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
  36 #include <asm/uaccess.h>
  37
  38 /*
  39  * Architectures can override it:
  40  */
  41 void __attribute__((weak)) early_printk(const char *fmt, ...)
  42 {
  43 }
  44
  45 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  46
  47 #ifdef CONFIG_DEBUG_LL
  48 extern void printascii(char *);
  49 #endif
  50
  51 /* printk's without a loglevel use this.. */
  52 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  53
  54 /* We show everything that is MORE important than this.. */
  55 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  56 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  57
  58 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  59
  60 int console_printk[4] = {
  61         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  62         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  63         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  64         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  65 };
  66
  67 /*
  68  * Low level drivers may need that to know if they can schedule in
  69  * their unblank() callback or not. So let's export it.
  70  */
  71 int oops_in_progress;
  72 EXPORT_SYMBOL(oops_in_progress);
  73
  74 /*
  75  * console_sem protects the console_drivers list, and also
  76  * provides serialisation for access to the entire console
  77  * driver system.
  78  */
  79 static DECLARE_MUTEX(console_sem);
  80 static DECLARE_MUTEX(secondary_console_sem);
  81 struct console *console_drivers;
  82 /*
  83  * This is used for debugging the mess that is the VT code by
  84  * keeping track if we have the console semaphore held. It's
  85  * definitely not the perfect debug tool (we don't know if _WE_
  86  * hold it are racing, but it helps tracking those weird code
  87  * path in the console code where we end up in places I want
  88  * locked without the console sempahore held
  89  */
  90 static int console_locked, console_suspended;
  91
  92 /*
  93  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  94  * It is also used in interesting ways to provide interlocking in
  95  * release_console_sem().
  96  */
  97 static DEFINE_SPINLOCK(logbuf_lock);
  98
  99 #define LOG_BUF_MASK (log_buf_len-1)
 100 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 101
 102 /*
 103  * The indices into log_buf are not constrained to log_buf_len - they
 104  * must be masked before subscripting
 105  */
 106 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 107 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 108 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 109
 110 /*
 111  *      Array of consoles built from command line options (console=)
 112  */
 113 struct console_cmdline
 114 {
 115         char    name[8];                        /* Name of the driver       */
 116         int     index;                          /* Minor dev. to use        */
 117         char    *options;                       /* Options for the driver   */
 118 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 119         char    *brl_options;                   /* Options for braille driver */
 120 #endif
 121 };
 122
 123 #define MAX_CMDLINECONSOLES 8
 124
 125 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 126 static int selected_console = -1;
 127 static int preferred_console = -1;
 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 static int __init log_buf_len_setup(char *str)
 140 {
 141         unsigned size = memparse(str, &str);
 142         unsigned long flags;
 143
 144         if (size)
 145                 size = roundup_pow_of_two(size);
 146         if (size > log_buf_len) {
 147                 unsigned start, dest_idx, offset;
 148                 char *new_log_buf;
 149
 150                 new_log_buf = alloc_bootmem(size);
 151                 if (!new_log_buf) {
 152                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 153                         goto out;
 154                 }
 155
 156                 spin_lock_irqsave(&logbuf_lock, flags);
 157                 log_buf_len = size;
 158                 log_buf = new_log_buf;
 159
 160                 offset = start = min(con_start, log_start);
 161                 dest_idx = 0;
 162                 while (start != log_end) {
 163                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 164                         start++;
 165                         dest_idx++;
 166                 }
 167                 log_start -= offset;
 168                 con_start -= offset;
 169                 log_end -= offset;
 170                 spin_unlock_irqrestore(&logbuf_lock, flags);
 171
 172                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 173         }
 174 out:
 175         return 1;
 176 }
 177
 178 __setup("log_buf_len=", log_buf_len_setup);
 179
 180 #ifdef CONFIG_BOOT_PRINTK_DELAY
 181
 182 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 183 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 184
 185 static int __init boot_delay_setup(char *str)
 186 {
 187         unsigned long lpj;
 188         unsigned long long loops_per_msec;
 189
 190         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 191         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 192
 193         get_option(&str, &boot_delay);
 194         if (boot_delay > 10 * 1000)
 195                 boot_delay = 0;
 196
 197         printk_delay_msec = loops_per_msec;
 198         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 199                 "HZ: %d, printk_delay_msec: %llu\n",
 200                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 201         return 1;
 202 }
 203 __setup("boot_delay=", boot_delay_setup);
 204
 205 static void boot_delay_msec(void)
 206 {
 207         unsigned long long k;
 208         unsigned long timeout;
 209
 210         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 211                 return;
 212
 213         k = (unsigned long long)printk_delay_msec * boot_delay;
 214
 215         timeout = jiffies + msecs_to_jiffies(boot_delay);
 216         while (k) {
 217                 k--;
 218                 cpu_relax();
 219                 /*
 220                  * use (volatile) jiffies to prevent
 221                  * compiler reduction; loop termination via jiffies
 222                  * is secondary and may or may not happen.
 223                  */
 224                 if (time_after(jiffies, timeout))
 225                         break;
 226                 touch_nmi_watchdog();
 227         }
 228 }
 229 #else
 230 static inline void boot_delay_msec(void)
 231 {
 232 }
 233 #endif
 234
 235 /*
 236  * Return the number of unread characters in the log buffer.
 237  */
 238 int log_buf_get_len(void)
 239 {
 240         return logged_chars;
 241 }
 242
 243 /*
 244  * Copy a range of characters from the log buffer.
 245  */
 246 int log_buf_copy(char *dest, int idx, int len)
 247 {
 248         int ret, max;
 249         bool took_lock = false;
 250
 251         if (!oops_in_progress) {
 252                 spin_lock_irq(&logbuf_lock);
 253                 took_lock = true;
 254         }
 255
 256         max = log_buf_get_len();
 257         if (idx < 0 || idx >= max) {
 258                 ret = -1;
 259         } else {
 260                 if (len > max)
 261                         len = max;
 262                 ret = len;
 263                 idx += (log_end - max);
 264                 while (len-- > 0)
 265                         dest[len] = LOG_BUF(idx + len);
 266         }
 267
 268         if (took_lock)
 269                 spin_unlock_irq(&logbuf_lock);
 270
 271         return ret;
 272 }
 273
 274 /*
 275  * Extract a single character from the log buffer.
 276  */
 277 int log_buf_read(int idx)
 278 {
 279         char ret;
 280
 281         if (log_buf_copy(&ret, idx, 1) == 1)
 282                 return ret;
 283         else
 284                 return -1;
 285 }
 286
 287 /*
 288  * Commands to do_syslog:
 289  *
 290  *      0 -- Close the log.  Currently a NOP.
 291  *      1 -- Open the log. Currently a NOP.
 292  *      2 -- Read from the log.
 293  *      3 -- Read all messages remaining in the ring buffer.
 294  *      4 -- Read and clear all messages remaining in the ring buffer
 295  *      5 -- Clear ring buffer.
 296  *      6 -- Disable printk's to console
 297  *      7 -- Enable printk's to console
 298  *      8 -- Set level of messages printed to console
 299  *      9 -- Return number of unread characters in the log buffer
 300  *     10 -- Return size of the log buffer
 301  */
 302 int do_syslog(int type, char __user *buf, int len)
 303 {
 304         unsigned i, j, limit, count;
 305         int do_clear = 0;
 306         char c;
 307         int error = 0;
 308
 309         error = security_syslog(type);
 310         if (error)
 311                 return error;
 312
 313         switch (type) {
 314         case 0:         /* Close log */
 315                 break;
 316         case 1:         /* Open log */
 317                 break;
 318         case 2:         /* Read from log */
 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                 error = wait_event_interruptible(log_wait,
 330                                                         (log_start - log_end));
 331                 if (error)
 332                         goto out;
 333                 i = 0;
 334                 spin_lock_irq(&logbuf_lock);
 335                 while (!error && (log_start != log_end) && i < len) {
 336                         c = LOG_BUF(log_start);
 337                         log_start++;
 338                         spin_unlock_irq(&logbuf_lock);
 339                         error = __put_user(c,buf);
 340                         buf++;
 341                         i++;
 342                         cond_resched();
 343                         spin_lock_irq(&logbuf_lock);
 344                 }
 345                 spin_unlock_irq(&logbuf_lock);
 346                 if (!error)
 347                         error = i;
 348                 break;
 349         case 4:         /* Read/clear last kernel messages */
 350                 do_clear = 1;
 351                 /* FALL THRU */
 352         case 3:         /* Read last kernel messages */
 353                 error = -EINVAL;
 354                 if (!buf || len < 0)
 355                         goto out;
 356                 error = 0;
 357                 if (!len)
 358                         goto out;
 359                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 360                         error = -EFAULT;
 361                         goto out;
 362                 }
 363                 count = len;
 364                 if (count > log_buf_len)
 365                         count = log_buf_len;
 366                 spin_lock_irq(&logbuf_lock);
 367                 if (count > logged_chars)
 368                         count = logged_chars;
 369                 if (do_clear)
 370                         logged_chars = 0;
 371                 limit = log_end;
 372                 /*
 373                  * __put_user() could sleep, and while we sleep
 374                  * printk() could overwrite the messages
 375                  * we try to copy to user space. Therefore
 376                  * the messages are copied in reverse. <manfreds>
 377                  */
 378                 for (i = 0; i < count && !error; i++) {
 379                         j = limit-1-i;
 380                         if (j + log_buf_len < log_end)
 381                                 break;
 382                         c = LOG_BUF(j);
 383                         spin_unlock_irq(&logbuf_lock);
 384                         error = __put_user(c,&buf[count-1-i]);
 385                         cond_resched();
 386                         spin_lock_irq(&logbuf_lock);
 387                 }
 388                 spin_unlock_irq(&logbuf_lock);
 389                 if (error)
 390                         break;
 391                 error = i;
 392                 if (i != count) {
 393                         int offset = count-error;
 394                         /* buffer overflow during copy, correct user buffer. */
 395                         for (i = 0; i < error; i++) {
 396                                 if (__get_user(c,&buf[i+offset]) ||
 397                                     __put_user(c,&buf[i])) {
 398                                         error = -EFAULT;
 399                                         break;
 400                                 }
 401                                 cond_resched();
 402                         }
 403                 }
 404                 break;
 405         case 5:         /* Clear ring buffer */
 406                 logged_chars = 0;
 407                 break;
 408         case 6:         /* Disable logging to console */
 409                 console_loglevel = minimum_console_loglevel;
 410                 break;
 411         case 7:         /* Enable logging to console */
 412                 console_loglevel = default_console_loglevel;
 413                 break;
 414         case 8:         /* Set level of messages printed to console */
 415                 error = -EINVAL;
 416                 if (len < 1 || len > 8)
 417                         goto out;
 418                 if (len < minimum_console_loglevel)
 419                         len = minimum_console_loglevel;
 420                 console_loglevel = len;
 421                 error = 0;
 422                 break;
 423         case 9:         /* Number of chars in the log buffer */
 424                 error = log_end - log_start;
 425                 break;
 426         case 10:        /* Size of the log buffer */
 427                 error = log_buf_len;
 428                 break;
 429         default:
 430                 error = -EINVAL;
 431                 break;
 432         }
 433 out:
 434         return error;
 435 }
 436
 437 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 438 {
 439         return do_syslog(type, buf, len);
 440 }
 441
 442 /*
 443  * Call the console drivers on a range of log_buf
 444  */
 445 static void __call_console_drivers(unsigned start, unsigned end)
 446 {
 447         struct console *con;
 448
 449         for (con = console_drivers; con; con = con->next) {
 450                 if ((con->flags & CON_ENABLED) && con->write &&
 451                                 (cpu_online(smp_processor_id()) ||
 452                                 (con->flags & CON_ANYTIME)))
 453                         con->write(con, &LOG_BUF(start), end - start);
 454         }
 455 }
 456
 457 static int __read_mostly ignore_loglevel;
 458
 459 static int __init ignore_loglevel_setup(char *str)
 460 {
 461         ignore_loglevel = 1;
 462         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 463
 464         return 0;
 465 }
 466
 467 early_param("ignore_loglevel", ignore_loglevel_setup);
 468
 469 /*
 470  * Write out chars from start to end - 1 inclusive
 471  */
 472 static void _call_console_drivers(unsigned start,
 473                                 unsigned end, int msg_log_level)
 474 {
 475         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 476                         console_drivers && start != end) {
 477                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 478                         /* wrapped write */
 479                         __call_console_drivers(start & LOG_BUF_MASK,
 480                                                 log_buf_len);
 481                         __call_console_drivers(0, end & LOG_BUF_MASK);
 482                 } else {
 483                         __call_console_drivers(start, end);
 484                 }
 485         }
 486 }
 487
 488 /*
 489  * Call the console drivers, asking them to write out
 490  * log_buf[start] to log_buf[end - 1].
 491  * The console_sem must be held.
 492  */
 493 static void call_console_drivers(unsigned start, unsigned end)
 494 {
 495         unsigned cur_index, start_print;
 496         static int msg_level = -1;
 497
 498         BUG_ON(((int)(start - end)) > 0);
 499
 500         cur_index = start;
 501         start_print = start;
 502         while (cur_index != end) {
 503                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 504                                 LOG_BUF(cur_index + 0) == '<' &&
 505                                 LOG_BUF(cur_index + 1) >= '0' &&
 506                                 LOG_BUF(cur_index + 1) <= '7' &&
 507                                 LOG_BUF(cur_index + 2) == '>') {
 508                         msg_level = LOG_BUF(cur_index + 1) - '0';
 509                         cur_index += 3;
 510                         start_print = cur_index;
 511                 }
 512                 while (cur_index != end) {
 513                         char c = LOG_BUF(cur_index);
 514
 515                         cur_index++;
 516                         if (c == '\n') {
 517                                 if (msg_level < 0) {
 518                                         /*
 519                                          * printk() has already given us loglevel tags in
 520                                          * the buffer.  This code is here in case the
 521                                          * log buffer has wrapped right round and scribbled
 522                                          * on those tags
 523                                          */
 524                                         msg_level = default_message_loglevel;
 525                                 }
 526                                 _call_console_drivers(start_print, cur_index, msg_level);
 527                                 msg_level = -1;
 528                                 start_print = cur_index;
 529                                 break;
 530                         }
 531                 }
 532         }
 533         _call_console_drivers(start_print, end, msg_level);
 534 }
 535
 536 static void emit_log_char(char c)
 537 {
 538         LOG_BUF(log_end) = c;
 539         log_end++;
 540         if (log_end - log_start > log_buf_len)
 541                 log_start = log_end - log_buf_len;
 542         if (log_end - con_start > log_buf_len)
 543                 con_start = log_end - log_buf_len;
 544         if (logged_chars < log_buf_len)
 545                 logged_chars++;
 546 }
 547
 548 /*
 549  * Zap console related locks when oopsing. Only zap at most once
 550  * every 10 seconds, to leave time for slow consoles to print a
 551  * full oops.
 552  */
 553 static void zap_locks(void)
 554 {
 555         static unsigned long oops_timestamp;
 556
 557         if (time_after_eq(jiffies, oops_timestamp) &&
 558                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 559                 return;
 560
 561         oops_timestamp = jiffies;
 562
 563         /* If a crash is occurring, make sure we can't deadlock */
 564         spin_lock_init(&logbuf_lock);
 565         /* And make sure that we print immediately */
 566         init_MUTEX(&console_sem);
 567 }
 568
 569 #if defined(CONFIG_PRINTK_TIME)
 570 static int printk_time = 1;
 571 #else
 572 static int printk_time = 0;
 573 #endif
 574 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 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 /*
 627  * Can we actually use the console at this time on this cpu?
 628  *
 629  * Console drivers may assume that per-cpu resources have
 630  * been allocated. So unless they're explicitly marked as
 631  * being able to cope (CON_ANYTIME) don't call them until
 632  * this CPU is officially up.
 633  */
 634 static inline int can_use_console(unsigned int cpu)
 635 {
 636         return cpu_online(cpu) || have_callable_console();
 637 }
 638
 639 /*
 640  * Try to get console ownership to actually show the kernel
 641  * messages from a 'printk'. Return true (and with the
 642  * console_semaphore held, and 'console_locked' set) if it
 643  * is successful, false otherwise.
 644  *
 645  * This gets called with the 'logbuf_lock' spinlock held and
 646  * interrupts disabled. It should return with 'lockbuf_lock'
 647  * released but interrupts still disabled.
 648  */
 649 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 650 {
 651         int retval = 0;
 652
 653         if (!try_acquire_console_sem()) {
 654                 retval = 1;
 655
 656                 /*
 657                  * If we can't use the console, we need to release
 658                  * the console semaphore by hand to avoid flushing
 659                  * the buffer. We need to hold the console semaphore
 660                  * in order to do this test safely.
 661                  */
 662                 if (!can_use_console(cpu)) {
 663                         console_locked = 0;
 664                         up(&console_sem);
 665                         retval = 0;
 666                 }
 667         }
 668         printk_cpu = UINT_MAX;
 669         spin_unlock(&logbuf_lock);
 670         return retval;
 671 }
 672
 673 static const char printk_recursion_bug_msg [] =
 674                         KERN_CRIT "BUG: recent printk recursion!\n";
 675 static int printk_recursion_bug;
 676
 677 asmlinkage int vprintk(const char *fmt, va_list args)
 678 {
 679         static int log_level_unknown = 1;
 680         static char printk_buf[1024];
 681
 682         unsigned long flags;
 683         int printed_len = 0;
 684         int this_cpu;
 685         char *p;
 686
 687         boot_delay_msec();
 688
 689         preempt_disable();
 690         /* This stops the holder of console_sem just where we want him */
 691         raw_local_irq_save(flags);
 692         this_cpu = smp_processor_id();
 693
 694         /*
 695          * Ouch, printk recursed into itself!
 696          */
 697         if (unlikely(printk_cpu == this_cpu)) {
 698                 /*
 699                  * If a crash is occurring during printk() on this CPU,
 700                  * then try to get the crash message out but make sure
 701                  * we can't deadlock. Otherwise just return to avoid the
 702                  * recursion and return - but flag the recursion so that
 703                  * it can be printed at the next appropriate moment:
 704                  */
 705                 if (!oops_in_progress) {
 706                         printk_recursion_bug = 1;
 707                         goto out_restore_irqs;
 708                 }
 709                 zap_locks();
 710         }
 711
 712         lockdep_off();
 713         spin_lock(&logbuf_lock);
 714         printk_cpu = this_cpu;
 715
 716         if (printk_recursion_bug) {
 717                 printk_recursion_bug = 0;
 718                 strcpy(printk_buf, printk_recursion_bug_msg);
 719                 printed_len = sizeof(printk_recursion_bug_msg);
 720         }
 721         /* Emit the output into the temporary buffer */
 722         printed_len += vscnprintf(printk_buf + printed_len,
 723                                   sizeof(printk_buf) - printed_len, fmt, args);
 724
 725 #ifdef  CONFIG_DEBUG_LL
 726         printascii(printk_buf);
 727 #endif
 728
 729         /*
 730          * Copy the output into log_buf.  If the caller didn't provide
 731          * appropriate log level tags, we insert them here
 732          */
 733         for (p = printk_buf; *p; p++) {
 734                 if (log_level_unknown) {
 735                         /* log_level_unknown signals the start of a new line */
 736                         if (printk_time) {
 737                                 int loglev_char;
 738                                 char tbuf[50], *tp;
 739                                 unsigned tlen;
 740                                 unsigned long long t;
 741                                 unsigned long nanosec_rem;
 742
 743                                 /*
 744                                  * force the log level token to be
 745                                  * before the time output.
 746                                  */
 747                                 if (p[0] == '<' && p[1] >='0' &&
 748                                    p[1] <= '7' && p[2] == '>') {
 749                                         loglev_char = p[1];
 750                                         p += 3;
 751                                         printed_len -= 3;
 752                                 } else {
 753                                         loglev_char = default_message_loglevel
 754                                                 + '0';
 755                                 }
 756                                 t = cpu_clock(printk_cpu);
 757                                 nanosec_rem = do_div(t, 1000000000);
 758                                 tlen = sprintf(tbuf,
 759                                                 "<%c>[%5lu.%06lu] ",
 760                                                 loglev_char,
 761                                                 (unsigned long)t,
 762                                                 nanosec_rem/1000);
 763
 764                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 765                                         emit_log_char(*tp);
 766                                 printed_len += tlen;
 767                         } else {
 768                                 if (p[0] != '<' || p[1] < '0' ||
 769                                    p[1] > '7' || p[2] != '>') {
 770                                         emit_log_char('<');
 771                                         emit_log_char(default_message_loglevel
 772                                                 + '0');
 773                                         emit_log_char('>');
 774                                         printed_len += 3;
 775                                 }
 776                         }
 777                         log_level_unknown = 0;
 778                         if (!*p)
 779                                 break;
 780                 }
 781                 emit_log_char(*p);
 782                 if (*p == '\n')
 783                         log_level_unknown = 1;
 784         }
 785
 786         /*
 787          * Try to acquire and then immediately release the
 788          * console semaphore. The release will do all the
 789          * actual magic (print out buffers, wake up klogd,
 790          * etc).
 791          *
 792          * The acquire_console_semaphore_for_printk() function
 793          * will release 'logbuf_lock' regardless of whether it
 794          * actually gets the semaphore or not.
 795          */
 796         if (acquire_console_semaphore_for_printk(this_cpu))
 797                 release_console_sem();
 798
 799         lockdep_on();
 800 out_restore_irqs:
 801         raw_local_irq_restore(flags);
 802
 803         preempt_enable();
 804         return printed_len;
 805 }
 806 EXPORT_SYMBOL(printk);
 807 EXPORT_SYMBOL(vprintk);
 808
 809 #else
 810
 811 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 812 {
 813         return -ENOSYS;
 814 }
 815
 816 static void call_console_drivers(unsigned start, unsigned end)
 817 {
 818 }
 819
 820 #endif
 821
 822 static int __add_preferred_console(char *name, int idx, char *options,
 823                                    char *brl_options)
 824 {
 825         struct console_cmdline *c;
 826         int i;
 827
 828         /*
 829          *      See if this tty is not yet registered, and
 830          *      if we have a slot free.
 831          */
 832         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 833                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 834                           console_cmdline[i].index == idx) {
 835                                 if (!brl_options)
 836                                         selected_console = i;
 837                                 return 0;
 838                 }
 839         if (i == MAX_CMDLINECONSOLES)
 840                 return -E2BIG;
 841         if (!brl_options)
 842                 selected_console = i;
 843         c = &console_cmdline[i];
 844         strlcpy(c->name, name, sizeof(c->name));
 845         c->options = options;
 846 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 847         c->brl_options = brl_options;
 848 #endif
 849         c->index = idx;
 850         return 0;
 851 }
 852 /*
 853  * Set up a list of consoles.  Called from init/main.c
 854  */
 855 static int __init console_setup(char *str)
 856 {
 857         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 858         char *s, *options, *brl_options = NULL;
 859         int idx;
 860
 861 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 862         if (!memcmp(str, "brl,", 4)) {
 863                 brl_options = "";
 864                 str += 4;
 865         } else if (!memcmp(str, "brl=", 4)) {
 866                 brl_options = str + 4;
 867                 str = strchr(brl_options, ',');
 868                 if (!str) {
 869                         printk(KERN_ERR "need port name after brl=\n");
 870                         return 1;
 871                 }
 872                 *(str++) = 0;
 873         }
 874 #endif
 875
 876         /*
 877          * Decode str into name, index, options.
 878          */
 879         if (str[0] >= '0' && str[0] <= '9') {
 880                 strcpy(buf, "ttyS");
 881                 strncpy(buf + 4, str, sizeof(buf) - 5);
 882         } else {
 883                 strncpy(buf, str, sizeof(buf) - 1);
 884         }
 885         buf[sizeof(buf) - 1] = 0;
 886         if ((options = strchr(str, ',')) != NULL)
 887                 *(options++) = 0;
 888 #ifdef __sparc__
 889         if (!strcmp(str, "ttya"))
 890                 strcpy(buf, "ttyS0");
 891         if (!strcmp(str, "ttyb"))
 892                 strcpy(buf, "ttyS1");
 893 #endif
 894         for (s = buf; *s; s++)
 895                 if ((*s >= '0' && *s <= '9') || *s == ',')
 896                         break;
 897         idx = simple_strtoul(s, NULL, 10);
 898         *s = 0;
 899
 900         __add_preferred_console(buf, idx, options, brl_options);
 901         return 1;
 902 }
 903 __setup("console=", console_setup);
 904
 905 /**
 906  * add_preferred_console - add a device to the list of preferred consoles.
 907  * @name: device name
 908  * @idx: device index
 909  * @options: options for this console
 910  *
 911  * The last preferred console added will be used for kernel messages
 912  * and stdin/out/err for init.  Normally this is used by console_setup
 913  * above to handle user-supplied console arguments; however it can also
 914  * be used by arch-specific code either to override the user or more
 915  * commonly to provide a default console (ie from PROM variables) when
 916  * the user has not supplied one.
 917  */
 918 int add_preferred_console(char *name, int idx, char *options)
 919 {
 920         return __add_preferred_console(name, idx, options, NULL);
 921 }
 922
 923 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 924 {
 925         struct console_cmdline *c;
 926         int i;
 927
 928         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 929                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 930                           console_cmdline[i].index == idx) {
 931                                 c = &console_cmdline[i];
 932                                 strlcpy(c->name, name_new, sizeof(c->name));
 933                                 c->name[sizeof(c->name) - 1] = 0;
 934                                 c->options = options;
 935                                 c->index = idx_new;
 936                                 return i;
 937                 }
 938         /* not found */
 939         return -1;
 940 }
 941
 942 int console_suspend_enabled = 1;
 943 EXPORT_SYMBOL(console_suspend_enabled);
 944
 945 static int __init console_suspend_disable(char *str)
 946 {
 947         console_suspend_enabled = 0;
 948         return 1;
 949 }
 950 __setup("no_console_suspend", console_suspend_disable);
 951
 952 /**
 953  * suspend_console - suspend the console subsystem
 954  *
 955  * This disables printk() while we go into suspend states
 956  */
 957 void suspend_console(void)
 958 {
 959         if (!console_suspend_enabled)
 960                 return;
 961         printk("Suspending console(s)\n");
 962         acquire_console_sem();
 963         console_suspended = 1;
 964 }
 965
 966 void resume_console(void)
 967 {
 968         if (!console_suspend_enabled)
 969                 return;
 970         console_suspended = 0;
 971         release_console_sem();
 972 }
 973
 974 /**
 975  * acquire_console_sem - lock the console system for exclusive use.
 976  *
 977  * Acquires a semaphore which guarantees that the caller has
 978  * exclusive access to the console system and the console_drivers list.
 979  *
 980  * Can sleep, returns nothing.
 981  */
 982 void acquire_console_sem(void)
 983 {
 984         BUG_ON(in_interrupt());
 985         if (console_suspended) {
 986                 down(&secondary_console_sem);
 987                 return;
 988         }
 989         down(&console_sem);
 990         console_locked = 1;
 991         console_may_schedule = 1;
 992 }
 993 EXPORT_SYMBOL(acquire_console_sem);
 994
 995 int try_acquire_console_sem(void)
 996 {
 997         if (down_trylock(&console_sem))
 998                 return -1;
 999         console_locked = 1;
1000         console_may_schedule = 0;
1001         return 0;
1002 }
1003 EXPORT_SYMBOL(try_acquire_console_sem);
1004
1005 int is_console_locked(void)
1006 {
1007         return console_locked;
1008 }
1009
1010 void wake_up_klogd(void)
1011 {
1012         if (!oops_in_progress && waitqueue_active(&log_wait))
1013                 wake_up_interruptible(&log_wait);
1014 }
1015
1016 /**
1017  * release_console_sem - unlock the console system
1018  *
1019  * Releases the semaphore which the caller holds on the console system
1020  * and the console driver list.
1021  *
1022  * While the semaphore was held, console output may have been buffered
1023  * by printk().  If this is the case, release_console_sem() emits
1024  * the output prior to releasing the semaphore.
1025  *
1026  * If there is output waiting for klogd, we wake it up.
1027  *
1028  * release_console_sem() may be called from any context.
1029  */
1030 void release_console_sem(void)
1031 {
1032         unsigned long flags;
1033         unsigned _con_start, _log_end;
1034         unsigned wake_klogd = 0;
1035
1036         if (console_suspended) {
1037                 up(&secondary_console_sem);
1038                 return;
1039         }
1040
1041         console_may_schedule = 0;
1042
1043         for ( ; ; ) {
1044                 spin_lock_irqsave(&logbuf_lock, flags);
1045                 wake_klogd |= log_start - log_end;
1046                 if (con_start == log_end)
1047                         break;                  /* Nothing to print */
1048                 _con_start = con_start;
1049                 _log_end = log_end;
1050                 con_start = log_end;            /* Flush */
1051                 spin_unlock(&logbuf_lock);
1052                 call_console_drivers(_con_start, _log_end);
1053                 local_irq_restore(flags);
1054         }
1055         console_locked = 0;
1056         up(&console_sem);
1057         spin_unlock_irqrestore(&logbuf_lock, flags);
1058         if (wake_klogd)
1059                 wake_up_klogd();
1060 }
1061 EXPORT_SYMBOL(release_console_sem);
1062
1063 /**
1064  * console_conditional_schedule - yield the CPU if required
1065  *
1066  * If the console code is currently allowed to sleep, and
1067  * if this CPU should yield the CPU to another task, do
1068  * so here.
1069  *
1070  * Must be called within acquire_console_sem().
1071  */
1072 void __sched console_conditional_schedule(void)
1073 {
1074         if (console_may_schedule)
1075                 cond_resched();
1076 }
1077 EXPORT_SYMBOL(console_conditional_schedule);
1078
1079 void console_print(const char *s)
1080 {
1081         printk(KERN_EMERG "%s", s);
1082 }
1083 EXPORT_SYMBOL(console_print);
1084
1085 void console_unblank(void)
1086 {
1087         struct console *c;
1088
1089         /*
1090          * console_unblank can no longer be called in interrupt context unless
1091          * oops_in_progress is set to 1..
1092          */
1093         if (oops_in_progress) {
1094                 if (down_trylock(&console_sem) != 0)
1095                         return;
1096         } else
1097                 acquire_console_sem();
1098
1099         console_locked = 1;
1100         console_may_schedule = 0;
1101         for (c = console_drivers; c != NULL; c = c->next)
1102                 if ((c->flags & CON_ENABLED) && c->unblank)
1103                         c->unblank();
1104         release_console_sem();
1105 }
1106
1107 /*
1108  * Return the console tty driver structure and its associated index
1109  */
1110 struct tty_driver *console_device(int *index)
1111 {
1112         struct console *c;
1113         struct tty_driver *driver = NULL;
1114
1115         acquire_console_sem();
1116         for (c = console_drivers; c != NULL; c = c->next) {
1117                 if (!c->device)
1118                         continue;
1119                 driver = c->device(c, index);
1120                 if (driver)
1121                         break;
1122         }
1123         release_console_sem();
1124         return driver;
1125 }
1126
1127 /*
1128  * Prevent further output on the passed console device so that (for example)
1129  * serial drivers can disable console output before suspending a port, and can
1130  * re-enable output afterwards.
1131  */
1132 void console_stop(struct console *console)
1133 {
1134         acquire_console_sem();
1135         console->flags &= ~CON_ENABLED;
1136         release_console_sem();
1137 }
1138 EXPORT_SYMBOL(console_stop);
1139
1140 void console_start(struct console *console)
1141 {
1142         acquire_console_sem();
1143         console->flags |= CON_ENABLED;
1144         release_console_sem();
1145 }
1146 EXPORT_SYMBOL(console_start);
1147
1148 /*
1149  * The console driver calls this routine during kernel initialization
1150  * to register the console printing procedure with printk() and to
1151  * print any messages that were printed by the kernel before the
1152  * console driver was initialized.
1153  */
1154 void register_console(struct console *console)
1155 {
1156         int i;
1157         unsigned long flags;
1158         struct console *bootconsole = NULL;
1159
1160         if (console_drivers) {
1161                 if (console->flags & CON_BOOT)
1162                         return;
1163                 if (console_drivers->flags & CON_BOOT)
1164                         bootconsole = console_drivers;
1165         }
1166
1167         if (preferred_console < 0 || bootconsole || !console_drivers)
1168                 preferred_console = selected_console;
1169
1170         if (console->early_setup)
1171                 console->early_setup();
1172
1173         /*
1174          *      See if we want to use this console driver. If we
1175          *      didn't select a console we take the first one
1176          *      that registers here.
1177          */
1178         if (preferred_console < 0) {
1179                 if (console->index < 0)
1180                         console->index = 0;
1181                 if (console->setup == NULL ||
1182                     console->setup(console, NULL) == 0) {
1183                         console->flags |= CON_ENABLED | CON_CONSDEV;
1184                         preferred_console = 0;
1185                 }
1186         }
1187
1188         /*
1189          *      See if this console matches one we selected on
1190          *      the command line.
1191          */
1192         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1193                         i++) {
1194                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1195                         continue;
1196                 if (console->index >= 0 &&
1197                     console->index != console_cmdline[i].index)
1198                         continue;
1199                 if (console->index < 0)
1200                         console->index = console_cmdline[i].index;
1201 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1202                 if (console_cmdline[i].brl_options) {
1203                         console->flags |= CON_BRL;
1204                         braille_register_console(console,
1205                                         console_cmdline[i].index,
1206                                         console_cmdline[i].options,
1207                                         console_cmdline[i].brl_options);
1208                         return;
1209                 }
1210 #endif
1211                 if (console->setup &&
1212                     console->setup(console, console_cmdline[i].options) != 0)
1213                         break;
1214                 console->flags |= CON_ENABLED;
1215                 console->index = console_cmdline[i].index;
1216                 if (i == selected_console) {
1217                         console->flags |= CON_CONSDEV;
1218                         preferred_console = selected_console;
1219                 }
1220                 break;
1221         }
1222
1223         if (!(console->flags & CON_ENABLED))
1224                 return;
1225
1226         if (bootconsole && (console->flags & CON_CONSDEV)) {
1227                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1228                        bootconsole->name, bootconsole->index,
1229                        console->name, console->index);
1230                 unregister_console(bootconsole);
1231                 console->flags &= ~CON_PRINTBUFFER;
1232         } else {
1233                 printk(KERN_INFO "console [%s%d] enabled\n",
1234                        console->name, console->index);
1235         }
1236
1237         /*
1238          *      Put this console in the list - keep the
1239          *      preferred driver at the head of the list.
1240          */
1241         acquire_console_sem();
1242         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1243                 console->next = console_drivers;
1244                 console_drivers = console;
1245                 if (console->next)
1246                         console->next->flags &= ~CON_CONSDEV;
1247         } else {
1248                 console->next = console_drivers->next;
1249                 console_drivers->next = console;
1250         }
1251         if (console->flags & CON_PRINTBUFFER) {
1252                 /*
1253                  * release_console_sem() will print out the buffered messages
1254                  * for us.
1255                  */
1256                 spin_lock_irqsave(&logbuf_lock, flags);
1257                 con_start = log_start;
1258                 spin_unlock_irqrestore(&logbuf_lock, flags);
1259         }
1260         release_console_sem();
1261 }
1262 EXPORT_SYMBOL(register_console);
1263
1264 int unregister_console(struct console *console)
1265 {
1266         struct console *a, *b;
1267         int res = 1;
1268
1269 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1270         if (console->flags & CON_BRL)
1271                 return braille_unregister_console(console);
1272 #endif
1273
1274         acquire_console_sem();
1275         if (console_drivers == console) {
1276                 console_drivers=console->next;
1277                 res = 0;
1278         } else if (console_drivers) {
1279                 for (a=console_drivers->next, b=console_drivers ;
1280                      a; b=a, a=b->next) {
1281                         if (a == console) {
1282                                 b->next = a->next;
1283                                 res = 0;
1284                                 break;
1285                         }
1286                 }
1287         }
1288
1289         /*
1290          * If this isn't the last console and it has CON_CONSDEV set, we
1291          * need to set it on the next preferred console.
1292          */
1293         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1294                 console_drivers->flags |= CON_CONSDEV;
1295
1296         release_console_sem();
1297         return res;
1298 }
1299 EXPORT_SYMBOL(unregister_console);
1300
1301 static int __init disable_boot_consoles(void)
1302 {
1303         if (console_drivers != NULL) {
1304                 if (console_drivers->flags & CON_BOOT) {
1305                         printk(KERN_INFO "turn off boot console %s%d\n",
1306                                 console_drivers->name, console_drivers->index);
1307                         return unregister_console(console_drivers);
1308                 }
1309         }
1310         return 0;
1311 }
1312 late_initcall(disable_boot_consoles);
1313
1314 /**
1315  * tty_write_message - write a message to a certain tty, not just the console.
1316  * @tty: the destination tty_struct
1317  * @msg: the message to write
1318  *
1319  * This is used for messages that need to be redirected to a specific tty.
1320  * We don't put it into the syslog queue right now maybe in the future if
1321  * really needed.
1322  */
1323 void tty_write_message(struct tty_struct *tty, char *msg)
1324 {
1325         if (tty && tty->ops->write)
1326                 tty->ops->write(tty, msg, strlen(msg));
1327         return;
1328 }
1329
1330 #if defined CONFIG_PRINTK
1331 /*
1332  * printk rate limiting, lifted from the networking subsystem.
1333  *
1334  * This enforces a rate limit: not more than one kernel message
1335  * every printk_ratelimit_jiffies to make a denial-of-service
1336  * attack impossible.
1337  */
1338 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1339 {
1340         return __ratelimit(ratelimit_jiffies, ratelimit_burst);
1341 }
1342 EXPORT_SYMBOL(__printk_ratelimit);
1343
1344 /* minimum time in jiffies between messages */
1345 int printk_ratelimit_jiffies = 5 * HZ;
1346
1347 /* number of messages we send before ratelimiting */
1348 int printk_ratelimit_burst = 10;
1349
1350 int printk_ratelimit(void)
1351 {
1352         return __printk_ratelimit(printk_ratelimit_jiffies,
1353                                 printk_ratelimit_burst);
1354 }
1355 EXPORT_SYMBOL(printk_ratelimit);
1356
1357 /**
1358  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1359  * @caller_jiffies: pointer to caller's state
1360  * @interval_msecs: minimum interval between prints
1361  *
1362  * printk_timed_ratelimit() returns true if more than @interval_msecs
1363  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1364  * returned true.
1365  */
1366 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1367                         unsigned int interval_msecs)
1368 {
1369         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1370                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1371                 return true;
1372         }
1373         return false;
1374 }
1375 EXPORT_SYMBOL(printk_timed_ratelimit);
1376 #endif