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 /* 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 /*
  79  * This is used for debugging the mess that is the VT code by
  80  * keeping track if we have the console semaphore held. It's
  81  * definitely not the perfect debug tool (we don't know if _WE_
  82  * hold it are racing, but it helps tracking those weird code
  83  * path in the console code where we end up in places I want
  84  * locked without the console sempahore held
  85  */
  86 static int console_locked, console_suspended;
  87
  88 /*
  89  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  90  * It is also used in interesting ways to provide interlocking in
  91  * release_console_sem().
  92  */
  93 static DEFINE_SPINLOCK(logbuf_lock);
  94
  95 #define LOG_BUF_MASK (log_buf_len-1)
  96 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  97
  98 /*
  99  * The indices into log_buf are not constrained to log_buf_len - they
 100  * must be masked before subscripting
 101  */
 102 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 103 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 104 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 105
 106 /*
 107  *      Array of consoles built from command line options (console=)
 108  */
 109 struct console_cmdline
 110 {
 111         char    name[8];                        /* Name of the driver       */
 112         int     index;                          /* Minor dev. to use        */
 113         char    *options;                       /* Options for the driver   */
 114 };
 115
 116 #define MAX_CMDLINECONSOLES 8
 117
 118 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 119 static int selected_console = -1;
 120 static int preferred_console = -1;
 121
 122 /* Flag: console code may call schedule() */
 123 static int console_may_schedule;
 124
 125 #ifdef CONFIG_PRINTK
 126
 127 static char __log_buf[__LOG_BUF_LEN];
 128 static char *log_buf = __log_buf;
 129 static int log_buf_len = __LOG_BUF_LEN;
 130 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 131
 132 static int __init log_buf_len_setup(char *str)
 133 {
 134         unsigned size = memparse(str, &str);
 135         unsigned long flags;
 136
 137         if (size)
 138                 size = roundup_pow_of_two(size);
 139         if (size > log_buf_len) {
 140                 unsigned start, dest_idx, offset;
 141                 char *new_log_buf;
 142
 143                 new_log_buf = alloc_bootmem(size);
 144                 if (!new_log_buf) {
 145                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 146                         goto out;
 147                 }
 148
 149                 spin_lock_irqsave(&logbuf_lock, flags);
 150                 log_buf_len = size;
 151                 log_buf = new_log_buf;
 152
 153                 offset = start = min(con_start, log_start);
 154                 dest_idx = 0;
 155                 while (start != log_end) {
 156                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 157                         start++;
 158                         dest_idx++;
 159                 }
 160                 log_start -= offset;
 161                 con_start -= offset;
 162                 log_end -= offset;
 163                 spin_unlock_irqrestore(&logbuf_lock, flags);
 164
 165                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 166         }
 167 out:
 168         return 1;
 169 }
 170
 171 __setup("log_buf_len=", log_buf_len_setup);
 172
 173 #ifdef CONFIG_BOOT_PRINTK_DELAY
 174
 175 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 176 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 177
 178 static int __init boot_delay_setup(char *str)
 179 {
 180         unsigned long lpj;
 181         unsigned long long loops_per_msec;
 182
 183         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 184         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 185
 186         get_option(&str, &boot_delay);
 187         if (boot_delay > 10 * 1000)
 188                 boot_delay = 0;
 189
 190         printk_delay_msec = loops_per_msec;
 191         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 192                 "HZ: %d, printk_delay_msec: %llu\n",
 193                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 194         return 1;
 195 }
 196 __setup("boot_delay=", boot_delay_setup);
 197
 198 static void boot_delay_msec(void)
 199 {
 200         unsigned long long k;
 201         unsigned long timeout;
 202
 203         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 204                 return;
 205
 206         k = (unsigned long long)printk_delay_msec * boot_delay;
 207
 208         timeout = jiffies + msecs_to_jiffies(boot_delay);
 209         while (k) {
 210                 k--;
 211                 cpu_relax();
 212                 /*
 213                  * use (volatile) jiffies to prevent
 214                  * compiler reduction; loop termination via jiffies
 215                  * is secondary and may or may not happen.
 216                  */
 217                 if (time_after(jiffies, timeout))
 218                         break;
 219                 touch_nmi_watchdog();
 220         }
 221 }
 222 #else
 223 static inline void boot_delay_msec(void)
 224 {
 225 }
 226 #endif
 227
 228 /*
 229  * Return the number of unread characters in the log buffer.
 230  */
 231 int log_buf_get_len(void)
 232 {
 233         return logged_chars;
 234 }
 235
 236 /*
 237  * Copy a range of characters from the log buffer.
 238  */
 239 int log_buf_copy(char *dest, int idx, int len)
 240 {
 241         int ret, max;
 242         bool took_lock = false;
 243
 244         if (!oops_in_progress) {
 245                 spin_lock_irq(&logbuf_lock);
 246                 took_lock = true;
 247         }
 248
 249         max = log_buf_get_len();
 250         if (idx < 0 || idx >= max) {
 251                 ret = -1;
 252         } else {
 253                 if (len > max)
 254                         len = max;
 255                 ret = len;
 256                 idx += (log_end - max);
 257                 while (len-- > 0)
 258                         dest[len] = LOG_BUF(idx + len);
 259         }
 260
 261         if (took_lock)
 262                 spin_unlock_irq(&logbuf_lock);
 263
 264         return ret;
 265 }
 266
 267 /*
 268  * Extract a single character from the log buffer.
 269  */
 270 int log_buf_read(int idx)
 271 {
 272         char ret;
 273
 274         if (log_buf_copy(&ret, idx, 1) == 1)
 275                 return ret;
 276         else
 277                 return -1;
 278 }
 279
 280 /*
 281  * Commands to do_syslog:
 282  *
 283  *      0 -- Close the log.  Currently a NOP.
 284  *      1 -- Open the log. Currently a NOP.
 285  *      2 -- Read from the log.
 286  *      3 -- Read all messages remaining in the ring buffer.
 287  *      4 -- Read and clear all messages remaining in the ring buffer
 288  *      5 -- Clear ring buffer.
 289  *      6 -- Disable printk's to console
 290  *      7 -- Enable printk's to console
 291  *      8 -- Set level of messages printed to console
 292  *      9 -- Return number of unread characters in the log buffer
 293  *     10 -- Return size of the log buffer
 294  */
 295 int do_syslog(int type, char __user *buf, int len)
 296 {
 297         unsigned i, j, limit, count;
 298         int do_clear = 0;
 299         char c;
 300         int error = 0;
 301
 302         error = security_syslog(type);
 303         if (error)
 304                 return error;
 305
 306         switch (type) {
 307         case 0:         /* Close log */
 308                 break;
 309         case 1:         /* Open log */
 310                 break;
 311         case 2:         /* Read from log */
 312                 error = -EINVAL;
 313                 if (!buf || len < 0)
 314                         goto out;
 315                 error = 0;
 316                 if (!len)
 317                         goto out;
 318                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 319                         error = -EFAULT;
 320                         goto out;
 321                 }
 322                 error = wait_event_interruptible(log_wait,
 323                                                         (log_start - log_end));
 324                 if (error)
 325                         goto out;
 326                 i = 0;
 327                 spin_lock_irq(&logbuf_lock);
 328                 while (!error && (log_start != log_end) && i < len) {
 329                         c = LOG_BUF(log_start);
 330                         log_start++;
 331                         spin_unlock_irq(&logbuf_lock);
 332                         error = __put_user(c,buf);
 333                         buf++;
 334                         i++;
 335                         cond_resched();
 336                         spin_lock_irq(&logbuf_lock);
 337                 }
 338                 spin_unlock_irq(&logbuf_lock);
 339                 if (!error)
 340                         error = i;
 341                 break;
 342         case 4:         /* Read/clear last kernel messages */
 343                 do_clear = 1;
 344                 /* FALL THRU */
 345         case 3:         /* Read last kernel messages */
 346                 error = -EINVAL;
 347                 if (!buf || len < 0)
 348                         goto out;
 349                 error = 0;
 350                 if (!len)
 351                         goto out;
 352                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 353                         error = -EFAULT;
 354                         goto out;
 355                 }
 356                 count = len;
 357                 if (count > log_buf_len)
 358                         count = log_buf_len;
 359                 spin_lock_irq(&logbuf_lock);
 360                 if (count > logged_chars)
 361                         count = logged_chars;
 362                 if (do_clear)
 363                         logged_chars = 0;
 364                 limit = log_end;
 365                 /*
 366                  * __put_user() could sleep, and while we sleep
 367                  * printk() could overwrite the messages
 368                  * we try to copy to user space. Therefore
 369                  * the messages are copied in reverse. <manfreds>
 370                  */
 371                 for (i = 0; i < count && !error; i++) {
 372                         j = limit-1-i;
 373                         if (j + log_buf_len < log_end)
 374                                 break;
 375                         c = LOG_BUF(j);
 376                         spin_unlock_irq(&logbuf_lock);
 377                         error = __put_user(c,&buf[count-1-i]);
 378                         cond_resched();
 379                         spin_lock_irq(&logbuf_lock);
 380                 }
 381                 spin_unlock_irq(&logbuf_lock);
 382                 if (error)
 383                         break;
 384                 error = i;
 385                 if (i != count) {
 386                         int offset = count-error;
 387                         /* buffer overflow during copy, correct user buffer. */
 388                         for (i = 0; i < error; i++) {
 389                                 if (__get_user(c,&buf[i+offset]) ||
 390                                     __put_user(c,&buf[i])) {
 391                                         error = -EFAULT;
 392                                         break;
 393                                 }
 394                                 cond_resched();
 395                         }
 396                 }
 397                 break;
 398         case 5:         /* Clear ring buffer */
 399                 logged_chars = 0;
 400                 break;
 401         case 6:         /* Disable logging to console */
 402                 console_loglevel = minimum_console_loglevel;
 403                 break;
 404         case 7:         /* Enable logging to console */
 405                 console_loglevel = default_console_loglevel;
 406                 break;
 407         case 8:         /* Set level of messages printed to console */
 408                 error = -EINVAL;
 409                 if (len < 1 || len > 8)
 410                         goto out;
 411                 if (len < minimum_console_loglevel)
 412                         len = minimum_console_loglevel;
 413                 console_loglevel = len;
 414                 error = 0;
 415                 break;
 416         case 9:         /* Number of chars in the log buffer */
 417                 error = log_end - log_start;
 418                 break;
 419         case 10:        /* Size of the log buffer */
 420                 error = log_buf_len;
 421                 break;
 422         default:
 423                 error = -EINVAL;
 424                 break;
 425         }
 426 out:
 427         return error;
 428 }
 429
 430 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 431 {
 432         return do_syslog(type, buf, len);
 433 }
 434
 435 /*
 436  * Call the console drivers on a range of log_buf
 437  */
 438 static void __call_console_drivers(unsigned start, unsigned end)
 439 {
 440         struct console *con;
 441
 442         for (con = console_drivers; con; con = con->next) {
 443                 if ((con->flags & CON_ENABLED) && con->write &&
 444                                 (cpu_online(smp_processor_id()) ||
 445                                 (con->flags & CON_ANYTIME)))
 446                         con->write(con, &LOG_BUF(start), end - start);
 447         }
 448 }
 449
 450 static int __read_mostly ignore_loglevel;
 451
 452 static int __init ignore_loglevel_setup(char *str)
 453 {
 454         ignore_loglevel = 1;
 455         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 456
 457         return 0;
 458 }
 459
 460 early_param("ignore_loglevel", ignore_loglevel_setup);
 461
 462 /*
 463  * Write out chars from start to end - 1 inclusive
 464  */
 465 static void _call_console_drivers(unsigned start,
 466                                 unsigned end, int msg_log_level)
 467 {
 468         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 469                         console_drivers && start != end) {
 470                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 471                         /* wrapped write */
 472                         __call_console_drivers(start & LOG_BUF_MASK,
 473                                                 log_buf_len);
 474                         __call_console_drivers(0, end & LOG_BUF_MASK);
 475                 } else {
 476                         __call_console_drivers(start, end);
 477                 }
 478         }
 479 }
 480
 481 /*
 482  * Call the console drivers, asking them to write out
 483  * log_buf[start] to log_buf[end - 1].
 484  * The console_sem must be held.
 485  */
 486 static void call_console_drivers(unsigned start, unsigned end)
 487 {
 488         unsigned cur_index, start_print;
 489         static int msg_level = -1;
 490
 491         BUG_ON(((int)(start - end)) > 0);
 492
 493         cur_index = start;
 494         start_print = start;
 495         while (cur_index != end) {
 496                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 497                                 LOG_BUF(cur_index + 0) == '<' &&
 498                                 LOG_BUF(cur_index + 1) >= '0' &&
 499                                 LOG_BUF(cur_index + 1) <= '7' &&
 500                                 LOG_BUF(cur_index + 2) == '>') {
 501                         msg_level = LOG_BUF(cur_index + 1) - '0';
 502                         cur_index += 3;
 503                         start_print = cur_index;
 504                 }
 505                 while (cur_index != end) {
 506                         char c = LOG_BUF(cur_index);
 507
 508                         cur_index++;
 509                         if (c == '\n') {
 510                                 if (msg_level < 0) {
 511                                         /*
 512                                          * printk() has already given us loglevel tags in
 513                                          * the buffer.  This code is here in case the
 514                                          * log buffer has wrapped right round and scribbled
 515                                          * on those tags
 516                                          */
 517                                         msg_level = default_message_loglevel;
 518                                 }
 519                                 _call_console_drivers(start_print, cur_index, msg_level);
 520                                 msg_level = -1;
 521                                 start_print = cur_index;
 522                                 break;
 523                         }
 524                 }
 525         }
 526         _call_console_drivers(start_print, end, msg_level);
 527 }
 528
 529 static void emit_log_char(char c)
 530 {
 531         LOG_BUF(log_end) = c;
 532         log_end++;
 533         if (log_end - log_start > log_buf_len)
 534                 log_start = log_end - log_buf_len;
 535         if (log_end - con_start > log_buf_len)
 536                 con_start = log_end - log_buf_len;
 537         if (logged_chars < log_buf_len)
 538                 logged_chars++;
 539 }
 540
 541 /*
 542  * Zap console related locks when oopsing. Only zap at most once
 543  * every 10 seconds, to leave time for slow consoles to print a
 544  * full oops.
 545  */
 546 static void zap_locks(void)
 547 {
 548         static unsigned long oops_timestamp;
 549
 550         if (time_after_eq(jiffies, oops_timestamp) &&
 551                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 552                 return;
 553
 554         oops_timestamp = jiffies;
 555
 556         /* If a crash is occurring, make sure we can't deadlock */
 557         spin_lock_init(&logbuf_lock);
 558         /* And make sure that we print immediately */
 559         init_MUTEX(&console_sem);
 560 }
 561
 562 #if defined(CONFIG_PRINTK_TIME)
 563 static int printk_time = 1;
 564 #else
 565 static int printk_time = 0;
 566 #endif
 567 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 568
 569 /* Check if we have any console registered that can be called early in boot. */
 570 static int have_callable_console(void)
 571 {
 572         struct console *con;
 573
 574         for (con = console_drivers; con; con = con->next)
 575                 if (con->flags & CON_ANYTIME)
 576                         return 1;
 577
 578         return 0;
 579 }
 580
 581 /**
 582  * printk - print a kernel message
 583  * @fmt: format string
 584  *
 585  * This is printk().  It can be called from any context.  We want it to work.
 586  * Be aware of the fact that if oops_in_progress is not set, we might try to
 587  * wake klogd up which could deadlock on runqueue lock if printk() is called
 588  * from scheduler code.
 589  *
 590  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 591  * call the console drivers.  If we fail to get the semaphore we place the output
 592  * into the log buffer and return.  The current holder of the console_sem will
 593  * notice the new output in release_console_sem() and will send it to the
 594  * consoles before releasing the semaphore.
 595  *
 596  * One effect of this deferred printing is that code which calls printk() and
 597  * then changes console_loglevel may break. This is because console_loglevel
 598  * is inspected when the actual printing occurs.
 599  *
 600  * See also:
 601  * printf(3)
 602  */
 603
 604 asmlinkage int printk(const char *fmt, ...)
 605 {
 606         va_list args;
 607         int r;
 608
 609         va_start(args, fmt);
 610         r = vprintk(fmt, args);
 611         va_end(args);
 612
 613         return r;
 614 }
 615
 616 /* cpu currently holding logbuf_lock */
 617 static volatile unsigned int printk_cpu = UINT_MAX;
 618
 619 const char printk_recursion_bug_msg [] =
 620                         KERN_CRIT "BUG: recent printk recursion!\n";
 621 static int printk_recursion_bug;
 622
 623 asmlinkage int vprintk(const char *fmt, va_list args)
 624 {
 625         static int log_level_unknown = 1;
 626         static char printk_buf[1024];
 627
 628         unsigned long flags;
 629         int printed_len = 0;
 630         int this_cpu;
 631         char *p;
 632
 633         boot_delay_msec();
 634
 635         preempt_disable();
 636         /* This stops the holder of console_sem just where we want him */
 637         raw_local_irq_save(flags);
 638         this_cpu = smp_processor_id();
 639
 640         /*
 641          * Ouch, printk recursed into itself!
 642          */
 643         if (unlikely(printk_cpu == this_cpu)) {
 644                 /*
 645                  * If a crash is occurring during printk() on this CPU,
 646                  * then try to get the crash message out but make sure
 647                  * we can't deadlock. Otherwise just return to avoid the
 648                  * recursion and return - but flag the recursion so that
 649                  * it can be printed at the next appropriate moment:
 650                  */
 651                 if (!oops_in_progress) {
 652                         printk_recursion_bug = 1;
 653                         goto out_restore_irqs;
 654                 }
 655                 zap_locks();
 656         }
 657
 658         lockdep_off();
 659         spin_lock(&logbuf_lock);
 660         printk_cpu = this_cpu;
 661
 662         if (printk_recursion_bug) {
 663                 printk_recursion_bug = 0;
 664                 strcpy(printk_buf, printk_recursion_bug_msg);
 665                 printed_len = sizeof(printk_recursion_bug_msg);
 666         }
 667         /* Emit the output into the temporary buffer */
 668         printed_len += vscnprintf(printk_buf + printed_len,
 669                                   sizeof(printk_buf), fmt, args);
 670
 671         /*
 672          * Copy the output into log_buf.  If the caller didn't provide
 673          * appropriate log level tags, we insert them here
 674          */
 675         for (p = printk_buf; *p; p++) {
 676                 if (log_level_unknown) {
 677                         /* log_level_unknown signals the start of a new line */
 678                         if (printk_time) {
 679                                 int loglev_char;
 680                                 char tbuf[50], *tp;
 681                                 unsigned tlen;
 682                                 unsigned long long t;
 683                                 unsigned long nanosec_rem;
 684
 685                                 /*
 686                                  * force the log level token to be
 687                                  * before the time output.
 688                                  */
 689                                 if (p[0] == '<' && p[1] >='0' &&
 690                                    p[1] <= '7' && p[2] == '>') {
 691                                         loglev_char = p[1];
 692                                         p += 3;
 693                                         printed_len -= 3;
 694                                 } else {
 695                                         loglev_char = default_message_loglevel
 696                                                 + '0';
 697                                 }
 698                                 t = cpu_clock(printk_cpu);
 699                                 nanosec_rem = do_div(t, 1000000000);
 700                                 tlen = sprintf(tbuf,
 701                                                 "<%c>[%5lu.%06lu] ",
 702                                                 loglev_char,
 703                                                 (unsigned long)t,
 704                                                 nanosec_rem/1000);
 705
 706                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 707                                         emit_log_char(*tp);
 708                                 printed_len += tlen;
 709                         } else {
 710                                 if (p[0] != '<' || p[1] < '0' ||
 711                                    p[1] > '7' || p[2] != '>') {
 712                                         emit_log_char('<');
 713                                         emit_log_char(default_message_loglevel
 714                                                 + '0');
 715                                         emit_log_char('>');
 716                                         printed_len += 3;
 717                                 }
 718                         }
 719                         log_level_unknown = 0;
 720                         if (!*p)
 721                                 break;
 722                 }
 723                 emit_log_char(*p);
 724                 if (*p == '\n')
 725                         log_level_unknown = 1;
 726         }
 727
 728         if (!down_trylock(&console_sem)) {
 729                 /*
 730                  * We own the drivers.  We can drop the spinlock and
 731                  * let release_console_sem() print the text, maybe ...
 732                  */
 733                 console_locked = 1;
 734                 printk_cpu = UINT_MAX;
 735                 spin_unlock(&logbuf_lock);
 736
 737                 /*
 738                  * Console drivers may assume that per-cpu resources have
 739                  * been allocated. So unless they're explicitly marked as
 740                  * being able to cope (CON_ANYTIME) don't call them until
 741                  * this CPU is officially up.
 742                  */
 743                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 744                         console_may_schedule = 0;
 745                         release_console_sem();
 746                 } else {
 747                         /* Release by hand to avoid flushing the buffer. */
 748                         console_locked = 0;
 749                         up(&console_sem);
 750                 }
 751                 lockdep_on();
 752                 raw_local_irq_restore(flags);
 753         } else {
 754                 /*
 755                  * Someone else owns the drivers.  We drop the spinlock, which
 756                  * allows the semaphore holder to proceed and to call the
 757                  * console drivers with the output which we just produced.
 758                  */
 759                 printk_cpu = UINT_MAX;
 760                 spin_unlock(&logbuf_lock);
 761                 lockdep_on();
 762 out_restore_irqs:
 763                 raw_local_irq_restore(flags);
 764         }
 765
 766         preempt_enable();
 767         return printed_len;
 768 }
 769 EXPORT_SYMBOL(printk);
 770 EXPORT_SYMBOL(vprintk);
 771
 772 #else
 773
 774 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 775 {
 776         return -ENOSYS;
 777 }
 778
 779 static void call_console_drivers(unsigned start, unsigned end)
 780 {
 781 }
 782
 783 #endif
 784
 785 /*
 786  * Set up a list of consoles.  Called from init/main.c
 787  */
 788 static int __init console_setup(char *str)
 789 {
 790         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 791         char *s, *options;
 792         int idx;
 793
 794         /*
 795          * Decode str into name, index, options.
 796          */
 797         if (str[0] >= '0' && str[0] <= '9') {
 798                 strcpy(buf, "ttyS");
 799                 strncpy(buf + 4, str, sizeof(buf) - 5);
 800         } else {
 801                 strncpy(buf, str, sizeof(buf) - 1);
 802         }
 803         buf[sizeof(buf) - 1] = 0;
 804         if ((options = strchr(str, ',')) != NULL)
 805                 *(options++) = 0;
 806 #ifdef __sparc__
 807         if (!strcmp(str, "ttya"))
 808                 strcpy(buf, "ttyS0");
 809         if (!strcmp(str, "ttyb"))
 810                 strcpy(buf, "ttyS1");
 811 #endif
 812         for (s = buf; *s; s++)
 813                 if ((*s >= '0' && *s <= '9') || *s == ',')
 814                         break;
 815         idx = simple_strtoul(s, NULL, 10);
 816         *s = 0;
 817
 818         add_preferred_console(buf, idx, options);
 819         return 1;
 820 }
 821 __setup("console=", console_setup);
 822
 823 /**
 824  * add_preferred_console - add a device to the list of preferred consoles.
 825  * @name: device name
 826  * @idx: device index
 827  * @options: options for this console
 828  *
 829  * The last preferred console added will be used for kernel messages
 830  * and stdin/out/err for init.  Normally this is used by console_setup
 831  * above to handle user-supplied console arguments; however it can also
 832  * be used by arch-specific code either to override the user or more
 833  * commonly to provide a default console (ie from PROM variables) when
 834  * the user has not supplied one.
 835  */
 836 int add_preferred_console(char *name, int idx, char *options)
 837 {
 838         struct console_cmdline *c;
 839         int i;
 840
 841         /*
 842          *      See if this tty is not yet registered, and
 843          *      if we have a slot free.
 844          */
 845         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 846                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 847                           console_cmdline[i].index == idx) {
 848                                 selected_console = i;
 849                                 return 0;
 850                 }
 851         if (i == MAX_CMDLINECONSOLES)
 852                 return -E2BIG;
 853         selected_console = i;
 854         c = &console_cmdline[i];
 855         memcpy(c->name, name, sizeof(c->name));
 856         c->name[sizeof(c->name) - 1] = 0;
 857         c->options = options;
 858         c->index = idx;
 859         return 0;
 860 }
 861
 862 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 863 {
 864         struct console_cmdline *c;
 865         int i;
 866
 867         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 868                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 869                           console_cmdline[i].index == idx) {
 870                                 c = &console_cmdline[i];
 871                                 memcpy(c->name, name_new, sizeof(c->name));
 872                                 c->name[sizeof(c->name) - 1] = 0;
 873                                 c->options = options;
 874                                 c->index = idx_new;
 875                                 return i;
 876                 }
 877         /* not found */
 878         return -1;
 879 }
 880
 881 int console_suspend_enabled = 1;
 882 EXPORT_SYMBOL(console_suspend_enabled);
 883
 884 static int __init console_suspend_disable(char *str)
 885 {
 886         console_suspend_enabled = 0;
 887         return 1;
 888 }
 889 __setup("no_console_suspend", console_suspend_disable);
 890
 891 /**
 892  * suspend_console - suspend the console subsystem
 893  *
 894  * This disables printk() while we go into suspend states
 895  */
 896 void suspend_console(void)
 897 {
 898         if (!console_suspend_enabled)
 899                 return;
 900         printk("Suspending console(s)\n");
 901         acquire_console_sem();
 902         console_suspended = 1;
 903 }
 904
 905 void resume_console(void)
 906 {
 907         if (!console_suspend_enabled)
 908                 return;
 909         console_suspended = 0;
 910         release_console_sem();
 911 }
 912
 913 /**
 914  * acquire_console_sem - lock the console system for exclusive use.
 915  *
 916  * Acquires a semaphore which guarantees that the caller has
 917  * exclusive access to the console system and the console_drivers list.
 918  *
 919  * Can sleep, returns nothing.
 920  */
 921 void acquire_console_sem(void)
 922 {
 923         BUG_ON(in_interrupt());
 924         if (console_suspended) {
 925                 down(&secondary_console_sem);
 926                 return;
 927         }
 928         down(&console_sem);
 929         console_locked = 1;
 930         console_may_schedule = 1;
 931 }
 932 EXPORT_SYMBOL(acquire_console_sem);
 933
 934 int try_acquire_console_sem(void)
 935 {
 936         if (down_trylock(&console_sem))
 937                 return -1;
 938         console_locked = 1;
 939         console_may_schedule = 0;
 940         return 0;
 941 }
 942 EXPORT_SYMBOL(try_acquire_console_sem);
 943
 944 int is_console_locked(void)
 945 {
 946         return console_locked;
 947 }
 948
 949 void wake_up_klogd(void)
 950 {
 951         if (!oops_in_progress && waitqueue_active(&log_wait))
 952                 wake_up_interruptible(&log_wait);
 953 }
 954
 955 /**
 956  * release_console_sem - unlock the console system
 957  *
 958  * Releases the semaphore which the caller holds on the console system
 959  * and the console driver list.
 960  *
 961  * While the semaphore was held, console output may have been buffered
 962  * by printk().  If this is the case, release_console_sem() emits
 963  * the output prior to releasing the semaphore.
 964  *
 965  * If there is output waiting for klogd, we wake it up.
 966  *
 967  * release_console_sem() may be called from any context.
 968  */
 969 void release_console_sem(void)
 970 {
 971         unsigned long flags;
 972         unsigned _con_start, _log_end;
 973         unsigned wake_klogd = 0;
 974
 975         if (console_suspended) {
 976                 up(&secondary_console_sem);
 977                 return;
 978         }
 979
 980         console_may_schedule = 0;
 981
 982         for ( ; ; ) {
 983                 spin_lock_irqsave(&logbuf_lock, flags);
 984                 wake_klogd |= log_start - log_end;
 985                 if (con_start == log_end)
 986                         break;                  /* Nothing to print */
 987                 _con_start = con_start;
 988                 _log_end = log_end;
 989                 con_start = log_end;            /* Flush */
 990                 spin_unlock(&logbuf_lock);
 991                 call_console_drivers(_con_start, _log_end);
 992                 local_irq_restore(flags);
 993         }
 994         console_locked = 0;
 995         up(&console_sem);
 996         spin_unlock_irqrestore(&logbuf_lock, flags);
 997         if (wake_klogd)
 998                 wake_up_klogd();
 999 }
1000 EXPORT_SYMBOL(release_console_sem);
1001
1002 /**
1003  * console_conditional_schedule - yield the CPU if required
1004  *
1005  * If the console code is currently allowed to sleep, and
1006  * if this CPU should yield the CPU to another task, do
1007  * so here.
1008  *
1009  * Must be called within acquire_console_sem().
1010  */
1011 void __sched console_conditional_schedule(void)
1012 {
1013         if (console_may_schedule)
1014                 cond_resched();
1015 }
1016 EXPORT_SYMBOL(console_conditional_schedule);
1017
1018 void console_print(const char *s)
1019 {
1020         printk(KERN_EMERG "%s", s);
1021 }
1022 EXPORT_SYMBOL(console_print);
1023
1024 void console_unblank(void)
1025 {
1026         struct console *c;
1027
1028         /*
1029          * console_unblank can no longer be called in interrupt context unless
1030          * oops_in_progress is set to 1..
1031          */
1032         if (oops_in_progress) {
1033                 if (down_trylock(&console_sem) != 0)
1034                         return;
1035         } else
1036                 acquire_console_sem();
1037
1038         console_locked = 1;
1039         console_may_schedule = 0;
1040         for (c = console_drivers; c != NULL; c = c->next)
1041                 if ((c->flags & CON_ENABLED) && c->unblank)
1042                         c->unblank();
1043         release_console_sem();
1044 }
1045
1046 /*
1047  * Return the console tty driver structure and its associated index
1048  */
1049 struct tty_driver *console_device(int *index)
1050 {
1051         struct console *c;
1052         struct tty_driver *driver = NULL;
1053
1054         acquire_console_sem();
1055         for (c = console_drivers; c != NULL; c = c->next) {
1056                 if (!c->device)
1057                         continue;
1058                 driver = c->device(c, index);
1059                 if (driver)
1060                         break;
1061         }
1062         release_console_sem();
1063         return driver;
1064 }
1065
1066 /*
1067  * Prevent further output on the passed console device so that (for example)
1068  * serial drivers can disable console output before suspending a port, and can
1069  * re-enable output afterwards.
1070  */
1071 void console_stop(struct console *console)
1072 {
1073         acquire_console_sem();
1074         console->flags &= ~CON_ENABLED;
1075         release_console_sem();
1076 }
1077 EXPORT_SYMBOL(console_stop);
1078
1079 void console_start(struct console *console)
1080 {
1081         acquire_console_sem();
1082         console->flags |= CON_ENABLED;
1083         release_console_sem();
1084 }
1085 EXPORT_SYMBOL(console_start);
1086
1087 /*
1088  * The console driver calls this routine during kernel initialization
1089  * to register the console printing procedure with printk() and to
1090  * print any messages that were printed by the kernel before the
1091  * console driver was initialized.
1092  */
1093 void register_console(struct console *console)
1094 {
1095         int i;
1096         unsigned long flags;
1097         struct console *bootconsole = NULL;
1098
1099         if (console_drivers) {
1100                 if (console->flags & CON_BOOT)
1101                         return;
1102                 if (console_drivers->flags & CON_BOOT)
1103                         bootconsole = console_drivers;
1104         }
1105
1106         if (preferred_console < 0 || bootconsole || !console_drivers)
1107                 preferred_console = selected_console;
1108
1109         if (console->early_setup)
1110                 console->early_setup();
1111
1112         /*
1113          *      See if we want to use this console driver. If we
1114          *      didn't select a console we take the first one
1115          *      that registers here.
1116          */
1117         if (preferred_console < 0) {
1118                 if (console->index < 0)
1119                         console->index = 0;
1120                 if (console->setup == NULL ||
1121                     console->setup(console, NULL) == 0) {
1122                         console->flags |= CON_ENABLED | CON_CONSDEV;
1123                         preferred_console = 0;
1124                 }
1125         }
1126
1127         /*
1128          *      See if this console matches one we selected on
1129          *      the command line.
1130          */
1131         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1132                         i++) {
1133                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1134                         continue;
1135                 if (console->index >= 0 &&
1136                     console->index != console_cmdline[i].index)
1137                         continue;
1138                 if (console->index < 0)
1139                         console->index = console_cmdline[i].index;
1140                 if (console->setup &&
1141                     console->setup(console, console_cmdline[i].options) != 0)
1142                         break;
1143                 console->flags |= CON_ENABLED;
1144                 console->index = console_cmdline[i].index;
1145                 if (i == selected_console) {
1146                         console->flags |= CON_CONSDEV;
1147                         preferred_console = selected_console;
1148                 }
1149                 break;
1150         }
1151
1152         if (!(console->flags & CON_ENABLED))
1153                 return;
1154
1155         if (bootconsole && (console->flags & CON_CONSDEV)) {
1156                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1157                        bootconsole->name, bootconsole->index,
1158                        console->name, console->index);
1159                 unregister_console(bootconsole);
1160                 console->flags &= ~CON_PRINTBUFFER;
1161         } else {
1162                 printk(KERN_INFO "console [%s%d] enabled\n",
1163                        console->name, console->index);
1164         }
1165
1166         /*
1167          *      Put this console in the list - keep the
1168          *      preferred driver at the head of the list.
1169          */
1170         acquire_console_sem();
1171         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1172                 console->next = console_drivers;
1173                 console_drivers = console;
1174                 if (console->next)
1175                         console->next->flags &= ~CON_CONSDEV;
1176         } else {
1177                 console->next = console_drivers->next;
1178                 console_drivers->next = console;
1179         }
1180         if (console->flags & CON_PRINTBUFFER) {
1181                 /*
1182                  * release_console_sem() will print out the buffered messages
1183                  * for us.
1184                  */
1185                 spin_lock_irqsave(&logbuf_lock, flags);
1186                 con_start = log_start;
1187                 spin_unlock_irqrestore(&logbuf_lock, flags);
1188         }
1189         release_console_sem();
1190 }
1191 EXPORT_SYMBOL(register_console);
1192
1193 int unregister_console(struct console *console)
1194 {
1195         struct console *a, *b;
1196         int res = 1;
1197
1198         acquire_console_sem();
1199         if (console_drivers == console) {
1200                 console_drivers=console->next;
1201                 res = 0;
1202         } else if (console_drivers) {
1203                 for (a=console_drivers->next, b=console_drivers ;
1204                      a; b=a, a=b->next) {
1205                         if (a == console) {
1206                                 b->next = a->next;
1207                                 res = 0;
1208                                 break;
1209                         }
1210                 }
1211         }
1212
1213         /*
1214          * If this isn't the last console and it has CON_CONSDEV set, we
1215          * need to set it on the next preferred console.
1216          */
1217         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1218                 console_drivers->flags |= CON_CONSDEV;
1219
1220         release_console_sem();
1221         return res;
1222 }
1223 EXPORT_SYMBOL(unregister_console);
1224
1225 static int __init disable_boot_consoles(void)
1226 {
1227         if (console_drivers != NULL) {
1228                 if (console_drivers->flags & CON_BOOT) {
1229                         printk(KERN_INFO "turn off boot console %s%d\n",
1230                                 console_drivers->name, console_drivers->index);
1231                         return unregister_console(console_drivers);
1232                 }
1233         }
1234         return 0;
1235 }
1236 late_initcall(disable_boot_consoles);
1237
1238 /**
1239  * tty_write_message - write a message to a certain tty, not just the console.
1240  * @tty: the destination tty_struct
1241  * @msg: the message to write
1242  *
1243  * This is used for messages that need to be redirected to a specific tty.
1244  * We don't put it into the syslog queue right now maybe in the future if
1245  * really needed.
1246  */
1247 void tty_write_message(struct tty_struct *tty, char *msg)
1248 {
1249         if (tty && tty->driver->write)
1250                 tty->driver->write(tty, msg, strlen(msg));
1251         return;
1252 }
1253
1254 #if defined CONFIG_PRINTK
1255 /*
1256  * printk rate limiting, lifted from the networking subsystem.
1257  *
1258  * This enforces a rate limit: not more than one kernel message
1259  * every printk_ratelimit_jiffies to make a denial-of-service
1260  * attack impossible.
1261  */
1262 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1263 {
1264         static DEFINE_SPINLOCK(ratelimit_lock);
1265         static unsigned toks = 10 * 5 * HZ;
1266         static unsigned long last_msg;
1267         static int missed;
1268         unsigned long flags;
1269         unsigned long now = jiffies;
1270
1271         spin_lock_irqsave(&ratelimit_lock, flags);
1272         toks += now - last_msg;
1273         last_msg = now;
1274         if (toks > (ratelimit_burst * ratelimit_jiffies))
1275                 toks = ratelimit_burst * ratelimit_jiffies;
1276         if (toks >= ratelimit_jiffies) {
1277                 int lost = missed;
1278
1279                 missed = 0;
1280                 toks -= ratelimit_jiffies;
1281                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1282                 if (lost)
1283                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1284                 return 1;
1285         }
1286         missed++;
1287         spin_unlock_irqrestore(&ratelimit_lock, flags);
1288         return 0;
1289 }
1290 EXPORT_SYMBOL(__printk_ratelimit);
1291
1292 /* minimum time in jiffies between messages */
1293 int printk_ratelimit_jiffies = 5 * HZ;
1294
1295 /* number of messages we send before ratelimiting */
1296 int printk_ratelimit_burst = 10;
1297
1298 int printk_ratelimit(void)
1299 {
1300         return __printk_ratelimit(printk_ratelimit_jiffies,
1301                                 printk_ratelimit_burst);
1302 }
1303 EXPORT_SYMBOL(printk_ratelimit);
1304
1305 /**
1306  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1307  * @caller_jiffies: pointer to caller's state
1308  * @interval_msecs: minimum interval between prints
1309  *
1310  * printk_timed_ratelimit() returns true if more than @interval_msecs
1311  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1312  * returned true.
1313  */
1314 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1315                         unsigned int interval_msecs)
1316 {
1317         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1318                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1319                 return true;
1320         }
1321         return false;
1322 }
1323 EXPORT_SYMBOL(printk_timed_ratelimit);
1324 #endif