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