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  * release_console_sem().
 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 int do_syslog(int type, char __user *buf, int len, bool from_file)
 266 {
 267         unsigned i, j, limit, count;
 268         int do_clear = 0;
 269         char c;
 270         int error = 0;
 271
 272         /*
 273          * If this is from /proc/kmsg we only do the capabilities checks
 274          * at open time.
 275          */
 276         if (type == SYSLOG_ACTION_OPEN || !from_file) {
 277                 if (dmesg_restrict && !capable(CAP_SYSLOG))
 278                         goto warn; /* switch to return -EPERM after 2.6.39 */
 279                 if ((type != SYSLOG_ACTION_READ_ALL &&
 280                      type != SYSLOG_ACTION_SIZE_BUFFER) &&
 281                     !capable(CAP_SYSLOG))
 282                         goto warn; /* switch to return -EPERM after 2.6.39 */
 283         }
 284
 285         error = security_syslog(type);
 286         if (error)
 287                 return error;
 288
 289         switch (type) {
 290         case SYSLOG_ACTION_CLOSE:       /* Close log */
 291                 break;
 292         case SYSLOG_ACTION_OPEN:        /* Open log */
 293                 break;
 294         case SYSLOG_ACTION_READ:        /* Read from log */
 295                 error = -EINVAL;
 296                 if (!buf || len < 0)
 297                         goto out;
 298                 error = 0;
 299                 if (!len)
 300                         goto out;
 301                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 302                         error = -EFAULT;
 303                         goto out;
 304                 }
 305                 error = wait_event_interruptible(log_wait,
 306                                                         (log_start - log_end));
 307                 if (error)
 308                         goto out;
 309                 i = 0;
 310                 spin_lock_irq(&logbuf_lock);
 311                 while (!error && (log_start != log_end) && i < len) {
 312                         c = LOG_BUF(log_start);
 313                         log_start++;
 314                         spin_unlock_irq(&logbuf_lock);
 315                         error = __put_user(c,buf);
 316                         buf++;
 317                         i++;
 318                         cond_resched();
 319                         spin_lock_irq(&logbuf_lock);
 320                 }
 321                 spin_unlock_irq(&logbuf_lock);
 322                 if (!error)
 323                         error = i;
 324                 break;
 325         /* Read/clear last kernel messages */
 326         case SYSLOG_ACTION_READ_CLEAR:
 327                 do_clear = 1;
 328                 /* FALL THRU */
 329         /* Read last kernel messages */
 330         case SYSLOG_ACTION_READ_ALL:
 331                 error = -EINVAL;
 332                 if (!buf || len < 0)
 333                         goto out;
 334                 error = 0;
 335                 if (!len)
 336                         goto out;
 337                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 338                         error = -EFAULT;
 339                         goto out;
 340                 }
 341                 count = len;
 342                 if (count > log_buf_len)
 343                         count = log_buf_len;
 344                 spin_lock_irq(&logbuf_lock);
 345                 if (count > logged_chars)
 346                         count = logged_chars;
 347                 if (do_clear)
 348                         logged_chars = 0;
 349                 limit = log_end;
 350                 /*
 351                  * __put_user() could sleep, and while we sleep
 352                  * printk() could overwrite the messages
 353                  * we try to copy to user space. Therefore
 354                  * the messages are copied in reverse. <manfreds>
 355                  */
 356                 for (i = 0; i < count && !error; i++) {
 357                         j = limit-1-i;
 358                         if (j + log_buf_len < log_end)
 359                                 break;
 360                         c = LOG_BUF(j);
 361                         spin_unlock_irq(&logbuf_lock);
 362                         error = __put_user(c,&buf[count-1-i]);
 363                         cond_resched();
 364                         spin_lock_irq(&logbuf_lock);
 365                 }
 366                 spin_unlock_irq(&logbuf_lock);
 367                 if (error)
 368                         break;
 369                 error = i;
 370                 if (i != count) {
 371                         int offset = count-error;
 372                         /* buffer overflow during copy, correct user buffer. */
 373                         for (i = 0; i < error; i++) {
 374                                 if (__get_user(c,&buf[i+offset]) ||
 375                                     __put_user(c,&buf[i])) {
 376                                         error = -EFAULT;
 377                                         break;
 378                                 }
 379                                 cond_resched();
 380                         }
 381                 }
 382                 break;
 383         /* Clear ring buffer */
 384         case SYSLOG_ACTION_CLEAR:
 385                 logged_chars = 0;
 386                 break;
 387         /* Disable logging to console */
 388         case SYSLOG_ACTION_CONSOLE_OFF:
 389                 if (saved_console_loglevel == -1)
 390                         saved_console_loglevel = console_loglevel;
 391                 console_loglevel = minimum_console_loglevel;
 392                 break;
 393         /* Enable logging to console */
 394         case SYSLOG_ACTION_CONSOLE_ON:
 395                 if (saved_console_loglevel != -1) {
 396                         console_loglevel = saved_console_loglevel;
 397                         saved_console_loglevel = -1;
 398                 }
 399                 break;
 400         /* Set level of messages printed to console */
 401         case SYSLOG_ACTION_CONSOLE_LEVEL:
 402                 error = -EINVAL;
 403                 if (len < 1 || len > 8)
 404                         goto out;
 405                 if (len < minimum_console_loglevel)
 406                         len = minimum_console_loglevel;
 407                 console_loglevel = len;
 408                 /* Implicitly re-enable logging to console */
 409                 saved_console_loglevel = -1;
 410                 error = 0;
 411                 break;
 412         /* Number of chars in the log buffer */
 413         case SYSLOG_ACTION_SIZE_UNREAD:
 414                 error = log_end - log_start;
 415                 break;
 416         /* Size of the log buffer */
 417         case SYSLOG_ACTION_SIZE_BUFFER:
 418                 error = log_buf_len;
 419                 break;
 420         default:
 421                 error = -EINVAL;
 422                 break;
 423         }
 424 out:
 425         return error;
 426 warn:
 427         /* remove after 2.6.39 */
 428         if (capable(CAP_SYS_ADMIN))
 429                 WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
 430                   "but no CAP_SYSLOG (deprecated and denied).\n");
 431         return -EPERM;
 432 }
 433
 434 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 435 {
 436         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 437 }
 438
 439 #ifdef  CONFIG_KGDB_KDB
 440 /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
 441  * uses locks so it cannot be used during debugging.  Just tell kdb
 442  * where the start and end of the physical and logical logs are.  This
 443  * is equivalent to do_syslog(3).
 444  */
 445 void kdb_syslog_data(char *syslog_data[4])
 446 {
 447         syslog_data[0] = log_buf;
 448         syslog_data[1] = log_buf + log_buf_len;
 449         syslog_data[2] = log_buf + log_end -
 450                 (logged_chars < log_buf_len ? logged_chars : log_buf_len);
 451         syslog_data[3] = log_buf + log_end;
 452 }
 453 #endif  /* CONFIG_KGDB_KDB */
 454
 455 /*
 456  * Call the console drivers on a range of log_buf
 457  */
 458 static void __call_console_drivers(unsigned start, unsigned end)
 459 {
 460         struct console *con;
 461
 462         for_each_console(con) {
 463                 if ((con->flags & CON_ENABLED) && con->write &&
 464                                 (cpu_online(smp_processor_id()) ||
 465                                 (con->flags & CON_ANYTIME)))
 466                         con->write(con, &LOG_BUF(start), end - start);
 467         }
 468 }
 469
 470 static int __read_mostly ignore_loglevel;
 471
 472 static int __init ignore_loglevel_setup(char *str)
 473 {
 474         ignore_loglevel = 1;
 475         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 476
 477         return 0;
 478 }
 479
 480 early_param("ignore_loglevel", ignore_loglevel_setup);
 481
 482 /*
 483  * Write out chars from start to end - 1 inclusive
 484  */
 485 static void _call_console_drivers(unsigned start,
 486                                 unsigned end, int msg_log_level)
 487 {
 488         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 489                         console_drivers && start != end) {
 490                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 491                         /* wrapped write */
 492                         __call_console_drivers(start & LOG_BUF_MASK,
 493                                                 log_buf_len);
 494                         __call_console_drivers(0, end & LOG_BUF_MASK);
 495                 } else {
 496                         __call_console_drivers(start, end);
 497                 }
 498         }
 499 }
 500
 501 /*
 502  * Call the console drivers, asking them to write out
 503  * log_buf[start] to log_buf[end - 1].
 504  * The console_sem must be held.
 505  */
 506 static void call_console_drivers(unsigned start, unsigned end)
 507 {
 508         unsigned cur_index, start_print;
 509         static int msg_level = -1;
 510
 511         BUG_ON(((int)(start - end)) > 0);
 512
 513         cur_index = start;
 514         start_print = start;
 515         while (cur_index != end) {
 516                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 517                                 LOG_BUF(cur_index + 0) == '<' &&
 518                                 LOG_BUF(cur_index + 1) >= '0' &&
 519                                 LOG_BUF(cur_index + 1) <= '7' &&
 520                                 LOG_BUF(cur_index + 2) == '>') {
 521                         msg_level = LOG_BUF(cur_index + 1) - '0';
 522                         cur_index += 3;
 523                         start_print = cur_index;
 524                 }
 525                 while (cur_index != end) {
 526                         char c = LOG_BUF(cur_index);
 527
 528                         cur_index++;
 529                         if (c == '\n') {
 530                                 if (msg_level < 0) {
 531                                         /*
 532                                          * printk() has already given us loglevel tags in
 533                                          * the buffer.  This code is here in case the
 534                                          * log buffer has wrapped right round and scribbled
 535                                          * on those tags
 536                                          */
 537                                         msg_level = default_message_loglevel;
 538                                 }
 539                                 _call_console_drivers(start_print, cur_index, msg_level);
 540                                 msg_level = -1;
 541                                 start_print = cur_index;
 542                                 break;
 543                         }
 544                 }
 545         }
 546         _call_console_drivers(start_print, end, msg_level);
 547 }
 548
 549 static void emit_log_char(char c)
 550 {
 551         LOG_BUF(log_end) = c;
 552         log_end++;
 553         if (log_end - log_start > log_buf_len)
 554                 log_start = log_end - log_buf_len;
 555         if (log_end - con_start > log_buf_len)
 556                 con_start = log_end - log_buf_len;
 557         if (logged_chars < log_buf_len)
 558                 logged_chars++;
 559 }
 560
 561 /*
 562  * Zap console related locks when oopsing. Only zap at most once
 563  * every 10 seconds, to leave time for slow consoles to print a
 564  * full oops.
 565  */
 566 static void zap_locks(void)
 567 {
 568         static unsigned long oops_timestamp;
 569
 570         if (time_after_eq(jiffies, oops_timestamp) &&
 571                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 572                 return;
 573
 574         oops_timestamp = jiffies;
 575
 576         /* If a crash is occurring, make sure we can't deadlock */
 577         spin_lock_init(&logbuf_lock);
 578         /* And make sure that we print immediately */
 579         sema_init(&console_sem, 1);
 580 }
 581
 582 #if defined(CONFIG_PRINTK_TIME)
 583 static int printk_time = 1;
 584 #else
 585 static int printk_time = 0;
 586 #endif
 587 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 588
 589 /* Check if we have any console registered that can be called early in boot. */
 590 static int have_callable_console(void)
 591 {
 592         struct console *con;
 593
 594         for_each_console(con)
 595                 if (con->flags & CON_ANYTIME)
 596                         return 1;
 597
 598         return 0;
 599 }
 600
 601 /**
 602  * printk - print a kernel message
 603  * @fmt: format string
 604  *
 605  * This is printk().  It can be called from any context.  We want it to work.
 606  *
 607  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 608  * call the console drivers.  If we fail to get the semaphore we place the output
 609  * into the log buffer and return.  The current holder of the console_sem will
 610  * notice the new output in release_console_sem() and will send it to the
 611  * consoles before releasing the semaphore.
 612  *
 613  * One effect of this deferred printing is that code which calls printk() and
 614  * then changes console_loglevel may break. This is because console_loglevel
 615  * is inspected when the actual printing occurs.
 616  *
 617  * See also:
 618  * printf(3)
 619  *
 620  * See the vsnprintf() documentation for format string extensions over C99.
 621  */
 622
 623 asmlinkage int printk(const char *fmt, ...)
 624 {
 625         va_list args;
 626         int r;
 627
 628 #ifdef CONFIG_KGDB_KDB
 629         if (unlikely(kdb_trap_printk)) {
 630                 va_start(args, fmt);
 631                 r = vkdb_printf(fmt, args);
 632                 va_end(args);
 633                 return r;
 634         }
 635 #endif
 636         va_start(args, fmt);
 637         r = vprintk(fmt, args);
 638         va_end(args);
 639
 640         return r;
 641 }
 642
 643 /* cpu currently holding logbuf_lock */
 644 static volatile unsigned int printk_cpu = UINT_MAX;
 645
 646 /*
 647  * Can we actually use the console at this time on this cpu?
 648  *
 649  * Console drivers may assume that per-cpu resources have
 650  * been allocated. So unless they're explicitly marked as
 651  * being able to cope (CON_ANYTIME) don't call them until
 652  * this CPU is officially up.
 653  */
 654 static inline int can_use_console(unsigned int cpu)
 655 {
 656         return cpu_online(cpu) || have_callable_console();
 657 }
 658
 659 /*
 660  * Try to get console ownership to actually show the kernel
 661  * messages from a 'printk'. Return true (and with the
 662  * console_semaphore held, and 'console_locked' set) if it
 663  * is successful, false otherwise.
 664  *
 665  * This gets called with the 'logbuf_lock' spinlock held and
 666  * interrupts disabled. It should return with 'lockbuf_lock'
 667  * released but interrupts still disabled.
 668  */
 669 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 670         __releases(&logbuf_lock)
 671 {
 672         int retval = 0;
 673
 674         if (!try_acquire_console_sem()) {
 675                 retval = 1;
 676
 677                 /*
 678                  * If we can't use the console, we need to release
 679                  * the console semaphore by hand to avoid flushing
 680                  * the buffer. We need to hold the console semaphore
 681                  * in order to do this test safely.
 682                  */
 683                 if (!can_use_console(cpu)) {
 684                         console_locked = 0;
 685                         up(&console_sem);
 686                         retval = 0;
 687                 }
 688         }
 689         printk_cpu = UINT_MAX;
 690         spin_unlock(&logbuf_lock);
 691         return retval;
 692 }
 693 static const char recursion_bug_msg [] =
 694                 KERN_CRIT "BUG: recent printk recursion!\n";
 695 static int recursion_bug;
 696 static int new_text_line = 1;
 697 static char printk_buf[1024];
 698
 699 int printk_delay_msec __read_mostly;
 700
 701 static inline void printk_delay(void)
 702 {
 703         if (unlikely(printk_delay_msec)) {
 704                 int m = printk_delay_msec;
 705
 706                 while (m--) {
 707                         mdelay(1);
 708                         touch_nmi_watchdog();
 709                 }
 710         }
 711 }
 712
 713 asmlinkage int vprintk(const char *fmt, va_list args)
 714 {
 715         int printed_len = 0;
 716         int current_log_level = default_message_loglevel;
 717         unsigned long flags;
 718         int this_cpu;
 719         char *p;
 720
 721         boot_delay_msec();
 722         printk_delay();
 723
 724         preempt_disable();
 725         /* This stops the holder of console_sem just where we want him */
 726         raw_local_irq_save(flags);
 727         this_cpu = smp_processor_id();
 728
 729         /*
 730          * Ouch, printk recursed into itself!
 731          */
 732         if (unlikely(printk_cpu == this_cpu)) {
 733                 /*
 734                  * If a crash is occurring during printk() on this CPU,
 735                  * then try to get the crash message out but make sure
 736                  * we can't deadlock. Otherwise just return to avoid the
 737                  * recursion and return - but flag the recursion so that
 738                  * it can be printed at the next appropriate moment:
 739                  */
 740                 if (!oops_in_progress) {
 741                         recursion_bug = 1;
 742                         goto out_restore_irqs;
 743                 }
 744                 zap_locks();
 745         }
 746
 747         lockdep_off();
 748         spin_lock(&logbuf_lock);
 749         printk_cpu = this_cpu;
 750
 751         if (recursion_bug) {
 752                 recursion_bug = 0;
 753                 strcpy(printk_buf, recursion_bug_msg);
 754                 printed_len = strlen(recursion_bug_msg);
 755         }
 756         /* Emit the output into the temporary buffer */
 757         printed_len += vscnprintf(printk_buf + printed_len,
 758                                   sizeof(printk_buf) - printed_len, fmt, args);
 759
 760
 761         p = printk_buf;
 762
 763         /* Do we have a loglevel in the string? */
 764         if (p[0] == '<') {
 765                 unsigned char c = p[1];
 766                 if (c && p[2] == '>') {
 767                         switch (c) {
 768                         case '0' ... '7': /* loglevel */
 769                                 current_log_level = c - '0';
 770                         /* Fallthrough - make sure we're on a new line */
 771                         case 'd': /* KERN_DEFAULT */
 772                                 if (!new_text_line) {
 773                                         emit_log_char('\n');
 774                                         new_text_line = 1;
 775                                 }
 776                         /* Fallthrough - skip the loglevel */
 777                         case 'c': /* KERN_CONT */
 778                                 p += 3;
 779                                 break;
 780                         }
 781                 }
 782         }
 783
 784         /*
 785          * Copy the output into log_buf.  If the caller didn't provide
 786          * appropriate log level tags, we insert them here
 787          */
 788         for ( ; *p; p++) {
 789                 if (new_text_line) {
 790                         /* Always output the token */
 791                         emit_log_char('<');
 792                         emit_log_char(current_log_level + '0');
 793                         emit_log_char('>');
 794                         printed_len += 3;
 795                         new_text_line = 0;
 796
 797                         if (printk_time) {
 798                                 /* Follow the token with the time */
 799                                 char tbuf[50], *tp;
 800                                 unsigned tlen;
 801                                 unsigned long long t;
 802                                 unsigned long nanosec_rem;
 803
 804                                 t = cpu_clock(printk_cpu);
 805                                 nanosec_rem = do_div(t, 1000000000);
 806                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 807                                                 (unsigned long) t,
 808                                                 nanosec_rem / 1000);
 809
 810                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 811                                         emit_log_char(*tp);
 812                                 printed_len += tlen;
 813                         }
 814
 815                         if (!*p)
 816                                 break;
 817                 }
 818
 819                 emit_log_char(*p);
 820                 if (*p == '\n')
 821                         new_text_line = 1;
 822         }
 823
 824         /*
 825          * Try to acquire and then immediately release the
 826          * console semaphore. The release will do all the
 827          * actual magic (print out buffers, wake up klogd,
 828          * etc).
 829          *
 830          * The acquire_console_semaphore_for_printk() function
 831          * will release 'logbuf_lock' regardless of whether it
 832          * actually gets the semaphore or not.
 833          */
 834         if (acquire_console_semaphore_for_printk(this_cpu))
 835                 release_console_sem();
 836
 837         lockdep_on();
 838 out_restore_irqs:
 839         raw_local_irq_restore(flags);
 840
 841         preempt_enable();
 842         return printed_len;
 843 }
 844 EXPORT_SYMBOL(printk);
 845 EXPORT_SYMBOL(vprintk);
 846
 847 #else
 848
 849 static void call_console_drivers(unsigned start, unsigned end)
 850 {
 851 }
 852
 853 #endif
 854
 855 static int __add_preferred_console(char *name, int idx, char *options,
 856                                    char *brl_options)
 857 {
 858         struct console_cmdline *c;
 859         int i;
 860
 861         /*
 862          *      See if this tty is not yet registered, and
 863          *      if we have a slot free.
 864          */
 865         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 866                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 867                           console_cmdline[i].index == idx) {
 868                                 if (!brl_options)
 869                                         selected_console = i;
 870                                 return 0;
 871                 }
 872         if (i == MAX_CMDLINECONSOLES)
 873                 return -E2BIG;
 874         if (!brl_options)
 875                 selected_console = i;
 876         c = &console_cmdline[i];
 877         strlcpy(c->name, name, sizeof(c->name));
 878         c->options = options;
 879 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 880         c->brl_options = brl_options;
 881 #endif
 882         c->index = idx;
 883         return 0;
 884 }
 885 /*
 886  * Set up a list of consoles.  Called from init/main.c
 887  */
 888 static int __init console_setup(char *str)
 889 {
 890         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 891         char *s, *options, *brl_options = NULL;
 892         int idx;
 893
 894 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 895         if (!memcmp(str, "brl,", 4)) {
 896                 brl_options = "";
 897                 str += 4;
 898         } else if (!memcmp(str, "brl=", 4)) {
 899                 brl_options = str + 4;
 900                 str = strchr(brl_options, ',');
 901                 if (!str) {
 902                         printk(KERN_ERR "need port name after brl=\n");
 903                         return 1;
 904                 }
 905                 *(str++) = 0;
 906         }
 907 #endif
 908
 909         /*
 910          * Decode str into name, index, options.
 911          */
 912         if (str[0] >= '0' && str[0] <= '9') {
 913                 strcpy(buf, "ttyS");
 914                 strncpy(buf + 4, str, sizeof(buf) - 5);
 915         } else {
 916                 strncpy(buf, str, sizeof(buf) - 1);
 917         }
 918         buf[sizeof(buf) - 1] = 0;
 919         if ((options = strchr(str, ',')) != NULL)
 920                 *(options++) = 0;
 921 #ifdef __sparc__
 922         if (!strcmp(str, "ttya"))
 923                 strcpy(buf, "ttyS0");
 924         if (!strcmp(str, "ttyb"))
 925                 strcpy(buf, "ttyS1");
 926 #endif
 927         for (s = buf; *s; s++)
 928                 if ((*s >= '0' && *s <= '9') || *s == ',')
 929                         break;
 930         idx = simple_strtoul(s, NULL, 10);
 931         *s = 0;
 932
 933         __add_preferred_console(buf, idx, options, brl_options);
 934         console_set_on_cmdline = 1;
 935         return 1;
 936 }
 937 __setup("console=", console_setup);
 938
 939 /**
 940  * add_preferred_console - add a device to the list of preferred consoles.
 941  * @name: device name
 942  * @idx: device index
 943  * @options: options for this console
 944  *
 945  * The last preferred console added will be used for kernel messages
 946  * and stdin/out/err for init.  Normally this is used by console_setup
 947  * above to handle user-supplied console arguments; however it can also
 948  * be used by arch-specific code either to override the user or more
 949  * commonly to provide a default console (ie from PROM variables) when
 950  * the user has not supplied one.
 951  */
 952 int add_preferred_console(char *name, int idx, char *options)
 953 {
 954         return __add_preferred_console(name, idx, options, NULL);
 955 }
 956
 957 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 958 {
 959         struct console_cmdline *c;
 960         int i;
 961
 962         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 963                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 964                           console_cmdline[i].index == idx) {
 965                                 c = &console_cmdline[i];
 966                                 strlcpy(c->name, name_new, sizeof(c->name));
 967                                 c->name[sizeof(c->name) - 1] = 0;
 968                                 c->options = options;
 969                                 c->index = idx_new;
 970                                 return i;
 971                 }
 972         /* not found */
 973         return -1;
 974 }
 975
 976 int console_suspend_enabled = 1;
 977 EXPORT_SYMBOL(console_suspend_enabled);
 978
 979 static int __init console_suspend_disable(char *str)
 980 {
 981         console_suspend_enabled = 0;
 982         return 1;
 983 }
 984 __setup("no_console_suspend", console_suspend_disable);
 985
 986 /**
 987  * suspend_console - suspend the console subsystem
 988  *
 989  * This disables printk() while we go into suspend states
 990  */
 991 void suspend_console(void)
 992 {
 993         if (!console_suspend_enabled)
 994                 return;
 995         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 996         acquire_console_sem();
 997         console_suspended = 1;
 998         up(&console_sem);
 999 }
1000
1001 void resume_console(void)
1002 {
1003         if (!console_suspend_enabled)
1004                 return;
1005         down(&console_sem);
1006         console_suspended = 0;
1007         release_console_sem();
1008 }
1009
1010 /**
1011  * console_cpu_notify - print deferred console messages after CPU hotplug
1012  * @self: notifier struct
1013  * @action: CPU hotplug event
1014  * @hcpu: unused
1015  *
1016  * If printk() is called from a CPU that is not online yet, the messages
1017  * will be spooled but will not show up on the console.  This function is
1018  * called when a new CPU comes online (or fails to come up), and ensures
1019  * that any such output gets printed.
1020  */
1021 static int __cpuinit console_cpu_notify(struct notifier_block *self,
1022         unsigned long action, void *hcpu)
1023 {
1024         switch (action) {
1025         case CPU_ONLINE:
1026         case CPU_DEAD:
1027         case CPU_DYING:
1028         case CPU_DOWN_FAILED:
1029         case CPU_UP_CANCELED:
1030                 acquire_console_sem();
1031                 release_console_sem();
1032         }
1033         return NOTIFY_OK;
1034 }
1035
1036 /**
1037  * acquire_console_sem - lock the console system for exclusive use.
1038  *
1039  * Acquires a semaphore which guarantees that the caller has
1040  * exclusive access to the console system and the console_drivers list.
1041  *
1042  * Can sleep, returns nothing.
1043  */
1044 void acquire_console_sem(void)
1045 {
1046         BUG_ON(in_interrupt());
1047         down(&console_sem);
1048         if (console_suspended)
1049                 return;
1050         console_locked = 1;
1051         console_may_schedule = 1;
1052 }
1053 EXPORT_SYMBOL(acquire_console_sem);
1054
1055 int try_acquire_console_sem(void)
1056 {
1057         if (down_trylock(&console_sem))
1058                 return -1;
1059         if (console_suspended) {
1060                 up(&console_sem);
1061                 return -1;
1062         }
1063         console_locked = 1;
1064         console_may_schedule = 0;
1065         return 0;
1066 }
1067 EXPORT_SYMBOL(try_acquire_console_sem);
1068
1069 int is_console_locked(void)
1070 {
1071         return console_locked;
1072 }
1073
1074 static DEFINE_PER_CPU(int, printk_pending);
1075
1076 void printk_tick(void)
1077 {
1078         if (__this_cpu_read(printk_pending)) {
1079                 __this_cpu_write(printk_pending, 0);
1080                 wake_up_interruptible(&log_wait);
1081         }
1082 }
1083
1084 int printk_needs_cpu(int cpu)
1085 {
1086         if (cpu_is_offline(cpu))
1087                 printk_tick();
1088         return __this_cpu_read(printk_pending);
1089 }
1090
1091 void wake_up_klogd(void)
1092 {
1093         if (waitqueue_active(&log_wait))
1094                 this_cpu_write(printk_pending, 1);
1095 }
1096
1097 /**
1098  * release_console_sem - unlock the console system
1099  *
1100  * Releases the semaphore which the caller holds on the console system
1101  * and the console driver list.
1102  *
1103  * While the semaphore was held, console output may have been buffered
1104  * by printk().  If this is the case, release_console_sem() emits
1105  * the output prior to releasing the semaphore.
1106  *
1107  * If there is output waiting for klogd, we wake it up.
1108  *
1109  * release_console_sem() may be called from any context.
1110  */
1111 void release_console_sem(void)
1112 {
1113         unsigned long flags;
1114         unsigned _con_start, _log_end;
1115         unsigned wake_klogd = 0;
1116
1117         if (console_suspended) {
1118                 up(&console_sem);
1119                 return;
1120         }
1121
1122         console_may_schedule = 0;
1123
1124         for ( ; ; ) {
1125                 spin_lock_irqsave(&logbuf_lock, flags);
1126                 wake_klogd |= log_start - log_end;
1127                 if (con_start == log_end)
1128                         break;                  /* Nothing to print */
1129                 _con_start = con_start;
1130                 _log_end = log_end;
1131                 con_start = log_end;            /* Flush */
1132                 spin_unlock(&logbuf_lock);
1133                 stop_critical_timings();        /* don't trace print latency */
1134                 call_console_drivers(_con_start, _log_end);
1135                 start_critical_timings();
1136                 local_irq_restore(flags);
1137         }
1138         console_locked = 0;
1139         up(&console_sem);
1140         spin_unlock_irqrestore(&logbuf_lock, flags);
1141         if (wake_klogd)
1142                 wake_up_klogd();
1143 }
1144 EXPORT_SYMBOL(release_console_sem);
1145
1146 /**
1147  * console_conditional_schedule - yield the CPU if required
1148  *
1149  * If the console code is currently allowed to sleep, and
1150  * if this CPU should yield the CPU to another task, do
1151  * so here.
1152  *
1153  * Must be called within acquire_console_sem().
1154  */
1155 void __sched console_conditional_schedule(void)
1156 {
1157         if (console_may_schedule)
1158                 cond_resched();
1159 }
1160 EXPORT_SYMBOL(console_conditional_schedule);
1161
1162 void console_unblank(void)
1163 {
1164         struct console *c;
1165
1166         /*
1167          * console_unblank can no longer be called in interrupt context unless
1168          * oops_in_progress is set to 1..
1169          */
1170         if (oops_in_progress) {
1171                 if (down_trylock(&console_sem) != 0)
1172                         return;
1173         } else
1174                 acquire_console_sem();
1175
1176         console_locked = 1;
1177         console_may_schedule = 0;
1178         for_each_console(c)
1179                 if ((c->flags & CON_ENABLED) && c->unblank)
1180                         c->unblank();
1181         release_console_sem();
1182 }
1183
1184 /*
1185  * Return the console tty driver structure and its associated index
1186  */
1187 struct tty_driver *console_device(int *index)
1188 {
1189         struct console *c;
1190         struct tty_driver *driver = NULL;
1191
1192         acquire_console_sem();
1193         for_each_console(c) {
1194                 if (!c->device)
1195                         continue;
1196                 driver = c->device(c, index);
1197                 if (driver)
1198                         break;
1199         }
1200         release_console_sem();
1201         return driver;
1202 }
1203
1204 /*
1205  * Prevent further output on the passed console device so that (for example)
1206  * serial drivers can disable console output before suspending a port, and can
1207  * re-enable output afterwards.
1208  */
1209 void console_stop(struct console *console)
1210 {
1211         acquire_console_sem();
1212         console->flags &= ~CON_ENABLED;
1213         release_console_sem();
1214 }
1215 EXPORT_SYMBOL(console_stop);
1216
1217 void console_start(struct console *console)
1218 {
1219         acquire_console_sem();
1220         console->flags |= CON_ENABLED;
1221         release_console_sem();
1222 }
1223 EXPORT_SYMBOL(console_start);
1224
1225 /*
1226  * The console driver calls this routine during kernel initialization
1227  * to register the console printing procedure with printk() and to
1228  * print any messages that were printed by the kernel before the
1229  * console driver was initialized.
1230  *
1231  * This can happen pretty early during the boot process (because of
1232  * early_printk) - sometimes before setup_arch() completes - be careful
1233  * of what kernel features are used - they may not be initialised yet.
1234  *
1235  * There are two types of consoles - bootconsoles (early_printk) and
1236  * "real" consoles (everything which is not a bootconsole) which are
1237  * handled differently.
1238  *  - Any number of bootconsoles can be registered at any time.
1239  *  - As soon as a "real" console is registered, all bootconsoles
1240  *    will be unregistered automatically.
1241  *  - Once a "real" console is registered, any attempt to register a
1242  *    bootconsoles will be rejected
1243  */
1244 void register_console(struct console *newcon)
1245 {
1246         int i;
1247         unsigned long flags;
1248         struct console *bcon = NULL;
1249
1250         /*
1251          * before we register a new CON_BOOT console, make sure we don't
1252          * already have a valid console
1253          */
1254         if (console_drivers && newcon->flags & CON_BOOT) {
1255                 /* find the last or real console */
1256                 for_each_console(bcon) {
1257                         if (!(bcon->flags & CON_BOOT)) {
1258                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1259                                         newcon->name, newcon->index);
1260                                 return;
1261                         }
1262                 }
1263         }
1264
1265         if (console_drivers && console_drivers->flags & CON_BOOT)
1266                 bcon = console_drivers;
1267
1268         if (preferred_console < 0 || bcon || !console_drivers)
1269                 preferred_console = selected_console;
1270
1271         if (newcon->early_setup)
1272                 newcon->early_setup();
1273
1274         /*
1275          *      See if we want to use this console driver. If we
1276          *      didn't select a console we take the first one
1277          *      that registers here.
1278          */
1279         if (preferred_console < 0) {
1280                 if (newcon->index < 0)
1281                         newcon->index = 0;
1282                 if (newcon->setup == NULL ||
1283                     newcon->setup(newcon, NULL) == 0) {
1284                         newcon->flags |= CON_ENABLED;
1285                         if (newcon->device) {
1286                                 newcon->flags |= CON_CONSDEV;
1287                                 preferred_console = 0;
1288                         }
1289                 }
1290         }
1291
1292         /*
1293          *      See if this console matches one we selected on
1294          *      the command line.
1295          */
1296         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1297                         i++) {
1298                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1299                         continue;
1300                 if (newcon->index >= 0 &&
1301                     newcon->index != console_cmdline[i].index)
1302                         continue;
1303                 if (newcon->index < 0)
1304                         newcon->index = console_cmdline[i].index;
1305 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1306                 if (console_cmdline[i].brl_options) {
1307                         newcon->flags |= CON_BRL;
1308                         braille_register_console(newcon,
1309                                         console_cmdline[i].index,
1310                                         console_cmdline[i].options,
1311                                         console_cmdline[i].brl_options);
1312                         return;
1313                 }
1314 #endif
1315                 if (newcon->setup &&
1316                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1317                         break;
1318                 newcon->flags |= CON_ENABLED;
1319                 newcon->index = console_cmdline[i].index;
1320                 if (i == selected_console) {
1321                         newcon->flags |= CON_CONSDEV;
1322                         preferred_console = selected_console;
1323                 }
1324                 break;
1325         }
1326
1327         if (!(newcon->flags & CON_ENABLED))
1328                 return;
1329
1330         /*
1331          * If we have a bootconsole, and are switching to a real console,
1332          * don't print everything out again, since when the boot console, and
1333          * the real console are the same physical device, it's annoying to
1334          * see the beginning boot messages twice
1335          */
1336         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1337                 newcon->flags &= ~CON_PRINTBUFFER;
1338
1339         /*
1340          *      Put this console in the list - keep the
1341          *      preferred driver at the head of the list.
1342          */
1343         acquire_console_sem();
1344         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1345                 newcon->next = console_drivers;
1346                 console_drivers = newcon;
1347                 if (newcon->next)
1348                         newcon->next->flags &= ~CON_CONSDEV;
1349         } else {
1350                 newcon->next = console_drivers->next;
1351                 console_drivers->next = newcon;
1352         }
1353         if (newcon->flags & CON_PRINTBUFFER) {
1354                 /*
1355                  * release_console_sem() will print out the buffered messages
1356                  * for us.
1357                  */
1358                 spin_lock_irqsave(&logbuf_lock, flags);
1359                 con_start = log_start;
1360                 spin_unlock_irqrestore(&logbuf_lock, flags);
1361         }
1362         release_console_sem();
1363         console_sysfs_notify();
1364
1365         /*
1366          * By unregistering the bootconsoles after we enable the real console
1367          * we get the "console xxx enabled" message on all the consoles -
1368          * boot consoles, real consoles, etc - this is to ensure that end
1369          * users know there might be something in the kernel's log buffer that
1370          * went to the bootconsole (that they do not see on the real console)
1371          */
1372         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1373                 /* we need to iterate through twice, to make sure we print
1374                  * everything out, before we unregister the console(s)
1375                  */
1376                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1377                         newcon->name, newcon->index);
1378                 for_each_console(bcon)
1379                         if (bcon->flags & CON_BOOT)
1380                                 unregister_console(bcon);
1381         } else {
1382                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1383                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1384                         newcon->name, newcon->index);
1385         }
1386 }
1387 EXPORT_SYMBOL(register_console);
1388
1389 int unregister_console(struct console *console)
1390 {
1391         struct console *a, *b;
1392         int res = 1;
1393
1394 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1395         if (console->flags & CON_BRL)
1396                 return braille_unregister_console(console);
1397 #endif
1398
1399         acquire_console_sem();
1400         if (console_drivers == console) {
1401                 console_drivers=console->next;
1402                 res = 0;
1403         } else if (console_drivers) {
1404                 for (a=console_drivers->next, b=console_drivers ;
1405                      a; b=a, a=b->next) {
1406                         if (a == console) {
1407                                 b->next = a->next;
1408                                 res = 0;
1409                                 break;
1410                         }
1411                 }
1412         }
1413
1414         /*
1415          * If this isn't the last console and it has CON_CONSDEV set, we
1416          * need to set it on the next preferred console.
1417          */
1418         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1419                 console_drivers->flags |= CON_CONSDEV;
1420
1421         release_console_sem();
1422         console_sysfs_notify();
1423         return res;
1424 }
1425 EXPORT_SYMBOL(unregister_console);
1426
1427 static int __init printk_late_init(void)
1428 {
1429         struct console *con;
1430
1431         for_each_console(con) {
1432                 if (con->flags & CON_BOOT) {
1433                         printk(KERN_INFO "turn off boot console %s%d\n",
1434                                 con->name, con->index);
1435                         unregister_console(con);
1436                 }
1437         }
1438         hotcpu_notifier(console_cpu_notify, 0);
1439         return 0;
1440 }
1441 late_initcall(printk_late_init);
1442
1443 #if defined CONFIG_PRINTK
1444
1445 /*
1446  * printk rate limiting, lifted from the networking subsystem.
1447  *
1448  * This enforces a rate limit: not more than 10 kernel messages
1449  * every 5s to make a denial-of-service attack impossible.
1450  */
1451 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1452
1453 int __printk_ratelimit(const char *func)
1454 {
1455         return ___ratelimit(&printk_ratelimit_state, func);
1456 }
1457 EXPORT_SYMBOL(__printk_ratelimit);
1458
1459 /**
1460  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1461  * @caller_jiffies: pointer to caller's state
1462  * @interval_msecs: minimum interval between prints
1463  *
1464  * printk_timed_ratelimit() returns true if more than @interval_msecs
1465  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1466  * returned true.
1467  */
1468 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1469                         unsigned int interval_msecs)
1470 {
1471         if (*caller_jiffies == 0
1472                         || !time_in_range(jiffies, *caller_jiffies,
1473                                         *caller_jiffies
1474                                         + msecs_to_jiffies(interval_msecs))) {
1475                 *caller_jiffies = jiffies;
1476                 return true;
1477         }
1478         return false;
1479 }
1480 EXPORT_SYMBOL(printk_timed_ratelimit);
1481
1482 static DEFINE_SPINLOCK(dump_list_lock);
1483 static LIST_HEAD(dump_list);
1484
1485 /**
1486  * kmsg_dump_register - register a kernel log dumper.
1487  * @dumper: pointer to the kmsg_dumper structure
1488  *
1489  * Adds a kernel log dumper to the system. The dump callback in the
1490  * structure will be called when the kernel oopses or panics and must be
1491  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1492  */
1493 int kmsg_dump_register(struct kmsg_dumper *dumper)
1494 {
1495         unsigned long flags;
1496         int err = -EBUSY;
1497
1498         /* The dump callback needs to be set */
1499         if (!dumper->dump)
1500                 return -EINVAL;
1501
1502         spin_lock_irqsave(&dump_list_lock, flags);
1503         /* Don't allow registering multiple times */
1504         if (!dumper->registered) {
1505                 dumper->registered = 1;
1506                 list_add_tail_rcu(&dumper->list, &dump_list);
1507                 err = 0;
1508         }
1509         spin_unlock_irqrestore(&dump_list_lock, flags);
1510
1511         return err;
1512 }
1513 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1514
1515 /**
1516  * kmsg_dump_unregister - unregister a kmsg dumper.
1517  * @dumper: pointer to the kmsg_dumper structure
1518  *
1519  * Removes a dump device from the system. Returns zero on success and
1520  * %-EINVAL otherwise.
1521  */
1522 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1523 {
1524         unsigned long flags;
1525         int err = -EINVAL;
1526
1527         spin_lock_irqsave(&dump_list_lock, flags);
1528         if (dumper->registered) {
1529                 dumper->registered = 0;
1530                 list_del_rcu(&dumper->list);
1531                 err = 0;
1532         }
1533         spin_unlock_irqrestore(&dump_list_lock, flags);
1534         synchronize_rcu();
1535
1536         return err;
1537 }
1538 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1539
1540 /**
1541  * kmsg_dump - dump kernel log to kernel message dumpers.
1542  * @reason: the reason (oops, panic etc) for dumping
1543  *
1544  * Iterate through each of the dump devices and call the oops/panic
1545  * callbacks with the log buffer.
1546  */
1547 void kmsg_dump(enum kmsg_dump_reason reason)
1548 {
1549         unsigned long end;
1550         unsigned chars;
1551         struct kmsg_dumper *dumper;
1552         const char *s1, *s2;
1553         unsigned long l1, l2;
1554         unsigned long flags;
1555
1556         /* Theoretically, the log could move on after we do this, but
1557            there's not a lot we can do about that. The new messages
1558            will overwrite the start of what we dump. */
1559         spin_lock_irqsave(&logbuf_lock, flags);
1560         end = log_end & LOG_BUF_MASK;
1561         chars = logged_chars;
1562         spin_unlock_irqrestore(&logbuf_lock, flags);
1563
1564         if (chars > end) {
1565                 s1 = log_buf + log_buf_len - chars + end;
1566                 l1 = chars - end;
1567
1568                 s2 = log_buf;
1569                 l2 = end;
1570         } else {
1571                 s1 = "";
1572                 l1 = 0;
1573
1574                 s2 = log_buf + end - chars;
1575                 l2 = chars;
1576         }
1577
1578         rcu_read_lock();
1579         list_for_each_entry_rcu(dumper, &dump_list, list)
1580                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1581         rcu_read_unlock();
1582 }
1583 #endif