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