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 #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 #include <linux/rculist.h>
  43
  44 #include <asm/uaccess.h>
  45
  46 /*
  47  * Architectures can override it:
  48  */
  49 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  50 {
  51 }
  52
  53 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  54
  55 /* printk's without a loglevel use this.. */
  56 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  57
  58 /* We show everything that is MORE important than this.. */
  59 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  60 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  61
  62 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  63
  64 int console_printk[4] = {
  65         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  66         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  67         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  68         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  69 };
  70
  71 /*
  72  * Low level drivers may need that to know if they can schedule in
  73  * their unblank() callback or not. So let's export it.
  74  */
  75 int oops_in_progress;
  76 EXPORT_SYMBOL(oops_in_progress);
  77
  78 /*
  79  * console_sem protects the console_drivers list, and also
  80  * provides serialisation for access to the entire console
  81  * driver system.
  82  */
  83 static DEFINE_SEMAPHORE(console_sem);
  84 struct console *console_drivers;
  85 EXPORT_SYMBOL_GPL(console_drivers);
  86
  87 /*
  88  * This is used for debugging the mess that is the VT code by
  89  * keeping track if we have the console semaphore held. It's
  90  * definitely not the perfect debug tool (we don't know if _WE_
  91  * hold it are racing, but it helps tracking those weird code
  92  * path in the console code where we end up in places I want
  93  * locked without the console sempahore held
  94  */
  95 static int console_locked, console_suspended;
  96
  97 /*
  98  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  99  * It is also used in interesting ways to provide interlocking in
 100  * console_unlock();.
 101  */
 102 static DEFINE_SPINLOCK(logbuf_lock);
 103
 104 #define LOG_BUF_MASK (log_buf_len-1)
 105 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 106
 107 /*
 108  * The indices into log_buf are not constrained to log_buf_len - they
 109  * must be masked before subscripting
 110  */
 111 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 112 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 113 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 114
 115 /*
 116  *      Array of consoles built from command line options (console=)
 117  */
 118 struct console_cmdline
 119 {
 120         char    name[8];                        /* Name of the driver       */
 121         int     index;                          /* Minor dev. to use        */
 122         char    *options;                       /* Options for the driver   */
 123 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 124         char    *brl_options;                   /* Options for braille driver */
 125 #endif
 126 };
 127
 128 #define MAX_CMDLINECONSOLES 8
 129
 130 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 131 static int selected_console = -1;
 132 static int preferred_console = -1;
 133 int console_set_on_cmdline;
 134 EXPORT_SYMBOL(console_set_on_cmdline);
 135
 136 /* Flag: console code may call schedule() */
 137 static int console_may_schedule;
 138
 139 #ifdef CONFIG_PRINTK
 140
 141 static char __log_buf[__LOG_BUF_LEN];
 142 static char *log_buf = __log_buf;
 143 static int log_buf_len = __LOG_BUF_LEN;
 144 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 145 static int saved_console_loglevel = -1;
 146
 147 #ifdef CONFIG_KEXEC
 148 /*
 149  * This appends the listed symbols to /proc/vmcoreinfo
 150  *
 151  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 152  * obtain access to symbols that are otherwise very difficult to locate.  These
 153  * symbols are specifically used so that utilities can access and extract the
 154  * dmesg log from a vmcore file after a crash.
 155  */
 156 void log_buf_kexec_setup(void)
 157 {
 158         VMCOREINFO_SYMBOL(log_buf);
 159         VMCOREINFO_SYMBOL(log_end);
 160         VMCOREINFO_SYMBOL(log_buf_len);
 161         VMCOREINFO_SYMBOL(logged_chars);
 162 }
 163 #endif
 164
 165 static int __init log_buf_len_setup(char *str)
 166 {
 167         unsigned size = memparse(str, &str);
 168         unsigned long flags;
 169
 170         if (size)
 171                 size = roundup_pow_of_two(size);
 172         if (size > log_buf_len) {
 173                 unsigned start, dest_idx, offset;
 174                 char *new_log_buf;
 175
 176                 new_log_buf = alloc_bootmem(size);
 177                 if (!new_log_buf) {
 178                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 179                         goto out;
 180                 }
 181
 182                 spin_lock_irqsave(&logbuf_lock, flags);
 183                 log_buf_len = size;
 184                 log_buf = new_log_buf;
 185
 186                 offset = start = min(con_start, log_start);
 187                 dest_idx = 0;
 188                 while (start != log_end) {
 189                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 190                         start++;
 191                         dest_idx++;
 192                 }
 193                 log_start -= offset;
 194                 con_start -= offset;
 195                 log_end -= offset;
 196                 spin_unlock_irqrestore(&logbuf_lock, flags);
 197
 198                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 199         }
 200 out:
 201         return 1;
 202 }
 203
 204 __setup("log_buf_len=", log_buf_len_setup);
 205
 206 #ifdef CONFIG_BOOT_PRINTK_DELAY
 207
 208 static int boot_delay; /* msecs delay after each printk during bootup */
 209 static unsigned long long loops_per_msec;       /* based on boot_delay */
 210
 211 static int __init boot_delay_setup(char *str)
 212 {
 213         unsigned long lpj;
 214
 215         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 216         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 217
 218         get_option(&str, &boot_delay);
 219         if (boot_delay > 10 * 1000)
 220                 boot_delay = 0;
 221
 222         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 223                 "HZ: %d, loops_per_msec: %llu\n",
 224                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
 225         return 1;
 226 }
 227 __setup("boot_delay=", boot_delay_setup);
 228
 229 static void boot_delay_msec(void)
 230 {
 231         unsigned long long k;
 232         unsigned long timeout;
 233
 234         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 235                 return;
 236
 237         k = (unsigned long long)loops_per_msec * boot_delay;
 238
 239         timeout = jiffies + msecs_to_jiffies(boot_delay);
 240         while (k) {
 241                 k--;
 242                 cpu_relax();
 243                 /*
 244                  * use (volatile) jiffies to prevent
 245                  * compiler reduction; loop termination via jiffies
 246                  * is secondary and may or may not happen.
 247                  */
 248                 if (time_after(jiffies, timeout))
 249                         break;
 250                 touch_nmi_watchdog();
 251         }
 252 }
 253 #else
 254 static inline void boot_delay_msec(void)
 255 {
 256 }
 257 #endif
 258
 259 #ifdef CONFIG_SECURITY_DMESG_RESTRICT
 260 int dmesg_restrict = 1;
 261 #else
 262 int dmesg_restrict;
 263 #endif
 264
 265 static int syslog_action_restricted(int type)
 266 {
 267         if (dmesg_restrict)
 268                 return 1;
 269         /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
 270         return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
 271 }
 272
 273 static int check_syslog_permissions(int type, bool from_file)
 274 {
 275         /*
 276          * If this is from /proc/kmsg and we've already opened it, then we've
 277          * already done the capabilities checks at open time.
 278          */
 279         if (from_file && type != SYSLOG_ACTION_OPEN)
 280                 return 0;
 281
 282         if (syslog_action_restricted(type)) {
 283                 if (capable(CAP_SYSLOG))
 284                         return 0;
 285                 /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
 286                 if (capable(CAP_SYS_ADMIN)) {
 287                         WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
 288                                  "but no CAP_SYSLOG (deprecated).\n");
 289                         return 0;
 290                 }
 291                 return -EPERM;
 292         }
 293         return 0;
 294 }
 295
 296 int do_syslog(int type, char __user *buf, int len, bool from_file)
 297 {
 298         unsigned i, j, limit, count;
 299         int do_clear = 0;
 300         char c;
 301         int error;
 302
 303         error = check_syslog_permissions(type, from_file);
 304         if (error)
 305                 goto out;
 306
 307         error = security_syslog(type);
 308         if (error)
 309                 return error;
 310
 311         switch (type) {
 312         case SYSLOG_ACTION_CLOSE:       /* Close log */
 313                 break;
 314         case SYSLOG_ACTION_OPEN:        /* Open log */
 315                 break;
 316         case SYSLOG_ACTION_READ:        /* Read from log */
 317                 error = -EINVAL;
 318                 if (!buf || len < 0)
 319                         goto out;
 320                 error = 0;
 321                 if (!len)
 322                         goto out;
 323                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 324                         error = -EFAULT;
 325                         goto out;
 326                 }
 327                 error = wait_event_interruptible(log_wait,
 328                                                         (log_start - log_end));
 329                 if (error)
 330                         goto out;
 331                 i = 0;
 332                 spin_lock_irq(&logbuf_lock);
 333                 while (!error && (log_start != log_end) && i < len) {
 334                         c = LOG_BUF(log_start);
 335                         log_start++;
 336                         spin_unlock_irq(&logbuf_lock);
 337                         error = __put_user(c,buf);
 338                         buf++;
 339                         i++;
 340                         cond_resched();
 341                         spin_lock_irq(&logbuf_lock);
 342                 }
 343                 spin_unlock_irq(&logbuf_lock);
 344                 if (!error)
 345                         error = i;
 346                 break;
 347         /* Read/clear last kernel messages */
 348         case SYSLOG_ACTION_READ_CLEAR:
 349                 do_clear = 1;
 350                 /* FALL THRU */
 351         /* Read last kernel messages */
 352         case SYSLOG_ACTION_READ_ALL:
 353                 error = -EINVAL;
 354                 if (!buf || len < 0)
 355                         goto out;
 356                 error = 0;
 357                 if (!len)
 358                         goto out;
 359                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 360                         error = -EFAULT;
 361                         goto out;
 362                 }
 363                 count = len;
 364                 if (count > log_buf_len)
 365                         count = log_buf_len;
 366                 spin_lock_irq(&logbuf_lock);
 367                 if (count > logged_chars)
 368                         count = logged_chars;
 369                 if (do_clear)
 370                         logged_chars = 0;
 371                 limit = log_end;
 372                 /*
 373                  * __put_user() could sleep, and while we sleep
 374                  * printk() could overwrite the messages
 375                  * we try to copy to user space. Therefore
 376                  * the messages are copied in reverse. <manfreds>
 377                  */
 378                 for (i = 0; i < count && !error; i++) {
 379                         j = limit-1-i;
 380                         if (j + log_buf_len < log_end)
 381                                 break;
 382                         c = LOG_BUF(j);
 383                         spin_unlock_irq(&logbuf_lock);
 384                         error = __put_user(c,&buf[count-1-i]);
 385                         cond_resched();
 386                         spin_lock_irq(&logbuf_lock);
 387                 }
 388                 spin_unlock_irq(&logbuf_lock);
 389                 if (error)
 390                         break;
 391                 error = i;
 392                 if (i != count) {
 393                         int offset = count-error;
 394                         /* buffer overflow during copy, correct user buffer. */
 395                         for (i = 0; i < error; i++) {
 396                                 if (__get_user(c,&buf[i+offset]) ||
 397                                     __put_user(c,&buf[i])) {
 398                                         error = -EFAULT;
 399                                         break;
 400                                 }
 401                                 cond_resched();
 402                         }
 403                 }
 404                 break;
 405         /* Clear ring buffer */
 406         case SYSLOG_ACTION_CLEAR:
 407                 logged_chars = 0;
 408                 break;
 409         /* Disable logging to console */
 410         case SYSLOG_ACTION_CONSOLE_OFF:
 411                 if (saved_console_loglevel == -1)
 412                         saved_console_loglevel = console_loglevel;
 413                 console_loglevel = minimum_console_loglevel;
 414                 break;
 415         /* Enable logging to console */
 416         case SYSLOG_ACTION_CONSOLE_ON:
 417                 if (saved_console_loglevel != -1) {
 418                         console_loglevel = saved_console_loglevel;
 419                         saved_console_loglevel = -1;
 420                 }
 421                 break;
 422         /* Set level of messages printed to console */
 423         case SYSLOG_ACTION_CONSOLE_LEVEL:
 424                 error = -EINVAL;
 425                 if (len < 1 || len > 8)
 426                         goto out;
 427                 if (len < minimum_console_loglevel)
 428                         len = minimum_console_loglevel;
 429                 console_loglevel = len;
 430                 /* Implicitly re-enable logging to console */
 431                 saved_console_loglevel = -1;
 432                 error = 0;
 433                 break;
 434         /* Number of chars in the log buffer */
 435         case SYSLOG_ACTION_SIZE_UNREAD:
 436                 error = log_end - log_start;
 437                 break;
 438         /* Size of the log buffer */
 439         case SYSLOG_ACTION_SIZE_BUFFER:
 440                 error = log_buf_len;
 441                 break;
 442         default:
 443                 error = -EINVAL;
 444                 break;
 445         }
 446 out:
 447         return error;
 448 }
 449
 450 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 451 {
 452         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 453 }
 454
 455 #ifdef  CONFIG_KGDB_KDB
 456 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
 457  * uses locks so it cannot be used during debugging.  Just tell kdb
 458  * where the start and end of the physical and logical logs are.  This
 459  * is equivalent to do_syslog(3).
 460  */
 461 void kdb_syslog_data(char *syslog_data[4])
 462 {
 463         syslog_data[0] = log_buf;
 464         syslog_data[1] = log_buf + log_buf_len;
 465         syslog_data[2] = log_buf + log_end -
 466                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
 467         syslog_data[3] = log_buf + log_end;
 468 }
 469 #endif  /* CONFIG_KGDB_KDB */
 470
 471 /*
 472  * Call the console drivers on a range of log_buf
 473  */
 474 static void __call_console_drivers(unsigned start, unsigned end)
 475 {
 476         struct console *con;
 477
 478         for_each_console(con) {
 479                 if ((con->flags & CON_ENABLED) && con->write &&
 480                                 (cpu_online(smp_processor_id()) ||
 481                                 (con->flags & CON_ANYTIME)))
 482                         con->write(con, &LOG_BUF(start), end - start);
 483         }
 484 }
 485
 486 static int __read_mostly ignore_loglevel;
 487
 488 static int __init ignore_loglevel_setup(char *str)
 489 {
 490         ignore_loglevel = 1;
 491         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 492
 493         return 0;
 494 }
 495
 496 early_param("ignore_loglevel", ignore_loglevel_setup);
 497
 498 /*
 499  * Write out chars from start to end - 1 inclusive
 500  */
 501 static void _call_console_drivers(unsigned start,
 502                                 unsigned end, int msg_log_level)
 503 {
 504         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 505                         console_drivers && start != end) {
 506                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 507                         /* wrapped write */
 508                         __call_console_drivers(start & LOG_BUF_MASK,
 509                                                 log_buf_len);
 510                         __call_console_drivers(0, end & LOG_BUF_MASK);
 511                 } else {
 512                         __call_console_drivers(start, end);
 513                 }
 514         }
 515 }
 516
 517 /*
 518  * Call the console drivers, asking them to write out
 519  * log_buf[start] to log_buf[end - 1].
 520  * The console_lock must be held.
 521  */
 522 static void call_console_drivers(unsigned start, unsigned end)
 523 {
 524         unsigned cur_index, start_print;
 525         static int msg_level = -1;
 526
 527         BUG_ON(((int)(start - end)) > 0);
 528
 529         cur_index = start;
 530         start_print = start;
 531         while (cur_index != end) {
 532                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 533                                 LOG_BUF(cur_index + 0) == '<' &&
 534                                 LOG_BUF(cur_index + 1) >= '0' &&
 535                                 LOG_BUF(cur_index + 1) <= '7' &&
 536                                 LOG_BUF(cur_index + 2) == '>') {
 537                         msg_level = LOG_BUF(cur_index + 1) - '0';
 538                         cur_index += 3;
 539                         start_print = cur_index;
 540                 }
 541                 while (cur_index != end) {
 542                         char c = LOG_BUF(cur_index);
 543
 544                         cur_index++;
 545                         if (c == '\n') {
 546                                 if (msg_level < 0) {
 547                                         /*
 548                                          * printk() has already given us loglevel tags in
 549                                          * the buffer.  This code is here in case the
 550                                          * log buffer has wrapped right round and scribbled
 551                                          * on those tags
 552                                          */
 553                                         msg_level = default_message_loglevel;
 554                                 }
 555                                 _call_console_drivers(start_print, cur_index, msg_level);
 556                                 msg_level = -1;
 557                                 start_print = cur_index;
 558                                 break;
 559                         }
 560                 }
 561         }
 562         _call_console_drivers(start_print, end, msg_level);
 563 }
 564
 565 static void emit_log_char(char c)
 566 {
 567         LOG_BUF(log_end) = c;
 568         log_end++;
 569         if (log_end - log_start > log_buf_len)
 570                 log_start = log_end - log_buf_len;
 571         if (log_end - con_start > log_buf_len)
 572                 con_start = log_end - log_buf_len;
 573         if (logged_chars < log_buf_len)
 574                 logged_chars++;
 575 }
 576
 577 /*
 578  * Zap console related locks when oopsing. Only zap at most once
 579  * every 10 seconds, to leave time for slow consoles to print a
 580  * full oops.
 581  */
 582 static void zap_locks(void)
 583 {
 584         static unsigned long oops_timestamp;
 585
 586         if (time_after_eq(jiffies, oops_timestamp) &&
 587                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 588                 return;
 589
 590         oops_timestamp = jiffies;
 591
 592         /* If a crash is occurring, make sure we can't deadlock */
 593         spin_lock_init(&logbuf_lock);
 594         /* And make sure that we print immediately */
 595         sema_init(&console_sem, 1);
 596 }
 597
 598 #if defined(CONFIG_PRINTK_TIME)
 599 static int printk_time = 1;
 600 #else
 601 static int printk_time = 0;
 602 #endif
 603 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 604
 605 /* Check if we have any console registered that can be called early in boot. */
 606 static int have_callable_console(void)
 607 {
 608         struct console *con;
 609
 610         for_each_console(con)
 611                 if (con->flags & CON_ANYTIME)
 612                         return 1;
 613
 614         return 0;
 615 }
 616
 617 /**
 618  * printk - print a kernel message
 619  * @fmt: format string
 620  *
 621  * This is printk().  It can be called from any context.  We want it to work.
 622  *
 623  * We try to grab the console_lock.  If we succeed, it's easy - we log the output and
 624  * call the console drivers.  If we fail to get the semaphore we place the output
 625  * into the log buffer and return.  The current holder of the console_sem will
 626  * notice the new output in console_unlock(); and will send it to the
 627  * consoles before releasing the lock.
 628  *
 629  * One effect of this deferred printing is that code which calls printk() and
 630  * then changes console_loglevel may break. This is because console_loglevel
 631  * is inspected when the actual printing occurs.
 632  *
 633  * See also:
 634  * printf(3)
 635  *
 636  * See the vsnprintf() documentation for format string extensions over C99.
 637  */
 638
 639 asmlinkage int printk(const char *fmt, ...)
 640 {
 641         va_list args;
 642         int r;
 643
 644 #ifdef CONFIG_KGDB_KDB
 645         if (unlikely(kdb_trap_printk)) {
 646                 va_start(args, fmt);
 647                 r = vkdb_printf(fmt, args);
 648                 va_end(args);
 649                 return r;
 650         }
 651 #endif
 652         va_start(args, fmt);
 653         r = vprintk(fmt, args);
 654         va_end(args);
 655
 656         return r;
 657 }
 658
 659 /* cpu currently holding logbuf_lock */
 660 static volatile unsigned int printk_cpu = UINT_MAX;
 661
 662 /*
 663  * Can we actually use the console at this time on this cpu?
 664  *
 665  * Console drivers may assume that per-cpu resources have
 666  * been allocated. So unless they're explicitly marked as
 667  * being able to cope (CON_ANYTIME) don't call them until
 668  * this CPU is officially up.
 669  */
 670 static inline int can_use_console(unsigned int cpu)
 671 {
 672         return cpu_online(cpu) || have_callable_console();
 673 }
 674
 675 /*
 676  * Try to get console ownership to actually show the kernel
 677  * messages from a 'printk'. Return true (and with the
 678  * console_lock held, and 'console_locked' set) if it
 679  * is successful, false otherwise.
 680  *
 681  * This gets called with the 'logbuf_lock' spinlock held and
 682  * interrupts disabled. It should return with 'lockbuf_lock'
 683  * released but interrupts still disabled.
 684  */
 685 static int console_trylock_for_printk(unsigned int cpu)
 686         __releases(&logbuf_lock)
 687 {
 688         int retval = 0;
 689
 690         if (console_trylock()) {
 691                 retval = 1;
 692
 693                 /*
 694                  * If we can't use the console, we need to release
 695                  * the console semaphore by hand to avoid flushing
 696                  * the buffer. We need to hold the console semaphore
 697                  * in order to do this test safely.
 698                  */
 699                 if (!can_use_console(cpu)) {
 700                         console_locked = 0;
 701                         up(&console_sem);
 702                         retval = 0;
 703                 }
 704         }
 705         printk_cpu = UINT_MAX;
 706         spin_unlock(&logbuf_lock);
 707         return retval;
 708 }
 709 static const char recursion_bug_msg [] =
 710                 KERN_CRIT "BUG: recent printk recursion!\n";
 711 static int recursion_bug;
 712 static int new_text_line = 1;
 713 static char printk_buf[1024];
 714
 715 int printk_delay_msec __read_mostly;
 716
 717 static inline void printk_delay(void)
 718 {
 719         if (unlikely(printk_delay_msec)) {
 720                 int m = printk_delay_msec;
 721
 722                 while (m--) {
 723                         mdelay(1);
 724                         touch_nmi_watchdog();
 725                 }
 726         }
 727 }
 728
 729 asmlinkage int vprintk(const char *fmt, va_list args)
 730 {
 731         int printed_len = 0;
 732         int current_log_level = default_message_loglevel;
 733         unsigned long flags;
 734         int this_cpu;
 735         char *p;
 736
 737         boot_delay_msec();
 738         printk_delay();
 739
 740         preempt_disable();
 741         /* This stops the holder of console_sem just where we want him */
 742         raw_local_irq_save(flags);
 743         this_cpu = smp_processor_id();
 744
 745         /*
 746          * Ouch, printk recursed into itself!
 747          */
 748         if (unlikely(printk_cpu == this_cpu)) {
 749                 /*
 750                  * If a crash is occurring during printk() on this CPU,
 751                  * then try to get the crash message out but make sure
 752                  * we can't deadlock. Otherwise just return to avoid the
 753                  * recursion and return - but flag the recursion so that
 754                  * it can be printed at the next appropriate moment:
 755                  */
 756                 if (!oops_in_progress) {
 757                         recursion_bug = 1;
 758                         goto out_restore_irqs;
 759                 }
 760                 zap_locks();
 761         }
 762
 763         lockdep_off();
 764         spin_lock(&logbuf_lock);
 765         printk_cpu = this_cpu;
 766
 767         if (recursion_bug) {
 768                 recursion_bug = 0;
 769                 strcpy(printk_buf, recursion_bug_msg);
 770                 printed_len = strlen(recursion_bug_msg);
 771         }
 772         /* Emit the output into the temporary buffer */
 773         printed_len += vscnprintf(printk_buf + printed_len,
 774                                   sizeof(printk_buf) - printed_len, fmt, args);
 775
 776
 777         p = printk_buf;
 778
 779         /* Do we have a loglevel in the string? */
 780         if (p[0] == '<') {
 781                 unsigned char c = p[1];
 782                 if (c && p[2] == '>') {
 783                         switch (c) {
 784                         case '0' ... '7': /* loglevel */
 785                                 current_log_level = c - '0';
 786                         /* Fallthrough - make sure we're on a new line */
 787                         case 'd': /* KERN_DEFAULT */
 788                                 if (!new_text_line) {
 789                                         emit_log_char('\n');
 790                                         new_text_line = 1;
 791                                 }
 792                         /* Fallthrough - skip the loglevel */
 793                         case 'c': /* KERN_CONT */
 794                                 p += 3;
 795                                 break;
 796                         }
 797                 }
 798         }
 799
 800         /*
 801          * Copy the output into log_buf.  If the caller didn't provide
 802          * appropriate log level tags, we insert them here
 803          */
 804         for ( ; *p; p++) {
 805                 if (new_text_line) {
 806                         /* Always output the token */
 807                         emit_log_char('<');
 808                         emit_log_char(current_log_level + '0');
 809                         emit_log_char('>');
 810                         printed_len += 3;
 811                         new_text_line = 0;
 812
 813                         if (printk_time) {
 814                                 /* Follow the token with the time */
 815                                 char tbuf[50], *tp;
 816                                 unsigned tlen;
 817                                 unsigned long long t;
 818                                 unsigned long nanosec_rem;
 819
 820                                 t = cpu_clock(printk_cpu);
 821                                 nanosec_rem = do_div(t, 1000000000);
 822                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 823                                                 (unsigned long) t,
 824                                                 nanosec_rem / 1000);
 825
 826                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 827                                         emit_log_char(*tp);
 828                                 printed_len += tlen;
 829                         }
 830
 831                         if (!*p)
 832                                 break;
 833                 }
 834
 835                 emit_log_char(*p);
 836                 if (*p == '\n')
 837                         new_text_line = 1;
 838         }
 839
 840         /*
 841          * Try to acquire and then immediately release the
 842          * console semaphore. The release will do all the
 843          * actual magic (print out buffers, wake up klogd,
 844          * etc).
 845          *
 846          * The console_trylock_for_printk() function
 847          * will release 'logbuf_lock' regardless of whether it
 848          * actually gets the semaphore or not.
 849          */
 850         if (console_trylock_for_printk(this_cpu))
 851                 console_unlock();
 852
 853         lockdep_on();
 854 out_restore_irqs:
 855         raw_local_irq_restore(flags);
 856
 857         preempt_enable();
 858         return printed_len;
 859 }
 860 EXPORT_SYMBOL(printk);
 861 EXPORT_SYMBOL(vprintk);
 862
 863 #else
 864
 865 static void call_console_drivers(unsigned start, unsigned end)
 866 {
 867 }
 868
 869 #endif
 870
 871 static int __add_preferred_console(char *name, int idx, char *options,
 872                                    char *brl_options)
 873 {
 874         struct console_cmdline *c;
 875         int i;
 876
 877         /*
 878          *      See if this tty is not yet registered, and
 879          *      if we have a slot free.
 880          */
 881         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 882                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 883                           console_cmdline[i].index == idx) {
 884                                 if (!brl_options)
 885                                         selected_console = i;
 886                                 return 0;
 887                 }
 888         if (i == MAX_CMDLINECONSOLES)
 889                 return -E2BIG;
 890         if (!brl_options)
 891                 selected_console = i;
 892         c = &console_cmdline[i];
 893         strlcpy(c->name, name, sizeof(c->name));
 894         c->options = options;
 895 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 896         c->brl_options = brl_options;
 897 #endif
 898         c->index = idx;
 899         return 0;
 900 }
 901 /*
 902  * Set up a list of consoles.  Called from init/main.c
 903  */
 904 static int __init console_setup(char *str)
 905 {
 906         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 907         char *s, *options, *brl_options = NULL;
 908         int idx;
 909
 910 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 911         if (!memcmp(str, "brl,", 4)) {
 912                 brl_options = "";
 913                 str += 4;
 914         } else if (!memcmp(str, "brl=", 4)) {
 915                 brl_options = str + 4;
 916                 str = strchr(brl_options, ',');
 917                 if (!str) {
 918                         printk(KERN_ERR "need port name after brl=\n");
 919                         return 1;
 920                 }
 921                 *(str++) = 0;
 922         }
 923 #endif
 924
 925         /*
 926          * Decode str into name, index, options.
 927          */
 928         if (str[0] >= '0' && str[0] <= '9') {
 929                 strcpy(buf, "ttyS");
 930                 strncpy(buf + 4, str, sizeof(buf) - 5);
 931         } else {
 932                 strncpy(buf, str, sizeof(buf) - 1);
 933         }
 934         buf[sizeof(buf) - 1] = 0;
 935         if ((options = strchr(str, ',')) != NULL)
 936                 *(options++) = 0;
 937 #ifdef __sparc__
 938         if (!strcmp(str, "ttya"))
 939                 strcpy(buf, "ttyS0");
 940         if (!strcmp(str, "ttyb"))
 941                 strcpy(buf, "ttyS1");
 942 #endif
 943         for (s = buf; *s; s++)
 944                 if ((*s >= '0' && *s <= '9') || *s == ',')
 945                         break;
 946         idx = simple_strtoul(s, NULL, 10);
 947         *s = 0;
 948
 949         __add_preferred_console(buf, idx, options, brl_options);
 950         console_set_on_cmdline = 1;
 951         return 1;
 952 }
 953 __setup("console=", console_setup);
 954
 955 /**
 956  * add_preferred_console - add a device to the list of preferred consoles.
 957  * @name: device name
 958  * @idx: device index
 959  * @options: options for this console
 960  *
 961  * The last preferred console added will be used for kernel messages
 962  * and stdin/out/err for init.  Normally this is used by console_setup
 963  * above to handle user-supplied console arguments; however it can also
 964  * be used by arch-specific code either to override the user or more
 965  * commonly to provide a default console (ie from PROM variables) when
 966  * the user has not supplied one.
 967  */
 968 int add_preferred_console(char *name, int idx, char *options)
 969 {
 970         return __add_preferred_console(name, idx, options, NULL);
 971 }
 972
 973 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 974 {
 975         struct console_cmdline *c;
 976         int i;
 977
 978         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 979                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 980                           console_cmdline[i].index == idx) {
 981                                 c = &console_cmdline[i];
 982                                 strlcpy(c->name, name_new, sizeof(c->name));
 983                                 c->name[sizeof(c->name) - 1] = 0;
 984                                 c->options = options;
 985                                 c->index = idx_new;
 986                                 return i;
 987                 }
 988         /* not found */
 989         return -1;
 990 }
 991
 992 int console_suspend_enabled = 1;
 993 EXPORT_SYMBOL(console_suspend_enabled);
 994
 995 static int __init console_suspend_disable(char *str)
 996 {
 997         console_suspend_enabled = 0;
 998         return 1;
 999 }
1000 __setup("no_console_suspend", console_suspend_disable);
1001
1002 /**
1003  * suspend_console - suspend the console subsystem
1004  *
1005  * This disables printk() while we go into suspend states
1006  */
1007 void suspend_console(void)
1008 {
1009         if (!console_suspend_enabled)
1010                 return;
1011         printk("Suspending console(s) (use no_console_suspend to debug)\n");
1012         console_lock();
1013         console_suspended = 1;
1014         up(&console_sem);
1015 }
1016
1017 void resume_console(void)
1018 {
1019         if (!console_suspend_enabled)
1020                 return;
1021         down(&console_sem);
1022         console_suspended = 0;
1023         console_unlock();
1024 }
1025
1026 /**
1027  * console_cpu_notify - print deferred console messages after CPU hotplug
1028  * @self: notifier struct
1029  * @action: CPU hotplug event
1030  * @hcpu: unused
1031  *
1032  * If printk() is called from a CPU that is not online yet, the messages
1033  * will be spooled but will not show up on the console.  This function is
1034  * called when a new CPU comes online (or fails to come up), and ensures
1035  * that any such output gets printed.
1036  */
1037 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1038         unsigned long action, void *hcpu)
1039 {
1040         switch (action) {
1041         case CPU_ONLINE:
1042         case CPU_DEAD:
1043         case CPU_DYING:
1044         case CPU_DOWN_FAILED:
1045         case CPU_UP_CANCELED:
1046                 console_lock();
1047                 console_unlock();
1048         }
1049         return NOTIFY_OK;
1050 }
1051
1052 /**
1053  * console_lock - lock the console system for exclusive use.
1054  *
1055  * Acquires a lock which guarantees that the caller has
1056  * exclusive access to the console system and the console_drivers list.
1057  *
1058  * Can sleep, returns nothing.
1059  */
1060 void console_lock(void)
1061 {
1062         BUG_ON(in_interrupt());
1063         down(&console_sem);
1064         if (console_suspended)
1065                 return;
1066         console_locked = 1;
1067         console_may_schedule = 1;
1068 }
1069 EXPORT_SYMBOL(console_lock);
1070
1071 /**
1072  * console_trylock - try to lock the console system for exclusive use.
1073  *
1074  * Tried to acquire a lock which guarantees that the caller has
1075  * exclusive access to the console system and the console_drivers list.
1076  *
1077  * returns 1 on success, and 0 on failure to acquire the lock.
1078  */
1079 int console_trylock(void)
1080 {
1081         if (down_trylock(&console_sem))
1082                 return 0;
1083         if (console_suspended) {
1084                 up(&console_sem);
1085                 return 0;
1086         }
1087         console_locked = 1;
1088         console_may_schedule = 0;
1089         return 1;
1090 }
1091 EXPORT_SYMBOL(console_trylock);
1092
1093 int is_console_locked(void)
1094 {
1095         return console_locked;
1096 }
1097
1098 static DEFINE_PER_CPU(int, printk_pending);
1099
1100 void printk_tick(void)
1101 {
1102         if (__this_cpu_read(printk_pending)) {
1103                 __this_cpu_write(printk_pending, 0);
1104                 wake_up_interruptible(&log_wait);
1105         }
1106 }
1107
1108 int printk_needs_cpu(int cpu)
1109 {
1110         if (cpu_is_offline(cpu))
1111                 printk_tick();
1112         return __this_cpu_read(printk_pending);
1113 }
1114
1115 void wake_up_klogd(void)
1116 {
1117         if (waitqueue_active(&log_wait))
1118                 this_cpu_write(printk_pending, 1);
1119 }
1120
1121 /**
1122  * console_unlock - unlock the console system
1123  *
1124  * Releases the console_lock which the caller holds on the console system
1125  * and the console driver list.
1126  *
1127  * While the console_lock was held, console output may have been buffered
1128  * by printk().  If this is the case, console_unlock(); emits
1129  * the output prior to releasing the lock.
1130  *
1131  * If there is output waiting for klogd, we wake it up.
1132  *
1133  * console_unlock(); may be called from any context.
1134  */
1135 void console_unlock(void)
1136 {
1137         unsigned long flags;
1138         unsigned _con_start, _log_end;
1139         unsigned wake_klogd = 0;
1140
1141         if (console_suspended) {
1142                 up(&console_sem);
1143                 return;
1144         }
1145
1146         console_may_schedule = 0;
1147
1148         for ( ; ; ) {
1149                 spin_lock_irqsave(&logbuf_lock, flags);
1150                 wake_klogd |= log_start - log_end;
1151                 if (con_start == log_end)
1152                         break;                  /* Nothing to print */
1153                 _con_start = con_start;
1154                 _log_end = log_end;
1155                 con_start = log_end;            /* Flush */
1156                 spin_unlock(&logbuf_lock);
1157                 stop_critical_timings();        /* don't trace print latency */
1158                 call_console_drivers(_con_start, _log_end);
1159                 start_critical_timings();
1160                 local_irq_restore(flags);
1161         }
1162         console_locked = 0;
1163         up(&console_sem);
1164         spin_unlock_irqrestore(&logbuf_lock, flags);
1165         if (wake_klogd)
1166                 wake_up_klogd();
1167 }
1168 EXPORT_SYMBOL(console_unlock);
1169
1170 /**
1171  * console_conditional_schedule - yield the CPU if required
1172  *
1173  * If the console code is currently allowed to sleep, and
1174  * if this CPU should yield the CPU to another task, do
1175  * so here.
1176  *
1177  * Must be called within console_lock();.
1178  */
1179 void __sched console_conditional_schedule(void)
1180 {
1181         if (console_may_schedule)
1182                 cond_resched();
1183 }
1184 EXPORT_SYMBOL(console_conditional_schedule);
1185
1186 void console_unblank(void)
1187 {
1188         struct console *c;
1189
1190         /*
1191          * console_unblank can no longer be called in interrupt context unless
1192          * oops_in_progress is set to 1..
1193          */
1194         if (oops_in_progress) {
1195                 if (down_trylock(&console_sem) != 0)
1196                         return;
1197         } else
1198                 console_lock();
1199
1200         console_locked = 1;
1201         console_may_schedule = 0;
1202         for_each_console(c)
1203                 if ((c->flags & CON_ENABLED) && c->unblank)
1204                         c->unblank();
1205         console_unlock();
1206 }
1207
1208 /*
1209  * Return the console tty driver structure and its associated index
1210  */
1211 struct tty_driver *console_device(int *index)
1212 {
1213         struct console *c;
1214         struct tty_driver *driver = NULL;
1215
1216         console_lock();
1217         for_each_console(c) {
1218                 if (!c->device)
1219                         continue;
1220                 driver = c->device(c, index);
1221                 if (driver)
1222                         break;
1223         }
1224         console_unlock();
1225         return driver;
1226 }
1227
1228 /*
1229  * Prevent further output on the passed console device so that (for example)
1230  * serial drivers can disable console output before suspending a port, and can
1231  * re-enable output afterwards.
1232  */
1233 void console_stop(struct console *console)
1234 {
1235         console_lock();
1236         console->flags &= ~CON_ENABLED;
1237         console_unlock();
1238 }
1239 EXPORT_SYMBOL(console_stop);
1240
1241 void console_start(struct console *console)
1242 {
1243         console_lock();
1244         console->flags |= CON_ENABLED;
1245         console_unlock();
1246 }
1247 EXPORT_SYMBOL(console_start);
1248
1249 /*
1250  * The console driver calls this routine during kernel initialization
1251  * to register the console printing procedure with printk() and to
1252  * print any messages that were printed by the kernel before the
1253  * console driver was initialized.
1254  *
1255  * This can happen pretty early during the boot process (because of
1256  * early_printk) - sometimes before setup_arch() completes - be careful
1257  * of what kernel features are used - they may not be initialised yet.
1258  *
1259  * There are two types of consoles - bootconsoles (early_printk) and
1260  * "real" consoles (everything which is not a bootconsole) which are
1261  * handled differently.
1262  *  - Any number of bootconsoles can be registered at any time.
1263  *  - As soon as a "real" console is registered, all bootconsoles
1264  *    will be unregistered automatically.
1265  *  - Once a "real" console is registered, any attempt to register a
1266  *    bootconsoles will be rejected
1267  */
1268 void register_console(struct console *newcon)
1269 {
1270         int i;
1271         unsigned long flags;
1272         struct console *bcon = NULL;
1273
1274         /*
1275          * before we register a new CON_BOOT console, make sure we don't
1276          * already have a valid console
1277          */
1278         if (console_drivers && newcon->flags & CON_BOOT) {
1279                 /* find the last or real console */
1280                 for_each_console(bcon) {
1281                         if (!(bcon->flags & CON_BOOT)) {
1282                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1283                                         newcon->name, newcon->index);
1284                                 return;
1285                         }
1286                 }
1287         }
1288
1289         if (console_drivers && console_drivers->flags & CON_BOOT)
1290                 bcon = console_drivers;
1291
1292         if (preferred_console < 0 || bcon || !console_drivers)
1293                 preferred_console = selected_console;
1294
1295         if (newcon->early_setup)
1296                 newcon->early_setup();
1297
1298         /*
1299          *      See if we want to use this console driver. If we
1300          *      didn't select a console we take the first one
1301          *      that registers here.
1302          */
1303         if (preferred_console < 0) {
1304                 if (newcon->index < 0)
1305                         newcon->index = 0;
1306                 if (newcon->setup == NULL ||
1307                     newcon->setup(newcon, NULL) == 0) {
1308                         newcon->flags |= CON_ENABLED;
1309                         if (newcon->device) {
1310                                 newcon->flags |= CON_CONSDEV;
1311                                 preferred_console = 0;
1312                         }
1313                 }
1314         }
1315
1316         /*
1317          *      See if this console matches one we selected on
1318          *      the command line.
1319          */
1320         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1321                         i++) {
1322                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1323                         continue;
1324                 if (newcon->index >= 0 &&
1325                     newcon->index != console_cmdline[i].index)
1326                         continue;
1327                 if (newcon->index < 0)
1328                         newcon->index = console_cmdline[i].index;
1329 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1330                 if (console_cmdline[i].brl_options) {
1331                         newcon->flags |= CON_BRL;
1332                         braille_register_console(newcon,
1333                                         console_cmdline[i].index,
1334                                         console_cmdline[i].options,
1335                                         console_cmdline[i].brl_options);
1336                         return;
1337                 }
1338 #endif
1339                 if (newcon->setup &&
1340                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1341                         break;
1342                 newcon->flags |= CON_ENABLED;
1343                 newcon->index = console_cmdline[i].index;
1344                 if (i == selected_console) {
1345                         newcon->flags |= CON_CONSDEV;
1346                         preferred_console = selected_console;
1347                 }
1348                 break;
1349         }
1350
1351         if (!(newcon->flags & CON_ENABLED))
1352                 return;
1353
1354         /*
1355          * If we have a bootconsole, and are switching to a real console,
1356          * don't print everything out again, since when the boot console, and
1357          * the real console are the same physical device, it's annoying to
1358          * see the beginning boot messages twice
1359          */
1360         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1361                 newcon->flags &= ~CON_PRINTBUFFER;
1362
1363         /*
1364          *      Put this console in the list - keep the
1365          *      preferred driver at the head of the list.
1366          */
1367         console_lock();
1368         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1369                 newcon->next = console_drivers;
1370                 console_drivers = newcon;
1371                 if (newcon->next)
1372                         newcon->next->flags &= ~CON_CONSDEV;
1373         } else {
1374                 newcon->next = console_drivers->next;
1375                 console_drivers->next = newcon;
1376         }
1377         if (newcon->flags & CON_PRINTBUFFER) {
1378                 /*
1379                  * console_unlock(); will print out the buffered messages
1380                  * for us.
1381                  */
1382                 spin_lock_irqsave(&logbuf_lock, flags);
1383                 con_start = log_start;
1384                 spin_unlock_irqrestore(&logbuf_lock, flags);
1385         }
1386         console_unlock();
1387         console_sysfs_notify();
1388
1389         /*
1390          * By unregistering the bootconsoles after we enable the real console
1391          * we get the "console xxx enabled" message on all the consoles -
1392          * boot consoles, real consoles, etc - this is to ensure that end
1393          * users know there might be something in the kernel's log buffer that
1394          * went to the bootconsole (that they do not see on the real console)
1395          */
1396         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1397                 /* we need to iterate through twice, to make sure we print
1398                  * everything out, before we unregister the console(s)
1399                  */
1400                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1401                         newcon->name, newcon->index);
1402                 for_each_console(bcon)
1403                         if (bcon->flags & CON_BOOT)
1404                                 unregister_console(bcon);
1405         } else {
1406                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1407                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1408                         newcon->name, newcon->index);
1409         }
1410 }
1411 EXPORT_SYMBOL(register_console);
1412
1413 int unregister_console(struct console *console)
1414 {
1415         struct console *a, *b;
1416         int res = 1;
1417
1418 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1419         if (console->flags & CON_BRL)
1420                 return braille_unregister_console(console);
1421 #endif
1422
1423         console_lock();
1424         if (console_drivers == console) {
1425                 console_drivers=console->next;
1426                 res = 0;
1427         } else if (console_drivers) {
1428                 for (a=console_drivers->next, b=console_drivers ;
1429                      a; b=a, a=b->next) {
1430                         if (a == console) {
1431                                 b->next = a->next;
1432                                 res = 0;
1433                                 break;
1434                         }
1435                 }
1436         }
1437
1438         /*
1439          * If this isn't the last console and it has CON_CONSDEV set, we
1440          * need to set it on the next preferred console.
1441          */
1442         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1443                 console_drivers->flags |= CON_CONSDEV;
1444
1445         console_unlock();
1446         console_sysfs_notify();
1447         return res;
1448 }
1449 EXPORT_SYMBOL(unregister_console);
1450
1451 static int __init printk_late_init(void)
1452 {
1453         struct console *con;
1454
1455         for_each_console(con) {
1456                 if (con->flags & CON_BOOT) {
1457                         printk(KERN_INFO "turn off boot console %s%d\n",
1458                                 con->name, con->index);
1459                         unregister_console(con);
1460                 }
1461         }
1462         hotcpu_notifier(console_cpu_notify, 0);
1463         return 0;
1464 }
1465 late_initcall(printk_late_init);
1466
1467 #if defined CONFIG_PRINTK
1468
1469 /*
1470  * printk rate limiting, lifted from the networking subsystem.
1471  *
1472  * This enforces a rate limit: not more than 10 kernel messages
1473  * every 5s to make a denial-of-service attack impossible.
1474  */
1475 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1476
1477 int __printk_ratelimit(const char *func)
1478 {
1479         return ___ratelimit(&printk_ratelimit_state, func);
1480 }
1481 EXPORT_SYMBOL(__printk_ratelimit);
1482
1483 /**
1484  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1485  * @caller_jiffies: pointer to caller's state
1486  * @interval_msecs: minimum interval between prints
1487  *
1488  * printk_timed_ratelimit() returns true if more than @interval_msecs
1489  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1490  * returned true.
1491  */
1492 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1493                         unsigned int interval_msecs)
1494 {
1495         if (*caller_jiffies == 0
1496                         || !time_in_range(jiffies, *caller_jiffies,
1497                                         *caller_jiffies
1498                                         + msecs_to_jiffies(interval_msecs))) {
1499                 *caller_jiffies = jiffies;
1500                 return true;
1501         }
1502         return false;
1503 }
1504 EXPORT_SYMBOL(printk_timed_ratelimit);
1505
1506 static DEFINE_SPINLOCK(dump_list_lock);
1507 static LIST_HEAD(dump_list);
1508
1509 /**
1510  * kmsg_dump_register - register a kernel log dumper.
1511  * @dumper: pointer to the kmsg_dumper structure
1512  *
1513  * Adds a kernel log dumper to the system. The dump callback in the
1514  * structure will be called when the kernel oopses or panics and must be
1515  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1516  */
1517 int kmsg_dump_register(struct kmsg_dumper *dumper)
1518 {
1519         unsigned long flags;
1520         int err = -EBUSY;
1521
1522         /* The dump callback needs to be set */
1523         if (!dumper->dump)
1524                 return -EINVAL;
1525
1526         spin_lock_irqsave(&dump_list_lock, flags);
1527         /* Don't allow registering multiple times */
1528         if (!dumper->registered) {
1529                 dumper->registered = 1;
1530                 list_add_tail_rcu(&dumper->list, &dump_list);
1531                 err = 0;
1532         }
1533         spin_unlock_irqrestore(&dump_list_lock, flags);
1534
1535         return err;
1536 }
1537 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1538
1539 /**
1540  * kmsg_dump_unregister - unregister a kmsg dumper.
1541  * @dumper: pointer to the kmsg_dumper structure
1542  *
1543  * Removes a dump device from the system. Returns zero on success and
1544  * %-EINVAL otherwise.
1545  */
1546 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1547 {
1548         unsigned long flags;
1549         int err = -EINVAL;
1550
1551         spin_lock_irqsave(&dump_list_lock, flags);
1552         if (dumper->registered) {
1553                 dumper->registered = 0;
1554                 list_del_rcu(&dumper->list);
1555                 err = 0;
1556         }
1557         spin_unlock_irqrestore(&dump_list_lock, flags);
1558         synchronize_rcu();
1559
1560         return err;
1561 }
1562 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1563
1564 /**
1565  * kmsg_dump - dump kernel log to kernel message dumpers.
1566  * @reason: the reason (oops, panic etc) for dumping
1567  *
1568  * Iterate through each of the dump devices and call the oops/panic
1569  * callbacks with the log buffer.
1570  */
1571 void kmsg_dump(enum kmsg_dump_reason reason)
1572 {
1573         unsigned long end;
1574         unsigned chars;
1575         struct kmsg_dumper *dumper;
1576         const char *s1, *s2;
1577         unsigned long l1, l2;
1578         unsigned long flags;
1579
1580         /* Theoretically, the log could move on after we do this, but
1581            there's not a lot we can do about that. The new messages
1582            will overwrite the start of what we dump. */
1583         spin_lock_irqsave(&logbuf_lock, flags);
1584         end = log_end & LOG_BUF_MASK;
1585         chars = logged_chars;
1586         spin_unlock_irqrestore(&logbuf_lock, flags);
1587
1588         if (chars > end) {
1589                 s1 = log_buf + log_buf_len - chars + end;
1590                 l1 = chars - end;
1591
1592                 s2 = log_buf;
1593                 l2 = end;
1594         } else {
1595                 s1 = "";
1596                 l1 = 0;
1597
1598                 s2 = log_buf + end - chars;
1599                 l2 = chars;
1600         }
1601
1602         rcu_read_lock();
1603         list_for_each_entry_rcu(dumper, &dump_list, list)
1604                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1605         rcu_read_unlock();
1606 }
1607 #endif