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>
37 #include <linux/kmsg_dump.h>
38 #include <linux/syslog.h>
40 #include <asm/uaccess.h>
43 * for_each_console() allows you to iterate on each console
45 #define for_each_console(con) \
46 for (con = console_drivers; con != NULL; con = con->next)
49 * Architectures can override it:
51 void asmlinkage
__attribute__((weak
)) early_printk(const char *fmt
, ...)
55 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
57 /* printk's without a loglevel use this.. */
58 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
60 /* We show everything that is MORE important than this.. */
61 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
62 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
64 DECLARE_WAIT_QUEUE_HEAD(log_wait
);
66 int console_printk
[4] = {
67 DEFAULT_CONSOLE_LOGLEVEL
, /* console_loglevel */
68 DEFAULT_MESSAGE_LOGLEVEL
, /* default_message_loglevel */
69 MINIMUM_CONSOLE_LOGLEVEL
, /* minimum_console_loglevel */
70 DEFAULT_CONSOLE_LOGLEVEL
, /* default_console_loglevel */
73 static int saved_console_loglevel
= -1;
76 * Low level drivers may need that to know if they can schedule in
77 * their unblank() callback or not. So let's export it.
80 EXPORT_SYMBOL(oops_in_progress
);
83 * console_sem protects the console_drivers list, and also
84 * provides serialisation for access to the entire console
87 static DECLARE_MUTEX(console_sem
);
88 struct console
*console_drivers
;
89 EXPORT_SYMBOL_GPL(console_drivers
);
92 * This is used for debugging the mess that is the VT code by
93 * keeping track if we have the console semaphore held. It's
94 * definitely not the perfect debug tool (we don't know if _WE_
95 * hold it are racing, but it helps tracking those weird code
96 * path in the console code where we end up in places I want
97 * locked without the console sempahore held
99 static int console_locked
, console_suspended
;
102 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
103 * It is also used in interesting ways to provide interlocking in
104 * release_console_sem().
106 static DEFINE_SPINLOCK(logbuf_lock
);
108 #define LOG_BUF_MASK (log_buf_len-1)
109 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
112 * The indices into log_buf are not constrained to log_buf_len - they
113 * must be masked before subscripting
115 static unsigned log_start
; /* Index into log_buf: next char to be read by syslog() */
116 static unsigned con_start
; /* Index into log_buf: next char to be sent to consoles */
117 static unsigned log_end
; /* Index into log_buf: most-recently-written-char + 1 */
120 * Array of consoles built from command line options (console=)
122 struct console_cmdline
124 char name
[8]; /* Name of the driver */
125 int index
; /* Minor dev. to use */
126 char *options
; /* Options for the driver */
127 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
128 char *brl_options
; /* Options for braille driver */
132 #define MAX_CMDLINECONSOLES 8
134 static struct console_cmdline console_cmdline
[MAX_CMDLINECONSOLES
];
135 static int selected_console
= -1;
136 static int preferred_console
= -1;
137 int console_set_on_cmdline
;
138 EXPORT_SYMBOL(console_set_on_cmdline
);
140 /* Flag: console code may call schedule() */
141 static int console_may_schedule
;
145 static char __log_buf
[__LOG_BUF_LEN
];
146 static char *log_buf
= __log_buf
;
147 static int log_buf_len
= __LOG_BUF_LEN
;
148 static unsigned logged_chars
; /* Number of chars produced since last read+clear operation */
152 * This appends the listed symbols to /proc/vmcoreinfo
154 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
155 * obtain access to symbols that are otherwise very difficult to locate. These
156 * symbols are specifically used so that utilities can access and extract the
157 * dmesg log from a vmcore file after a crash.
159 void log_buf_kexec_setup(void)
161 VMCOREINFO_SYMBOL(log_buf
);
162 VMCOREINFO_SYMBOL(log_end
);
163 VMCOREINFO_SYMBOL(log_buf_len
);
164 VMCOREINFO_SYMBOL(logged_chars
);
168 static int __init
log_buf_len_setup(char *str
)
170 unsigned size
= memparse(str
, &str
);
174 size
= roundup_pow_of_two(size
);
175 if (size
> log_buf_len
) {
176 unsigned start
, dest_idx
, offset
;
179 new_log_buf
= alloc_bootmem(size
);
181 printk(KERN_WARNING
"log_buf_len: allocation failed\n");
185 spin_lock_irqsave(&logbuf_lock
, flags
);
187 log_buf
= new_log_buf
;
189 offset
= start
= min(con_start
, log_start
);
191 while (start
!= log_end
) {
192 log_buf
[dest_idx
] = __log_buf
[start
& (__LOG_BUF_LEN
- 1)];
199 spin_unlock_irqrestore(&logbuf_lock
, flags
);
201 printk(KERN_NOTICE
"log_buf_len: %d\n", log_buf_len
);
207 __setup("log_buf_len=", log_buf_len_setup
);
209 #ifdef CONFIG_BOOT_PRINTK_DELAY
211 static unsigned int boot_delay
; /* msecs delay after each printk during bootup */
212 static unsigned long long loops_per_msec
; /* based on boot_delay */
214 static int __init
boot_delay_setup(char *str
)
218 lpj
= preset_lpj
? preset_lpj
: 1000000; /* some guess */
219 loops_per_msec
= (unsigned long long)lpj
/ 1000 * HZ
;
221 get_option(&str
, &boot_delay
);
222 if (boot_delay
> 10 * 1000)
225 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
226 "HZ: %d, loops_per_msec: %llu\n",
227 boot_delay
, preset_lpj
, lpj
, HZ
, loops_per_msec
);
230 __setup("boot_delay=", boot_delay_setup
);
232 static void boot_delay_msec(void)
234 unsigned long long k
;
235 unsigned long timeout
;
237 if (boot_delay
== 0 || system_state
!= SYSTEM_BOOTING
)
240 k
= (unsigned long long)loops_per_msec
* boot_delay
;
242 timeout
= jiffies
+ msecs_to_jiffies(boot_delay
);
247 * use (volatile) jiffies to prevent
248 * compiler reduction; loop termination via jiffies
249 * is secondary and may or may not happen.
251 if (time_after(jiffies
, timeout
))
253 touch_nmi_watchdog();
257 static inline void boot_delay_msec(void)
263 * Commands to do_syslog:
265 * 0 -- Close the log. Currently a NOP.
266 * 1 -- Open the log. Currently a NOP.
267 * 2 -- Read from the log.
268 * 3 -- Read all messages remaining in the ring buffer.
269 * 4 -- Read and clear all messages remaining in the ring buffer
270 * 5 -- Clear ring buffer.
271 * 6 -- Disable printk's to console
272 * 7 -- Enable printk's to console
273 * 8 -- Set level of messages printed to console
274 * 9 -- Return number of unread characters in the log buffer
275 * 10 -- Return size of the log buffer
277 int do_syslog(int type
, char __user
*buf
, int len
, bool from_file
)
279 unsigned i
, j
, limit
, count
;
284 error
= security_syslog(type
, from_file
);
289 case 0: /* Close log */
291 case 1: /* Open log */
293 case 2: /* Read from log */
300 if (!access_ok(VERIFY_WRITE
, buf
, len
)) {
304 error
= wait_event_interruptible(log_wait
,
305 (log_start
- log_end
));
309 spin_lock_irq(&logbuf_lock
);
310 while (!error
&& (log_start
!= log_end
) && i
< len
) {
311 c
= LOG_BUF(log_start
);
313 spin_unlock_irq(&logbuf_lock
);
314 error
= __put_user(c
,buf
);
318 spin_lock_irq(&logbuf_lock
);
320 spin_unlock_irq(&logbuf_lock
);
324 case 4: /* Read/clear last kernel messages */
327 case 3: /* Read last kernel messages */
334 if (!access_ok(VERIFY_WRITE
, buf
, len
)) {
339 if (count
> log_buf_len
)
341 spin_lock_irq(&logbuf_lock
);
342 if (count
> logged_chars
)
343 count
= logged_chars
;
348 * __put_user() could sleep, and while we sleep
349 * printk() could overwrite the messages
350 * we try to copy to user space. Therefore
351 * the messages are copied in reverse. <manfreds>
353 for (i
= 0; i
< count
&& !error
; i
++) {
355 if (j
+ log_buf_len
< log_end
)
358 spin_unlock_irq(&logbuf_lock
);
359 error
= __put_user(c
,&buf
[count
-1-i
]);
361 spin_lock_irq(&logbuf_lock
);
363 spin_unlock_irq(&logbuf_lock
);
368 int offset
= count
-error
;
369 /* buffer overflow during copy, correct user buffer. */
370 for (i
= 0; i
< error
; i
++) {
371 if (__get_user(c
,&buf
[i
+offset
]) ||
372 __put_user(c
,&buf
[i
])) {
380 case 5: /* Clear ring buffer */
383 case 6: /* Disable logging to console */
384 if (saved_console_loglevel
== -1)
385 saved_console_loglevel
= console_loglevel
;
386 console_loglevel
= minimum_console_loglevel
;
388 case 7: /* Enable logging to console */
389 if (saved_console_loglevel
!= -1) {
390 console_loglevel
= saved_console_loglevel
;
391 saved_console_loglevel
= -1;
394 case 8: /* Set level of messages printed to console */
396 if (len
< 1 || len
> 8)
398 if (len
< minimum_console_loglevel
)
399 len
= minimum_console_loglevel
;
400 console_loglevel
= len
;
401 /* Implicitly re-enable logging to console */
402 saved_console_loglevel
= -1;
405 case 9: /* Number of chars in the log buffer */
406 error
= log_end
- log_start
;
408 case 10: /* Size of the log buffer */
419 SYSCALL_DEFINE3(syslog
, int, type
, char __user
*, buf
, int, len
)
421 return do_syslog(type
, buf
, len
, SYSLOG_FROM_CALL
);
425 * Call the console drivers on a range of log_buf
427 static void __call_console_drivers(unsigned start
, unsigned end
)
431 for_each_console(con
) {
432 if ((con
->flags
& CON_ENABLED
) && con
->write
&&
433 (cpu_online(smp_processor_id()) ||
434 (con
->flags
& CON_ANYTIME
)))
435 con
->write(con
, &LOG_BUF(start
), end
- start
);
439 static int __read_mostly ignore_loglevel
;
441 static int __init
ignore_loglevel_setup(char *str
)
444 printk(KERN_INFO
"debug: ignoring loglevel setting.\n");
449 early_param("ignore_loglevel", ignore_loglevel_setup
);
452 * Write out chars from start to end - 1 inclusive
454 static void _call_console_drivers(unsigned start
,
455 unsigned end
, int msg_log_level
)
457 if ((msg_log_level
< console_loglevel
|| ignore_loglevel
) &&
458 console_drivers
&& start
!= end
) {
459 if ((start
& LOG_BUF_MASK
) > (end
& LOG_BUF_MASK
)) {
461 __call_console_drivers(start
& LOG_BUF_MASK
,
463 __call_console_drivers(0, end
& LOG_BUF_MASK
);
465 __call_console_drivers(start
, end
);
471 * Call the console drivers, asking them to write out
472 * log_buf[start] to log_buf[end - 1].
473 * The console_sem must be held.
475 static void call_console_drivers(unsigned start
, unsigned end
)
477 unsigned cur_index
, start_print
;
478 static int msg_level
= -1;
480 BUG_ON(((int)(start
- end
)) > 0);
484 while (cur_index
!= end
) {
485 if (msg_level
< 0 && ((end
- cur_index
) > 2) &&
486 LOG_BUF(cur_index
+ 0) == '<' &&
487 LOG_BUF(cur_index
+ 1) >= '0' &&
488 LOG_BUF(cur_index
+ 1) <= '7' &&
489 LOG_BUF(cur_index
+ 2) == '>') {
490 msg_level
= LOG_BUF(cur_index
+ 1) - '0';
492 start_print
= cur_index
;
494 while (cur_index
!= end
) {
495 char c
= LOG_BUF(cur_index
);
501 * printk() has already given us loglevel tags in
502 * the buffer. This code is here in case the
503 * log buffer has wrapped right round and scribbled
506 msg_level
= default_message_loglevel
;
508 _call_console_drivers(start_print
, cur_index
, msg_level
);
510 start_print
= cur_index
;
515 _call_console_drivers(start_print
, end
, msg_level
);
518 static void emit_log_char(char c
)
520 LOG_BUF(log_end
) = c
;
522 if (log_end
- log_start
> log_buf_len
)
523 log_start
= log_end
- log_buf_len
;
524 if (log_end
- con_start
> log_buf_len
)
525 con_start
= log_end
- log_buf_len
;
526 if (logged_chars
< log_buf_len
)
531 * Zap console related locks when oopsing. Only zap at most once
532 * every 10 seconds, to leave time for slow consoles to print a
535 static void zap_locks(void)
537 static unsigned long oops_timestamp
;
539 if (time_after_eq(jiffies
, oops_timestamp
) &&
540 !time_after(jiffies
, oops_timestamp
+ 30 * HZ
))
543 oops_timestamp
= jiffies
;
545 /* If a crash is occurring, make sure we can't deadlock */
546 spin_lock_init(&logbuf_lock
);
547 /* And make sure that we print immediately */
548 init_MUTEX(&console_sem
);
551 #if defined(CONFIG_PRINTK_TIME)
552 static int printk_time
= 1;
554 static int printk_time
= 0;
556 module_param_named(time
, printk_time
, bool, S_IRUGO
| S_IWUSR
);
558 /* Check if we have any console registered that can be called early in boot. */
559 static int have_callable_console(void)
563 for_each_console(con
)
564 if (con
->flags
& CON_ANYTIME
)
571 * printk - print a kernel message
572 * @fmt: format string
574 * This is printk(). It can be called from any context. We want it to work.
576 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
577 * call the console drivers. If we fail to get the semaphore we place the output
578 * into the log buffer and return. The current holder of the console_sem will
579 * notice the new output in release_console_sem() and will send it to the
580 * consoles before releasing the semaphore.
582 * One effect of this deferred printing is that code which calls printk() and
583 * then changes console_loglevel may break. This is because console_loglevel
584 * is inspected when the actual printing occurs.
589 * See the vsnprintf() documentation for format string extensions over C99.
592 asmlinkage
int printk(const char *fmt
, ...)
598 r
= vprintk(fmt
, args
);
604 /* cpu currently holding logbuf_lock */
605 static volatile unsigned int printk_cpu
= UINT_MAX
;
608 * Can we actually use the console at this time on this cpu?
610 * Console drivers may assume that per-cpu resources have
611 * been allocated. So unless they're explicitly marked as
612 * being able to cope (CON_ANYTIME) don't call them until
613 * this CPU is officially up.
615 static inline int can_use_console(unsigned int cpu
)
617 return cpu_online(cpu
) || have_callable_console();
621 * Try to get console ownership to actually show the kernel
622 * messages from a 'printk'. Return true (and with the
623 * console_semaphore held, and 'console_locked' set) if it
624 * is successful, false otherwise.
626 * This gets called with the 'logbuf_lock' spinlock held and
627 * interrupts disabled. It should return with 'lockbuf_lock'
628 * released but interrupts still disabled.
630 static int acquire_console_semaphore_for_printk(unsigned int cpu
)
634 if (!try_acquire_console_sem()) {
638 * If we can't use the console, we need to release
639 * the console semaphore by hand to avoid flushing
640 * the buffer. We need to hold the console semaphore
641 * in order to do this test safely.
643 if (!can_use_console(cpu
)) {
649 printk_cpu
= UINT_MAX
;
650 spin_unlock(&logbuf_lock
);
653 static const char recursion_bug_msg
[] =
654 KERN_CRIT
"BUG: recent printk recursion!\n";
655 static int recursion_bug
;
656 static int new_text_line
= 1;
657 static char printk_buf
[1024];
659 int printk_delay_msec __read_mostly
;
661 static inline void printk_delay(void)
663 if (unlikely(printk_delay_msec
)) {
664 int m
= printk_delay_msec
;
668 touch_nmi_watchdog();
673 asmlinkage
int vprintk(const char *fmt
, va_list args
)
676 int current_log_level
= default_message_loglevel
;
685 /* This stops the holder of console_sem just where we want him */
686 raw_local_irq_save(flags
);
687 this_cpu
= smp_processor_id();
690 * Ouch, printk recursed into itself!
692 if (unlikely(printk_cpu
== this_cpu
)) {
694 * If a crash is occurring during printk() on this CPU,
695 * then try to get the crash message out but make sure
696 * we can't deadlock. Otherwise just return to avoid the
697 * recursion and return - but flag the recursion so that
698 * it can be printed at the next appropriate moment:
700 if (!oops_in_progress
) {
702 goto out_restore_irqs
;
708 spin_lock(&logbuf_lock
);
709 printk_cpu
= this_cpu
;
713 strcpy(printk_buf
, recursion_bug_msg
);
714 printed_len
= strlen(recursion_bug_msg
);
716 /* Emit the output into the temporary buffer */
717 printed_len
+= vscnprintf(printk_buf
+ printed_len
,
718 sizeof(printk_buf
) - printed_len
, fmt
, args
);
723 /* Do we have a loglevel in the string? */
725 unsigned char c
= p
[1];
726 if (c
&& p
[2] == '>') {
728 case '0' ... '7': /* loglevel */
729 current_log_level
= c
- '0';
730 /* Fallthrough - make sure we're on a new line */
731 case 'd': /* KERN_DEFAULT */
732 if (!new_text_line
) {
736 /* Fallthrough - skip the loglevel */
737 case 'c': /* KERN_CONT */
745 * Copy the output into log_buf. If the caller didn't provide
746 * appropriate log level tags, we insert them here
750 /* Always output the token */
752 emit_log_char(current_log_level
+ '0');
758 /* Follow the token with the time */
761 unsigned long long t
;
762 unsigned long nanosec_rem
;
764 t
= cpu_clock(printk_cpu
);
765 nanosec_rem
= do_div(t
, 1000000000);
766 tlen
= sprintf(tbuf
, "[%5lu.%06lu] ",
770 for (tp
= tbuf
; tp
< tbuf
+ tlen
; tp
++)
785 * Try to acquire and then immediately release the
786 * console semaphore. The release will do all the
787 * actual magic (print out buffers, wake up klogd,
790 * The acquire_console_semaphore_for_printk() function
791 * will release 'logbuf_lock' regardless of whether it
792 * actually gets the semaphore or not.
794 if (acquire_console_semaphore_for_printk(this_cpu
))
795 release_console_sem();
799 raw_local_irq_restore(flags
);
804 EXPORT_SYMBOL(printk
);
805 EXPORT_SYMBOL(vprintk
);
809 static void call_console_drivers(unsigned start
, unsigned end
)
815 static int __add_preferred_console(char *name
, int idx
, char *options
,
818 struct console_cmdline
*c
;
822 * See if this tty is not yet registered, and
823 * if we have a slot free.
825 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++)
826 if (strcmp(console_cmdline
[i
].name
, name
) == 0 &&
827 console_cmdline
[i
].index
== idx
) {
829 selected_console
= i
;
832 if (i
== MAX_CMDLINECONSOLES
)
835 selected_console
= i
;
836 c
= &console_cmdline
[i
];
837 strlcpy(c
->name
, name
, sizeof(c
->name
));
838 c
->options
= options
;
839 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
840 c
->brl_options
= brl_options
;
846 * Set up a list of consoles. Called from init/main.c
848 static int __init
console_setup(char *str
)
850 char buf
[sizeof(console_cmdline
[0].name
) + 4]; /* 4 for index */
851 char *s
, *options
, *brl_options
= NULL
;
854 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
855 if (!memcmp(str
, "brl,", 4)) {
858 } else if (!memcmp(str
, "brl=", 4)) {
859 brl_options
= str
+ 4;
860 str
= strchr(brl_options
, ',');
862 printk(KERN_ERR
"need port name after brl=\n");
870 * Decode str into name, index, options.
872 if (str
[0] >= '0' && str
[0] <= '9') {
874 strncpy(buf
+ 4, str
, sizeof(buf
) - 5);
876 strncpy(buf
, str
, sizeof(buf
) - 1);
878 buf
[sizeof(buf
) - 1] = 0;
879 if ((options
= strchr(str
, ',')) != NULL
)
882 if (!strcmp(str
, "ttya"))
883 strcpy(buf
, "ttyS0");
884 if (!strcmp(str
, "ttyb"))
885 strcpy(buf
, "ttyS1");
887 for (s
= buf
; *s
; s
++)
888 if ((*s
>= '0' && *s
<= '9') || *s
== ',')
890 idx
= simple_strtoul(s
, NULL
, 10);
893 __add_preferred_console(buf
, idx
, options
, brl_options
);
894 console_set_on_cmdline
= 1;
897 __setup("console=", console_setup
);
900 * add_preferred_console - add a device to the list of preferred consoles.
903 * @options: options for this console
905 * The last preferred console added will be used for kernel messages
906 * and stdin/out/err for init. Normally this is used by console_setup
907 * above to handle user-supplied console arguments; however it can also
908 * be used by arch-specific code either to override the user or more
909 * commonly to provide a default console (ie from PROM variables) when
910 * the user has not supplied one.
912 int add_preferred_console(char *name
, int idx
, char *options
)
914 return __add_preferred_console(name
, idx
, options
, NULL
);
917 int update_console_cmdline(char *name
, int idx
, char *name_new
, int idx_new
, char *options
)
919 struct console_cmdline
*c
;
922 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++)
923 if (strcmp(console_cmdline
[i
].name
, name
) == 0 &&
924 console_cmdline
[i
].index
== idx
) {
925 c
= &console_cmdline
[i
];
926 strlcpy(c
->name
, name_new
, sizeof(c
->name
));
927 c
->name
[sizeof(c
->name
) - 1] = 0;
928 c
->options
= options
;
936 int console_suspend_enabled
= 1;
937 EXPORT_SYMBOL(console_suspend_enabled
);
939 static int __init
console_suspend_disable(char *str
)
941 console_suspend_enabled
= 0;
944 __setup("no_console_suspend", console_suspend_disable
);
947 * suspend_console - suspend the console subsystem
949 * This disables printk() while we go into suspend states
951 void suspend_console(void)
953 if (!console_suspend_enabled
)
955 printk("Suspending console(s) (use no_console_suspend to debug)\n");
956 acquire_console_sem();
957 console_suspended
= 1;
961 void resume_console(void)
963 if (!console_suspend_enabled
)
966 console_suspended
= 0;
967 release_console_sem();
971 * acquire_console_sem - lock the console system for exclusive use.
973 * Acquires a semaphore which guarantees that the caller has
974 * exclusive access to the console system and the console_drivers list.
976 * Can sleep, returns nothing.
978 void acquire_console_sem(void)
980 BUG_ON(in_interrupt());
982 if (console_suspended
)
985 console_may_schedule
= 1;
987 EXPORT_SYMBOL(acquire_console_sem
);
989 int try_acquire_console_sem(void)
991 if (down_trylock(&console_sem
))
993 if (console_suspended
) {
998 console_may_schedule
= 0;
1001 EXPORT_SYMBOL(try_acquire_console_sem
);
1003 int is_console_locked(void)
1005 return console_locked
;
1008 static DEFINE_PER_CPU(int, printk_pending
);
1010 void printk_tick(void)
1012 if (__get_cpu_var(printk_pending
)) {
1013 __get_cpu_var(printk_pending
) = 0;
1014 wake_up_interruptible(&log_wait
);
1018 int printk_needs_cpu(int cpu
)
1020 return per_cpu(printk_pending
, cpu
);
1023 void wake_up_klogd(void)
1025 if (waitqueue_active(&log_wait
))
1026 __raw_get_cpu_var(printk_pending
) = 1;
1030 * release_console_sem - unlock the console system
1032 * Releases the semaphore which the caller holds on the console system
1033 * and the console driver list.
1035 * While the semaphore was held, console output may have been buffered
1036 * by printk(). If this is the case, release_console_sem() emits
1037 * the output prior to releasing the semaphore.
1039 * If there is output waiting for klogd, we wake it up.
1041 * release_console_sem() may be called from any context.
1043 void release_console_sem(void)
1045 unsigned long flags
;
1046 unsigned _con_start
, _log_end
;
1047 unsigned wake_klogd
= 0;
1049 if (console_suspended
) {
1054 console_may_schedule
= 0;
1057 spin_lock_irqsave(&logbuf_lock
, flags
);
1058 wake_klogd
|= log_start
- log_end
;
1059 if (con_start
== log_end
)
1060 break; /* Nothing to print */
1061 _con_start
= con_start
;
1063 con_start
= log_end
; /* Flush */
1064 spin_unlock(&logbuf_lock
);
1065 stop_critical_timings(); /* don't trace print latency */
1066 call_console_drivers(_con_start
, _log_end
);
1067 start_critical_timings();
1068 local_irq_restore(flags
);
1072 spin_unlock_irqrestore(&logbuf_lock
, flags
);
1076 EXPORT_SYMBOL(release_console_sem
);
1079 * console_conditional_schedule - yield the CPU if required
1081 * If the console code is currently allowed to sleep, and
1082 * if this CPU should yield the CPU to another task, do
1085 * Must be called within acquire_console_sem().
1087 void __sched
console_conditional_schedule(void)
1089 if (console_may_schedule
)
1092 EXPORT_SYMBOL(console_conditional_schedule
);
1094 void console_unblank(void)
1099 * console_unblank can no longer be called in interrupt context unless
1100 * oops_in_progress is set to 1..
1102 if (oops_in_progress
) {
1103 if (down_trylock(&console_sem
) != 0)
1106 acquire_console_sem();
1109 console_may_schedule
= 0;
1111 if ((c
->flags
& CON_ENABLED
) && c
->unblank
)
1113 release_console_sem();
1117 * Return the console tty driver structure and its associated index
1119 struct tty_driver
*console_device(int *index
)
1122 struct tty_driver
*driver
= NULL
;
1124 acquire_console_sem();
1125 for_each_console(c
) {
1128 driver
= c
->device(c
, index
);
1132 release_console_sem();
1137 * Prevent further output on the passed console device so that (for example)
1138 * serial drivers can disable console output before suspending a port, and can
1139 * re-enable output afterwards.
1141 void console_stop(struct console
*console
)
1143 acquire_console_sem();
1144 console
->flags
&= ~CON_ENABLED
;
1145 release_console_sem();
1147 EXPORT_SYMBOL(console_stop
);
1149 void console_start(struct console
*console
)
1151 acquire_console_sem();
1152 console
->flags
|= CON_ENABLED
;
1153 release_console_sem();
1155 EXPORT_SYMBOL(console_start
);
1158 * The console driver calls this routine during kernel initialization
1159 * to register the console printing procedure with printk() and to
1160 * print any messages that were printed by the kernel before the
1161 * console driver was initialized.
1163 * This can happen pretty early during the boot process (because of
1164 * early_printk) - sometimes before setup_arch() completes - be careful
1165 * of what kernel features are used - they may not be initialised yet.
1167 * There are two types of consoles - bootconsoles (early_printk) and
1168 * "real" consoles (everything which is not a bootconsole) which are
1169 * handled differently.
1170 * - Any number of bootconsoles can be registered at any time.
1171 * - As soon as a "real" console is registered, all bootconsoles
1172 * will be unregistered automatically.
1173 * - Once a "real" console is registered, any attempt to register a
1174 * bootconsoles will be rejected
1176 void register_console(struct console
*newcon
)
1179 unsigned long flags
;
1180 struct console
*bcon
= NULL
;
1183 * before we register a new CON_BOOT console, make sure we don't
1184 * already have a valid console
1186 if (console_drivers
&& newcon
->flags
& CON_BOOT
) {
1187 /* find the last or real console */
1188 for_each_console(bcon
) {
1189 if (!(bcon
->flags
& CON_BOOT
)) {
1190 printk(KERN_INFO
"Too late to register bootconsole %s%d\n",
1191 newcon
->name
, newcon
->index
);
1197 if (console_drivers
&& console_drivers
->flags
& CON_BOOT
)
1198 bcon
= console_drivers
;
1200 if (preferred_console
< 0 || bcon
|| !console_drivers
)
1201 preferred_console
= selected_console
;
1203 if (newcon
->early_setup
)
1204 newcon
->early_setup();
1207 * See if we want to use this console driver. If we
1208 * didn't select a console we take the first one
1209 * that registers here.
1211 if (preferred_console
< 0) {
1212 if (newcon
->index
< 0)
1214 if (newcon
->setup
== NULL
||
1215 newcon
->setup(newcon
, NULL
) == 0) {
1216 newcon
->flags
|= CON_ENABLED
;
1217 if (newcon
->device
) {
1218 newcon
->flags
|= CON_CONSDEV
;
1219 preferred_console
= 0;
1225 * See if this console matches one we selected on
1228 for (i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0];
1230 if (strcmp(console_cmdline
[i
].name
, newcon
->name
) != 0)
1232 if (newcon
->index
>= 0 &&
1233 newcon
->index
!= console_cmdline
[i
].index
)
1235 if (newcon
->index
< 0)
1236 newcon
->index
= console_cmdline
[i
].index
;
1237 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1238 if (console_cmdline
[i
].brl_options
) {
1239 newcon
->flags
|= CON_BRL
;
1240 braille_register_console(newcon
,
1241 console_cmdline
[i
].index
,
1242 console_cmdline
[i
].options
,
1243 console_cmdline
[i
].brl_options
);
1247 if (newcon
->setup
&&
1248 newcon
->setup(newcon
, console_cmdline
[i
].options
) != 0)
1250 newcon
->flags
|= CON_ENABLED
;
1251 newcon
->index
= console_cmdline
[i
].index
;
1252 if (i
== selected_console
) {
1253 newcon
->flags
|= CON_CONSDEV
;
1254 preferred_console
= selected_console
;
1259 if (!(newcon
->flags
& CON_ENABLED
))
1263 * If we have a bootconsole, and are switching to a real console,
1264 * don't print everything out again, since when the boot console, and
1265 * the real console are the same physical device, it's annoying to
1266 * see the beginning boot messages twice
1268 if (bcon
&& ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
))
1269 newcon
->flags
&= ~CON_PRINTBUFFER
;
1272 * Put this console in the list - keep the
1273 * preferred driver at the head of the list.
1275 acquire_console_sem();
1276 if ((newcon
->flags
& CON_CONSDEV
) || console_drivers
== NULL
) {
1277 newcon
->next
= console_drivers
;
1278 console_drivers
= newcon
;
1280 newcon
->next
->flags
&= ~CON_CONSDEV
;
1282 newcon
->next
= console_drivers
->next
;
1283 console_drivers
->next
= newcon
;
1285 if (newcon
->flags
& CON_PRINTBUFFER
) {
1287 * release_console_sem() will print out the buffered messages
1290 spin_lock_irqsave(&logbuf_lock
, flags
);
1291 con_start
= log_start
;
1292 spin_unlock_irqrestore(&logbuf_lock
, flags
);
1294 release_console_sem();
1297 * By unregistering the bootconsoles after we enable the real console
1298 * we get the "console xxx enabled" message on all the consoles -
1299 * boot consoles, real consoles, etc - this is to ensure that end
1300 * users know there might be something in the kernel's log buffer that
1301 * went to the bootconsole (that they do not see on the real console)
1303 if (bcon
&& ((newcon
->flags
& (CON_CONSDEV
| CON_BOOT
)) == CON_CONSDEV
)) {
1304 /* we need to iterate through twice, to make sure we print
1305 * everything out, before we unregister the console(s)
1307 printk(KERN_INFO
"console [%s%d] enabled, bootconsole disabled\n",
1308 newcon
->name
, newcon
->index
);
1309 for_each_console(bcon
)
1310 if (bcon
->flags
& CON_BOOT
)
1311 unregister_console(bcon
);
1313 printk(KERN_INFO
"%sconsole [%s%d] enabled\n",
1314 (newcon
->flags
& CON_BOOT
) ? "boot" : "" ,
1315 newcon
->name
, newcon
->index
);
1318 EXPORT_SYMBOL(register_console
);
1320 int unregister_console(struct console
*console
)
1322 struct console
*a
, *b
;
1325 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1326 if (console
->flags
& CON_BRL
)
1327 return braille_unregister_console(console
);
1330 acquire_console_sem();
1331 if (console_drivers
== console
) {
1332 console_drivers
=console
->next
;
1334 } else if (console_drivers
) {
1335 for (a
=console_drivers
->next
, b
=console_drivers
;
1336 a
; b
=a
, a
=b
->next
) {
1346 * If this isn't the last console and it has CON_CONSDEV set, we
1347 * need to set it on the next preferred console.
1349 if (console_drivers
!= NULL
&& console
->flags
& CON_CONSDEV
)
1350 console_drivers
->flags
|= CON_CONSDEV
;
1352 release_console_sem();
1355 EXPORT_SYMBOL(unregister_console
);
1357 static int __init
disable_boot_consoles(void)
1359 struct console
*con
;
1361 for_each_console(con
) {
1362 if (con
->flags
& CON_BOOT
) {
1363 printk(KERN_INFO
"turn off boot console %s%d\n",
1364 con
->name
, con
->index
);
1365 unregister_console(con
);
1370 late_initcall(disable_boot_consoles
);
1372 #if defined CONFIG_PRINTK
1375 * printk rate limiting, lifted from the networking subsystem.
1377 * This enforces a rate limit: not more than 10 kernel messages
1378 * every 5s to make a denial-of-service attack impossible.
1380 DEFINE_RATELIMIT_STATE(printk_ratelimit_state
, 5 * HZ
, 10);
1382 int __printk_ratelimit(const char *func
)
1384 return ___ratelimit(&printk_ratelimit_state
, func
);
1386 EXPORT_SYMBOL(__printk_ratelimit
);
1389 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1390 * @caller_jiffies: pointer to caller's state
1391 * @interval_msecs: minimum interval between prints
1393 * printk_timed_ratelimit() returns true if more than @interval_msecs
1394 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1397 bool printk_timed_ratelimit(unsigned long *caller_jiffies
,
1398 unsigned int interval_msecs
)
1400 if (*caller_jiffies
== 0
1401 || !time_in_range(jiffies
, *caller_jiffies
,
1403 + msecs_to_jiffies(interval_msecs
))) {
1404 *caller_jiffies
= jiffies
;
1409 EXPORT_SYMBOL(printk_timed_ratelimit
);
1411 static DEFINE_SPINLOCK(dump_list_lock
);
1412 static LIST_HEAD(dump_list
);
1415 * kmsg_dump_register - register a kernel log dumper.
1416 * @dumper: pointer to the kmsg_dumper structure
1418 * Adds a kernel log dumper to the system. The dump callback in the
1419 * structure will be called when the kernel oopses or panics and must be
1420 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1422 int kmsg_dump_register(struct kmsg_dumper
*dumper
)
1424 unsigned long flags
;
1427 /* The dump callback needs to be set */
1431 spin_lock_irqsave(&dump_list_lock
, flags
);
1432 /* Don't allow registering multiple times */
1433 if (!dumper
->registered
) {
1434 dumper
->registered
= 1;
1435 list_add_tail(&dumper
->list
, &dump_list
);
1438 spin_unlock_irqrestore(&dump_list_lock
, flags
);
1442 EXPORT_SYMBOL_GPL(kmsg_dump_register
);
1445 * kmsg_dump_unregister - unregister a kmsg dumper.
1446 * @dumper: pointer to the kmsg_dumper structure
1448 * Removes a dump device from the system. Returns zero on success and
1449 * %-EINVAL otherwise.
1451 int kmsg_dump_unregister(struct kmsg_dumper
*dumper
)
1453 unsigned long flags
;
1456 spin_lock_irqsave(&dump_list_lock
, flags
);
1457 if (dumper
->registered
) {
1458 dumper
->registered
= 0;
1459 list_del(&dumper
->list
);
1462 spin_unlock_irqrestore(&dump_list_lock
, flags
);
1466 EXPORT_SYMBOL_GPL(kmsg_dump_unregister
);
1468 static const char const *kmsg_reasons
[] = {
1469 [KMSG_DUMP_OOPS
] = "oops",
1470 [KMSG_DUMP_PANIC
] = "panic",
1473 static const char *kmsg_to_str(enum kmsg_dump_reason reason
)
1475 if (reason
>= ARRAY_SIZE(kmsg_reasons
) || reason
< 0)
1478 return kmsg_reasons
[reason
];
1482 * kmsg_dump - dump kernel log to kernel message dumpers.
1483 * @reason: the reason (oops, panic etc) for dumping
1485 * Iterate through each of the dump devices and call the oops/panic
1486 * callbacks with the log buffer.
1488 void kmsg_dump(enum kmsg_dump_reason reason
)
1492 struct kmsg_dumper
*dumper
;
1493 const char *s1
, *s2
;
1494 unsigned long l1
, l2
;
1495 unsigned long flags
;
1497 /* Theoretically, the log could move on after we do this, but
1498 there's not a lot we can do about that. The new messages
1499 will overwrite the start of what we dump. */
1500 spin_lock_irqsave(&logbuf_lock
, flags
);
1501 end
= log_end
& LOG_BUF_MASK
;
1502 chars
= logged_chars
;
1503 spin_unlock_irqrestore(&logbuf_lock
, flags
);
1505 if (logged_chars
> end
) {
1506 s1
= log_buf
+ log_buf_len
- logged_chars
+ end
;
1507 l1
= logged_chars
- end
;
1515 s2
= log_buf
+ end
- logged_chars
;
1519 if (!spin_trylock_irqsave(&dump_list_lock
, flags
)) {
1520 printk(KERN_ERR
"dump_kmsg: dump list lock is held during %s, skipping dump\n",
1521 kmsg_to_str(reason
));
1524 list_for_each_entry(dumper
, &dump_list
, list
)
1525 dumper
->dump(dumper
, reason
, s1
, l1
, s2
, l2
);
1526 spin_unlock_irqrestore(&dump_list_lock
, flags
);