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