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/console.h>
  24 #include <linux/init.h>
  25 #include <linux/jiffies.h>
  26 #include <linux/nmi.h>
  27 #include <linux/module.h>
  28 #include <linux/moduleparam.h>
  29 #include <linux/interrupt.h>                    /* For in_interrupt() */
  30 #include <linux/delay.h>
  31 #include <linux/smp.h>
  32 #include <linux/security.h>
  33 #include <linux/bootmem.h>
  34 #include <linux/syscalls.h>
  35 #include <linux/jiffies.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 /*
  40  * Architectures can override it:
  41  */
  42 void __attribute__((weak)) early_printk(const char *fmt, ...)
  43 {
  44 }
  45
  46 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  47
  48 /* printk's without a loglevel use this.. */
  49 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  50
  51 /* We show everything that is MORE important than this.. */
  52 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  53 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  54
  55 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  56
  57 int console_printk[4] = {
  58         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  59         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  60         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  61         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  62 };
  63
  64 /*
  65  * Low level drivers may need that to know if they can schedule in
  66  * their unblank() callback or not. So let's export it.
  67  */
  68 int oops_in_progress;
  69 EXPORT_SYMBOL(oops_in_progress);
  70
  71 /*
  72  * console_sem protects the console_drivers list, and also
  73  * provides serialisation for access to the entire console
  74  * driver system.
  75  */
  76 static DECLARE_MUTEX(console_sem);
  77 static DECLARE_MUTEX(secondary_console_sem);
  78 struct console *console_drivers;
  79 /*
  80  * This is used for debugging the mess that is the VT code by
  81  * keeping track if we have the console semaphore held. It's
  82  * definitely not the perfect debug tool (we don't know if _WE_
  83  * hold it are racing, but it helps tracking those weird code
  84  * path in the console code where we end up in places I want
  85  * locked without the console sempahore held
  86  */
  87 static int console_locked, console_suspended;
  88
  89 /*
  90  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  91  * It is also used in interesting ways to provide interlocking in
  92  * release_console_sem().
  93  */
  94 static DEFINE_SPINLOCK(logbuf_lock);
  95
  96 #define LOG_BUF_MASK (log_buf_len-1)
  97 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  98
  99 /*
 100  * The indices into log_buf are not constrained to log_buf_len - they
 101  * must be masked before subscripting
 102  */
 103 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 104 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 105 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 106
 107 /*
 108  *      Array of consoles built from command line options (console=)
 109  */
 110 struct console_cmdline
 111 {
 112         char    name[8];                        /* Name of the driver       */
 113         int     index;                          /* Minor dev. to use        */
 114         char    *options;                       /* Options for the driver   */
 115 };
 116
 117 #define MAX_CMDLINECONSOLES 8
 118
 119 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 120 static int selected_console = -1;
 121 static int preferred_console = -1;
 122
 123 /* Flag: console code may call schedule() */
 124 static int console_may_schedule;
 125
 126 #ifdef CONFIG_PRINTK
 127
 128 static char __log_buf[__LOG_BUF_LEN];
 129 static char *log_buf = __log_buf;
 130 static int log_buf_len = __LOG_BUF_LEN;
 131 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 132
 133 static int __init log_buf_len_setup(char *str)
 134 {
 135         unsigned size = memparse(str, &str);
 136         unsigned long flags;
 137
 138         if (size)
 139                 size = roundup_pow_of_two(size);
 140         if (size > log_buf_len) {
 141                 unsigned start, dest_idx, offset;
 142                 char *new_log_buf;
 143
 144                 new_log_buf = alloc_bootmem(size);
 145                 if (!new_log_buf) {
 146                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 147                         goto out;
 148                 }
 149
 150                 spin_lock_irqsave(&logbuf_lock, flags);
 151                 log_buf_len = size;
 152                 log_buf = new_log_buf;
 153
 154                 offset = start = min(con_start, log_start);
 155                 dest_idx = 0;
 156                 while (start != log_end) {
 157                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 158                         start++;
 159                         dest_idx++;
 160                 }
 161                 log_start -= offset;
 162                 con_start -= offset;
 163                 log_end -= offset;
 164                 spin_unlock_irqrestore(&logbuf_lock, flags);
 165
 166                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 167         }
 168 out:
 169         return 1;
 170 }
 171
 172 __setup("log_buf_len=", log_buf_len_setup);
 173
 174 #ifdef CONFIG_BOOT_PRINTK_DELAY
 175
 176 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 177 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 178
 179 static int __init boot_delay_setup(char *str)
 180 {
 181         unsigned long lpj;
 182         unsigned long long loops_per_msec;
 183
 184         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 185         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 186
 187         get_option(&str, &boot_delay);
 188         if (boot_delay > 10 * 1000)
 189                 boot_delay = 0;
 190
 191         printk_delay_msec = loops_per_msec;
 192         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 193                 "HZ: %d, printk_delay_msec: %llu\n",
 194                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 195         return 1;
 196 }
 197 __setup("boot_delay=", boot_delay_setup);
 198
 199 static void boot_delay_msec(void)
 200 {
 201         unsigned long long k;
 202         unsigned long timeout;
 203
 204         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 205                 return;
 206
 207         k = (unsigned long long)printk_delay_msec * boot_delay;
 208
 209         timeout = jiffies + msecs_to_jiffies(boot_delay);
 210         while (k) {
 211                 k--;
 212                 cpu_relax();
 213                 /*
 214                  * use (volatile) jiffies to prevent
 215                  * compiler reduction; loop termination via jiffies
 216                  * is secondary and may or may not happen.
 217                  */
 218                 if (time_after(jiffies, timeout))
 219                         break;
 220                 touch_nmi_watchdog();
 221         }
 222 }
 223 #else
 224 static inline void boot_delay_msec(void)
 225 {
 226 }
 227 #endif
 228
 229 /*
 230  * Return the number of unread characters in the log buffer.
 231  */
 232 int log_buf_get_len(void)
 233 {
 234         return logged_chars;
 235 }
 236
 237 /*
 238  * Copy a range of characters from the log buffer.
 239  */
 240 int log_buf_copy(char *dest, int idx, int len)
 241 {
 242         int ret, max;
 243         bool took_lock = false;
 244
 245         if (!oops_in_progress) {
 246                 spin_lock_irq(&logbuf_lock);
 247                 took_lock = true;
 248         }
 249
 250         max = log_buf_get_len();
 251         if (idx < 0 || idx >= max) {
 252                 ret = -1;
 253         } else {
 254                 if (len > max)
 255                         len = max;
 256                 ret = len;
 257                 idx += (log_end - max);
 258                 while (len-- > 0)
 259                         dest[len] = LOG_BUF(idx + len);
 260         }
 261
 262         if (took_lock)
 263                 spin_unlock_irq(&logbuf_lock);
 264
 265         return ret;
 266 }
 267
 268 /*
 269  * Extract a single character from the log buffer.
 270  */
 271 int log_buf_read(int idx)
 272 {
 273         char ret;
 274
 275         if (log_buf_copy(&ret, idx, 1) == 1)
 276                 return ret;
 277         else
 278                 return -1;
 279 }
 280
 281 /*
 282  * Commands to do_syslog:
 283  *
 284  *      0 -- Close the log.  Currently a NOP.
 285  *      1 -- Open the log. Currently a NOP.
 286  *      2 -- Read from the log.
 287  *      3 -- Read all messages remaining in the ring buffer.
 288  *      4 -- Read and clear all messages remaining in the ring buffer
 289  *      5 -- Clear ring buffer.
 290  *      6 -- Disable printk's to console
 291  *      7 -- Enable printk's to console
 292  *      8 -- Set level of messages printed to console
 293  *      9 -- Return number of unread characters in the log buffer
 294  *     10 -- Return size of the log buffer
 295  */
 296 int do_syslog(int type, char __user *buf, int len)
 297 {
 298         unsigned i, j, limit, count;
 299         int do_clear = 0;
 300         char c;
 301         int error = 0;
 302
 303         error = security_syslog(type);
 304         if (error)
 305                 return error;
 306
 307         switch (type) {
 308         case 0:         /* Close log */
 309                 break;
 310         case 1:         /* Open log */
 311                 break;
 312         case 2:         /* Read from log */
 313                 error = -EINVAL;
 314                 if (!buf || len < 0)
 315                         goto out;
 316                 error = 0;
 317                 if (!len)
 318                         goto out;
 319                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 320                         error = -EFAULT;
 321                         goto out;
 322                 }
 323                 error = wait_event_interruptible(log_wait,
 324                                                         (log_start - log_end));
 325                 if (error)
 326                         goto out;
 327                 i = 0;
 328                 spin_lock_irq(&logbuf_lock);
 329                 while (!error && (log_start != log_end) && i < len) {
 330                         c = LOG_BUF(log_start);
 331                         log_start++;
 332                         spin_unlock_irq(&logbuf_lock);
 333                         error = __put_user(c,buf);
 334                         buf++;
 335                         i++;
 336                         cond_resched();
 337                         spin_lock_irq(&logbuf_lock);
 338                 }
 339                 spin_unlock_irq(&logbuf_lock);
 340                 if (!error)
 341                         error = i;
 342                 break;
 343         case 4:         /* Read/clear last kernel messages */
 344                 do_clear = 1;
 345                 /* FALL THRU */
 346         case 3:         /* Read last kernel messages */
 347                 error = -EINVAL;
 348                 if (!buf || len < 0)
 349                         goto out;
 350                 error = 0;
 351                 if (!len)
 352                         goto out;
 353                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 354                         error = -EFAULT;
 355                         goto out;
 356                 }
 357                 count = len;
 358                 if (count > log_buf_len)
 359                         count = log_buf_len;
 360                 spin_lock_irq(&logbuf_lock);
 361                 if (count > logged_chars)
 362                         count = logged_chars;
 363                 if (do_clear)
 364                         logged_chars = 0;
 365                 limit = log_end;
 366                 /*
 367                  * __put_user() could sleep, and while we sleep
 368                  * printk() could overwrite the messages
 369                  * we try to copy to user space. Therefore
 370                  * the messages are copied in reverse. <manfreds>
 371                  */
 372                 for (i = 0; i < count && !error; i++) {
 373                         j = limit-1-i;
 374                         if (j + log_buf_len < log_end)
 375                                 break;
 376                         c = LOG_BUF(j);
 377                         spin_unlock_irq(&logbuf_lock);
 378                         error = __put_user(c,&buf[count-1-i]);
 379                         cond_resched();
 380                         spin_lock_irq(&logbuf_lock);
 381                 }
 382                 spin_unlock_irq(&logbuf_lock);
 383                 if (error)
 384                         break;
 385                 error = i;
 386                 if (i != count) {
 387                         int offset = count-error;
 388                         /* buffer overflow during copy, correct user buffer. */
 389                         for (i = 0; i < error; i++) {
 390                                 if (__get_user(c,&buf[i+offset]) ||
 391                                     __put_user(c,&buf[i])) {
 392                                         error = -EFAULT;
 393                                         break;
 394                                 }
 395                                 cond_resched();
 396                         }
 397                 }
 398                 break;
 399         case 5:         /* Clear ring buffer */
 400                 logged_chars = 0;
 401                 break;
 402         case 6:         /* Disable logging to console */
 403                 console_loglevel = minimum_console_loglevel;
 404                 break;
 405         case 7:         /* Enable logging to console */
 406                 console_loglevel = default_console_loglevel;
 407                 break;
 408         case 8:         /* Set level of messages printed to console */
 409                 error = -EINVAL;
 410                 if (len < 1 || len > 8)
 411                         goto out;
 412                 if (len < minimum_console_loglevel)
 413                         len = minimum_console_loglevel;
 414                 console_loglevel = len;
 415                 error = 0;
 416                 break;
 417         case 9:         /* Number of chars in the log buffer */
 418                 error = log_end - log_start;
 419                 break;
 420         case 10:        /* Size of the log buffer */
 421                 error = log_buf_len;
 422                 break;
 423         default:
 424                 error = -EINVAL;
 425                 break;
 426         }
 427 out:
 428         return error;
 429 }
 430
 431 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 432 {
 433         return do_syslog(type, buf, len);
 434 }
 435
 436 /*
 437  * Call the console drivers on a range of log_buf
 438  */
 439 static void __call_console_drivers(unsigned start, unsigned end)
 440 {
 441         struct console *con;
 442
 443         for (con = console_drivers; con; con = con->next) {
 444                 if ((con->flags & CON_ENABLED) && con->write &&
 445                                 (cpu_online(smp_processor_id()) ||
 446                                 (con->flags & CON_ANYTIME)))
 447                         con->write(con, &LOG_BUF(start), end - start);
 448         }
 449 }
 450
 451 static int __read_mostly ignore_loglevel;
 452
 453 static int __init ignore_loglevel_setup(char *str)
 454 {
 455         ignore_loglevel = 1;
 456         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 457
 458         return 0;
 459 }
 460
 461 early_param("ignore_loglevel", ignore_loglevel_setup);
 462
 463 /*
 464  * Write out chars from start to end - 1 inclusive
 465  */
 466 static void _call_console_drivers(unsigned start,
 467                                 unsigned end, int msg_log_level)
 468 {
 469         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 470                         console_drivers && start != end) {
 471                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 472                         /* wrapped write */
 473                         __call_console_drivers(start & LOG_BUF_MASK,
 474                                                 log_buf_len);
 475                         __call_console_drivers(0, end & LOG_BUF_MASK);
 476                 } else {
 477                         __call_console_drivers(start, end);
 478                 }
 479         }
 480 }
 481
 482 /*
 483  * Call the console drivers, asking them to write out
 484  * log_buf[start] to log_buf[end - 1].
 485  * The console_sem must be held.
 486  */
 487 static void call_console_drivers(unsigned start, unsigned end)
 488 {
 489         unsigned cur_index, start_print;
 490         static int msg_level = -1;
 491
 492         BUG_ON(((int)(start - end)) > 0);
 493
 494         cur_index = start;
 495         start_print = start;
 496         while (cur_index != end) {
 497                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 498                                 LOG_BUF(cur_index + 0) == '<' &&
 499                                 LOG_BUF(cur_index + 1) >= '0' &&
 500                                 LOG_BUF(cur_index + 1) <= '7' &&
 501                                 LOG_BUF(cur_index + 2) == '>') {
 502                         msg_level = LOG_BUF(cur_index + 1) - '0';
 503                         cur_index += 3;
 504                         start_print = cur_index;
 505                 }
 506                 while (cur_index != end) {
 507                         char c = LOG_BUF(cur_index);
 508
 509                         cur_index++;
 510                         if (c == '\n') {
 511                                 if (msg_level < 0) {
 512                                         /*
 513                                          * printk() has already given us loglevel tags in
 514                                          * the buffer.  This code is here in case the
 515                                          * log buffer has wrapped right round and scribbled
 516                                          * on those tags
 517                                          */
 518                                         msg_level = default_message_loglevel;
 519                                 }
 520                                 _call_console_drivers(start_print, cur_index, msg_level);
 521                                 msg_level = -1;
 522                                 start_print = cur_index;
 523                                 break;
 524                         }
 525                 }
 526         }
 527         _call_console_drivers(start_print, end, msg_level);
 528 }
 529
 530 static void emit_log_char(char c)
 531 {
 532         LOG_BUF(log_end) = c;
 533         log_end++;
 534         if (log_end - log_start > log_buf_len)
 535                 log_start = log_end - log_buf_len;
 536         if (log_end - con_start > log_buf_len)
 537                 con_start = log_end - log_buf_len;
 538         if (logged_chars < log_buf_len)
 539                 logged_chars++;
 540 }
 541
 542 /*
 543  * Zap console related locks when oopsing. Only zap at most once
 544  * every 10 seconds, to leave time for slow consoles to print a
 545  * full oops.
 546  */
 547 static void zap_locks(void)
 548 {
 549         static unsigned long oops_timestamp;
 550
 551         if (time_after_eq(jiffies, oops_timestamp) &&
 552                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 553                 return;
 554
 555         oops_timestamp = jiffies;
 556
 557         /* If a crash is occurring, make sure we can't deadlock */
 558         spin_lock_init(&logbuf_lock);
 559         /* And make sure that we print immediately */
 560         init_MUTEX(&console_sem);
 561 }
 562
 563 #if defined(CONFIG_PRINTK_TIME)
 564 static int printk_time = 1;
 565 #else
 566 static int printk_time = 0;
 567 #endif
 568 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 569
 570 static int __init printk_time_setup(char *str)
 571 {
 572         if (*str)
 573                 return 0;
 574         printk_time = 1;
 575         printk(KERN_NOTICE "The 'time' option is deprecated and "
 576                 "is scheduled for removal in early 2008\n");
 577         printk(KERN_NOTICE "Use 'printk.time=<value>' instead\n");
 578         return 1;
 579 }
 580
 581 __setup("time", printk_time_setup);
 582
 583 /* Check if we have any console registered that can be called early in boot. */
 584 static int have_callable_console(void)
 585 {
 586         struct console *con;
 587
 588         for (con = console_drivers; con; con = con->next)
 589                 if (con->flags & CON_ANYTIME)
 590                         return 1;
 591
 592         return 0;
 593 }
 594
 595 /**
 596  * printk - print a kernel message
 597  * @fmt: format string
 598  *
 599  * This is printk().  It can be called from any context.  We want it to work.
 600  * Be aware of the fact that if oops_in_progress is not set, we might try to
 601  * wake klogd up which could deadlock on runqueue lock if printk() is called
 602  * from scheduler code.
 603  *
 604  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 605  * call the console drivers.  If we fail to get the semaphore we place the output
 606  * into the log buffer and return.  The current holder of the console_sem will
 607  * notice the new output in release_console_sem() and will send it to the
 608  * consoles before releasing the semaphore.
 609  *
 610  * One effect of this deferred printing is that code which calls printk() and
 611  * then changes console_loglevel may break. This is because console_loglevel
 612  * is inspected when the actual printing occurs.
 613  *
 614  * See also:
 615  * printf(3)
 616  */
 617
 618 asmlinkage int printk(const char *fmt, ...)
 619 {
 620         va_list args;
 621         int r;
 622
 623         va_start(args, fmt);
 624         r = vprintk(fmt, args);
 625         va_end(args);
 626
 627         return r;
 628 }
 629
 630 /* cpu currently holding logbuf_lock */
 631 static volatile unsigned int printk_cpu = UINT_MAX;
 632
 633 const char printk_recursion_bug_msg [] =
 634                         KERN_CRIT "BUG: recent printk recursion!\n";
 635 static int printk_recursion_bug;
 636
 637 asmlinkage int vprintk(const char *fmt, va_list args)
 638 {
 639         static int log_level_unknown = 1;
 640         static char printk_buf[1024];
 641
 642         unsigned long flags;
 643         int printed_len = 0;
 644         int this_cpu;
 645         char *p;
 646
 647         boot_delay_msec();
 648
 649         preempt_disable();
 650         /* This stops the holder of console_sem just where we want him */
 651         raw_local_irq_save(flags);
 652         this_cpu = smp_processor_id();
 653
 654         /*
 655          * Ouch, printk recursed into itself!
 656          */
 657         if (unlikely(printk_cpu == this_cpu)) {
 658                 /*
 659                  * If a crash is occurring during printk() on this CPU,
 660                  * then try to get the crash message out but make sure
 661                  * we can't deadlock. Otherwise just return to avoid the
 662                  * recursion and return - but flag the recursion so that
 663                  * it can be printed at the next appropriate moment:
 664                  */
 665                 if (!oops_in_progress) {
 666                         printk_recursion_bug = 1;
 667                         goto out_restore_irqs;
 668                 }
 669                 zap_locks();
 670         }
 671
 672         lockdep_off();
 673         spin_lock(&logbuf_lock);
 674         printk_cpu = this_cpu;
 675
 676         if (printk_recursion_bug) {
 677                 printk_recursion_bug = 0;
 678                 strcpy(printk_buf, printk_recursion_bug_msg);
 679                 printed_len = sizeof(printk_recursion_bug_msg);
 680         }
 681         /* Emit the output into the temporary buffer */
 682         printed_len += vscnprintf(printk_buf + printed_len,
 683                                   sizeof(printk_buf), fmt, args);
 684
 685         /*
 686          * Copy the output into log_buf.  If the caller didn't provide
 687          * appropriate log level tags, we insert them here
 688          */
 689         for (p = printk_buf; *p; p++) {
 690                 if (log_level_unknown) {
 691                         /* log_level_unknown signals the start of a new line */
 692                         if (printk_time) {
 693                                 int loglev_char;
 694                                 char tbuf[50], *tp;
 695                                 unsigned tlen;
 696                                 unsigned long long t;
 697                                 unsigned long nanosec_rem;
 698
 699                                 /*
 700                                  * force the log level token to be
 701                                  * before the time output.
 702                                  */
 703                                 if (p[0] == '<' && p[1] >='0' &&
 704                                    p[1] <= '7' && p[2] == '>') {
 705                                         loglev_char = p[1];
 706                                         p += 3;
 707                                         printed_len -= 3;
 708                                 } else {
 709                                         loglev_char = default_message_loglevel
 710                                                 + '0';
 711                                 }
 712                                 t = cpu_clock(printk_cpu);
 713                                 nanosec_rem = do_div(t, 1000000000);
 714                                 tlen = sprintf(tbuf,
 715                                                 "<%c>[%5lu.%06lu] ",
 716                                                 loglev_char,
 717                                                 (unsigned long)t,
 718                                                 nanosec_rem/1000);
 719
 720                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 721                                         emit_log_char(*tp);
 722                                 printed_len += tlen;
 723                         } else {
 724                                 if (p[0] != '<' || p[1] < '0' ||
 725                                    p[1] > '7' || p[2] != '>') {
 726                                         emit_log_char('<');
 727                                         emit_log_char(default_message_loglevel
 728                                                 + '0');
 729                                         emit_log_char('>');
 730                                         printed_len += 3;
 731                                 }
 732                         }
 733                         log_level_unknown = 0;
 734                         if (!*p)
 735                                 break;
 736                 }
 737                 emit_log_char(*p);
 738                 if (*p == '\n')
 739                         log_level_unknown = 1;
 740         }
 741
 742         if (!down_trylock(&console_sem)) {
 743                 /*
 744                  * We own the drivers.  We can drop the spinlock and
 745                  * let release_console_sem() print the text, maybe ...
 746                  */
 747                 console_locked = 1;
 748                 printk_cpu = UINT_MAX;
 749                 spin_unlock(&logbuf_lock);
 750
 751                 /*
 752                  * Console drivers may assume that per-cpu resources have
 753                  * been allocated. So unless they're explicitly marked as
 754                  * being able to cope (CON_ANYTIME) don't call them until
 755                  * this CPU is officially up.
 756                  */
 757                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 758                         console_may_schedule = 0;
 759                         release_console_sem();
 760                 } else {
 761                         /* Release by hand to avoid flushing the buffer. */
 762                         console_locked = 0;
 763                         up(&console_sem);
 764                 }
 765                 lockdep_on();
 766                 raw_local_irq_restore(flags);
 767         } else {
 768                 /*
 769                  * Someone else owns the drivers.  We drop the spinlock, which
 770                  * allows the semaphore holder to proceed and to call the
 771                  * console drivers with the output which we just produced.
 772                  */
 773                 printk_cpu = UINT_MAX;
 774                 spin_unlock(&logbuf_lock);
 775                 lockdep_on();
 776 out_restore_irqs:
 777                 raw_local_irq_restore(flags);
 778         }
 779
 780         preempt_enable();
 781         return printed_len;
 782 }
 783 EXPORT_SYMBOL(printk);
 784 EXPORT_SYMBOL(vprintk);
 785
 786 #else
 787
 788 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 789 {
 790         return -ENOSYS;
 791 }
 792
 793 static void call_console_drivers(unsigned start, unsigned end)
 794 {
 795 }
 796
 797 #endif
 798
 799 /*
 800  * Set up a list of consoles.  Called from init/main.c
 801  */
 802 static int __init console_setup(char *str)
 803 {
 804         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 805         char *s, *options;
 806         int idx;
 807
 808         /*
 809          * Decode str into name, index, options.
 810          */
 811         if (str[0] >= '0' && str[0] <= '9') {
 812                 strcpy(buf, "ttyS");
 813                 strncpy(buf + 4, str, sizeof(buf) - 5);
 814         } else {
 815                 strncpy(buf, str, sizeof(buf) - 1);
 816         }
 817         buf[sizeof(buf) - 1] = 0;
 818         if ((options = strchr(str, ',')) != NULL)
 819                 *(options++) = 0;
 820 #ifdef __sparc__
 821         if (!strcmp(str, "ttya"))
 822                 strcpy(buf, "ttyS0");
 823         if (!strcmp(str, "ttyb"))
 824                 strcpy(buf, "ttyS1");
 825 #endif
 826         for (s = buf; *s; s++)
 827                 if ((*s >= '0' && *s <= '9') || *s == ',')
 828                         break;
 829         idx = simple_strtoul(s, NULL, 10);
 830         *s = 0;
 831
 832         add_preferred_console(buf, idx, options);
 833         return 1;
 834 }
 835 __setup("console=", console_setup);
 836
 837 /**
 838  * add_preferred_console - add a device to the list of preferred consoles.
 839  * @name: device name
 840  * @idx: device index
 841  * @options: options for this console
 842  *
 843  * The last preferred console added will be used for kernel messages
 844  * and stdin/out/err for init.  Normally this is used by console_setup
 845  * above to handle user-supplied console arguments; however it can also
 846  * be used by arch-specific code either to override the user or more
 847  * commonly to provide a default console (ie from PROM variables) when
 848  * the user has not supplied one.
 849  */
 850 int add_preferred_console(char *name, int idx, char *options)
 851 {
 852         struct console_cmdline *c;
 853         int i;
 854
 855         /*
 856          *      See if this tty is not yet registered, and
 857          *      if we have a slot free.
 858          */
 859         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 860                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 861                           console_cmdline[i].index == idx) {
 862                                 selected_console = i;
 863                                 return 0;
 864                 }
 865         if (i == MAX_CMDLINECONSOLES)
 866                 return -E2BIG;
 867         selected_console = i;
 868         c = &console_cmdline[i];
 869         memcpy(c->name, name, sizeof(c->name));
 870         c->name[sizeof(c->name) - 1] = 0;
 871         c->options = options;
 872         c->index = idx;
 873         return 0;
 874 }
 875
 876 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 877 {
 878         struct console_cmdline *c;
 879         int i;
 880
 881         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 882                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 883                           console_cmdline[i].index == idx) {
 884                                 c = &console_cmdline[i];
 885                                 memcpy(c->name, name_new, sizeof(c->name));
 886                                 c->name[sizeof(c->name) - 1] = 0;
 887                                 c->options = options;
 888                                 c->index = idx_new;
 889                                 return i;
 890                 }
 891         /* not found */
 892         return -1;
 893 }
 894
 895 int console_suspend_enabled = 1;
 896 EXPORT_SYMBOL(console_suspend_enabled);
 897
 898 static int __init console_suspend_disable(char *str)
 899 {
 900         console_suspend_enabled = 0;
 901         return 1;
 902 }
 903 __setup("no_console_suspend", console_suspend_disable);
 904
 905 /**
 906  * suspend_console - suspend the console subsystem
 907  *
 908  * This disables printk() while we go into suspend states
 909  */
 910 void suspend_console(void)
 911 {
 912         if (!console_suspend_enabled)
 913                 return;
 914         printk("Suspending console(s)\n");
 915         acquire_console_sem();
 916         console_suspended = 1;
 917 }
 918
 919 void resume_console(void)
 920 {
 921         if (!console_suspend_enabled)
 922                 return;
 923         console_suspended = 0;
 924         release_console_sem();
 925 }
 926
 927 /**
 928  * acquire_console_sem - lock the console system for exclusive use.
 929  *
 930  * Acquires a semaphore which guarantees that the caller has
 931  * exclusive access to the console system and the console_drivers list.
 932  *
 933  * Can sleep, returns nothing.
 934  */
 935 void acquire_console_sem(void)
 936 {
 937         BUG_ON(in_interrupt());
 938         if (console_suspended) {
 939                 down(&secondary_console_sem);
 940                 return;
 941         }
 942         down(&console_sem);
 943         console_locked = 1;
 944         console_may_schedule = 1;
 945 }
 946 EXPORT_SYMBOL(acquire_console_sem);
 947
 948 int try_acquire_console_sem(void)
 949 {
 950         if (down_trylock(&console_sem))
 951                 return -1;
 952         console_locked = 1;
 953         console_may_schedule = 0;
 954         return 0;
 955 }
 956 EXPORT_SYMBOL(try_acquire_console_sem);
 957
 958 int is_console_locked(void)
 959 {
 960         return console_locked;
 961 }
 962
 963 void wake_up_klogd(void)
 964 {
 965         if (!oops_in_progress && waitqueue_active(&log_wait))
 966                 wake_up_interruptible(&log_wait);
 967 }
 968
 969 /**
 970  * release_console_sem - unlock the console system
 971  *
 972  * Releases the semaphore which the caller holds on the console system
 973  * and the console driver list.
 974  *
 975  * While the semaphore was held, console output may have been buffered
 976  * by printk().  If this is the case, release_console_sem() emits
 977  * the output prior to releasing the semaphore.
 978  *
 979  * If there is output waiting for klogd, we wake it up.
 980  *
 981  * release_console_sem() may be called from any context.
 982  */
 983 void release_console_sem(void)
 984 {
 985         unsigned long flags;
 986         unsigned _con_start, _log_end;
 987         unsigned wake_klogd = 0;
 988
 989         if (console_suspended) {
 990                 up(&secondary_console_sem);
 991                 return;
 992         }
 993
 994         console_may_schedule = 0;
 995
 996         for ( ; ; ) {
 997                 spin_lock_irqsave(&logbuf_lock, flags);
 998                 wake_klogd |= log_start - log_end;
 999                 if (con_start == log_end)
1000                         break;                  /* Nothing to print */
1001                 _con_start = con_start;
1002                 _log_end = log_end;
1003                 con_start = log_end;            /* Flush */
1004                 spin_unlock(&logbuf_lock);
1005                 call_console_drivers(_con_start, _log_end);
1006                 local_irq_restore(flags);
1007         }
1008         console_locked = 0;
1009         up(&console_sem);
1010         spin_unlock_irqrestore(&logbuf_lock, flags);
1011         if (wake_klogd)
1012                 wake_up_klogd();
1013 }
1014 EXPORT_SYMBOL(release_console_sem);
1015
1016 /**
1017  * console_conditional_schedule - yield the CPU if required
1018  *
1019  * If the console code is currently allowed to sleep, and
1020  * if this CPU should yield the CPU to another task, do
1021  * so here.
1022  *
1023  * Must be called within acquire_console_sem().
1024  */
1025 void __sched console_conditional_schedule(void)
1026 {
1027         if (console_may_schedule)
1028                 cond_resched();
1029 }
1030 EXPORT_SYMBOL(console_conditional_schedule);
1031
1032 void console_print(const char *s)
1033 {
1034         printk(KERN_EMERG "%s", s);
1035 }
1036 EXPORT_SYMBOL(console_print);
1037
1038 void console_unblank(void)
1039 {
1040         struct console *c;
1041
1042         /*
1043          * console_unblank can no longer be called in interrupt context unless
1044          * oops_in_progress is set to 1..
1045          */
1046         if (oops_in_progress) {
1047                 if (down_trylock(&console_sem) != 0)
1048                         return;
1049         } else
1050                 acquire_console_sem();
1051
1052         console_locked = 1;
1053         console_may_schedule = 0;
1054         for (c = console_drivers; c != NULL; c = c->next)
1055                 if ((c->flags & CON_ENABLED) && c->unblank)
1056                         c->unblank();
1057         release_console_sem();
1058 }
1059
1060 /*
1061  * Return the console tty driver structure and its associated index
1062  */
1063 struct tty_driver *console_device(int *index)
1064 {
1065         struct console *c;
1066         struct tty_driver *driver = NULL;
1067
1068         acquire_console_sem();
1069         for (c = console_drivers; c != NULL; c = c->next) {
1070                 if (!c->device)
1071                         continue;
1072                 driver = c->device(c, index);
1073                 if (driver)
1074                         break;
1075         }
1076         release_console_sem();
1077         return driver;
1078 }
1079
1080 /*
1081  * Prevent further output on the passed console device so that (for example)
1082  * serial drivers can disable console output before suspending a port, and can
1083  * re-enable output afterwards.
1084  */
1085 void console_stop(struct console *console)
1086 {
1087         acquire_console_sem();
1088         console->flags &= ~CON_ENABLED;
1089         release_console_sem();
1090 }
1091 EXPORT_SYMBOL(console_stop);
1092
1093 void console_start(struct console *console)
1094 {
1095         acquire_console_sem();
1096         console->flags |= CON_ENABLED;
1097         release_console_sem();
1098 }
1099 EXPORT_SYMBOL(console_start);
1100
1101 /*
1102  * The console driver calls this routine during kernel initialization
1103  * to register the console printing procedure with printk() and to
1104  * print any messages that were printed by the kernel before the
1105  * console driver was initialized.
1106  */
1107 void register_console(struct console *console)
1108 {
1109         int i;
1110         unsigned long flags;
1111         struct console *bootconsole = NULL;
1112
1113         if (console_drivers) {
1114                 if (console->flags & CON_BOOT)
1115                         return;
1116                 if (console_drivers->flags & CON_BOOT)
1117                         bootconsole = console_drivers;
1118         }
1119
1120         if (preferred_console < 0 || bootconsole || !console_drivers)
1121                 preferred_console = selected_console;
1122
1123         if (console->early_setup)
1124                 console->early_setup();
1125
1126         /*
1127          *      See if we want to use this console driver. If we
1128          *      didn't select a console we take the first one
1129          *      that registers here.
1130          */
1131         if (preferred_console < 0) {
1132                 if (console->index < 0)
1133                         console->index = 0;
1134                 if (console->setup == NULL ||
1135                     console->setup(console, NULL) == 0) {
1136                         console->flags |= CON_ENABLED | CON_CONSDEV;
1137                         preferred_console = 0;
1138                 }
1139         }
1140
1141         /*
1142          *      See if this console matches one we selected on
1143          *      the command line.
1144          */
1145         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1146                         i++) {
1147                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1148                         continue;
1149                 if (console->index >= 0 &&
1150                     console->index != console_cmdline[i].index)
1151                         continue;
1152                 if (console->index < 0)
1153                         console->index = console_cmdline[i].index;
1154                 if (console->setup &&
1155                     console->setup(console, console_cmdline[i].options) != 0)
1156                         break;
1157                 console->flags |= CON_ENABLED;
1158                 console->index = console_cmdline[i].index;
1159                 if (i == selected_console) {
1160                         console->flags |= CON_CONSDEV;
1161                         preferred_console = selected_console;
1162                 }
1163                 break;
1164         }
1165
1166         if (!(console->flags & CON_ENABLED))
1167                 return;
1168
1169         if (bootconsole && (console->flags & CON_CONSDEV)) {
1170                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1171                        bootconsole->name, bootconsole->index,
1172                        console->name, console->index);
1173                 unregister_console(bootconsole);
1174                 console->flags &= ~CON_PRINTBUFFER;
1175         } else {
1176                 printk(KERN_INFO "console [%s%d] enabled\n",
1177                        console->name, console->index);
1178         }
1179
1180         /*
1181          *      Put this console in the list - keep the
1182          *      preferred driver at the head of the list.
1183          */
1184         acquire_console_sem();
1185         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1186                 console->next = console_drivers;
1187                 console_drivers = console;
1188                 if (console->next)
1189                         console->next->flags &= ~CON_CONSDEV;
1190         } else {
1191                 console->next = console_drivers->next;
1192                 console_drivers->next = console;
1193         }
1194         if (console->flags & CON_PRINTBUFFER) {
1195                 /*
1196                  * release_console_sem() will print out the buffered messages
1197                  * for us.
1198                  */
1199                 spin_lock_irqsave(&logbuf_lock, flags);
1200                 con_start = log_start;
1201                 spin_unlock_irqrestore(&logbuf_lock, flags);
1202         }
1203         release_console_sem();
1204 }
1205 EXPORT_SYMBOL(register_console);
1206
1207 int unregister_console(struct console *console)
1208 {
1209         struct console *a, *b;
1210         int res = 1;
1211
1212         acquire_console_sem();
1213         if (console_drivers == console) {
1214                 console_drivers=console->next;
1215                 res = 0;
1216         } else if (console_drivers) {
1217                 for (a=console_drivers->next, b=console_drivers ;
1218                      a; b=a, a=b->next) {
1219                         if (a == console) {
1220                                 b->next = a->next;
1221                                 res = 0;
1222                                 break;
1223                         }
1224                 }
1225         }
1226
1227         /*
1228          * If this isn't the last console and it has CON_CONSDEV set, we
1229          * need to set it on the next preferred console.
1230          */
1231         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1232                 console_drivers->flags |= CON_CONSDEV;
1233
1234         release_console_sem();
1235         return res;
1236 }
1237 EXPORT_SYMBOL(unregister_console);
1238
1239 static int __init disable_boot_consoles(void)
1240 {
1241         if (console_drivers != NULL) {
1242                 if (console_drivers->flags & CON_BOOT) {
1243                         printk(KERN_INFO "turn off boot console %s%d\n",
1244                                 console_drivers->name, console_drivers->index);
1245                         return unregister_console(console_drivers);
1246                 }
1247         }
1248         return 0;
1249 }
1250 late_initcall(disable_boot_consoles);
1251
1252 /**
1253  * tty_write_message - write a message to a certain tty, not just the console.
1254  * @tty: the destination tty_struct
1255  * @msg: the message to write
1256  *
1257  * This is used for messages that need to be redirected to a specific tty.
1258  * We don't put it into the syslog queue right now maybe in the future if
1259  * really needed.
1260  */
1261 void tty_write_message(struct tty_struct *tty, char *msg)
1262 {
1263         if (tty && tty->driver->write)
1264                 tty->driver->write(tty, msg, strlen(msg));
1265         return;
1266 }
1267
1268 /*
1269  * printk rate limiting, lifted from the networking subsystem.
1270  *
1271  * This enforces a rate limit: not more than one kernel message
1272  * every printk_ratelimit_jiffies to make a denial-of-service
1273  * attack impossible.
1274  */
1275 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1276 {
1277         static DEFINE_SPINLOCK(ratelimit_lock);
1278         static unsigned toks = 10 * 5 * HZ;
1279         static unsigned long last_msg;
1280         static int missed;
1281         unsigned long flags;
1282         unsigned long now = jiffies;
1283
1284         spin_lock_irqsave(&ratelimit_lock, flags);
1285         toks += now - last_msg;
1286         last_msg = now;
1287         if (toks > (ratelimit_burst * ratelimit_jiffies))
1288                 toks = ratelimit_burst * ratelimit_jiffies;
1289         if (toks >= ratelimit_jiffies) {
1290                 int lost = missed;
1291
1292                 missed = 0;
1293                 toks -= ratelimit_jiffies;
1294                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1295                 if (lost)
1296                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1297                 return 1;
1298         }
1299         missed++;
1300         spin_unlock_irqrestore(&ratelimit_lock, flags);
1301         return 0;
1302 }
1303 EXPORT_SYMBOL(__printk_ratelimit);
1304
1305 /* minimum time in jiffies between messages */
1306 int printk_ratelimit_jiffies = 5 * HZ;
1307
1308 /* number of messages we send before ratelimiting */
1309 int printk_ratelimit_burst = 10;
1310
1311 int printk_ratelimit(void)
1312 {
1313         return __printk_ratelimit(printk_ratelimit_jiffies,
1314                                 printk_ratelimit_burst);
1315 }
1316 EXPORT_SYMBOL(printk_ratelimit);
1317
1318 /**
1319  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1320  * @caller_jiffies: pointer to caller's state
1321  * @interval_msecs: minimum interval between prints
1322  *
1323  * printk_timed_ratelimit() returns true if more than @interval_msecs
1324  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1325  * returned true.
1326  */
1327 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1328                         unsigned int interval_msecs)
1329 {
1330         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1331                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1332                 return true;
1333         }
1334         return false;
1335 }
1336 EXPORT_SYMBOL(printk_timed_ratelimit);