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 asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  42 {
  43 }
  44
  45 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  46
  47 /* printk's without a loglevel use this.. */
  48 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  49
  50 /* We show everything that is MORE important than this.. */
  51 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  52 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  53
  54 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  55
  56 int console_printk[4] = {
  57         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  58         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  59         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  60         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  61 };
  62
  63 /*
  64  * Low level drivers may need that to know if they can schedule in
  65  * their unblank() callback or not. So let's export it.
  66  */
  67 int oops_in_progress;
  68 EXPORT_SYMBOL(oops_in_progress);
  69
  70 /*
  71  * console_sem protects the console_drivers list, and also
  72  * provides serialisation for access to the entire console
  73  * driver system.
  74  */
  75 static DECLARE_MUTEX(console_sem);
  76 static DECLARE_MUTEX(secondary_console_sem);
  77 struct console *console_drivers;
  78 EXPORT_SYMBOL_GPL(console_drivers);
  79
  80 /*
  81  * This is used for debugging the mess that is the VT code by
  82  * keeping track if we have the console semaphore held. It's
  83  * definitely not the perfect debug tool (we don't know if _WE_
  84  * hold it are racing, but it helps tracking those weird code
  85  * path in the console code where we end up in places I want
  86  * locked without the console sempahore held
  87  */
  88 static int console_locked, console_suspended;
  89
  90 /*
  91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  92  * It is also used in interesting ways to provide interlocking in
  93  * release_console_sem().
  94  */
  95 static DEFINE_SPINLOCK(logbuf_lock);
  96
  97 #define LOG_BUF_MASK (log_buf_len-1)
  98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  99
 100 /*
 101  * The indices into log_buf are not constrained to log_buf_len - they
 102  * must be masked before subscripting
 103  */
 104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 107
 108 /*
 109  *      Array of consoles built from command line options (console=)
 110  */
 111 struct console_cmdline
 112 {
 113         char    name[8];                        /* Name of the driver       */
 114         int     index;                          /* Minor dev. to use        */
 115         char    *options;                       /* Options for the driver   */
 116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 117         char    *brl_options;                   /* Options for braille driver */
 118 #endif
 119 };
 120
 121 #define MAX_CMDLINECONSOLES 8
 122
 123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 124 static int selected_console = -1;
 125 static int preferred_console = -1;
 126 int console_set_on_cmdline;
 127 EXPORT_SYMBOL(console_set_on_cmdline);
 128
 129 /* Flag: console code may call schedule() */
 130 static int console_may_schedule;
 131
 132 #ifdef CONFIG_PRINTK
 133
 134 static char __log_buf[__LOG_BUF_LEN];
 135 static char *log_buf = __log_buf;
 136 static int log_buf_len = __LOG_BUF_LEN;
 137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 138
 139 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 static 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  * 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 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 start, unsigned 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 0;
 452 }
 453
 454 early_param("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 start,
 460                                 unsigned 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 start, unsigned end)
 481 {
 482         unsigned cur_index, start_print;
 483         static int msg_level = -1;
 484
 485         BUG_ON(((int)(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 /* Check if we have any console registered that can be called early in boot. */
 564 static int have_callable_console(void)
 565 {
 566         struct console *con;
 567
 568         for (con = console_drivers; con; con = con->next)
 569                 if (con->flags & CON_ANYTIME)
 570                         return 1;
 571
 572         return 0;
 573 }
 574
 575 /**
 576  * printk - print a kernel message
 577  * @fmt: format string
 578  *
 579  * This is printk().  It can be called from any context.  We want it to work.
 580  *
 581  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 582  * call the console drivers.  If we fail to get the semaphore we place the output
 583  * into the log buffer and return.  The current holder of the console_sem will
 584  * notice the new output in release_console_sem() and will send it to the
 585  * consoles before releasing the semaphore.
 586  *
 587  * One effect of this deferred printing is that code which calls printk() and
 588  * then changes console_loglevel may break. This is because console_loglevel
 589  * is inspected when the actual printing occurs.
 590  *
 591  * See also:
 592  * printf(3)
 593  */
 594
 595 asmlinkage int printk(const char *fmt, ...)
 596 {
 597         va_list args;
 598         int r;
 599
 600         va_start(args, fmt);
 601         r = vprintk(fmt, args);
 602         va_end(args);
 603
 604         return r;
 605 }
 606
 607 /* cpu currently holding logbuf_lock */
 608 static volatile unsigned int printk_cpu = UINT_MAX;
 609
 610 /*
 611  * Can we actually use the console at this time on this cpu?
 612  *
 613  * Console drivers may assume that per-cpu resources have
 614  * been allocated. So unless they're explicitly marked as
 615  * being able to cope (CON_ANYTIME) don't call them until
 616  * this CPU is officially up.
 617  */
 618 static inline int can_use_console(unsigned int cpu)
 619 {
 620         return cpu_online(cpu) || have_callable_console();
 621 }
 622
 623 /*
 624  * Try to get console ownership to actually show the kernel
 625  * messages from a 'printk'. Return true (and with the
 626  * console_semaphore held, and 'console_locked' set) if it
 627  * is successful, false otherwise.
 628  *
 629  * This gets called with the 'logbuf_lock' spinlock held and
 630  * interrupts disabled. It should return with 'lockbuf_lock'
 631  * released but interrupts still disabled.
 632  */
 633 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 634 {
 635         int retval = 0;
 636
 637         if (!try_acquire_console_sem()) {
 638                 retval = 1;
 639
 640                 /*
 641                  * If we can't use the console, we need to release
 642                  * the console semaphore by hand to avoid flushing
 643                  * the buffer. We need to hold the console semaphore
 644                  * in order to do this test safely.
 645                  */
 646                 if (!can_use_console(cpu)) {
 647                         console_locked = 0;
 648                         up(&console_sem);
 649                         retval = 0;
 650                 }
 651         }
 652         printk_cpu = UINT_MAX;
 653         spin_unlock(&logbuf_lock);
 654         return retval;
 655 }
 656 static const char recursion_bug_msg [] =
 657                 KERN_CRIT "BUG: recent printk recursion!\n";
 658 static int recursion_bug;
 659         static int new_text_line = 1;
 660 static char printk_buf[1024];
 661
 662 asmlinkage int vprintk(const char *fmt, va_list args)
 663 {
 664         int printed_len = 0;
 665         int current_log_level = default_message_loglevel;
 666         unsigned long flags;
 667         int this_cpu;
 668         char *p;
 669
 670         boot_delay_msec();
 671
 672         preempt_disable();
 673         /* This stops the holder of console_sem just where we want him */
 674         raw_local_irq_save(flags);
 675         this_cpu = smp_processor_id();
 676
 677         /*
 678          * Ouch, printk recursed into itself!
 679          */
 680         if (unlikely(printk_cpu == this_cpu)) {
 681                 /*
 682                  * If a crash is occurring during printk() on this CPU,
 683                  * then try to get the crash message out but make sure
 684                  * we can't deadlock. Otherwise just return to avoid the
 685                  * recursion and return - but flag the recursion so that
 686                  * it can be printed at the next appropriate moment:
 687                  */
 688                 if (!oops_in_progress) {
 689                         recursion_bug = 1;
 690                         goto out_restore_irqs;
 691                 }
 692                 zap_locks();
 693         }
 694
 695         lockdep_off();
 696         spin_lock(&logbuf_lock);
 697         printk_cpu = this_cpu;
 698
 699         if (recursion_bug) {
 700                 recursion_bug = 0;
 701                 strcpy(printk_buf, recursion_bug_msg);
 702                 printed_len = sizeof(recursion_bug_msg);
 703         }
 704         /* Emit the output into the temporary buffer */
 705         printed_len += vscnprintf(printk_buf + printed_len,
 706                                   sizeof(printk_buf) - printed_len, fmt, args);
 707
 708
 709         /*
 710          * Copy the output into log_buf.  If the caller didn't provide
 711          * appropriate log level tags, we insert them here
 712          */
 713         for (p = printk_buf; *p; p++) {
 714                 if (new_text_line) {
 715                         /* If a token, set current_log_level and skip over */
 716                         if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
 717                             p[2] == '>') {
 718                                 current_log_level = p[1] - '0';
 719                                 p += 3;
 720                                 printed_len -= 3;
 721                         }
 722
 723                         /* Always output the token */
 724                         emit_log_char('<');
 725                         emit_log_char(current_log_level + '0');
 726                         emit_log_char('>');
 727                         printed_len += 3;
 728                         new_text_line = 0;
 729
 730                         if (printk_time) {
 731                                 /* Follow the token with the time */
 732                                 char tbuf[50], *tp;
 733                                 unsigned tlen;
 734                                 unsigned long long t;
 735                                 unsigned long nanosec_rem;
 736
 737                                 t = cpu_clock(printk_cpu);
 738                                 nanosec_rem = do_div(t, 1000000000);
 739                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 740                                                 (unsigned long) t,
 741                                                 nanosec_rem / 1000);
 742
 743                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 744                                         emit_log_char(*tp);
 745                                 printed_len += tlen;
 746                         }
 747
 748                         if (!*p)
 749                                 break;
 750                 }
 751
 752                 emit_log_char(*p);
 753                 if (*p == '\n')
 754                         new_text_line = 1;
 755         }
 756
 757         /*
 758          * Try to acquire and then immediately release the
 759          * console semaphore. The release will do all the
 760          * actual magic (print out buffers, wake up klogd,
 761          * etc).
 762          *
 763          * The acquire_console_semaphore_for_printk() function
 764          * will release 'logbuf_lock' regardless of whether it
 765          * actually gets the semaphore or not.
 766          */
 767         if (acquire_console_semaphore_for_printk(this_cpu))
 768                 release_console_sem();
 769
 770         lockdep_on();
 771 out_restore_irqs:
 772         raw_local_irq_restore(flags);
 773
 774         preempt_enable();
 775         return printed_len;
 776 }
 777 EXPORT_SYMBOL(printk);
 778 EXPORT_SYMBOL(vprintk);
 779
 780 #else
 781
 782 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 783 {
 784         return -ENOSYS;
 785 }
 786
 787 static void call_console_drivers(unsigned start, unsigned end)
 788 {
 789 }
 790
 791 #endif
 792
 793 static int __add_preferred_console(char *name, int idx, char *options,
 794                                    char *brl_options)
 795 {
 796         struct console_cmdline *c;
 797         int i;
 798
 799         /*
 800          *      See if this tty is not yet registered, and
 801          *      if we have a slot free.
 802          */
 803         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 804                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 805                           console_cmdline[i].index == idx) {
 806                                 if (!brl_options)
 807                                         selected_console = i;
 808                                 return 0;
 809                 }
 810         if (i == MAX_CMDLINECONSOLES)
 811                 return -E2BIG;
 812         if (!brl_options)
 813                 selected_console = i;
 814         c = &console_cmdline[i];
 815         strlcpy(c->name, name, sizeof(c->name));
 816         c->options = options;
 817 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 818         c->brl_options = brl_options;
 819 #endif
 820         c->index = idx;
 821         return 0;
 822 }
 823 /*
 824  * Set up a list of consoles.  Called from init/main.c
 825  */
 826 static int __init console_setup(char *str)
 827 {
 828         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 829         char *s, *options, *brl_options = NULL;
 830         int idx;
 831
 832 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 833         if (!memcmp(str, "brl,", 4)) {
 834                 brl_options = "";
 835                 str += 4;
 836         } else if (!memcmp(str, "brl=", 4)) {
 837                 brl_options = str + 4;
 838                 str = strchr(brl_options, ',');
 839                 if (!str) {
 840                         printk(KERN_ERR "need port name after brl=\n");
 841                         return 1;
 842                 }
 843                 *(str++) = 0;
 844         }
 845 #endif
 846
 847         /*
 848          * Decode str into name, index, options.
 849          */
 850         if (str[0] >= '0' && str[0] <= '9') {
 851                 strcpy(buf, "ttyS");
 852                 strncpy(buf + 4, str, sizeof(buf) - 5);
 853         } else {
 854                 strncpy(buf, str, sizeof(buf) - 1);
 855         }
 856         buf[sizeof(buf) - 1] = 0;
 857         if ((options = strchr(str, ',')) != NULL)
 858                 *(options++) = 0;
 859 #ifdef __sparc__
 860         if (!strcmp(str, "ttya"))
 861                 strcpy(buf, "ttyS0");
 862         if (!strcmp(str, "ttyb"))
 863                 strcpy(buf, "ttyS1");
 864 #endif
 865         for (s = buf; *s; s++)
 866                 if ((*s >= '0' && *s <= '9') || *s == ',')
 867                         break;
 868         idx = simple_strtoul(s, NULL, 10);
 869         *s = 0;
 870
 871         __add_preferred_console(buf, idx, options, brl_options);
 872         console_set_on_cmdline = 1;
 873         return 1;
 874 }
 875 __setup("console=", console_setup);
 876
 877 /**
 878  * add_preferred_console - add a device to the list of preferred consoles.
 879  * @name: device name
 880  * @idx: device index
 881  * @options: options for this console
 882  *
 883  * The last preferred console added will be used for kernel messages
 884  * and stdin/out/err for init.  Normally this is used by console_setup
 885  * above to handle user-supplied console arguments; however it can also
 886  * be used by arch-specific code either to override the user or more
 887  * commonly to provide a default console (ie from PROM variables) when
 888  * the user has not supplied one.
 889  */
 890 int add_preferred_console(char *name, int idx, char *options)
 891 {
 892         return __add_preferred_console(name, idx, options, NULL);
 893 }
 894
 895 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 896 {
 897         struct console_cmdline *c;
 898         int i;
 899
 900         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 901                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 902                           console_cmdline[i].index == idx) {
 903                                 c = &console_cmdline[i];
 904                                 strlcpy(c->name, name_new, sizeof(c->name));
 905                                 c->name[sizeof(c->name) - 1] = 0;
 906                                 c->options = options;
 907                                 c->index = idx_new;
 908                                 return i;
 909                 }
 910         /* not found */
 911         return -1;
 912 }
 913
 914 int console_suspend_enabled = 1;
 915 EXPORT_SYMBOL(console_suspend_enabled);
 916
 917 static int __init console_suspend_disable(char *str)
 918 {
 919         console_suspend_enabled = 0;
 920         return 1;
 921 }
 922 __setup("no_console_suspend", console_suspend_disable);
 923
 924 /**
 925  * suspend_console - suspend the console subsystem
 926  *
 927  * This disables printk() while we go into suspend states
 928  */
 929 void suspend_console(void)
 930 {
 931         if (!console_suspend_enabled)
 932                 return;
 933         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 934         acquire_console_sem();
 935         console_suspended = 1;
 936 }
 937
 938 void resume_console(void)
 939 {
 940         if (!console_suspend_enabled)
 941                 return;
 942         console_suspended = 0;
 943         release_console_sem();
 944 }
 945
 946 /**
 947  * acquire_console_sem - lock the console system for exclusive use.
 948  *
 949  * Acquires a semaphore which guarantees that the caller has
 950  * exclusive access to the console system and the console_drivers list.
 951  *
 952  * Can sleep, returns nothing.
 953  */
 954 void acquire_console_sem(void)
 955 {
 956         BUG_ON(in_interrupt());
 957         if (console_suspended) {
 958                 down(&secondary_console_sem);
 959                 return;
 960         }
 961         down(&console_sem);
 962         console_locked = 1;
 963         console_may_schedule = 1;
 964 }
 965 EXPORT_SYMBOL(acquire_console_sem);
 966
 967 int try_acquire_console_sem(void)
 968 {
 969         if (down_trylock(&console_sem))
 970                 return -1;
 971         console_locked = 1;
 972         console_may_schedule = 0;
 973         return 0;
 974 }
 975 EXPORT_SYMBOL(try_acquire_console_sem);
 976
 977 int is_console_locked(void)
 978 {
 979         return console_locked;
 980 }
 981
 982 static DEFINE_PER_CPU(int, printk_pending);
 983
 984 void printk_tick(void)
 985 {
 986         if (__get_cpu_var(printk_pending)) {
 987                 __get_cpu_var(printk_pending) = 0;
 988                 wake_up_interruptible(&log_wait);
 989         }
 990 }
 991
 992 int printk_needs_cpu(int cpu)
 993 {
 994         return per_cpu(printk_pending, cpu);
 995 }
 996
 997 void wake_up_klogd(void)
 998 {
 999         if (waitqueue_active(&log_wait))
1000                 __raw_get_cpu_var(printk_pending) = 1;
1001 }
1002
1003 /**
1004  * release_console_sem - unlock the console system
1005  *
1006  * Releases the semaphore which the caller holds on the console system
1007  * and the console driver list.
1008  *
1009  * While the semaphore was held, console output may have been buffered
1010  * by printk().  If this is the case, release_console_sem() emits
1011  * the output prior to releasing the semaphore.
1012  *
1013  * If there is output waiting for klogd, we wake it up.
1014  *
1015  * release_console_sem() may be called from any context.
1016  */
1017 void release_console_sem(void)
1018 {
1019         unsigned long flags;
1020         unsigned _con_start, _log_end;
1021         unsigned wake_klogd = 0;
1022
1023         if (console_suspended) {
1024                 up(&secondary_console_sem);
1025                 return;
1026         }
1027
1028         console_may_schedule = 0;
1029
1030         for ( ; ; ) {
1031                 spin_lock_irqsave(&logbuf_lock, flags);
1032                 wake_klogd |= log_start - log_end;
1033                 if (con_start == log_end)
1034                         break;                  /* Nothing to print */
1035                 _con_start = con_start;
1036                 _log_end = log_end;
1037                 con_start = log_end;            /* Flush */
1038                 spin_unlock(&logbuf_lock);
1039                 stop_critical_timings();        /* don't trace print latency */
1040                 call_console_drivers(_con_start, _log_end);
1041                 start_critical_timings();
1042                 local_irq_restore(flags);
1043         }
1044         console_locked = 0;
1045         up(&console_sem);
1046         spin_unlock_irqrestore(&logbuf_lock, flags);
1047         if (wake_klogd)
1048                 wake_up_klogd();
1049 }
1050 EXPORT_SYMBOL(release_console_sem);
1051
1052 /**
1053  * console_conditional_schedule - yield the CPU if required
1054  *
1055  * If the console code is currently allowed to sleep, and
1056  * if this CPU should yield the CPU to another task, do
1057  * so here.
1058  *
1059  * Must be called within acquire_console_sem().
1060  */
1061 void __sched console_conditional_schedule(void)
1062 {
1063         if (console_may_schedule)
1064                 cond_resched();
1065 }
1066 EXPORT_SYMBOL(console_conditional_schedule);
1067
1068 void console_print(const char *s)
1069 {
1070         printk(KERN_EMERG "%s", s);
1071 }
1072 EXPORT_SYMBOL(console_print);
1073
1074 void console_unblank(void)
1075 {
1076         struct console *c;
1077
1078         /*
1079          * console_unblank can no longer be called in interrupt context unless
1080          * oops_in_progress is set to 1..
1081          */
1082         if (oops_in_progress) {
1083                 if (down_trylock(&console_sem) != 0)
1084                         return;
1085         } else
1086                 acquire_console_sem();
1087
1088         console_locked = 1;
1089         console_may_schedule = 0;
1090         for (c = console_drivers; c != NULL; c = c->next)
1091                 if ((c->flags & CON_ENABLED) && c->unblank)
1092                         c->unblank();
1093         release_console_sem();
1094 }
1095
1096 /*
1097  * Return the console tty driver structure and its associated index
1098  */
1099 struct tty_driver *console_device(int *index)
1100 {
1101         struct console *c;
1102         struct tty_driver *driver = NULL;
1103
1104         acquire_console_sem();
1105         for (c = console_drivers; c != NULL; c = c->next) {
1106                 if (!c->device)
1107                         continue;
1108                 driver = c->device(c, index);
1109                 if (driver)
1110                         break;
1111         }
1112         release_console_sem();
1113         return driver;
1114 }
1115
1116 /*
1117  * Prevent further output on the passed console device so that (for example)
1118  * serial drivers can disable console output before suspending a port, and can
1119  * re-enable output afterwards.
1120  */
1121 void console_stop(struct console *console)
1122 {
1123         acquire_console_sem();
1124         console->flags &= ~CON_ENABLED;
1125         release_console_sem();
1126 }
1127 EXPORT_SYMBOL(console_stop);
1128
1129 void console_start(struct console *console)
1130 {
1131         acquire_console_sem();
1132         console->flags |= CON_ENABLED;
1133         release_console_sem();
1134 }
1135 EXPORT_SYMBOL(console_start);
1136
1137 /*
1138  * The console driver calls this routine during kernel initialization
1139  * to register the console printing procedure with printk() and to
1140  * print any messages that were printed by the kernel before the
1141  * console driver was initialized.
1142  */
1143 void register_console(struct console *console)
1144 {
1145         int i;
1146         unsigned long flags;
1147         struct console *bootconsole = NULL;
1148
1149         if (console_drivers) {
1150                 if (console->flags & CON_BOOT)
1151                         return;
1152                 if (console_drivers->flags & CON_BOOT)
1153                         bootconsole = console_drivers;
1154         }
1155
1156         if (preferred_console < 0 || bootconsole || !console_drivers)
1157                 preferred_console = selected_console;
1158
1159         if (console->early_setup)
1160                 console->early_setup();
1161
1162         /*
1163          *      See if we want to use this console driver. If we
1164          *      didn't select a console we take the first one
1165          *      that registers here.
1166          */
1167         if (preferred_console < 0) {
1168                 if (console->index < 0)
1169                         console->index = 0;
1170                 if (console->setup == NULL ||
1171                     console->setup(console, NULL) == 0) {
1172                         console->flags |= CON_ENABLED;
1173                         if (console->device) {
1174                                 console->flags |= CON_CONSDEV;
1175                                 preferred_console = 0;
1176                         }
1177                 }
1178         }
1179
1180         /*
1181          *      See if this console matches one we selected on
1182          *      the command line.
1183          */
1184         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1185                         i++) {
1186                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1187                         continue;
1188                 if (console->index >= 0 &&
1189                     console->index != console_cmdline[i].index)
1190                         continue;
1191                 if (console->index < 0)
1192                         console->index = console_cmdline[i].index;
1193 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1194                 if (console_cmdline[i].brl_options) {
1195                         console->flags |= CON_BRL;
1196                         braille_register_console(console,
1197                                         console_cmdline[i].index,
1198                                         console_cmdline[i].options,
1199                                         console_cmdline[i].brl_options);
1200                         return;
1201                 }
1202 #endif
1203                 if (console->setup &&
1204                     console->setup(console, console_cmdline[i].options) != 0)
1205                         break;
1206                 console->flags |= CON_ENABLED;
1207                 console->index = console_cmdline[i].index;
1208                 if (i == selected_console) {
1209                         console->flags |= CON_CONSDEV;
1210                         preferred_console = selected_console;
1211                 }
1212                 break;
1213         }
1214
1215         if (!(console->flags & CON_ENABLED))
1216                 return;
1217
1218         if (bootconsole && (console->flags & CON_CONSDEV)) {
1219                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1220                        bootconsole->name, bootconsole->index,
1221                        console->name, console->index);
1222                 unregister_console(bootconsole);
1223                 console->flags &= ~CON_PRINTBUFFER;
1224         } else {
1225                 printk(KERN_INFO "console [%s%d] enabled\n",
1226                        console->name, console->index);
1227         }
1228
1229         /*
1230          *      Put this console in the list - keep the
1231          *      preferred driver at the head of the list.
1232          */
1233         acquire_console_sem();
1234         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1235                 console->next = console_drivers;
1236                 console_drivers = console;
1237                 if (console->next)
1238                         console->next->flags &= ~CON_CONSDEV;
1239         } else {
1240                 console->next = console_drivers->next;
1241                 console_drivers->next = console;
1242         }
1243         if (console->flags & CON_PRINTBUFFER) {
1244                 /*
1245                  * release_console_sem() will print out the buffered messages
1246                  * for us.
1247                  */
1248                 spin_lock_irqsave(&logbuf_lock, flags);
1249                 con_start = log_start;
1250                 spin_unlock_irqrestore(&logbuf_lock, flags);
1251         }
1252         release_console_sem();
1253 }
1254 EXPORT_SYMBOL(register_console);
1255
1256 int unregister_console(struct console *console)
1257 {
1258         struct console *a, *b;
1259         int res = 1;
1260
1261 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1262         if (console->flags & CON_BRL)
1263                 return braille_unregister_console(console);
1264 #endif
1265
1266         acquire_console_sem();
1267         if (console_drivers == console) {
1268                 console_drivers=console->next;
1269                 res = 0;
1270         } else if (console_drivers) {
1271                 for (a=console_drivers->next, b=console_drivers ;
1272                      a; b=a, a=b->next) {
1273                         if (a == console) {
1274                                 b->next = a->next;
1275                                 res = 0;
1276                                 break;
1277                         }
1278                 }
1279         }
1280
1281         /*
1282          * If this isn't the last console and it has CON_CONSDEV set, we
1283          * need to set it on the next preferred console.
1284          */
1285         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1286                 console_drivers->flags |= CON_CONSDEV;
1287
1288         release_console_sem();
1289         return res;
1290 }
1291 EXPORT_SYMBOL(unregister_console);
1292
1293 static int __init disable_boot_consoles(void)
1294 {
1295         if (console_drivers != NULL) {
1296                 if (console_drivers->flags & CON_BOOT) {
1297                         printk(KERN_INFO "turn off boot console %s%d\n",
1298                                 console_drivers->name, console_drivers->index);
1299                         return unregister_console(console_drivers);
1300                 }
1301         }
1302         return 0;
1303 }
1304 late_initcall(disable_boot_consoles);
1305
1306 #if defined CONFIG_PRINTK
1307
1308 /*
1309  * printk rate limiting, lifted from the networking subsystem.
1310  *
1311  * This enforces a rate limit: not more than 10 kernel messages
1312  * every 5s to make a denial-of-service attack impossible.
1313  */
1314 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1315
1316 int printk_ratelimit(void)
1317 {
1318         return __ratelimit(&printk_ratelimit_state);
1319 }
1320 EXPORT_SYMBOL(printk_ratelimit);
1321
1322 /**
1323  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1324  * @caller_jiffies: pointer to caller's state
1325  * @interval_msecs: minimum interval between prints
1326  *
1327  * printk_timed_ratelimit() returns true if more than @interval_msecs
1328  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1329  * returned true.
1330  */
1331 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1332                         unsigned int interval_msecs)
1333 {
1334         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1335                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1336                 return true;
1337         }
1338         return false;
1339 }
1340 EXPORT_SYMBOL(printk_timed_ratelimit);
1341 #endif