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   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
  37 #include <asm/uaccess.h>
  38
  39 /*
  40  * Architectures can override it:
  41  */
  42 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  43 {
  44 }
  45
  46 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  47
  48 /* printk's without a loglevel use this.. */
  49 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  50
  51 /* We show everything that is MORE important than this.. */
  52 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  53 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  54
  55 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  56
  57 int console_printk[4] = {
  58         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  59         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  60         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  61         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  62 };
  63
  64 /*
  65  * Low level drivers may need that to know if they can schedule in
  66  * their unblank() callback or not. So let's export it.
  67  */
  68 int oops_in_progress;
  69 EXPORT_SYMBOL(oops_in_progress);
  70
  71 /*
  72  * console_sem protects the console_drivers list, and also
  73  * provides serialisation for access to the entire console
  74  * driver system.
  75  */
  76 static DECLARE_MUTEX(console_sem);
  77 struct console *console_drivers;
  78 EXPORT_SYMBOL_GPL(console_drivers);
  79
  80 /*
  81  * This is used for debugging the mess that is the VT code by
  82  * keeping track if we have the console semaphore held. It's
  83  * definitely not the perfect debug tool (we don't know if _WE_
  84  * hold it are racing, but it helps tracking those weird code
  85  * path in the console code where we end up in places I want
  86  * locked without the console sempahore held
  87  */
  88 static int console_locked, console_suspended;
  89
  90 /*
  91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  92  * It is also used in interesting ways to provide interlocking in
  93  * release_console_sem().
  94  */
  95 static DEFINE_SPINLOCK(logbuf_lock);
  96
  97 #define LOG_BUF_MASK (log_buf_len-1)
  98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  99
 100 /*
 101  * The indices into log_buf are not constrained to log_buf_len - they
 102  * must be masked before subscripting
 103  */
 104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 107
 108 /*
 109  *      Array of consoles built from command line options (console=)
 110  */
 111 struct console_cmdline
 112 {
 113         char    name[8];                        /* Name of the driver       */
 114         int     index;                          /* Minor dev. to use        */
 115         char    *options;                       /* Options for the driver   */
 116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 117         char    *brl_options;                   /* Options for braille driver */
 118 #endif
 119 };
 120
 121 #define MAX_CMDLINECONSOLES 8
 122
 123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 124 static int selected_console = -1;
 125 static int preferred_console = -1;
 126 int console_set_on_cmdline;
 127 EXPORT_SYMBOL(console_set_on_cmdline);
 128
 129 /* Flag: console code may call schedule() */
 130 static int console_may_schedule;
 131
 132 #ifdef CONFIG_PRINTK
 133
 134 static char __log_buf[__LOG_BUF_LEN];
 135 static char *log_buf = __log_buf;
 136 static int log_buf_len = __LOG_BUF_LEN;
 137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 138
 139 #ifdef CONFIG_KEXEC
 140 /*
 141  * This appends the listed symbols to /proc/vmcoreinfo
 142  *
 143  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 144  * obtain access to symbols that are otherwise very difficult to locate.  These
 145  * symbols are specifically used so that utilities can access and extract the
 146  * dmesg log from a vmcore file after a crash.
 147  */
 148 void log_buf_kexec_setup(void)
 149 {
 150         VMCOREINFO_SYMBOL(log_buf);
 151         VMCOREINFO_SYMBOL(log_end);
 152         VMCOREINFO_SYMBOL(log_buf_len);
 153         VMCOREINFO_SYMBOL(logged_chars);
 154 }
 155 #endif
 156
 157 static int __init log_buf_len_setup(char *str)
 158 {
 159         unsigned size = memparse(str, &str);
 160         unsigned long flags;
 161
 162         if (size)
 163                 size = roundup_pow_of_two(size);
 164         if (size > log_buf_len) {
 165                 unsigned start, dest_idx, offset;
 166                 char *new_log_buf;
 167
 168                 new_log_buf = alloc_bootmem(size);
 169                 if (!new_log_buf) {
 170                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 171                         goto out;
 172                 }
 173
 174                 spin_lock_irqsave(&logbuf_lock, flags);
 175                 log_buf_len = size;
 176                 log_buf = new_log_buf;
 177
 178                 offset = start = min(con_start, log_start);
 179                 dest_idx = 0;
 180                 while (start != log_end) {
 181                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 182                         start++;
 183                         dest_idx++;
 184                 }
 185                 log_start -= offset;
 186                 con_start -= offset;
 187                 log_end -= offset;
 188                 spin_unlock_irqrestore(&logbuf_lock, flags);
 189
 190                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 191         }
 192 out:
 193         return 1;
 194 }
 195
 196 __setup("log_buf_len=", log_buf_len_setup);
 197
 198 #ifdef CONFIG_BOOT_PRINTK_DELAY
 199
 200 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 201 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 202
 203 static int __init boot_delay_setup(char *str)
 204 {
 205         unsigned long lpj;
 206         unsigned long long loops_per_msec;
 207
 208         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 209         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 210
 211         get_option(&str, &boot_delay);
 212         if (boot_delay > 10 * 1000)
 213                 boot_delay = 0;
 214
 215         printk_delay_msec = loops_per_msec;
 216         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 217                 "HZ: %d, printk_delay_msec: %llu\n",
 218                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 219         return 1;
 220 }
 221 __setup("boot_delay=", boot_delay_setup);
 222
 223 static void boot_delay_msec(void)
 224 {
 225         unsigned long long k;
 226         unsigned long timeout;
 227
 228         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 229                 return;
 230
 231         k = (unsigned long long)printk_delay_msec * boot_delay;
 232
 233         timeout = jiffies + msecs_to_jiffies(boot_delay);
 234         while (k) {
 235                 k--;
 236                 cpu_relax();
 237                 /*
 238                  * use (volatile) jiffies to prevent
 239                  * compiler reduction; loop termination via jiffies
 240                  * is secondary and may or may not happen.
 241                  */
 242                 if (time_after(jiffies, timeout))
 243                         break;
 244                 touch_nmi_watchdog();
 245         }
 246 }
 247 #else
 248 static inline void boot_delay_msec(void)
 249 {
 250 }
 251 #endif
 252
 253 /*
 254  * Commands to do_syslog:
 255  *
 256  *      0 -- Close the log.  Currently a NOP.
 257  *      1 -- Open the log. Currently a NOP.
 258  *      2 -- Read from the log.
 259  *      3 -- Read all messages remaining in the ring buffer.
 260  *      4 -- Read and clear all messages remaining in the ring buffer
 261  *      5 -- Clear ring buffer.
 262  *      6 -- Disable printk's to console
 263  *      7 -- Enable printk's to console
 264  *      8 -- Set level of messages printed to console
 265  *      9 -- Return number of unread characters in the log buffer
 266  *     10 -- Return size of the log buffer
 267  */
 268 int do_syslog(int type, char __user *buf, int len)
 269 {
 270         unsigned i, j, limit, count;
 271         int do_clear = 0;
 272         char c;
 273         int error = 0;
 274
 275         error = security_syslog(type);
 276         if (error)
 277                 return error;
 278
 279         switch (type) {
 280         case 0:         /* Close log */
 281                 break;
 282         case 1:         /* Open log */
 283                 break;
 284         case 2:         /* Read from log */
 285                 error = -EINVAL;
 286                 if (!buf || len < 0)
 287                         goto out;
 288                 error = 0;
 289                 if (!len)
 290                         goto out;
 291                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 292                         error = -EFAULT;
 293                         goto out;
 294                 }
 295                 error = wait_event_interruptible(log_wait,
 296                                                         (log_start - log_end));
 297                 if (error)
 298                         goto out;
 299                 i = 0;
 300                 spin_lock_irq(&logbuf_lock);
 301                 while (!error && (log_start != log_end) && i < len) {
 302                         c = LOG_BUF(log_start);
 303                         log_start++;
 304                         spin_unlock_irq(&logbuf_lock);
 305                         error = __put_user(c,buf);
 306                         buf++;
 307                         i++;
 308                         cond_resched();
 309                         spin_lock_irq(&logbuf_lock);
 310                 }
 311                 spin_unlock_irq(&logbuf_lock);
 312                 if (!error)
 313                         error = i;
 314                 break;
 315         case 4:         /* Read/clear last kernel messages */
 316                 do_clear = 1;
 317                 /* FALL THRU */
 318         case 3:         /* Read last kernel messages */
 319                 error = -EINVAL;
 320                 if (!buf || len < 0)
 321                         goto out;
 322                 error = 0;
 323                 if (!len)
 324                         goto out;
 325                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 326                         error = -EFAULT;
 327                         goto out;
 328                 }
 329                 count = len;
 330                 if (count > log_buf_len)
 331                         count = log_buf_len;
 332                 spin_lock_irq(&logbuf_lock);
 333                 if (count > logged_chars)
 334                         count = logged_chars;
 335                 if (do_clear)
 336                         logged_chars = 0;
 337                 limit = log_end;
 338                 /*
 339                  * __put_user() could sleep, and while we sleep
 340                  * printk() could overwrite the messages
 341                  * we try to copy to user space. Therefore
 342                  * the messages are copied in reverse. <manfreds>
 343                  */
 344                 for (i = 0; i < count && !error; i++) {
 345                         j = limit-1-i;
 346                         if (j + log_buf_len < log_end)
 347                                 break;
 348                         c = LOG_BUF(j);
 349                         spin_unlock_irq(&logbuf_lock);
 350                         error = __put_user(c,&buf[count-1-i]);
 351                         cond_resched();
 352                         spin_lock_irq(&logbuf_lock);
 353                 }
 354                 spin_unlock_irq(&logbuf_lock);
 355                 if (error)
 356                         break;
 357                 error = i;
 358                 if (i != count) {
 359                         int offset = count-error;
 360                         /* buffer overflow during copy, correct user buffer. */
 361                         for (i = 0; i < error; i++) {
 362                                 if (__get_user(c,&buf[i+offset]) ||
 363                                     __put_user(c,&buf[i])) {
 364                                         error = -EFAULT;
 365                                         break;
 366                                 }
 367                                 cond_resched();
 368                         }
 369                 }
 370                 break;
 371         case 5:         /* Clear ring buffer */
 372                 logged_chars = 0;
 373                 break;
 374         case 6:         /* Disable logging to console */
 375                 console_loglevel = minimum_console_loglevel;
 376                 break;
 377         case 7:         /* Enable logging to console */
 378                 console_loglevel = default_console_loglevel;
 379                 break;
 380         case 8:         /* Set level of messages printed to console */
 381                 error = -EINVAL;
 382                 if (len < 1 || len > 8)
 383                         goto out;
 384                 if (len < minimum_console_loglevel)
 385                         len = minimum_console_loglevel;
 386                 console_loglevel = len;
 387                 error = 0;
 388                 break;
 389         case 9:         /* Number of chars in the log buffer */
 390                 error = log_end - log_start;
 391                 break;
 392         case 10:        /* Size of the log buffer */
 393                 error = log_buf_len;
 394                 break;
 395         default:
 396                 error = -EINVAL;
 397                 break;
 398         }
 399 out:
 400         return error;
 401 }
 402
 403 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 404 {
 405         return do_syslog(type, buf, len);
 406 }
 407
 408 /*
 409  * Call the console drivers on a range of log_buf
 410  */
 411 static void __call_console_drivers(unsigned start, unsigned end)
 412 {
 413         struct console *con;
 414
 415         for (con = console_drivers; con; con = con->next) {
 416                 if ((con->flags & CON_ENABLED) && con->write &&
 417                                 (cpu_online(smp_processor_id()) ||
 418                                 (con->flags & CON_ANYTIME)))
 419                         con->write(con, &LOG_BUF(start), end - start);
 420         }
 421 }
 422
 423 static int __read_mostly ignore_loglevel;
 424
 425 static int __init ignore_loglevel_setup(char *str)
 426 {
 427         ignore_loglevel = 1;
 428         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 429
 430         return 0;
 431 }
 432
 433 early_param("ignore_loglevel", ignore_loglevel_setup);
 434
 435 /*
 436  * Write out chars from start to end - 1 inclusive
 437  */
 438 static void _call_console_drivers(unsigned start,
 439                                 unsigned end, int msg_log_level)
 440 {
 441         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 442                         console_drivers && start != end) {
 443                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 444                         /* wrapped write */
 445                         __call_console_drivers(start & LOG_BUF_MASK,
 446                                                 log_buf_len);
 447                         __call_console_drivers(0, end & LOG_BUF_MASK);
 448                 } else {
 449                         __call_console_drivers(start, end);
 450                 }
 451         }
 452 }
 453
 454 /*
 455  * Call the console drivers, asking them to write out
 456  * log_buf[start] to log_buf[end - 1].
 457  * The console_sem must be held.
 458  */
 459 static void call_console_drivers(unsigned start, unsigned end)
 460 {
 461         unsigned cur_index, start_print;
 462         static int msg_level = -1;
 463
 464         BUG_ON(((int)(start - end)) > 0);
 465
 466         cur_index = start;
 467         start_print = start;
 468         while (cur_index != end) {
 469                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 470                                 LOG_BUF(cur_index + 0) == '<' &&
 471                                 LOG_BUF(cur_index + 1) >= '0' &&
 472                                 LOG_BUF(cur_index + 1) <= '7' &&
 473                                 LOG_BUF(cur_index + 2) == '>') {
 474                         msg_level = LOG_BUF(cur_index + 1) - '0';
 475                         cur_index += 3;
 476                         start_print = cur_index;
 477                 }
 478                 while (cur_index != end) {
 479                         char c = LOG_BUF(cur_index);
 480
 481                         cur_index++;
 482                         if (c == '\n') {
 483                                 if (msg_level < 0) {
 484                                         /*
 485                                          * printk() has already given us loglevel tags in
 486                                          * the buffer.  This code is here in case the
 487                                          * log buffer has wrapped right round and scribbled
 488                                          * on those tags
 489                                          */
 490                                         msg_level = default_message_loglevel;
 491                                 }
 492                                 _call_console_drivers(start_print, cur_index, msg_level);
 493                                 msg_level = -1;
 494                                 start_print = cur_index;
 495                                 break;
 496                         }
 497                 }
 498         }
 499         _call_console_drivers(start_print, end, msg_level);
 500 }
 501
 502 static void emit_log_char(char c)
 503 {
 504         LOG_BUF(log_end) = c;
 505         log_end++;
 506         if (log_end - log_start > log_buf_len)
 507                 log_start = log_end - log_buf_len;
 508         if (log_end - con_start > log_buf_len)
 509                 con_start = log_end - log_buf_len;
 510         if (logged_chars < log_buf_len)
 511                 logged_chars++;
 512 }
 513
 514 /*
 515  * Zap console related locks when oopsing. Only zap at most once
 516  * every 10 seconds, to leave time for slow consoles to print a
 517  * full oops.
 518  */
 519 static void zap_locks(void)
 520 {
 521         static unsigned long oops_timestamp;
 522
 523         if (time_after_eq(jiffies, oops_timestamp) &&
 524                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 525                 return;
 526
 527         oops_timestamp = jiffies;
 528
 529         /* If a crash is occurring, make sure we can't deadlock */
 530         spin_lock_init(&logbuf_lock);
 531         /* And make sure that we print immediately */
 532         init_MUTEX(&console_sem);
 533 }
 534
 535 #if defined(CONFIG_PRINTK_TIME)
 536 static int printk_time = 1;
 537 #else
 538 static int printk_time = 0;
 539 #endif
 540 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 541
 542 /* Check if we have any console registered that can be called early in boot. */
 543 static int have_callable_console(void)
 544 {
 545         struct console *con;
 546
 547         for (con = console_drivers; con; con = con->next)
 548                 if (con->flags & CON_ANYTIME)
 549                         return 1;
 550
 551         return 0;
 552 }
 553
 554 /**
 555  * printk - print a kernel message
 556  * @fmt: format string
 557  *
 558  * This is printk().  It can be called from any context.  We want it to work.
 559  *
 560  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 561  * call the console drivers.  If we fail to get the semaphore we place the output
 562  * into the log buffer and return.  The current holder of the console_sem will
 563  * notice the new output in release_console_sem() and will send it to the
 564  * consoles before releasing the semaphore.
 565  *
 566  * One effect of this deferred printing is that code which calls printk() and
 567  * then changes console_loglevel may break. This is because console_loglevel
 568  * is inspected when the actual printing occurs.
 569  *
 570  * See also:
 571  * printf(3)
 572  *
 573  * See the vsnprintf() documentation for format string extensions over C99.
 574  */
 575
 576 asmlinkage int printk(const char *fmt, ...)
 577 {
 578         va_list args;
 579         int r;
 580
 581         va_start(args, fmt);
 582         r = vprintk(fmt, args);
 583         va_end(args);
 584
 585         return r;
 586 }
 587
 588 /* cpu currently holding logbuf_lock */
 589 static volatile unsigned int printk_cpu = UINT_MAX;
 590
 591 /*
 592  * Can we actually use the console at this time on this cpu?
 593  *
 594  * Console drivers may assume that per-cpu resources have
 595  * been allocated. So unless they're explicitly marked as
 596  * being able to cope (CON_ANYTIME) don't call them until
 597  * this CPU is officially up.
 598  */
 599 static inline int can_use_console(unsigned int cpu)
 600 {
 601         return cpu_online(cpu) || have_callable_console();
 602 }
 603
 604 /*
 605  * Try to get console ownership to actually show the kernel
 606  * messages from a 'printk'. Return true (and with the
 607  * console_semaphore held, and 'console_locked' set) if it
 608  * is successful, false otherwise.
 609  *
 610  * This gets called with the 'logbuf_lock' spinlock held and
 611  * interrupts disabled. It should return with 'lockbuf_lock'
 612  * released but interrupts still disabled.
 613  */
 614 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 615 {
 616         int retval = 0;
 617
 618         if (!try_acquire_console_sem()) {
 619                 retval = 1;
 620
 621                 /*
 622                  * If we can't use the console, we need to release
 623                  * the console semaphore by hand to avoid flushing
 624                  * the buffer. We need to hold the console semaphore
 625                  * in order to do this test safely.
 626                  */
 627                 if (!can_use_console(cpu)) {
 628                         console_locked = 0;
 629                         up(&console_sem);
 630                         retval = 0;
 631                 }
 632         }
 633         printk_cpu = UINT_MAX;
 634         spin_unlock(&logbuf_lock);
 635         return retval;
 636 }
 637 static const char recursion_bug_msg [] =
 638                 KERN_CRIT "BUG: recent printk recursion!\n";
 639 static int recursion_bug;
 640 static int new_text_line = 1;
 641 static char printk_buf[1024];
 642
 643 asmlinkage int vprintk(const char *fmt, va_list args)
 644 {
 645         int printed_len = 0;
 646         int current_log_level = default_message_loglevel;
 647         unsigned long flags;
 648         int this_cpu;
 649         char *p;
 650
 651         boot_delay_msec();
 652
 653         preempt_disable();
 654         /* This stops the holder of console_sem just where we want him */
 655         raw_local_irq_save(flags);
 656         this_cpu = smp_processor_id();
 657
 658         /*
 659          * Ouch, printk recursed into itself!
 660          */
 661         if (unlikely(printk_cpu == this_cpu)) {
 662                 /*
 663                  * If a crash is occurring during printk() on this CPU,
 664                  * then try to get the crash message out but make sure
 665                  * we can't deadlock. Otherwise just return to avoid the
 666                  * recursion and return - but flag the recursion so that
 667                  * it can be printed at the next appropriate moment:
 668                  */
 669                 if (!oops_in_progress) {
 670                         recursion_bug = 1;
 671                         goto out_restore_irqs;
 672                 }
 673                 zap_locks();
 674         }
 675
 676         lockdep_off();
 677         spin_lock(&logbuf_lock);
 678         printk_cpu = this_cpu;
 679
 680         if (recursion_bug) {
 681                 recursion_bug = 0;
 682                 strcpy(printk_buf, recursion_bug_msg);
 683                 printed_len = strlen(recursion_bug_msg);
 684         }
 685         /* Emit the output into the temporary buffer */
 686         printed_len += vscnprintf(printk_buf + printed_len,
 687                                   sizeof(printk_buf) - printed_len, fmt, args);
 688
 689
 690         /*
 691          * Copy the output into log_buf.  If the caller didn't provide
 692          * appropriate log level tags, we insert them here
 693          */
 694         for (p = printk_buf; *p; p++) {
 695                 if (new_text_line) {
 696                         /* If a token, set current_log_level and skip over */
 697                         if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
 698                             p[2] == '>') {
 699                                 current_log_level = p[1] - '0';
 700                                 p += 3;
 701                                 printed_len -= 3;
 702                         }
 703
 704                         /* Always output the token */
 705                         emit_log_char('<');
 706                         emit_log_char(current_log_level + '0');
 707                         emit_log_char('>');
 708                         printed_len += 3;
 709                         new_text_line = 0;
 710
 711                         if (printk_time) {
 712                                 /* Follow the token with the time */
 713                                 char tbuf[50], *tp;
 714                                 unsigned tlen;
 715                                 unsigned long long t;
 716                                 unsigned long nanosec_rem;
 717
 718                                 t = cpu_clock(printk_cpu);
 719                                 nanosec_rem = do_div(t, 1000000000);
 720                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 721                                                 (unsigned long) t,
 722                                                 nanosec_rem / 1000);
 723
 724                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 725                                         emit_log_char(*tp);
 726                                 printed_len += tlen;
 727                         }
 728
 729                         if (!*p)
 730                                 break;
 731                 }
 732
 733                 emit_log_char(*p);
 734                 if (*p == '\n')
 735                         new_text_line = 1;
 736         }
 737
 738         /*
 739          * Try to acquire and then immediately release the
 740          * console semaphore. The release will do all the
 741          * actual magic (print out buffers, wake up klogd,
 742          * etc).
 743          *
 744          * The acquire_console_semaphore_for_printk() function
 745          * will release 'logbuf_lock' regardless of whether it
 746          * actually gets the semaphore or not.
 747          */
 748         if (acquire_console_semaphore_for_printk(this_cpu))
 749                 release_console_sem();
 750
 751         lockdep_on();
 752 out_restore_irqs:
 753         raw_local_irq_restore(flags);
 754
 755         preempt_enable();
 756         return printed_len;
 757 }
 758 EXPORT_SYMBOL(printk);
 759 EXPORT_SYMBOL(vprintk);
 760
 761 #else
 762
 763 static void call_console_drivers(unsigned start, unsigned end)
 764 {
 765 }
 766
 767 #endif
 768
 769 static int __add_preferred_console(char *name, int idx, char *options,
 770                                    char *brl_options)
 771 {
 772         struct console_cmdline *c;
 773         int i;
 774
 775         /*
 776          *      See if this tty is not yet registered, and
 777          *      if we have a slot free.
 778          */
 779         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 780                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 781                           console_cmdline[i].index == idx) {
 782                                 if (!brl_options)
 783                                         selected_console = i;
 784                                 return 0;
 785                 }
 786         if (i == MAX_CMDLINECONSOLES)
 787                 return -E2BIG;
 788         if (!brl_options)
 789                 selected_console = i;
 790         c = &console_cmdline[i];
 791         strlcpy(c->name, name, sizeof(c->name));
 792         c->options = options;
 793 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 794         c->brl_options = brl_options;
 795 #endif
 796         c->index = idx;
 797         return 0;
 798 }
 799 /*
 800  * Set up a list of consoles.  Called from init/main.c
 801  */
 802 static int __init console_setup(char *str)
 803 {
 804         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 805         char *s, *options, *brl_options = NULL;
 806         int idx;
 807
 808 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 809         if (!memcmp(str, "brl,", 4)) {
 810                 brl_options = "";
 811                 str += 4;
 812         } else if (!memcmp(str, "brl=", 4)) {
 813                 brl_options = str + 4;
 814                 str = strchr(brl_options, ',');
 815                 if (!str) {
 816                         printk(KERN_ERR "need port name after brl=\n");
 817                         return 1;
 818                 }
 819                 *(str++) = 0;
 820         }
 821 #endif
 822
 823         /*
 824          * Decode str into name, index, options.
 825          */
 826         if (str[0] >= '0' && str[0] <= '9') {
 827                 strcpy(buf, "ttyS");
 828                 strncpy(buf + 4, str, sizeof(buf) - 5);
 829         } else {
 830                 strncpy(buf, str, sizeof(buf) - 1);
 831         }
 832         buf[sizeof(buf) - 1] = 0;
 833         if ((options = strchr(str, ',')) != NULL)
 834                 *(options++) = 0;
 835 #ifdef __sparc__
 836         if (!strcmp(str, "ttya"))
 837                 strcpy(buf, "ttyS0");
 838         if (!strcmp(str, "ttyb"))
 839                 strcpy(buf, "ttyS1");
 840 #endif
 841         for (s = buf; *s; s++)
 842                 if ((*s >= '0' && *s <= '9') || *s == ',')
 843                         break;
 844         idx = simple_strtoul(s, NULL, 10);
 845         *s = 0;
 846
 847         __add_preferred_console(buf, idx, options, brl_options);
 848         console_set_on_cmdline = 1;
 849         return 1;
 850 }
 851 __setup("console=", console_setup);
 852
 853 /**
 854  * add_preferred_console - add a device to the list of preferred consoles.
 855  * @name: device name
 856  * @idx: device index
 857  * @options: options for this console
 858  *
 859  * The last preferred console added will be used for kernel messages
 860  * and stdin/out/err for init.  Normally this is used by console_setup
 861  * above to handle user-supplied console arguments; however it can also
 862  * be used by arch-specific code either to override the user or more
 863  * commonly to provide a default console (ie from PROM variables) when
 864  * the user has not supplied one.
 865  */
 866 int add_preferred_console(char *name, int idx, char *options)
 867 {
 868         return __add_preferred_console(name, idx, options, NULL);
 869 }
 870
 871 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 872 {
 873         struct console_cmdline *c;
 874         int i;
 875
 876         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 877                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 878                           console_cmdline[i].index == idx) {
 879                                 c = &console_cmdline[i];
 880                                 strlcpy(c->name, name_new, sizeof(c->name));
 881                                 c->name[sizeof(c->name) - 1] = 0;
 882                                 c->options = options;
 883                                 c->index = idx_new;
 884                                 return i;
 885                 }
 886         /* not found */
 887         return -1;
 888 }
 889
 890 int console_suspend_enabled = 1;
 891 EXPORT_SYMBOL(console_suspend_enabled);
 892
 893 static int __init console_suspend_disable(char *str)
 894 {
 895         console_suspend_enabled = 0;
 896         return 1;
 897 }
 898 __setup("no_console_suspend", console_suspend_disable);
 899
 900 /**
 901  * suspend_console - suspend the console subsystem
 902  *
 903  * This disables printk() while we go into suspend states
 904  */
 905 void suspend_console(void)
 906 {
 907         if (!console_suspend_enabled)
 908                 return;
 909         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 910         acquire_console_sem();
 911         console_suspended = 1;
 912         up(&console_sem);
 913 }
 914
 915 void resume_console(void)
 916 {
 917         if (!console_suspend_enabled)
 918                 return;
 919         down(&console_sem);
 920         console_suspended = 0;
 921         release_console_sem();
 922 }
 923
 924 /**
 925  * acquire_console_sem - lock the console system for exclusive use.
 926  *
 927  * Acquires a semaphore which guarantees that the caller has
 928  * exclusive access to the console system and the console_drivers list.
 929  *
 930  * Can sleep, returns nothing.
 931  */
 932 void acquire_console_sem(void)
 933 {
 934         BUG_ON(in_interrupt());
 935         down(&console_sem);
 936         if (console_suspended)
 937                 return;
 938         console_locked = 1;
 939         console_may_schedule = 1;
 940 }
 941 EXPORT_SYMBOL(acquire_console_sem);
 942
 943 int try_acquire_console_sem(void)
 944 {
 945         if (down_trylock(&console_sem))
 946                 return -1;
 947         if (console_suspended) {
 948                 up(&console_sem);
 949                 return -1;
 950         }
 951         console_locked = 1;
 952         console_may_schedule = 0;
 953         return 0;
 954 }
 955 EXPORT_SYMBOL(try_acquire_console_sem);
 956
 957 int is_console_locked(void)
 958 {
 959         return console_locked;
 960 }
 961
 962 static DEFINE_PER_CPU(int, printk_pending);
 963
 964 void printk_tick(void)
 965 {
 966         if (__get_cpu_var(printk_pending)) {
 967                 __get_cpu_var(printk_pending) = 0;
 968                 wake_up_interruptible(&log_wait);
 969         }
 970 }
 971
 972 int printk_needs_cpu(int cpu)
 973 {
 974         return per_cpu(printk_pending, cpu);
 975 }
 976
 977 void wake_up_klogd(void)
 978 {
 979         if (waitqueue_active(&log_wait))
 980                 __raw_get_cpu_var(printk_pending) = 1;
 981 }
 982
 983 /**
 984  * release_console_sem - unlock the console system
 985  *
 986  * Releases the semaphore which the caller holds on the console system
 987  * and the console driver list.
 988  *
 989  * While the semaphore was held, console output may have been buffered
 990  * by printk().  If this is the case, release_console_sem() emits
 991  * the output prior to releasing the semaphore.
 992  *
 993  * If there is output waiting for klogd, we wake it up.
 994  *
 995  * release_console_sem() may be called from any context.
 996  */
 997 void release_console_sem(void)
 998 {
 999         unsigned long flags;
1000         unsigned _con_start, _log_end;
1001         unsigned wake_klogd = 0;
1002
1003         if (console_suspended) {
1004                 up(&console_sem);
1005                 return;
1006         }
1007
1008         console_may_schedule = 0;
1009
1010         for ( ; ; ) {
1011                 spin_lock_irqsave(&logbuf_lock, flags);
1012                 wake_klogd |= log_start - log_end;
1013                 if (con_start == log_end)
1014                         break;                  /* Nothing to print */
1015                 _con_start = con_start;
1016                 _log_end = log_end;
1017                 con_start = log_end;            /* Flush */
1018                 spin_unlock(&logbuf_lock);
1019                 stop_critical_timings();        /* don't trace print latency */
1020                 call_console_drivers(_con_start, _log_end);
1021                 start_critical_timings();
1022                 local_irq_restore(flags);
1023         }
1024         console_locked = 0;
1025         up(&console_sem);
1026         spin_unlock_irqrestore(&logbuf_lock, flags);
1027         if (wake_klogd)
1028                 wake_up_klogd();
1029 }
1030 EXPORT_SYMBOL(release_console_sem);
1031
1032 /**
1033  * console_conditional_schedule - yield the CPU if required
1034  *
1035  * If the console code is currently allowed to sleep, and
1036  * if this CPU should yield the CPU to another task, do
1037  * so here.
1038  *
1039  * Must be called within acquire_console_sem().
1040  */
1041 void __sched console_conditional_schedule(void)
1042 {
1043         if (console_may_schedule)
1044                 cond_resched();
1045 }
1046 EXPORT_SYMBOL(console_conditional_schedule);
1047
1048 void console_print(const char *s)
1049 {
1050         printk(KERN_EMERG "%s", s);
1051 }
1052 EXPORT_SYMBOL(console_print);
1053
1054 void console_unblank(void)
1055 {
1056         struct console *c;
1057
1058         /*
1059          * console_unblank can no longer be called in interrupt context unless
1060          * oops_in_progress is set to 1..
1061          */
1062         if (oops_in_progress) {
1063                 if (down_trylock(&console_sem) != 0)
1064                         return;
1065         } else
1066                 acquire_console_sem();
1067
1068         console_locked = 1;
1069         console_may_schedule = 0;
1070         for (c = console_drivers; c != NULL; c = c->next)
1071                 if ((c->flags & CON_ENABLED) && c->unblank)
1072                         c->unblank();
1073         release_console_sem();
1074 }
1075
1076 /*
1077  * Return the console tty driver structure and its associated index
1078  */
1079 struct tty_driver *console_device(int *index)
1080 {
1081         struct console *c;
1082         struct tty_driver *driver = NULL;
1083
1084         acquire_console_sem();
1085         for (c = console_drivers; c != NULL; c = c->next) {
1086                 if (!c->device)
1087                         continue;
1088                 driver = c->device(c, index);
1089                 if (driver)
1090                         break;
1091         }
1092         release_console_sem();
1093         return driver;
1094 }
1095
1096 /*
1097  * Prevent further output on the passed console device so that (for example)
1098  * serial drivers can disable console output before suspending a port, and can
1099  * re-enable output afterwards.
1100  */
1101 void console_stop(struct console *console)
1102 {
1103         acquire_console_sem();
1104         console->flags &= ~CON_ENABLED;
1105         release_console_sem();
1106 }
1107 EXPORT_SYMBOL(console_stop);
1108
1109 void console_start(struct console *console)
1110 {
1111         acquire_console_sem();
1112         console->flags |= CON_ENABLED;
1113         release_console_sem();
1114 }
1115 EXPORT_SYMBOL(console_start);
1116
1117 /*
1118  * The console driver calls this routine during kernel initialization
1119  * to register the console printing procedure with printk() and to
1120  * print any messages that were printed by the kernel before the
1121  * console driver was initialized.
1122  */
1123 void register_console(struct console *console)
1124 {
1125         int i;
1126         unsigned long flags;
1127         struct console *bootconsole = NULL;
1128
1129         if (console_drivers) {
1130                 if (console->flags & CON_BOOT)
1131                         return;
1132                 if (console_drivers->flags & CON_BOOT)
1133                         bootconsole = console_drivers;
1134         }
1135
1136         if (preferred_console < 0 || bootconsole || !console_drivers)
1137                 preferred_console = selected_console;
1138
1139         if (console->early_setup)
1140                 console->early_setup();
1141
1142         /*
1143          *      See if we want to use this console driver. If we
1144          *      didn't select a console we take the first one
1145          *      that registers here.
1146          */
1147         if (preferred_console < 0) {
1148                 if (console->index < 0)
1149                         console->index = 0;
1150                 if (console->setup == NULL ||
1151                     console->setup(console, NULL) == 0) {
1152                         console->flags |= CON_ENABLED;
1153                         if (console->device) {
1154                                 console->flags |= CON_CONSDEV;
1155                                 preferred_console = 0;
1156                         }
1157                 }
1158         }
1159
1160         /*
1161          *      See if this console matches one we selected on
1162          *      the command line.
1163          */
1164         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1165                         i++) {
1166                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1167                         continue;
1168                 if (console->index >= 0 &&
1169                     console->index != console_cmdline[i].index)
1170                         continue;
1171                 if (console->index < 0)
1172                         console->index = console_cmdline[i].index;
1173 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1174                 if (console_cmdline[i].brl_options) {
1175                         console->flags |= CON_BRL;
1176                         braille_register_console(console,
1177                                         console_cmdline[i].index,
1178                                         console_cmdline[i].options,
1179                                         console_cmdline[i].brl_options);
1180                         return;
1181                 }
1182 #endif
1183                 if (console->setup &&
1184                     console->setup(console, console_cmdline[i].options) != 0)
1185                         break;
1186                 console->flags |= CON_ENABLED;
1187                 console->index = console_cmdline[i].index;
1188                 if (i == selected_console) {
1189                         console->flags |= CON_CONSDEV;
1190                         preferred_console = selected_console;
1191                 }
1192                 break;
1193         }
1194
1195         if (!(console->flags & CON_ENABLED))
1196                 return;
1197
1198         if (bootconsole && (console->flags & CON_CONSDEV)) {
1199                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1200                        bootconsole->name, bootconsole->index,
1201                        console->name, console->index);
1202                 unregister_console(bootconsole);
1203                 console->flags &= ~CON_PRINTBUFFER;
1204         } else {
1205                 printk(KERN_INFO "console [%s%d] enabled\n",
1206                        console->name, console->index);
1207         }
1208
1209         /*
1210          *      Put this console in the list - keep the
1211          *      preferred driver at the head of the list.
1212          */
1213         acquire_console_sem();
1214         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1215                 console->next = console_drivers;
1216                 console_drivers = console;
1217                 if (console->next)
1218                         console->next->flags &= ~CON_CONSDEV;
1219         } else {
1220                 console->next = console_drivers->next;
1221                 console_drivers->next = console;
1222         }
1223         if (console->flags & CON_PRINTBUFFER) {
1224                 /*
1225                  * release_console_sem() will print out the buffered messages
1226                  * for us.
1227                  */
1228                 spin_lock_irqsave(&logbuf_lock, flags);
1229                 con_start = log_start;
1230                 spin_unlock_irqrestore(&logbuf_lock, flags);
1231         }
1232         release_console_sem();
1233 }
1234 EXPORT_SYMBOL(register_console);
1235
1236 int unregister_console(struct console *console)
1237 {
1238         struct console *a, *b;
1239         int res = 1;
1240
1241 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1242         if (console->flags & CON_BRL)
1243                 return braille_unregister_console(console);
1244 #endif
1245
1246         acquire_console_sem();
1247         if (console_drivers == console) {
1248                 console_drivers=console->next;
1249                 res = 0;
1250         } else if (console_drivers) {
1251                 for (a=console_drivers->next, b=console_drivers ;
1252                      a; b=a, a=b->next) {
1253                         if (a == console) {
1254                                 b->next = a->next;
1255                                 res = 0;
1256                                 break;
1257                         }
1258                 }
1259         }
1260
1261         /*
1262          * If this isn't the last console and it has CON_CONSDEV set, we
1263          * need to set it on the next preferred console.
1264          */
1265         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1266                 console_drivers->flags |= CON_CONSDEV;
1267
1268         release_console_sem();
1269         return res;
1270 }
1271 EXPORT_SYMBOL(unregister_console);
1272
1273 static int __init disable_boot_consoles(void)
1274 {
1275         if (console_drivers != NULL) {
1276                 if (console_drivers->flags & CON_BOOT) {
1277                         printk(KERN_INFO "turn off boot console %s%d\n",
1278                                 console_drivers->name, console_drivers->index);
1279                         return unregister_console(console_drivers);
1280                 }
1281         }
1282         return 0;
1283 }
1284 late_initcall(disable_boot_consoles);
1285
1286 #if defined CONFIG_PRINTK
1287
1288 /*
1289  * printk rate limiting, lifted from the networking subsystem.
1290  *
1291  * This enforces a rate limit: not more than 10 kernel messages
1292  * every 5s to make a denial-of-service attack impossible.
1293  */
1294 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1295
1296 int printk_ratelimit(void)
1297 {
1298         return __ratelimit(&printk_ratelimit_state);
1299 }
1300 EXPORT_SYMBOL(printk_ratelimit);
1301
1302 /**
1303  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1304  * @caller_jiffies: pointer to caller's state
1305  * @interval_msecs: minimum interval between prints
1306  *
1307  * printk_timed_ratelimit() returns true if more than @interval_msecs
1308  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1309  * returned true.
1310  */
1311 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1312                         unsigned int interval_msecs)
1313 {
1314         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1315                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1316                 return true;
1317         }
1318         return false;
1319 }
1320 EXPORT_SYMBOL(printk_timed_ratelimit);
1321 #endif