len-1)
107 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
110 * The indices into log_buf are not constrained to log_buf_len - they
111 * must be masked before subscripting
113 static unsigned log_start
; /* Index into log_buf: next char to be read by syslog() */
114 static unsigned con_start
; /* Index into log_buf: next char to be sent to consoles */
115 static unsigned log_end
; /* Index into log_buf: most-recently-written-char + 1 */
118 * Array of consoles built from command line options (console=)
120 struct console_cmdline
122 char name
[8]; /* Name of the driver */
123 int index
; /* Minor dev. to use */
124 char *options
; /* Options for the driver */
125 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
126 char *brl_options
; /* Options for braille driver */
130 #define MAX_CMDLINECONSOLES 8
132 static struct console_cmdline console_cmdline
[MAX_CMDLINECONSOLES
];
133 static int selected_console
= -1;
134 static int preferred_console
= -1;
135 int console_set_on_cmdline
;
136 EXPORT_SYMBOL(console_set_on_cmdline
);
138 /* Flag: console code may call schedule() */
139 static int console_may_schedule
;
143 static char __log_buf
[__LOG_BUF_LEN
];
144 static char *log_buf
= __log_buf
;
145 static int log_buf_len
= __LOG_BUF_LEN
;
146 static unsigned logged_chars
; /* Number of chars produced since last read+clear operation */
150 * This appends the listed symbols to /proc/vmcoreinfo
152 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
153 * obtain access to symbols that are otherwise very difficult to locate. These
154 * symbols are specifically used so that utilities can access and extract the
155 * dmesg log from a vmcore file after a crash.
157 void log_buf_kexec_setup(void)
159 VMCOREINFO_SYMBOL(log_buf
);
160 VMCOREINFO_SYMBOL(log_end
);
161 VMCOREINFO_SYMBOL(log_buf_len
);
162 VMCOREINFO_SYMBOL(logged_chars
);
166 static int __init
log_buf_len_setup(char *str
)
168 unsigned size
= memparse(str
, &str
);
172 size
= roundup_pow_of_two(size
);
173 if (size
> log_buf_len
) {
174 unsigned start
, dest_idx
, offset
;
177 new_log_buf
= alloc_bootmem(size
);
179 printk(KERN_WARNING
"log_buf_len: allocation failed\n");
183 spin_lock_irqsave(&logbuf_lock
, flags
);
185 log_buf
= new_log_buf
;
187 offset
= start
= min(con_start
, log_start
);
189 while (start
!= log_end
) {
190 log_buf
[dest_idx
] = __log_buf
[start
& (__LOG_BUF_LEN
- 1)];
197 spin_unlock_irqrestore(&logbuf_lock
, flags
);
199 printk(KERN_NOTICE
"log_buf_len: %d\n", log_buf_len
);
205 __setup("log_buf_len=", log_buf_len_setup
);
207 #ifdef CONFIG_BOOT_PRINTK_DELAY
209 static unsigned int boot_delay
; /* msecs delay after each printk during bootup */
210 static unsigned long long loops_per_msec
; /* based on boot_delay */
212 static int __init
boot_delay_setup(char *str
)
216 lpj
= preset_lpj
? preset_lpj
: 1000000; /* some guess */
217 loops_per_msec
= (unsigned long long)lpj
/ 1000 * HZ
;
219 get_option(&str
, &boot_delay
);
220 if (boot_delay
> 10 * 1000)
223 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
224 "HZ: %d, loops_per_msec: %llu\n",
225 boot_delay
, preset_lpj
, lpj
, HZ
, loops_per_msec
);
228 __setup("boot_delay=", boot_delay_setup
);
230 static void boot_delay_msec(void)
232 unsigned long long k
;
233 unsigned long timeout
;
235 if (boot_delay
== 0 || system_state
!= SYSTEM_BOOTING
)
238 k
= (unsigned long long)loops_per_msec
* boot_delay
;
240 timeout
= jiffies
+ msecs_to_jiffies(boot_delay
);
245 * use (volatile) jiffies to prevent
246 * compiler reduction; loop termination via jiffies
247 * is secondary and may or may not happen.
249 if (time_after(jiffies
, timeout
))
251 touch_nmi_watchdog();
255 static inline void boot_delay_msec(void)
261 * Commands to do_syslog:
263 * 0 -- Close the log. Currently a NOP.
264 * 1 -- Open the log. Currently a NOP.
265 * 2 -- Read from the log.
266 * 3 -- Read all messages remaining in the ring buffer.
267 * 4 -- Read and clear all messages remaining in the ring buffer
268 * 5 -- Clear ring buffer.
269 * 6 -- Disable printk's to console
270 * 7 -- Enable printk's to console
271 * 8 -- Set level of messages printed to console
272 * 9 -- Return number of unread characters in the log buffer
273 * 10 -- Return size of the log buffer
275 int do_syslog(int type
, char __user
*buf
, int len
)
277 unsigned i
, j
, limit
, count
;
282 error
= security_syslog(type
);
287 case 0: /* Close log */
289 case 1: /* Open log */
291 case 2: /* Read from log */
298 if (!access_ok(VERIFY_WRITE
, buf
, len
)) {
302 error
= wait_event_interruptible(log_wait
,
303 (log_start
- log_end
));
307 spin_lock_irq(&logbuf_lock
);
308 while (!error
&& (log_start
!= log_end
) && i
< len
) {
309 c
= LOG_BUF(log_start
);
311 spin_unlock_irq(&logbuf_lock
);
312 error
= __put_user(c
,buf
);
316 spin_lock_irq(&logbuf_lock
);
318 spin_unlock_irq(&logbuf_lock
);
322 case 4: /* Read/clear last kernel messages */
325 case 3: /* Read last kernel messages */
332 if (!access_ok(VERIFY_WRITE
, buf
, len
)) {
337 if (count
> log_buf_len
)
339 spin_lock_irq(&logbuf_lock
);
340 if (count
> logged_chars
)
341 count
= logged_chars
;
346 * __put_user() could sleep, and while we sleep
347 * printk() could overwrite the messages
348 * we try to copy to user space. Therefore
349 * the messages are copied in reverse. <manfreds>
351 for (i
= 0; i
< count
&& !error
; i
++) {
353 if (j
+ log_buf_len
< log_end
)
356 spin_unlock_irq(&logbuf_lock
);
357 error
= __put_user(c
,&buf
[count
-1-i
]);
359 spin_lock_irq(&logbuf_lock
);
361 spin_unlock_irq(&logbuf_lock
);
366 int offset
= count
-error
;
367 /* buffer overflow during copy, correct user buffer. */
368 for (i
= 0; i
< error
; i
++) {
369 if (__get_user(c
,&buf
[i
+offset
]) ||
370 __put_user(c
,&buf
[i
])) {
378 case 5: /* Clear ring buffer */
381 case 6: /* Disable logging to console */
382 if (saved_console_loglevel
== -1)
383 saved_console_loglevel
= console_loglevel
;
384 console_loglevel
= minimum_console_loglevel
;
386 case 7: /* Enable logging to console */
387 if (saved_console_loglevel
!= -1) {
388 console_loglevel
= saved_console_loglevel
;
389 saved_console_loglevel
= -1;
392 case 8: /* Set level of messages printed to console */
394 if (len
< 1 || len
> 8)
396 if (len
< minimum_console_loglevel
)
397 len
= minimum_console_loglevel
;
398 console_loglevel
= len
;
399 /* Implicitly re-enable logging to console */
400 saved_console_loglevel
= -1;
403 case 9: /* Number of chars in the log buffer */
404 error
= log_end
- log_start
;
406 case 10: /* Size of the log buffer */
417 SYSCALL_DEFINE3(syslog
, int, type
, char __user
*, buf
, int, len
)
419 return do_syslog(type
, buf
, len
);
423 * Call the console drivers on a range of log_buf
425 static void __call_console_drivers(unsigned start
, unsigned end
)
429 for_each_console(con
) {
430 if ((con
->flags
& CON_ENABLED
) && con
->write
&&
431 (cpu_online(smp_processor_id()) ||
432 (con
->flags
& CON_ANYTIME
)))
433 con
->write(con
, &LOG_BUF(start
), end
- start
);
437 static int __read_mostly ignore_loglevel
;
439 static int __init
ignore_loglevel_setup(char *str
)
442 printk(KERN_INFO
"debug: ignoring loglevel setting.\n");
447 early_param("ignore_loglevel", ignore_loglevel_setup
);
450 * Write out chars from start to end - 1 inclusive
452 static void _call_console_drivers(unsigned start
,
453 unsigned end
, int msg_log_level
)
455 if ((msg_log_level
< console_loglevel
|| ignore_loglevel
) &&
456 console_drivers
&& start
!= end
) {
457 if ((start
& LOG_BUF_MASK
) > (end
& LOG_BUF_MASK
)) {
459 __call_console_drivers(start
& LOG_BUF_MASK
,
461 __call_console_drivers(0, end
& LOG_BUF_MASK
);
463 __call_console_drivers(start
, end
);
469 * Call the console drivers, asking them to write out
470 * log_buf[start] to log_buf[end - 1].
471 * The console_sem must be held.
473 static void call_console_drivers(unsigned start
, unsigned end
)
475 unsigned cur_index
, start_print
;
476 static int msg_level
= -1;
478 BUG_ON(((int)(start
- end
)) > 0);
482 while (cur_index
!= end
) {
483 if (msg_level
< 0 && ((end
- cur_index
) > 2) &&
484 LOG_BUF(cur_index
+ 0) == '<' &&
485 LOG_BUF(cur_index
+ 1) >= '0' &&
486 LOG_BUF(cur_index
+ 1) <= '7' &&
487 LOG_BUF(cur_index
+ 2) == '>') {
488 msg_level
= LOG_BUF(cur_index
+ 1) - '0';
490 start_print
= cur_index
;
492 while (cur_index
!= end
) {
493 char c
= LOG_BUF(cur_index
);
499 * printk() has already given us loglevel tags in
500 * the buffer. This code is here in case the
501 * log buffer has wrapped right round and scribbled
504 msg_level
= default_message_loglevel
;
506 _call_console_drivers(start_print
, cur_index
, msg_level
);
508 start_print
= cur_index
;
513 _call_console_drivers(start_print
, end
, msg_level
);
516 static void emit_log_char(char c
)
518 LOG_BUF(log_end
) = c
;
520 if (log_end
- log_start
> log_buf_len
)
521 log_start
= log_end
- log_buf_len
;
522 if (log_end
- con_start
> log_buf_len
)
523 con_start
= log_end
- log_buf_len
;
524 if (logged_chars
< log_buf_len
)
529 * Zap console related locks when oopsing. Only zap at most once
530 * every 10 seconds, to leave time for slow consoles to print a
533 static void zap_locks(void)
535 static unsigned long oops_timestamp
;
537 if (time_after_eq(jiffies
, oops_timestamp
) &&
538 !time_after(jiffies
, oops_timestamp
+ 30 * HZ
))
541 oops_timestamp
= jiffies
;
543 /* If a crash is occurring, make sure we can't deadlock */
544 spin_lock_init(&logbuf_lock
);
545 /* And make sure that we print immediately */
546 init_MUTEX(&console_sem
);
549 #if defined(CONFIG_PRINTK_TIME)
550 static int printk_time
= 1;
552 static int printk_time
= 0;
554 module_param_named(time
, printk_time
, bool, S_IRUGO
| S_IWUSR
);
556 /* Check if we have any console registered that can be called early in boot. */
557 static int have_callable_console(void)
561 for_each_console(con
)
562 if (con
->flags
& CON_ANYTIME
)
569 * printk - print a kernel message
570 * @fmt: format string
572 * This is printk(). It can be called from any context. We want it to work.
574 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
575 * call the console drivers. If we fail to get the semaphore we place the output
576 * into the log buffer and return. The current holder of the console_sem will
577 * notice the new output in release_console_sem() and will send it to the
578 * consoles before releasing the semaphore.
580 * One effect of this deferred printing is that code which calls printk() and
581 * then changes console_loglevel may break. This is because console_loglevel
582 * is inspected when the actual printing occurs.
587 * See the vsnprintf() documentation for format string extensions over C99.
590 asmlinkage
int printk(const char *fmt
, ...)
596 r
= vprintk(fmt
, args
);
602 /* cpu currently holding logbuf_lock */
603 static volatile unsigned int printk_cpu
= UINT_MAX
;
606 * Can we actually use the console at this time on this cpu?
608 * Console drivers may assume that per-cpu resources have
609 * been allocated. So unless they're explicitly marked as
610 * being able to cope (CON_ANYTIME) don't call them until
611 * this CPU is officially up.
613 static inline int can_use_console(unsigned int cpu
)
615 return cpu_online(cpu
) || have_callable_console();
619 * Try to get console ownership to actually show the kernel
620 * messages from a 'printk'. Return true (and with the
621 * console_semaphore held, and 'console_locked' set) if it
622 * is successful, false otherwise.
624 * This gets called with the 'logbuf_lock' spinlock held and
625 * interrupts disabled. It should return with 'lockbuf_lock'
626 * released but interrupts still disabled.
628 static int acquire_console_semaphore_for_printk(unsigned int cpu
)
632 if (!try_acquire_console_sem()) {
636 * If we can't use the console, we need to release
637 * the console semaphore by hand to avoid flushing
638 * the buffer. We need to hold the console semaphore
639 * in order to do this test safely.
641 if (!can_use_console(cpu
)) {
647 printk_cpu
= UINT_MAX
;
648 spin_unlock(&logbuf_lock
);
651 static const char recursion_bug_msg
[] =
652 KERN_CRIT
"BUG: recent printk recursion!\n";
653 static int recursion_bug
;
654 static int new_text_line
= 1;
655 static char printk_buf
[1024];
657 int printk_delay_msec __read_mostly
;
659 static inline void printk_delay(void)
661 if (unlikely(printk_delay_msec
)) {
662 int m
= printk_delay_msec
;
666 touch_nmi_watchdog();
671 asmlinkage
int vprintk(const char *fmt
, va_list args
)
674 int current_log_level
= default_message_loglevel
;
683 /* This stops the holder of console_sem just where we want him */
684 raw_local_irq_save(flags
);
685 this_cpu
= smp_processor_id();
688 * Ouch, printk recursed into itself!
690 if (unlikely(printk_cpu
== this_cpu
)) {
692 * If a crash is occurring during printk() on this CPU,
693 * then try to get the crash message out but make sure
694 * we can't deadlock. Otherwise just return to avoid the
695 * recursion and return - but flag the recursion so that
696 * it can be printed at the next appropriate moment:
698 if (!oops_in_progress
) {
700 goto out_restore_irqs
;
706 spin_lock(&logbuf_lock
);
707 printk_cpu
= this_cpu
;
711 strcpy(printk_buf
, recursion_bug_msg
);
712 printed_len
= strlen(recursion_bug_msg
);
714 /* Emit the output into the temporary buffer */
715 printed_len
+= vscnprintf(printk_buf
+ printed_len
,
716 sizeof(printk_buf
) - printed_len
, fmt
, args
);
721 /* Do we have a loglevel in the string? */
723 unsigned char c
= p
[1];
724 if (c
&& p
[2] == '>') {
726 case '0' ... '7': /* loglevel */
727 current_log_level
= c
- '0';
728 /* Fallthrough - make sure we're on a new line */
729 case 'd': /* KERN_DEFAULT */
730 if (!new_text_line
) {
734 /* Fallthrough - skip the loglevel */
735 case 'c': /* KERN_CONT */
743 * Copy the output into log_buf. If the caller didn't provide
744 * appropriate log level tags, we insert them here
748 /* Always output the token */
750 emit_log_char(current_log_level
+ '0');
756 /* Follow the token with the time */
759 unsigned long long t
;
760 unsigned long nanosec_rem
;
762 t
= cpu_clock(printk_cpu
);
763 nanosec_rem
= do_div(t
, 1000000000);
764 tlen
= sprintf(tbuf
, "[%5lu.%06lu] ",
768 for (tp
= tbuf
; tp
< tbuf
+ tlen
; tp
++)
783 * Try to acquire and then immediately release the
784 * console semaphore. The release will do all the
785 * actual magic (print out buffers, wake up klogd,
788 * The acquire_console_semaphore_for_printk() function
789 * will release 'logbuf_lock' regardless of whether it
790 * actually gets the semaphore or not.
792 if (acquire_console_semaphore_for_printk(this_cpu
))
793 release_console_sem();
797 raw_local_irq_restore(flags
);
802 EXPORT_SYMBOL(printk
);
803 EXPORT_SYMBOL(vprintk
);
807 static void call_console_drivers(unsigned start
, unsigned end
)
813 static int __add_preferred_console(char *name
, int idx
, char *options
,
816 struct console_cmdline
*c
;
820 * See if this tty is not yet registered, and
821 * if we have a slot free.
823 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++)
824 if (strcmp(console_cmdline
[i
].name
, name
) == 0 &&
825 console_cmdline
[i
].index
== idx
) {
827 selected_console
= i
;
830 if (i
== MAX_CMDLINECONSOLES
)
833 selected_console
= i
;
834 c
= &console_cmdline
[i
];
835 strlcpy(c
->name
, name
, sizeof(c
->name
));
836 c
->options
= options
;
837 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
838 c
->brl_options
= brl_options
;
844 * Set up a list of consoles. Called from init/main.c
846 static int __init
console_setup(char *str
)
848 char buf
[sizeof(console_cmdline
[0].name
) + 4]; /* 4 for index */
849 char *s
, *options
, *brl_options
= NULL
;
852 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
853 if (!memcmp(str
, "brl,", 4)) {
856 } else if (!memcmp(str
, "brl=", 4)) {
857 brl_options
= str
+ 4;
858 str
= strchr(brl_options
, ',');
860 printk(KERN_ERR
"need port name after brl=\n");
868 * Decode str into name, index, options.
870 if (str
[0] >= '0' && str
[0] <= '9') {
872 strncpy(buf
+ 4, str
, sizeof(buf
) - 5);
874 strncpy(buf
, str
, sizeof(buf
) - 1);
876 buf
[sizeof(buf
) - 1] = 0;
877 if ((options
= strchr(str
, ',')) != NULL
)
880 if (!strcmp(str
, "ttya"))
881 strcpy(buf
, "ttyS0");
882 if (!strcmp(str
, "ttyb"))
883 strcpy(buf
, "ttyS1");
885 for (s
= buf
; *s
; s
++)
886 if ((*s
>= '0' && *s
<= '9') || *s
== ',')
888 idx
= simple_strtoul(s
, NULL
, 10);
891 __add_preferred_console(buf
, idx
, options
, brl_options
);
892 console_set_on_cmdline
= 1;
895 __setup("console=", console_setup
);
898 * add_preferred_console - add a device to the list of preferred consoles.
901 * @options: options for this console
903 * The last preferred console added will be used for kernel messages
904 * and stdin/out/err for init. Normally this is used by console_setup
905 * above to handle user-supplied console arguments; however it can also
906 * be used by arch-specific code either to override the user or more
907 * commonly to provide a default console (ie from PROM variables) when
908 * the user has not supplied one.
910 int add_preferred_console(char *name
, int idx
, char *options
)
912 return __add_preferred_console(name
, idx
, options
, NULL
);
915 int update_console_cmdline(char *name
, int idx
, char *name_new
, int idx_new
, char *options
)
917 struct console_cmdline
*c
;
920 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++)
921 if (strcmp(console_cmdline
[i
].name
, name
) == 0 &&
922 console_cmdline
[i
].index
== idx
) {
923 c
= &console_cmdline
[i
];
924 strlcpy(c
->name
, name_new
, sizeof(c
->name
));
925 c
->name
[sizeof(c
->name
) - 1] = 0;
926 c
->options
= options
;
934 int console_suspend_enabled
= 1;
935 EXPORT_SYMBOL(console_suspend_enabled
);
937 static int __init
console_suspend_disable(char *str
)
939 console_suspend_enabled
= 0;
942 __setup("no_console_suspend", console_suspend_disable
);
945 * suspend_console - suspend the console subsystem
947 * This disables printk() while we go into suspend states
949 void suspend_console(void)
951 if (!console_suspend_enabled
)
953 printk("Suspending console(s) (use no_console_suspend to debug)\n");
954 acquire_console_sem();
955 console_suspended
= 1;
959 void resume_console(void)
961 if (!console_suspend_enabled
)
964 console_suspended
= 0;
965 release_console_sem();
969 * acquire_console_sem - lock the console system for exclusive use.
971 * Acquires a semaphore which guarantees that the caller has
972 * exclusive access to the console system and the console_drivers list.
974 * Can sleep, returns nothing.
976 void acquire_console_sem(void)
978 BUG_ON(in_interrupt());
980 if (console_suspended
)
983 console_may_schedule
= 1;
985 EXPORT_SYMBOL(acquire_console_sem
);
987 int try_acquire_console_sem(void)
989 if (down_trylock(&console_sem
))
991 if (console_suspended
) {
996 console_may_schedule
= 0;
999 EXPORT_SYMBOL(try_acquire_console_sem
);
1001 int is_console_locked(void)
1003 return console_locked
;
1006 static DEFINE_PER_CPU(int, printk_pending
);
1008 void printk_tick(void)
1010 if (__get_cpu_var(printk_pending
)) {
1011 __get_cpu_var(printk_pending
) = 0;
1012 wake_up_interruptible(&log_wait
);
1016 int printk_needs_cpu(int cpu
)
1018 return per_cpu(printk_pending
, cpu
);
1021 void wake_up_klogd(void)
1023 if (waitqueue_active(&log_wait
))
1024 __raw_get_cpu_var(printk_pending
) = 1;
1028 * release_console_sem - unlock the console system
1030 * Releases the semaphore which the caller holds on the console system
1031 * and the console driver list.
1033 * While the semaphore was held, console output may have been buffered
1034 * by printk(). If this is the case, release_console_sem() emits
1035 * the output prior to releasing the semaphore.
1037 * If there is output waiting for klogd, we wake it up.
1039 * release_console_sem() may be called from any context.
1041 void release_console_sem(void)
1043 unsigned long flags
;
1044 unsigned _con_start
, _log_end
;
1045 unsigned wake_klogd
= 0;
1047 if (console_suspended
) {
1052 console_may_schedule
= 0;
1055 spin_lock_irqsave(&logbuf_lock
, flags
);
1056 wake_klogd
|= log_start
- log_end
;
1057 if (con_start
== log_end
)
1058 break; /* Nothing to print */
1059 _con_start
= con_start
;
1061 con_start
= log_end
; /* Flush */
1062 spin_unlock(&logbuf_lock
);
1063 stop_critical_timings(); /* don't trace print latency */
1064 call_console_drivers(_con_start
, _log_end
);
1065 start_critical_timings();
1066 local_irq_restore(flags
);
1070 spin_unlock_irqrestore(&logbuf_lock
, flags
);
1074 EXPORT_SYMBOL(release_console_sem
);
1077 * console_conditional_schedule - yield the CPU if required
1079 * If the console code is currently allowed to sleep, and
1080 * if this CPU should yield the CPU to another task, do
1083 * Must be called within acquire_console_sem().
1085 void __sched
console_conditional_schedule(void)
1087 if (console_may_schedule
)
1090 EXPORT_SYMBOL(console_conditional_schedule
);
1092 void console_unblank(void)
1097 * console_unblank can no longer be called in interrupt context unless
1098 * oops_in_progress is set to 1..
1100 if (oops_in_progress
) {
1101 if (down_trylock(&console_sem
) != 0)
1104 acquire_console_sem();
1107 console_may_schedule
= 0;
1109 if ((c
->flags
& CON_ENABLED
) && c
->unblank
)
1111 release_console_sem();
1115 * Return the console tty driver structure and its associated index
1117 struct tty_driver
*console_device(int *index
)
1120 struct tty_driver
*driver
= NULL
;
1122 acquire_console_sem();
1123 for_each_console(c
) {
1126 driver
= c
->device(c
, index
);
1130 release_console_sem();
1135 * Prevent further output on the passed console device so that (for example)
1136 * serial drivers can disable console output before suspending a port, and can
1137 * re-enable output afterwards.
1139 void console_stop(struct console
*console
)
1141 acquire_console_sem();
1142 console
->flags
&= ~CON_ENABLED
;
1143 release_console_sem();
1145 EXPORT_SYMBOL(console_stop
);
1147 void console_start(struct console
*console
)
1149 acquire_console_sem();
1150 console
->flags
|= CON_ENABLED
;
1151 release_console_sem();
1153 EXPORT_SYMBOL(console_start
);
1156 * The console driver calls this routine during kernel initialization
1157 * to register the console printing procedure with printk() and to
1158 * print any messages that were printed by the kernel before the
1159 * console driver was initialized.
1161 * This can happen pretty early during the boot process (because of
1162 * early_printk) - sometimes before setup_arch() completes - be careful
1163 * of what kernel features are used - they may not be initialised yet.
1165 * There are two types of consoles - bootconsoles (early_printk) and
1166 * "real" consoles (everything which is not a bootconsole) which are
1167 * handled differently.
1168 * - Any number of bootconsoles can be registered at any time.
1169 * - As soon as a "real" console is registered, all bootconsoles
1170 * will be unregistered automatically.
1171 * - Once a "real" console is registered, any attempt to register a
1172 * bootconsoles will be rejected
1174 void register_console(struct console
*newcon
)
1177 unsigned long flags
;
1178 struct console
*bcon
= NULL
;
1181 * before we register a new CON_BOOT console, make sure we don't
1182 * already have a valid console
1184 if (console_drivers
&& newcon
->flags
& CON_BOOT
) {
1185 /* find the last or real console */
1186 for_each_console(bcon
) {
1187 if (!(bcon
->flags
& CON_BOOT
)) {
1188 printk(KERN_INFO
"Too late to register bootconsole %s%d\n",
1189 newcon
->name
, newcon
->index
);
1195 if (console_drivers
&& console_drivers
->flags
& CON_BOOT
)
1196 bcon
= console_drivers
;
1198 if (preferred_console
< 0 || bcon
|| !console_drivers
)
1199 preferred_console
= selected_console
;
1201 if (newcon
->early_setup
)
1202 newcon
->early_setup();
1205 * See if we want to use this console driver. If we
1206 * didn't select a console we take the first one
1207 * that registers here.
1209 if (preferred_console
< 0) {
1210 if (newcon
->index
< 0)
1212 if (newcon
->setup
== NULL
||
1213 newcon
->setup(newcon
, NULL
) == 0) {
1214 newcon
->flags
|= CON_ENABLED
;
1215 if (newcon
->device
) {
1216 newcon
->flags
|= CON_CONSDEV
;
1217 preferred_console
= 0;
1223 * See if this console matches one we selected on
1226 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0];
1228 if (strcmp(console_cmdline
[i
].name
, newcon
->name
) != 0)
1230 if (newcon
->index
>= 0 &&
1231 newcon
->index
!= console_cmdline
[i
].index
)
1233 if (newcon
->index
< 0)
1234 newcon
->index
= console_cmdline
[i
].index
;
1235 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1236 if (console_cmdline
[i
].brl_options
) {
1237 newcon
->flags
|= CON_BRL
;
1238 braille_register_console(newcon
,
1239 console_cmdline
[i
].index
,
1240 console_cmdline
[i
].options
,
1241 console_cmdline
[i
].brl_options
);
1245 if (newcon
->setup
&&
1246 newcon
->setup(newcon
, console_cmdline
[i
].options
) != 0)
1248 newcon
->flags
|= CON_ENABLED
;
1249 newcon
->index
= console_cmdline
[i
].index
;
1250 if (i
== selected_console
) {
1251 newcon
->flags
|= CON_CONSDEV
;
1252 preferred_console
= selected_console
;
1257 if (!(newcon
->flags
& CON_ENABLED
))
1261 * If we have a bootconsole, and are switching to a real console,
1262 * don't print everything out again, since when the boot console, and
1263 * the real console are the same physical device, it's annoying to
1264 * see the beginning boot messages twice
1266 if (bcon
&& ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
))
1267 newcon
->flags
&= ~CON_PRINTBUFFER
;
1270 * Put this console in the list - keep the
1271 * preferred driver at the head of the list.
1273 acquire_console_sem();
1274 if ((newcon
->flags
& CON_CONSDEV
) || console_drivers
== NULL
) {
1275 newcon
->next
= console_drivers
;
1276 console_drivers
= newcon
;
1278 newcon
->next
->flags
&= ~CON_CONSDEV
;
1280 newcon
->next
= console_drivers
->next
;
1281 console_drivers
->next
= newcon
;
1283 if (newcon
->flags
& CON_PRINTBUFFER
) {
1285 * release_console_sem() will print out the buffered messages
1288 spin_lock_irqsave(&logbuf_lock
, flags
);
1289 con_start
= log_start
;
1290 spin_unlock_irqrestore(&logbuf_lock
, flags
);
1292 release_console_sem();
1295 * By unregistering the bootconsoles after we enable the real console
1296 * we get the "console xxx enabled" message on all the consoles -
1297 * boot consoles, real consoles, etc - this is to ensure that end
1298 * users know there might be something in the kernel's log buffer that
1299 * went to the bootconsole (that they do not see on the real console)
1301 if (bcon
&& ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
)) {
1302 /* we need to iterate through twice, to make sure we print
1303 * everything out, before we unregister the console(s)
1305 printk(KERN_INFO
"console [%s%d] enabled, bootconsole disabled\n",
1306 newcon
->name
, newcon
->index
);
1307 for_each_console(bcon
)
1308 if (bcon
->flags
& CON_BOOT
)
1309 unregister_console(bcon
);
1311 printk(KERN_INFO
"%sconsole [%s%d] enabled\n",
1312 (newcon
->flags
& CON_BOOT
) ? "boot" : "" ,
1313 newcon
->name
, newcon
->index
);
1316 EXPORT_SYMBOL(register_console
);
1318 int unregister_console(struct console
*console
)
1320 struct console
*a
, *b
;
1323 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1324 if (console
->flags
& CON_BRL
)
1325 return braille_unregister_console(console
);
1328 acquire_console_sem();
1329 if (console_drivers
== console
) {
1330 console_drivers
=console
->next
;
1332 } else if (console_drivers
) {
1333 for (a
=console_drivers
->next
, b
=console_drivers
;
1334 a
; b
=a
, a
=b
->next
) {
1344 * If this isn't the last console and it has CON_CONSDEV set, we
1345 * need to set it on the next preferred console.
1347 if (console_drivers
!= NULL
&& console
->flags
& CON_CONSDEV
)
1348 console_drivers
->flags
|= CON_CONSDEV
;
1350 release_console_sem();
1353 EXPORT_SYMBOL(unregister_console
);
1355 static int __init
disable_boot_consoles(void)
1357 struct console
*con
;
1359 for_each_console(con
) {
1360 if (con
->flags
& CON_BOOT
) {
1361 printk(KERN_INFO
"turn off boot console %s%d\n",
1362 con
->name
, con
->index
);
1363 unregister_console(con
);
1368 late_initcall(disable_boot_consoles
);
1370 #if defined CONFIG_PRINTK
1373 * printk rate limiting, lifted from the networking subsystem.
1375 * This enforces a rate limit: not more than 10 kernel messages
1376 * every 5s to make a denial-of-service attack impossible.
1378 DEFINE_RATELIMIT_STATE(printk_ratelimit_state
, 5 * HZ
, 10);
1380 int printk_ratelimit(void)
1382 return __ratelimit(&printk_ratelimit_state
);
1384 EXPORT_SYMBOL(printk_ratelimit
);
1387 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1388 * @caller_jiffies: pointer to caller's state
1389 * @interval_msecs: minimum interval between prints
1391 * printk_timed_ratelimit() returns true if more than @interval_msecs
1392 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1395 bool printk_timed_ratelimit(unsigned long *caller_jiffies
,
1396 unsigned int interval_msecs
)
1398 if (*caller_jiffies
== 0
1399 || !time_in_range(jiffies
, *caller_jiffies
,
1401 + msecs_to_jiffies(interval_msecs
))) {
1402 *caller_jiffies
= jiffies
;
1407 EXPORT_SYMBOL(printk_timed_ratelimit
);