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 <andrewm@uow.edu.au>
  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/jiffies.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  40
  41 /* printk's without a loglevel use this.. */
  42 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  43
  44 /* We show everything that is MORE important than this.. */
  45 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  46 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  47
  48 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  49
  50 int console_printk[4] = {
  51         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  52         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  53         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  54         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  55 };
  56
  57 /*
  58  * Low level drivers may need that to know if they can schedule in
  59  * their unblank() callback or not. So let's export it.
  60  */
  61 int oops_in_progress;
  62 EXPORT_SYMBOL(oops_in_progress);
  63
  64 /*
  65  * console_sem protects the console_drivers list, and also
  66  * provides serialisation for access to the entire console
  67  * driver system.
  68  */
  69 static DECLARE_MUTEX(console_sem);
  70 static DECLARE_MUTEX(secondary_console_sem);
  71 struct console *console_drivers;
  72 /*
  73  * This is used for debugging the mess that is the VT code by
  74  * keeping track if we have the console semaphore held. It's
  75  * definitely not the perfect debug tool (we don't know if _WE_
  76  * hold it are racing, but it helps tracking those weird code
  77  * path in the console code where we end up in places I want
  78  * locked without the console sempahore held
  79  */
  80 static int console_locked, console_suspended;
  81
  82 /*
  83  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  84  * It is also used in interesting ways to provide interlocking in
  85  * release_console_sem().
  86  */
  87 static DEFINE_SPINLOCK(logbuf_lock);
  88
  89 #define LOG_BUF_MASK    (log_buf_len-1)
  90 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  91
  92 /*
  93  * The indices into log_buf are not constrained to log_buf_len - they
  94  * must be masked before subscripting
  95  */
  96 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  97 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  98 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  99
 100 /*
 101  *      Array of consoles built from command line options (console=)
 102  */
 103 struct console_cmdline
 104 {
 105         char    name[8];                        /* Name of the driver       */
 106         int     index;                          /* Minor dev. to use        */
 107         char    *options;                       /* Options for the driver   */
 108 };
 109
 110 #define MAX_CMDLINECONSOLES 8
 111
 112 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 113 static int selected_console = -1;
 114 static int preferred_console = -1;
 115
 116 /* Flag: console code may call schedule() */
 117 static int console_may_schedule;
 118
 119 #ifdef CONFIG_PRINTK
 120
 121 static char __log_buf[__LOG_BUF_LEN];
 122 static char *log_buf = __log_buf;
 123 static int log_buf_len = __LOG_BUF_LEN;
 124 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 125
 126 static int __init log_buf_len_setup(char *str)
 127 {
 128         unsigned long size = memparse(str, &str);
 129         unsigned long flags;
 130
 131         if (size)
 132                 size = roundup_pow_of_two(size);
 133         if (size > log_buf_len) {
 134                 unsigned long start, dest_idx, offset;
 135                 char *new_log_buf;
 136
 137                 new_log_buf = alloc_bootmem(size);
 138                 if (!new_log_buf) {
 139                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 140                         goto out;
 141                 }
 142
 143                 spin_lock_irqsave(&logbuf_lock, flags);
 144                 log_buf_len = size;
 145                 log_buf = new_log_buf;
 146
 147                 offset = start = min(con_start, log_start);
 148                 dest_idx = 0;
 149                 while (start != log_end) {
 150                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 151                         start++;
 152                         dest_idx++;
 153                 }
 154                 log_start -= offset;
 155                 con_start -= offset;
 156                 log_end -= offset;
 157                 spin_unlock_irqrestore(&logbuf_lock, flags);
 158
 159                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 160         }
 161 out:
 162         return 1;
 163 }
 164
 165 __setup("log_buf_len=", log_buf_len_setup);
 166
 167 #ifdef CONFIG_BOOT_PRINTK_DELAY
 168
 169 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 170 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 171
 172 static int __init boot_delay_setup(char *str)
 173 {
 174         unsigned long lpj;
 175         unsigned long long loops_per_msec;
 176
 177         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 178         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 179
 180         get_option(&str, &boot_delay);
 181         if (boot_delay > 10 * 1000)
 182                 boot_delay = 0;
 183
 184         printk_delay_msec = loops_per_msec;
 185         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 186                 "HZ: %d, printk_delay_msec: %llu\n",
 187                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 188         return 1;
 189 }
 190 __setup("boot_delay=", boot_delay_setup);
 191
 192 static void boot_delay_msec(void)
 193 {
 194         unsigned long long k;
 195         unsigned long timeout;
 196
 197         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 198                 return;
 199
 200         k = (unsigned long long)printk_delay_msec * boot_delay;
 201
 202         timeout = jiffies + msecs_to_jiffies(boot_delay);
 203         while (k) {
 204                 k--;
 205                 cpu_relax();
 206                 /*
 207                  * use (volatile) jiffies to prevent
 208                  * compiler reduction; loop termination via jiffies
 209                  * is secondary and may or may not happen.
 210                  */
 211                 if (time_after(jiffies, timeout))
 212                         break;
 213                 touch_nmi_watchdog();
 214         }
 215 }
 216 #else
 217 static inline void boot_delay_msec(void)
 218 {
 219 }
 220 #endif
 221
 222 /*
 223  * Return the number of unread characters in the log buffer.
 224  */
 225 int log_buf_get_len(void)
 226 {
 227         return logged_chars;
 228 }
 229
 230 /*
 231  * Copy a range of characters from the log buffer.
 232  */
 233 int log_buf_copy(char *dest, int idx, int len)
 234 {
 235         int ret, max;
 236         bool took_lock = false;
 237
 238         if (!oops_in_progress) {
 239                 spin_lock_irq(&logbuf_lock);
 240                 took_lock = true;
 241         }
 242
 243         max = log_buf_get_len();
 244         if (idx < 0 || idx >= max) {
 245                 ret = -1;
 246         } else {
 247                 if (len > max)
 248                         len = max;
 249                 ret = len;
 250                 idx += (log_end - max);
 251                 while (len-- > 0)
 252                         dest[len] = LOG_BUF(idx + len);
 253         }
 254
 255         if (took_lock)
 256                 spin_unlock_irq(&logbuf_lock);
 257
 258         return ret;
 259 }
 260
 261 /*
 262  * Extract a single character from the log buffer.
 263  */
 264 int log_buf_read(int idx)
 265 {
 266         char ret;
 267
 268         if (log_buf_copy(&ret, idx, 1) == 1)
 269                 return ret;
 270         else
 271                 return -1;
 272 }
 273
 274 /*
 275  * Commands to do_syslog:
 276  *
 277  *      0 -- Close the log.  Currently a NOP.
 278  *      1 -- Open the log. Currently a NOP.
 279  *      2 -- Read from the log.
 280  *      3 -- Read all messages remaining in the ring buffer.
 281  *      4 -- Read and clear all messages remaining in the ring buffer
 282  *      5 -- Clear ring buffer.
 283  *      6 -- Disable printk's to console
 284  *      7 -- Enable printk's to console
 285  *      8 -- Set level of messages printed to console
 286  *      9 -- Return number of unread characters in the log buffer
 287  *     10 -- Return size of the log buffer
 288  */
 289 int do_syslog(int type, char __user *buf, int len)
 290 {
 291         unsigned long i, j, limit, count;
 292         int do_clear = 0;
 293         char c;
 294         int error = 0;
 295
 296         error = security_syslog(type);
 297         if (error)
 298                 return error;
 299
 300         switch (type) {
 301         case 0:         /* Close log */
 302                 break;
 303         case 1:         /* Open log */
 304                 break;
 305         case 2:         /* Read from log */
 306                 error = -EINVAL;
 307                 if (!buf || len < 0)
 308                         goto out;
 309                 error = 0;
 310                 if (!len)
 311                         goto out;
 312                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 313                         error = -EFAULT;
 314                         goto out;
 315                 }
 316                 error = wait_event_interruptible(log_wait,
 317                                                         (log_start - log_end));
 318                 if (error)
 319                         goto out;
 320                 i = 0;
 321                 spin_lock_irq(&logbuf_lock);
 322                 while (!error && (log_start != log_end) && i < len) {
 323                         c = LOG_BUF(log_start);
 324                         log_start++;
 325                         spin_unlock_irq(&logbuf_lock);
 326                         error = __put_user(c,buf);
 327                         buf++;
 328                         i++;
 329                         cond_resched();
 330                         spin_lock_irq(&logbuf_lock);
 331                 }
 332                 spin_unlock_irq(&logbuf_lock);
 333                 if (!error)
 334                         error = i;
 335                 break;
 336         case 4:         /* Read/clear last kernel messages */
 337                 do_clear = 1;
 338                 /* FALL THRU */
 339         case 3:         /* Read last kernel messages */
 340                 error = -EINVAL;
 341                 if (!buf || len < 0)
 342                         goto out;
 343                 error = 0;
 344                 if (!len)
 345                         goto out;
 346                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 347                         error = -EFAULT;
 348                         goto out;
 349                 }
 350                 count = len;
 351                 if (count > log_buf_len)
 352                         count = log_buf_len;
 353                 spin_lock_irq(&logbuf_lock);
 354                 if (count > logged_chars)
 355                         count = logged_chars;
 356                 if (do_clear)
 357                         logged_chars = 0;
 358                 limit = log_end;
 359                 /*
 360                  * __put_user() could sleep, and while we sleep
 361                  * printk() could overwrite the messages
 362                  * we try to copy to user space. Therefore
 363                  * the messages are copied in reverse. <manfreds>
 364                  */
 365                 for (i = 0; i < count && !error; i++) {
 366                         j = limit-1-i;
 367                         if (j + log_buf_len < log_end)
 368                                 break;
 369                         c = LOG_BUF(j);
 370                         spin_unlock_irq(&logbuf_lock);
 371                         error = __put_user(c,&buf[count-1-i]);
 372                         cond_resched();
 373                         spin_lock_irq(&logbuf_lock);
 374                 }
 375                 spin_unlock_irq(&logbuf_lock);
 376                 if (error)
 377                         break;
 378                 error = i;
 379                 if (i != count) {
 380                         int offset = count-error;
 381                         /* buffer overflow during copy, correct user buffer. */
 382                         for (i = 0; i < error; i++) {
 383                                 if (__get_user(c,&buf[i+offset]) ||
 384                                     __put_user(c,&buf[i])) {
 385                                         error = -EFAULT;
 386                                         break;
 387                                 }
 388                                 cond_resched();
 389                         }
 390                 }
 391                 break;
 392         case 5:         /* Clear ring buffer */
 393                 logged_chars = 0;
 394                 break;
 395         case 6:         /* Disable logging to console */
 396                 console_loglevel = minimum_console_loglevel;
 397                 break;
 398         case 7:         /* Enable logging to console */
 399                 console_loglevel = default_console_loglevel;
 400                 break;
 401         case 8:         /* Set level of messages printed to console */
 402                 error = -EINVAL;
 403                 if (len < 1 || len > 8)
 404                         goto out;
 405                 if (len < minimum_console_loglevel)
 406                         len = minimum_console_loglevel;
 407                 console_loglevel = len;
 408                 error = 0;
 409                 break;
 410         case 9:         /* Number of chars in the log buffer */
 411                 error = log_end - log_start;
 412                 break;
 413         case 10:        /* Size of the log buffer */
 414                 error = log_buf_len;
 415                 break;
 416         default:
 417                 error = -EINVAL;
 418                 break;
 419         }
 420 out:
 421         return error;
 422 }
 423
 424 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 425 {
 426         return do_syslog(type, buf, len);
 427 }
 428
 429 /*
 430  * Call the console drivers on a range of log_buf
 431  */
 432 static void __call_console_drivers(unsigned long start, unsigned long end)
 433 {
 434         struct console *con;
 435
 436         for (con = console_drivers; con; con = con->next) {
 437                 if ((con->flags & CON_ENABLED) && con->write &&
 438                                 (cpu_online(smp_processor_id()) ||
 439                                 (con->flags & CON_ANYTIME)))
 440                         con->write(con, &LOG_BUF(start), end - start);
 441         }
 442 }
 443
 444 static int __read_mostly ignore_loglevel;
 445
 446 static int __init ignore_loglevel_setup(char *str)
 447 {
 448         ignore_loglevel = 1;
 449         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 450
 451         return 1;
 452 }
 453
 454 __setup("ignore_loglevel", ignore_loglevel_setup);
 455
 456 /*
 457  * Write out chars from start to end - 1 inclusive
 458  */
 459 static void _call_console_drivers(unsigned long start,
 460                                 unsigned long end, int msg_log_level)
 461 {
 462         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 463                         console_drivers && start != end) {
 464                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 465                         /* wrapped write */
 466                         __call_console_drivers(start & LOG_BUF_MASK,
 467                                                 log_buf_len);
 468                         __call_console_drivers(0, end & LOG_BUF_MASK);
 469                 } else {
 470                         __call_console_drivers(start, end);
 471                 }
 472         }
 473 }
 474
 475 /*
 476  * Call the console drivers, asking them to write out
 477  * log_buf[start] to log_buf[end - 1].
 478  * The console_sem must be held.
 479  */
 480 static void call_console_drivers(unsigned long start, unsigned long end)
 481 {
 482         unsigned long cur_index, start_print;
 483         static int msg_level = -1;
 484
 485         BUG_ON(((long)(start - end)) > 0);
 486
 487         cur_index = start;
 488         start_print = start;
 489         while (cur_index != end) {
 490                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 491                                 LOG_BUF(cur_index + 0) == '<' &&
 492                                 LOG_BUF(cur_index + 1) >= '0' &&
 493                                 LOG_BUF(cur_index + 1) <= '7' &&
 494                                 LOG_BUF(cur_index + 2) == '>') {
 495                         msg_level = LOG_BUF(cur_index + 1) - '0';
 496                         cur_index += 3;
 497                         start_print = cur_index;
 498                 }
 499                 while (cur_index != end) {
 500                         char c = LOG_BUF(cur_index);
 501
 502                         cur_index++;
 503                         if (c == '\n') {
 504                                 if (msg_level < 0) {
 505                                         /*
 506                                          * printk() has already given us loglevel tags in
 507                                          * the buffer.  This code is here in case the
 508                                          * log buffer has wrapped right round and scribbled
 509                                          * on those tags
 510                                          */
 511                                         msg_level = default_message_loglevel;
 512                                 }
 513                                 _call_console_drivers(start_print, cur_index, msg_level);
 514                                 msg_level = -1;
 515                                 start_print = cur_index;
 516                                 break;
 517                         }
 518                 }
 519         }
 520         _call_console_drivers(start_print, end, msg_level);
 521 }
 522
 523 static void emit_log_char(char c)
 524 {
 525         LOG_BUF(log_end) = c;
 526         log_end++;
 527         if (log_end - log_start > log_buf_len)
 528                 log_start = log_end - log_buf_len;
 529         if (log_end - con_start > log_buf_len)
 530                 con_start = log_end - log_buf_len;
 531         if (logged_chars < log_buf_len)
 532                 logged_chars++;
 533 }
 534
 535 /*
 536  * Zap console related locks when oopsing. Only zap at most once
 537  * every 10 seconds, to leave time for slow consoles to print a
 538  * full oops.
 539  */
 540 static void zap_locks(void)
 541 {
 542         static unsigned long oops_timestamp;
 543
 544         if (time_after_eq(jiffies, oops_timestamp) &&
 545                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 546                 return;
 547
 548         oops_timestamp = jiffies;
 549
 550         /* If a crash is occurring, make sure we can't deadlock */
 551         spin_lock_init(&logbuf_lock);
 552         /* And make sure that we print immediately */
 553         init_MUTEX(&console_sem);
 554 }
 555
 556 #if defined(CONFIG_PRINTK_TIME)
 557 static int printk_time = 1;
 558 #else
 559 static int printk_time = 0;
 560 #endif
 561 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 562
 563 static int __init printk_time_setup(char *str)
 564 {
 565         if (*str)
 566                 return 0;
 567         printk_time = 1;
 568         printk(KERN_NOTICE "The 'time' option is deprecated and "
 569                 "is scheduled for removal in early 2008\n");
 570         printk(KERN_NOTICE "Use 'printk.time=<value>' instead\n");
 571         return 1;
 572 }
 573
 574 __setup("time", printk_time_setup);
 575
 576 /* Check if we have any console registered that can be called early in boot. */
 577 static int have_callable_console(void)
 578 {
 579         struct console *con;
 580
 581         for (con = console_drivers; con; con = con->next)
 582                 if (con->flags & CON_ANYTIME)
 583                         return 1;
 584
 585         return 0;
 586 }
 587
 588 /**
 589  * printk - print a kernel message
 590  * @fmt: format string
 591  *
 592  * This is printk().  It can be called from any context.  We want it to work.
 593  * Be aware of the fact that if oops_in_progress is not set, we might try to
 594  * wake klogd up which could deadlock on runqueue lock if printk() is called
 595  * from scheduler code.
 596  *
 597  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 598  * call the console drivers.  If we fail to get the semaphore we place the output
 599  * into the log buffer and return.  The current holder of the console_sem will
 600  * notice the new output in release_console_sem() and will send it to the
 601  * consoles before releasing the semaphore.
 602  *
 603  * One effect of this deferred printing is that code which calls printk() and
 604  * then changes console_loglevel may break. This is because console_loglevel
 605  * is inspected when the actual printing occurs.
 606  *
 607  * See also:
 608  * printf(3)
 609  */
 610
 611 asmlinkage int printk(const char *fmt, ...)
 612 {
 613         va_list args;
 614         int r;
 615
 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 const char printk_recursion_bug_msg [] =
 627                         KERN_CRIT "BUG: recent printk recursion!\n";
 628 static int printk_recursion_bug;
 629
 630 asmlinkage int vprintk(const char *fmt, va_list args)
 631 {
 632         static int log_level_unknown = 1;
 633         static char printk_buf[1024];
 634
 635         unsigned long flags;
 636         int printed_len = 0;
 637         int this_cpu;
 638         char *p;
 639
 640         boot_delay_msec();
 641
 642         preempt_disable();
 643         /* This stops the holder of console_sem just where we want him */
 644         raw_local_irq_save(flags);
 645         this_cpu = smp_processor_id();
 646
 647         /*
 648          * Ouch, printk recursed into itself!
 649          */
 650         if (unlikely(printk_cpu == this_cpu)) {
 651                 /*
 652                  * If a crash is occurring during printk() on this CPU,
 653                  * then try to get the crash message out but make sure
 654                  * we can't deadlock. Otherwise just return to avoid the
 655                  * recursion and return - but flag the recursion so that
 656                  * it can be printed at the next appropriate moment:
 657                  */
 658                 if (!oops_in_progress) {
 659                         printk_recursion_bug = 1;
 660                         goto out_restore_irqs;
 661                 }
 662                 zap_locks();
 663         }
 664
 665         lockdep_off();
 666         spin_lock(&logbuf_lock);
 667         printk_cpu = this_cpu;
 668
 669         if (printk_recursion_bug) {
 670                 printk_recursion_bug = 0;
 671                 strcpy(printk_buf, printk_recursion_bug_msg);
 672                 printed_len = sizeof(printk_recursion_bug_msg);
 673         }
 674         /* Emit the output into the temporary buffer */
 675         printed_len += vscnprintf(printk_buf + printed_len,
 676                                   sizeof(printk_buf), fmt, args);
 677
 678         /*
 679          * Copy the output into log_buf.  If the caller didn't provide
 680          * appropriate log level tags, we insert them here
 681          */
 682         for (p = printk_buf; *p; p++) {
 683                 if (log_level_unknown) {
 684                         /* log_level_unknown signals the start of a new line */
 685                         if (printk_time) {
 686                                 int loglev_char;
 687                                 char tbuf[50], *tp;
 688                                 unsigned tlen;
 689                                 unsigned long long t;
 690                                 unsigned long nanosec_rem;
 691
 692                                 /*
 693                                  * force the log level token to be
 694                                  * before the time output.
 695                                  */
 696                                 if (p[0] == '<' && p[1] >='0' &&
 697                                    p[1] <= '7' && p[2] == '>') {
 698                                         loglev_char = p[1];
 699                                         p += 3;
 700                                         printed_len -= 3;
 701                                 } else {
 702                                         loglev_char = default_message_loglevel
 703                                                 + '0';
 704                                 }
 705                                 t = 0;
 706                                 if (system_state != SYSTEM_BOOTING)
 707                                         t = ktime_to_ns(ktime_get());
 708                                 nanosec_rem = do_div(t, 1000000000);
 709                                 tlen = sprintf(tbuf,
 710                                                 "<%c>[%5lu.%06lu] ",
 711                                                 loglev_char,
 712                                                 (unsigned long)t,
 713                                                 nanosec_rem/1000);
 714
 715                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 716                                         emit_log_char(*tp);
 717                                 printed_len += tlen;
 718                         } else {
 719                                 if (p[0] != '<' || p[1] < '0' ||
 720                                    p[1] > '7' || p[2] != '>') {
 721                                         emit_log_char('<');
 722                                         emit_log_char(default_message_loglevel
 723                                                 + '0');
 724                                         emit_log_char('>');
 725                                         printed_len += 3;
 726                                 }
 727                         }
 728                         log_level_unknown = 0;
 729                         if (!*p)
 730                                 break;
 731                 }
 732                 emit_log_char(*p);
 733                 if (*p == '\n')
 734                         log_level_unknown = 1;
 735         }
 736
 737         if (!down_trylock(&console_sem)) {
 738                 /*
 739                  * We own the drivers.  We can drop the spinlock and
 740                  * let release_console_sem() print the text, maybe ...
 741                  */
 742                 console_locked = 1;
 743                 printk_cpu = UINT_MAX;
 744                 spin_unlock(&logbuf_lock);
 745
 746                 /*
 747                  * Console drivers may assume that per-cpu resources have
 748                  * been allocated. So unless they're explicitly marked as
 749                  * being able to cope (CON_ANYTIME) don't call them until
 750                  * this CPU is officially up.
 751                  */
 752                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 753                         console_may_schedule = 0;
 754                         release_console_sem();
 755                 } else {
 756                         /* Release by hand to avoid flushing the buffer. */
 757                         console_locked = 0;
 758                         up(&console_sem);
 759                 }
 760                 lockdep_on();
 761                 raw_local_irq_restore(flags);
 762         } else {
 763                 /*
 764                  * Someone else owns the drivers.  We drop the spinlock, which
 765                  * allows the semaphore holder to proceed and to call the
 766                  * console drivers with the output which we just produced.
 767                  */
 768                 printk_cpu = UINT_MAX;
 769                 spin_unlock(&logbuf_lock);
 770                 lockdep_on();
 771 out_restore_irqs:
 772                 raw_local_irq_restore(flags);
 773         }
 774
 775         preempt_enable();
 776         return printed_len;
 777 }
 778 EXPORT_SYMBOL(printk);
 779 EXPORT_SYMBOL(vprintk);
 780
 781 #else
 782
 783 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 784 {
 785         return -ENOSYS;
 786 }
 787
 788 static void call_console_drivers(unsigned long start, unsigned long end)
 789 {
 790 }
 791
 792 #endif
 793
 794 /*
 795  * Set up a list of consoles.  Called from init/main.c
 796  */
 797 static int __init console_setup(char *str)
 798 {
 799         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 800         char *s, *options;
 801         int idx;
 802
 803         /*
 804          * Decode str into name, index, options.
 805          */
 806         if (str[0] >= '0' && str[0] <= '9') {
 807                 strcpy(buf, "ttyS");
 808                 strncpy(buf + 4, str, sizeof(buf) - 5);
 809         } else {
 810                 strncpy(buf, str, sizeof(buf) - 1);
 811         }
 812         buf[sizeof(buf) - 1] = 0;
 813         if ((options = strchr(str, ',')) != NULL)
 814                 *(options++) = 0;
 815 #ifdef __sparc__
 816         if (!strcmp(str, "ttya"))
 817                 strcpy(buf, "ttyS0");
 818         if (!strcmp(str, "ttyb"))
 819                 strcpy(buf, "ttyS1");
 820 #endif
 821         for (s = buf; *s; s++)
 822                 if ((*s >= '0' && *s <= '9') || *s == ',')
 823                         break;
 824         idx = simple_strtoul(s, NULL, 10);
 825         *s = 0;
 826
 827         add_preferred_console(buf, idx, options);
 828         return 1;
 829 }
 830 __setup("console=", console_setup);
 831
 832 /**
 833  * add_preferred_console - add a device to the list of preferred consoles.
 834  * @name: device name
 835  * @idx: device index
 836  * @options: options for this console
 837  *
 838  * The last preferred console added will be used for kernel messages
 839  * and stdin/out/err for init.  Normally this is used by console_setup
 840  * above to handle user-supplied console arguments; however it can also
 841  * be used by arch-specific code either to override the user or more
 842  * commonly to provide a default console (ie from PROM variables) when
 843  * the user has not supplied one.
 844  */
 845 int add_preferred_console(char *name, int idx, char *options)
 846 {
 847         struct console_cmdline *c;
 848         int i;
 849
 850         /*
 851          *      See if this tty is not yet registered, and
 852          *      if we have a slot free.
 853          */
 854         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 855                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 856                           console_cmdline[i].index == idx) {
 857                                 selected_console = i;
 858                                 return 0;
 859                 }
 860         if (i == MAX_CMDLINECONSOLES)
 861                 return -E2BIG;
 862         selected_console = i;
 863         c = &console_cmdline[i];
 864         memcpy(c->name, name, sizeof(c->name));
 865         c->name[sizeof(c->name) - 1] = 0;
 866         c->options = options;
 867         c->index = idx;
 868         return 0;
 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                                 memcpy(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)\n");
 910         acquire_console_sem();
 911         console_suspended = 1;
 912 }
 913
 914 void resume_console(void)
 915 {
 916         if (!console_suspend_enabled)
 917                 return;
 918         console_suspended = 0;
 919         release_console_sem();
 920 }
 921
 922 /**
 923  * acquire_console_sem - lock the console system for exclusive use.
 924  *
 925  * Acquires a semaphore which guarantees that the caller has
 926  * exclusive access to the console system and the console_drivers list.
 927  *
 928  * Can sleep, returns nothing.
 929  */
 930 void acquire_console_sem(void)
 931 {
 932         BUG_ON(in_interrupt());
 933         if (console_suspended) {
 934                 down(&secondary_console_sem);
 935                 return;
 936         }
 937         down(&console_sem);
 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         console_locked = 1;
 948         console_may_schedule = 0;
 949         return 0;
 950 }
 951 EXPORT_SYMBOL(try_acquire_console_sem);
 952
 953 int is_console_locked(void)
 954 {
 955         return console_locked;
 956 }
 957
 958 void wake_up_klogd(void)
 959 {
 960         if (!oops_in_progress && waitqueue_active(&log_wait))
 961                 wake_up_interruptible(&log_wait);
 962 }
 963
 964 /**
 965  * release_console_sem - unlock the console system
 966  *
 967  * Releases the semaphore which the caller holds on the console system
 968  * and the console driver list.
 969  *
 970  * While the semaphore was held, console output may have been buffered
 971  * by printk().  If this is the case, release_console_sem() emits
 972  * the output prior to releasing the semaphore.
 973  *
 974  * If there is output waiting for klogd, we wake it up.
 975  *
 976  * release_console_sem() may be called from any context.
 977  */
 978 void release_console_sem(void)
 979 {
 980         unsigned long flags;
 981         unsigned long _con_start, _log_end;
 982         unsigned long wake_klogd = 0;
 983
 984         if (console_suspended) {
 985                 up(&secondary_console_sem);
 986                 return;
 987         }
 988
 989         console_may_schedule = 0;
 990
 991         for ( ; ; ) {
 992                 spin_lock_irqsave(&logbuf_lock, flags);
 993                 wake_klogd |= log_start - log_end;
 994                 if (con_start == log_end)
 995                         break;                  /* Nothing to print */
 996                 _con_start = con_start;
 997                 _log_end = log_end;
 998                 con_start = log_end;            /* Flush */
 999                 spin_unlock(&logbuf_lock);
1000                 call_console_drivers(_con_start, _log_end);
1001                 local_irq_restore(flags);
1002         }
1003         console_locked = 0;
1004         up(&console_sem);
1005         spin_unlock_irqrestore(&logbuf_lock, flags);
1006         if (wake_klogd)
1007                 wake_up_klogd();
1008 }
1009 EXPORT_SYMBOL(release_console_sem);
1010
1011 /**
1012  * console_conditional_schedule - yield the CPU if required
1013  *
1014  * If the console code is currently allowed to sleep, and
1015  * if this CPU should yield the CPU to another task, do
1016  * so here.
1017  *
1018  * Must be called within acquire_console_sem().
1019  */
1020 void __sched console_conditional_schedule(void)
1021 {
1022         if (console_may_schedule)
1023                 cond_resched();
1024 }
1025 EXPORT_SYMBOL(console_conditional_schedule);
1026
1027 void console_print(const char *s)
1028 {
1029         printk(KERN_EMERG "%s", s);
1030 }
1031 EXPORT_SYMBOL(console_print);
1032
1033 void console_unblank(void)
1034 {
1035         struct console *c;
1036
1037         /*
1038          * console_unblank can no longer be called in interrupt context unless
1039          * oops_in_progress is set to 1..
1040          */
1041         if (oops_in_progress) {
1042                 if (down_trylock(&console_sem) != 0)
1043                         return;
1044         } else
1045                 acquire_console_sem();
1046
1047         console_locked = 1;
1048         console_may_schedule = 0;
1049         for (c = console_drivers; c != NULL; c = c->next)
1050                 if ((c->flags & CON_ENABLED) && c->unblank)
1051                         c->unblank();
1052         release_console_sem();
1053 }
1054
1055 /*
1056  * Return the console tty driver structure and its associated index
1057  */
1058 struct tty_driver *console_device(int *index)
1059 {
1060         struct console *c;
1061         struct tty_driver *driver = NULL;
1062
1063         acquire_console_sem();
1064         for (c = console_drivers; c != NULL; c = c->next) {
1065                 if (!c->device)
1066                         continue;
1067                 driver = c->device(c, index);
1068                 if (driver)
1069                         break;
1070         }
1071         release_console_sem();
1072         return driver;
1073 }
1074
1075 /*
1076  * Prevent further output on the passed console device so that (for example)
1077  * serial drivers can disable console output before suspending a port, and can
1078  * re-enable output afterwards.
1079  */
1080 void console_stop(struct console *console)
1081 {
1082         acquire_console_sem();
1083         console->flags &= ~CON_ENABLED;
1084         release_console_sem();
1085 }
1086 EXPORT_SYMBOL(console_stop);
1087
1088 void console_start(struct console *console)
1089 {
1090         acquire_console_sem();
1091         console->flags |= CON_ENABLED;
1092         release_console_sem();
1093 }
1094 EXPORT_SYMBOL(console_start);
1095
1096 /*
1097  * The console driver calls this routine during kernel initialization
1098  * to register the console printing procedure with printk() and to
1099  * print any messages that were printed by the kernel before the
1100  * console driver was initialized.
1101  */
1102 void register_console(struct console *console)
1103 {
1104         int i;
1105         unsigned long flags;
1106         struct console *bootconsole = NULL;
1107
1108         if (console_drivers) {
1109                 if (console->flags & CON_BOOT)
1110                         return;
1111                 if (console_drivers->flags & CON_BOOT)
1112                         bootconsole = console_drivers;
1113         }
1114
1115         if (preferred_console < 0 || bootconsole || !console_drivers)
1116                 preferred_console = selected_console;
1117
1118         if (console->early_setup)
1119                 console->early_setup();
1120
1121         /*
1122          *      See if we want to use this console driver. If we
1123          *      didn't select a console we take the first one
1124          *      that registers here.
1125          */
1126         if (preferred_console < 0) {
1127                 if (console->index < 0)
1128                         console->index = 0;
1129                 if (console->setup == NULL ||
1130                     console->setup(console, NULL) == 0) {
1131                         console->flags |= CON_ENABLED | CON_CONSDEV;
1132                         preferred_console = 0;
1133                 }
1134         }
1135
1136         /*
1137          *      See if this console matches one we selected on
1138          *      the command line.
1139          */
1140         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1141                         i++) {
1142                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1143                         continue;
1144                 if (console->index >= 0 &&
1145                     console->index != console_cmdline[i].index)
1146                         continue;
1147                 if (console->index < 0)
1148                         console->index = console_cmdline[i].index;
1149                 if (console->setup &&
1150                     console->setup(console, console_cmdline[i].options) != 0)
1151                         break;
1152                 console->flags |= CON_ENABLED;
1153                 console->index = console_cmdline[i].index;
1154                 if (i == selected_console) {
1155                         console->flags |= CON_CONSDEV;
1156                         preferred_console = selected_console;
1157                 }
1158                 break;
1159         }
1160
1161         if (!(console->flags & CON_ENABLED))
1162                 return;
1163
1164         if (bootconsole && (console->flags & CON_CONSDEV)) {
1165                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1166                        bootconsole->name, bootconsole->index,
1167                        console->name, console->index);
1168                 unregister_console(bootconsole);
1169                 console->flags &= ~CON_PRINTBUFFER;
1170         } else {
1171                 printk(KERN_INFO "console [%s%d] enabled\n",
1172                        console->name, console->index);
1173         }
1174
1175         /*
1176          *      Put this console in the list - keep the
1177          *      preferred driver at the head of the list.
1178          */
1179         acquire_console_sem();
1180         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1181                 console->next = console_drivers;
1182                 console_drivers = console;
1183                 if (console->next)
1184                         console->next->flags &= ~CON_CONSDEV;
1185         } else {
1186                 console->next = console_drivers->next;
1187                 console_drivers->next = console;
1188         }
1189         if (console->flags & CON_PRINTBUFFER) {
1190                 /*
1191                  * release_console_sem() will print out the buffered messages
1192                  * for us.
1193                  */
1194                 spin_lock_irqsave(&logbuf_lock, flags);
1195                 con_start = log_start;
1196                 spin_unlock_irqrestore(&logbuf_lock, flags);
1197         }
1198         release_console_sem();
1199 }
1200 EXPORT_SYMBOL(register_console);
1201
1202 int unregister_console(struct console *console)
1203 {
1204         struct console *a, *b;
1205         int res = 1;
1206
1207         acquire_console_sem();
1208         if (console_drivers == console) {
1209                 console_drivers=console->next;
1210                 res = 0;
1211         } else if (console_drivers) {
1212                 for (a=console_drivers->next, b=console_drivers ;
1213                      a; b=a, a=b->next) {
1214                         if (a == console) {
1215                                 b->next = a->next;
1216                                 res = 0;
1217                                 break;
1218                         }
1219                 }
1220         }
1221
1222         /*
1223          * If this isn't the last console and it has CON_CONSDEV set, we
1224          * need to set it on the next preferred console.
1225          */
1226         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1227                 console_drivers->flags |= CON_CONSDEV;
1228
1229         release_console_sem();
1230         return res;
1231 }
1232 EXPORT_SYMBOL(unregister_console);
1233
1234 static int __init disable_boot_consoles(void)
1235 {
1236         if (console_drivers != NULL) {
1237                 if (console_drivers->flags & CON_BOOT) {
1238                         printk(KERN_INFO "turn off boot console %s%d\n",
1239                                 console_drivers->name, console_drivers->index);
1240                         return unregister_console(console_drivers);
1241                 }
1242         }
1243         return 0;
1244 }
1245 late_initcall(disable_boot_consoles);
1246
1247 /**
1248  * tty_write_message - write a message to a certain tty, not just the console.
1249  * @tty: the destination tty_struct
1250  * @msg: the message to write
1251  *
1252  * This is used for messages that need to be redirected to a specific tty.
1253  * We don't put it into the syslog queue right now maybe in the future if
1254  * really needed.
1255  */
1256 void tty_write_message(struct tty_struct *tty, char *msg)
1257 {
1258         if (tty && tty->driver->write)
1259                 tty->driver->write(tty, msg, strlen(msg));
1260         return;
1261 }
1262
1263 /*
1264  * printk rate limiting, lifted from the networking subsystem.
1265  *
1266  * This enforces a rate limit: not more than one kernel message
1267  * every printk_ratelimit_jiffies to make a denial-of-service
1268  * attack impossible.
1269  */
1270 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1271 {
1272         static DEFINE_SPINLOCK(ratelimit_lock);
1273         static unsigned long toks = 10 * 5 * HZ;
1274         static unsigned long last_msg;
1275         static int missed;
1276         unsigned long flags;
1277         unsigned long now = jiffies;
1278
1279         spin_lock_irqsave(&ratelimit_lock, flags);
1280         toks += now - last_msg;
1281         last_msg = now;
1282         if (toks > (ratelimit_burst * ratelimit_jiffies))
1283                 toks = ratelimit_burst * ratelimit_jiffies;
1284         if (toks >= ratelimit_jiffies) {
1285                 int lost = missed;
1286
1287                 missed = 0;
1288                 toks -= ratelimit_jiffies;
1289                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1290                 if (lost)
1291                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1292                 return 1;
1293         }
1294         missed++;
1295         spin_unlock_irqrestore(&ratelimit_lock, flags);
1296         return 0;
1297 }
1298 EXPORT_SYMBOL(__printk_ratelimit);
1299
1300 /* minimum time in jiffies between messages */
1301 int printk_ratelimit_jiffies = 5 * HZ;
1302
1303 /* number of messages we send before ratelimiting */
1304 int printk_ratelimit_burst = 10;
1305
1306 int printk_ratelimit(void)
1307 {
1308         return __printk_ratelimit(printk_ratelimit_jiffies,
1309                                 printk_ratelimit_burst);
1310 }
1311 EXPORT_SYMBOL(printk_ratelimit);
1312
1313 /**
1314  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1315  * @caller_jiffies: pointer to caller's state
1316  * @interval_msecs: minimum interval between prints
1317  *
1318  * printk_timed_ratelimit() returns true if more than @interval_msecs
1319  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1320  * returned true.
1321  */
1322 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1323                         unsigned int interval_msecs)
1324 {
1325         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1326                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1327                 return true;
1328         }
1329         return false;
1330 }
1331 EXPORT_SYMBOL(printk_timed_ratelimit);