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/smp_lock.h>
  24 #include <linux/console.h>
  25 #include <linux/init.h>
  26 #include <linux/jiffies.h>
  27 #include <linux/nmi.h>
  28 #include <linux/module.h>
  29 #include <linux/moduleparam.h>
  30 #include <linux/interrupt.h>                    /* For in_interrupt() */
  31 #include <linux/delay.h>
  32 #include <linux/smp.h>
  33 #include <linux/security.h>
  34 #include <linux/bootmem.h>
  35 #include <linux/syscalls.h>
  36 #include <linux/vs_context.h>
  37 #include <linux/vserver/cvirt.h>
  38
  39 #include <asm/uaccess.h>
  40
  41 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  42
  43 /* printk's without a loglevel use this.. */
  44 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  45
  46 /* We show everything that is MORE important than this.. */
  47 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  48 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  49
  50 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  51
  52 int console_printk[4] = {
  53         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  54         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  55         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  56         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  57 };
  58
  59 EXPORT_UNUSED_SYMBOL(console_printk);  /*  June 2006  */
  60
  61 /*
  62  * Low lever drivers may need that to know if they can schedule in
  63  * their unblank() callback or not. So let's export it.
  64  */
  65 int oops_in_progress;
  66 EXPORT_SYMBOL(oops_in_progress);
  67
  68 /*
  69  * console_sem protects the console_drivers list, and also
  70  * provides serialisation for access to the entire console
  71  * driver system.
  72  */
  73 static DECLARE_MUTEX(console_sem);
  74 static DECLARE_MUTEX(secondary_console_sem);
  75 struct console *console_drivers;
  76 /*
  77  * This is used for debugging the mess that is the VT code by
  78  * keeping track if we have the console semaphore held. It's
  79  * definitely not the perfect debug tool (we don't know if _WE_
  80  * hold it are racing, but it helps tracking those weird code
  81  * path in the console code where we end up in places I want
  82  * locked without the console sempahore held
  83  */
  84 static int console_locked, console_suspended;
  85
  86 /*
  87  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  88  * It is also used in interesting ways to provide interlocking in
  89  * release_console_sem().
  90  */
  91 static DEFINE_SPINLOCK(logbuf_lock);
  92
  93 #define LOG_BUF_MASK    (log_buf_len-1)
  94 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  95
  96 /*
  97  * The indices into log_buf are not constrained to log_buf_len - they
  98  * must be masked before subscripting
  99  */
 100 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
 101 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
 102 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
 103
 104 /*
 105  *      Array of consoles built from command line options (console=)
 106  */
 107 struct console_cmdline
 108 {
 109         char    name[8];                        /* Name of the driver       */
 110         int     index;                          /* Minor dev. to use        */
 111         char    *options;                       /* Options for the driver   */
 112 };
 113
 114 #define MAX_CMDLINECONSOLES 8
 115
 116 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 117 static int selected_console = -1;
 118 static int preferred_console = -1;
 119
 120 /* Flag: console code may call schedule() */
 121 static int console_may_schedule;
 122
 123 #ifdef CONFIG_PRINTK
 124
 125 static char __log_buf[__LOG_BUF_LEN];
 126 static char *log_buf = __log_buf;
 127 static int log_buf_len = __LOG_BUF_LEN;
 128 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 129
 130 static int __init log_buf_len_setup(char *str)
 131 {
 132         unsigned long size = memparse(str, &str);
 133         unsigned long flags;
 134
 135         if (size)
 136                 size = roundup_pow_of_two(size);
 137         if (size > log_buf_len) {
 138                 unsigned long start, dest_idx, offset;
 139                 char *new_log_buf;
 140
 141                 new_log_buf = alloc_bootmem(size);
 142                 if (!new_log_buf) {
 143                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 144                         goto out;
 145                 }
 146
 147                 spin_lock_irqsave(&logbuf_lock, flags);
 148                 log_buf_len = size;
 149                 log_buf = new_log_buf;
 150
 151                 offset = start = min(con_start, log_start);
 152                 dest_idx = 0;
 153                 while (start != log_end) {
 154                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 155                         start++;
 156                         dest_idx++;
 157                 }
 158                 log_start -= offset;
 159                 con_start -= offset;
 160                 log_end -= offset;
 161                 spin_unlock_irqrestore(&logbuf_lock, flags);
 162
 163                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 164         }
 165 out:
 166         return 1;
 167 }
 168
 169 __setup("log_buf_len=", log_buf_len_setup);
 170
 171 #ifdef CONFIG_BOOT_DELAY
 172
 173 extern unsigned int boot_delay; /* msecs to delay after each printk during bootup */
 174 extern long preset_lpj;
 175 extern unsigned long long printk_delay_msec;
 176
 177 static void boot_delay_msec(int millisecs)
 178 {
 179         unsigned long long k = printk_delay_msec * millisecs;
 180         unsigned long timeout;
 181
 182         timeout = jiffies + msecs_to_jiffies(millisecs);
 183         while (k) {
 184                 k--;
 185                 cpu_relax();
 186                 /*
 187                  * use (volatile) jiffies to prevent
 188                  * compiler reduction; loop termination via jiffies
 189                  * is secondary and may or may not happen.
 190                  */
 191                 if (time_after(jiffies, timeout))
 192                         break;
 193                 touch_nmi_watchdog();
 194         }
 195 }
 196
 197 #endif
 198
 199 /*
 200  * Commands to do_syslog:
 201  *
 202  *      0 -- Close the log.  Currently a NOP.
 203  *      1 -- Open the log. Currently a NOP.
 204  *      2 -- Read from the log.
 205  *      3 -- Read all messages remaining in the ring buffer.
 206  *      4 -- Read and clear all messages remaining in the ring buffer
 207  *      5 -- Clear ring buffer.
 208  *      6 -- Disable printk's to console
 209  *      7 -- Enable printk's to console
 210  *      8 -- Set level of messages printed to console
 211  *      9 -- Return number of unread characters in the log buffer
 212  *     10 -- Return size of the log buffer
 213  */
 214 int do_syslog(int type, char __user *buf, int len)
 215 {
 216         unsigned long i, j, limit, count;
 217         int do_clear = 0;
 218         char c;
 219         int error;
 220
 221         error = security_syslog(type);
 222         if (error)
 223                 return error;
 224
 225         if ((type >= 2) && (type <= 4)) {
 226                 error = -EINVAL;
 227                 if (!buf || len < 0)
 228                         goto out;
 229                 error = 0;
 230                 if (!len)
 231                         goto out;
 232                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 233                         error = -EFAULT;
 234                         goto out;
 235                 }
 236         }
 237         if (!vx_check(0, VX_ADMIN|VX_WATCH))
 238                 return vx_do_syslog(type, buf, len);
 239
 240         switch (type) {
 241         case 0:         /* Close log */
 242                 break;
 243         case 1:         /* Open log */
 244                 break;
 245         case 2:         /* Read from log */
 246                 error = wait_event_interruptible(log_wait,
 247                                                         (log_start - log_end));
 248                 if (error)
 249                         goto out;
 250                 i = 0;
 251                 spin_lock_irq(&logbuf_lock);
 252                 while (!error && (log_start != log_end) && i < len) {
 253                         c = LOG_BUF(log_start);
 254                         log_start++;
 255                         spin_unlock_irq(&logbuf_lock);
 256                         error = __put_user(c,buf);
 257                         buf++;
 258                         i++;
 259                         cond_resched();
 260                         spin_lock_irq(&logbuf_lock);
 261                 }
 262                 spin_unlock_irq(&logbuf_lock);
 263                 if (!error)
 264                         error = i;
 265                 break;
 266         case 4:         /* Read/clear last kernel messages */
 267                 do_clear = 1;
 268                 /* FALL THRU */
 269         case 3:         /* Read last kernel messages */
 270                 count = len;
 271                 if (count > log_buf_len)
 272                         count = log_buf_len;
 273                 spin_lock_irq(&logbuf_lock);
 274                 if (count > logged_chars)
 275                         count = logged_chars;
 276                 if (do_clear)
 277                         logged_chars = 0;
 278                 limit = log_end;
 279                 /*
 280                  * __put_user() could sleep, and while we sleep
 281                  * printk() could overwrite the messages
 282                  * we try to copy to user space. Therefore
 283                  * the messages are copied in reverse. <manfreds>
 284                  */
 285                 for (i = 0; i < count && !error; i++) {
 286                         j = limit-1-i;
 287                         if (j + log_buf_len < log_end)
 288                                 break;
 289                         c = LOG_BUF(j);
 290                         spin_unlock_irq(&logbuf_lock);
 291                         error = __put_user(c,&buf[count-1-i]);
 292                         cond_resched();
 293                         spin_lock_irq(&logbuf_lock);
 294                 }
 295                 spin_unlock_irq(&logbuf_lock);
 296                 if (error)
 297                         break;
 298                 error = i;
 299                 if (i != count) {
 300                         int offset = count-error;
 301                         /* buffer overflow during copy, correct user buffer. */
 302                         for (i = 0; i < error; i++) {
 303                                 if (__get_user(c,&buf[i+offset]) ||
 304                                     __put_user(c,&buf[i])) {
 305                                         error = -EFAULT;
 306                                         break;
 307                                 }
 308                                 cond_resched();
 309                         }
 310                 }
 311                 break;
 312         case 5:         /* Clear ring buffer */
 313                 logged_chars = 0;
 314                 break;
 315         case 6:         /* Disable logging to console */
 316                 console_loglevel = minimum_console_loglevel;
 317                 break;
 318         case 7:         /* Enable logging to console */
 319                 console_loglevel = default_console_loglevel;
 320                 break;
 321         case 8:         /* Set level of messages printed to console */
 322                 error = -EINVAL;
 323                 if (len < 1 || len > 8)
 324                         goto out;
 325                 if (len < minimum_console_loglevel)
 326                         len = minimum_console_loglevel;
 327                 console_loglevel = len;
 328                 error = 0;
 329                 break;
 330         case 9:         /* Number of chars in the log buffer */
 331                 error = log_end - log_start;
 332                 break;
 333         case 10:        /* Size of the log buffer */
 334                 error = log_buf_len;
 335                 break;
 336         default:
 337                 error = -EINVAL;
 338                 break;
 339         }
 340 out:
 341         return error;
 342 }
 343
 344 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 345 {
 346         return do_syslog(type, buf, len);
 347 }
 348
 349 /*
 350  * Call the console drivers on a range of log_buf
 351  */
 352 static void __call_console_drivers(unsigned long start, unsigned long end)
 353 {
 354         struct console *con;
 355
 356         for (con = console_drivers; con; con = con->next) {
 357                 if ((con->flags & CON_ENABLED) && con->write &&
 358                                 (cpu_online(smp_processor_id()) ||
 359                                 (con->flags & CON_ANYTIME)))
 360                         con->write(con, &LOG_BUF(start), end - start);
 361         }
 362 }
 363
 364 /*
 365  * Write out chars from start to end - 1 inclusive
 366  */
 367 static void _call_console_drivers(unsigned long start,
 368                                 unsigned long end, int msg_log_level)
 369 {
 370         if (msg_log_level < console_loglevel &&
 371                         console_drivers && start != end) {
 372                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 373                         /* wrapped write */
 374                         __call_console_drivers(start & LOG_BUF_MASK,
 375                                                 log_buf_len);
 376                         __call_console_drivers(0, end & LOG_BUF_MASK);
 377                 } else {
 378                         __call_console_drivers(start, end);
 379                 }
 380         }
 381 }
 382
 383 /*
 384  * Call the console drivers, asking them to write out
 385  * log_buf[start] to log_buf[end - 1].
 386  * The console_sem must be held.
 387  */
 388 static void call_console_drivers(unsigned long start, unsigned long end)
 389 {
 390         unsigned long cur_index, start_print;
 391         static int msg_level = -1;
 392
 393         BUG_ON(((long)(start - end)) > 0);
 394
 395         cur_index = start;
 396         start_print = start;
 397         while (cur_index != end) {
 398                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 399                                 LOG_BUF(cur_index + 0) == '<' &&
 400                                 LOG_BUF(cur_index + 1) >= '0' &&
 401                                 LOG_BUF(cur_index + 1) <= '7' &&
 402                                 LOG_BUF(cur_index + 2) == '>') {
 403                         msg_level = LOG_BUF(cur_index + 1) - '0';
 404                         cur_index += 3;
 405                         start_print = cur_index;
 406                 }
 407                 while (cur_index != end) {
 408                         char c = LOG_BUF(cur_index);
 409
 410                         cur_index++;
 411                         if (c == '\n') {
 412                                 if (msg_level < 0) {
 413                                         /*
 414                                          * printk() has already given us loglevel tags in
 415                                          * the buffer.  This code is here in case the
 416                                          * log buffer has wrapped right round and scribbled
 417                                          * on those tags
 418                                          */
 419                                         msg_level = default_message_loglevel;
 420                                 }
 421                                 _call_console_drivers(start_print, cur_index, msg_level);
 422                                 msg_level = -1;
 423                                 start_print = cur_index;
 424                                 break;
 425                         }
 426                 }
 427         }
 428         _call_console_drivers(start_print, end, msg_level);
 429 }
 430
 431 static void emit_log_char(char c)
 432 {
 433         LOG_BUF(log_end) = c;
 434         log_end++;
 435         if (log_end - log_start > log_buf_len)
 436                 log_start = log_end - log_buf_len;
 437         if (log_end - con_start > log_buf_len)
 438                 con_start = log_end - log_buf_len;
 439         if (logged_chars < log_buf_len)
 440                 logged_chars++;
 441 }
 442
 443 /*
 444  * Zap console related locks when oopsing. Only zap at most once
 445  * every 10 seconds, to leave time for slow consoles to print a
 446  * full oops.
 447  */
 448 static void zap_locks(void)
 449 {
 450         static unsigned long oops_timestamp;
 451
 452         if (time_after_eq(jiffies, oops_timestamp) &&
 453                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 454                 return;
 455
 456         oops_timestamp = jiffies;
 457
 458         /* If a crash is occurring, make sure we can't deadlock */
 459         spin_lock_init(&logbuf_lock);
 460         /* And make sure that we print immediately */
 461         init_MUTEX(&console_sem);
 462 }
 463
 464 #if defined(CONFIG_PRINTK_TIME)
 465 static int printk_time = 1;
 466 #else
 467 static int printk_time = 0;
 468 #endif
 469 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 470
 471 static int __init printk_time_setup(char *str)
 472 {
 473         if (*str)
 474                 return 0;
 475         printk_time = 1;
 476         return 1;
 477 }
 478
 479 __setup("time", printk_time_setup);
 480
 481 __attribute__((weak)) unsigned long long printk_clock(void)
 482 {
 483         return sched_clock();
 484 }
 485
 486 /* Check if we have any console registered that can be called early in boot. */
 487 static int have_callable_console(void)
 488 {
 489         struct console *con;
 490
 491         for (con = console_drivers; con; con = con->next)
 492                 if (con->flags & CON_ANYTIME)
 493                         return 1;
 494
 495         return 0;
 496 }
 497
 498 /**
 499  * printk - print a kernel message
 500  * @fmt: format string
 501  *
 502  * This is printk.  It can be called from any context.  We want it to work.
 503  *
 504  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 505  * call the console drivers.  If we fail to get the semaphore we place the output
 506  * into the log buffer and return.  The current holder of the console_sem will
 507  * notice the new output in release_console_sem() and will send it to the
 508  * consoles before releasing the semaphore.
 509  *
 510  * One effect of this deferred printing is that code which calls printk() and
 511  * then changes console_loglevel may break. This is because console_loglevel
 512  * is inspected when the actual printing occurs.
 513  *
 514  * See also:
 515  * printf(3)
 516  */
 517
 518 asmlinkage int printk(const char *fmt, ...)
 519 {
 520         va_list args;
 521         int r;
 522
 523         va_start(args, fmt);
 524         r = vprintk(fmt, args);
 525         va_end(args);
 526
 527 #ifdef CONFIG_BOOT_DELAY
 528         if (boot_delay && system_state == SYSTEM_BOOTING)
 529                 boot_delay_msec(boot_delay);
 530 #endif
 531
 532         return r;
 533 }
 534
 535 /* cpu currently holding logbuf_lock */
 536 static volatile unsigned int printk_cpu = UINT_MAX;
 537
 538 asmlinkage int vprintk(const char *fmt, va_list args)
 539 {
 540         unsigned long flags;
 541         int printed_len;
 542         char *p;
 543         static char printk_buf[1024];
 544         static int log_level_unknown = 1;
 545         struct vx_info_save vxis;
 546
 547         preempt_disable();
 548         __enter_vx_admin(&vxis);
 549         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 550                 /* If a crash is occurring during printk() on this CPU,
 551                  * make sure we can't deadlock */
 552                 zap_locks();
 553
 554         /* This stops the holder of console_sem just where we want him */
 555         local_irq_save(flags);
 556         lockdep_off();
 557         spin_lock(&logbuf_lock);
 558         printk_cpu = smp_processor_id();
 559
 560         /* Emit the output into the temporary buffer */
 561         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 562
 563         /*
 564          * Copy the output into log_buf.  If the caller didn't provide
 565          * appropriate log level tags, we insert them here
 566          */
 567         for (p = printk_buf; *p; p++) {
 568                 if (log_level_unknown) {
 569                         /* log_level_unknown signals the start of a new line */
 570                         if (printk_time) {
 571                                 int loglev_char;
 572                                 char tbuf[50], *tp;
 573                                 unsigned tlen;
 574                                 unsigned long long t;
 575                                 unsigned long nanosec_rem;
 576
 577                                 /*
 578                                  * force the log level token to be
 579                                  * before the time output.
 580                                  */
 581                                 if (p[0] == '<' && p[1] >='0' &&
 582                                    p[1] <= '7' && p[2] == '>') {
 583                                         loglev_char = p[1];
 584                                         p += 3;
 585                                         printed_len -= 3;
 586                                 } else {
 587                                         loglev_char = default_message_loglevel
 588                                                 + '0';
 589                                 }
 590                                 t = printk_clock();
 591                                 nanosec_rem = do_div(t, 1000000000);
 592                                 tlen = sprintf(tbuf,
 593                                                 "<%c>[%5lu.%06lu] ",
 594                                                 loglev_char,
 595                                                 (unsigned long)t,
 596                                                 nanosec_rem/1000);
 597
 598                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 599                                         emit_log_char(*tp);
 600                                 printed_len += tlen;
 601                         } else {
 602                                 if (p[0] != '<' || p[1] < '0' ||
 603                                    p[1] > '7' || p[2] != '>') {
 604                                         emit_log_char('<');
 605                                         emit_log_char(default_message_loglevel
 606                                                 + '0');
 607                                         emit_log_char('>');
 608                                         printed_len += 3;
 609                                 }
 610                         }
 611                         log_level_unknown = 0;
 612                         if (!*p)
 613                                 break;
 614                 }
 615                 emit_log_char(*p);
 616                 if (*p == '\n')
 617                         log_level_unknown = 1;
 618         }
 619
 620         if (!down_trylock(&console_sem)) {
 621                 /*
 622                  * We own the drivers.  We can drop the spinlock and
 623                  * let release_console_sem() print the text, maybe ...
 624                  */
 625                 console_locked = 1;
 626                 printk_cpu = UINT_MAX;
 627                 spin_unlock(&logbuf_lock);
 628
 629                 /*
 630                  * Console drivers may assume that per-cpu resources have
 631                  * been allocated. So unless they're explicitly marked as
 632                  * being able to cope (CON_ANYTIME) don't call them until
 633                  * this CPU is officially up.
 634                  */
 635                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 636                         console_may_schedule = 0;
 637                         release_console_sem();
 638                 } else {
 639                         /* Release by hand to avoid flushing the buffer. */
 640                         console_locked = 0;
 641                         up(&console_sem);
 642                 }
 643                 lockdep_on();
 644                 local_irq_restore(flags);
 645         } else {
 646                 /*
 647                  * Someone else owns the drivers.  We drop the spinlock, which
 648                  * allows the semaphore holder to proceed and to call the
 649                  * console drivers with the output which we just produced.
 650                  */
 651                 printk_cpu = UINT_MAX;
 652                 spin_unlock(&logbuf_lock);
 653                 lockdep_on();
 654                 local_irq_restore(flags);
 655         }
 656
 657         __leave_vx_admin(&vxis);
 658         preempt_enable();
 659         return printed_len;
 660 }
 661 EXPORT_SYMBOL(printk);
 662 EXPORT_SYMBOL(vprintk);
 663
 664 #else
 665
 666 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 667 {
 668         return 0;
 669 }
 670
 671 int do_syslog(int type, char __user *buf, int len)
 672 {
 673         return 0;
 674 }
 675
 676 static void call_console_drivers(unsigned long start, unsigned long end)
 677 {
 678 }
 679
 680 #endif
 681
 682 /*
 683  * Set up a list of consoles.  Called from init/main.c
 684  */
 685 static int __init console_setup(char *str)
 686 {
 687         char name[sizeof(console_cmdline[0].name)];
 688         char *s, *options;
 689         int idx;
 690
 691         /*
 692          * Decode str into name, index, options.
 693          */
 694         if (str[0] >= '0' && str[0] <= '9') {
 695                 strcpy(name, "ttyS");
 696                 strncpy(name + 4, str, sizeof(name) - 5);
 697         } else {
 698                 strncpy(name, str, sizeof(name) - 1);
 699         }
 700         name[sizeof(name) - 1] = 0;
 701         if ((options = strchr(str, ',')) != NULL)
 702                 *(options++) = 0;
 703 #ifdef __sparc__
 704         if (!strcmp(str, "ttya"))
 705                 strcpy(name, "ttyS0");
 706         if (!strcmp(str, "ttyb"))
 707                 strcpy(name, "ttyS1");
 708 #endif
 709         for (s = name; *s; s++)
 710                 if ((*s >= '0' && *s <= '9') || *s == ',')
 711                         break;
 712         idx = simple_strtoul(s, NULL, 10);
 713         *s = 0;
 714
 715         add_preferred_console(name, idx, options);
 716         return 1;
 717 }
 718 __setup("console=", console_setup);
 719
 720 /**
 721  * add_preferred_console - add a device to the list of preferred consoles.
 722  * @name: device name
 723  * @idx: device index
 724  * @options: options for this console
 725  *
 726  * The last preferred console added will be used for kernel messages
 727  * and stdin/out/err for init.  Normally this is used by console_setup
 728  * above to handle user-supplied console arguments; however it can also
 729  * be used by arch-specific code either to override the user or more
 730  * commonly to provide a default console (ie from PROM variables) when
 731  * the user has not supplied one.
 732  */
 733 int __init add_preferred_console(char *name, int idx, char *options)
 734 {
 735         struct console_cmdline *c;
 736         int i;
 737
 738         /*
 739          *      See if this tty is not yet registered, and
 740          *      if we have a slot free.
 741          */
 742         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 743                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 744                           console_cmdline[i].index == idx) {
 745                                 selected_console = i;
 746                                 return 0;
 747                 }
 748         if (i == MAX_CMDLINECONSOLES)
 749                 return -E2BIG;
 750         selected_console = i;
 751         c = &console_cmdline[i];
 752         memcpy(c->name, name, sizeof(c->name));
 753         c->name[sizeof(c->name) - 1] = 0;
 754         c->options = options;
 755         c->index = idx;
 756         return 0;
 757 }
 758
 759 /**
 760  * suspend_console - suspend the console subsystem
 761  *
 762  * This disables printk() while we go into suspend states
 763  */
 764 void suspend_console(void)
 765 {
 766         acquire_console_sem();
 767         console_suspended = 1;
 768 }
 769
 770 void resume_console(void)
 771 {
 772         console_suspended = 0;
 773         release_console_sem();
 774 }
 775
 776 /**
 777  * acquire_console_sem - lock the console system for exclusive use.
 778  *
 779  * Acquires a semaphore which guarantees that the caller has
 780  * exclusive access to the console system and the console_drivers list.
 781  *
 782  * Can sleep, returns nothing.
 783  */
 784 void acquire_console_sem(void)
 785 {
 786         BUG_ON(in_interrupt());
 787         if (console_suspended) {
 788                 down(&secondary_console_sem);
 789                 return;
 790         }
 791         down(&console_sem);
 792         console_locked = 1;
 793         console_may_schedule = 1;
 794 }
 795 EXPORT_SYMBOL(acquire_console_sem);
 796
 797 int try_acquire_console_sem(void)
 798 {
 799         if (down_trylock(&console_sem))
 800                 return -1;
 801         console_locked = 1;
 802         console_may_schedule = 0;
 803         return 0;
 804 }
 805 EXPORT_SYMBOL(try_acquire_console_sem);
 806
 807 int is_console_locked(void)
 808 {
 809         return console_locked;
 810 }
 811 EXPORT_UNUSED_SYMBOL(is_console_locked);  /*  June 2006  */
 812
 813 /**
 814  * release_console_sem - unlock the console system
 815  *
 816  * Releases the semaphore which the caller holds on the console system
 817  * and the console driver list.
 818  *
 819  * While the semaphore was held, console output may have been buffered
 820  * by printk().  If this is the case, release_console_sem() emits
 821  * the output prior to releasing the semaphore.
 822  *
 823  * If there is output waiting for klogd, we wake it up.
 824  *
 825  * release_console_sem() may be called from any context.
 826  */
 827 void release_console_sem(void)
 828 {
 829         unsigned long flags;
 830         unsigned long _con_start, _log_end;
 831         unsigned long wake_klogd = 0;
 832
 833         if (console_suspended) {
 834                 up(&secondary_console_sem);
 835                 return;
 836         }
 837
 838         console_may_schedule = 0;
 839
 840         for ( ; ; ) {
 841                 spin_lock_irqsave(&logbuf_lock, flags);
 842                 wake_klogd |= log_start - log_end;
 843                 if (con_start == log_end)
 844                         break;                  /* Nothing to print */
 845                 _con_start = con_start;
 846                 _log_end = log_end;
 847                 con_start = log_end;            /* Flush */
 848                 spin_unlock(&logbuf_lock);
 849                 call_console_drivers(_con_start, _log_end);
 850                 local_irq_restore(flags);
 851         }
 852         console_locked = 0;
 853         up(&console_sem);
 854         spin_unlock_irqrestore(&logbuf_lock, flags);
 855         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) {
 856                 /*
 857                  * If we printk from within the lock dependency code,
 858                  * from within the scheduler code, then do not lock
 859                  * up due to self-recursion:
 860                  */
 861                 if (!lockdep_internal())
 862                         wake_up_interruptible(&log_wait);
 863         }
 864 }
 865 EXPORT_SYMBOL(release_console_sem);
 866
 867 /**
 868  * console_conditional_schedule - yield the CPU if required
 869  *
 870  * If the console code is currently allowed to sleep, and
 871  * if this CPU should yield the CPU to another task, do
 872  * so here.
 873  *
 874  * Must be called within acquire_console_sem().
 875  */
 876 void __sched console_conditional_schedule(void)
 877 {
 878         if (console_may_schedule)
 879                 cond_resched();
 880 }
 881 EXPORT_SYMBOL(console_conditional_schedule);
 882
 883 void console_print(const char *s)
 884 {
 885         printk(KERN_EMERG "%s", s);
 886 }
 887 EXPORT_SYMBOL(console_print);
 888
 889 void console_unblank(void)
 890 {
 891         struct console *c;
 892
 893         /*
 894          * console_unblank can no longer be called in interrupt context unless
 895          * oops_in_progress is set to 1..
 896          */
 897         if (oops_in_progress) {
 898                 if (down_trylock(&console_sem) != 0)
 899                         return;
 900         } else
 901                 acquire_console_sem();
 902
 903         console_locked = 1;
 904         console_may_schedule = 0;
 905         for (c = console_drivers; c != NULL; c = c->next)
 906                 if ((c->flags & CON_ENABLED) && c->unblank)
 907                         c->unblank();
 908         release_console_sem();
 909 }
 910
 911 /*
 912  * Return the console tty driver structure and its associated index
 913  */
 914 struct tty_driver *console_device(int *index)
 915 {
 916         struct console *c;
 917         struct tty_driver *driver = NULL;
 918
 919         acquire_console_sem();
 920         for (c = console_drivers; c != NULL; c = c->next) {
 921                 if (!c->device)
 922                         continue;
 923                 driver = c->device(c, index);
 924                 if (driver)
 925                         break;
 926         }
 927         release_console_sem();
 928         return driver;
 929 }
 930
 931 /*
 932  * Prevent further output on the passed console device so that (for example)
 933  * serial drivers can disable console output before suspending a port, and can
 934  * re-enable output afterwards.
 935  */
 936 void console_stop(struct console *console)
 937 {
 938         acquire_console_sem();
 939         console->flags &= ~CON_ENABLED;
 940         release_console_sem();
 941 }
 942 EXPORT_SYMBOL(console_stop);
 943
 944 void console_start(struct console *console)
 945 {
 946         acquire_console_sem();
 947         console->flags |= CON_ENABLED;
 948         release_console_sem();
 949 }
 950 EXPORT_SYMBOL(console_start);
 951
 952 /*
 953  * The console driver calls this routine during kernel initialization
 954  * to register the console printing procedure with printk() and to
 955  * print any messages that were printed by the kernel before the
 956  * console driver was initialized.
 957  */
 958 void register_console(struct console *console)
 959 {
 960         int i;
 961         unsigned long flags;
 962
 963         if (preferred_console < 0)
 964                 preferred_console = selected_console;
 965
 966         /*
 967          *      See if we want to use this console driver. If we
 968          *      didn't select a console we take the first one
 969          *      that registers here.
 970          */
 971         if (preferred_console < 0) {
 972                 if (console->index < 0)
 973                         console->index = 0;
 974                 if (console->setup == NULL ||
 975                     console->setup(console, NULL) == 0) {
 976                         console->flags |= CON_ENABLED | CON_CONSDEV;
 977                         preferred_console = 0;
 978                 }
 979         }
 980
 981         /*
 982          *      See if this console matches one we selected on
 983          *      the command line.
 984          */
 985         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 986                         i++) {
 987                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 988                         continue;
 989                 if (console->index >= 0 &&
 990                     console->index != console_cmdline[i].index)
 991                         continue;
 992                 if (console->index < 0)
 993                         console->index = console_cmdline[i].index;
 994                 if (console->setup &&
 995                     console->setup(console, console_cmdline[i].options) != 0)
 996                         break;
 997                 console->flags |= CON_ENABLED;
 998                 console->index = console_cmdline[i].index;
 999                 if (i == selected_console) {
1000                         console->flags |= CON_CONSDEV;
1001                         preferred_console = selected_console;
1002                 }
1003                 break;
1004         }
1005
1006         if (!(console->flags & CON_ENABLED))
1007                 return;
1008
1009         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
1010                 unregister_console(console_drivers);
1011                 console->flags &= ~CON_PRINTBUFFER;
1012         }
1013
1014         /*
1015          *      Put this console in the list - keep the
1016          *      preferred driver at the head of the list.
1017          */
1018         acquire_console_sem();
1019         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1020                 console->next = console_drivers;
1021                 console_drivers = console;
1022                 if (console->next)
1023                         console->next->flags &= ~CON_CONSDEV;
1024         } else {
1025                 console->next = console_drivers->next;
1026                 console_drivers->next = console;
1027         }
1028         if (console->flags & CON_PRINTBUFFER) {
1029                 /*
1030                  * release_console_sem() will print out the buffered messages
1031                  * for us.
1032                  */
1033                 spin_lock_irqsave(&logbuf_lock, flags);
1034                 con_start = log_start;
1035                 spin_unlock_irqrestore(&logbuf_lock, flags);
1036         }
1037         release_console_sem();
1038 }
1039 EXPORT_SYMBOL(register_console);
1040
1041 int unregister_console(struct console *console)
1042 {
1043         struct console *a, *b;
1044         int res = 1;
1045
1046         acquire_console_sem();
1047         if (console_drivers == console) {
1048                 console_drivers=console->next;
1049                 res = 0;
1050         } else if (console_drivers) {
1051                 for (a=console_drivers->next, b=console_drivers ;
1052                      a; b=a, a=b->next) {
1053                         if (a == console) {
1054                                 b->next = a->next;
1055                                 res = 0;
1056                                 break;
1057                         }
1058                 }
1059         }
1060
1061         /* If last console is removed, we re-enable picking the first
1062          * one that gets registered. Without that, pmac early boot console
1063          * would prevent fbcon from taking over.
1064          *
1065          * If this isn't the last console and it has CON_CONSDEV set, we
1066          * need to set it on the next preferred console.
1067          */
1068         if (console_drivers == NULL)
1069                 preferred_console = selected_console;
1070         else if (console->flags & CON_CONSDEV)
1071                 console_drivers->flags |= CON_CONSDEV;
1072
1073         release_console_sem();
1074         return res;
1075 }
1076 EXPORT_SYMBOL(unregister_console);
1077
1078 /**
1079  * tty_write_message - write a message to a certain tty, not just the console.
1080  * @tty: the destination tty_struct
1081  * @msg: the message to write
1082  *
1083  * This is used for messages that need to be redirected to a specific tty.
1084  * We don't put it into the syslog queue right now maybe in the future if
1085  * really needed.
1086  */
1087 void tty_write_message(struct tty_struct *tty, char *msg)
1088 {
1089         if (tty && tty->driver->write)
1090                 tty->driver->write(tty, msg, strlen(msg));
1091         return;
1092 }
1093
1094 /*
1095  * printk rate limiting, lifted from the networking subsystem.
1096  *
1097  * This enforces a rate limit: not more than one kernel message
1098  * every printk_ratelimit_jiffies to make a denial-of-service
1099  * attack impossible.
1100  */
1101 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1102 {
1103         static DEFINE_SPINLOCK(ratelimit_lock);
1104         static unsigned long toks = 10 * 5 * HZ;
1105         static unsigned long last_msg;
1106         static int missed;
1107         unsigned long flags;
1108         unsigned long now = jiffies;
1109
1110         spin_lock_irqsave(&ratelimit_lock, flags);
1111         toks += now - last_msg;
1112         last_msg = now;
1113         if (toks > (ratelimit_burst * ratelimit_jiffies))
1114                 toks = ratelimit_burst * ratelimit_jiffies;
1115         if (toks >= ratelimit_jiffies) {
1116                 int lost = missed;
1117
1118                 missed = 0;
1119                 toks -= ratelimit_jiffies;
1120                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1121                 if (lost)
1122                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1123                 return 1;
1124         }
1125         missed++;
1126         spin_unlock_irqrestore(&ratelimit_lock, flags);
1127         return 0;
1128 }
1129 EXPORT_SYMBOL(__printk_ratelimit);
1130
1131 /* minimum time in jiffies between messages */
1132 int printk_ratelimit_jiffies = 5 * HZ;
1133
1134 /* number of messages we send before ratelimiting */
1135 int printk_ratelimit_burst = 10;
1136
1137 int printk_ratelimit(void)
1138 {
1139         return __printk_ratelimit(printk_ratelimit_jiffies,
1140                                 printk_ratelimit_burst);
1141 }
1142 EXPORT_SYMBOL(printk_ratelimit);