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 * manfreds@colorfullife.com
15 * Rewrote bits to get rid of console_lock
16 * 01Mar01 Andrew Morton <andrewm@uow.edu.au>
19 #include <linux/kernel.h>
21 #include <linux/tty.h>
22 #include <linux/tty_driver.h>
23 #include <linux/smp_lock.h>
24 #include <linux/console.h>
25 #include <linux/init.h>
26 #include <linux/module.h>
27 #include <linux/interrupt.h> /* For in_interrupt() */
28 #include <linux/config.h>
29 #include <linux/delay.h>
30 #include <linux/smp.h>
31 #include <linux/security.h>
33 #include <asm/uaccess.h>
35 #define LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
36 #define LOG_BUF_MASK (LOG_BUF_LEN-1)
38 /* printk's without a loglevel use this.. */
39 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
41 /* We show everything that is MORE important than this.. */
42 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
43 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
45 DECLARE_WAIT_QUEUE_HEAD(log_wait
);
47 int console_printk
[4] = {
48 DEFAULT_CONSOLE_LOGLEVEL
, /* console_loglevel */
49 DEFAULT_MESSAGE_LOGLEVEL
, /* default_message_loglevel */
50 MINIMUM_CONSOLE_LOGLEVEL
, /* minimum_console_loglevel */
51 DEFAULT_CONSOLE_LOGLEVEL
, /* default_console_loglevel */
57 * console_sem protects the console_drivers list, and also
58 * provides serialisation for access to the entire console
61 static DECLARE_MUTEX(console_sem
);
62 struct console
*console_drivers
;
65 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
66 * It is also used in interesting ways to provide interlocking in
67 * release_console_sem().
69 static spinlock_t logbuf_lock
= SPIN_LOCK_UNLOCKED
;
71 static char log_buf
[LOG_BUF_LEN
];
72 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
75 * The indices into log_buf are not constrained to LOG_BUF_LEN - they
76 * must be masked before subscripting
78 static unsigned long log_start
; /* Index into log_buf: next char to be read by syslog() */
79 static unsigned long con_start
; /* Index into log_buf: next char to be sent to consoles */
80 static unsigned long log_end
; /* Index into log_buf: most-recently-written-char + 1 */
81 static unsigned long logged_chars
; /* Number of chars produced since last read+clear operation */
83 struct console_cmdline console_cmdline
[MAX_CMDLINECONSOLES
];
84 static int preferred_console
= -1;
86 /* Flag: console code may call schedule() */
87 static int console_may_schedule
;
90 * Setup a list of consoles. Called from init/main.c
92 static int __init
console_setup(char *str
)
94 struct console_cmdline
*c
;
95 char name
[sizeof(c
->name
)];
100 * Decode str into name, index, options.
102 if (str
[0] >= '0' && str
[0] <= '9') {
103 strcpy(name
, "ttyS");
104 strncpy(name
+ 4, str
, sizeof(name
) - 5);
106 strncpy(name
, str
, sizeof(name
) - 1);
107 name
[sizeof(name
) - 1] = 0;
108 if ((options
= strchr(str
, ',')) != NULL
)
111 if (!strcmp(str
, "ttya"))
112 strcpy(name
, "ttyS0");
113 if (!strcmp(str
, "ttyb"))
114 strcpy(name
, "ttyS1");
116 for(s
= name
; *s
; s
++)
117 if (*s
>= '0' && *s
<= '9')
119 idx
= simple_strtoul(s
, NULL
, 10);
123 * See if this tty is not yet registered, and
124 * if we have a slot free.
126 for(i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++)
127 if (strcmp(console_cmdline
[i
].name
, name
) == 0 &&
128 console_cmdline
[i
].index
== idx
) {
129 preferred_console
= i
;
132 if (i
== MAX_CMDLINECONSOLES
)
134 preferred_console
= i
;
135 c
= &console_cmdline
[i
];
136 memcpy(c
->name
, name
, sizeof(c
->name
));
137 c
->options
= options
;
142 __setup("console=", console_setup
);
145 * Commands to do_syslog:
147 * 0 -- Close the log. Currently a NOP.
148 * 1 -- Open the log. Currently a NOP.
149 * 2 -- Read from the log.
150 * 3 -- Read all messages remaining in the ring buffer.
151 * 4 -- Read and clear all messages remaining in the ring buffer
152 * 5 -- Clear ring buffer.
153 * 6 -- Disable printk's to console
154 * 7 -- Enable printk's to console
155 * 8 -- Set level of messages printed to console
156 * 9 -- Return number of unread characters in the log buffer
158 int do_syslog(int type
, char __user
* buf
, int len
)
160 unsigned long i
, j
, limit
, count
;
165 error
= security_syslog(type
);
170 case 0: /* Close log */
172 case 1: /* Open log */
174 case 2: /* Read from log */
181 error
= verify_area(VERIFY_WRITE
,buf
,len
);
184 error
= wait_event_interruptible(log_wait
, (log_start
- log_end
));
188 spin_lock_irq(&logbuf_lock
);
189 while (!error
&& (log_start
!= log_end
) && i
< len
) {
190 c
= LOG_BUF(log_start
);
192 spin_unlock_irq(&logbuf_lock
);
193 error
= __put_user(c
,buf
);
196 spin_lock_irq(&logbuf_lock
);
198 spin_unlock_irq(&logbuf_lock
);
202 case 4: /* Read/clear last kernel messages */
205 case 3: /* Read last kernel messages */
212 error
= verify_area(VERIFY_WRITE
,buf
,len
);
216 if (count
> LOG_BUF_LEN
)
218 spin_lock_irq(&logbuf_lock
);
219 if (count
> logged_chars
)
220 count
= logged_chars
;
225 * __put_user() could sleep, and while we sleep
226 * printk() could overwrite the messages
227 * we try to copy to user space. Therefore
228 * the messages are copied in reverse. <manfreds>
230 for(i
= 0; i
< count
&& !error
; i
++) {
232 if (j
+LOG_BUF_LEN
< log_end
)
235 spin_unlock_irq(&logbuf_lock
);
236 error
= __put_user(c
,&buf
[count
-1-i
]);
237 spin_lock_irq(&logbuf_lock
);
239 spin_unlock_irq(&logbuf_lock
);
244 int offset
= count
-error
;
245 /* buffer overflow during copy, correct user buffer. */
246 for(i
=0;i
<error
;i
++) {
247 if (__get_user(c
,&buf
[i
+offset
]) ||
248 __put_user(c
,&buf
[i
])) {
255 case 5: /* Clear ring buffer */
258 case 6: /* Disable logging to console */
259 console_loglevel
= minimum_console_loglevel
;
261 case 7: /* Enable logging to console */
262 console_loglevel
= default_console_loglevel
;
264 case 8: /* Set level of messages printed to console */
266 if (len
< 1 || len
> 8)
268 if (len
< minimum_console_loglevel
)
269 len
= minimum_console_loglevel
;
270 console_loglevel
= len
;
273 case 9: /* Number of chars in the log buffer */
274 error
= log_end
- log_start
;
284 asmlinkage
long sys_syslog(int type
, char __user
* buf
, int len
)
286 return do_syslog(type
, buf
, len
);
290 * Call the console drivers on a range of log_buf
292 static void __call_console_drivers(unsigned long start
, unsigned long end
)
296 for (con
= console_drivers
; con
; con
= con
->next
) {
297 if ((con
->flags
& CON_ENABLED
) && con
->write
)
298 con
->write(con
, &LOG_BUF(start
), end
- start
);
303 * Write out chars from start to end - 1 inclusive
305 static void _call_console_drivers(unsigned long start
, unsigned long end
, int msg_log_level
)
307 if (msg_log_level
< console_loglevel
&& console_drivers
&& start
!= end
) {
308 if ((start
& LOG_BUF_MASK
) > (end
& LOG_BUF_MASK
)) {
310 __call_console_drivers(start
& LOG_BUF_MASK
, LOG_BUF_LEN
);
311 __call_console_drivers(0, end
& LOG_BUF_MASK
);
313 __call_console_drivers(start
, end
);
319 * Call the console drivers, asking them to write out
320 * log_buf[start] to log_buf[end - 1].
321 * The console_sem must be held.
323 static void call_console_drivers(unsigned long start
, unsigned long end
)
325 unsigned long cur_index
, start_print
;
326 static int msg_level
= -1;
328 if (((long)(start
- end
)) > 0)
333 while (cur_index
!= end
) {
334 if ( msg_level
< 0 &&
335 ((end
- cur_index
) > 2) &&
336 LOG_BUF(cur_index
+ 0) == '<' &&
337 LOG_BUF(cur_index
+ 1) >= '0' &&
338 LOG_BUF(cur_index
+ 1) <= '7' &&
339 LOG_BUF(cur_index
+ 2) == '>')
341 msg_level
= LOG_BUF(cur_index
+ 1) - '0';
343 start_print
= cur_index
;
345 while (cur_index
!= end
) {
346 char c
= LOG_BUF(cur_index
);
352 * printk() has already given us loglevel tags in
353 * the buffer. This code is here in case the
354 * log buffer has wrapped right round and scribbled
357 msg_level
= default_message_loglevel
;
359 _call_console_drivers(start_print
, cur_index
, msg_level
);
361 start_print
= cur_index
;
366 _call_console_drivers(start_print
, end
, msg_level
);
369 static void emit_log_char(char c
)
371 LOG_BUF(log_end
) = c
;
373 if (log_end
- log_start
> LOG_BUF_LEN
)
374 log_start
= log_end
- LOG_BUF_LEN
;
375 if (log_end
- con_start
> LOG_BUF_LEN
)
376 con_start
= log_end
- LOG_BUF_LEN
;
377 if (logged_chars
< LOG_BUF_LEN
)
382 * This is printk. It can be called from any context. We want it to work.
384 * We try to grab the console_sem. If we succeed, it's easy - we log the output and
385 * call the console drivers. If we fail to get the semaphore we place the output
386 * into the log buffer and return. The current holder of the console_sem will
387 * notice the new output in release_console_sem() and will send it to the
388 * consoles before releasing the semaphore.
390 * One effect of this deferred printing is that code which calls printk() and
391 * then changes console_loglevel may break. This is because console_loglevel
392 * is inspected when the actual printing occurs.
394 asmlinkage
int printk(const char *fmt
, ...)
400 static char printk_buf
[1024];
401 static int log_level_unknown
= 1;
403 if (oops_in_progress
) {
404 /* If a crash is occurring, make sure we can't deadlock */
405 spin_lock_init(&logbuf_lock
);
406 /* And make sure that we print immediately */
407 init_MUTEX(&console_sem
);
410 /* This stops the holder of console_sem just where we want him */
411 spin_lock_irqsave(&logbuf_lock
, flags
);
413 /* Emit the output into the temporary buffer */
415 printed_len
= vsnprintf(printk_buf
, sizeof(printk_buf
), fmt
, args
);
419 * Copy the output into log_buf. If the caller didn't provide
420 * appropriate log level tags, we insert them here
422 for (p
= printk_buf
; *p
; p
++) {
423 if (log_level_unknown
) {
424 if (p
[0] != '<' || p
[1] < '0' || p
[1] > '7' || p
[2] != '>') {
426 emit_log_char(default_message_loglevel
+ '0');
429 log_level_unknown
= 0;
433 log_level_unknown
= 1;
436 if (!cpu_online(smp_processor_id())) {
438 * Some console drivers may assume that per-cpu resources have
439 * been allocated. So don't allow them to be called by this
440 * CPU until it is officially up. We shouldn't be calling into
441 * random console drivers on a CPU which doesn't exist yet..
443 spin_unlock_irqrestore(&logbuf_lock
, flags
);
446 if (!down_trylock(&console_sem
)) {
448 * We own the drivers. We can drop the spinlock and let
449 * release_console_sem() print the text
451 spin_unlock_irqrestore(&logbuf_lock
, flags
);
452 console_may_schedule
= 0;
453 release_console_sem();
456 * Someone else owns the drivers. We drop the spinlock, which
457 * allows the semaphore holder to proceed and to call the
458 * console drivers with the output which we just produced.
460 spin_unlock_irqrestore(&logbuf_lock
, flags
);
465 EXPORT_SYMBOL(printk
);
468 * acquire_console_sem - lock the console system for exclusive use.
470 * Acquires a semaphore which guarantees that the caller has
471 * exclusive access to the console system and the console_drivers list.
473 * Can sleep, returns nothing.
475 void acquire_console_sem(void)
480 console_may_schedule
= 1;
482 EXPORT_SYMBOL(acquire_console_sem
);
485 * release_console_sem - unlock the console system
487 * Releases the semaphore which the caller holds on the console system
488 * and the console driver list.
490 * While the semaphore was held, console output may have been buffered
491 * by printk(). If this is the case, release_console_sem() emits
492 * the output prior to releasing the semaphore.
494 * If there is output waiting for klogd, we wake it up.
496 * release_console_sem() may be called from any context.
498 void release_console_sem(void)
501 unsigned long _con_start
, _log_end
;
502 unsigned long wake_klogd
= 0;
505 spin_lock_irqsave(&logbuf_lock
, flags
);
506 wake_klogd
|= log_start
- log_end
;
507 if (con_start
== log_end
)
508 break; /* Nothing to print */
509 _con_start
= con_start
;
511 con_start
= log_end
; /* Flush */
512 spin_unlock_irqrestore(&logbuf_lock
, flags
);
513 call_console_drivers(_con_start
, _log_end
);
515 console_may_schedule
= 0;
517 spin_unlock_irqrestore(&logbuf_lock
, flags
);
518 if (wake_klogd
&& !oops_in_progress
&& waitqueue_active(&log_wait
))
519 wake_up_interruptible(&log_wait
);
522 /** console_conditional_schedule - yield the CPU if required
524 * If the console code is currently allowed to sleep, and
525 * if this CPU should yield the CPU to another task, do
528 * Must be called within acquire_console_sem().
530 void console_conditional_schedule(void)
532 if (console_may_schedule
&& need_resched()) {
533 set_current_state(TASK_RUNNING
);
537 EXPORT_SYMBOL(console_conditional_schedule
);
539 void console_print(const char *s
)
541 printk(KERN_EMERG
"%s", s
);
543 EXPORT_SYMBOL(console_print
);
545 void console_unblank(void)
550 * Try to get the console semaphore. If someone else owns it
551 * we have to return without unblanking because console_unblank
552 * may be called in interrupt context.
554 if (down_trylock(&console_sem
) != 0)
556 console_may_schedule
= 0;
557 for (c
= console_drivers
; c
!= NULL
; c
= c
->next
)
558 if ((c
->flags
& CON_ENABLED
) && c
->unblank
)
560 release_console_sem();
562 EXPORT_SYMBOL(console_unblank
);
565 * The console driver calls this routine during kernel initialization
566 * to register the console printing procedure with printk() and to
567 * print any messages that were printed by the kernel before the
568 * console driver was initialized.
570 void register_console(struct console
* console
)
576 * See if we want to use this console driver. If we
577 * didn't select a console we take the first one
578 * that registers here.
580 if (preferred_console
< 0) {
581 if (console
->index
< 0)
583 if (console
->setup
== NULL
||
584 console
->setup(console
, NULL
) == 0) {
585 console
->flags
|= CON_ENABLED
| CON_CONSDEV
;
586 preferred_console
= 0;
591 * See if this console matches one we selected on
594 for(i
= 0; i
< MAX_CMDLINECONSOLES
&& console_cmdline
[i
].name
[0]; i
++) {
595 if (strcmp(console_cmdline
[i
].name
, console
->name
) != 0)
597 if (console
->index
>= 0 &&
598 console
->index
!= console_cmdline
[i
].index
)
600 if (console
->index
< 0)
601 console
->index
= console_cmdline
[i
].index
;
602 if (console
->setup
&&
603 console
->setup(console
, console_cmdline
[i
].options
) != 0)
605 console
->flags
|= CON_ENABLED
;
606 console
->index
= console_cmdline
[i
].index
;
607 if (i
== preferred_console
)
608 console
->flags
|= CON_CONSDEV
;
612 if (!(console
->flags
& CON_ENABLED
))
616 * Put this console in the list - keep the
617 * preferred driver at the head of the list.
619 acquire_console_sem();
620 if ((console
->flags
& CON_CONSDEV
) || console_drivers
== NULL
) {
621 console
->next
= console_drivers
;
622 console_drivers
= console
;
624 console
->next
= console_drivers
->next
;
625 console_drivers
->next
= console
;
627 if (console
->flags
& CON_PRINTBUFFER
) {
629 * release_console_sem() will print out the buffered messages
632 spin_lock_irqsave(&logbuf_lock
, flags
);
633 con_start
= log_start
;
634 spin_unlock_irqrestore(&logbuf_lock
, flags
);
636 release_console_sem();
638 EXPORT_SYMBOL(register_console
);
640 int unregister_console(struct console
* console
)
642 struct console
*a
,*b
;
645 acquire_console_sem();
646 if (console_drivers
== console
) {
647 console_drivers
=console
->next
;
650 for (a
=console_drivers
->next
, b
=console_drivers
;
660 /* If last console is removed, we re-enable picking the first
661 * one that gets registered. Without that, pmac early boot console
662 * would prevent fbcon from taking over.
664 if (console_drivers
== NULL
)
665 preferred_console
= -1;
668 release_console_sem();
671 EXPORT_SYMBOL(unregister_console
);
674 * tty_write_message - write a message to a certain tty, not just the console.
676 * This is used for messages that need to be redirected to a specific tty.
677 * We don't put it into the syslog queue right now maybe in the future if
680 void tty_write_message(struct tty_struct
*tty
, char *msg
)
682 if (tty
&& tty
->driver
->write
)
683 tty
->driver
->write(tty
, 0, msg
, strlen(msg
));