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  *     manfred@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 #include <linux/vserver/cvirt.h>
  35
  36 #include <asm/uaccess.h>
  37
  38 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  39
  40 /* printk's without a loglevel use this.. */
  41 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  42
  43 /* We show everything that is MORE important than this.. */
  44 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  45 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  46
  47 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  48
  49 int console_printk[4] = {
  50         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  51         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  52         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  53         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  54 };
  55
  56 EXPORT_SYMBOL(console_printk);
  57
  58 /*
  59  * Low lever drivers may need that to know if they can schedule in
  60  * their unblank() callback or not. So let's export it.
  61  */
  62 int oops_in_progress;
  63 EXPORT_SYMBOL(oops_in_progress);
  64
  65 /*
  66  * console_sem protects the console_drivers list, and also
  67  * provides serialisation for access to the entire console
  68  * driver system.
  69  */
  70 static DECLARE_MUTEX(console_sem);
  71 struct console *console_drivers;
  72 /*
  73  * This is used for debugging the mess that is the VT code by
  74  * keeping track if we have the console semaphore held. It's
  75  * definitely not the perfect debug tool (we don't know if _WE_
  76  * hold it are racing, but it helps tracking those weird code
  77  * path in the console code where we end up in places I want
  78  * locked without the console sempahore held
  79  */
  80 static int console_locked;
  81
  82 /*
  83  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  84  * It is also used in interesting ways to provide interlocking in
  85  * release_console_sem().
  86  */
  87 static DEFINE_SPINLOCK(logbuf_lock);
  88
  89 #define LOG_BUF_MASK    (log_buf_len-1)
  90 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  91
  92 /*
  93  * The indices into log_buf are not constrained to log_buf_len - they
  94  * must be masked before subscripting
  95  */
  96 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  97 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  98 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  99
 100 /*
 101  *      Array of consoles built from command line options (console=)
 102  */
 103 struct console_cmdline
 104 {
 105         char    name[8];                        /* Name of the driver       */
 106         int     index;                          /* Minor dev. to use        */
 107         char    *options;                       /* Options for the driver   */
 108 };
 109
 110 #define MAX_CMDLINECONSOLES 8
 111
 112 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 113 static int selected_console = -1;
 114 static int preferred_console = -1;
 115
 116 /* Flag: console code may call schedule() */
 117 static int console_may_schedule;
 118
 119 #ifdef CONFIG_PRINTK
 120
 121 static char __log_buf[__LOG_BUF_LEN];
 122 static char *log_buf = __log_buf;
 123 static int log_buf_len = __LOG_BUF_LEN;
 124 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 125
 126 /*
 127  *      Setup a list of consoles. Called from init/main.c
 128  */
 129 static int __init console_setup(char *str)
 130 {
 131         char name[sizeof(console_cmdline[0].name)];
 132         char *s, *options;
 133         int idx;
 134
 135         /*
 136          *      Decode str into name, index, options.
 137          */
 138         if (str[0] >= '0' && str[0] <= '9') {
 139                 strcpy(name, "ttyS");
 140                 strncpy(name + 4, str, sizeof(name) - 5);
 141         } else
 142                 strncpy(name, str, sizeof(name) - 1);
 143         name[sizeof(name) - 1] = 0;
 144         if ((options = strchr(str, ',')) != NULL)
 145                 *(options++) = 0;
 146 #ifdef __sparc__
 147         if (!strcmp(str, "ttya"))
 148                 strcpy(name, "ttyS0");
 149         if (!strcmp(str, "ttyb"))
 150                 strcpy(name, "ttyS1");
 151 #endif
 152         for (s = name; *s; s++)
 153                 if ((*s >= '0' && *s <= '9') || *s == ',')
 154                         break;
 155         idx = simple_strtoul(s, NULL, 10);
 156         *s = 0;
 157
 158         add_preferred_console(name, idx, options);
 159         return 1;
 160 }
 161
 162 __setup("console=", console_setup);
 163
 164 static int __init log_buf_len_setup(char *str)
 165 {
 166         unsigned long size = memparse(str, &str);
 167         unsigned long flags;
 168
 169         if (size)
 170                 size = roundup_pow_of_two(size);
 171         if (size > log_buf_len) {
 172                 unsigned long start, dest_idx, offset;
 173                 char *new_log_buf;
 174
 175                 new_log_buf = alloc_bootmem(size);
 176                 if (!new_log_buf) {
 177                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 178                         goto out;
 179                 }
 180
 181                 spin_lock_irqsave(&logbuf_lock, flags);
 182                 log_buf_len = size;
 183                 log_buf = new_log_buf;
 184
 185                 offset = start = min(con_start, log_start);
 186                 dest_idx = 0;
 187                 while (start != log_end) {
 188                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 189                         start++;
 190                         dest_idx++;
 191                 }
 192                 log_start -= offset;
 193                 con_start -= offset;
 194                 log_end -= offset;
 195                 spin_unlock_irqrestore(&logbuf_lock, flags);
 196
 197                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 198         }
 199 out:
 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;
 226
 227         error = security_syslog(type);
 228         if (error)
 229                 return error;
 230
 231         if ((type >= 2) && (type <= 4)) {
 232                 error = -EINVAL;
 233                 if (!buf || len < 0)
 234                         goto out;
 235                 error = 0;
 236                 if (!len)
 237                         goto out;
 238                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 239                         error = -EFAULT;
 240                         goto out;
 241                 }
 242         }
 243         if (!vx_check(0, VX_ADMIN|VX_WATCH))
 244                 return vx_do_syslog(type, buf, len);
 245
 246         switch (type) {
 247         case 0:         /* Close log */
 248                 break;
 249         case 1:         /* Open log */
 250                 break;
 251         case 2:         /* Read from log */
 252                 error = wait_event_interruptible(log_wait,
 253                                                         (log_start - log_end));
 254                 if (error)
 255                         goto out;
 256                 i = 0;
 257                 spin_lock_irq(&logbuf_lock);
 258                 while (!error && (log_start != log_end) && i < len) {
 259                         c = LOG_BUF(log_start);
 260                         log_start++;
 261                         spin_unlock_irq(&logbuf_lock);
 262                         error = __put_user(c,buf);
 263                         buf++;
 264                         i++;
 265                         cond_resched();
 266                         spin_lock_irq(&logbuf_lock);
 267                 }
 268                 spin_unlock_irq(&logbuf_lock);
 269                 if (!error)
 270                         error = i;
 271                 break;
 272         case 4:         /* Read/clear last kernel messages */
 273                 do_clear = 1;
 274                 /* FALL THRU */
 275         case 3:         /* Read last kernel messages */
 276                 count = len;
 277                 if (count > log_buf_len)
 278                         count = log_buf_len;
 279                 spin_lock_irq(&logbuf_lock);
 280                 if (count > logged_chars)
 281                         count = logged_chars;
 282                 if (do_clear)
 283                         logged_chars = 0;
 284                 limit = log_end;
 285                 /*
 286                  * __put_user() could sleep, and while we sleep
 287                  * printk() could overwrite the messages
 288                  * we try to copy to user space. Therefore
 289                  * the messages are copied in reverse. <manfreds>
 290                  */
 291                 for (i = 0; i < count && !error; i++) {
 292                         j = limit-1-i;
 293                         if (j + log_buf_len < log_end)
 294                                 break;
 295                         c = LOG_BUF(j);
 296                         spin_unlock_irq(&logbuf_lock);
 297                         error = __put_user(c,&buf[count-1-i]);
 298                         cond_resched();
 299                         spin_lock_irq(&logbuf_lock);
 300                 }
 301                 spin_unlock_irq(&logbuf_lock);
 302                 if (error)
 303                         break;
 304                 error = i;
 305                 if (i != count) {
 306                         int offset = count-error;
 307                         /* buffer overflow during copy, correct user buffer. */
 308                         for (i = 0; i < error; i++) {
 309                                 if (__get_user(c,&buf[i+offset]) ||
 310                                     __put_user(c,&buf[i])) {
 311                                         error = -EFAULT;
 312                                         break;
 313                                 }
 314                                 cond_resched();
 315                         }
 316                 }
 317                 break;
 318         case 5:         /* Clear ring buffer */
 319                 logged_chars = 0;
 320                 break;
 321         case 6:         /* Disable logging to console */
 322                 console_loglevel = minimum_console_loglevel;
 323                 break;
 324         case 7:         /* Enable logging to console */
 325                 console_loglevel = default_console_loglevel;
 326                 break;
 327         case 8:         /* Set level of messages printed to console */
 328                 error = -EINVAL;
 329                 if (len < 1 || len > 8)
 330                         goto out;
 331                 if (len < minimum_console_loglevel)
 332                         len = minimum_console_loglevel;
 333                 console_loglevel = len;
 334                 error = 0;
 335                 break;
 336         case 9:         /* Number of chars in the log buffer */
 337                 error = log_end - log_start;
 338                 break;
 339         case 10:        /* Size of the log buffer */
 340                 error = log_buf_len;
 341                 break;
 342         default:
 343                 error = -EINVAL;
 344                 break;
 345         }
 346 out:
 347         return error;
 348 }
 349
 350 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 351 {
 352         return do_syslog(type, buf, len);
 353 }
 354
 355 /*
 356  * Call the console drivers on a range of log_buf
 357  */
 358 static void __call_console_drivers(unsigned long start, unsigned long end)
 359 {
 360         struct console *con;
 361
 362         for (con = console_drivers; con; con = con->next) {
 363                 if ((con->flags & CON_ENABLED) && con->write)
 364                         con->write(con, &LOG_BUF(start), end - start);
 365         }
 366 }
 367
 368 /*
 369  * Write out chars from start to end - 1 inclusive
 370  */
 371 static void _call_console_drivers(unsigned long start,
 372                                 unsigned long end, int msg_log_level)
 373 {
 374         if (msg_log_level < console_loglevel &&
 375                         console_drivers && start != end) {
 376                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 377                         /* wrapped write */
 378                         __call_console_drivers(start & LOG_BUF_MASK,
 379                                                 log_buf_len);
 380                         __call_console_drivers(0, end & LOG_BUF_MASK);
 381                 } else {
 382                         __call_console_drivers(start, end);
 383                 }
 384         }
 385 }
 386
 387 /*
 388  * Call the console drivers, asking them to write out
 389  * log_buf[start] to log_buf[end - 1].
 390  * The console_sem must be held.
 391  */
 392 static void call_console_drivers(unsigned long start, unsigned long end)
 393 {
 394         unsigned long cur_index, start_print;
 395         static int msg_level = -1;
 396
 397         if (((long)(start - end)) > 0)
 398                 BUG();
 399
 400         cur_index = start;
 401         start_print = start;
 402         while (cur_index != end) {
 403                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 404                                 LOG_BUF(cur_index + 0) == '<' &&
 405                                 LOG_BUF(cur_index + 1) >= '0' &&
 406                                 LOG_BUF(cur_index + 1) <= '7' &&
 407                                 LOG_BUF(cur_index + 2) == '>') {
 408                         msg_level = LOG_BUF(cur_index + 1) - '0';
 409                         cur_index += 3;
 410                         start_print = cur_index;
 411                 }
 412                 while (cur_index != end) {
 413                         char c = LOG_BUF(cur_index);
 414
 415                         cur_index++;
 416                         if (c == '\n') {
 417                                 if (msg_level < 0) {
 418                                         /*
 419                                          * printk() has already given us loglevel tags in
 420                                          * the buffer.  This code is here in case the
 421                                          * log buffer has wrapped right round and scribbled
 422                                          * on those tags
 423                                          */
 424                                         msg_level = default_message_loglevel;
 425                                 }
 426                                 _call_console_drivers(start_print, cur_index, msg_level);
 427                                 msg_level = -1;
 428                                 start_print = cur_index;
 429                                 break;
 430                         }
 431                 }
 432         }
 433         _call_console_drivers(start_print, end, msg_level);
 434 }
 435
 436 static void emit_log_char(char c)
 437 {
 438         LOG_BUF(log_end) = c;
 439         log_end++;
 440         if (log_end - log_start > log_buf_len)
 441                 log_start = log_end - log_buf_len;
 442         if (log_end - con_start > log_buf_len)
 443                 con_start = log_end - log_buf_len;
 444         if (logged_chars < log_buf_len)
 445                 logged_chars++;
 446 }
 447
 448 /*
 449  * Zap console related locks when oopsing. Only zap at most once
 450  * every 10 seconds, to leave time for slow consoles to print a
 451  * full oops.
 452  */
 453 static void zap_locks(void)
 454 {
 455         static unsigned long oops_timestamp;
 456
 457         if (time_after_eq(jiffies, oops_timestamp) &&
 458                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 459                 return;
 460
 461         oops_timestamp = jiffies;
 462
 463         /* If a crash is occurring, make sure we can't deadlock */
 464         spin_lock_init(&logbuf_lock);
 465         /* And make sure that we print immediately */
 466         init_MUTEX(&console_sem);
 467 }
 468
 469 #if defined(CONFIG_PRINTK_TIME)
 470 static int printk_time = 1;
 471 #else
 472 static int printk_time = 0;
 473 #endif
 474
 475 static int __init printk_time_setup(char *str)
 476 {
 477         if (*str)
 478                 return 0;
 479         printk_time = 1;
 480         return 1;
 481 }
 482
 483 __setup("time", printk_time_setup);
 484
 485 __attribute__((weak)) unsigned long long printk_clock(void)
 486 {
 487         return sched_clock();
 488 }
 489
 490 /**
 491  * printk - print a kernel message
 492  * @fmt: format string
 493  *
 494  * This is printk.  It can be called from any context.  We want it to work.
 495  *
 496  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 497  * call the console drivers.  If we fail to get the semaphore we place the output
 498  * into the log buffer and return.  The current holder of the console_sem will
 499  * notice the new output in release_console_sem() and will send it to the
 500  * consoles before releasing the semaphore.
 501  *
 502  * One effect of this deferred printing is that code which calls printk() and
 503  * then changes console_loglevel may break. This is because console_loglevel
 504  * is inspected when the actual printing occurs.
 505  *
 506  * See also:
 507  * printf(3)
 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;
 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                                         printed_len += 3;
 592                                 }
 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)
 648 {
 649         return 0;
 650 }
 651
 652 static void call_console_drivers(unsigned long start, unsigned long end)
 653 {
 654 }
 655
 656 #endif
 657
 658 /**
 659  * add_preferred_console - add a device to the list of preferred consoles.
 660  * @name: device name
 661  * @idx: device index
 662  * @options: options for this console
 663  *
 664  * The last preferred console added will be used for kernel messages
 665  * and stdin/out/err for init.  Normally this is used by console_setup
 666  * above to handle user-supplied console arguments; however it can also
 667  * be used by arch-specific code either to override the user or more
 668  * commonly to provide a default console (ie from PROM variables) when
 669  * the user has not supplied one.
 670  */
 671 int __init add_preferred_console(char *name, int idx, char *options)
 672 {
 673         struct console_cmdline *c;
 674         int i;
 675
 676         /*
 677          *      See if this tty is not yet registered, and
 678          *      if we have a slot free.
 679          */
 680         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 681                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 682                           console_cmdline[i].index == idx) {
 683                                 selected_console = i;
 684                                 return 0;
 685                 }
 686         if (i == MAX_CMDLINECONSOLES)
 687                 return -E2BIG;
 688         selected_console = i;
 689         c = &console_cmdline[i];
 690         memcpy(c->name, name, sizeof(c->name));
 691         c->name[sizeof(c->name) - 1] = 0;
 692         c->options = options;
 693         c->index = idx;
 694         return 0;
 695 }
 696
 697 /**
 698  * acquire_console_sem - lock the console system for exclusive use.
 699  *
 700  * Acquires a semaphore which guarantees that the caller has
 701  * exclusive access to the console system and the console_drivers list.
 702  *
 703  * Can sleep, returns nothing.
 704  */
 705 void acquire_console_sem(void)
 706 {
 707         if (in_interrupt())
 708                 BUG();
 709         down(&console_sem);
 710         console_locked = 1;
 711         console_may_schedule = 1;
 712 }
 713 EXPORT_SYMBOL(acquire_console_sem);
 714
 715 int try_acquire_console_sem(void)
 716 {
 717         if (down_trylock(&console_sem))
 718                 return -1;
 719         console_locked = 1;
 720         console_may_schedule = 0;
 721         return 0;
 722 }
 723 EXPORT_SYMBOL(try_acquire_console_sem);
 724
 725 int is_console_locked(void)
 726 {
 727         return console_locked;
 728 }
 729 EXPORT_SYMBOL(is_console_locked);
 730
 731 /**
 732  * release_console_sem - unlock the console system
 733  *
 734  * Releases the semaphore which the caller holds on the console system
 735  * and the console driver list.
 736  *
 737  * While the semaphore was held, console output may have been buffered
 738  * by printk().  If this is the case, release_console_sem() emits
 739  * the output prior to releasing the semaphore.
 740  *
 741  * If there is output waiting for klogd, we wake it up.
 742  *
 743  * release_console_sem() may be called from any context.
 744  */
 745 void release_console_sem(void)
 746 {
 747         unsigned long flags;
 748         unsigned long _con_start, _log_end;
 749         unsigned long wake_klogd = 0;
 750
 751         for ( ; ; ) {
 752                 spin_lock_irqsave(&logbuf_lock, flags);
 753                 wake_klogd |= log_start - log_end;
 754                 if (con_start == log_end)
 755                         break;                  /* Nothing to print */
 756                 _con_start = con_start;
 757                 _log_end = log_end;
 758                 con_start = log_end;            /* Flush */
 759                 spin_unlock(&logbuf_lock);
 760                 call_console_drivers(_con_start, _log_end);
 761                 local_irq_restore(flags);
 762         }
 763         console_locked = 0;
 764         console_may_schedule = 0;
 765         up(&console_sem);
 766         spin_unlock_irqrestore(&logbuf_lock, flags);
 767         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 768                 wake_up_interruptible(&log_wait);
 769 }
 770 EXPORT_SYMBOL(release_console_sem);
 771
 772 /**
 773  * console_conditional_schedule - yield the CPU if required
 774  *
 775  * If the console code is currently allowed to sleep, and
 776  * if this CPU should yield the CPU to another task, do
 777  * so here.
 778  *
 779  * Must be called within acquire_console_sem().
 780  */
 781 void __sched console_conditional_schedule(void)
 782 {
 783         if (console_may_schedule)
 784                 cond_resched();
 785 }
 786 EXPORT_SYMBOL(console_conditional_schedule);
 787
 788 void console_print(const char *s)
 789 {
 790         printk(KERN_EMERG "%s", s);
 791 }
 792 EXPORT_SYMBOL(console_print);
 793
 794 void console_unblank(void)
 795 {
 796         struct console *c;
 797
 798         /*
 799          * console_unblank can no longer be called in interrupt context unless
 800          * oops_in_progress is set to 1..
 801          */
 802         if (oops_in_progress) {
 803                 if (down_trylock(&console_sem) != 0)
 804                         return;
 805         } else
 806                 acquire_console_sem();
 807
 808         console_locked = 1;
 809         console_may_schedule = 0;
 810         for (c = console_drivers; c != NULL; c = c->next)
 811                 if ((c->flags & CON_ENABLED) && c->unblank)
 812                         c->unblank();
 813         release_console_sem();
 814 }
 815
 816 /*
 817  * Return the console tty driver structure and its associated index
 818  */
 819 struct tty_driver *console_device(int *index)
 820 {
 821         struct console *c;
 822         struct tty_driver *driver = NULL;
 823
 824         acquire_console_sem();
 825         for (c = console_drivers; c != NULL; c = c->next) {
 826                 if (!c->device)
 827                         continue;
 828                 driver = c->device(c, index);
 829                 if (driver)
 830                         break;
 831         }
 832         release_console_sem();
 833         return driver;
 834 }
 835
 836 /*
 837  * Prevent further output on the passed console device so that (for example)
 838  * serial drivers can disable console output before suspending a port, and can
 839  * re-enable output afterwards.
 840  */
 841 void console_stop(struct console *console)
 842 {
 843         acquire_console_sem();
 844         console->flags &= ~CON_ENABLED;
 845         release_console_sem();
 846 }
 847 EXPORT_SYMBOL(console_stop);
 848
 849 void console_start(struct console *console)
 850 {
 851         acquire_console_sem();
 852         console->flags |= CON_ENABLED;
 853         release_console_sem();
 854 }
 855 EXPORT_SYMBOL(console_start);
 856
 857 /*
 858  * The console driver calls this routine during kernel initialization
 859  * to register the console printing procedure with printk() and to
 860  * print any messages that were printed by the kernel before the
 861  * console driver was initialized.
 862  */
 863 void register_console(struct console *console)
 864 {
 865         int i;
 866         unsigned long flags;
 867
 868         if (preferred_console < 0)
 869                 preferred_console = selected_console;
 870
 871         /*
 872          *      See if we want to use this console driver. If we
 873          *      didn't select a console we take the first one
 874          *      that registers here.
 875          */
 876         if (preferred_console < 0) {
 877                 if (console->index < 0)
 878                         console->index = 0;
 879                 if (console->setup == NULL ||
 880                     console->setup(console, NULL) == 0) {
 881                         console->flags |= CON_ENABLED | CON_CONSDEV;
 882                         preferred_console = 0;
 883                 }
 884         }
 885
 886         /*
 887          *      See if this console matches one we selected on
 888          *      the command line.
 889          */
 890         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 891                         i++) {
 892                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 893                         continue;
 894                 if (console->index >= 0 &&
 895                     console->index != console_cmdline[i].index)
 896                         continue;
 897                 if (console->index < 0)
 898                         console->index = console_cmdline[i].index;
 899                 if (console->setup &&
 900                     console->setup(console, console_cmdline[i].options) != 0)
 901                         break;
 902                 console->flags |= CON_ENABLED;
 903                 console->index = console_cmdline[i].index;
 904                 if (i == selected_console) {
 905                         console->flags |= CON_CONSDEV;
 906                         preferred_console = selected_console;
 907                 }
 908                 break;
 909         }
 910
 911         if (!(console->flags & CON_ENABLED))
 912                 return;
 913
 914         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 915                 unregister_console(console_drivers);
 916                 console->flags &= ~CON_PRINTBUFFER;
 917         }
 918
 919         /*
 920          *      Put this console in the list - keep the
 921          *      preferred driver at the head of the list.
 922          */
 923         acquire_console_sem();
 924         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 925                 console->next = console_drivers;
 926                 console_drivers = console;
 927                 if (console->next)
 928                         console->next->flags &= ~CON_CONSDEV;
 929         } else {
 930                 console->next = console_drivers->next;
 931                 console_drivers->next = console;
 932         }
 933         if (console->flags & CON_PRINTBUFFER) {
 934                 /*
 935                  * release_console_sem() will print out the buffered messages
 936                  * for us.
 937                  */
 938                 spin_lock_irqsave(&logbuf_lock, flags);
 939                 con_start = log_start;
 940                 spin_unlock_irqrestore(&logbuf_lock, flags);
 941         }
 942         release_console_sem();
 943 }
 944 EXPORT_SYMBOL(register_console);
 945
 946 int unregister_console(struct console *console)
 947 {
 948         struct console *a, *b;
 949         int res = 1;
 950
 951         acquire_console_sem();
 952         if (console_drivers == console) {
 953                 console_drivers=console->next;
 954                 res = 0;
 955         } else if (console_drivers) {
 956                 for (a=console_drivers->next, b=console_drivers ;
 957                      a; b=a, a=b->next) {
 958                         if (a == console) {
 959                                 b->next = a->next;
 960                                 res = 0;
 961                                 break;
 962                         }
 963                 }
 964         }
 965
 966         /* If last console is removed, we re-enable picking the first
 967          * one that gets registered. Without that, pmac early boot console
 968          * would prevent fbcon from taking over.
 969          *
 970          * If this isn't the last console and it has CON_CONSDEV set, we
 971          * need to set it on the next preferred console.
 972          */
 973         if (console_drivers == NULL)
 974                 preferred_console = selected_console;
 975         else if (console->flags & CON_CONSDEV)
 976                 console_drivers->flags |= CON_CONSDEV;
 977
 978         release_console_sem();
 979         return res;
 980 }
 981 EXPORT_SYMBOL(unregister_console);
 982
 983 /**
 984  * tty_write_message - write a message to a certain tty, not just the console.
 985  * @tty: the destination tty_struct
 986  * @msg: the message to write
 987  *
 988  * This is used for messages that need to be redirected to a specific tty.
 989  * We don't put it into the syslog queue right now maybe in the future if
 990  * really needed.
 991  */
 992 void tty_write_message(struct tty_struct *tty, char *msg)
 993 {
 994         if (tty && tty->driver->write)
 995                 tty->driver->write(tty, msg, strlen(msg));
 996         return;
 997 }
 998
 999 /*
1000  * printk rate limiting, lifted from the networking subsystem.
1001  *
1002  * This enforces a rate limit: not more than one kernel message
1003  * every printk_ratelimit_jiffies to make a denial-of-service
1004  * attack impossible.
1005  */
1006 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1007 {
1008         static DEFINE_SPINLOCK(ratelimit_lock);
1009         static unsigned long toks = 10 * 5 * HZ;
1010         static unsigned long last_msg;
1011         static int missed;
1012         unsigned long flags;
1013         unsigned long now = jiffies;
1014
1015         spin_lock_irqsave(&ratelimit_lock, flags);
1016         toks += now - last_msg;
1017         last_msg = now;
1018         if (toks > (ratelimit_burst * ratelimit_jiffies))
1019                 toks = ratelimit_burst * ratelimit_jiffies;
1020         if (toks >= ratelimit_jiffies) {
1021                 int lost = missed;
1022
1023                 missed = 0;
1024                 toks -= ratelimit_jiffies;
1025                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1026                 if (lost)
1027                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1028                 return 1;
1029         }
1030         missed++;
1031         spin_unlock_irqrestore(&ratelimit_lock, flags);
1032         return 0;
1033 }
1034 EXPORT_SYMBOL(__printk_ratelimit);
1035
1036 /* minimum time in jiffies between messages */
1037 int printk_ratelimit_jiffies = 5 * HZ;
1038
1039 /* number of messages we send before ratelimiting */
1040 int printk_ratelimit_burst = 10;
1041
1042 int printk_ratelimit(void)
1043 {
1044         return __printk_ratelimit(printk_ratelimit_jiffies,
1045                                 printk_ratelimit_burst);
1046 }
1047 EXPORT_SYMBOL(printk_ratelimit);