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