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/moduleparam.h>
  28 #include <linux/interrupt.h>                    /* For in_interrupt() */
  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 static DECLARE_MUTEX(secondary_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, console_suspended;
  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 static int __init log_buf_len_setup(char *str)
 127 {
 128         unsigned long size = memparse(str, &str);
 129         unsigned long flags;
 130
 131         if (size)
 132                 size = roundup_pow_of_two(size);
 133         if (size > log_buf_len) {
 134                 unsigned long start, dest_idx, offset;
 135                 char *new_log_buf;
 136
 137                 new_log_buf = alloc_bootmem(size);
 138                 if (!new_log_buf) {
 139                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 140                         goto out;
 141                 }
 142
 143                 spin_lock_irqsave(&logbuf_lock, flags);
 144                 log_buf_len = size;
 145                 log_buf = new_log_buf;
 146
 147                 offset = start = min(con_start, log_start);
 148                 dest_idx = 0;
 149                 while (start != log_end) {
 150                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 151                         start++;
 152                         dest_idx++;
 153                 }
 154                 log_start -= offset;
 155                 con_start -= offset;
 156                 log_end -= offset;
 157                 spin_unlock_irqrestore(&logbuf_lock, flags);
 158
 159                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 160         }
 161 out:
 162         return 1;
 163 }
 164
 165 __setup("log_buf_len=", log_buf_len_setup);
 166
 167 /*
 168  * Commands to do_syslog:
 169  *
 170  *      0 -- Close the log.  Currently a NOP.
 171  *      1 -- Open the log. Currently a NOP.
 172  *      2 -- Read from the log.
 173  *      3 -- Read all messages remaining in the ring buffer.
 174  *      4 -- Read and clear all messages remaining in the ring buffer
 175  *      5 -- Clear ring buffer.
 176  *      6 -- Disable printk's to console
 177  *      7 -- Enable printk's to console
 178  *      8 -- Set level of messages printed to console
 179  *      9 -- Return number of unread characters in the log buffer
 180  *     10 -- Return size of the log buffer
 181  */
 182 int do_syslog(int type, char __user *buf, int len)
 183 {
 184         unsigned long i, j, limit, count;
 185         int do_clear = 0;
 186         char c;
 187         int error = 0;
 188
 189         error = security_syslog(type);
 190         if (error)
 191                 return error;
 192
 193         switch (type) {
 194         case 0:         /* Close log */
 195                 break;
 196         case 1:         /* Open log */
 197                 break;
 198         case 2:         /* Read from log */
 199                 error = -EINVAL;
 200                 if (!buf || len < 0)
 201                         goto out;
 202                 error = 0;
 203                 if (!len)
 204                         goto out;
 205                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 206                         error = -EFAULT;
 207                         goto out;
 208                 }
 209                 error = wait_event_interruptible(log_wait,
 210                                                         (log_start - log_end));
 211                 if (error)
 212                         goto out;
 213                 i = 0;
 214                 spin_lock_irq(&logbuf_lock);
 215                 while (!error && (log_start != log_end) && i < len) {
 216                         c = LOG_BUF(log_start);
 217                         log_start++;
 218                         spin_unlock_irq(&logbuf_lock);
 219                         error = __put_user(c,buf);
 220                         buf++;
 221                         i++;
 222                         cond_resched();
 223                         spin_lock_irq(&logbuf_lock);
 224                 }
 225                 spin_unlock_irq(&logbuf_lock);
 226                 if (!error)
 227                         error = i;
 228                 break;
 229         case 4:         /* Read/clear last kernel messages */
 230                 do_clear = 1;
 231                 /* FALL THRU */
 232         case 3:         /* Read last kernel messages */
 233                 error = -EINVAL;
 234                 if (!buf || len < 0)
 235                         goto out;
 236                 error = 0;
 237                 if (!len)
 238                         goto out;
 239                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 240                         error = -EFAULT;
 241                         goto out;
 242                 }
 243                 count = len;
 244                 if (count > log_buf_len)
 245                         count = log_buf_len;
 246                 spin_lock_irq(&logbuf_lock);
 247                 if (count > logged_chars)
 248                         count = logged_chars;
 249                 if (do_clear)
 250                         logged_chars = 0;
 251                 limit = log_end;
 252                 /*
 253                  * __put_user() could sleep, and while we sleep
 254                  * printk() could overwrite the messages
 255                  * we try to copy to user space. Therefore
 256                  * the messages are copied in reverse. <manfreds>
 257                  */
 258                 for (i = 0; i < count && !error; i++) {
 259                         j = limit-1-i;
 260                         if (j + log_buf_len < log_end)
 261                                 break;
 262                         c = LOG_BUF(j);
 263                         spin_unlock_irq(&logbuf_lock);
 264                         error = __put_user(c,&buf[count-1-i]);
 265                         cond_resched();
 266                         spin_lock_irq(&logbuf_lock);
 267                 }
 268                 spin_unlock_irq(&logbuf_lock);
 269                 if (error)
 270                         break;
 271                 error = i;
 272                 if (i != count) {
 273                         int offset = count-error;
 274                         /* buffer overflow during copy, correct user buffer. */
 275                         for (i = 0; i < error; i++) {
 276                                 if (__get_user(c,&buf[i+offset]) ||
 277                                     __put_user(c,&buf[i])) {
 278                                         error = -EFAULT;
 279                                         break;
 280                                 }
 281                                 cond_resched();
 282                         }
 283                 }
 284                 break;
 285         case 5:         /* Clear ring buffer */
 286                 logged_chars = 0;
 287                 break;
 288         case 6:         /* Disable logging to console */
 289                 console_loglevel = minimum_console_loglevel;
 290                 break;
 291         case 7:         /* Enable logging to console */
 292                 console_loglevel = default_console_loglevel;
 293                 break;
 294         case 8:         /* Set level of messages printed to console */
 295                 error = -EINVAL;
 296                 if (len < 1 || len > 8)
 297                         goto out;
 298                 if (len < minimum_console_loglevel)
 299                         len = minimum_console_loglevel;
 300                 console_loglevel = len;
 301                 error = 0;
 302                 break;
 303         case 9:         /* Number of chars in the log buffer */
 304                 error = log_end - log_start;
 305                 break;
 306         case 10:        /* Size of the log buffer */
 307                 error = log_buf_len;
 308                 break;
 309         default:
 310                 error = -EINVAL;
 311                 break;
 312         }
 313 out:
 314         return error;
 315 }
 316
 317 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 318 {
 319         return do_syslog(type, buf, len);
 320 }
 321
 322 /*
 323  * Call the console drivers on a range of log_buf
 324  */
 325 static void __call_console_drivers(unsigned long start, unsigned long end)
 326 {
 327         struct console *con;
 328
 329         for (con = console_drivers; con; con = con->next) {
 330                 if ((con->flags & CON_ENABLED) && con->write &&
 331                                 (cpu_online(smp_processor_id()) ||
 332                                 (con->flags & CON_ANYTIME)))
 333                         con->write(con, &LOG_BUF(start), end - start);
 334         }
 335 }
 336
 337 /*
 338  * Write out chars from start to end - 1 inclusive
 339  */
 340 static void _call_console_drivers(unsigned long start,
 341                                 unsigned long end, int msg_log_level)
 342 {
 343         if (msg_log_level < console_loglevel &&
 344                         console_drivers && start != end) {
 345                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 346                         /* wrapped write */
 347                         __call_console_drivers(start & LOG_BUF_MASK,
 348                                                 log_buf_len);
 349                         __call_console_drivers(0, end & LOG_BUF_MASK);
 350                 } else {
 351                         __call_console_drivers(start, end);
 352                 }
 353         }
 354 }
 355
 356 /*
 357  * Call the console drivers, asking them to write out
 358  * log_buf[start] to log_buf[end - 1].
 359  * The console_sem must be held.
 360  */
 361 static void call_console_drivers(unsigned long start, unsigned long end)
 362 {
 363         unsigned long cur_index, start_print;
 364         static int msg_level = -1;
 365
 366         BUG_ON(((long)(start - end)) > 0);
 367
 368         cur_index = start;
 369         start_print = start;
 370         while (cur_index != end) {
 371                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 372                                 LOG_BUF(cur_index + 0) == '<' &&
 373                                 LOG_BUF(cur_index + 1) >= '0' &&
 374                                 LOG_BUF(cur_index + 1) <= '7' &&
 375                                 LOG_BUF(cur_index + 2) == '>') {
 376                         msg_level = LOG_BUF(cur_index + 1) - '0';
 377                         cur_index += 3;
 378                         start_print = cur_index;
 379                 }
 380                 while (cur_index != end) {
 381                         char c = LOG_BUF(cur_index);
 382
 383                         cur_index++;
 384                         if (c == '\n') {
 385                                 if (msg_level < 0) {
 386                                         /*
 387                                          * printk() has already given us loglevel tags in
 388                                          * the buffer.  This code is here in case the
 389                                          * log buffer has wrapped right round and scribbled
 390                                          * on those tags
 391                                          */
 392                                         msg_level = default_message_loglevel;
 393                                 }
 394                                 _call_console_drivers(start_print, cur_index, msg_level);
 395                                 msg_level = -1;
 396                                 start_print = cur_index;
 397                                 break;
 398                         }
 399                 }
 400         }
 401         _call_console_drivers(start_print, end, msg_level);
 402 }
 403
 404 static void emit_log_char(char c)
 405 {
 406         LOG_BUF(log_end) = c;
 407         log_end++;
 408         if (log_end - log_start > log_buf_len)
 409                 log_start = log_end - log_buf_len;
 410         if (log_end - con_start > log_buf_len)
 411                 con_start = log_end - log_buf_len;
 412         if (logged_chars < log_buf_len)
 413                 logged_chars++;
 414 }
 415
 416 /*
 417  * Zap console related locks when oopsing. Only zap at most once
 418  * every 10 seconds, to leave time for slow consoles to print a
 419  * full oops.
 420  */
 421 static void zap_locks(void)
 422 {
 423         static unsigned long oops_timestamp;
 424
 425         if (time_after_eq(jiffies, oops_timestamp) &&
 426                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 427                 return;
 428
 429         oops_timestamp = jiffies;
 430
 431         /* If a crash is occurring, make sure we can't deadlock */
 432         spin_lock_init(&logbuf_lock);
 433         /* And make sure that we print immediately */
 434         init_MUTEX(&console_sem);
 435 }
 436
 437 #if defined(CONFIG_PRINTK_TIME)
 438 static int printk_time = 1;
 439 #else
 440 static int printk_time = 0;
 441 #endif
 442 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 443
 444 static int __init printk_time_setup(char *str)
 445 {
 446         if (*str)
 447                 return 0;
 448         printk_time = 1;
 449         return 1;
 450 }
 451
 452 __setup("time", printk_time_setup);
 453
 454 __attribute__((weak)) unsigned long long printk_clock(void)
 455 {
 456         return sched_clock();
 457 }
 458
 459 /* Check if we have any console registered that can be called early in boot. */
 460 static int have_callable_console(void)
 461 {
 462         struct console *con;
 463
 464         for (con = console_drivers; con; con = con->next)
 465                 if (con->flags & CON_ANYTIME)
 466                         return 1;
 467
 468         return 0;
 469 }
 470
 471 /**
 472  * printk - print a kernel message
 473  * @fmt: format string
 474  *
 475  * This is printk.  It can be called from any context.  We want it to work.
 476  *
 477  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 478  * call the console drivers.  If we fail to get the semaphore we place the output
 479  * into the log buffer and return.  The current holder of the console_sem will
 480  * notice the new output in release_console_sem() and will send it to the
 481  * consoles before releasing the semaphore.
 482  *
 483  * One effect of this deferred printing is that code which calls printk() and
 484  * then changes console_loglevel may break. This is because console_loglevel
 485  * is inspected when the actual printing occurs.
 486  *
 487  * See also:
 488  * printf(3)
 489  */
 490
 491 asmlinkage int printk(const char *fmt, ...)
 492 {
 493         va_list args;
 494         int r;
 495
 496         va_start(args, fmt);
 497         r = vprintk(fmt, args);
 498         va_end(args);
 499
 500         return r;
 501 }
 502
 503 /* cpu currently holding logbuf_lock */
 504 static volatile unsigned int printk_cpu = UINT_MAX;
 505
 506 asmlinkage int vprintk(const char *fmt, va_list args)
 507 {
 508         unsigned long flags;
 509         int printed_len;
 510         char *p;
 511         static char printk_buf[1024];
 512         static int log_level_unknown = 1;
 513
 514         preempt_disable();
 515         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 516                 /* If a crash is occurring during printk() on this CPU,
 517                  * make sure we can't deadlock */
 518                 zap_locks();
 519
 520         /* This stops the holder of console_sem just where we want him */
 521         spin_lock_irqsave(&logbuf_lock, flags);
 522         printk_cpu = smp_processor_id();
 523
 524         /* Emit the output into the temporary buffer */
 525         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 526
 527         /*
 528          * Copy the output into log_buf.  If the caller didn't provide
 529          * appropriate log level tags, we insert them here
 530          */
 531         for (p = printk_buf; *p; p++) {
 532                 if (log_level_unknown) {
 533                         /* log_level_unknown signals the start of a new line */
 534                         if (printk_time) {
 535                                 int loglev_char;
 536                                 char tbuf[50], *tp;
 537                                 unsigned tlen;
 538                                 unsigned long long t;
 539                                 unsigned long nanosec_rem;
 540
 541                                 /*
 542                                  * force the log level token to be
 543                                  * before the time output.
 544                                  */
 545                                 if (p[0] == '<' && p[1] >='0' &&
 546                                    p[1] <= '7' && p[2] == '>') {
 547                                         loglev_char = p[1];
 548                                         p += 3;
 549                                         printed_len -= 3;
 550                                 } else {
 551                                         loglev_char = default_message_loglevel
 552                                                 + '0';
 553                                 }
 554                                 t = printk_clock();
 555                                 nanosec_rem = do_div(t, 1000000000);
 556                                 tlen = sprintf(tbuf,
 557                                                 "<%c>[%5lu.%06lu] ",
 558                                                 loglev_char,
 559                                                 (unsigned long)t,
 560                                                 nanosec_rem/1000);
 561
 562                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 563                                         emit_log_char(*tp);
 564                                 printed_len += tlen;
 565                         } else {
 566                                 if (p[0] != '<' || p[1] < '0' ||
 567                                    p[1] > '7' || p[2] != '>') {
 568                                         emit_log_char('<');
 569                                         emit_log_char(default_message_loglevel
 570                                                 + '0');
 571                                         emit_log_char('>');
 572                                         printed_len += 3;
 573                                 }
 574                         }
 575                         log_level_unknown = 0;
 576                         if (!*p)
 577                                 break;
 578                 }
 579                 emit_log_char(*p);
 580                 if (*p == '\n')
 581                         log_level_unknown = 1;
 582         }
 583
 584         if (!down_trylock(&console_sem)) {
 585                 /*
 586                  * We own the drivers.  We can drop the spinlock and
 587                  * let release_console_sem() print the text, maybe ...
 588                  */
 589                 console_locked = 1;
 590                 printk_cpu = UINT_MAX;
 591                 spin_unlock_irqrestore(&logbuf_lock, flags);
 592
 593                 /*
 594                  * Console drivers may assume that per-cpu resources have
 595                  * been allocated. So unless they're explicitly marked as
 596                  * being able to cope (CON_ANYTIME) don't call them until
 597                  * this CPU is officially up.
 598                  */
 599                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 600                         console_may_schedule = 0;
 601                         release_console_sem();
 602                 } else {
 603                         /* Release by hand to avoid flushing the buffer. */
 604                         console_locked = 0;
 605                         up(&console_sem);
 606                 }
 607         } else {
 608                 /*
 609                  * Someone else owns the drivers.  We drop the spinlock, which
 610                  * allows the semaphore holder to proceed and to call the
 611                  * console drivers with the output which we just produced.
 612                  */
 613                 printk_cpu = UINT_MAX;
 614                 spin_unlock_irqrestore(&logbuf_lock, flags);
 615         }
 616
 617         preempt_enable();
 618         return printed_len;
 619 }
 620 EXPORT_SYMBOL(printk);
 621 EXPORT_SYMBOL(vprintk);
 622
 623 #else
 624
 625 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 626 {
 627         return 0;
 628 }
 629
 630 int do_syslog(int type, char __user *buf, int len)
 631 {
 632         return 0;
 633 }
 634
 635 static void call_console_drivers(unsigned long start, unsigned long end)
 636 {
 637 }
 638
 639 #endif
 640
 641 /*
 642  * Set up a list of consoles.  Called from init/main.c
 643  */
 644 static int __init console_setup(char *str)
 645 {
 646         char name[sizeof(console_cmdline[0].name)];
 647         char *s, *options;
 648         int idx;
 649
 650         /*
 651          * Decode str into name, index, options.
 652          */
 653         if (str[0] >= '0' && str[0] <= '9') {
 654                 strcpy(name, "ttyS");
 655                 strncpy(name + 4, str, sizeof(name) - 5);
 656         } else {
 657                 strncpy(name, str, sizeof(name) - 1);
 658         }
 659         name[sizeof(name) - 1] = 0;
 660         if ((options = strchr(str, ',')) != NULL)
 661                 *(options++) = 0;
 662 #ifdef __sparc__
 663         if (!strcmp(str, "ttya"))
 664                 strcpy(name, "ttyS0");
 665         if (!strcmp(str, "ttyb"))
 666                 strcpy(name, "ttyS1");
 667 #endif
 668         for (s = name; *s; s++)
 669                 if ((*s >= '0' && *s <= '9') || *s == ',')
 670                         break;
 671         idx = simple_strtoul(s, NULL, 10);
 672         *s = 0;
 673
 674         add_preferred_console(name, idx, options);
 675         return 1;
 676 }
 677 __setup("console=", console_setup);
 678
 679 /**
 680  * add_preferred_console - add a device to the list of preferred consoles.
 681  * @name: device name
 682  * @idx: device index
 683  * @options: options for this console
 684  *
 685  * The last preferred console added will be used for kernel messages
 686  * and stdin/out/err for init.  Normally this is used by console_setup
 687  * above to handle user-supplied console arguments; however it can also
 688  * be used by arch-specific code either to override the user or more
 689  * commonly to provide a default console (ie from PROM variables) when
 690  * the user has not supplied one.
 691  */
 692 int __init add_preferred_console(char *name, int idx, char *options)
 693 {
 694         struct console_cmdline *c;
 695         int i;
 696
 697         /*
 698          *      See if this tty is not yet registered, and
 699          *      if we have a slot free.
 700          */
 701         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 702                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 703                           console_cmdline[i].index == idx) {
 704                                 selected_console = i;
 705                                 return 0;
 706                 }
 707         if (i == MAX_CMDLINECONSOLES)
 708                 return -E2BIG;
 709         selected_console = i;
 710         c = &console_cmdline[i];
 711         memcpy(c->name, name, sizeof(c->name));
 712         c->name[sizeof(c->name) - 1] = 0;
 713         c->options = options;
 714         c->index = idx;
 715         return 0;
 716 }
 717
 718 /**
 719  * suspend_console - suspend the console subsystem
 720  *
 721  * This disables printk() while we go into suspend states
 722  */
 723 void suspend_console(void)
 724 {
 725         acquire_console_sem();
 726         console_suspended = 1;
 727 }
 728
 729 void resume_console(void)
 730 {
 731         console_suspended = 0;
 732         release_console_sem();
 733 }
 734
 735 /**
 736  * acquire_console_sem - lock the console system for exclusive use.
 737  *
 738  * Acquires a semaphore which guarantees that the caller has
 739  * exclusive access to the console system and the console_drivers list.
 740  *
 741  * Can sleep, returns nothing.
 742  */
 743 void acquire_console_sem(void)
 744 {
 745         BUG_ON(in_interrupt());
 746         if (console_suspended) {
 747                 down(&secondary_console_sem);
 748                 return;
 749         }
 750         down(&console_sem);
 751         console_locked = 1;
 752         console_may_schedule = 1;
 753 }
 754 EXPORT_SYMBOL(acquire_console_sem);
 755
 756 int try_acquire_console_sem(void)
 757 {
 758         if (down_trylock(&console_sem))
 759                 return -1;
 760         console_locked = 1;
 761         console_may_schedule = 0;
 762         return 0;
 763 }
 764 EXPORT_SYMBOL(try_acquire_console_sem);
 765
 766 int is_console_locked(void)
 767 {
 768         return console_locked;
 769 }
 770 EXPORT_SYMBOL(is_console_locked);
 771
 772 /**
 773  * release_console_sem - unlock the console system
 774  *
 775  * Releases the semaphore which the caller holds on the console system
 776  * and the console driver list.
 777  *
 778  * While the semaphore was held, console output may have been buffered
 779  * by printk().  If this is the case, release_console_sem() emits
 780  * the output prior to releasing the semaphore.
 781  *
 782  * If there is output waiting for klogd, we wake it up.
 783  *
 784  * release_console_sem() may be called from any context.
 785  */
 786 void release_console_sem(void)
 787 {
 788         unsigned long flags;
 789         unsigned long _con_start, _log_end;
 790         unsigned long wake_klogd = 0;
 791
 792         if (console_suspended) {
 793                 up(&secondary_console_sem);
 794                 return;
 795         }
 796         for ( ; ; ) {
 797                 spin_lock_irqsave(&logbuf_lock, flags);
 798                 wake_klogd |= log_start - log_end;
 799                 if (con_start == log_end)
 800                         break;                  /* Nothing to print */
 801                 _con_start = con_start;
 802                 _log_end = log_end;
 803                 con_start = log_end;            /* Flush */
 804                 spin_unlock(&logbuf_lock);
 805                 call_console_drivers(_con_start, _log_end);
 806                 local_irq_restore(flags);
 807         }
 808         console_locked = 0;
 809         console_may_schedule = 0;
 810         up(&console_sem);
 811         spin_unlock_irqrestore(&logbuf_lock, flags);
 812         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 813                 wake_up_interruptible(&log_wait);
 814 }
 815 EXPORT_SYMBOL(release_console_sem);
 816
 817 /**
 818  * console_conditional_schedule - yield the CPU if required
 819  *
 820  * If the console code is currently allowed to sleep, and
 821  * if this CPU should yield the CPU to another task, do
 822  * so here.
 823  *
 824  * Must be called within acquire_console_sem().
 825  */
 826 void __sched console_conditional_schedule(void)
 827 {
 828         if (console_may_schedule)
 829                 cond_resched();
 830 }
 831 EXPORT_SYMBOL(console_conditional_schedule);
 832
 833 void console_print(const char *s)
 834 {
 835         printk(KERN_EMERG "%s", s);
 836 }
 837 EXPORT_SYMBOL(console_print);
 838
 839 void console_unblank(void)
 840 {
 841         struct console *c;
 842
 843         /*
 844          * console_unblank can no longer be called in interrupt context unless
 845          * oops_in_progress is set to 1..
 846          */
 847         if (oops_in_progress) {
 848                 if (down_trylock(&console_sem) != 0)
 849                         return;
 850         } else
 851                 acquire_console_sem();
 852
 853         console_locked = 1;
 854         console_may_schedule = 0;
 855         for (c = console_drivers; c != NULL; c = c->next)
 856                 if ((c->flags & CON_ENABLED) && c->unblank)
 857                         c->unblank();
 858         release_console_sem();
 859 }
 860
 861 /*
 862  * Return the console tty driver structure and its associated index
 863  */
 864 struct tty_driver *console_device(int *index)
 865 {
 866         struct console *c;
 867         struct tty_driver *driver = NULL;
 868
 869         acquire_console_sem();
 870         for (c = console_drivers; c != NULL; c = c->next) {
 871                 if (!c->device)
 872                         continue;
 873                 driver = c->device(c, index);
 874                 if (driver)
 875                         break;
 876         }
 877         release_console_sem();
 878         return driver;
 879 }
 880
 881 /*
 882  * Prevent further output on the passed console device so that (for example)
 883  * serial drivers can disable console output before suspending a port, and can
 884  * re-enable output afterwards.
 885  */
 886 void console_stop(struct console *console)
 887 {
 888         acquire_console_sem();
 889         console->flags &= ~CON_ENABLED;
 890         release_console_sem();
 891 }
 892 EXPORT_SYMBOL(console_stop);
 893
 894 void console_start(struct console *console)
 895 {
 896         acquire_console_sem();
 897         console->flags |= CON_ENABLED;
 898         release_console_sem();
 899 }
 900 EXPORT_SYMBOL(console_start);
 901
 902 /*
 903  * The console driver calls this routine during kernel initialization
 904  * to register the console printing procedure with printk() and to
 905  * print any messages that were printed by the kernel before the
 906  * console driver was initialized.
 907  */
 908 void register_console(struct console *console)
 909 {
 910         int i;
 911         unsigned long flags;
 912
 913         if (preferred_console < 0)
 914                 preferred_console = selected_console;
 915
 916         /*
 917          *      See if we want to use this console driver. If we
 918          *      didn't select a console we take the first one
 919          *      that registers here.
 920          */
 921         if (preferred_console < 0) {
 922                 if (console->index < 0)
 923                         console->index = 0;
 924                 if (console->setup == NULL ||
 925                     console->setup(console, NULL) == 0) {
 926                         console->flags |= CON_ENABLED | CON_CONSDEV;
 927                         preferred_console = 0;
 928                 }
 929         }
 930
 931         /*
 932          *      See if this console matches one we selected on
 933          *      the command line.
 934          */
 935         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 936                         i++) {
 937                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 938                         continue;
 939                 if (console->index >= 0 &&
 940                     console->index != console_cmdline[i].index)
 941                         continue;
 942                 if (console->index < 0)
 943                         console->index = console_cmdline[i].index;
 944                 if (console->setup &&
 945                     console->setup(console, console_cmdline[i].options) != 0)
 946                         break;
 947                 console->flags |= CON_ENABLED;
 948                 console->index = console_cmdline[i].index;
 949                 if (i == selected_console) {
 950                         console->flags |= CON_CONSDEV;
 951                         preferred_console = selected_console;
 952                 }
 953                 break;
 954         }
 955
 956         if (!(console->flags & CON_ENABLED))
 957                 return;
 958
 959         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 960                 unregister_console(console_drivers);
 961                 console->flags &= ~CON_PRINTBUFFER;
 962         }
 963
 964         /*
 965          *      Put this console in the list - keep the
 966          *      preferred driver at the head of the list.
 967          */
 968         acquire_console_sem();
 969         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 970                 console->next = console_drivers;
 971                 console_drivers = console;
 972                 if (console->next)
 973                         console->next->flags &= ~CON_CONSDEV;
 974         } else {
 975                 console->next = console_drivers->next;
 976                 console_drivers->next = console;
 977         }
 978         if (console->flags & CON_PRINTBUFFER) {
 979                 /*
 980                  * release_console_sem() will print out the buffered messages
 981                  * for us.
 982                  */
 983                 spin_lock_irqsave(&logbuf_lock, flags);
 984                 con_start = log_start;
 985                 spin_unlock_irqrestore(&logbuf_lock, flags);
 986         }
 987         release_console_sem();
 988 }
 989 EXPORT_SYMBOL(register_console);
 990
 991 int unregister_console(struct console *console)
 992 {
 993         struct console *a, *b;
 994         int res = 1;
 995
 996         acquire_console_sem();
 997         if (console_drivers == console) {
 998                 console_drivers=console->next;
 999                 res = 0;
1000         } else if (console_drivers) {
1001                 for (a=console_drivers->next, b=console_drivers ;
1002                      a; b=a, a=b->next) {
1003                         if (a == console) {
1004                                 b->next = a->next;
1005                                 res = 0;
1006                                 break;
1007                         }
1008                 }
1009         }
1010
1011         /* If last console is removed, we re-enable picking the first
1012          * one that gets registered. Without that, pmac early boot console
1013          * would prevent fbcon from taking over.
1014          *
1015          * If this isn't the last console and it has CON_CONSDEV set, we
1016          * need to set it on the next preferred console.
1017          */
1018         if (console_drivers == NULL)
1019                 preferred_console = selected_console;
1020         else if (console->flags & CON_CONSDEV)
1021                 console_drivers->flags |= CON_CONSDEV;
1022
1023         release_console_sem();
1024         return res;
1025 }
1026 EXPORT_SYMBOL(unregister_console);
1027
1028 /**
1029  * tty_write_message - write a message to a certain tty, not just the console.
1030  * @tty: the destination tty_struct
1031  * @msg: the message to write
1032  *
1033  * This is used for messages that need to be redirected to a specific tty.
1034  * We don't put it into the syslog queue right now maybe in the future if
1035  * really needed.
1036  */
1037 void tty_write_message(struct tty_struct *tty, char *msg)
1038 {
1039         if (tty && tty->driver->write)
1040                 tty->driver->write(tty, msg, strlen(msg));
1041         return;
1042 }
1043 EXPORT_SYMBOL_GPL(tty_write_message);
1044
1045 /*
1046  * printk rate limiting, lifted from the networking subsystem.
1047  *
1048  * This enforces a rate limit: not more than one kernel message
1049  * every printk_ratelimit_jiffies to make a denial-of-service
1050  * attack impossible.
1051  */
1052 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1053 {
1054         static DEFINE_SPINLOCK(ratelimit_lock);
1055         static unsigned long toks = 10 * 5 * HZ;
1056         static unsigned long last_msg;
1057         static int missed;
1058         unsigned long flags;
1059         unsigned long now = jiffies;
1060
1061         spin_lock_irqsave(&ratelimit_lock, flags);
1062         toks += now - last_msg;
1063         last_msg = now;
1064         if (toks > (ratelimit_burst * ratelimit_jiffies))
1065                 toks = ratelimit_burst * ratelimit_jiffies;
1066         if (toks >= ratelimit_jiffies) {
1067                 int lost = missed;
1068
1069                 missed = 0;
1070                 toks -= ratelimit_jiffies;
1071                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1072                 if (lost)
1073                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1074                 return 1;
1075         }
1076         missed++;
1077         spin_unlock_irqrestore(&ratelimit_lock, flags);
1078         return 0;
1079 }
1080 EXPORT_SYMBOL(__printk_ratelimit);
1081
1082 /* minimum time in jiffies between messages */
1083 int printk_ratelimit_jiffies = 5 * HZ;
1084
1085 /* number of messages we send before ratelimiting */
1086 int printk_ratelimit_burst = 10;
1087
1088 int printk_ratelimit(void)
1089 {
1090         return __printk_ratelimit(printk_ratelimit_jiffies,
1091                                 printk_ratelimit_burst);
1092 }
1093 EXPORT_SYMBOL(printk_ratelimit);