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
  36 #include <asm/uaccess.h>
  37
  38 /*
  39  * Architectures can override it:
  40  */
  41 void __attribute__((weak)) early_printk(const char *fmt, ...)
  42 {
  43 }
  44
  45 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  46
  47 /* printk's without a loglevel use this.. */
  48 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  49
  50 /* We show everything that is MORE important than this.. */
  51 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  52 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  53
  54 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  55
  56 int console_printk[4] = {
  57         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  58         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  59         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  60         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  61 };
  62
  63 /*
  64  * Low level drivers may need that to know if they can schedule in
  65  * their unblank() callback or not. So let's export it.
  66  */
  67 int oops_in_progress;
  68 EXPORT_SYMBOL(oops_in_progress);
  69
  70 /*
  71  * console_sem protects the console_drivers list, and also
  72  * provides serialisation for access to the entire console
  73  * driver system.
  74  */
  75 static DECLARE_MUTEX(console_sem);
  76 static DECLARE_MUTEX(secondary_console_sem);
  77 struct console *console_drivers;
  78 /*
  79  * This is used for debugging the mess that is the VT code by
  80  * keeping track if we have the console semaphore held. It's
  81  * definitely not the perfect debug tool (we don't know if _WE_
  82  * hold it are racing, but it helps tracking those weird code
  83  * path in the console code where we end up in places I want
  84  * locked without the console sempahore held
  85  */
  86 static int console_locked, console_suspended;
  87
  88 /*
  89  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  90  * It is also used in interesting ways to provide interlocking in
  91  * release_console_sem().
  92  */
  93 static DEFINE_SPINLOCK(logbuf_lock);
  94
  95 #define LOG_BUF_MASK (log_buf_len-1)
  96 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  97
  98 /*
  99  * The indices into log_buf are not constrained to log_buf_len - they
 100  * must be masked before subscripting
 101  */
 102 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 103 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 104 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 105
 106 /*
 107  *      Array of consoles built from command line options (console=)
 108  */
 109 struct console_cmdline
 110 {
 111         char    name[8];                        /* Name of the driver       */
 112         int     index;                          /* Minor dev. to use        */
 113         char    *options;                       /* Options for the driver   */
 114 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 115         char    *brl_options;                   /* Options for braille driver */
 116 #endif
 117 };
 118
 119 #define MAX_CMDLINECONSOLES 8
 120
 121 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 122 static int selected_console = -1;
 123 static int preferred_console = -1;
 124 int console_set_on_cmdline;
 125 EXPORT_SYMBOL(console_set_on_cmdline);
 126
 127 /* Flag: console code may call schedule() */
 128 static int console_may_schedule;
 129
 130 #ifdef CONFIG_PRINTK
 131
 132 static char __log_buf[__LOG_BUF_LEN];
 133 static char *log_buf = __log_buf;
 134 static int log_buf_len = __LOG_BUF_LEN;
 135 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 136
 137 static int __init log_buf_len_setup(char *str)
 138 {
 139         unsigned size = memparse(str, &str);
 140         unsigned long flags;
 141
 142         if (size)
 143                 size = roundup_pow_of_two(size);
 144         if (size > log_buf_len) {
 145                 unsigned start, dest_idx, offset;
 146                 char *new_log_buf;
 147
 148                 new_log_buf = alloc_bootmem(size);
 149                 if (!new_log_buf) {
 150                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 151                         goto out;
 152                 }
 153
 154                 spin_lock_irqsave(&logbuf_lock, flags);
 155                 log_buf_len = size;
 156                 log_buf = new_log_buf;
 157
 158                 offset = start = min(con_start, log_start);
 159                 dest_idx = 0;
 160                 while (start != log_end) {
 161                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 162                         start++;
 163                         dest_idx++;
 164                 }
 165                 log_start -= offset;
 166                 con_start -= offset;
 167                 log_end -= offset;
 168                 spin_unlock_irqrestore(&logbuf_lock, flags);
 169
 170                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 171         }
 172 out:
 173         return 1;
 174 }
 175
 176 __setup("log_buf_len=", log_buf_len_setup);
 177
 178 #ifdef CONFIG_BOOT_PRINTK_DELAY
 179
 180 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 181 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 182
 183 static int __init boot_delay_setup(char *str)
 184 {
 185         unsigned long lpj;
 186         unsigned long long loops_per_msec;
 187
 188         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 189         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 190
 191         get_option(&str, &boot_delay);
 192         if (boot_delay > 10 * 1000)
 193                 boot_delay = 0;
 194
 195         printk_delay_msec = loops_per_msec;
 196         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 197                 "HZ: %d, printk_delay_msec: %llu\n",
 198                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 199         return 1;
 200 }
 201 __setup("boot_delay=", boot_delay_setup);
 202
 203 static void boot_delay_msec(void)
 204 {
 205         unsigned long long k;
 206         unsigned long timeout;
 207
 208         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 209                 return;
 210
 211         k = (unsigned long long)printk_delay_msec * boot_delay;
 212
 213         timeout = jiffies + msecs_to_jiffies(boot_delay);
 214         while (k) {
 215                 k--;
 216                 cpu_relax();
 217                 /*
 218                  * use (volatile) jiffies to prevent
 219                  * compiler reduction; loop termination via jiffies
 220                  * is secondary and may or may not happen.
 221                  */
 222                 if (time_after(jiffies, timeout))
 223                         break;
 224                 touch_nmi_watchdog();
 225         }
 226 }
 227 #else
 228 static inline void boot_delay_msec(void)
 229 {
 230 }
 231 #endif
 232
 233 /*
 234  * Return the number of unread characters in the log buffer.
 235  */
 236 int log_buf_get_len(void)
 237 {
 238         return logged_chars;
 239 }
 240
 241 /*
 242  * Copy a range of characters from the log buffer.
 243  */
 244 int log_buf_copy(char *dest, int idx, int len)
 245 {
 246         int ret, max;
 247         bool took_lock = false;
 248
 249         if (!oops_in_progress) {
 250                 spin_lock_irq(&logbuf_lock);
 251                 took_lock = true;
 252         }
 253
 254         max = log_buf_get_len();
 255         if (idx < 0 || idx >= max) {
 256                 ret = -1;
 257         } else {
 258                 if (len > max)
 259                         len = max;
 260                 ret = len;
 261                 idx += (log_end - max);
 262                 while (len-- > 0)
 263                         dest[len] = LOG_BUF(idx + len);
 264         }
 265
 266         if (took_lock)
 267                 spin_unlock_irq(&logbuf_lock);
 268
 269         return ret;
 270 }
 271
 272 /*
 273  * Extract a single character from the log buffer.
 274  */
 275 int log_buf_read(int idx)
 276 {
 277         char ret;
 278
 279         if (log_buf_copy(&ret, idx, 1) == 1)
 280                 return ret;
 281         else
 282                 return -1;
 283 }
 284
 285 /*
 286  * Commands to do_syslog:
 287  *
 288  *      0 -- Close the log.  Currently a NOP.
 289  *      1 -- Open the log. Currently a NOP.
 290  *      2 -- Read from the log.
 291  *      3 -- Read all messages remaining in the ring buffer.
 292  *      4 -- Read and clear all messages remaining in the ring buffer
 293  *      5 -- Clear ring buffer.
 294  *      6 -- Disable printk's to console
 295  *      7 -- Enable printk's to console
 296  *      8 -- Set level of messages printed to console
 297  *      9 -- Return number of unread characters in the log buffer
 298  *     10 -- Return size of the log buffer
 299  */
 300 int do_syslog(int type, char __user *buf, int len)
 301 {
 302         unsigned i, j, limit, count;
 303         int do_clear = 0;
 304         char c;
 305         int error = 0;
 306
 307         error = security_syslog(type);
 308         if (error)
 309                 return error;
 310
 311         switch (type) {
 312         case 0:         /* Close log */
 313                 break;
 314         case 1:         /* Open log */
 315                 break;
 316         case 2:         /* Read from log */
 317                 error = -EINVAL;
 318                 if (!buf || len < 0)
 319                         goto out;
 320                 error = 0;
 321                 if (!len)
 322                         goto out;
 323                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 324                         error = -EFAULT;
 325                         goto out;
 326                 }
 327                 error = wait_event_interruptible(log_wait,
 328                                                         (log_start - log_end));
 329                 if (error)
 330                         goto out;
 331                 i = 0;
 332                 spin_lock_irq(&logbuf_lock);
 333                 while (!error && (log_start != log_end) && i < len) {
 334                         c = LOG_BUF(log_start);
 335                         log_start++;
 336                         spin_unlock_irq(&logbuf_lock);
 337                         error = __put_user(c,buf);
 338                         buf++;
 339                         i++;
 340                         cond_resched();
 341                         spin_lock_irq(&logbuf_lock);
 342                 }
 343                 spin_unlock_irq(&logbuf_lock);
 344                 if (!error)
 345                         error = i;
 346                 break;
 347         case 4:         /* Read/clear last kernel messages */
 348                 do_clear = 1;
 349                 /* FALL THRU */
 350         case 3:         /* Read last kernel messages */
 351                 error = -EINVAL;
 352                 if (!buf || len < 0)
 353                         goto out;
 354                 error = 0;
 355                 if (!len)
 356                         goto out;
 357                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 358                         error = -EFAULT;
 359                         goto out;
 360                 }
 361                 count = len;
 362                 if (count > log_buf_len)
 363                         count = log_buf_len;
 364                 spin_lock_irq(&logbuf_lock);
 365                 if (count > logged_chars)
 366                         count = logged_chars;
 367                 if (do_clear)
 368                         logged_chars = 0;
 369                 limit = log_end;
 370                 /*
 371                  * __put_user() could sleep, and while we sleep
 372                  * printk() could overwrite the messages
 373                  * we try to copy to user space. Therefore
 374                  * the messages are copied in reverse. <manfreds>
 375                  */
 376                 for (i = 0; i < count && !error; i++) {
 377                         j = limit-1-i;
 378                         if (j + log_buf_len < log_end)
 379                                 break;
 380                         c = LOG_BUF(j);
 381                         spin_unlock_irq(&logbuf_lock);
 382                         error = __put_user(c,&buf[count-1-i]);
 383                         cond_resched();
 384                         spin_lock_irq(&logbuf_lock);
 385                 }
 386                 spin_unlock_irq(&logbuf_lock);
 387                 if (error)
 388                         break;
 389                 error = i;
 390                 if (i != count) {
 391                         int offset = count-error;
 392                         /* buffer overflow during copy, correct user buffer. */
 393                         for (i = 0; i < error; i++) {
 394                                 if (__get_user(c,&buf[i+offset]) ||
 395                                     __put_user(c,&buf[i])) {
 396                                         error = -EFAULT;
 397                                         break;
 398                                 }
 399                                 cond_resched();
 400                         }
 401                 }
 402                 break;
 403         case 5:         /* Clear ring buffer */
 404                 logged_chars = 0;
 405                 break;
 406         case 6:         /* Disable logging to console */
 407                 console_loglevel = minimum_console_loglevel;
 408                 break;
 409         case 7:         /* Enable logging to console */
 410                 console_loglevel = default_console_loglevel;
 411                 break;
 412         case 8:         /* Set level of messages printed to console */
 413                 error = -EINVAL;
 414                 if (len < 1 || len > 8)
 415                         goto out;
 416                 if (len < minimum_console_loglevel)
 417                         len = minimum_console_loglevel;
 418                 console_loglevel = len;
 419                 error = 0;
 420                 break;
 421         case 9:         /* Number of chars in the log buffer */
 422                 error = log_end - log_start;
 423                 break;
 424         case 10:        /* Size of the log buffer */
 425                 error = log_buf_len;
 426                 break;
 427         default:
 428                 error = -EINVAL;
 429                 break;
 430         }
 431 out:
 432         return error;
 433 }
 434
 435 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 436 {
 437         return do_syslog(type, buf, len);
 438 }
 439
 440 /*
 441  * Call the console drivers on a range of log_buf
 442  */
 443 static void __call_console_drivers(unsigned start, unsigned end)
 444 {
 445         struct console *con;
 446
 447         for (con = console_drivers; con; con = con->next) {
 448                 if ((con->flags & CON_ENABLED) && con->write &&
 449                                 (cpu_online(smp_processor_id()) ||
 450                                 (con->flags & CON_ANYTIME)))
 451                         con->write(con, &LOG_BUF(start), end - start);
 452         }
 453 }
 454
 455 static int __read_mostly ignore_loglevel;
 456
 457 static int __init ignore_loglevel_setup(char *str)
 458 {
 459         ignore_loglevel = 1;
 460         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 461
 462         return 0;
 463 }
 464
 465 early_param("ignore_loglevel", ignore_loglevel_setup);
 466
 467 /*
 468  * Write out chars from start to end - 1 inclusive
 469  */
 470 static void _call_console_drivers(unsigned start,
 471                                 unsigned end, int msg_log_level)
 472 {
 473         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 474                         console_drivers && start != end) {
 475                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 476                         /* wrapped write */
 477                         __call_console_drivers(start & LOG_BUF_MASK,
 478                                                 log_buf_len);
 479                         __call_console_drivers(0, end & LOG_BUF_MASK);
 480                 } else {
 481                         __call_console_drivers(start, end);
 482                 }
 483         }
 484 }
 485
 486 /*
 487  * Call the console drivers, asking them to write out
 488  * log_buf[start] to log_buf[end - 1].
 489  * The console_sem must be held.
 490  */
 491 static void call_console_drivers(unsigned start, unsigned end)
 492 {
 493         unsigned cur_index, start_print;
 494         static int msg_level = -1;
 495
 496         BUG_ON(((int)(start - end)) > 0);
 497
 498         cur_index = start;
 499         start_print = start;
 500         while (cur_index != end) {
 501                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 502                                 LOG_BUF(cur_index + 0) == '<' &&
 503                                 LOG_BUF(cur_index + 1) >= '0' &&
 504                                 LOG_BUF(cur_index + 1) <= '7' &&
 505                                 LOG_BUF(cur_index + 2) == '>') {
 506                         msg_level = LOG_BUF(cur_index + 1) - '0';
 507                         cur_index += 3;
 508                         start_print = cur_index;
 509                 }
 510                 while (cur_index != end) {
 511                         char c = LOG_BUF(cur_index);
 512
 513                         cur_index++;
 514                         if (c == '\n') {
 515                                 if (msg_level < 0) {
 516                                         /*
 517                                          * printk() has already given us loglevel tags in
 518                                          * the buffer.  This code is here in case the
 519                                          * log buffer has wrapped right round and scribbled
 520                                          * on those tags
 521                                          */
 522                                         msg_level = default_message_loglevel;
 523                                 }
 524                                 _call_console_drivers(start_print, cur_index, msg_level);
 525                                 msg_level = -1;
 526                                 start_print = cur_index;
 527                                 break;
 528                         }
 529                 }
 530         }
 531         _call_console_drivers(start_print, end, msg_level);
 532 }
 533
 534 static void emit_log_char(char c)
 535 {
 536         LOG_BUF(log_end) = c;
 537         log_end++;
 538         if (log_end - log_start > log_buf_len)
 539                 log_start = log_end - log_buf_len;
 540         if (log_end - con_start > log_buf_len)
 541                 con_start = log_end - log_buf_len;
 542         if (logged_chars < log_buf_len)
 543                 logged_chars++;
 544 }
 545
 546 /*
 547  * Zap console related locks when oopsing. Only zap at most once
 548  * every 10 seconds, to leave time for slow consoles to print a
 549  * full oops.
 550  */
 551 static void zap_locks(void)
 552 {
 553         static unsigned long oops_timestamp;
 554
 555         if (time_after_eq(jiffies, oops_timestamp) &&
 556                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 557                 return;
 558
 559         oops_timestamp = jiffies;
 560
 561         /* If a crash is occurring, make sure we can't deadlock */
 562         spin_lock_init(&logbuf_lock);
 563         /* And make sure that we print immediately */
 564         init_MUTEX(&console_sem);
 565 }
 566
 567 #if defined(CONFIG_PRINTK_TIME)
 568 static int printk_time = 1;
 569 #else
 570 static int printk_time = 0;
 571 #endif
 572 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 573
 574 /* Check if we have any console registered that can be called early in boot. */
 575 static int have_callable_console(void)
 576 {
 577         struct console *con;
 578
 579         for (con = console_drivers; con; con = con->next)
 580                 if (con->flags & CON_ANYTIME)
 581                         return 1;
 582
 583         return 0;
 584 }
 585
 586 /**
 587  * printk - print a kernel message
 588  * @fmt: format string
 589  *
 590  * This is printk().  It can be called from any context.  We want it to work.
 591  * Be aware of the fact that if oops_in_progress is not set, we might try to
 592  * wake klogd up which could deadlock on runqueue lock if printk() is called
 593  * from scheduler code.
 594  *
 595  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 596  * call the console drivers.  If we fail to get the semaphore we place the output
 597  * into the log buffer and return.  The current holder of the console_sem will
 598  * notice the new output in release_console_sem() and will send it to the
 599  * consoles before releasing the semaphore.
 600  *
 601  * One effect of this deferred printing is that code which calls printk() and
 602  * then changes console_loglevel may break. This is because console_loglevel
 603  * is inspected when the actual printing occurs.
 604  *
 605  * See also:
 606  * printf(3)
 607  */
 608
 609 asmlinkage int printk(const char *fmt, ...)
 610 {
 611         va_list args;
 612         int r;
 613
 614         va_start(args, fmt);
 615         r = vprintk(fmt, args);
 616         va_end(args);
 617
 618         return r;
 619 }
 620
 621 /* cpu currently holding logbuf_lock */
 622 static volatile unsigned int printk_cpu = UINT_MAX;
 623
 624 /*
 625  * Can we actually use the console at this time on this cpu?
 626  *
 627  * Console drivers may assume that per-cpu resources have
 628  * been allocated. So unless they're explicitly marked as
 629  * being able to cope (CON_ANYTIME) don't call them until
 630  * this CPU is officially up.
 631  */
 632 static inline int can_use_console(unsigned int cpu)
 633 {
 634         return cpu_online(cpu) || have_callable_console();
 635 }
 636
 637 /*
 638  * Try to get console ownership to actually show the kernel
 639  * messages from a 'printk'. Return true (and with the
 640  * console_semaphore held, and 'console_locked' set) if it
 641  * is successful, false otherwise.
 642  *
 643  * This gets called with the 'logbuf_lock' spinlock held and
 644  * interrupts disabled. It should return with 'lockbuf_lock'
 645  * released but interrupts still disabled.
 646  */
 647 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 648 {
 649         int retval = 0;
 650
 651         if (!try_acquire_console_sem()) {
 652                 retval = 1;
 653
 654                 /*
 655                  * If we can't use the console, we need to release
 656                  * the console semaphore by hand to avoid flushing
 657                  * the buffer. We need to hold the console semaphore
 658                  * in order to do this test safely.
 659                  */
 660                 if (!can_use_console(cpu)) {
 661                         console_locked = 0;
 662                         up(&console_sem);
 663                         retval = 0;
 664                 }
 665         }
 666         printk_cpu = UINT_MAX;
 667         spin_unlock(&logbuf_lock);
 668         return retval;
 669 }
 670
 671 const char printk_recursion_bug_msg [] =
 672                         KERN_CRIT "BUG: recent printk recursion!\n";
 673 static int printk_recursion_bug;
 674
 675 asmlinkage int vprintk(const char *fmt, va_list args)
 676 {
 677         static int log_level_unknown = 1;
 678         static char printk_buf[1024];
 679
 680         unsigned long flags;
 681         int printed_len = 0;
 682         int this_cpu;
 683         char *p;
 684
 685         boot_delay_msec();
 686
 687         preempt_disable();
 688         /* This stops the holder of console_sem just where we want him */
 689         raw_local_irq_save(flags);
 690         this_cpu = smp_processor_id();
 691
 692         /*
 693          * Ouch, printk recursed into itself!
 694          */
 695         if (unlikely(printk_cpu == this_cpu)) {
 696                 /*
 697                  * If a crash is occurring during printk() on this CPU,
 698                  * then try to get the crash message out but make sure
 699                  * we can't deadlock. Otherwise just return to avoid the
 700                  * recursion and return - but flag the recursion so that
 701                  * it can be printed at the next appropriate moment:
 702                  */
 703                 if (!oops_in_progress) {
 704                         printk_recursion_bug = 1;
 705                         goto out_restore_irqs;
 706                 }
 707                 zap_locks();
 708         }
 709
 710         lockdep_off();
 711         spin_lock(&logbuf_lock);
 712         printk_cpu = this_cpu;
 713
 714         if (printk_recursion_bug) {
 715                 printk_recursion_bug = 0;
 716                 strcpy(printk_buf, printk_recursion_bug_msg);
 717                 printed_len = sizeof(printk_recursion_bug_msg);
 718         }
 719         /* Emit the output into the temporary buffer */
 720         printed_len += vscnprintf(printk_buf + printed_len,
 721                                   sizeof(printk_buf) - printed_len, fmt, args);
 722
 723         /*
 724          * Copy the output into log_buf.  If the caller didn't provide
 725          * appropriate log level tags, we insert them here
 726          */
 727         for (p = printk_buf; *p; p++) {
 728                 if (log_level_unknown) {
 729                         /* log_level_unknown signals the start of a new line */
 730                         if (printk_time) {
 731                                 int loglev_char;
 732                                 char tbuf[50], *tp;
 733                                 unsigned tlen;
 734                                 unsigned long long t;
 735                                 unsigned long nanosec_rem;
 736
 737                                 /*
 738                                  * force the log level token to be
 739                                  * before the time output.
 740                                  */
 741                                 if (p[0] == '<' && p[1] >='0' &&
 742                                    p[1] <= '7' && p[2] == '>') {
 743                                         loglev_char = p[1];
 744                                         p += 3;
 745                                         printed_len -= 3;
 746                                 } else {
 747                                         loglev_char = default_message_loglevel
 748                                                 + '0';
 749                                 }
 750                                 t = cpu_clock(printk_cpu);
 751                                 nanosec_rem = do_div(t, 1000000000);
 752                                 tlen = sprintf(tbuf,
 753                                                 "<%c>[%5lu.%06lu] ",
 754                                                 loglev_char,
 755                                                 (unsigned long)t,
 756                                                 nanosec_rem/1000);
 757
 758                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 759                                         emit_log_char(*tp);
 760                                 printed_len += tlen;
 761                         } else {
 762                                 if (p[0] != '<' || p[1] < '0' ||
 763                                    p[1] > '7' || p[2] != '>') {
 764                                         emit_log_char('<');
 765                                         emit_log_char(default_message_loglevel
 766                                                 + '0');
 767                                         emit_log_char('>');
 768                                         printed_len += 3;
 769                                 }
 770                         }
 771                         log_level_unknown = 0;
 772                         if (!*p)
 773                                 break;
 774                 }
 775                 emit_log_char(*p);
 776                 if (*p == '\n')
 777                         log_level_unknown = 1;
 778         }
 779
 780         /*
 781          * Try to acquire and then immediately release the
 782          * console semaphore. The release will do all the
 783          * actual magic (print out buffers, wake up klogd,
 784          * etc).
 785          *
 786          * The acquire_console_semaphore_for_printk() function
 787          * will release 'logbuf_lock' regardless of whether it
 788          * actually gets the semaphore or not.
 789          */
 790         if (acquire_console_semaphore_for_printk(this_cpu))
 791                 release_console_sem();
 792
 793         lockdep_on();
 794 out_restore_irqs:
 795         raw_local_irq_restore(flags);
 796
 797         preempt_enable();
 798         return printed_len;
 799 }
 800 EXPORT_SYMBOL(printk);
 801 EXPORT_SYMBOL(vprintk);
 802
 803 #else
 804
 805 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 806 {
 807         return -ENOSYS;
 808 }
 809
 810 static void call_console_drivers(unsigned start, unsigned end)
 811 {
 812 }
 813
 814 #endif
 815
 816 static int __add_preferred_console(char *name, int idx, char *options,
 817                                    char *brl_options)
 818 {
 819         struct console_cmdline *c;
 820         int i;
 821
 822         /*
 823          *      See if this tty is not yet registered, and
 824          *      if we have a slot free.
 825          */
 826         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 827                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 828                           console_cmdline[i].index == idx) {
 829                                 if (!brl_options)
 830                                         selected_console = i;
 831                                 return 0;
 832                 }
 833         if (i == MAX_CMDLINECONSOLES)
 834                 return -E2BIG;
 835         if (!brl_options)
 836                 selected_console = i;
 837         c = &console_cmdline[i];
 838         strlcpy(c->name, name, sizeof(c->name));
 839         c->options = options;
 840 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 841         c->brl_options = brl_options;
 842 #endif
 843         c->index = idx;
 844         return 0;
 845 }
 846 /*
 847  * Set up a list of consoles.  Called from init/main.c
 848  */
 849 static int __init console_setup(char *str)
 850 {
 851         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 852         char *s, *options, *brl_options = NULL;
 853         int idx;
 854
 855 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 856         if (!memcmp(str, "brl,", 4)) {
 857                 brl_options = "";
 858                 str += 4;
 859         } else if (!memcmp(str, "brl=", 4)) {
 860                 brl_options = str + 4;
 861                 str = strchr(brl_options, ',');
 862                 if (!str) {
 863                         printk(KERN_ERR "need port name after brl=\n");
 864                         return 1;
 865                 }
 866                 *(str++) = 0;
 867         }
 868 #endif
 869
 870         /*
 871          * Decode str into name, index, options.
 872          */
 873         if (str[0] >= '0' && str[0] <= '9') {
 874                 strcpy(buf, "ttyS");
 875                 strncpy(buf + 4, str, sizeof(buf) - 5);
 876         } else {
 877                 strncpy(buf, str, sizeof(buf) - 1);
 878         }
 879         buf[sizeof(buf) - 1] = 0;
 880         if ((options = strchr(str, ',')) != NULL)
 881                 *(options++) = 0;
 882 #ifdef __sparc__
 883         if (!strcmp(str, "ttya"))
 884                 strcpy(buf, "ttyS0");
 885         if (!strcmp(str, "ttyb"))
 886                 strcpy(buf, "ttyS1");
 887 #endif
 888         for (s = buf; *s; s++)
 889                 if ((*s >= '0' && *s <= '9') || *s == ',')
 890                         break;
 891         idx = simple_strtoul(s, NULL, 10);
 892         *s = 0;
 893
 894         __add_preferred_console(buf, idx, options, brl_options);
 895         console_set_on_cmdline = 1;
 896         return 1;
 897 }
 898 __setup("console=", console_setup);
 899
 900 /**
 901  * add_preferred_console - add a device to the list of preferred consoles.
 902  * @name: device name
 903  * @idx: device index
 904  * @options: options for this console
 905  *
 906  * The last preferred console added will be used for kernel messages
 907  * and stdin/out/err for init.  Normally this is used by console_setup
 908  * above to handle user-supplied console arguments; however it can also
 909  * be used by arch-specific code either to override the user or more
 910  * commonly to provide a default console (ie from PROM variables) when
 911  * the user has not supplied one.
 912  */
 913 int add_preferred_console(char *name, int idx, char *options)
 914 {
 915         return __add_preferred_console(name, idx, options, NULL);
 916 }
 917
 918 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 919 {
 920         struct console_cmdline *c;
 921         int i;
 922
 923         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 924                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 925                           console_cmdline[i].index == idx) {
 926                                 c = &console_cmdline[i];
 927                                 strlcpy(c->name, name_new, sizeof(c->name));
 928                                 c->name[sizeof(c->name) - 1] = 0;
 929                                 c->options = options;
 930                                 c->index = idx_new;
 931                                 return i;
 932                 }
 933         /* not found */
 934         return -1;
 935 }
 936
 937 int console_suspend_enabled = 1;
 938 EXPORT_SYMBOL(console_suspend_enabled);
 939
 940 static int __init console_suspend_disable(char *str)
 941 {
 942         console_suspend_enabled = 0;
 943         return 1;
 944 }
 945 __setup("no_console_suspend", console_suspend_disable);
 946
 947 /**
 948  * suspend_console - suspend the console subsystem
 949  *
 950  * This disables printk() while we go into suspend states
 951  */
 952 void suspend_console(void)
 953 {
 954         if (!console_suspend_enabled)
 955                 return;
 956         printk("Suspending console(s)\n");
 957         acquire_console_sem();
 958         console_suspended = 1;
 959 }
 960
 961 void resume_console(void)
 962 {
 963         if (!console_suspend_enabled)
 964                 return;
 965         console_suspended = 0;
 966         release_console_sem();
 967 }
 968
 969 /**
 970  * acquire_console_sem - lock the console system for exclusive use.
 971  *
 972  * Acquires a semaphore which guarantees that the caller has
 973  * exclusive access to the console system and the console_drivers list.
 974  *
 975  * Can sleep, returns nothing.
 976  */
 977 void acquire_console_sem(void)
 978 {
 979         BUG_ON(in_interrupt());
 980         if (console_suspended) {
 981                 down(&secondary_console_sem);
 982                 return;
 983         }
 984         down(&console_sem);
 985         console_locked = 1;
 986         console_may_schedule = 1;
 987 }
 988 EXPORT_SYMBOL(acquire_console_sem);
 989
 990 int try_acquire_console_sem(void)
 991 {
 992         if (down_trylock(&console_sem))
 993                 return -1;
 994         console_locked = 1;
 995         console_may_schedule = 0;
 996         return 0;
 997 }
 998 EXPORT_SYMBOL(try_acquire_console_sem);
 999
1000 int is_console_locked(void)
1001 {
1002         return console_locked;
1003 }
1004
1005 void wake_up_klogd(void)
1006 {
1007         if (!oops_in_progress && waitqueue_active(&log_wait))
1008                 wake_up_interruptible(&log_wait);
1009 }
1010
1011 /**
1012  * release_console_sem - unlock the console system
1013  *
1014  * Releases the semaphore which the caller holds on the console system
1015  * and the console driver list.
1016  *
1017  * While the semaphore was held, console output may have been buffered
1018  * by printk().  If this is the case, release_console_sem() emits
1019  * the output prior to releasing the semaphore.
1020  *
1021  * If there is output waiting for klogd, we wake it up.
1022  *
1023  * release_console_sem() may be called from any context.
1024  */
1025 void release_console_sem(void)
1026 {
1027         unsigned long flags;
1028         unsigned _con_start, _log_end;
1029         unsigned wake_klogd = 0;
1030
1031         if (console_suspended) {
1032                 up(&secondary_console_sem);
1033                 return;
1034         }
1035
1036         console_may_schedule = 0;
1037
1038         for ( ; ; ) {
1039                 spin_lock_irqsave(&logbuf_lock, flags);
1040                 wake_klogd |= log_start - log_end;
1041                 if (con_start == log_end)
1042                         break;                  /* Nothing to print */
1043                 _con_start = con_start;
1044                 _log_end = log_end;
1045                 con_start = log_end;            /* Flush */
1046                 spin_unlock(&logbuf_lock);
1047                 call_console_drivers(_con_start, _log_end);
1048                 local_irq_restore(flags);
1049         }
1050         console_locked = 0;
1051         up(&console_sem);
1052         spin_unlock_irqrestore(&logbuf_lock, flags);
1053         if (wake_klogd)
1054                 wake_up_klogd();
1055 }
1056 EXPORT_SYMBOL(release_console_sem);
1057
1058 /**
1059  * console_conditional_schedule - yield the CPU if required
1060  *
1061  * If the console code is currently allowed to sleep, and
1062  * if this CPU should yield the CPU to another task, do
1063  * so here.
1064  *
1065  * Must be called within acquire_console_sem().
1066  */
1067 void __sched console_conditional_schedule(void)
1068 {
1069         if (console_may_schedule)
1070                 cond_resched();
1071 }
1072 EXPORT_SYMBOL(console_conditional_schedule);
1073
1074 void console_print(const char *s)
1075 {
1076         printk(KERN_EMERG "%s", s);
1077 }
1078 EXPORT_SYMBOL(console_print);
1079
1080 void console_unblank(void)
1081 {
1082         struct console *c;
1083
1084         /*
1085          * console_unblank can no longer be called in interrupt context unless
1086          * oops_in_progress is set to 1..
1087          */
1088         if (oops_in_progress) {
1089                 if (down_trylock(&console_sem) != 0)
1090                         return;
1091         } else
1092                 acquire_console_sem();
1093
1094         console_locked = 1;
1095         console_may_schedule = 0;
1096         for (c = console_drivers; c != NULL; c = c->next)
1097                 if ((c->flags & CON_ENABLED) && c->unblank)
1098                         c->unblank();
1099         release_console_sem();
1100 }
1101
1102 /*
1103  * Return the console tty driver structure and its associated index
1104  */
1105 struct tty_driver *console_device(int *index)
1106 {
1107         struct console *c;
1108         struct tty_driver *driver = NULL;
1109
1110         acquire_console_sem();
1111         for (c = console_drivers; c != NULL; c = c->next) {
1112                 if (!c->device)
1113                         continue;
1114                 driver = c->device(c, index);
1115                 if (driver)
1116                         break;
1117         }
1118         release_console_sem();
1119         return driver;
1120 }
1121
1122 /*
1123  * Prevent further output on the passed console device so that (for example)
1124  * serial drivers can disable console output before suspending a port, and can
1125  * re-enable output afterwards.
1126  */
1127 void console_stop(struct console *console)
1128 {
1129         acquire_console_sem();
1130         console->flags &= ~CON_ENABLED;
1131         release_console_sem();
1132 }
1133 EXPORT_SYMBOL(console_stop);
1134
1135 void console_start(struct console *console)
1136 {
1137         acquire_console_sem();
1138         console->flags |= CON_ENABLED;
1139         release_console_sem();
1140 }
1141 EXPORT_SYMBOL(console_start);
1142
1143 /*
1144  * The console driver calls this routine during kernel initialization
1145  * to register the console printing procedure with printk() and to
1146  * print any messages that were printed by the kernel before the
1147  * console driver was initialized.
1148  */
1149 void register_console(struct console *console)
1150 {
1151         int i;
1152         unsigned long flags;
1153         struct console *bootconsole = NULL;
1154
1155         if (console_drivers) {
1156                 if (console->flags & CON_BOOT)
1157                         return;
1158                 if (console_drivers->flags & CON_BOOT)
1159                         bootconsole = console_drivers;
1160         }
1161
1162         if (preferred_console < 0 || bootconsole || !console_drivers)
1163                 preferred_console = selected_console;
1164
1165         if (console->early_setup)
1166                 console->early_setup();
1167
1168         /*
1169          *      See if we want to use this console driver. If we
1170          *      didn't select a console we take the first one
1171          *      that registers here.
1172          */
1173         if (preferred_console < 0) {
1174                 if (console->index < 0)
1175                         console->index = 0;
1176                 if (console->setup == NULL ||
1177                     console->setup(console, NULL) == 0) {
1178                         console->flags |= CON_ENABLED | CON_CONSDEV;
1179                         preferred_console = 0;
1180                 }
1181         }
1182
1183         /*
1184          *      See if this console matches one we selected on
1185          *      the command line.
1186          */
1187         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1188                         i++) {
1189                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1190                         continue;
1191                 if (console->index >= 0 &&
1192                     console->index != console_cmdline[i].index)
1193                         continue;
1194                 if (console->index < 0)
1195                         console->index = console_cmdline[i].index;
1196 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1197                 if (console_cmdline[i].brl_options) {
1198                         console->flags |= CON_BRL;
1199                         braille_register_console(console,
1200                                         console_cmdline[i].index,
1201                                         console_cmdline[i].options,
1202                                         console_cmdline[i].brl_options);
1203                         return;
1204                 }
1205 #endif
1206                 if (console->setup &&
1207                     console->setup(console, console_cmdline[i].options) != 0)
1208                         break;
1209                 console->flags |= CON_ENABLED;
1210                 console->index = console_cmdline[i].index;
1211                 if (i == selected_console) {
1212                         console->flags |= CON_CONSDEV;
1213                         preferred_console = selected_console;
1214                 }
1215                 break;
1216         }
1217
1218         if (!(console->flags & CON_ENABLED))
1219                 return;
1220
1221         if (bootconsole && (console->flags & CON_CONSDEV)) {
1222                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1223                        bootconsole->name, bootconsole->index,
1224                        console->name, console->index);
1225                 unregister_console(bootconsole);
1226                 console->flags &= ~CON_PRINTBUFFER;
1227         } else {
1228                 printk(KERN_INFO "console [%s%d] enabled\n",
1229                        console->name, console->index);
1230         }
1231
1232         /*
1233          *      Put this console in the list - keep the
1234          *      preferred driver at the head of the list.
1235          */
1236         acquire_console_sem();
1237         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1238                 console->next = console_drivers;
1239                 console_drivers = console;
1240                 if (console->next)
1241                         console->next->flags &= ~CON_CONSDEV;
1242         } else {
1243                 console->next = console_drivers->next;
1244                 console_drivers->next = console;
1245         }
1246         if (console->flags & CON_PRINTBUFFER) {
1247                 /*
1248                  * release_console_sem() will print out the buffered messages
1249                  * for us.
1250                  */
1251                 spin_lock_irqsave(&logbuf_lock, flags);
1252                 con_start = log_start;
1253                 spin_unlock_irqrestore(&logbuf_lock, flags);
1254         }
1255         release_console_sem();
1256 }
1257 EXPORT_SYMBOL(register_console);
1258
1259 int unregister_console(struct console *console)
1260 {
1261         struct console *a, *b;
1262         int res = 1;
1263
1264 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1265         if (console->flags & CON_BRL)
1266                 return braille_unregister_console(console);
1267 #endif
1268
1269         acquire_console_sem();
1270         if (console_drivers == console) {
1271                 console_drivers=console->next;
1272                 res = 0;
1273         } else if (console_drivers) {
1274                 for (a=console_drivers->next, b=console_drivers ;
1275                      a; b=a, a=b->next) {
1276                         if (a == console) {
1277                                 b->next = a->next;
1278                                 res = 0;
1279                                 break;
1280                         }
1281                 }
1282         }
1283
1284         /*
1285          * If this isn't the last console and it has CON_CONSDEV set, we
1286          * need to set it on the next preferred console.
1287          */
1288         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1289                 console_drivers->flags |= CON_CONSDEV;
1290
1291         release_console_sem();
1292         return res;
1293 }
1294 EXPORT_SYMBOL(unregister_console);
1295
1296 static int __init disable_boot_consoles(void)
1297 {
1298         if (console_drivers != NULL) {
1299                 if (console_drivers->flags & CON_BOOT) {
1300                         printk(KERN_INFO "turn off boot console %s%d\n",
1301                                 console_drivers->name, console_drivers->index);
1302                         return unregister_console(console_drivers);
1303                 }
1304         }
1305         return 0;
1306 }
1307 late_initcall(disable_boot_consoles);
1308
1309 /**
1310  * tty_write_message - write a message to a certain tty, not just the console.
1311  * @tty: the destination tty_struct
1312  * @msg: the message to write
1313  *
1314  * This is used for messages that need to be redirected to a specific tty.
1315  * We don't put it into the syslog queue right now maybe in the future if
1316  * really needed.
1317  */
1318 void tty_write_message(struct tty_struct *tty, char *msg)
1319 {
1320         if (tty && tty->ops->write)
1321                 tty->ops->write(tty, msg, strlen(msg));
1322         return;
1323 }
1324
1325 #if defined CONFIG_PRINTK
1326 /*
1327  * printk rate limiting, lifted from the networking subsystem.
1328  *
1329  * This enforces a rate limit: not more than one kernel message
1330  * every printk_ratelimit_jiffies to make a denial-of-service
1331  * attack impossible.
1332  */
1333 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1334 {
1335         return __ratelimit(ratelimit_jiffies, ratelimit_burst);
1336 }
1337 EXPORT_SYMBOL(__printk_ratelimit);
1338
1339 /* minimum time in jiffies between messages */
1340 int printk_ratelimit_jiffies = 5 * HZ;
1341
1342 /* number of messages we send before ratelimiting */
1343 int printk_ratelimit_burst = 10;
1344
1345 int printk_ratelimit(void)
1346 {
1347         return __printk_ratelimit(printk_ratelimit_jiffies,
1348                                 printk_ratelimit_burst);
1349 }
1350 EXPORT_SYMBOL(printk_ratelimit);
1351
1352 /**
1353  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1354  * @caller_jiffies: pointer to caller's state
1355  * @interval_msecs: minimum interval between prints
1356  *
1357  * printk_timed_ratelimit() returns true if more than @interval_msecs
1358  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1359  * returned true.
1360  */
1361 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1362                         unsigned int interval_msecs)
1363 {
1364         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1365                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1366                 return true;
1367         }
1368         return false;
1369 }
1370 EXPORT_SYMBOL(printk_timed_ratelimit);
1371 #endif