Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  1 /*
  2  *  linux/kernel/printk.c
  3  *
  4  *  Copyright (C) 1991, 1992  Linus Torvalds
  5  *
  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).
 11  * Ted Ts'o, 2/11/93.
 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
 17  */
 18 
 19 #include <linux/kernel.h>
 20 #include <linux/mm.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 
 37 #include <asm/uaccess.h>
 38 
 39 /*
 40  * Architectures can override it:
 41  */
 42 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
 43 {
 44 }
 45 
 46 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
 47 
 48 /* printk's without a loglevel use this.. */
 49 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
 50 
 51 /* We show everything that is MORE important than this.. */
 52 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
 53 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
 54 
 55 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 56 
 57 int console_printk[4] = {
 58         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
 59         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
 60         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
 61         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
 62 };
 63 
 64 /*
 65  * Low level drivers may need that to know if they can schedule in
 66  * their unblank() callback or not. So let's export it.
 67  */
 68 int oops_in_progress;
 69 EXPORT_SYMBOL(oops_in_progress);
 70 
 71 /*
 72  * console_sem protects the console_drivers list, and also
 73  * provides serialisation for access to the entire console
 74  * driver system.
 75  */
 76 static DECLARE_MUTEX(console_sem);
 77 struct console *console_drivers;
 78 EXPORT_SYMBOL_GPL(console_drivers);
 79 
 80 /*
 81  * This is used for debugging the mess that is the VT code by
 82  * keeping track if we have the console semaphore held. It's
 83  * definitely not the perfect debug tool (we don't know if _WE_
 84  * hold it are racing, but it helps tracking those weird code
 85  * path in the console code where we end up in places I want
 86  * locked without the console sempahore held
 87  */
 88 static int console_locked, console_suspended;
 89 
 90 /*
 91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 92  * It is also used in interesting ways to provide interlocking in
 93  * release_console_sem().
 94  */
 95 static DEFINE_SPINLOCK(logbuf_lock);
 96 
 97 #define LOG_BUF_MASK (log_buf_len-1)
 98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 99 
100 /*
101  * The indices into log_buf are not constrained to log_buf_len - they
102  * must be masked before subscripting
103  */
104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
107 
108 /*
109  *      Array of consoles built from command line options (console=)
110  */
111 struct console_cmdline
112 {
113         char    name[8];                        /* Name of the driver       */
114         int     index;                          /* Minor dev. to use        */
115         char    *options;                       /* Options for the driver   */
116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
117         char    *brl_options;                   /* Options for braille driver */
118 #endif
119 };
120 
121 #define MAX_CMDLINECONSOLES 8
122 
123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
124 static int selected_console = -1;
125 static int preferred_console = -1;
126 int console_set_on_cmdline;
127 EXPORT_SYMBOL(console_set_on_cmdline);
128 
129 /* Flag: console code may call schedule() */
130 static int console_may_schedule;
131 
132 #ifdef CONFIG_PRINTK
133 
134 static char __log_buf[__LOG_BUF_LEN];
135 static char *log_buf = __log_buf;
136 static int log_buf_len = __LOG_BUF_LEN;
137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
138 
139 #ifdef CONFIG_KEXEC
140 /*
141  * This appends the listed symbols to /proc/vmcoreinfo
142  *
143  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
144  * obtain access to symbols that are otherwise very difficult to locate.  These
145  * symbols are specifically used so that utilities can access and extract the
146  * dmesg log from a vmcore file after a crash.
147  */
148 void log_buf_kexec_setup(void)
149 {
150         VMCOREINFO_SYMBOL(log_buf);
151         VMCOREINFO_SYMBOL(log_end);
152         VMCOREINFO_SYMBOL(log_buf_len);
153         VMCOREINFO_SYMBOL(logged_chars);
154 }
155 #endif
156 
157 static int __init log_buf_len_setup(char *str)
158 {
159         unsigned size = memparse(str, &str);
160         unsigned long flags;
161 
162         if (size)
163                 size = roundup_pow_of_two(size);
164         if (size > log_buf_len) {
165                 unsigned start, dest_idx, offset;
166                 char *new_log_buf;
167 
168                 new_log_buf = alloc_bootmem(size);
169                 if (!new_log_buf) {
170                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
171                         goto out;
172                 }
173 
174                 spin_lock_irqsave(&logbuf_lock, flags);
175                 log_buf_len = size;
176                 log_buf = new_log_buf;
177 
178                 offset = start = min(con_start, log_start);
179                 dest_idx = 0;
180                 while (start != log_end) {
181                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
182                         start++;
183                         dest_idx++;
184                 }
185                 log_start -= offset;
186                 con_start -= offset;
187                 log_end -= offset;
188                 spin_unlock_irqrestore(&logbuf_lock, flags);
189 
190                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
191         }
192 out:
193         return 1;
194 }
195 
196 __setup("log_buf_len=", log_buf_len_setup);
197 
198 #ifdef CONFIG_BOOT_PRINTK_DELAY
199 
200 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
201 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
202 
203 static int __init boot_delay_setup(char *str)
204 {
205         unsigned long lpj;
206         unsigned long long loops_per_msec;
207 
208         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
209         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
210 
211         get_option(&str, &boot_delay);
212         if (boot_delay > 10 * 1000)
213                 boot_delay = 0;
214 
215         printk_delay_msec = loops_per_msec;
216         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
217                 "HZ: %d, printk_delay_msec: %llu\n",
218                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
219         return 1;
220 }
221 __setup("boot_delay=", boot_delay_setup);
222 
223 static void boot_delay_msec(void)
224 {
225         unsigned long long k;
226         unsigned long timeout;
227 
228         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
229                 return;
230 
231         k = (unsigned long long)printk_delay_msec * boot_delay;
232 
233         timeout = jiffies + msecs_to_jiffies(boot_delay);
234         while (k) {
235                 k--;
236                 cpu_relax();
237                 /*
238                  * use (volatile) jiffies to prevent
239                  * compiler reduction; loop termination via jiffies
240                  * is secondary and may or may not happen.
241                  */
242                 if (time_after(jiffies, timeout))
243                         break;
244                 touch_nmi_watchdog();
245         }
246 }
247 #else
248 static inline void boot_delay_msec(void)
249 {
250 }
251 #endif
252 
253 /*
254  * Commands to do_syslog:
255  *
256  *      0 -- Close the log.  Currently a NOP.
257  *      1 -- Open the log. Currently a NOP.
258  *      2 -- Read from the log.
259  *      3 -- Read all messages remaining in the ring buffer.
260  *      4 -- Read and clear all messages remaining in the ring buffer
261  *      5 -- Clear ring buffer.
262  *      6 -- Disable printk's to console
263  *      7 -- Enable printk's to console
264  *      8 -- Set level of messages printed to console
265  *      9 -- Return number of unread characters in the log buffer
266  *     10 -- Return size of the log buffer
267  */
268 int do_syslog(int type, char __user *buf, int len)
269 {
270         unsigned i, j, limit, count;
271         int do_clear = 0;
272         char c;
273         int error = 0;
274 
275         error = security_syslog(type);
276         if (error)
277                 return error;
278 
279         switch (type) {
280         case 0:         /* Close log */
281                 break;
282         case 1:         /* Open log */
283                 break;
284         case 2:         /* Read from log */
285                 error = -EINVAL;
286                 if (!buf || len < 0)
287                         goto out;
288                 error = 0;
289                 if (!len)
290                         goto out;
291                 if (!access_ok(VERIFY_WRITE, buf, len)) {
292                         error = -EFAULT;
293                         goto out;
294                 }
295                 error = wait_event_interruptible(log_wait,
296                                                         (log_start - log_end));
297                 if (error)
298                         goto out;
299                 i = 0;
300                 spin_lock_irq(&logbuf_lock);
301                 while (!error && (log_start != log_end) && i < len) {
302                         c = LOG_BUF(log_start);
303                         log_start++;
304                         spin_unlock_irq(&logbuf_lock);
305                         error = __put_user(c,buf);
306                         buf++;
307                         i++;
308                         cond_resched();
309                         spin_lock_irq(&logbuf_lock);
310                 }
311                 spin_unlock_irq(&logbuf_lock);
312                 if (!error)
313                         error = i;
314                 break;
315         case 4:         /* Read/clear last kernel messages */
316                 do_clear = 1;
317                 /* FALL THRU */
318         case 3:         /* Read last kernel messages */
319                 error = -EINVAL;
320                 if (!buf || len < 0)
321                         goto out;
322                 error = 0;
323                 if (!len)
324                         goto out;
325                 if (!access_ok(VERIFY_WRITE, buf, len)) {
326                         error = -EFAULT;
327                         goto out;
328                 }
329                 count = len;
330                 if (count > log_buf_len)
331                         count = log_buf_len;
332                 spin_lock_irq(&logbuf_lock);
333                 if (count > logged_chars)
334                         count = logged_chars;
335                 if (do_clear)
336                         logged_chars = 0;
337                 limit = log_end;
338                 /*
339                  * __put_user() could sleep, and while we sleep
340                  * printk() could overwrite the messages
341                  * we try to copy to user space. Therefore
342                  * the messages are copied in reverse. <manfreds>
343                  */
344                 for (i = 0; i < count && !error; i++) {
345                         j = limit-1-i;
346                         if (j + log_buf_len < log_end)
347                                 break;
348                         c = LOG_BUF(j);
349                         spin_unlock_irq(&logbuf_lock);
350                         error = __put_user(c,&buf[count-1-i]);
351                         cond_resched();
352                         spin_lock_irq(&logbuf_lock);
353                 }
354                 spin_unlock_irq(&logbuf_lock);
355                 if (error)
356                         break;
357                 error = i;
358                 if (i != count) {
359                         int offset = count-error;
360                         /* buffer overflow during copy, correct user buffer. */
361                         for (i = 0; i < error; i++) {
362                                 if (__get_user(c,&buf[i+offset]) ||
363                                     __put_user(c,&buf[i])) {
364                                         error = -EFAULT;
365                                         break;
366                                 }
367                                 cond_resched();
368                         }
369                 }
370                 break;
371         case 5:         /* Clear ring buffer */
372                 logged_chars = 0;
373                 break;
374         case 6:         /* Disable logging to console */
375                 console_loglevel = minimum_console_loglevel;
376                 break;
377         case 7:         /* Enable logging to console */
378                 console_loglevel = default_console_loglevel;
379                 break;
380         case 8:         /* Set level of messages printed to console */
381                 error = -EINVAL;
382                 if (len < 1 || len > 8)
383                         goto out;
384                 if (len < minimum_console_loglevel)
385                         len = minimum_console_loglevel;
386                 console_loglevel = len;
387                 error = 0;
388                 break;
389         case 9:         /* Number of chars in the log buffer */
390                 error = log_end - log_start;
391                 break;
392         case 10:        /* Size of the log buffer */
393                 error = log_buf_len;
394                 break;
395         default:
396                 error = -EINVAL;
397                 break;
398         }
399 out:
400         return error;
401 }
402 
403 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
404 {
405         return do_syslog(type, buf, len);
406 }
407 
408 /*
409  * Call the console drivers on a range of log_buf
410  */
411 static void __call_console_drivers(unsigned start, unsigned end)
412 {
413         struct console *con;
414 
415         for (con = console_drivers; con; con = con->next) {
416                 if ((con->flags & CON_ENABLED) && con->write &&
417                                 (cpu_online(smp_processor_id()) ||
418                                 (con->flags & CON_ANYTIME)))
419                         con->write(con, &LOG_BUF(start), end - start);
420         }
421 }
422 
423 static int __read_mostly ignore_loglevel;
424 
425 static int __init ignore_loglevel_setup(char *str)
426 {
427         ignore_loglevel = 1;
428         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
429 
430         return 0;
431 }
432 
433 early_param("ignore_loglevel", ignore_loglevel_setup);
434 
435 /*
436  * Write out chars from start to end - 1 inclusive
437  */
438 static void _call_console_drivers(unsigned start,
439                                 unsigned end, int msg_log_level)
440 {
441         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
442                         console_drivers && start != end) {
443                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
444                         /* wrapped write */
445                         __call_console_drivers(start & LOG_BUF_MASK,
446                                                 log_buf_len);
447                         __call_console_drivers(0, end & LOG_BUF_MASK);
448                 } else {
449                         __call_console_drivers(start, end);
450                 }
451         }
452 }
453 
454 /*
455  * Call the console drivers, asking them to write out
456  * log_buf[start] to log_buf[end - 1].
457  * The console_sem must be held.
458  */
459 static void call_console_drivers(unsigned start, unsigned end)
460 {
461         unsigned cur_index, start_print;
462         static int msg_level = -1;
463 
464         BUG_ON(((int)(start - end)) > 0);
465 
466         cur_index = start;
467         start_print = start;
468         while (cur_index != end) {
469                 if (msg_level < 0 && ((end - cur_index) > 2) &&
470                                 LOG_BUF(cur_index + 0) == '<' &&
471                                 LOG_BUF(cur_index + 1) >= '' &&
472                                 LOG_BUF(cur_index + 1) <= '7' &&
473                                 LOG_BUF(cur_index + 2) == '>') {
474                         msg_level = LOG_BUF(cur_index + 1) - '';
475                         cur_index += 3;
476                         start_print = cur_index;
477                 }
478                 while (cur_index != end) {
479                         char c = LOG_BUF(cur_index);
480 
481                         cur_index++;
482                         if (c == '\n') {
483                                 if (msg_level < 0) {
484                                         /*
485                                          * printk() has already given us loglevel tags in
486                                          * the buffer.  This code is here in case the
487                                          * log buffer has wrapped right round and scribbled
488                                          * on those tags
489                                          */
490                                         msg_level = default_message_loglevel;
491                                 }
492                                 _call_console_drivers(start_print, cur_index, msg_level);
493                                 msg_level = -1;
494                                 start_print = cur_index;
495                                 break;
496                         }
497                 }
498         }
499         _call_console_drivers(start_print, end, msg_level);
500 }
501 
502 static void emit_log_char(char c)
503 {
504         LOG_BUF(log_end) = c;
505         log_end++;
506         if (log_end - log_start > log_buf_len)
507                 log_start = log_end - log_buf_len;
508         if (log_end - con_start > log_buf_len)
509                 con_start = log_end - log_buf_len;
510         if (logged_chars < log_buf_len)
511                 logged_chars++;
512 }
513 
514 /*
515  * Zap console related locks when oopsing. Only zap at most once
516  * every 10 seconds, to leave time for slow consoles to print a
517  * full oops.
518  */
519 static void zap_locks(void)
520 {
521         static unsigned long oops_timestamp;
522 
523         if (time_after_eq(jiffies, oops_timestamp) &&
524                         !time_after(jiffies, oops_timestamp + 30 * HZ))
525                 return;
526 
527         oops_timestamp = jiffies;
528 
529         /* If a crash is occurring, make sure we can't deadlock */
530         spin_lock_init(&logbuf_lock);
531         /* And make sure that we print immediately */
532         init_MUTEX(&console_sem);
533 }
534 
535 #if defined(CONFIG_PRINTK_TIME)
536 static int printk_time = 1;
537 #else
538 static int printk_time = 0;
539 #endif
540 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
541 
542 /* Check if we have any console registered that can be called early in boot. */
543 static int have_callable_console(void)
544 {
545         struct console *con;
546 
547         for (con = console_drivers; con; con = con->next)
548                 if (con->flags & CON_ANYTIME)
549                         return 1;
550 
551         return 0;
552 }
553 
554 /**
555  * printk - print a kernel message
556  * @fmt: format string
557  *
558  * This is printk().  It can be called from any context.  We want it to work.
559  *
560  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
561  * call the console drivers.  If we fail to get the semaphore we place the output
562  * into the log buffer and return.  The current holder of the console_sem will
563  * notice the new output in release_console_sem() and will send it to the
564  * consoles before releasing the semaphore.
565  *
566  * One effect of this deferred printing is that code which calls printk() and
567  * then changes console_loglevel may break. This is because console_loglevel
568  * is inspected when the actual printing occurs.
569  *
570  * See also:
571  * printf(3)
572  *
573  * See the vsnprintf() documentation for format string extensions over C99.
574  */
575 
576 asmlinkage int printk(const char *fmt, ...)
577 {
578         va_list args;
579         int r;
580 
581         va_start(args, fmt);
582         r = vprintk(fmt, args);
583         va_end(args);
584 
585         return r;
586 }
587 
588 /* cpu currently holding logbuf_lock */
589 static volatile unsigned int printk_cpu = UINT_MAX;
590 
591 /*
592  * Can we actually use the console at this time on this cpu?
593  *
594  * Console drivers may assume that per-cpu resources have
595  * been allocated. So unless they're explicitly marked as
596  * being able to cope (CON_ANYTIME) don't call them until
597  * this CPU is officially up.
598  */
599 static inline int can_use_console(unsigned int cpu)
600 {
601         return cpu_online(cpu) || have_callable_console();
602 }
603 
604 /*
605  * Try to get console ownership to actually show the kernel
606  * messages from a 'printk'. Return true (and with the
607  * console_semaphore held, and 'console_locked' set) if it
608  * is successful, false otherwise.
609  *
610  * This gets called with the 'logbuf_lock' spinlock held and
611  * interrupts disabled. It should return with 'lockbuf_lock'
612  * released but interrupts still disabled.
613  */
614 static int acquire_console_semaphore_for_printk(unsigned int cpu)
615 {
616         int retval = 0;
617 
618         if (!try_acquire_console_sem()) {
619                 retval = 1;
620 
621                 /*
622                  * If we can't use the console, we need to release
623                  * the console semaphore by hand to avoid flushing
624                  * the buffer. We need to hold the console semaphore
625                  * in order to do this test safely.
626                  */
627                 if (!can_use_console(cpu)) {
628                         console_locked = 0;
629                         up(&console_sem);
630                         retval = 0;
631                 }
632         }
633         printk_cpu = UINT_MAX;
634         spin_unlock(&logbuf_lock);
635         return retval;
636 }
637 static const char recursion_bug_msg [] =
638                 KERN_CRIT "BUG: recent printk recursion!\n";
639 static int recursion_bug;
640 static int new_text_line = 1;
641 static char printk_buf[1024];
642 
643 asmlinkage int vprintk(const char *fmt, va_list args)
644 {
645         int printed_len = 0;
646         int current_log_level = default_message_loglevel;
647         unsigned long flags;
648         int this_cpu;
649         char *p;
650 
651         boot_delay_msec();
652 
653         preempt_disable();
654         /* This stops the holder of console_sem just where we want him */
655         raw_local_irq_save(flags);
656         this_cpu = smp_processor_id();
657 
658         /*
659          * Ouch, printk recursed into itself!
660          */
661         if (unlikely(printk_cpu == this_cpu)) {
662                 /*
663                  * If a crash is occurring during printk() on this CPU,
664                  * then try to get the crash message out but make sure
665                  * we can't deadlock. Otherwise just return to avoid the
666                  * recursion and return - but flag the recursion so that
667                  * it can be printed at the next appropriate moment:
668                  */
669                 if (!oops_in_progress) {
670                         recursion_bug = 1;
671                         goto out_restore_irqs;
672                 }
673                 zap_locks();
674         }
675 
676         lockdep_off();
677         spin_lock(&logbuf_lock);
678         printk_cpu = this_cpu;
679 
680         if (recursion_bug) {
681                 recursion_bug = 0;
682                 strcpy(printk_buf, recursion_bug_msg);
683                 printed_len = strlen(recursion_bug_msg);
684         }
685         /* Emit the output into the temporary buffer */
686         printed_len += vscnprintf(printk_buf + printed_len,
687                                   sizeof(printk_buf) - printed_len, fmt, args);
688 
689 
690         p = printk_buf;
691 
692         /* Do we have a loglevel in the string? */
693         if (p[0] == '<') {
694                 unsigned char c = p[1];
695                 if (c && p[2] == '>') {
696                         switch (c) {
697                         case '' ... '7': /* loglevel */
698                                 current_log_level = c - '';
699                         /* Fallthrough - make sure we're on a new line */
700                         case 'd': /* KERN_DEFAULT */
701                                 if (!new_text_line) {
702                                         emit_log_char('\n');
703                                         new_text_line = 1;
704                                 }
705                         /* Fallthrough - skip the loglevel */
706                         case 'c': /* KERN_CONT */
707                                 p += 3;
708                                 break;
709                         }
710                 }
711         }
712 
713         /*
714          * Copy the output into log_buf.  If the caller didn't provide
715          * appropriate log level tags, we insert them here
716          */
717         for ( ; *p; p++) {
718                 if (new_text_line) {
719                         /* Always output the token */
720                         emit_log_char('<');
721                         emit_log_char(current_log_level + '');
722                         emit_log_char('>');
723                         printed_len += 3;
724                         new_text_line = 0;
725 
726                         if (printk_time) {
727                                 /* Follow the token with the time */
728                                 char tbuf[50], *tp;
729                                 unsigned tlen;
730                                 unsigned long long t;
731                                 unsigned long nanosec_rem;
732 
733                                 t = cpu_clock(printk_cpu);
734                                 nanosec_rem = do_div(t, 1000000000);
735                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
736                                                 (unsigned long) t,
737                                                 nanosec_rem / 1000);
738 
739                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
740                                         emit_log_char(*tp);
741                                 printed_len += tlen;
742                         }
743 
744                         if (!*p)
745                                 break;
746                 }
747 
748                 emit_log_char(*p);
749                 if (*p == '\n')
750                         new_text_line = 1;
751         }
752 
753         /*
754          * Try to acquire and then immediately release the
755          * console semaphore. The release will do all the
756          * actual magic (print out buffers, wake up klogd,
757          * etc). 
758          *
759          * The acquire_console_semaphore_for_printk() function
760          * will release 'logbuf_lock' regardless of whether it
761          * actually gets the semaphore or not.
762          */
763         if (acquire_console_semaphore_for_printk(this_cpu))
764                 release_console_sem();
765 
766         lockdep_on();
767 out_restore_irqs:
768         raw_local_irq_restore(flags);
769 
770         preempt_enable();
771         return printed_len;
772 }
773 EXPORT_SYMBOL(printk);
774 EXPORT_SYMBOL(vprintk);
775 
776 #else
777 
778 static void call_console_drivers(unsigned start, unsigned end)
779 {
780 }
781 
782 #endif
783 
784 static int __add_preferred_console(char *name, int idx, char *options,
785                                    char *brl_options)
786 {
787         struct console_cmdline *c;
788         int i;
789 
790         /*
791          *      See if this tty is not yet registered, and
792          *      if we have a slot free.
793          */
794         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
795                 if (strcmp(console_cmdline[i].name, name) == 0 &&
796                           console_cmdline[i].index == idx) {
797                                 if (!brl_options)
798                                         selected_console = i;
799                                 return 0;
800                 }
801         if (i == MAX_CMDLINECONSOLES)
802                 return -E2BIG;
803         if (!brl_options)
804                 selected_console = i;
805         c = &console_cmdline[i];
806         strlcpy(c->name, name, sizeof(c->name));
807         c->options = options;
808 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
809         c->brl_options = brl_options;
810 #endif
811         c->index = idx;
812         return 0;
813 }
814 /*
815  * Set up a list of consoles.  Called from init/main.c
816  */
817 static int __init console_setup(char *str)
818 {
819         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
820         char *s, *options, *brl_options = NULL;
821         int idx;
822 
823 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
824         if (!memcmp(str, "brl,", 4)) {
825                 brl_options = "";
826                 str += 4;
827         } else if (!memcmp(str, "brl=", 4)) {
828                 brl_options = str + 4;
829                 str = strchr(brl_options, ',');
830                 if (!str) {
831                         printk(KERN_ERR "need port name after brl=\n");
832                         return 1;
833                 }
834                 *(str++) = 0;
835         }
836 #endif
837 
838         /*
839          * Decode str into name, index, options.
840          */
841         if (str[0] >= '' && str[0] <= '9') {
842                 strcpy(buf, "ttyS");
843                 strncpy(buf + 4, str, sizeof(buf) - 5);
844         } else {
845                 strncpy(buf, str, sizeof(buf) - 1);
846         }
847         buf[sizeof(buf) - 1] = 0;
848         if ((options = strchr(str, ',')) != NULL)
849                 *(options++) = 0;
850 #ifdef __sparc__
851         if (!strcmp(str, "ttya"))
852                 strcpy(buf, "ttyS0");
853         if (!strcmp(str, "ttyb"))
854                 strcpy(buf, "ttyS1");
855 #endif
856         for (s = buf; *s; s++)
857                 if ((*s >= '' && *s <= '9') || *s == ',')
858                         break;
859         idx = simple_strtoul(s, NULL, 10);
860         *s = 0;
861 
862         __add_preferred_console(buf, idx, options, brl_options);
863         console_set_on_cmdline = 1;
864         return 1;
865 }
866 __setup("console=", console_setup);
867 
868 /**
869  * add_preferred_console - add a device to the list of preferred consoles.
870  * @name: device name
871  * @idx: device index
872  * @options: options for this console
873  *
874  * The last preferred console added will be used for kernel messages
875  * and stdin/out/err for init.  Normally this is used by console_setup
876  * above to handle user-supplied console arguments; however it can also
877  * be used by arch-specific code either to override the user or more
878  * commonly to provide a default console (ie from PROM variables) when
879  * the user has not supplied one.
880  */
881 int add_preferred_console(char *name, int idx, char *options)
882 {
883         return __add_preferred_console(name, idx, options, NULL);
884 }
885 
886 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
887 {
888         struct console_cmdline *c;
889         int i;
890 
891         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
892                 if (strcmp(console_cmdline[i].name, name) == 0 &&
893                           console_cmdline[i].index == idx) {
894                                 c = &console_cmdline[i];
895                                 strlcpy(c->name, name_new, sizeof(c->name));
896                                 c->name[sizeof(c->name) - 1] = 0;
897                                 c->options = options;
898                                 c->index = idx_new;
899                                 return i;
900                 }
901         /* not found */
902         return -1;
903 }
904 
905 int console_suspend_enabled = 1;
906 EXPORT_SYMBOL(console_suspend_enabled);
907 
908 static int __init console_suspend_disable(char *str)
909 {
910         console_suspend_enabled = 0;
911         return 1;
912 }
913 __setup("no_console_suspend", console_suspend_disable);
914 
915 /**
916  * suspend_console - suspend the console subsystem
917  *
918  * This disables printk() while we go into suspend states
919  */
920 void suspend_console(void)
921 {
922         if (!console_suspend_enabled)
923                 return;
924         printk("Suspending console(s) (use no_console_suspend to debug)\n");
925         acquire_console_sem();
926         console_suspended = 1;
927         up(&console_sem);
928 }
929 
930 void resume_console(void)
931 {
932         if (!console_suspend_enabled)
933                 return;
934         down(&console_sem);
935         console_suspended = 0;
936         release_console_sem();
937 }
938 
939 /**
940  * acquire_console_sem - lock the console system for exclusive use.
941  *
942  * Acquires a semaphore which guarantees that the caller has
943  * exclusive access to the console system and the console_drivers list.
944  *
945  * Can sleep, returns nothing.
946  */
947 void acquire_console_sem(void)
948 {
949         BUG_ON(in_interrupt());
950         down(&console_sem);
951         if (console_suspended)
952                 return;
953         console_locked = 1;
954         console_may_schedule = 1;
955 }
956 EXPORT_SYMBOL(acquire_console_sem);
957 
958 int try_acquire_console_sem(void)
959 {
960         if (down_trylock(&console_sem))
961                 return -1;
962         if (console_suspended) {
963                 up(&console_sem);
964                 return -1;
965         }
966         console_locked = 1;
967         console_may_schedule = 0;
968         return 0;
969 }
970 EXPORT_SYMBOL(try_acquire_console_sem);
971 
972 int is_console_locked(void)
973 {
974         return console_locked;
975 }
976 
977 static DEFINE_PER_CPU(int, printk_pending);
978 
979 void printk_tick(void)
980 {
981         if (__get_cpu_var(printk_pending)) {
982                 __get_cpu_var(printk_pending) = 0;
983                 wake_up_interruptible(&log_wait);
984         }
985 }
986 
987 int printk_needs_cpu(int cpu)
988 {
989         return per_cpu(printk_pending, cpu);
990 }
991 
992 void wake_up_klogd(void)
993 {
994         if (waitqueue_active(&log_wait))
995                 __raw_get_cpu_var(printk_pending) = 1;
996 }
997 
998 /**
999  * release_console_sem - unlock the console system
1000  *
1001  * Releases the semaphore which the caller holds on the console system
1002  * and the console driver list.
1003  *
1004  * While the semaphore was held, console output may have been buffered
1005  * by printk().  If this is the case, release_console_sem() emits
1006  * the output prior to releasing the semaphore.
1007  *
1008  * If there is output waiting for klogd, we wake it up.
1009  *
1010  * release_console_sem() may be called from any context.
1011  */
1012 void release_console_sem(void)
1013 {
1014         unsigned long flags;
1015         unsigned _con_start, _log_end;
1016         unsigned wake_klogd = 0;
1017 
1018         if (console_suspended) {
1019                 up(&console_sem);
1020                 return;
1021         }
1022 
1023         console_may_schedule = 0;
1024 
1025         for ( ; ; ) {
1026                 spin_lock_irqsave(&logbuf_lock, flags);
1027                 wake_klogd |= log_start - log_end;
1028                 if (con_start == log_end)
1029                         break;                  /* Nothing to print */
1030                 _con_start = con_start;
1031                 _log_end = log_end;
1032                 con_start = log_end;            /* Flush */
1033                 spin_unlock(&logbuf_lock);
1034                 stop_critical_timings();        /* don't trace print latency */
1035                 call_console_drivers(_con_start, _log_end);
1036                 start_critical_timings();
1037                 local_irq_restore(flags);
1038         }
1039         console_locked = 0;
1040         up(&console_sem);
1041         spin_unlock_irqrestore(&logbuf_lock, flags);
1042         if (wake_klogd)
1043                 wake_up_klogd();
1044 }
1045 EXPORT_SYMBOL(release_console_sem);
1046 
1047 /**
1048  * console_conditional_schedule - yield the CPU if required
1049  *
1050  * If the console code is currently allowed to sleep, and
1051  * if this CPU should yield the CPU to another task, do
1052  * so here.
1053  *
1054  * Must be called within acquire_console_sem().
1055  */
1056 void __sched console_conditional_schedule(void)
1057 {
1058         if (console_may_schedule)
1059                 cond_resched();
1060 }
1061 EXPORT_SYMBOL(console_conditional_schedule);
1062 
1063 void console_print(const char *s)
1064 {
1065         printk(KERN_EMERG "%s", s);
1066 }
1067 EXPORT_SYMBOL(console_print);
1068 
1069 void console_unblank(void)
1070 {
1071         struct console *c;
1072 
1073         /*
1074          * console_unblank can no longer be called in interrupt context unless
1075          * oops_in_progress is set to 1..
1076          */
1077         if (oops_in_progress) {
1078                 if (down_trylock(&console_sem) != 0)
1079                         return;
1080         } else
1081                 acquire_console_sem();
1082 
1083         console_locked = 1;
1084         console_may_schedule = 0;
1085         for (c = console_drivers; c != NULL; c = c->next)
1086                 if ((c->flags & CON_ENABLED) && c->unblank)
1087                         c->unblank();
1088         release_console_sem();
1089 }
1090 
1091 /*
1092  * Return the console tty driver structure and its associated index
1093  */
1094 struct tty_driver *console_device(int *index)
1095 {
1096         struct console *c;
1097         struct tty_driver *driver = NULL;
1098 
1099         acquire_console_sem();
1100         for (c = console_drivers; c != NULL; c = c->next) {
1101                 if (!c->device)
1102                         continue;
1103                 driver = c->device(c, index);
1104                 if (driver)
1105                         break;
1106         }
1107         release_console_sem();
1108         return driver;
1109 }
1110 
1111 /*
1112  * Prevent further output on the passed console device so that (for example)
1113  * serial drivers can disable console output before suspending a port, and can
1114  * re-enable output afterwards.
1115  */
1116 void console_stop(struct console *console)
1117 {
1118         acquire_console_sem();
1119         console->flags &= ~CON_ENABLED;
1120         release_console_sem();
1121 }
1122 EXPORT_SYMBOL(console_stop);
1123 
1124 void console_start(struct console *console)
1125 {
1126         acquire_console_sem();
1127         console->flags |= CON_ENABLED;
1128         release_console_sem();
1129 }
1130 EXPORT_SYMBOL(console_start);
1131 
1132 /*
1133  * The console driver calls this routine during kernel initialization
1134  * to register the console printing procedure with printk() and to
1135  * print any messages that were printed by the kernel before the
1136  * console driver was initialized.
1137  */
1138 void register_console(struct console *console)
1139 {
1140         int i;
1141         unsigned long flags;
1142         struct console *bootconsole = NULL;
1143 
1144         if (console_drivers) {
1145                 if (console->flags & CON_BOOT)
1146                         return;
1147                 if (console_drivers->flags & CON_BOOT)
1148                         bootconsole = console_drivers;
1149         }
1150 
1151         if (preferred_console < 0 || bootconsole || !console_drivers)
1152                 preferred_console = selected_console;
1153 
1154         if (console->early_setup)
1155                 console->early_setup();
1156 
1157         /*
1158          *      See if we want to use this console driver. If we
1159          *      didn't select a console we take the first one
1160          *      that registers here.
1161          */
1162         if (preferred_console < 0) {
1163                 if (console->index < 0)
1164                         console->index = 0;
1165                 if (console->setup == NULL ||
1166                     console->setup(console, NULL) == 0) {
1167                         console->flags |= CON_ENABLED;
1168                         if (console->device) {
1169                                 console->flags |= CON_CONSDEV;
1170                                 preferred_console = 0;
1171                         }
1172                 }
1173         }
1174 
1175         /*
1176          *      See if this console matches one we selected on
1177          *      the command line.
1178          */
1179         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1180                         i++) {
1181                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1182                         continue;
1183                 if (console->index >= 0 &&
1184                     console->index != console_cmdline[i].index)
1185                         continue;
1186                 if (console->index < 0)
1187                         console->index = console_cmdline[i].index;
1188 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1189                 if (console_cmdline[i].brl_options) {
1190                         console->flags |= CON_BRL;
1191                         braille_register_console(console,
1192                                         console_cmdline[i].index,
1193                                         console_cmdline[i].options,
1194                                         console_cmdline[i].brl_options);
1195                         return;
1196                 }
1197 #endif
1198                 if (console->setup &&
1199                     console->setup(console, console_cmdline[i].options) != 0)
1200                         break;
1201                 console->flags |= CON_ENABLED;
1202                 console->index = console_cmdline[i].index;
1203                 if (i == selected_console) {
1204                         console->flags |= CON_CONSDEV;
1205                         preferred_console = selected_console;
1206                 }
1207                 break;
1208         }
1209 
1210         if (!(console->flags & CON_ENABLED))
1211                 return;
1212 
1213         if (bootconsole && (console->flags & CON_CONSDEV)) {
1214                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1215                        bootconsole->name, bootconsole->index,
1216                        console->name, console->index);
1217                 unregister_console(bootconsole);
1218                 console->flags &= ~CON_PRINTBUFFER;
1219         } else {
1220                 printk(KERN_INFO "console [%s%d] enabled\n",
1221                        console->name, console->index);
1222         }
1223 
1224         /*
1225          *      Put this console in the list - keep the
1226          *      preferred driver at the head of the list.
1227          */
1228         acquire_console_sem();
1229         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1230                 console->next = console_drivers;
1231                 console_drivers = console;
1232                 if (console->next)
1233                         console->next->flags &= ~CON_CONSDEV;
1234         } else {
1235                 console->next = console_drivers->next;
1236                 console_drivers->next = console;
1237         }
1238         if (console->flags & CON_PRINTBUFFER) {
1239                 /*
1240                  * release_console_sem() will print out the buffered messages
1241                  * for us.
1242                  */
1243                 spin_lock_irqsave(&logbuf_lock, flags);
1244                 con_start = log_start;
1245                 spin_unlock_irqrestore(&logbuf_lock, flags);
1246         }
1247         release_console_sem();
1248 }
1249 EXPORT_SYMBOL(register_console);
1250 
1251 int unregister_console(struct console *console)
1252 {
1253         struct console *a, *b;
1254         int res = 1;
1255 
1256 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1257         if (console->flags & CON_BRL)
1258                 return braille_unregister_console(console);
1259 #endif
1260 
1261         acquire_console_sem();
1262         if (console_drivers == console) {
1263                 console_drivers=console->next;
1264                 res = 0;
1265         } else if (console_drivers) {
1266                 for (a=console_drivers->next, b=console_drivers ;
1267                      a; b=a, a=b->next) {
1268                         if (a == console) {
1269                                 b->next = a->next;
1270                                 res = 0;
1271                                 break;
1272                         }
1273                 }
1274         }
1275 
1276         /*
1277          * If this isn't the last console and it has CON_CONSDEV set, we
1278          * need to set it on the next preferred console.
1279          */
1280         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1281                 console_drivers->flags |= CON_CONSDEV;
1282 
1283         release_console_sem();
1284         return res;
1285 }
1286 EXPORT_SYMBOL(unregister_console);
1287 
1288 static int __init disable_boot_consoles(void)
1289 {
1290         if (console_drivers != NULL) {
1291                 if (console_drivers->flags & CON_BOOT) {
1292                         printk(KERN_INFO "turn off boot console %s%d\n",
1293                                 console_drivers->name, console_drivers->index);
1294                         return unregister_console(console_drivers);
1295                 }
1296         }
1297         return 0;
1298 }
1299 late_initcall(disable_boot_consoles);
1300 
1301 #if defined CONFIG_PRINTK
1302 
1303 /*
1304  * printk rate limiting, lifted from the networking subsystem.
1305  *
1306  * This enforces a rate limit: not more than 10 kernel messages
1307  * every 5s to make a denial-of-service attack impossible.
1308  */
1309 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1310 
1311 int printk_ratelimit(void)
1312 {
1313         return __ratelimit(&printk_ratelimit_state);
1314 }
1315 EXPORT_SYMBOL(printk_ratelimit);
1316 
1317 /**
1318  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1319  * @caller_jiffies: pointer to caller's state
1320  * @interval_msecs: minimum interval between prints
1321  *
1322  * printk_timed_ratelimit() returns true if more than @interval_msecs
1323  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1324  * returned true.
1325  */
1326 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1327                         unsigned int interval_msecs)
1328 {
1329         if (*caller_jiffies == 0
1330                         || !time_in_range(jiffies, *caller_jiffies,
1331                                         *caller_jiffies
1332                                         + msecs_to_jiffies(interval_msecs))) {
1333                 *caller_jiffies = jiffies;
1334                 return true;
1335         }
1336         return false;
1337 }
1338 EXPORT_SYMBOL(printk_timed_ratelimit);
1339 #endif
1340 
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