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