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