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