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
  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 asmlinkage __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 EXPORT_SYMBOL_GPL(console_drivers);
  79
  80 /*
  81  * This is used for debugging the mess that is the VT code by
  82  * keeping track if we have the console semaphore held. It's
  83  * definitely not the perfect debug tool (we don't know if _WE_
  84  * hold it are racing, but it helps tracking those weird code
  85  * path in the console code where we end up in places I want
  86  * locked without the console sempahore held
  87  */
  88 static int console_locked, console_suspended;
  89
  90 /*
  91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  92  * It is also used in interesting ways to provide interlocking in
  93  * release_console_sem().
  94  */
  95 static DEFINE_SPINLOCK(logbuf_lock);
  96
  97 #define LOG_BUF_MASK (log_buf_len-1)
  98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  99
 100 /*
 101  * The indices into log_buf are not constrained to log_buf_len - they
 102  * must be masked before subscripting
 103  */
 104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 107
 108 /*
 109  *      Array of consoles built from command line options (console=)
 110  */
 111 struct console_cmdline
 112 {
 113         char    name[8];                        /* Name of the driver       */
 114         int     index;                          /* Minor dev. to use        */
 115         char    *options;                       /* Options for the driver   */
 116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 117         char    *brl_options;                   /* Options for braille driver */
 118 #endif
 119 };
 120
 121 #define MAX_CMDLINECONSOLES 8
 122
 123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 124 static int selected_console = -1;
 125 static int preferred_console = -1;
 126 int console_set_on_cmdline;
 127 EXPORT_SYMBOL(console_set_on_cmdline);
 128
 129 /* Flag: console code may call schedule() */
 130 static int console_may_schedule;
 131
 132 #ifdef CONFIG_PRINTK
 133
 134 static char __log_buf[__LOG_BUF_LEN];
 135 static char *log_buf = __log_buf;
 136 static int log_buf_len = __LOG_BUF_LEN;
 137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 138
 139 static int __init log_buf_len_setup(char *str)
 140 {
 141         unsigned size = memparse(str, &str);
 142         unsigned long flags;
 143
 144         if (size)
 145                 size = roundup_pow_of_two(size);
 146         if (size > log_buf_len) {
 147                 unsigned start, dest_idx, offset;
 148                 char *new_log_buf;
 149
 150                 new_log_buf = alloc_bootmem(size);
 151                 if (!new_log_buf) {
 152                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 153                         goto out;
 154                 }
 155
 156                 spin_lock_irqsave(&logbuf_lock, flags);
 157                 log_buf_len = size;
 158                 log_buf = new_log_buf;
 159
 160                 offset = start = min(con_start, log_start);
 161                 dest_idx = 0;
 162                 while (start != log_end) {
 163                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 164                         start++;
 165                         dest_idx++;
 166                 }
 167                 log_start -= offset;
 168                 con_start -= offset;
 169                 log_end -= offset;
 170                 spin_unlock_irqrestore(&logbuf_lock, flags);
 171
 172                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 173         }
 174 out:
 175         return 1;
 176 }
 177
 178 __setup("log_buf_len=", log_buf_len_setup);
 179
 180 #ifdef CONFIG_BOOT_PRINTK_DELAY
 181
 182 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 183 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 184
 185 static int __init boot_delay_setup(char *str)
 186 {
 187         unsigned long lpj;
 188         unsigned long long loops_per_msec;
 189
 190         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 191         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 192
 193         get_option(&str, &boot_delay);
 194         if (boot_delay > 10 * 1000)
 195                 boot_delay = 0;
 196
 197         printk_delay_msec = loops_per_msec;
 198         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 199                 "HZ: %d, printk_delay_msec: %llu\n",
 200                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 201         return 1;
 202 }
 203 __setup("boot_delay=", boot_delay_setup);
 204
 205 static void boot_delay_msec(void)
 206 {
 207         unsigned long long k;
 208         unsigned long timeout;
 209
 210         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 211                 return;
 212
 213         k = (unsigned long long)printk_delay_msec * boot_delay;
 214
 215         timeout = jiffies + msecs_to_jiffies(boot_delay);
 216         while (k) {
 217                 k--;
 218                 cpu_relax();
 219                 /*
 220                  * use (volatile) jiffies to prevent
 221                  * compiler reduction; loop termination via jiffies
 222                  * is secondary and may or may not happen.
 223                  */
 224                 if (time_after(jiffies, timeout))
 225                         break;
 226                 touch_nmi_watchdog();
 227         }
 228 }
 229 #else
 230 static inline void boot_delay_msec(void)
 231 {
 232 }
 233 #endif
 234
 235 /*
 236  * Commands to do_syslog:
 237  *
 238  *      0 -- Close the log.  Currently a NOP.
 239  *      1 -- Open the log. Currently a NOP.
 240  *      2 -- Read from the log.
 241  *      3 -- Read all messages remaining in the ring buffer.
 242  *      4 -- Read and clear all messages remaining in the ring buffer
 243  *      5 -- Clear ring buffer.
 244  *      6 -- Disable printk's to console
 245  *      7 -- Enable printk's to console
 246  *      8 -- Set level of messages printed to console
 247  *      9 -- Return number of unread characters in the log buffer
 248  *     10 -- Return size of the log buffer
 249  */
 250 int do_syslog(int type, char __user *buf, int len)
 251 {
 252         unsigned i, j, limit, count;
 253         int do_clear = 0;
 254         char c;
 255         int error = 0;
 256
 257         error = security_syslog(type);
 258         if (error)
 259                 return error;
 260
 261         switch (type) {
 262         case 0:         /* Close log */
 263                 break;
 264         case 1:         /* Open log */
 265                 break;
 266         case 2:         /* Read from log */
 267                 error = -EINVAL;
 268                 if (!buf || len < 0)
 269                         goto out;
 270                 error = 0;
 271                 if (!len)
 272                         goto out;
 273                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 274                         error = -EFAULT;
 275                         goto out;
 276                 }
 277                 error = wait_event_interruptible(log_wait,
 278                                                         (log_start - log_end));
 279                 if (error)
 280                         goto out;
 281                 i = 0;
 282                 spin_lock_irq(&logbuf_lock);
 283                 while (!error && (log_start != log_end) && i < len) {
 284                         c = LOG_BUF(log_start);
 285                         log_start++;
 286                         spin_unlock_irq(&logbuf_lock);
 287                         error = __put_user(c,buf);
 288                         buf++;
 289                         i++;
 290                         cond_resched();
 291                         spin_lock_irq(&logbuf_lock);
 292                 }
 293                 spin_unlock_irq(&logbuf_lock);
 294                 if (!error)
 295                         error = i;
 296                 break;
 297         case 4:         /* Read/clear last kernel messages */
 298                 do_clear = 1;
 299                 /* FALL THRU */
 300         case 3:         /* Read last kernel messages */
 301                 error = -EINVAL;
 302                 if (!buf || len < 0)
 303                         goto out;
 304                 error = 0;
 305                 if (!len)
 306                         goto out;
 307                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 308                         error = -EFAULT;
 309                         goto out;
 310                 }
 311                 count = len;
 312                 if (count > log_buf_len)
 313                         count = log_buf_len;
 314                 spin_lock_irq(&logbuf_lock);
 315                 if (count > logged_chars)
 316                         count = logged_chars;
 317                 if (do_clear)
 318                         logged_chars = 0;
 319                 limit = log_end;
 320                 /*
 321                  * __put_user() could sleep, and while we sleep
 322                  * printk() could overwrite the messages
 323                  * we try to copy to user space. Therefore
 324                  * the messages are copied in reverse. <manfreds>
 325                  */
 326                 for (i = 0; i < count && !error; i++) {
 327                         j = limit-1-i;
 328                         if (j + log_buf_len < log_end)
 329                                 break;
 330                         c = LOG_BUF(j);
 331                         spin_unlock_irq(&logbuf_lock);
 332                         error = __put_user(c,&buf[count-1-i]);
 333                         cond_resched();
 334                         spin_lock_irq(&logbuf_lock);
 335                 }
 336                 spin_unlock_irq(&logbuf_lock);
 337                 if (error)
 338                         break;
 339                 error = i;
 340                 if (i != count) {
 341                         int offset = count-error;
 342                         /* buffer overflow during copy, correct user buffer. */
 343                         for (i = 0; i < error; i++) {
 344                                 if (__get_user(c,&buf[i+offset]) ||
 345                                     __put_user(c,&buf[i])) {
 346                                         error = -EFAULT;
 347                                         break;
 348                                 }
 349                                 cond_resched();
 350                         }
 351                 }
 352                 break;
 353         case 5:         /* Clear ring buffer */
 354                 logged_chars = 0;
 355                 break;
 356         case 6:         /* Disable logging to console */
 357                 console_loglevel = minimum_console_loglevel;
 358                 break;
 359         case 7:         /* Enable logging to console */
 360                 console_loglevel = default_console_loglevel;
 361                 break;
 362         case 8:         /* Set level of messages printed to console */
 363                 error = -EINVAL;
 364                 if (len < 1 || len > 8)
 365                         goto out;
 366                 if (len < minimum_console_loglevel)
 367                         len = minimum_console_loglevel;
 368                 console_loglevel = len;
 369                 error = 0;
 370                 break;
 371         case 9:         /* Number of chars in the log buffer */
 372                 error = log_end - log_start;
 373                 break;
 374         case 10:        /* Size of the log buffer */
 375                 error = log_buf_len;
 376                 break;
 377         default:
 378                 error = -EINVAL;
 379                 break;
 380         }
 381 out:
 382         return error;
 383 }
 384
 385 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 386 {
 387         return do_syslog(type, buf, len);
 388 }
 389
 390 /*
 391  * Call the console drivers on a range of log_buf
 392  */
 393 static void __call_console_drivers(unsigned start, unsigned end)
 394 {
 395         struct console *con;
 396
 397         for (con = console_drivers; con; con = con->next) {
 398                 if ((con->flags & CON_ENABLED) && con->write &&
 399                                 (cpu_online(smp_processor_id()) ||
 400                                 (con->flags & CON_ANYTIME)))
 401                         con->write(con, &LOG_BUF(start), end - start);
 402         }
 403 }
 404
 405 static int __read_mostly ignore_loglevel;
 406
 407 static int __init ignore_loglevel_setup(char *str)
 408 {
 409         ignore_loglevel = 1;
 410         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 411
 412         return 0;
 413 }
 414
 415 early_param("ignore_loglevel", ignore_loglevel_setup);
 416
 417 /*
 418  * Write out chars from start to end - 1 inclusive
 419  */
 420 static void _call_console_drivers(unsigned start,
 421                                 unsigned end, int msg_log_level)
 422 {
 423         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 424                         console_drivers && start != end) {
 425                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 426                         /* wrapped write */
 427                         __call_console_drivers(start & LOG_BUF_MASK,
 428                                                 log_buf_len);
 429                         __call_console_drivers(0, end & LOG_BUF_MASK);
 430                 } else {
 431                         __call_console_drivers(start, end);
 432                 }
 433         }
 434 }
 435
 436 /*
 437  * Call the console drivers, asking them to write out
 438  * log_buf[start] to log_buf[end - 1].
 439  * The console_sem must be held.
 440  */
 441 static void call_console_drivers(unsigned start, unsigned end)
 442 {
 443         unsigned cur_index, start_print;
 444         static int msg_level = -1;
 445
 446         BUG_ON(((int)(start - end)) > 0);
 447
 448         cur_index = start;
 449         start_print = start;
 450         while (cur_index != end) {
 451                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 452                                 LOG_BUF(cur_index + 0) == '<' &&
 453                                 LOG_BUF(cur_index + 1) >= '0' &&
 454                                 LOG_BUF(cur_index + 1) <= '7' &&
 455                                 LOG_BUF(cur_index + 2) == '>') {
 456                         msg_level = LOG_BUF(cur_index + 1) - '0';
 457                         cur_index += 3;
 458                         start_print = cur_index;
 459                 }
 460                 while (cur_index != end) {
 461                         char c = LOG_BUF(cur_index);
 462
 463                         cur_index++;
 464                         if (c == '\n') {
 465                                 if (msg_level < 0) {
 466                                         /*
 467                                          * printk() has already given us loglevel tags in
 468                                          * the buffer.  This code is here in case the
 469                                          * log buffer has wrapped right round and scribbled
 470                                          * on those tags
 471                                          */
 472                                         msg_level = default_message_loglevel;
 473                                 }
 474                                 _call_console_drivers(start_print, cur_index, msg_level);
 475                                 msg_level = -1;
 476                                 start_print = cur_index;
 477                                 break;
 478                         }
 479                 }
 480         }
 481         _call_console_drivers(start_print, end, msg_level);
 482 }
 483
 484 static void emit_log_char(char c)
 485 {
 486         LOG_BUF(log_end) = c;
 487         log_end++;
 488         if (log_end - log_start > log_buf_len)
 489                 log_start = log_end - log_buf_len;
 490         if (log_end - con_start > log_buf_len)
 491                 con_start = log_end - log_buf_len;
 492         if (logged_chars < log_buf_len)
 493                 logged_chars++;
 494 }
 495
 496 /*
 497  * Zap console related locks when oopsing. Only zap at most once
 498  * every 10 seconds, to leave time for slow consoles to print a
 499  * full oops.
 500  */
 501 static void zap_locks(void)
 502 {
 503         static unsigned long oops_timestamp;
 504
 505         if (time_after_eq(jiffies, oops_timestamp) &&
 506                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 507                 return;
 508
 509         oops_timestamp = jiffies;
 510
 511         /* If a crash is occurring, make sure we can't deadlock */
 512         spin_lock_init(&logbuf_lock);
 513         /* And make sure that we print immediately */
 514         init_MUTEX(&console_sem);
 515 }
 516
 517 #if defined(CONFIG_PRINTK_TIME)
 518 static int printk_time = 1;
 519 #else
 520 static int printk_time = 0;
 521 #endif
 522 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 523
 524 /* Check if we have any console registered that can be called early in boot. */
 525 static int have_callable_console(void)
 526 {
 527         struct console *con;
 528
 529         for (con = console_drivers; con; con = con->next)
 530                 if (con->flags & CON_ANYTIME)
 531                         return 1;
 532
 533         return 0;
 534 }
 535
 536 /**
 537  * printk - print a kernel message
 538  * @fmt: format string
 539  *
 540  * This is printk().  It can be called from any context.  We want it to work.
 541  *
 542  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 543  * call the console drivers.  If we fail to get the semaphore we place the output
 544  * into the log buffer and return.  The current holder of the console_sem will
 545  * notice the new output in release_console_sem() and will send it to the
 546  * consoles before releasing the semaphore.
 547  *
 548  * One effect of this deferred printing is that code which calls printk() and
 549  * then changes console_loglevel may break. This is because console_loglevel
 550  * is inspected when the actual printing occurs.
 551  *
 552  * See also:
 553  * printf(3)
 554  *
 555  * See the vsnprintf() documentation for format string extensions over C99.
 556  */
 557
 558 asmlinkage int printk(const char *fmt, ...)
 559 {
 560         va_list args;
 561         int r;
 562
 563         va_start(args, fmt);
 564         r = vprintk(fmt, args);
 565         va_end(args);
 566
 567         return r;
 568 }
 569
 570 /* cpu currently holding logbuf_lock */
 571 static volatile unsigned int printk_cpu = UINT_MAX;
 572
 573 /*
 574  * Can we actually use the console at this time on this cpu?
 575  *
 576  * Console drivers may assume that per-cpu resources have
 577  * been allocated. So unless they're explicitly marked as
 578  * being able to cope (CON_ANYTIME) don't call them until
 579  * this CPU is officially up.
 580  */
 581 static inline int can_use_console(unsigned int cpu)
 582 {
 583         return cpu_online(cpu) || have_callable_console();
 584 }
 585
 586 /*
 587  * Try to get console ownership to actually show the kernel
 588  * messages from a 'printk'. Return true (and with the
 589  * console_semaphore held, and 'console_locked' set) if it
 590  * is successful, false otherwise.
 591  *
 592  * This gets called with the 'logbuf_lock' spinlock held and
 593  * interrupts disabled. It should return with 'lockbuf_lock'
 594  * released but interrupts still disabled.
 595  */
 596 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 597 {
 598         int retval = 0;
 599
 600         if (!try_acquire_console_sem()) {
 601                 retval = 1;
 602
 603                 /*
 604                  * If we can't use the console, we need to release
 605                  * the console semaphore by hand to avoid flushing
 606                  * the buffer. We need to hold the console semaphore
 607                  * in order to do this test safely.
 608                  */
 609                 if (!can_use_console(cpu)) {
 610                         console_locked = 0;
 611                         up(&console_sem);
 612                         retval = 0;
 613                 }
 614         }
 615         printk_cpu = UINT_MAX;
 616         spin_unlock(&logbuf_lock);
 617         return retval;
 618 }
 619 static const char recursion_bug_msg [] =
 620                 KERN_CRIT "BUG: recent printk recursion!\n";
 621 static int recursion_bug;
 622 static int new_text_line = 1;
 623 static char printk_buf[1024];
 624
 625 asmlinkage int vprintk(const char *fmt, va_list args)
 626 {
 627         int printed_len = 0;
 628         int current_log_level = default_message_loglevel;
 629         unsigned long flags;
 630         int this_cpu;
 631         char *p;
 632
 633         boot_delay_msec();
 634
 635         preempt_disable();
 636         /* This stops the holder of console_sem just where we want him */
 637         raw_local_irq_save(flags);
 638         this_cpu = smp_processor_id();
 639
 640         /*
 641          * Ouch, printk recursed into itself!
 642          */
 643         if (unlikely(printk_cpu == this_cpu)) {
 644                 /*
 645                  * If a crash is occurring during printk() on this CPU,
 646                  * then try to get the crash message out but make sure
 647                  * we can't deadlock. Otherwise just return to avoid the
 648                  * recursion and return - but flag the recursion so that
 649                  * it can be printed at the next appropriate moment:
 650                  */
 651                 if (!oops_in_progress) {
 652                         recursion_bug = 1;
 653                         goto out_restore_irqs;
 654                 }
 655                 zap_locks();
 656         }
 657
 658         lockdep_off();
 659         spin_lock(&logbuf_lock);
 660         printk_cpu = this_cpu;
 661
 662         if (recursion_bug) {
 663                 recursion_bug = 0;
 664                 strcpy(printk_buf, recursion_bug_msg);
 665                 printed_len = strlen(recursion_bug_msg);
 666         }
 667         /* Emit the output into the temporary buffer */
 668         printed_len += vscnprintf(printk_buf + printed_len,
 669                                   sizeof(printk_buf) - printed_len, fmt, args);
 670
 671
 672         /*
 673          * Copy the output into log_buf.  If the caller didn't provide
 674          * appropriate log level tags, we insert them here
 675          */
 676         for (p = printk_buf; *p; p++) {
 677                 if (new_text_line) {
 678                         /* If a token, set current_log_level and skip over */
 679                         if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
 680                             p[2] == '>') {
 681                                 current_log_level = p[1] - '0';
 682                                 p += 3;
 683                                 printed_len -= 3;
 684                         }
 685
 686                         /* Always output the token */
 687                         emit_log_char('<');
 688                         emit_log_char(current_log_level + '0');
 689                         emit_log_char('>');
 690                         printed_len += 3;
 691                         new_text_line = 0;
 692
 693                         if (printk_time) {
 694                                 /* Follow the token with the time */
 695                                 char tbuf[50], *tp;
 696                                 unsigned tlen;
 697                                 unsigned long long t;
 698                                 unsigned long nanosec_rem;
 699
 700                                 t = cpu_clock(printk_cpu);
 701                                 nanosec_rem = do_div(t, 1000000000);
 702                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 703                                                 (unsigned long) t,
 704                                                 nanosec_rem / 1000);
 705
 706                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 707                                         emit_log_char(*tp);
 708                                 printed_len += tlen;
 709                         }
 710
 711                         if (!*p)
 712                                 break;
 713                 }
 714
 715                 emit_log_char(*p);
 716                 if (*p == '\n')
 717                         new_text_line = 1;
 718         }
 719
 720         /*
 721          * Try to acquire and then immediately release the
 722          * console semaphore. The release will do all the
 723          * actual magic (print out buffers, wake up klogd,
 724          * etc).
 725          *
 726          * The acquire_console_semaphore_for_printk() function
 727          * will release 'logbuf_lock' regardless of whether it
 728          * actually gets the semaphore or not.
 729          */
 730         if (acquire_console_semaphore_for_printk(this_cpu))
 731                 release_console_sem();
 732
 733         lockdep_on();
 734 out_restore_irqs:
 735         raw_local_irq_restore(flags);
 736
 737         preempt_enable();
 738         return printed_len;
 739 }
 740 EXPORT_SYMBOL(printk);
 741 EXPORT_SYMBOL(vprintk);
 742
 743 #else
 744
 745 static void call_console_drivers(unsigned start, unsigned end)
 746 {
 747 }
 748
 749 #endif
 750
 751 static int __add_preferred_console(char *name, int idx, char *options,
 752                                    char *brl_options)
 753 {
 754         struct console_cmdline *c;
 755         int i;
 756
 757         /*
 758          *      See if this tty is not yet registered, and
 759          *      if we have a slot free.
 760          */
 761         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 762                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 763                           console_cmdline[i].index == idx) {
 764                                 if (!brl_options)
 765                                         selected_console = i;
 766                                 return 0;
 767                 }
 768         if (i == MAX_CMDLINECONSOLES)
 769                 return -E2BIG;
 770         if (!brl_options)
 771                 selected_console = i;
 772         c = &console_cmdline[i];
 773         strlcpy(c->name, name, sizeof(c->name));
 774         c->options = options;
 775 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 776         c->brl_options = brl_options;
 777 #endif
 778         c->index = idx;
 779         return 0;
 780 }
 781 /*
 782  * Set up a list of consoles.  Called from init/main.c
 783  */
 784 static int __init console_setup(char *str)
 785 {
 786         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 787         char *s, *options, *brl_options = NULL;
 788         int idx;
 789
 790 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 791         if (!memcmp(str, "brl,", 4)) {
 792                 brl_options = "";
 793                 str += 4;
 794         } else if (!memcmp(str, "brl=", 4)) {
 795                 brl_options = str + 4;
 796                 str = strchr(brl_options, ',');
 797                 if (!str) {
 798                         printk(KERN_ERR "need port name after brl=\n");
 799                         return 1;
 800                 }
 801                 *(str++) = 0;
 802         }
 803 #endif
 804
 805         /*
 806          * Decode str into name, index, options.
 807          */
 808         if (str[0] >= '0' && str[0] <= '9') {
 809                 strcpy(buf, "ttyS");
 810                 strncpy(buf + 4, str, sizeof(buf) - 5);
 811         } else {
 812                 strncpy(buf, str, sizeof(buf) - 1);
 813         }
 814         buf[sizeof(buf) - 1] = 0;
 815         if ((options = strchr(str, ',')) != NULL)
 816                 *(options++) = 0;
 817 #ifdef __sparc__
 818         if (!strcmp(str, "ttya"))
 819                 strcpy(buf, "ttyS0");
 820         if (!strcmp(str, "ttyb"))
 821                 strcpy(buf, "ttyS1");
 822 #endif
 823         for (s = buf; *s; s++)
 824                 if ((*s >= '0' && *s <= '9') || *s == ',')
 825                         break;
 826         idx = simple_strtoul(s, NULL, 10);
 827         *s = 0;
 828
 829         __add_preferred_console(buf, idx, options, brl_options);
 830         console_set_on_cmdline = 1;
 831         return 1;
 832 }
 833 __setup("console=", console_setup);
 834
 835 /**
 836  * add_preferred_console - add a device to the list of preferred consoles.
 837  * @name: device name
 838  * @idx: device index
 839  * @options: options for this console
 840  *
 841  * The last preferred console added will be used for kernel messages
 842  * and stdin/out/err for init.  Normally this is used by console_setup
 843  * above to handle user-supplied console arguments; however it can also
 844  * be used by arch-specific code either to override the user or more
 845  * commonly to provide a default console (ie from PROM variables) when
 846  * the user has not supplied one.
 847  */
 848 int add_preferred_console(char *name, int idx, char *options)
 849 {
 850         return __add_preferred_console(name, idx, options, NULL);
 851 }
 852
 853 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 854 {
 855         struct console_cmdline *c;
 856         int i;
 857
 858         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 859                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 860                           console_cmdline[i].index == idx) {
 861                                 c = &console_cmdline[i];
 862                                 strlcpy(c->name, name_new, sizeof(c->name));
 863                                 c->name[sizeof(c->name) - 1] = 0;
 864                                 c->options = options;
 865                                 c->index = idx_new;
 866                                 return i;
 867                 }
 868         /* not found */
 869         return -1;
 870 }
 871
 872 int console_suspend_enabled = 1;
 873 EXPORT_SYMBOL(console_suspend_enabled);
 874
 875 static int __init console_suspend_disable(char *str)
 876 {
 877         console_suspend_enabled = 0;
 878         return 1;
 879 }
 880 __setup("no_console_suspend", console_suspend_disable);
 881
 882 /**
 883  * suspend_console - suspend the console subsystem
 884  *
 885  * This disables printk() while we go into suspend states
 886  */
 887 void suspend_console(void)
 888 {
 889         if (!console_suspend_enabled)
 890                 return;
 891         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 892         acquire_console_sem();
 893         console_suspended = 1;
 894 }
 895
 896 void resume_console(void)
 897 {
 898         if (!console_suspend_enabled)
 899                 return;
 900         console_suspended = 0;
 901         release_console_sem();
 902 }
 903
 904 /**
 905  * acquire_console_sem - lock the console system for exclusive use.
 906  *
 907  * Acquires a semaphore which guarantees that the caller has
 908  * exclusive access to the console system and the console_drivers list.
 909  *
 910  * Can sleep, returns nothing.
 911  */
 912 void acquire_console_sem(void)
 913 {
 914         BUG_ON(in_interrupt());
 915         if (console_suspended) {
 916                 down(&secondary_console_sem);
 917                 return;
 918         }
 919         down(&console_sem);
 920         console_locked = 1;
 921         console_may_schedule = 1;
 922 }
 923 EXPORT_SYMBOL(acquire_console_sem);
 924
 925 int try_acquire_console_sem(void)
 926 {
 927         if (down_trylock(&console_sem))
 928                 return -1;
 929         console_locked = 1;
 930         console_may_schedule = 0;
 931         return 0;
 932 }
 933 EXPORT_SYMBOL(try_acquire_console_sem);
 934
 935 int is_console_locked(void)
 936 {
 937         return console_locked;
 938 }
 939
 940 static DEFINE_PER_CPU(int, printk_pending);
 941
 942 void printk_tick(void)
 943 {
 944         if (__get_cpu_var(printk_pending)) {
 945                 __get_cpu_var(printk_pending) = 0;
 946                 wake_up_interruptible(&log_wait);
 947         }
 948 }
 949
 950 int printk_needs_cpu(int cpu)
 951 {
 952         return per_cpu(printk_pending, cpu);
 953 }
 954
 955 void wake_up_klogd(void)
 956 {
 957         if (waitqueue_active(&log_wait))
 958                 __raw_get_cpu_var(printk_pending) = 1;
 959 }
 960
 961 /**
 962  * release_console_sem - unlock the console system
 963  *
 964  * Releases the semaphore which the caller holds on the console system
 965  * and the console driver list.
 966  *
 967  * While the semaphore was held, console output may have been buffered
 968  * by printk().  If this is the case, release_console_sem() emits
 969  * the output prior to releasing the semaphore.
 970  *
 971  * If there is output waiting for klogd, we wake it up.
 972  *
 973  * release_console_sem() may be called from any context.
 974  */
 975 void release_console_sem(void)
 976 {
 977         unsigned long flags;
 978         unsigned _con_start, _log_end;
 979         unsigned wake_klogd = 0;
 980
 981         if (console_suspended) {
 982                 up(&secondary_console_sem);
 983                 return;
 984         }
 985
 986         console_may_schedule = 0;
 987
 988         for ( ; ; ) {
 989                 spin_lock_irqsave(&logbuf_lock, flags);
 990                 wake_klogd |= log_start - log_end;
 991                 if (con_start == log_end)
 992                         break;                  /* Nothing to print */
 993                 _con_start = con_start;
 994                 _log_end = log_end;
 995                 con_start = log_end;            /* Flush */
 996                 spin_unlock(&logbuf_lock);
 997                 stop_critical_timings();        /* don't trace print latency */
 998                 call_console_drivers(_con_start, _log_end);
 999                 start_critical_timings();
1000                 local_irq_restore(flags);
1001         }
1002         console_locked = 0;
1003         up(&console_sem);
1004         spin_unlock_irqrestore(&logbuf_lock, flags);
1005         if (wake_klogd)
1006                 wake_up_klogd();
1007 }
1008 EXPORT_SYMBOL(release_console_sem);
1009
1010 /**
1011  * console_conditional_schedule - yield the CPU if required
1012  *
1013  * If the console code is currently allowed to sleep, and
1014  * if this CPU should yield the CPU to another task, do
1015  * so here.
1016  *
1017  * Must be called within acquire_console_sem().
1018  */
1019 void __sched console_conditional_schedule(void)
1020 {
1021         if (console_may_schedule)
1022                 cond_resched();
1023 }
1024 EXPORT_SYMBOL(console_conditional_schedule);
1025
1026 void console_print(const char *s)
1027 {
1028         printk(KERN_EMERG "%s", s);
1029 }
1030 EXPORT_SYMBOL(console_print);
1031
1032 void console_unblank(void)
1033 {
1034         struct console *c;
1035
1036         /*
1037          * console_unblank can no longer be called in interrupt context unless
1038          * oops_in_progress is set to 1..
1039          */
1040         if (oops_in_progress) {
1041                 if (down_trylock(&console_sem) != 0)
1042                         return;
1043         } else
1044                 acquire_console_sem();
1045
1046         console_locked = 1;
1047         console_may_schedule = 0;
1048         for (c = console_drivers; c != NULL; c = c->next)
1049                 if ((c->flags & CON_ENABLED) && c->unblank)
1050                         c->unblank();
1051         release_console_sem();
1052 }
1053
1054 /*
1055  * Return the console tty driver structure and its associated index
1056  */
1057 struct tty_driver *console_device(int *index)
1058 {
1059         struct console *c;
1060         struct tty_driver *driver = NULL;
1061
1062         acquire_console_sem();
1063         for (c = console_drivers; c != NULL; c = c->next) {
1064                 if (!c->device)
1065                         continue;
1066                 driver = c->device(c, index);
1067                 if (driver)
1068                         break;
1069         }
1070         release_console_sem();
1071         return driver;
1072 }
1073
1074 /*
1075  * Prevent further output on the passed console device so that (for example)
1076  * serial drivers can disable console output before suspending a port, and can
1077  * re-enable output afterwards.
1078  */
1079 void console_stop(struct console *console)
1080 {
1081         acquire_console_sem();
1082         console->flags &= ~CON_ENABLED;
1083         release_console_sem();
1084 }
1085 EXPORT_SYMBOL(console_stop);
1086
1087 void console_start(struct console *console)
1088 {
1089         acquire_console_sem();
1090         console->flags |= CON_ENABLED;
1091         release_console_sem();
1092 }
1093 EXPORT_SYMBOL(console_start);
1094
1095 /*
1096  * The console driver calls this routine during kernel initialization
1097  * to register the console printing procedure with printk() and to
1098  * print any messages that were printed by the kernel before the
1099  * console driver was initialized.
1100  */
1101 void register_console(struct console *console)
1102 {
1103         int i;
1104         unsigned long flags;
1105         struct console *bootconsole = NULL;
1106
1107         if (console_drivers) {
1108                 if (console->flags & CON_BOOT)
1109                         return;
1110                 if (console_drivers->flags & CON_BOOT)
1111                         bootconsole = console_drivers;
1112         }
1113
1114         if (preferred_console < 0 || bootconsole || !console_drivers)
1115                 preferred_console = selected_console;
1116
1117         if (console->early_setup)
1118                 console->early_setup();
1119
1120         /*
1121          *      See if we want to use this console driver. If we
1122          *      didn't select a console we take the first one
1123          *      that registers here.
1124          */
1125         if (preferred_console < 0) {
1126                 if (console->index < 0)
1127                         console->index = 0;
1128                 if (console->setup == NULL ||
1129                     console->setup(console, NULL) == 0) {
1130                         console->flags |= CON_ENABLED;
1131                         if (console->device) {
1132                                 console->flags |= CON_CONSDEV;
1133                                 preferred_console = 0;
1134                         }
1135                 }
1136         }
1137
1138         /*
1139          *      See if this console matches one we selected on
1140          *      the command line.
1141          */
1142         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1143                         i++) {
1144                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1145                         continue;
1146                 if (console->index >= 0 &&
1147                     console->index != console_cmdline[i].index)
1148                         continue;
1149                 if (console->index < 0)
1150                         console->index = console_cmdline[i].index;
1151 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1152                 if (console_cmdline[i].brl_options) {
1153                         console->flags |= CON_BRL;
1154                         braille_register_console(console,
1155                                         console_cmdline[i].index,
1156                                         console_cmdline[i].options,
1157                                         console_cmdline[i].brl_options);
1158                         return;
1159                 }
1160 #endif
1161                 if (console->setup &&
1162                     console->setup(console, console_cmdline[i].options) != 0)
1163                         break;
1164                 console->flags |= CON_ENABLED;
1165                 console->index = console_cmdline[i].index;
1166                 if (i == selected_console) {
1167                         console->flags |= CON_CONSDEV;
1168                         preferred_console = selected_console;
1169                 }
1170                 break;
1171         }
1172
1173         if (!(console->flags & CON_ENABLED))
1174                 return;
1175
1176         if (bootconsole && (console->flags & CON_CONSDEV)) {
1177                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1178                        bootconsole->name, bootconsole->index,
1179                        console->name, console->index);
1180                 unregister_console(bootconsole);
1181                 console->flags &= ~CON_PRINTBUFFER;
1182         } else {
1183                 printk(KERN_INFO "console [%s%d] enabled\n",
1184                        console->name, console->index);
1185         }
1186
1187         /*
1188          *      Put this console in the list - keep the
1189          *      preferred driver at the head of the list.
1190          */
1191         acquire_console_sem();
1192         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1193                 console->next = console_drivers;
1194                 console_drivers = console;
1195                 if (console->next)
1196                         console->next->flags &= ~CON_CONSDEV;
1197         } else {
1198                 console->next = console_drivers->next;
1199                 console_drivers->next = console;
1200         }
1201         if (console->flags & CON_PRINTBUFFER) {
1202                 /*
1203                  * release_console_sem() will print out the buffered messages
1204                  * for us.
1205                  */
1206                 spin_lock_irqsave(&logbuf_lock, flags);
1207                 con_start = log_start;
1208                 spin_unlock_irqrestore(&logbuf_lock, flags);
1209         }
1210         release_console_sem();
1211 }
1212 EXPORT_SYMBOL(register_console);
1213
1214 int unregister_console(struct console *console)
1215 {
1216         struct console *a, *b;
1217         int res = 1;
1218
1219 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1220         if (console->flags & CON_BRL)
1221                 return braille_unregister_console(console);
1222 #endif
1223
1224         acquire_console_sem();
1225         if (console_drivers == console) {
1226                 console_drivers=console->next;
1227                 res = 0;
1228         } else if (console_drivers) {
1229                 for (a=console_drivers->next, b=console_drivers ;
1230                      a; b=a, a=b->next) {
1231                         if (a == console) {
1232                                 b->next = a->next;
1233                                 res = 0;
1234                                 break;
1235                         }
1236                 }
1237         }
1238
1239         /*
1240          * If this isn't the last console and it has CON_CONSDEV set, we
1241          * need to set it on the next preferred console.
1242          */
1243         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1244                 console_drivers->flags |= CON_CONSDEV;
1245
1246         release_console_sem();
1247         return res;
1248 }
1249 EXPORT_SYMBOL(unregister_console);
1250
1251 static int __init disable_boot_consoles(void)
1252 {
1253         if (console_drivers != NULL) {
1254                 if (console_drivers->flags & CON_BOOT) {
1255                         printk(KERN_INFO "turn off boot console %s%d\n",
1256                                 console_drivers->name, console_drivers->index);
1257                         return unregister_console(console_drivers);
1258                 }
1259         }
1260         return 0;
1261 }
1262 late_initcall(disable_boot_consoles);
1263
1264 #if defined CONFIG_PRINTK
1265
1266 /*
1267  * printk rate limiting, lifted from the networking subsystem.
1268  *
1269  * This enforces a rate limit: not more than 10 kernel messages
1270  * every 5s to make a denial-of-service attack impossible.
1271  */
1272 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1273
1274 int printk_ratelimit(void)
1275 {
1276         return __ratelimit(&printk_ratelimit_state);
1277 }
1278 EXPORT_SYMBOL(printk_ratelimit);
1279
1280 /**
1281  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1282  * @caller_jiffies: pointer to caller's state
1283  * @interval_msecs: minimum interval between prints
1284  *
1285  * printk_timed_ratelimit() returns true if more than @interval_msecs
1286  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1287  * returned true.
1288  */
1289 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1290                         unsigned int interval_msecs)
1291 {
1292         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1293                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1294                 return true;
1295         }
1296         return false;
1297 }
1298 EXPORT_SYMBOL(printk_timed_ratelimit);
1299 #endif