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  *     [email protected]
  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 #include <linux/kexec.h>
  36 #include <linux/kdb.h>
  37 #include <linux/ratelimit.h>
  38 #include <linux/kmsg_dump.h>
  39 #include <linux/syslog.h>
  40 #include <linux/cpu.h>
  41 #include <linux/notifier.h>
  42
  43 #include <asm/uaccess.h>
  44
  45 /*
  46  * for_each_console() allows you to iterate on each console
  47  */
  48 #define for_each_console(con) \
  49         for (con = console_drivers; con != NULL; con = con->next)
  50
  51 /*
  52  * Architectures can override it:
  53  */
  54 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  55 {
  56 }
  57
  58 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  59
  60 /* printk's without a loglevel use this.. */
  61 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  62
  63 /* We show everything that is MORE important than this.. */
  64 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  65 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  66
  67 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  68
  69 int console_printk[4] = {
  70         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  71         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  72         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  73         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  74 };
  75
  76 /*
  77  * Low level drivers may need that to know if they can schedule in
  78  * their unblank() callback or not. So let's export it.
  79  */
  80 int oops_in_progress;
  81 EXPORT_SYMBOL(oops_in_progress);
  82
  83 /*
  84  * console_sem protects the console_drivers list, and also
  85  * provides serialisation for access to the entire console
  86  * driver system.
  87  */
  88 static DEFINE_SEMAPHORE(console_sem);
  89 struct console *console_drivers;
  90 EXPORT_SYMBOL_GPL(console_drivers);
  91
  92 /*
  93  * This is used for debugging the mess that is the VT code by
  94  * keeping track if we have the console semaphore held. It's
  95  * definitely not the perfect debug tool (we don't know if _WE_
  96  * hold it are racing, but it helps tracking those weird code
  97  * path in the console code where we end up in places I want
  98  * locked without the console sempahore held
  99  */
 100 static int console_locked, console_suspended;
 101
 102 /*
 103  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 104  * It is also used in interesting ways to provide interlocking in
 105  * release_console_sem().
 106  */
 107 static DEFINE_SPINLOCK(logbuf_lock);
 108
 109 #define LOG_BUF_MASK (log_buf_len-1)
 110 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 111
 112 /*
 113  * The indices into log_buf are not constrained to log_buf_len - they
 114  * must be masked before subscripting
 115  */
 116 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 117 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 118 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 119
 120 /*
 121  *      Array of consoles built from command line options (console=)
 122  */
 123 struct console_cmdline
 124 {
 125         char    name[8];                        /* Name of the driver       */
 126         int     index;                          /* Minor dev. to use        */
 127         char    *options;                       /* Options for the driver   */
 128 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 129         char    *brl_options;                   /* Options for braille driver */
 130 #endif
 131 };
 132
 133 #define MAX_CMDLINECONSOLES 8
 134
 135 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 136 static int selected_console = -1;
 137 static int preferred_console = -1;
 138 int console_set_on_cmdline;
 139 EXPORT_SYMBOL(console_set_on_cmdline);
 140
 141 /* Flag: console code may call schedule() */
 142 static int console_may_schedule;
 143
 144 #ifdef CONFIG_PRINTK
 145
 146 static char __log_buf[__LOG_BUF_LEN];
 147 static char *log_buf = __log_buf;
 148 static int log_buf_len = __LOG_BUF_LEN;
 149 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 150 static int saved_console_loglevel = -1;
 151
 152 #ifdef CONFIG_KEXEC
 153 /*
 154  * This appends the listed symbols to /proc/vmcoreinfo
 155  *
 156  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 157  * obtain access to symbols that are otherwise very difficult to locate.  These
 158  * symbols are specifically used so that utilities can access and extract the
 159  * dmesg log from a vmcore file after a crash.
 160  */
 161 void log_buf_kexec_setup(void)
 162 {
 163         VMCOREINFO_SYMBOL(log_buf);
 164         VMCOREINFO_SYMBOL(log_end);
 165         VMCOREINFO_SYMBOL(log_buf_len);
 166         VMCOREINFO_SYMBOL(logged_chars);
 167 }
 168 #endif
 169
 170 static int __init log_buf_len_setup(char *str)
 171 {
 172         unsigned size = memparse(str, &str);
 173         unsigned long flags;
 174
 175         if (size)
 176                 size = roundup_pow_of_two(size);
 177         if (size > log_buf_len) {
 178                 unsigned start, dest_idx, offset;
 179                 char *new_log_buf;
 180
 181                 new_log_buf = alloc_bootmem(size);
 182                 if (!new_log_buf) {
 183                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 184                         goto out;
 185                 }
 186
 187                 spin_lock_irqsave(&logbuf_lock, flags);
 188                 log_buf_len = size;
 189                 log_buf = new_log_buf;
 190
 191                 offset = start = min(con_start, log_start);
 192                 dest_idx = 0;
 193                 while (start != log_end) {
 194                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 195                         start++;
 196                         dest_idx++;
 197                 }
 198                 log_start -= offset;
 199                 con_start -= offset;
 200                 log_end -= offset;
 201                 spin_unlock_irqrestore(&logbuf_lock, flags);
 202
 203                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 204         }
 205 out:
 206         return 1;
 207 }
 208
 209 __setup("log_buf_len=", log_buf_len_setup);
 210
 211 #ifdef CONFIG_BOOT_PRINTK_DELAY
 212
 213 static int boot_delay; /* msecs delay after each printk during bootup */
 214 static unsigned long long loops_per_msec;       /* based on boot_delay */
 215
 216 static int __init boot_delay_setup(char *str)
 217 {
 218         unsigned long lpj;
 219
 220         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 221         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 222
 223         get_option(&str, &boot_delay);
 224         if (boot_delay > 10 * 1000)
 225                 boot_delay = 0;
 226
 227         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 228                 "HZ: %d, loops_per_msec: %llu\n",
 229                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
 230         return 1;
 231 }
 232 __setup("boot_delay=", boot_delay_setup);
 233
 234 static void boot_delay_msec(void)
 235 {
 236         unsigned long long k;
 237         unsigned long timeout;
 238
 239         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 240                 return;
 241
 242         k = (unsigned long long)loops_per_msec * boot_delay;
 243
 244         timeout = jiffies + msecs_to_jiffies(boot_delay);
 245         while (k) {
 246                 k--;
 247                 cpu_relax();
 248                 /*
 249                  * use (volatile) jiffies to prevent
 250                  * compiler reduction; loop termination via jiffies
 251                  * is secondary and may or may not happen.
 252                  */
 253                 if (time_after(jiffies, timeout))
 254                         break;
 255                 touch_nmi_watchdog();
 256         }
 257 }
 258 #else
 259 static inline void boot_delay_msec(void)
 260 {
 261 }
 262 #endif
 263
 264 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
 265 int dmesg_restrict = 1;
 266 #else
 267 int dmesg_restrict;
 268 #endif
 269
 270 int do_syslog(int type, char __user *buf, int len, bool from_file)
 271 {
 272         unsigned i, j, limit, count;
 273         int do_clear = 0;
 274         char c;
 275         int error = 0;
 276
 277         /*
 278          * If this is from /proc/kmsg we only do the capabilities checks
 279          * at open time.
 280          */
 281         if (type == SYSLOG_ACTION_OPEN || !from_file) {
 282                 if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
 283                         return -EPERM;
 284                 if ((type != SYSLOG_ACTION_READ_ALL &&
 285                      type != SYSLOG_ACTION_SIZE_BUFFER) &&
 286                     !capable(CAP_SYS_ADMIN))
 287                         return -EPERM;
 288         }
 289
 290         error = security_syslog(type);
 291         if (error)
 292                 return error;
 293
 294         switch (type) {
 295         case SYSLOG_ACTION_CLOSE:       /* Close log */
 296                 break;
 297         case SYSLOG_ACTION_OPEN:        /* Open log */
 298                 break;
 299         case SYSLOG_ACTION_READ:        /* Read from log */
 300                 error = -EINVAL;
 301                 if (!buf || len < 0)
 302                         goto out;
 303                 error = 0;
 304                 if (!len)
 305                         goto out;
 306                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 307                         error = -EFAULT;
 308                         goto out;
 309                 }
 310                 error = wait_event_interruptible(log_wait,
 311                                                         (log_start - log_end));
 312                 if (error)
 313                         goto out;
 314                 i = 0;
 315                 spin_lock_irq(&logbuf_lock);
 316                 while (!error && (log_start != log_end) && i < len) {
 317                         c = LOG_BUF(log_start);
 318                         log_start++;
 319                         spin_unlock_irq(&logbuf_lock);
 320                         error = __put_user(c,buf);
 321                         buf++;
 322                         i++;
 323                         cond_resched();
 324                         spin_lock_irq(&logbuf_lock);
 325                 }
 326                 spin_unlock_irq(&logbuf_lock);
 327                 if (!error)
 328                         error = i;
 329                 break;
 330         /* Read/clear last kernel messages */
 331         case SYSLOG_ACTION_READ_CLEAR:
 332                 do_clear = 1;
 333                 /* FALL THRU */
 334         /* Read last kernel messages */
 335         case SYSLOG_ACTION_READ_ALL:
 336                 error = -EINVAL;
 337                 if (!buf || len < 0)
 338                         goto out;
 339                 error = 0;
 340                 if (!len)
 341                         goto out;
 342                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 343                         error = -EFAULT;
 344                         goto out;
 345                 }
 346                 count = len;
 347                 if (count > log_buf_len)
 348                         count = log_buf_len;
 349                 spin_lock_irq(&logbuf_lock);
 350                 if (count > logged_chars)
 351                         count = logged_chars;
 352                 if (do_clear)
 353                         logged_chars = 0;
 354                 limit = log_end;
 355                 /*
 356                  * __put_user() could sleep, and while we sleep
 357                  * printk() could overwrite the messages
 358                  * we try to copy to user space. Therefore
 359                  * the messages are copied in reverse. <manfreds>
 360                  */
 361                 for (i = 0; i < count && !error; i++) {
 362                         j = limit-1-i;
 363                         if (j + log_buf_len < log_end)
 364                                 break;
 365                         c = LOG_BUF(j);
 366                         spin_unlock_irq(&logbuf_lock);
 367                         error = __put_user(c,&buf[count-1-i]);
 368                         cond_resched();
 369                         spin_lock_irq(&logbuf_lock);
 370                 }
 371                 spin_unlock_irq(&logbuf_lock);
 372                 if (error)
 373                         break;
 374                 error = i;
 375                 if (i != count) {
 376                         int offset = count-error;
 377                         /* buffer overflow during copy, correct user buffer. */
 378                         for (i = 0; i < error; i++) {
 379                                 if (__get_user(c,&buf[i+offset]) ||
 380                                     __put_user(c,&buf[i])) {
 381                                         error = -EFAULT;
 382                                         break;
 383                                 }
 384                                 cond_resched();
 385                         }
 386                 }
 387                 break;
 388         /* Clear ring buffer */
 389         case SYSLOG_ACTION_CLEAR:
 390                 logged_chars = 0;
 391                 break;
 392         /* Disable logging to console */
 393         case SYSLOG_ACTION_CONSOLE_OFF:
 394                 if (saved_console_loglevel == -1)
 395                         saved_console_loglevel = console_loglevel;
 396                 console_loglevel = minimum_console_loglevel;
 397                 break;
 398         /* Enable logging to console */
 399         case SYSLOG_ACTION_CONSOLE_ON:
 400                 if (saved_console_loglevel != -1) {
 401                         console_loglevel = saved_console_loglevel;
 402                         saved_console_loglevel = -1;
 403                 }
 404                 break;
 405         /* Set level of messages printed to console */
 406         case SYSLOG_ACTION_CONSOLE_LEVEL:
 407                 error = -EINVAL;
 408                 if (len < 1 || len > 8)
 409                         goto out;
 410                 if (len < minimum_console_loglevel)
 411                         len = minimum_console_loglevel;
 412                 console_loglevel = len;
 413                 /* Implicitly re-enable logging to console */
 414                 saved_console_loglevel = -1;
 415                 error = 0;
 416                 break;
 417         /* Number of chars in the log buffer */
 418         case SYSLOG_ACTION_SIZE_UNREAD:
 419                 error = log_end - log_start;
 420                 break;
 421         /* Size of the log buffer */
 422         case SYSLOG_ACTION_SIZE_BUFFER:
 423                 error = log_buf_len;
 424                 break;
 425         default:
 426                 error = -EINVAL;
 427                 break;
 428         }
 429 out:
 430         return error;
 431 }
 432
 433 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 434 {
 435         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 436 }
 437
 438 #ifdef  CONFIG_KGDB_KDB
 439 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
 440  * uses locks so it cannot be used during debugging.  Just tell kdb
 441  * where the start and end of the physical and logical logs are.  This
 442  * is equivalent to do_syslog(3).
 443  */
 444 void kdb_syslog_data(char *syslog_data[4])
 445 {
 446         syslog_data[0] = log_buf;
 447         syslog_data[1] = log_buf + log_buf_len;
 448         syslog_data[2] = log_buf + log_end -
 449                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
 450         syslog_data[3] = log_buf + log_end;
 451 }
 452 #endif  /* CONFIG_KGDB_KDB */
 453
 454 /*
 455  * Call the console drivers on a range of log_buf
 456  */
 457 static void __call_console_drivers(unsigned start, unsigned end)
 458 {
 459         struct console *con;
 460
 461         for_each_console(con) {
 462                 if ((con->flags & CON_ENABLED) && con->write &&
 463                                 (cpu_online(smp_processor_id()) ||
 464                                 (con->flags & CON_ANYTIME)))
 465                         con->write(con, &LOG_BUF(start), end - start);
 466         }
 467 }
 468
 469 static int __read_mostly ignore_loglevel;
 470
 471 static int __init ignore_loglevel_setup(char *str)
 472 {
 473         ignore_loglevel = 1;
 474         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 475
 476         return 0;
 477 }
 478
 479 early_param("ignore_loglevel", ignore_loglevel_setup);
 480
 481 /*
 482  * Write out chars from start to end - 1 inclusive
 483  */
 484 static void _call_console_drivers(unsigned start,
 485                                 unsigned end, int msg_log_level)
 486 {
 487         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 488                         console_drivers && start != end) {
 489                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 490                         /* wrapped write */
 491                         __call_console_drivers(start & LOG_BUF_MASK,
 492                                                 log_buf_len);
 493                         __call_console_drivers(0, end & LOG_BUF_MASK);
 494                 } else {
 495                         __call_console_drivers(start, end);
 496                 }
 497         }
 498 }
 499
 500 /*
 501  * Call the console drivers, asking them to write out
 502  * log_buf[start] to log_buf[end - 1].
 503  * The console_sem must be held.
 504  */
 505 static void call_console_drivers(unsigned start, unsigned end)
 506 {
 507         unsigned cur_index, start_print;
 508         static int msg_level = -1;
 509
 510         BUG_ON(((int)(start - end)) > 0);
 511
 512         cur_index = start;
 513         start_print = start;
 514         while (cur_index != end) {
 515                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 516                                 LOG_BUF(cur_index + 0) == '<' &&
 517                                 LOG_BUF(cur_index + 1) >= '0' &&
 518                                 LOG_BUF(cur_index + 1) <= '7' &&
 519                                 LOG_BUF(cur_index + 2) == '>') {
 520                         msg_level = LOG_BUF(cur_index + 1) - '0';
 521                         cur_index += 3;
 522                         start_print = cur_index;
 523                 }
 524                 while (cur_index != end) {
 525                         char c = LOG_BUF(cur_index);
 526
 527                         cur_index++;
 528                         if (c == '\n') {
 529                                 if (msg_level < 0) {
 530                                         /*
 531                                          * printk() has already given us loglevel tags in
 532                                          * the buffer.  This code is here in case the
 533                                          * log buffer has wrapped right round and scribbled
 534                                          * on those tags
 535                                          */
 536                                         msg_level = default_message_loglevel;
 537                                 }
 538                                 _call_console_drivers(start_print, cur_index, msg_level);
 539                                 msg_level = -1;
 540                                 start_print = cur_index;
 541                                 break;
 542                         }
 543                 }
 544         }
 545         _call_console_drivers(start_print, end, msg_level);
 546 }
 547
 548 static void emit_log_char(char c)
 549 {
 550         LOG_BUF(log_end) = c;
 551         log_end++;
 552         if (log_end - log_start > log_buf_len)
 553                 log_start = log_end - log_buf_len;
 554         if (log_end - con_start > log_buf_len)
 555                 con_start = log_end - log_buf_len;
 556         if (logged_chars < log_buf_len)
 557                 logged_chars++;
 558 }
 559
 560 /*
 561  * Zap console related locks when oopsing. Only zap at most once
 562  * every 10 seconds, to leave time for slow consoles to print a
 563  * full oops.
 564  */
 565 static void zap_locks(void)
 566 {
 567         static unsigned long oops_timestamp;
 568
 569         if (time_after_eq(jiffies, oops_timestamp) &&
 570                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 571                 return;
 572
 573         oops_timestamp = jiffies;
 574
 575         /* If a crash is occurring, make sure we can't deadlock */
 576         spin_lock_init(&logbuf_lock);
 577         /* And make sure that we print immediately */
 578         sema_init(&console_sem, 1);
 579 }
 580
 581 #if defined(CONFIG_PRINTK_TIME)
 582 static int printk_time = 1;
 583 #else
 584 static int printk_time = 0;
 585 #endif
 586 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 587
 588 /* Check if we have any console registered that can be called early in boot. */
 589 static int have_callable_console(void)
 590 {
 591         struct console *con;
 592
 593         for_each_console(con)
 594                 if (con->flags & CON_ANYTIME)
 595                         return 1;
 596
 597         return 0;
 598 }
 599
 600 /**
 601  * printk - print a kernel message
 602  * @fmt: format string
 603  *
 604  * This is printk().  It can be called from any context.  We want it to work.
 605  *
 606  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 607  * call the console drivers.  If we fail to get the semaphore we place the output
 608  * into the log buffer and return.  The current holder of the console_sem will
 609  * notice the new output in release_console_sem() and will send it to the
 610  * consoles before releasing the semaphore.
 611  *
 612  * One effect of this deferred printing is that code which calls printk() and
 613  * then changes console_loglevel may break. This is because console_loglevel
 614  * is inspected when the actual printing occurs.
 615  *
 616  * See also:
 617  * printf(3)
 618  *
 619  * See the vsnprintf() documentation for format string extensions over C99.
 620  */
 621
 622 asmlinkage int printk(const char *fmt, ...)
 623 {
 624         va_list args;
 625         int r;
 626
 627 #ifdef CONFIG_KGDB_KDB
 628         if (unlikely(kdb_trap_printk)) {
 629                 va_start(args, fmt);
 630                 r = vkdb_printf(fmt, args);
 631                 va_end(args);
 632                 return r;
 633         }
 634 #endif
 635         va_start(args, fmt);
 636         r = vprintk(fmt, args);
 637         va_end(args);
 638
 639         return r;
 640 }
 641
 642 /* cpu currently holding logbuf_lock */
 643 static volatile unsigned int printk_cpu = UINT_MAX;
 644
 645 /*
 646  * Can we actually use the console at this time on this cpu?
 647  *
 648  * Console drivers may assume that per-cpu resources have
 649  * been allocated. So unless they're explicitly marked as
 650  * being able to cope (CON_ANYTIME) don't call them until
 651  * this CPU is officially up.
 652  */
 653 static inline int can_use_console(unsigned int cpu)
 654 {
 655         return cpu_online(cpu) || have_callable_console();
 656 }
 657
 658 /*
 659  * Try to get console ownership to actually show the kernel
 660  * messages from a 'printk'. Return true (and with the
 661  * console_semaphore held, and 'console_locked' set) if it
 662  * is successful, false otherwise.
 663  *
 664  * This gets called with the 'logbuf_lock' spinlock held and
 665  * interrupts disabled. It should return with 'lockbuf_lock'
 666  * released but interrupts still disabled.
 667  */
 668 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 669         __releases(&logbuf_lock)
 670 {
 671         int retval = 0;
 672
 673         if (!try_acquire_console_sem()) {
 674                 retval = 1;
 675
 676                 /*
 677                  * If we can't use the console, we need to release
 678                  * the console semaphore by hand to avoid flushing
 679                  * the buffer. We need to hold the console semaphore
 680                  * in order to do this test safely.
 681                  */
 682                 if (!can_use_console(cpu)) {
 683                         console_locked = 0;
 684                         up(&console_sem);
 685                         retval = 0;
 686                 }
 687         }
 688         printk_cpu = UINT_MAX;
 689         spin_unlock(&logbuf_lock);
 690         return retval;
 691 }
 692 static const char recursion_bug_msg [] =
 693                 KERN_CRIT "BUG: recent printk recursion!\n";
 694 static int recursion_bug;
 695 static int new_text_line = 1;
 696 static char printk_buf[1024];
 697
 698 int printk_delay_msec __read_mostly;
 699
 700 static inline void printk_delay(void)
 701 {
 702         if (unlikely(printk_delay_msec)) {
 703                 int m = printk_delay_msec;
 704
 705                 while (m--) {
 706                         mdelay(1);
 707                         touch_nmi_watchdog();
 708                 }
 709         }
 710 }
 711
 712 asmlinkage int vprintk(const char *fmt, va_list args)
 713 {
 714         int printed_len = 0;
 715         int current_log_level = default_message_loglevel;
 716         unsigned long flags;
 717         int this_cpu;
 718         char *p;
 719
 720         boot_delay_msec();
 721         printk_delay();
 722
 723         preempt_disable();
 724         /* This stops the holder of console_sem just where we want him */
 725         raw_local_irq_save(flags);
 726         this_cpu = smp_processor_id();
 727
 728         /*
 729          * Ouch, printk recursed into itself!
 730          */
 731         if (unlikely(printk_cpu == this_cpu)) {
 732                 /*
 733                  * If a crash is occurring during printk() on this CPU,
 734                  * then try to get the crash message out but make sure
 735                  * we can't deadlock. Otherwise just return to avoid the
 736                  * recursion and return - but flag the recursion so that
 737                  * it can be printed at the next appropriate moment:
 738                  */
 739                 if (!oops_in_progress) {
 740                         recursion_bug = 1;
 741                         goto out_restore_irqs;
 742                 }
 743                 zap_locks();
 744         }
 745
 746         lockdep_off();
 747         spin_lock(&logbuf_lock);
 748         printk_cpu = this_cpu;
 749
 750         if (recursion_bug) {
 751                 recursion_bug = 0;
 752                 strcpy(printk_buf, recursion_bug_msg);
 753                 printed_len = strlen(recursion_bug_msg);
 754         }
 755         /* Emit the output into the temporary buffer */
 756         printed_len += vscnprintf(printk_buf + printed_len,
 757                                   sizeof(printk_buf) - printed_len, fmt, args);
 758
 759
 760         p = printk_buf;
 761
 762         /* Do we have a loglevel in the string? */
 763         if (p[0] == '<') {
 764                 unsigned char c = p[1];
 765                 if (c && p[2] == '>') {
 766                         switch (c) {
 767                         case '0' ... '7': /* loglevel */
 768                                 current_log_level = c - '0';
 769                         /* Fallthrough - make sure we're on a new line */
 770                         case 'd': /* KERN_DEFAULT */
 771                                 if (!new_text_line) {
 772                                         emit_log_char('\n');
 773                                         new_text_line = 1;
 774                                 }
 775                         /* Fallthrough - skip the loglevel */
 776                         case 'c': /* KERN_CONT */
 777                                 p += 3;
 778                                 break;
 779                         }
 780                 }
 781         }
 782
 783         /*
 784          * Copy the output into log_buf.  If the caller didn't provide
 785          * appropriate log level tags, we insert them here
 786          */
 787         for ( ; *p; p++) {
 788                 if (new_text_line) {
 789                         /* Always output the token */
 790                         emit_log_char('<');
 791                         emit_log_char(current_log_level + '0');
 792                         emit_log_char('>');
 793                         printed_len += 3;
 794                         new_text_line = 0;
 795
 796                         if (printk_time) {
 797                                 /* Follow the token with the time */
 798                                 char tbuf[50], *tp;
 799                                 unsigned tlen;
 800                                 unsigned long long t;
 801                                 unsigned long nanosec_rem;
 802
 803                                 t = cpu_clock(printk_cpu);
 804                                 nanosec_rem = do_div(t, 1000000000);
 805                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 806                                                 (unsigned long) t,
 807                                                 nanosec_rem / 1000);
 808
 809                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 810                                         emit_log_char(*tp);
 811                                 printed_len += tlen;
 812                         }
 813
 814                         if (!*p)
 815                                 break;
 816                 }
 817
 818                 emit_log_char(*p);
 819                 if (*p == '\n')
 820                         new_text_line = 1;
 821         }
 822
 823         /*
 824          * Try to acquire and then immediately release the
 825          * console semaphore. The release will do all the
 826          * actual magic (print out buffers, wake up klogd,
 827          * etc).
 828          *
 829          * The acquire_console_semaphore_for_printk() function
 830          * will release 'logbuf_lock' regardless of whether it
 831          * actually gets the semaphore or not.
 832          */
 833         if (acquire_console_semaphore_for_printk(this_cpu))
 834                 release_console_sem();
 835
 836         lockdep_on();
 837 out_restore_irqs:
 838         raw_local_irq_restore(flags);
 839
 840         preempt_enable();
 841         return printed_len;
 842 }
 843 EXPORT_SYMBOL(printk);
 844 EXPORT_SYMBOL(vprintk);
 845
 846 #else
 847
 848 static void call_console_drivers(unsigned start, unsigned end)
 849 {
 850 }
 851
 852 #endif
 853
 854 static int __add_preferred_console(char *name, int idx, char *options,
 855                                    char *brl_options)
 856 {
 857         struct console_cmdline *c;
 858         int i;
 859
 860         /*
 861          *      See if this tty is not yet registered, and
 862          *      if we have a slot free.
 863          */
 864         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 865                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 866                           console_cmdline[i].index == idx) {
 867                                 if (!brl_options)
 868                                         selected_console = i;
 869                                 return 0;
 870                 }
 871         if (i == MAX_CMDLINECONSOLES)
 872                 return -E2BIG;
 873         if (!brl_options)
 874                 selected_console = i;
 875         c = &console_cmdline[i];
 876         strlcpy(c->name, name, sizeof(c->name));
 877         c->options = options;
 878 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 879         c->brl_options = brl_options;
 880 #endif
 881         c->index = idx;
 882         return 0;
 883 }
 884 /*
 885  * Set up a list of consoles.  Called from init/main.c
 886  */
 887 static int __init console_setup(char *str)
 888 {
 889         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 890         char *s, *options, *brl_options = NULL;
 891         int idx;
 892
 893 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 894         if (!memcmp(str, "brl,", 4)) {
 895                 brl_options = "";
 896                 str += 4;
 897         } else if (!memcmp(str, "brl=", 4)) {
 898                 brl_options = str + 4;
 899                 str = strchr(brl_options, ',');
 900                 if (!str) {
 901                         printk(KERN_ERR "need port name after brl=\n");
 902                         return 1;
 903                 }
 904                 *(str++) = 0;
 905         }
 906 #endif
 907
 908         /*
 909          * Decode str into name, index, options.
 910          */
 911         if (str[0] >= '0' && str[0] <= '9') {
 912                 strcpy(buf, "ttyS");
 913                 strncpy(buf + 4, str, sizeof(buf) - 5);
 914         } else {
 915                 strncpy(buf, str, sizeof(buf) - 1);
 916         }
 917         buf[sizeof(buf) - 1] = 0;
 918         if ((options = strchr(str, ',')) != NULL)
 919                 *(options++) = 0;
 920 #ifdef __sparc__
 921         if (!strcmp(str, "ttya"))
 922                 strcpy(buf, "ttyS0");
 923         if (!strcmp(str, "ttyb"))
 924                 strcpy(buf, "ttyS1");
 925 #endif
 926         for (s = buf; *s; s++)
 927                 if ((*s >= '0' && *s <= '9') || *s == ',')
 928                         break;
 929         idx = simple_strtoul(s, NULL, 10);
 930         *s = 0;
 931
 932         __add_preferred_console(buf, idx, options, brl_options);
 933         console_set_on_cmdline = 1;
 934         return 1;
 935 }
 936 __setup("console=", console_setup);
 937
 938 /**
 939  * add_preferred_console - add a device to the list of preferred consoles.
 940  * @name: device name
 941  * @idx: device index
 942  * @options: options for this console
 943  *
 944  * The last preferred console added will be used for kernel messages
 945  * and stdin/out/err for init.  Normally this is used by console_setup
 946  * above to handle user-supplied console arguments; however it can also
 947  * be used by arch-specific code either to override the user or more
 948  * commonly to provide a default console (ie from PROM variables) when
 949  * the user has not supplied one.
 950  */
 951 int add_preferred_console(char *name, int idx, char *options)
 952 {
 953         return __add_preferred_console(name, idx, options, NULL);
 954 }
 955
 956 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 957 {
 958         struct console_cmdline *c;
 959         int i;
 960
 961         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 962                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 963                           console_cmdline[i].index == idx) {
 964                                 c = &console_cmdline[i];
 965                                 strlcpy(c->name, name_new, sizeof(c->name));
 966                                 c->name[sizeof(c->name) - 1] = 0;
 967                                 c->options = options;
 968                                 c->index = idx_new;
 969                                 return i;
 970                 }
 971         /* not found */
 972         return -1;
 973 }
 974
 975 int console_suspend_enabled = 1;
 976 EXPORT_SYMBOL(console_suspend_enabled);
 977
 978 static int __init console_suspend_disable(char *str)
 979 {
 980         console_suspend_enabled = 0;
 981         return 1;
 982 }
 983 __setup("no_console_suspend", console_suspend_disable);
 984
 985 /**
 986  * suspend_console - suspend the console subsystem
 987  *
 988  * This disables printk() while we go into suspend states
 989  */
 990 void suspend_console(void)
 991 {
 992         if (!console_suspend_enabled)
 993                 return;
 994         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 995         acquire_console_sem();
 996         console_suspended = 1;
 997         up(&console_sem);
 998 }
 999
1000 void resume_console(void)
1001 {
1002         if (!console_suspend_enabled)
1003                 return;
1004         down(&console_sem);
1005         console_suspended = 0;
1006         release_console_sem();
1007 }
1008
1009 /**
1010  * console_cpu_notify - print deferred console messages after CPU hotplug
1011  * @self: notifier struct
1012  * @action: CPU hotplug event
1013  * @hcpu: unused
1014  *
1015  * If printk() is called from a CPU that is not online yet, the messages
1016  * will be spooled but will not show up on the console.  This function is
1017  * called when a new CPU comes online (or fails to come up), and ensures
1018  * that any such output gets printed.
1019  */
1020 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1021         unsigned long action, void *hcpu)
1022 {
1023         switch (action) {
1024         case CPU_ONLINE:
1025         case CPU_DEAD:
1026         case CPU_DYING:
1027         case CPU_DOWN_FAILED:
1028         case CPU_UP_CANCELED:
1029                 acquire_console_sem();
1030                 release_console_sem();
1031         }
1032         return NOTIFY_OK;
1033 }
1034
1035 /**
1036  * acquire_console_sem - lock the console system for exclusive use.
1037  *
1038  * Acquires a semaphore which guarantees that the caller has
1039  * exclusive access to the console system and the console_drivers list.
1040  *
1041  * Can sleep, returns nothing.
1042  */
1043 void acquire_console_sem(void)
1044 {
1045         BUG_ON(in_interrupt());
1046         down(&console_sem);
1047         if (console_suspended)
1048                 return;
1049         console_locked = 1;
1050         console_may_schedule = 1;
1051 }
1052 EXPORT_SYMBOL(acquire_console_sem);
1053
1054 int try_acquire_console_sem(void)
1055 {
1056         if (down_trylock(&console_sem))
1057                 return -1;
1058         if (console_suspended) {
1059                 up(&console_sem);
1060                 return -1;
1061         }
1062         console_locked = 1;
1063         console_may_schedule = 0;
1064         return 0;
1065 }
1066 EXPORT_SYMBOL(try_acquire_console_sem);
1067
1068 int is_console_locked(void)
1069 {
1070         return console_locked;
1071 }
1072
1073 static DEFINE_PER_CPU(int, printk_pending);
1074
1075 void printk_tick(void)
1076 {
1077         if (__get_cpu_var(printk_pending)) {
1078                 __get_cpu_var(printk_pending) = 0;
1079                 wake_up_interruptible(&log_wait);
1080         }
1081 }
1082
1083 int printk_needs_cpu(int cpu)
1084 {
1085         return per_cpu(printk_pending, cpu);
1086 }
1087
1088 void wake_up_klogd(void)
1089 {
1090         if (waitqueue_active(&log_wait))
1091                 __raw_get_cpu_var(printk_pending) = 1;
1092 }
1093
1094 /**
1095  * release_console_sem - unlock the console system
1096  *
1097  * Releases the semaphore which the caller holds on the console system
1098  * and the console driver list.
1099  *
1100  * While the semaphore was held, console output may have been buffered
1101  * by printk().  If this is the case, release_console_sem() emits
1102  * the output prior to releasing the semaphore.
1103  *
1104  * If there is output waiting for klogd, we wake it up.
1105  *
1106  * release_console_sem() may be called from any context.
1107  */
1108 void release_console_sem(void)
1109 {
1110         unsigned long flags;
1111         unsigned _con_start, _log_end;
1112         unsigned wake_klogd = 0;
1113
1114         if (console_suspended) {
1115                 up(&console_sem);
1116                 return;
1117         }
1118
1119         console_may_schedule = 0;
1120
1121         for ( ; ; ) {
1122                 spin_lock_irqsave(&logbuf_lock, flags);
1123                 wake_klogd |= log_start - log_end;
1124                 if (con_start == log_end)
1125                         break;                  /* Nothing to print */
1126                 _con_start = con_start;
1127                 _log_end = log_end;
1128                 con_start = log_end;            /* Flush */
1129                 spin_unlock(&logbuf_lock);
1130                 stop_critical_timings();        /* don't trace print latency */
1131                 call_console_drivers(_con_start, _log_end);
1132                 start_critical_timings();
1133                 local_irq_restore(flags);
1134         }
1135         console_locked = 0;
1136         up(&console_sem);
1137         spin_unlock_irqrestore(&logbuf_lock, flags);
1138         if (wake_klogd)
1139                 wake_up_klogd();
1140 }
1141 EXPORT_SYMBOL(release_console_sem);
1142
1143 /**
1144  * console_conditional_schedule - yield the CPU if required
1145  *
1146  * If the console code is currently allowed to sleep, and
1147  * if this CPU should yield the CPU to another task, do
1148  * so here.
1149  *
1150  * Must be called within acquire_console_sem().
1151  */
1152 void __sched console_conditional_schedule(void)
1153 {
1154         if (console_may_schedule)
1155                 cond_resched();
1156 }
1157 EXPORT_SYMBOL(console_conditional_schedule);
1158
1159 void console_unblank(void)
1160 {
1161         struct console *c;
1162
1163         /*
1164          * console_unblank can no longer be called in interrupt context unless
1165          * oops_in_progress is set to 1..
1166          */
1167         if (oops_in_progress) {
1168                 if (down_trylock(&console_sem) != 0)
1169                         return;
1170         } else
1171                 acquire_console_sem();
1172
1173         console_locked = 1;
1174         console_may_schedule = 0;
1175         for_each_console(c)
1176                 if ((c->flags & CON_ENABLED) && c->unblank)
1177                         c->unblank();
1178         release_console_sem();
1179 }
1180
1181 /*
1182  * Return the console tty driver structure and its associated index
1183  */
1184 struct tty_driver *console_device(int *index)
1185 {
1186         struct console *c;
1187         struct tty_driver *driver = NULL;
1188
1189         acquire_console_sem();
1190         for_each_console(c) {
1191                 if (!c->device)
1192                         continue;
1193                 driver = c->device(c, index);
1194                 if (driver)
1195                         break;
1196         }
1197         release_console_sem();
1198         return driver;
1199 }
1200
1201 /*
1202  * Prevent further output on the passed console device so that (for example)
1203  * serial drivers can disable console output before suspending a port, and can
1204  * re-enable output afterwards.
1205  */
1206 void console_stop(struct console *console)
1207 {
1208         acquire_console_sem();
1209         console->flags &= ~CON_ENABLED;
1210         release_console_sem();
1211 }
1212 EXPORT_SYMBOL(console_stop);
1213
1214 void console_start(struct console *console)
1215 {
1216         acquire_console_sem();
1217         console->flags |= CON_ENABLED;
1218         release_console_sem();
1219 }
1220 EXPORT_SYMBOL(console_start);
1221
1222 /*
1223  * The console driver calls this routine during kernel initialization
1224  * to register the console printing procedure with printk() and to
1225  * print any messages that were printed by the kernel before the
1226  * console driver was initialized.
1227  *
1228  * This can happen pretty early during the boot process (because of
1229  * early_printk) - sometimes before setup_arch() completes - be careful
1230  * of what kernel features are used - they may not be initialised yet.
1231  *
1232  * There are two types of consoles - bootconsoles (early_printk) and
1233  * "real" consoles (everything which is not a bootconsole) which are
1234  * handled differently.
1235  *  - Any number of bootconsoles can be registered at any time.
1236  *  - As soon as a "real" console is registered, all bootconsoles
1237  *    will be unregistered automatically.
1238  *  - Once a "real" console is registered, any attempt to register a
1239  *    bootconsoles will be rejected
1240  */
1241 void register_console(struct console *newcon)
1242 {
1243         int i;
1244         unsigned long flags;
1245         struct console *bcon = NULL;
1246
1247         /*
1248          * before we register a new CON_BOOT console, make sure we don't
1249          * already have a valid console
1250          */
1251         if (console_drivers && newcon->flags & CON_BOOT) {
1252                 /* find the last or real console */
1253                 for_each_console(bcon) {
1254                         if (!(bcon->flags & CON_BOOT)) {
1255                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1256                                         newcon->name, newcon->index);
1257                                 return;
1258                         }
1259                 }
1260         }
1261
1262         if (console_drivers && console_drivers->flags & CON_BOOT)
1263                 bcon = console_drivers;
1264
1265         if (preferred_console < 0 || bcon || !console_drivers)
1266                 preferred_console = selected_console;
1267
1268         if (newcon->early_setup)
1269                 newcon->early_setup();
1270
1271         /*
1272          *      See if we want to use this console driver. If we
1273          *      didn't select a console we take the first one
1274          *      that registers here.
1275          */
1276         if (preferred_console < 0) {
1277                 if (newcon->index < 0)
1278                         newcon->index = 0;
1279                 if (newcon->setup == NULL ||
1280                     newcon->setup(newcon, NULL) == 0) {
1281                         newcon->flags |= CON_ENABLED;
1282                         if (newcon->device) {
1283                                 newcon->flags |= CON_CONSDEV;
1284                                 preferred_console = 0;
1285                         }
1286                 }
1287         }
1288
1289         /*
1290          *      See if this console matches one we selected on
1291          *      the command line.
1292          */
1293         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1294                         i++) {
1295                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1296                         continue;
1297                 if (newcon->index >= 0 &&
1298                     newcon->index != console_cmdline[i].index)
1299                         continue;
1300                 if (newcon->index < 0)
1301                         newcon->index = console_cmdline[i].index;
1302 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1303                 if (console_cmdline[i].brl_options) {
1304                         newcon->flags |= CON_BRL;
1305                         braille_register_console(newcon,
1306                                         console_cmdline[i].index,
1307                                         console_cmdline[i].options,
1308                                         console_cmdline[i].brl_options);
1309                         return;
1310                 }
1311 #endif
1312                 if (newcon->setup &&
1313                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1314                         break;
1315                 newcon->flags |= CON_ENABLED;
1316                 newcon->index = console_cmdline[i].index;
1317                 if (i == selected_console) {
1318                         newcon->flags |= CON_CONSDEV;
1319                         preferred_console = selected_console;
1320                 }
1321                 break;
1322         }
1323
1324         if (!(newcon->flags & CON_ENABLED))
1325                 return;
1326
1327         /*
1328          * If we have a bootconsole, and are switching to a real console,
1329          * don't print everything out again, since when the boot console, and
1330          * the real console are the same physical device, it's annoying to
1331          * see the beginning boot messages twice
1332          */
1333         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1334                 newcon->flags &= ~CON_PRINTBUFFER;
1335
1336         /*
1337          *      Put this console in the list - keep the
1338          *      preferred driver at the head of the list.
1339          */
1340         acquire_console_sem();
1341         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1342                 newcon->next = console_drivers;
1343                 console_drivers = newcon;
1344                 if (newcon->next)
1345                         newcon->next->flags &= ~CON_CONSDEV;
1346         } else {
1347                 newcon->next = console_drivers->next;
1348                 console_drivers->next = newcon;
1349         }
1350         if (newcon->flags & CON_PRINTBUFFER) {
1351                 /*
1352                  * release_console_sem() will print out the buffered messages
1353                  * for us.
1354                  */
1355                 spin_lock_irqsave(&logbuf_lock, flags);
1356                 con_start = log_start;
1357                 spin_unlock_irqrestore(&logbuf_lock, flags);
1358         }
1359         release_console_sem();
1360
1361         /*
1362          * By unregistering the bootconsoles after we enable the real console
1363          * we get the "console xxx enabled" message on all the consoles -
1364          * boot consoles, real consoles, etc - this is to ensure that end
1365          * users know there might be something in the kernel's log buffer that
1366          * went to the bootconsole (that they do not see on the real console)
1367          */
1368         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1369                 /* we need to iterate through twice, to make sure we print
1370                  * everything out, before we unregister the console(s)
1371                  */
1372                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1373                         newcon->name, newcon->index);
1374                 for_each_console(bcon)
1375                         if (bcon->flags & CON_BOOT)
1376                                 unregister_console(bcon);
1377         } else {
1378                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1379                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1380                         newcon->name, newcon->index);
1381         }
1382 }
1383 EXPORT_SYMBOL(register_console);
1384
1385 int unregister_console(struct console *console)
1386 {
1387         struct console *a, *b;
1388         int res = 1;
1389
1390 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1391         if (console->flags & CON_BRL)
1392                 return braille_unregister_console(console);
1393 #endif
1394
1395         acquire_console_sem();
1396         if (console_drivers == console) {
1397                 console_drivers=console->next;
1398                 res = 0;
1399         } else if (console_drivers) {
1400                 for (a=console_drivers->next, b=console_drivers ;
1401                      a; b=a, a=b->next) {
1402                         if (a == console) {
1403                                 b->next = a->next;
1404                                 res = 0;
1405                                 break;
1406                         }
1407                 }
1408         }
1409
1410         /*
1411          * If this isn't the last console and it has CON_CONSDEV set, we
1412          * need to set it on the next preferred console.
1413          */
1414         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1415                 console_drivers->flags |= CON_CONSDEV;
1416
1417         release_console_sem();
1418         return res;
1419 }
1420 EXPORT_SYMBOL(unregister_console);
1421
1422 static int __init printk_late_init(void)
1423 {
1424         struct console *con;
1425
1426         for_each_console(con) {
1427                 if (con->flags & CON_BOOT) {
1428                         printk(KERN_INFO "turn off boot console %s%d\n",
1429                                 con->name, con->index);
1430                         unregister_console(con);
1431                 }
1432         }
1433         hotcpu_notifier(console_cpu_notify, 0);
1434         return 0;
1435 }
1436 late_initcall(printk_late_init);
1437
1438 #if defined CONFIG_PRINTK
1439
1440 /*
1441  * printk rate limiting, lifted from the networking subsystem.
1442  *
1443  * This enforces a rate limit: not more than 10 kernel messages
1444  * every 5s to make a denial-of-service attack impossible.
1445  */
1446 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1447
1448 int __printk_ratelimit(const char *func)
1449 {
1450         return ___ratelimit(&printk_ratelimit_state, func);
1451 }
1452 EXPORT_SYMBOL(__printk_ratelimit);
1453
1454 /**
1455  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1456  * @caller_jiffies: pointer to caller's state
1457  * @interval_msecs: minimum interval between prints
1458  *
1459  * printk_timed_ratelimit() returns true if more than @interval_msecs
1460  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1461  * returned true.
1462  */
1463 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1464                         unsigned int interval_msecs)
1465 {
1466         if (*caller_jiffies == 0
1467                         || !time_in_range(jiffies, *caller_jiffies,
1468                                         *caller_jiffies
1469                                         + msecs_to_jiffies(interval_msecs))) {
1470                 *caller_jiffies = jiffies;
1471                 return true;
1472         }
1473         return false;
1474 }
1475 EXPORT_SYMBOL(printk_timed_ratelimit);
1476
1477 static DEFINE_SPINLOCK(dump_list_lock);
1478 static LIST_HEAD(dump_list);
1479
1480 /**
1481  * kmsg_dump_register - register a kernel log dumper.
1482  * @dumper: pointer to the kmsg_dumper structure
1483  *
1484  * Adds a kernel log dumper to the system. The dump callback in the
1485  * structure will be called when the kernel oopses or panics and must be
1486  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1487  */
1488 int kmsg_dump_register(struct kmsg_dumper *dumper)
1489 {
1490         unsigned long flags;
1491         int err = -EBUSY;
1492
1493         /* The dump callback needs to be set */
1494         if (!dumper->dump)
1495                 return -EINVAL;
1496
1497         spin_lock_irqsave(&dump_list_lock, flags);
1498         /* Don't allow registering multiple times */
1499         if (!dumper->registered) {
1500                 dumper->registered = 1;
1501                 list_add_tail(&dumper->list, &dump_list);
1502                 err = 0;
1503         }
1504         spin_unlock_irqrestore(&dump_list_lock, flags);
1505
1506         return err;
1507 }
1508 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1509
1510 /**
1511  * kmsg_dump_unregister - unregister a kmsg dumper.
1512  * @dumper: pointer to the kmsg_dumper structure
1513  *
1514  * Removes a dump device from the system. Returns zero on success and
1515  * %-EINVAL otherwise.
1516  */
1517 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1518 {
1519         unsigned long flags;
1520         int err = -EINVAL;
1521
1522         spin_lock_irqsave(&dump_list_lock, flags);
1523         if (dumper->registered) {
1524                 dumper->registered = 0;
1525                 list_del(&dumper->list);
1526                 err = 0;
1527         }
1528         spin_unlock_irqrestore(&dump_list_lock, flags);
1529
1530         return err;
1531 }
1532 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1533
1534 static const char * const kmsg_reasons[] = {
1535         [KMSG_DUMP_OOPS]        = "oops",
1536         [KMSG_DUMP_PANIC]       = "panic",
1537         [KMSG_DUMP_KEXEC]       = "kexec",
1538 };
1539
1540 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1541 {
1542         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1543                 return "unknown";
1544
1545         return kmsg_reasons[reason];
1546 }
1547
1548 /**
1549  * kmsg_dump - dump kernel log to kernel message dumpers.
1550  * @reason: the reason (oops, panic etc) for dumping
1551  *
1552  * Iterate through each of the dump devices and call the oops/panic
1553  * callbacks with the log buffer.
1554  */
1555 void kmsg_dump(enum kmsg_dump_reason reason)
1556 {
1557         unsigned long end;
1558         unsigned chars;
1559         struct kmsg_dumper *dumper;
1560         const char *s1, *s2;
1561         unsigned long l1, l2;
1562         unsigned long flags;
1563
1564         /* Theoretically, the log could move on after we do this, but
1565            there's not a lot we can do about that. The new messages
1566            will overwrite the start of what we dump. */
1567         spin_lock_irqsave(&logbuf_lock, flags);
1568         end = log_end & LOG_BUF_MASK;
1569         chars = logged_chars;
1570         spin_unlock_irqrestore(&logbuf_lock, flags);
1571
1572         if (chars > end) {
1573                 s1 = log_buf + log_buf_len - chars + end;
1574                 l1 = chars - end;
1575
1576                 s2 = log_buf;
1577                 l2 = end;
1578         } else {
1579                 s1 = "";
1580                 l1 = 0;
1581
1582                 s2 = log_buf + end - chars;
1583                 l2 = chars;
1584         }
1585
1586         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1587                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1588                                 kmsg_to_str(reason));
1589                 return;
1590         }
1591         list_for_each_entry(dumper, &dump_list, list)
1592                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1593         spin_unlock_irqrestore(&dump_list_lock, flags);
1594 }
1595 #endif