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  * Crashdump special routine. Don't print to global log_buf, just to the
 357  * actual console device(s).
 358  */
 359 static void crashdump_call_console_drivers(const char *buf, unsigned long len)
 360 {
 361         struct console *con;
 362
 363         for (con = console_drivers; con; con = con->next) {
 364                 if ((con->flags & CON_ENABLED) && con->write)
 365                         con->write(con, buf, len);
 366         }
 367 }
 368
 369 /*
 370  * Call the console drivers on a range of log_buf
 371  */
 372 static void __call_console_drivers(unsigned long start, unsigned long end)
 373 {
 374         struct console *con;
 375
 376         for (con = console_drivers; con; con = con->next) {
 377                 if ((con->flags & CON_ENABLED) && con->write)
 378                         con->write(con, &LOG_BUF(start), end - start);
 379         }
 380 }
 381
 382 /*
 383  * Write out chars from start to end - 1 inclusive
 384  */
 385 static void _call_console_drivers(unsigned long start,
 386                                 unsigned long end, int msg_log_level)
 387 {
 388         if (msg_log_level < console_loglevel &&
 389                         console_drivers && start != end) {
 390                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 391                         /* wrapped write */
 392                         __call_console_drivers(start & LOG_BUF_MASK,
 393                                                 log_buf_len);
 394                         __call_console_drivers(0, end & LOG_BUF_MASK);
 395                 } else {
 396                         __call_console_drivers(start, end);
 397                 }
 398         }
 399 }
 400
 401 /*
 402  * Call the console drivers, asking them to write out
 403  * log_buf[start] to log_buf[end - 1].
 404  * The console_sem must be held.
 405  */
 406 static void call_console_drivers(unsigned long start, unsigned long end)
 407 {
 408         unsigned long cur_index, start_print;
 409         static int msg_level = -1;
 410
 411         if (((long)(start - end)) > 0)
 412                 BUG();
 413
 414         cur_index = start;
 415         start_print = start;
 416         while (cur_index != end) {
 417                 if (    msg_level < 0 &&
 418                         ((end - cur_index) > 2) &&
 419                         LOG_BUF(cur_index + 0) == '<' &&
 420                         LOG_BUF(cur_index + 1) >= '0' &&
 421                         LOG_BUF(cur_index + 1) <= '7' &&
 422                         LOG_BUF(cur_index + 2) == '>')
 423                 {
 424                         msg_level = LOG_BUF(cur_index + 1) - '0';
 425                         cur_index += 3;
 426                         start_print = cur_index;
 427                 }
 428                 while (cur_index != end) {
 429                         char c = LOG_BUF(cur_index);
 430                         cur_index++;
 431
 432                         if (c == '\n') {
 433                                 if (msg_level < 0) {
 434                                         /*
 435                                          * printk() has already given us loglevel tags in
 436                                          * the buffer.  This code is here in case the
 437                                          * log buffer has wrapped right round and scribbled
 438                                          * on those tags
 439                                          */
 440                                         msg_level = default_message_loglevel;
 441                                 }
 442                                 _call_console_drivers(start_print, cur_index, msg_level);
 443                                 msg_level = -1;
 444                                 start_print = cur_index;
 445                                 break;
 446                         }
 447                 }
 448         }
 449         _call_console_drivers(start_print, end, msg_level);
 450 }
 451
 452 static void emit_log_char(char c)
 453 {
 454         LOG_BUF(log_end) = c;
 455         log_end++;
 456         if (log_end - log_start > log_buf_len)
 457                 log_start = log_end - log_buf_len;
 458         if (log_end - con_start > log_buf_len)
 459                 con_start = log_end - log_buf_len;
 460         if (logged_chars < log_buf_len)
 461                 logged_chars++;
 462 }
 463
 464 /*
 465  * Zap console related locks when oopsing. Only zap at most once
 466  * every 10 seconds, to leave time for slow consoles to print a
 467  * full oops.
 468  */
 469 static void zap_locks(void)
 470 {
 471         static unsigned long oops_timestamp;
 472
 473         if (time_after_eq(jiffies, oops_timestamp) &&
 474                         !time_after(jiffies, oops_timestamp + 30*HZ))
 475                 return;
 476
 477         oops_timestamp = jiffies;
 478
 479         /* If a crash is occurring, make sure we can't deadlock */
 480         spin_lock_init(&logbuf_lock);
 481         /* And make sure that we print immediately */
 482         init_MUTEX(&console_sem);
 483 }
 484
 485 #if defined(CONFIG_PRINTK_TIME)
 486 static int printk_time = 1;
 487 #else
 488 static int printk_time = 0;
 489 #endif
 490
 491 static int __init printk_time_setup(char *str)
 492 {
 493         if (*str)
 494                 return 0;
 495         printk_time = 1;
 496         return 1;
 497 }
 498
 499 __setup("time", printk_time_setup);
 500
 501 /*
 502  * This is printk.  It can be called from any context.  We want it to work.
 503  *
 504  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 505  * call the console drivers.  If we fail to get the semaphore we place the output
 506  * into the log buffer and return.  The current holder of the console_sem will
 507  * notice the new output in release_console_sem() and will send it to the
 508  * consoles before releasing the semaphore.
 509  *
 510  * One effect of this deferred printing is that code which calls printk() and
 511  * then changes console_loglevel may break. This is because console_loglevel
 512  * is inspected when the actual printing occurs.
 513  */
 514
 515 asmlinkage int printk(const char *fmt, ...)
 516 {
 517         va_list args;
 518         int r;
 519
 520         va_start(args, fmt);
 521         r = vprintk(fmt, args);
 522         va_end(args);
 523
 524         return r;
 525 }
 526
 527 static volatile int printk_cpu = -1;
 528
 529 asmlinkage int vprintk(const char *fmt, va_list args)
 530 {
 531         unsigned long flags;
 532         int printed_len;
 533         char *p;
 534         static char printk_buf[1024];
 535         static int log_level_unknown = 1;
 536
 537         if (unlikely(oops_in_progress && printk_cpu == smp_processor_id()))
 538                 zap_locks();
 539
 540         /* This stops the holder of console_sem just where we want him */
 541         spin_lock_irqsave(&logbuf_lock, flags);
 542         printk_cpu = smp_processor_id();
 543
 544         /* Emit the output into the temporary buffer */
 545         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 546
 547         if (unlikely(crashdump_mode())) {
 548                 crashdump_call_console_drivers(printk_buf, printed_len);
 549                 spin_unlock_irqrestore(&logbuf_lock, flags);
 550                 goto out;
 551         }
 552
 553         /*
 554          * Copy the output into log_buf.  If the caller didn't provide
 555          * appropriate log level tags, we insert them here
 556          */
 557         for (p = printk_buf; *p; p++) {
 558                 if (log_level_unknown) {
 559                         /* log_level_unknown signals the start of a new line */
 560                         if (printk_time) {
 561                                 int loglev_char;
 562                                 char tbuf[50], *tp;
 563                                 unsigned tlen;
 564                                 unsigned long long t;
 565                                 unsigned long nanosec_rem;
 566
 567                                 /*
 568                                  * force the log level token to be
 569                                  * before the time output.
 570                                  */
 571                                 if (p[0] == '<' && p[1] >='0' &&
 572                                    p[1] <= '7' && p[2] == '>') {
 573                                         loglev_char = p[1];
 574                                         p += 3;
 575                                         printed_len += 3;
 576                                 } else {
 577                                         loglev_char = default_message_loglevel
 578                                                 + '0';
 579                                 }
 580                                 t = sched_clock();
 581                                 nanosec_rem = do_div(t, 1000000000);
 582                                 tlen = sprintf(tbuf,
 583                                                 "<%c>[%5lu.%06lu] ",
 584                                                 loglev_char,
 585                                                 (unsigned long)t,
 586                                                 nanosec_rem/1000);
 587
 588                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 589                                         emit_log_char(*tp);
 590                                 printed_len += tlen - 3;
 591                         } else {
 592                                 if (p[0] != '<' || p[1] < '0' ||
 593                                    p[1] > '7' || p[2] != '>') {
 594                                         emit_log_char('<');
 595                                         emit_log_char(default_message_loglevel
 596                                                 + '0');
 597                                         emit_log_char('>');
 598                                 }
 599                                 printed_len += 3;
 600                         }
 601                         log_level_unknown = 0;
 602                         if (!*p)
 603                                 break;
 604                 }
 605                 emit_log_char(*p);
 606                 if (*p == '\n')
 607                         log_level_unknown = 1;
 608         }
 609
 610         if (!cpu_online(smp_processor_id()) &&
 611             system_state != SYSTEM_RUNNING) {
 612                 /*
 613                  * Some console drivers may assume that per-cpu resources have
 614                  * been allocated.  So don't allow them to be called by this
 615                  * CPU until it is officially up.  We shouldn't be calling into
 616                  * random console drivers on a CPU which doesn't exist yet..
 617                  */
 618                 spin_unlock_irqrestore(&logbuf_lock, flags);
 619                 goto out;
 620         }
 621         if (!down_trylock(&console_sem)) {
 622                 console_locked = 1;
 623                 /*
 624                  * We own the drivers.  We can drop the spinlock and let
 625                  * release_console_sem() print the text
 626                  */
 627                 spin_unlock_irqrestore(&logbuf_lock, flags);
 628                 console_may_schedule = 0;
 629                 release_console_sem();
 630         } else {
 631                 /*
 632                  * Someone else owns the drivers.  We drop the spinlock, which
 633                  * allows the semaphore holder to proceed and to call the
 634                  * console drivers with the output which we just produced.
 635                  */
 636                 spin_unlock_irqrestore(&logbuf_lock, flags);
 637         }
 638 out:
 639         return printed_len;
 640 }
 641 EXPORT_SYMBOL(printk);
 642 EXPORT_SYMBOL(vprintk);
 643
 644 #else
 645
 646 asmlinkage long sys_syslog(int type, char __user * buf, int len)
 647 {
 648         return 0;
 649 }
 650
 651 int do_syslog(int type, char __user * buf, int len) { return 0; }
 652 static void call_console_drivers(unsigned long start, unsigned long end) {}
 653
 654 #endif
 655
 656 /**
 657  * add_preferred_console - add a device to the list of preferred consoles.
 658  *
 659  * The last preferred console added will be used for kernel messages
 660  * and stdin/out/err for init.  Normally this is used by console_setup
 661  * above to handle user-supplied console arguments; however it can also
 662  * be used by arch-specific code either to override the user or more
 663  * commonly to provide a default console (ie from PROM variables) when
 664  * the user has not supplied one.
 665  */
 666 int __init add_preferred_console(char *name, int idx, char *options)
 667 {
 668         struct console_cmdline *c;
 669         int i;
 670
 671         /*
 672          *      See if this tty is not yet registered, and
 673          *      if we have a slot free.
 674          */
 675         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 676                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 677                           console_cmdline[i].index == idx) {
 678                                 selected_console = i;
 679                                 return 0;
 680                 }
 681         if (i == MAX_CMDLINECONSOLES)
 682                 return -E2BIG;
 683         selected_console = i;
 684         c = &console_cmdline[i];
 685         memcpy(c->name, name, sizeof(c->name));
 686         c->name[sizeof(c->name) - 1] = 0;
 687         c->options = options;
 688         c->index = idx;
 689         return 0;
 690 }
 691
 692 /**
 693  * acquire_console_sem - lock the console system for exclusive use.
 694  *
 695  * Acquires a semaphore which guarantees that the caller has
 696  * exclusive access to the console system and the console_drivers list.
 697  *
 698  * Can sleep, returns nothing.
 699  */
 700 void acquire_console_sem(void)
 701 {
 702         if (in_interrupt())
 703                 BUG();
 704         down(&console_sem);
 705         console_locked = 1;
 706         console_may_schedule = 1;
 707 }
 708 EXPORT_SYMBOL(acquire_console_sem);
 709
 710 int try_acquire_console_sem(void)
 711 {
 712         if (down_trylock(&console_sem))
 713                 return -1;
 714         console_locked = 1;
 715         console_may_schedule = 0;
 716         return 0;
 717 }
 718 EXPORT_SYMBOL(try_acquire_console_sem);
 719
 720 int is_console_locked(void)
 721 {
 722         return console_locked;
 723 }
 724 EXPORT_SYMBOL(is_console_locked);
 725
 726 /**
 727  * release_console_sem - unlock the console system
 728  *
 729  * Releases the semaphore which the caller holds on the console system
 730  * and the console driver list.
 731  *
 732  * While the semaphore was held, console output may have been buffered
 733  * by printk().  If this is the case, release_console_sem() emits
 734  * the output prior to releasing the semaphore.
 735  *
 736  * If there is output waiting for klogd, we wake it up.
 737  *
 738  * release_console_sem() may be called from any context.
 739  */
 740 void release_console_sem(void)
 741 {
 742         unsigned long flags;
 743         unsigned long _con_start, _log_end;
 744         unsigned long wake_klogd = 0;
 745
 746         for ( ; ; ) {
 747                 spin_lock_irqsave(&logbuf_lock, flags);
 748                 wake_klogd |= log_start - log_end;
 749                 if (con_start == log_end)
 750                         break;                  /* Nothing to print */
 751                 _con_start = con_start;
 752                 _log_end = log_end;
 753                 con_start = log_end;            /* Flush */
 754                 spin_unlock(&logbuf_lock);
 755                 call_console_drivers(_con_start, _log_end);
 756                 local_irq_restore(flags);
 757         }
 758         console_locked = 0;
 759         console_may_schedule = 0;
 760         up(&console_sem);
 761         spin_unlock_irqrestore(&logbuf_lock, flags);
 762         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 763                 wake_up_interruptible(&log_wait);
 764 }
 765 EXPORT_SYMBOL(release_console_sem);
 766
 767 /** console_conditional_schedule - yield the CPU if required
 768  *
 769  * If the console code is currently allowed to sleep, and
 770  * if this CPU should yield the CPU to another task, do
 771  * so here.
 772  *
 773  * Must be called within acquire_console_sem().
 774  */
 775 void __sched console_conditional_schedule(void)
 776 {
 777         if (console_may_schedule)
 778                 cond_resched();
 779 }
 780 EXPORT_SYMBOL(console_conditional_schedule);
 781
 782 void console_print(const char *s)
 783 {
 784         printk(KERN_EMERG "%s", s);
 785 }
 786 EXPORT_SYMBOL(console_print);
 787
 788 void console_unblank(void)
 789 {
 790         struct console *c;
 791
 792         /*
 793          * console_unblank can no longer be called in interrupt context unless
 794          * oops_in_progress is set to 1..
 795          */
 796         if (oops_in_progress) {
 797                 if (down_trylock(&console_sem) != 0)
 798                         return;
 799         } else
 800                 acquire_console_sem();
 801
 802         console_locked = 1;
 803         console_may_schedule = 0;
 804         for (c = console_drivers; c != NULL; c = c->next)
 805                 if ((c->flags & CON_ENABLED) && c->unblank)
 806                         c->unblank();
 807         release_console_sem();
 808 }
 809 EXPORT_SYMBOL(console_unblank);
 810
 811 /*
 812  * Return the console tty driver structure and its associated index
 813  */
 814 struct tty_driver *console_device(int *index)
 815 {
 816         struct console *c;
 817         struct tty_driver *driver = NULL;
 818
 819         acquire_console_sem();
 820         for (c = console_drivers; c != NULL; c = c->next) {
 821                 if (!c->device)
 822                         continue;
 823                 driver = c->device(c, index);
 824                 if (driver)
 825                         break;
 826         }
 827         release_console_sem();
 828         return driver;
 829 }
 830
 831 /*
 832  * Prevent further output on the passed console device so that (for example)
 833  * serial drivers can disable console output before suspending a port, and can
 834  * re-enable output afterwards.
 835  */
 836 void console_stop(struct console *console)
 837 {
 838         acquire_console_sem();
 839         console->flags &= ~CON_ENABLED;
 840         release_console_sem();
 841 }
 842 EXPORT_SYMBOL(console_stop);
 843
 844 void console_start(struct console *console)
 845 {
 846         acquire_console_sem();
 847         console->flags |= CON_ENABLED;
 848         release_console_sem();
 849 }
 850 EXPORT_SYMBOL(console_start);
 851
 852 /*
 853  * The console driver calls this routine during kernel initialization
 854  * to register the console printing procedure with printk() and to
 855  * print any messages that were printed by the kernel before the
 856  * console driver was initialized.
 857  */
 858 void register_console(struct console * console)
 859 {
 860         int     i;
 861         unsigned long flags;
 862
 863         if (preferred_console < 0)
 864                 preferred_console = selected_console;
 865
 866         /*
 867          *      See if we want to use this console driver. If we
 868          *      didn't select a console we take the first one
 869          *      that registers here.
 870          */
 871         if (preferred_console < 0) {
 872                 if (console->index < 0)
 873                         console->index = 0;
 874                 if (console->setup == NULL ||
 875                     console->setup(console, NULL) == 0) {
 876                         console->flags |= CON_ENABLED | CON_CONSDEV;
 877                         preferred_console = 0;
 878                 }
 879         }
 880
 881         /*
 882          *      See if this console matches one we selected on
 883          *      the command line.
 884          */
 885         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++) {
 886                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 887                         continue;
 888                 if (console->index >= 0 &&
 889                     console->index != console_cmdline[i].index)
 890                         continue;
 891                 if (console->index < 0)
 892                         console->index = console_cmdline[i].index;
 893                 if (console->setup &&
 894                     console->setup(console, console_cmdline[i].options) != 0)
 895                         break;
 896                 console->flags |= CON_ENABLED;
 897                 console->index = console_cmdline[i].index;
 898                 if (i == preferred_console)
 899                         console->flags |= CON_CONSDEV;
 900                 break;
 901         }
 902
 903         if (!(console->flags & CON_ENABLED))
 904                 return;
 905
 906         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 907                 unregister_console(console_drivers);
 908                 console->flags &= ~CON_PRINTBUFFER;
 909         }
 910
 911         /*
 912          *      Put this console in the list - keep the
 913          *      preferred driver at the head of the list.
 914          */
 915         acquire_console_sem();
 916         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 917                 console->next = console_drivers;
 918                 console_drivers = console;
 919         } else {
 920                 console->next = console_drivers->next;
 921                 console_drivers->next = console;
 922         }
 923         if (console->flags & CON_PRINTBUFFER) {
 924                 /*
 925                  * release_console_sem() will print out the buffered messages
 926                  * for us.
 927                  */
 928                 spin_lock_irqsave(&logbuf_lock, flags);
 929                 con_start = log_start;
 930                 spin_unlock_irqrestore(&logbuf_lock, flags);
 931         }
 932         release_console_sem();
 933 }
 934 EXPORT_SYMBOL(register_console);
 935
 936 int unregister_console(struct console * console)
 937 {
 938         struct console *a,*b;
 939         int res = 1;
 940
 941         acquire_console_sem();
 942         if (console_drivers == console) {
 943                 console_drivers=console->next;
 944                 res = 0;
 945         } else {
 946                 for (a=console_drivers->next, b=console_drivers ;
 947                      a; b=a, a=b->next) {
 948                         if (a == console) {
 949                                 b->next = a->next;
 950                                 res = 0;
 951                                 break;
 952                         }
 953                 }
 954         }
 955
 956         /* If last console is removed, we re-enable picking the first
 957          * one that gets registered. Without that, pmac early boot console
 958          * would prevent fbcon from taking over.
 959          */
 960         if (console_drivers == NULL)
 961                 preferred_console = selected_console;
 962
 963
 964         release_console_sem();
 965         return res;
 966 }
 967 EXPORT_SYMBOL(unregister_console);
 968
 969 /**
 970  * tty_write_message - write a message to a certain tty, not just the console.
 971  *
 972  * This is used for messages that need to be redirected to a specific tty.
 973  * We don't put it into the syslog queue right now maybe in the future if
 974  * really needed.
 975  */
 976 void tty_write_message(struct tty_struct *tty, char *msg)
 977 {
 978         if (tty && tty->driver->write)
 979                 tty->driver->write(tty, msg, strlen(msg));
 980         return;
 981 }
 982
 983 /*
 984  * printk rate limiting, lifted from the networking subsystem.
 985  *
 986  * This enforces a rate limit: not more than one kernel message
 987  * every printk_ratelimit_jiffies to make a denial-of-service
 988  * attack impossible.
 989  */
 990 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
 991 {
 992         static DEFINE_SPINLOCK(ratelimit_lock);
 993         static unsigned long toks = 10*5*HZ;
 994         static unsigned long last_msg;
 995         static int missed;
 996         unsigned long flags;
 997         unsigned long now = jiffies;
 998
 999         spin_lock_irqsave(&ratelimit_lock, flags);
1000         toks += now - last_msg;
1001         last_msg = now;
1002         if (toks > (ratelimit_burst * ratelimit_jiffies))
1003                 toks = ratelimit_burst * ratelimit_jiffies;
1004         if (toks >= ratelimit_jiffies) {
1005                 int lost = missed;
1006                 missed = 0;
1007                 toks -= ratelimit_jiffies;
1008                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1009                 if (lost)
1010                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1011                 return 1;
1012         }
1013         missed++;
1014         spin_unlock_irqrestore(&ratelimit_lock, flags);
1015         return 0;
1016 }
1017 EXPORT_SYMBOL(__printk_ratelimit);
1018
1019 /* minimum time in jiffies between messages */
1020 int printk_ratelimit_jiffies = 5*HZ;
1021
1022 /* number of messages we send before ratelimiting */
1023 int printk_ratelimit_burst = 10;
1024
1025 int printk_ratelimit(void)
1026 {
1027         return __printk_ratelimit(printk_ratelimit_jiffies,
1028                                 printk_ratelimit_burst);
1029 }
1030 EXPORT_SYMBOL(printk_ratelimit);