git.oblomov.eu Git - linux-2.6/blob - kernel/printk.c

   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  *     manfreds@colorfullife.com
  15  * Rewrote bits to get rid of console_lock
  16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
  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/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>
  32 #include <linux/bootmem.h>
  33 #include <linux/syscalls.h>
  34
  35 #include <asm/uaccess.h>
  36
  37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  38
  39 /* printk's without a loglevel use this.. */
  40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  41
  42 /* We show everything that is MORE important than this.. */
  43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  45
  46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  47
  48 int console_printk[4] = {
  49         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  50         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  51         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  52         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  53 };
  54
  55 EXPORT_SYMBOL(console_printk);
  56
  57 /*
  58  * Low lever drivers may need that to know if they can schedule in
  59  * their unblank() callback or not. So let's export it.
  60  */
  61 int oops_in_progress;
  62 EXPORT_SYMBOL(oops_in_progress);
  63
  64 /*
  65  * console_sem protects the console_drivers list, and also
  66  * provides serialisation for access to the entire console
  67  * driver system.
  68  */
  69 static DECLARE_MUTEX(console_sem);
  70 struct console *console_drivers;
  71 /*
  72  * This is used for debugging the mess that is the VT code by
  73  * keeping track if we have the console semaphore held. It's
  74  * definitely not the perfect debug tool (we don't know if _WE_
  75  * hold it are racing, but it helps tracking those weird code
  76  * path in the console code where we end up in places I want
  77  * locked without the console sempahore held
  78  */
  79 static int console_locked;
  80
  81 /*
  82  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  83  * It is also used in interesting ways to provide interlocking in
  84  * release_console_sem().
  85  */
  86 static DEFINE_SPINLOCK(logbuf_lock);
  87
  88 #define LOG_BUF_MASK    (log_buf_len-1)
  89 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  90
  91 /*
  92  * The indices into log_buf are not constrained to log_buf_len - they
  93  * must be masked before subscripting
  94  */
  95 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  96 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  97 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  98
  99 /*
 100  *      Array of consoles built from command line options (console=)
 101  */
 102 struct console_cmdline
 103 {
 104         char    name[8];                        /* Name of the driver       */
 105         int     index;                          /* Minor dev. to use        */
 106         char    *options;                       /* Options for the driver   */
 107 };
 108
 109 #define MAX_CMDLINECONSOLES 8
 110
 111 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 112 static int selected_console = -1;
 113 static int preferred_console = -1;
 114
 115 /* Flag: console code may call schedule() */
 116 static int console_may_schedule;
 117
 118 #ifdef CONFIG_PRINTK
 119
 120 static char __log_buf[__LOG_BUF_LEN];
 121 static char *log_buf = __log_buf;
 122 static int log_buf_len = __LOG_BUF_LEN;
 123 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 124
 125 /*
 126  *      Setup a list of consoles. Called from init/main.c
 127  */
 128 static int __init console_setup(char *str)
 129 {
 130         char name[sizeof(console_cmdline[0].name)];
 131         char *s, *options;
 132         int idx;
 133
 134         /*
 135          *      Decode str into name, index, options.
 136          */
 137         if (str[0] >= '0' && str[0] <= '9') {
 138                 strcpy(name, "ttyS");
 139                 strncpy(name + 4, str, sizeof(name) - 5);
 140         } else
 141                 strncpy(name, str, sizeof(name) - 1);
 142         name[sizeof(name) - 1] = 0;
 143         if ((options = strchr(str, ',')) != NULL)
 144                 *(options++) = 0;
 145 #ifdef __sparc__
 146         if (!strcmp(str, "ttya"))
 147                 strcpy(name, "ttyS0");
 148         if (!strcmp(str, "ttyb"))
 149                 strcpy(name, "ttyS1");
 150 #endif
 151         for(s = name; *s; s++)
 152                 if ((*s >= '0' && *s <= '9') || *s == ',')
 153                         break;
 154         idx = simple_strtoul(s, NULL, 10);
 155         *s = 0;
 156
 157         add_preferred_console(name, idx, options);
 158         return 1;
 159 }
 160
 161 __setup("console=", console_setup);
 162
 163 static int __init log_buf_len_setup(char *str)
 164 {
 165         unsigned long size = memparse(str, &str);
 166         unsigned long flags;
 167
 168         if (size)
 169                 size = roundup_pow_of_two(size);
 170         if (size > log_buf_len) {
 171                 unsigned long start, dest_idx, offset;
 172                 char * new_log_buf;
 173
 174                 new_log_buf = alloc_bootmem(size);
 175                 if (!new_log_buf) {
 176                         printk("log_buf_len: allocation failed\n");
 177                         goto out;
 178                 }
 179
 180                 spin_lock_irqsave(&logbuf_lock, flags);
 181                 log_buf_len = size;
 182                 log_buf = new_log_buf;
 183
 184                 offset = start = min(con_start, log_start);
 185                 dest_idx = 0;
 186                 while (start != log_end) {
 187                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 188                         start++;
 189                         dest_idx++;
 190                 }
 191                 log_start -= offset;
 192                 con_start -= offset;
 193                 log_end -= offset;
 194                 spin_unlock_irqrestore(&logbuf_lock, flags);
 195
 196                 printk("log_buf_len: %d\n", log_buf_len);
 197         }
 198 out:
 199
 200         return 1;
 201 }
 202
 203 __setup("log_buf_len=", log_buf_len_setup);
 204
 205 /*
 206  * Commands to do_syslog:
 207  *
 208  *      0 -- Close the log.  Currently a NOP.
 209  *      1 -- Open the log. Currently a NOP.
 210  *      2 -- Read from the log.
 211  *      3 -- Read all messages remaining in the ring buffer.
 212  *      4 -- Read and clear all messages remaining in the ring buffer
 213  *      5 -- Clear ring buffer.
 214  *      6 -- Disable printk's to console
 215  *      7 -- Enable printk's to console
 216  *      8 -- Set level of messages printed to console
 217  *      9 -- Return number of unread characters in the log buffer
 218  *     10 -- Return size of the log buffer
 219  */
 220 int do_syslog(int type, char __user * buf, int len)
 221 {
 222         unsigned long i, j, limit, count;
 223         int do_clear = 0;
 224         char c;
 225         int error = 0;
 226
 227         error = security_syslog(type);
 228         if (error)
 229                 return error;
 230
 231         switch (type) {
 232         case 0:         /* Close log */
 233                 break;
 234         case 1:         /* Open log */
 235                 break;
 236         case 2:         /* Read from log */
 237                 error = -EINVAL;
 238                 if (!buf || len < 0)
 239                         goto out;
 240                 error = 0;
 241                 if (!len)
 242                         goto out;
 243                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 244                         error = -EFAULT;
 245                         goto out;
 246                 }
 247                 error = wait_event_interruptible(log_wait, (log_start - log_end));
 248                 if (error)
 249                         goto out;
 250                 i = 0;
 251                 spin_lock_irq(&logbuf_lock);
 252                 while (!error && (log_start != log_end) && i < len) {
 253                         c = LOG_BUF(log_start);
 254                         log_start++;
 255                         spin_unlock_irq(&logbuf_lock);
 256                         error = __put_user(c,buf);
 257                         buf++;
 258                         i++;
 259                         cond_resched();
 260                         spin_lock_irq(&logbuf_lock);
 261                 }
 262                 spin_unlock_irq(&logbuf_lock);
 263                 if (!error)
 264                         error = i;
 265                 break;
 266         case 4:         /* Read/clear last kernel messages */
 267                 do_clear = 1;
 268                 /* FALL THRU */
 269         case 3:         /* Read last kernel messages */
 270                 error = -EINVAL;
 271                 if (!buf || len < 0)
 272                         goto out;
 273                 error = 0;
 274                 if (!len)
 275                         goto out;
 276                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 277                         error = -EFAULT;
 278                         goto out;
 279                 }
 280                 count = len;
 281                 if (count > log_buf_len)
 282                         count = log_buf_len;
 283                 spin_lock_irq(&logbuf_lock);
 284                 if (count > logged_chars)
 285                         count = logged_chars;
 286                 if (do_clear)
 287                         logged_chars = 0;
 288                 limit = log_end;
 289                 /*
 290                  * __put_user() could sleep, and while we sleep
 291                  * printk() could overwrite the messages
 292                  * we try to copy to user space. Therefore
 293                  * the messages are copied in reverse. <manfreds>
 294                  */
 295                 for(i = 0; i < count && !error; i++) {
 296                         j = limit-1-i;
 297                         if (j + log_buf_len < log_end)
 298                                 break;
 299                         c = LOG_BUF(j);
 300                         spin_unlock_irq(&logbuf_lock);
 301                         error = __put_user(c,&buf[count-1-i]);
 302                         cond_resched();
 303                         spin_lock_irq(&logbuf_lock);
 304                 }
 305                 spin_unlock_irq(&logbuf_lock);
 306                 if (error)
 307                         break;
 308                 error = i;
 309                 if(i != count) {
 310                         int offset = count-error;
 311                         /* buffer overflow during copy, correct user buffer. */
 312                         for(i=0;i<error;i++) {
 313                                 if (__get_user(c,&buf[i+offset]) ||
 314                                     __put_user(c,&buf[i])) {
 315                                         error = -EFAULT;
 316                                         break;
 317                                 }
 318                                 cond_resched();
 319                         }
 320                 }
 321                 break;
 322         case 5:         /* Clear ring buffer */
 323                 logged_chars = 0;
 324                 break;
 325         case 6:         /* Disable logging to console */
 326                 console_loglevel = minimum_console_loglevel;
 327                 break;
 328         case 7:         /* Enable logging to console */
 329                 console_loglevel = default_console_loglevel;
 330                 break;
 331         case 8:         /* Set level of messages printed to console */
 332                 error = -EINVAL;
 333                 if (len < 1 || len > 8)
 334                         goto out;
 335                 if (len < minimum_console_loglevel)
 336                         len = minimum_console_loglevel;
 337                 console_loglevel = len;
 338                 error = 0;
 339                 break;
 340         case 9:         /* Number of chars in the log buffer */
 341                 error = log_end - log_start;
 342                 break;
 343         case 10:        /* Size of the log buffer */
 344                 error = log_buf_len;
 345                 break;
 346         default:
 347                 error = -EINVAL;
 348                 break;
 349         }
 350 out:
 351         return error;
 352 }
 353
 354 asmlinkage long sys_syslog(int type, char __user * buf, int len)
 355 {
 356         return do_syslog(type, buf, len);
 357 }
 358
 359 /*
 360  * Call the console drivers on a range of log_buf
 361  */
 362 static void __call_console_drivers(unsigned long start, unsigned long end)
 363 {
 364         struct console *con;
 365
 366         for (con = console_drivers; con; con = con->next) {
 367                 if ((con->flags & CON_ENABLED) && con->write)
 368                         con->write(con, &LOG_BUF(start), end - start);
 369         }
 370 }
 371
 372 /*
 373  * Write out chars from start to end - 1 inclusive
 374  */
 375 static void _call_console_drivers(unsigned long start,
 376                                 unsigned long end, int msg_log_level)
 377 {
 378         if (msg_log_level < console_loglevel &&
 379                         console_drivers && start != end) {
 380                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 381                         /* wrapped write */
 382                         __call_console_drivers(start & LOG_BUF_MASK,
 383                                                 log_buf_len);
 384                         __call_console_drivers(0, end & LOG_BUF_MASK);
 385                 } else {
 386                         __call_console_drivers(start, end);
 387                 }
 388         }
 389 }
 390
 391 /*
 392  * Call the console drivers, asking them to write out
 393  * log_buf[start] to log_buf[end - 1].
 394  * The console_sem must be held.
 395  */
 396 static void call_console_drivers(unsigned long start, unsigned long end)
 397 {
 398         unsigned long cur_index, start_print;
 399         static int msg_level = -1;
 400
 401         if (((long)(start - end)) > 0)
 402                 BUG();
 403
 404         cur_index = start;
 405         start_print = start;
 406         while (cur_index != end) {
 407                 if (    msg_level < 0 &&
 408                         ((end - cur_index) > 2) &&
 409                         LOG_BUF(cur_index + 0) == '<' &&
 410                         LOG_BUF(cur_index + 1) >= '0' &&
 411                         LOG_BUF(cur_index + 1) <= '7' &&
 412                         LOG_BUF(cur_index + 2) == '>')
 413                 {
 414                         msg_level = LOG_BUF(cur_index + 1) - '0';
 415                         cur_index += 3;
 416                         start_print = cur_index;
 417                 }
 418                 while (cur_index != end) {
 419                         char c = LOG_BUF(cur_index);
 420                         cur_index++;
 421
 422                         if (c == '\n') {
 423                                 if (msg_level < 0) {
 424                                         /*
 425                                          * printk() has already given us loglevel tags in
 426                                          * the buffer.  This code is here in case the
 427                                          * log buffer has wrapped right round and scribbled
 428                                          * on those tags
 429                                          */
 430                                         msg_level = default_message_loglevel;
 431                                 }
 432                                 _call_console_drivers(start_print, cur_index, msg_level);
 433                                 msg_level = -1;
 434                                 start_print = cur_index;
 435                                 break;
 436                         }
 437                 }
 438         }
 439         _call_console_drivers(start_print, end, msg_level);
 440 }
 441
 442 static void emit_log_char(char c)
 443 {
 444         LOG_BUF(log_end) = c;
 445         log_end++;
 446         if (log_end - log_start > log_buf_len)
 447                 log_start = log_end - log_buf_len;
 448         if (log_end - con_start > log_buf_len)
 449                 con_start = log_end - log_buf_len;
 450         if (logged_chars < log_buf_len)
 451                 logged_chars++;
 452 }
 453
 454 /*
 455  * Zap console related locks when oopsing. Only zap at most once
 456  * every 10 seconds, to leave time for slow consoles to print a
 457  * full oops.
 458  */
 459 static void zap_locks(void)
 460 {
 461         static unsigned long oops_timestamp;
 462
 463         if (time_after_eq(jiffies, oops_timestamp) &&
 464                         !time_after(jiffies, oops_timestamp + 30*HZ))
 465                 return;
 466
 467         oops_timestamp = jiffies;
 468
 469         /* If a crash is occurring, make sure we can't deadlock */
 470         spin_lock_init(&logbuf_lock);
 471         /* And make sure that we print immediately */
 472         init_MUTEX(&console_sem);
 473 }
 474
 475 #if defined(CONFIG_PRINTK_TIME)
 476 static int printk_time = 1;
 477 #else
 478 static int printk_time = 0;
 479 #endif
 480
 481 static int __init printk_time_setup(char *str)
 482 {
 483         if (*str)
 484                 return 0;
 485         printk_time = 1;
 486         return 1;
 487 }
 488
 489 __setup("time", printk_time_setup);
 490
 491 __attribute__((weak)) unsigned long long printk_clock(void)
 492 {
 493         return sched_clock();
 494 }
 495
 496 /*
 497  * This is printk.  It can be called from any context.  We want it to work.
 498  *
 499  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 500  * call the console drivers.  If we fail to get the semaphore we place the output
 501  * into the log buffer and return.  The current holder of the console_sem will
 502  * notice the new output in release_console_sem() and will send it to the
 503  * consoles before releasing the semaphore.
 504  *
 505  * One effect of this deferred printing is that code which calls printk() and
 506  * then changes console_loglevel may break. This is because console_loglevel
 507  * is inspected when the actual printing occurs.
 508  */
 509
 510 asmlinkage int printk(const char *fmt, ...)
 511 {
 512         va_list args;
 513         int r;
 514
 515         va_start(args, fmt);
 516         r = vprintk(fmt, args);
 517         va_end(args);
 518
 519         return r;
 520 }
 521
 522 /* cpu currently holding logbuf_lock */
 523 static volatile unsigned int printk_cpu = UINT_MAX;
 524
 525 asmlinkage int vprintk(const char *fmt, va_list args)
 526 {
 527         unsigned long flags;
 528         int printed_len;
 529         char *p;
 530         static char printk_buf[1024];
 531         static int log_level_unknown = 1;
 532
 533         preempt_disable();
 534         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 535                 /* If a crash is occurring during printk() on this CPU,
 536                  * make sure we can't deadlock */
 537                 zap_locks();
 538
 539         /* This stops the holder of console_sem just where we want him */
 540         spin_lock_irqsave(&logbuf_lock, flags);
 541         printk_cpu = smp_processor_id();
 542
 543         /* Emit the output into the temporary buffer */
 544         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 545
 546         /*
 547          * Copy the output into log_buf.  If the caller didn't provide
 548          * appropriate log level tags, we insert them here
 549          */
 550         for (p = printk_buf; *p; p++) {
 551                 if (log_level_unknown) {
 552                         /* log_level_unknown signals the start of a new line */
 553                         if (printk_time) {
 554                                 int loglev_char;
 555                                 char tbuf[50], *tp;
 556                                 unsigned tlen;
 557                                 unsigned long long t;
 558                                 unsigned long nanosec_rem;
 559
 560                                 /*
 561                                  * force the log level token to be
 562                                  * before the time output.
 563                                  */
 564                                 if (p[0] == '<' && p[1] >='0' &&
 565                                    p[1] <= '7' && p[2] == '>') {
 566                                         loglev_char = p[1];
 567                                         p += 3;
 568                                         printed_len += 3;
 569                                 } else {
 570                                         loglev_char = default_message_loglevel
 571                                                 + '0';
 572                                 }
 573                                 t = printk_clock();
 574                                 nanosec_rem = do_div(t, 1000000000);
 575                                 tlen = sprintf(tbuf,
 576                                                 "<%c>[%5lu.%06lu] ",
 577                                                 loglev_char,
 578                                                 (unsigned long)t,
 579                                                 nanosec_rem/1000);
 580
 581                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 582                                         emit_log_char(*tp);
 583                                 printed_len += tlen - 3;
 584                         } else {
 585                                 if (p[0] != '<' || p[1] < '0' ||
 586                                    p[1] > '7' || p[2] != '>') {
 587                                         emit_log_char('<');
 588                                         emit_log_char(default_message_loglevel
 589                                                 + '0');
 590                                         emit_log_char('>');
 591                                 }
 592                                 printed_len += 3;
 593                         }
 594                         log_level_unknown = 0;
 595                         if (!*p)
 596                                 break;
 597                 }
 598                 emit_log_char(*p);
 599                 if (*p == '\n')
 600                         log_level_unknown = 1;
 601         }
 602
 603         if (!cpu_online(smp_processor_id())) {
 604                 /*
 605                  * Some console drivers may assume that per-cpu resources have
 606                  * been allocated.  So don't allow them to be called by this
 607                  * CPU until it is officially up.  We shouldn't be calling into
 608                  * random console drivers on a CPU which doesn't exist yet..
 609                  */
 610                 printk_cpu = UINT_MAX;
 611                 spin_unlock_irqrestore(&logbuf_lock, flags);
 612                 goto out;
 613         }
 614         if (!down_trylock(&console_sem)) {
 615                 console_locked = 1;
 616                 /*
 617                  * We own the drivers.  We can drop the spinlock and let
 618                  * release_console_sem() print the text
 619                  */
 620                 printk_cpu = UINT_MAX;
 621                 spin_unlock_irqrestore(&logbuf_lock, flags);
 622                 console_may_schedule = 0;
 623                 release_console_sem();
 624         } else {
 625                 /*
 626                  * Someone else owns the drivers.  We drop the spinlock, which
 627                  * allows the semaphore holder to proceed and to call the
 628                  * console drivers with the output which we just produced.
 629                  */
 630                 printk_cpu = UINT_MAX;
 631                 spin_unlock_irqrestore(&logbuf_lock, flags);
 632         }
 633 out:
 634         preempt_enable();
 635         return printed_len;
 636 }
 637 EXPORT_SYMBOL(printk);
 638 EXPORT_SYMBOL(vprintk);
 639
 640 #else
 641
 642 asmlinkage long sys_syslog(int type, char __user * buf, int len)
 643 {
 644         return 0;
 645 }
 646
 647 int do_syslog(int type, char __user * buf, int len) { return 0; }
 648 static void call_console_drivers(unsigned long start, unsigned long end) {}
 649
 650 #endif
 651
 652 /**
 653  * add_preferred_console - add a device to the list of preferred consoles.
 654  *
 655  * The last preferred console added will be used for kernel messages
 656  * and stdin/out/err for init.  Normally this is used by console_setup
 657  * above to handle user-supplied console arguments; however it can also
 658  * be used by arch-specific code either to override the user or more
 659  * commonly to provide a default console (ie from PROM variables) when
 660  * the user has not supplied one.
 661  */
 662 int __init add_preferred_console(char *name, int idx, char *options)
 663 {
 664         struct console_cmdline *c;
 665         int i;
 666
 667         /*
 668          *      See if this tty is not yet registered, and
 669          *      if we have a slot free.
 670          */
 671         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 672                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 673                           console_cmdline[i].index == idx) {
 674                                 selected_console = i;
 675                                 return 0;
 676                 }
 677         if (i == MAX_CMDLINECONSOLES)
 678                 return -E2BIG;
 679         selected_console = i;
 680         c = &console_cmdline[i];
 681         memcpy(c->name, name, sizeof(c->name));
 682         c->name[sizeof(c->name) - 1] = 0;
 683         c->options = options;
 684         c->index = idx;
 685         return 0;
 686 }
 687
 688 /**
 689  * acquire_console_sem - lock the console system for exclusive use.
 690  *
 691  * Acquires a semaphore which guarantees that the caller has
 692  * exclusive access to the console system and the console_drivers list.
 693  *
 694  * Can sleep, returns nothing.
 695  */
 696 void acquire_console_sem(void)
 697 {
 698         if (in_interrupt())
 699                 BUG();
 700         down(&console_sem);
 701         console_locked = 1;
 702         console_may_schedule = 1;
 703 }
 704 EXPORT_SYMBOL(acquire_console_sem);
 705
 706 int try_acquire_console_sem(void)
 707 {
 708         if (down_trylock(&console_sem))
 709                 return -1;
 710         console_locked = 1;
 711         console_may_schedule = 0;
 712         return 0;
 713 }
 714 EXPORT_SYMBOL(try_acquire_console_sem);
 715
 716 int is_console_locked(void)
 717 {
 718         return console_locked;
 719 }
 720 EXPORT_SYMBOL(is_console_locked);
 721
 722 /**
 723  * release_console_sem - unlock the console system
 724  *
 725  * Releases the semaphore which the caller holds on the console system
 726  * and the console driver list.
 727  *
 728  * While the semaphore was held, console output may have been buffered
 729  * by printk().  If this is the case, release_console_sem() emits
 730  * the output prior to releasing the semaphore.
 731  *
 732  * If there is output waiting for klogd, we wake it up.
 733  *
 734  * release_console_sem() may be called from any context.
 735  */
 736 void release_console_sem(void)
 737 {
 738         unsigned long flags;
 739         unsigned long _con_start, _log_end;
 740         unsigned long wake_klogd = 0;
 741
 742         for ( ; ; ) {
 743                 spin_lock_irqsave(&logbuf_lock, flags);
 744                 wake_klogd |= log_start - log_end;
 745                 if (con_start == log_end)
 746                         break;                  /* Nothing to print */
 747                 _con_start = con_start;
 748                 _log_end = log_end;
 749                 con_start = log_end;            /* Flush */
 750                 spin_unlock(&logbuf_lock);
 751                 call_console_drivers(_con_start, _log_end);
 752                 local_irq_restore(flags);
 753         }
 754         console_locked = 0;
 755         console_may_schedule = 0;
 756         up(&console_sem);
 757         spin_unlock_irqrestore(&logbuf_lock, flags);
 758         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 759                 wake_up_interruptible(&log_wait);
 760 }
 761 EXPORT_SYMBOL(release_console_sem);
 762
 763 /** console_conditional_schedule - yield the CPU if required
 764  *
 765  * If the console code is currently allowed to sleep, and
 766  * if this CPU should yield the CPU to another task, do
 767  * so here.
 768  *
 769  * Must be called within acquire_console_sem().
 770  */
 771 void __sched console_conditional_schedule(void)
 772 {
 773         if (console_may_schedule)
 774                 cond_resched();
 775 }
 776 EXPORT_SYMBOL(console_conditional_schedule);
 777
 778 void console_print(const char *s)
 779 {
 780         printk(KERN_EMERG "%s", s);
 781 }
 782 EXPORT_SYMBOL(console_print);
 783
 784 void console_unblank(void)
 785 {
 786         struct console *c;
 787
 788         /*
 789          * console_unblank can no longer be called in interrupt context unless
 790          * oops_in_progress is set to 1..
 791          */
 792         if (oops_in_progress) {
 793                 if (down_trylock(&console_sem) != 0)
 794                         return;
 795         } else
 796                 acquire_console_sem();
 797
 798         console_locked = 1;
 799         console_may_schedule = 0;
 800         for (c = console_drivers; c != NULL; c = c->next)
 801                 if ((c->flags & CON_ENABLED) && c->unblank)
 802                         c->unblank();
 803         release_console_sem();
 804 }
 805 EXPORT_SYMBOL(console_unblank);
 806
 807 /*
 808  * Return the console tty driver structure and its associated index
 809  */
 810 struct tty_driver *console_device(int *index)
 811 {
 812         struct console *c;
 813         struct tty_driver *driver = NULL;
 814
 815         acquire_console_sem();
 816         for (c = console_drivers; c != NULL; c = c->next) {
 817                 if (!c->device)
 818                         continue;
 819                 driver = c->device(c, index);
 820                 if (driver)
 821                         break;
 822         }
 823         release_console_sem();
 824         return driver;
 825 }
 826
 827 /*
 828  * Prevent further output on the passed console device so that (for example)
 829  * serial drivers can disable console output before suspending a port, and can
 830  * re-enable output afterwards.
 831  */
 832 void console_stop(struct console *console)
 833 {
 834         acquire_console_sem();
 835         console->flags &= ~CON_ENABLED;
 836         release_console_sem();
 837 }
 838 EXPORT_SYMBOL(console_stop);
 839
 840 void console_start(struct console *console)
 841 {
 842         acquire_console_sem();
 843         console->flags |= CON_ENABLED;
 844         release_console_sem();
 845 }
 846 EXPORT_SYMBOL(console_start);
 847
 848 /*
 849  * The console driver calls this routine during kernel initialization
 850  * to register the console printing procedure with printk() and to
 851  * print any messages that were printed by the kernel before the
 852  * console driver was initialized.
 853  */
 854 void register_console(struct console * console)
 855 {
 856         int     i;
 857         unsigned long flags;
 858
 859         if (preferred_console < 0)
 860                 preferred_console = selected_console;
 861
 862         /*
 863          *      See if we want to use this console driver. If we
 864          *      didn't select a console we take the first one
 865          *      that registers here.
 866          */
 867         if (preferred_console < 0) {
 868                 if (console->index < 0)
 869                         console->index = 0;
 870                 if (console->setup == NULL ||
 871                     console->setup(console, NULL) == 0) {
 872                         console->flags |= CON_ENABLED | CON_CONSDEV;
 873                         preferred_console = 0;
 874                 }
 875         }
 876
 877         /*
 878          *      See if this console matches one we selected on
 879          *      the command line.
 880          */
 881         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
 882                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 883                         continue;
 884                 if (console->index >= 0 &&
 885                     console->index != console_cmdline[i].index)
 886                         continue;
 887                 if (console->index < 0)
 888                         console->index = console_cmdline[i].index;
 889                 if (console->setup &&
 890                     console->setup(console, console_cmdline[i].options) != 0)
 891                         break;
 892                 console->flags |= CON_ENABLED;
 893                 console->index = console_cmdline[i].index;
 894                 if (i == selected_console) {
 895                         console->flags |= CON_CONSDEV;
 896                         preferred_console = selected_console;
 897                 }
 898                 break;
 899         }
 900
 901         if (!(console->flags & CON_ENABLED))
 902                 return;
 903
 904         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 905                 unregister_console(console_drivers);
 906                 console->flags &= ~CON_PRINTBUFFER;
 907         }
 908
 909         /*
 910          *      Put this console in the list - keep the
 911          *      preferred driver at the head of the list.
 912          */
 913         acquire_console_sem();
 914         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 915                 console->next = console_drivers;
 916                 console_drivers = console;
 917                 if (console->next)
 918                         console->next->flags &= ~CON_CONSDEV;
 919         } else {
 920                 console->next = console_drivers->next;
 921                 console_drivers->next = console;
 922         }
 923         if (console->flags & CON_PRINTBUFFER) {
 924                 /*
 925                  * release_console_sem() will print out the buffered messages
 926                  * for us.
 927                  */
 928                 spin_lock_irqsave(&logbuf_lock, flags);
 929                 con_start = log_start;
 930                 spin_unlock_irqrestore(&logbuf_lock, flags);
 931         }
 932         release_console_sem();
 933 }
 934 EXPORT_SYMBOL(register_console);
 935
 936 int unregister_console(struct console * console)
 937 {
 938         struct console *a,*b;
 939         int res = 1;
 940
 941         acquire_console_sem();
 942         if (console_drivers == console) {
 943                 console_drivers=console->next;
 944                 res = 0;
 945         } else {
 946                 for (a=console_drivers->next, b=console_drivers ;
 947                      a; b=a, a=b->next) {
 948                         if (a == console) {
 949                                 b->next = a->next;
 950                                 res = 0;
 951                                 break;
 952                         }
 953                 }
 954         }
 955
 956         /* If last console is removed, we re-enable picking the first
 957          * one that gets registered. Without that, pmac early boot console
 958          * would prevent fbcon from taking over.
 959          *
 960          * If this isn't the last console and it has CON_CONSDEV set, we
 961          * need to set it on the next preferred console.
 962          */
 963         if (console_drivers == NULL)
 964                 preferred_console = selected_console;
 965         else if (console->flags & CON_CONSDEV)
 966                 console_drivers->flags |= CON_CONSDEV;
 967
 968         release_console_sem();
 969         return res;
 970 }
 971 EXPORT_SYMBOL(unregister_console);
 972
 973 /**
 974  * tty_write_message - write a message to a certain tty, not just the console.
 975  *
 976  * This is used for messages that need to be redirected to a specific tty.
 977  * We don't put it into the syslog queue right now maybe in the future if
 978  * really needed.
 979  */
 980 void tty_write_message(struct tty_struct *tty, char *msg)
 981 {
 982         if (tty && tty->driver->write)
 983                 tty->driver->write(tty, msg, strlen(msg));
 984         return;
 985 }
 986
 987 /*
 988  * printk rate limiting, lifted from the networking subsystem.
 989  *
 990  * This enforces a rate limit: not more than one kernel message
 991  * every printk_ratelimit_jiffies to make a denial-of-service
 992  * attack impossible.
 993  */
 994 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
 995 {
 996         static DEFINE_SPINLOCK(ratelimit_lock);
 997         static unsigned long toks = 10*5*HZ;
 998         static unsigned long last_msg;
 999         static int missed;
1000         unsigned long flags;
1001         unsigned long now = jiffies;
1002
1003         spin_lock_irqsave(&ratelimit_lock, flags);
1004         toks += now - last_msg;
1005         last_msg = now;
1006         if (toks > (ratelimit_burst * ratelimit_jiffies))
1007                 toks = ratelimit_burst * ratelimit_jiffies;
1008         if (toks >= ratelimit_jiffies) {
1009                 int lost = missed;
1010                 missed = 0;
1011                 toks -= ratelimit_jiffies;
1012                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1013                 if (lost)
1014                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1015                 return 1;
1016         }
1017         missed++;
1018         spin_unlock_irqrestore(&ratelimit_lock, flags);
1019         return 0;
1020 }
1021 EXPORT_SYMBOL(__printk_ratelimit);
1022
1023 /* minimum time in jiffies between messages */
1024 int printk_ratelimit_jiffies = 5*HZ;
1025
1026 /* number of messages we send before ratelimiting */
1027 int printk_ratelimit_burst = 10;
1028
1029 int printk_ratelimit(void)
1030 {
1031         return __printk_ratelimit(printk_ratelimit_jiffies,
1032                                 printk_ratelimit_burst);
1033 }
1034 EXPORT_SYMBOL(printk_ratelimit);