kernel/printk.c

   1 /*
   2  *  linux/kernel/printk.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  * Modified to make sys_syslog() more flexible: added commands to
   7  * return the last 4k of kernel messages, regardless of whether
   8  * they've been read or not.  Added option to suppress kernel printk's
   9  * to the console.  Added hook for sending the console messages
  10  * elsewhere, in preparation for a serial line console (someday).
  11  * Ted Ts'o, 2/11/93.
  12  * Modified for sysctl support, 1/8/97, Chris Horn.
  13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
  14  *     manfred@colorfullife.com
  15  * Rewrote bits to get rid of console_lock
  16  *      01Mar01 Andrew Morton <andrewm@uow.edu.au>
  17  */
  18
  19 #include <linux/kernel.h>
  20 #include <linux/mm.h>
  21 #include <linux/tty.h>
  22 #include <linux/tty_driver.h>
  23 #include <linux/console.h>
  24 #include <linux/init.h>
  25 #include <linux/module.h>
  26 #include <linux/moduleparam.h>
  27 #include <linux/interrupt.h>                    /* For in_interrupt() */
  28 #include <linux/delay.h>
  29 #include <linux/smp.h>
  30 #include <linux/security.h>
  31 #include <linux/bootmem.h>
  32 #include <linux/syscalls.h>
  33 #include <linux/jiffies.h>
  34
  35 #include <asm/uaccess.h>
  36
  37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  38
  39 /* printk's without a loglevel use this.. */
  40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  41
  42 /* We show everything that is MORE important than this.. */
  43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  45
  46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  47
  48 int console_printk[4] = {
  49         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  50         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  51         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  52         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  53 };
  54
  55 /*
  56  * Low level drivers may need that to know if they can schedule in
  57  * their unblank() callback or not. So let's export it.
  58  */
  59 int oops_in_progress;
  60 EXPORT_SYMBOL(oops_in_progress);
  61
  62 /*
  63  * console_sem protects the console_drivers list, and also
  64  * provides serialisation for access to the entire console
  65  * driver system.
  66  */
  67 static DECLARE_MUTEX(console_sem);
  68 static DECLARE_MUTEX(secondary_console_sem);
  69 struct console *console_drivers;
  70 /*
  71  * This is used for debugging the mess that is the VT code by
  72  * keeping track if we have the console semaphore held. It's
  73  * definitely not the perfect debug tool (we don't know if _WE_
  74  * hold it are racing, but it helps tracking those weird code
  75  * path in the console code where we end up in places I want
  76  * locked without the console sempahore held
  77  */
  78 static int console_locked, console_suspended;
  79
  80 /*
  81  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  82  * It is also used in interesting ways to provide interlocking in
  83  * release_console_sem().
  84  */
  85 static DEFINE_SPINLOCK(logbuf_lock);
  86
  87 #define LOG_BUF_MASK    (log_buf_len-1)
  88 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  89
  90 /*
  91  * The indices into log_buf are not constrained to log_buf_len - they
  92  * must be masked before subscripting
  93  */
  94 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  95 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  96 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  97
  98 /*
  99  *      Array of consoles built from command line options (console=)
 100  */
 101 struct console_cmdline
 102 {
 103         char    name[8];                        /* Name of the driver       */
 104         int     index;                          /* Minor dev. to use        */
 105         char    *options;                       /* Options for the driver   */
 106 };
 107
 108 #define MAX_CMDLINECONSOLES 8
 109
 110 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 111 static int selected_console = -1;
 112 static int preferred_console = -1;
 113
 114 /* Flag: console code may call schedule() */
 115 static int console_may_schedule;
 116
 117 #ifdef CONFIG_PRINTK
 118
 119 static char __log_buf[__LOG_BUF_LEN];
 120 static char *log_buf = __log_buf;
 121 static int log_buf_len = __LOG_BUF_LEN;
 122 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 123
 124 static int __init log_buf_len_setup(char *str)
 125 {
 126         unsigned long size = memparse(str, &str);
 127         unsigned long flags;
 128
 129         if (size)
 130                 size = roundup_pow_of_two(size);
 131         if (size > log_buf_len) {
 132                 unsigned long start, dest_idx, offset;
 133                 char *new_log_buf;
 134
 135                 new_log_buf = alloc_bootmem(size);
 136                 if (!new_log_buf) {
 137                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 138                         goto out;
 139                 }
 140
 141                 spin_lock_irqsave(&logbuf_lock, flags);
 142                 log_buf_len = size;
 143                 log_buf = new_log_buf;
 144
 145                 offset = start = min(con_start, log_start);
 146                 dest_idx = 0;
 147                 while (start != log_end) {
 148                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 149                         start++;
 150                         dest_idx++;
 151                 }
 152                 log_start -= offset;
 153                 con_start -= offset;
 154                 log_end -= offset;
 155                 spin_unlock_irqrestore(&logbuf_lock, flags);
 156
 157                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 158         }
 159 out:
 160         return 1;
 161 }
 162
 163 __setup("log_buf_len=", log_buf_len_setup);
 164
 165 /*
 166  * Commands to do_syslog:
 167  *
 168  *      0 -- Close the log.  Currently a NOP.
 169  *      1 -- Open the log. Currently a NOP.
 170  *      2 -- Read from the log.
 171  *      3 -- Read all messages remaining in the ring buffer.
 172  *      4 -- Read and clear all messages remaining in the ring buffer
 173  *      5 -- Clear ring buffer.
 174  *      6 -- Disable printk's to console
 175  *      7 -- Enable printk's to console
 176  *      8 -- Set level of messages printed to console
 177  *      9 -- Return number of unread characters in the log buffer
 178  *     10 -- Return size of the log buffer
 179  */
 180 int do_syslog(int type, char __user *buf, int len)
 181 {
 182         unsigned long i, j, limit, count;
 183         int do_clear = 0;
 184         char c;
 185         int error = 0;
 186
 187         error = security_syslog(type);
 188         if (error)
 189                 return error;
 190
 191         switch (type) {
 192         case 0:         /* Close log */
 193                 break;
 194         case 1:         /* Open log */
 195                 break;
 196         case 2:         /* Read from log */
 197                 error = -EINVAL;
 198                 if (!buf || len < 0)
 199                         goto out;
 200                 error = 0;
 201                 if (!len)
 202                         goto out;
 203                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 204                         error = -EFAULT;
 205                         goto out;
 206                 }
 207                 error = wait_event_interruptible(log_wait,
 208                                                         (log_start - log_end));
 209                 if (error)
 210                         goto out;
 211                 i = 0;
 212                 spin_lock_irq(&logbuf_lock);
 213                 while (!error && (log_start != log_end) && i < len) {
 214                         c = LOG_BUF(log_start);
 215                         log_start++;
 216                         spin_unlock_irq(&logbuf_lock);
 217                         error = __put_user(c,buf);
 218                         buf++;
 219                         i++;
 220                         cond_resched();
 221                         spin_lock_irq(&logbuf_lock);
 222                 }
 223                 spin_unlock_irq(&logbuf_lock);
 224                 if (!error)
 225                         error = i;
 226                 break;
 227         case 4:         /* Read/clear last kernel messages */
 228                 do_clear = 1;
 229                 /* FALL THRU */
 230         case 3:         /* Read last kernel messages */
 231                 error = -EINVAL;
 232                 if (!buf || len < 0)
 233                         goto out;
 234                 error = 0;
 235                 if (!len)
 236                         goto out;
 237                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 238                         error = -EFAULT;
 239                         goto out;
 240                 }
 241                 count = len;
 242                 if (count > log_buf_len)
 243                         count = log_buf_len;
 244                 spin_lock_irq(&logbuf_lock);
 245                 if (count > logged_chars)
 246                         count = logged_chars;
 247                 if (do_clear)
 248                         logged_chars = 0;
 249                 limit = log_end;
 250                 /*
 251                  * __put_user() could sleep, and while we sleep
 252                  * printk() could overwrite the messages
 253                  * we try to copy to user space. Therefore
 254                  * the messages are copied in reverse. <manfreds>
 255                  */
 256                 for (i = 0; i < count && !error; i++) {
 257                         j = limit-1-i;
 258                         if (j + log_buf_len < log_end)
 259                                 break;
 260                         c = LOG_BUF(j);
 261                         spin_unlock_irq(&logbuf_lock);
 262                         error = __put_user(c,&buf[count-1-i]);
 263                         cond_resched();
 264                         spin_lock_irq(&logbuf_lock);
 265                 }
 266                 spin_unlock_irq(&logbuf_lock);
 267                 if (error)
 268                         break;
 269                 error = i;
 270                 if (i != count) {
 271                         int offset = count-error;
 272                         /* buffer overflow during copy, correct user buffer. */
 273                         for (i = 0; i < error; i++) {
 274                                 if (__get_user(c,&buf[i+offset]) ||
 275                                     __put_user(c,&buf[i])) {
 276                                         error = -EFAULT;
 277                                         break;
 278                                 }
 279                                 cond_resched();
 280                         }
 281                 }
 282                 break;
 283         case 5:         /* Clear ring buffer */
 284                 logged_chars = 0;
 285                 break;
 286         case 6:         /* Disable logging to console */
 287                 console_loglevel = minimum_console_loglevel;
 288                 break;
 289         case 7:         /* Enable logging to console */
 290                 console_loglevel = default_console_loglevel;
 291                 break;
 292         case 8:         /* Set level of messages printed to console */
 293                 error = -EINVAL;
 294                 if (len < 1 || len > 8)
 295                         goto out;
 296                 if (len < minimum_console_loglevel)
 297                         len = minimum_console_loglevel;
 298                 console_loglevel = len;
 299                 error = 0;
 300                 break;
 301         case 9:         /* Number of chars in the log buffer */
 302                 error = log_end - log_start;
 303                 break;
 304         case 10:        /* Size of the log buffer */
 305                 error = log_buf_len;
 306                 break;
 307         default:
 308                 error = -EINVAL;
 309                 break;
 310         }
 311 out:
 312         return error;
 313 }
 314
 315 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 316 {
 317         return do_syslog(type, buf, len);
 318 }
 319
 320 /*
 321  * Call the console drivers on a range of log_buf
 322  */
 323 static void __call_console_drivers(unsigned long start, unsigned long end)
 324 {
 325         struct console *con;
 326
 327         for (con = console_drivers; con; con = con->next) {
 328                 if ((con->flags & CON_ENABLED) && con->write &&
 329                                 (cpu_online(smp_processor_id()) ||
 330                                 (con->flags & CON_ANYTIME)))
 331                         con->write(con, &LOG_BUF(start), end - start);
 332         }
 333 }
 334
 335 static int __read_mostly ignore_loglevel;
 336
 337 static int __init ignore_loglevel_setup(char *str)
 338 {
 339         ignore_loglevel = 1;
 340         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 341
 342         return 1;
 343 }
 344
 345 __setup("ignore_loglevel", ignore_loglevel_setup);
 346
 347 /*
 348  * Write out chars from start to end - 1 inclusive
 349  */
 350 static void _call_console_drivers(unsigned long start,
 351                                 unsigned long end, int msg_log_level)
 352 {
 353         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 354                         console_drivers && start != end) {
 355                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 356                         /* wrapped write */
 357                         __call_console_drivers(start & LOG_BUF_MASK,
 358                                                 log_buf_len);
 359                         __call_console_drivers(0, end & LOG_BUF_MASK);
 360                 } else {
 361                         __call_console_drivers(start, end);
 362                 }
 363         }
 364 }
 365
 366 /*
 367  * Call the console drivers, asking them to write out
 368  * log_buf[start] to log_buf[end - 1].
 369  * The console_sem must be held.
 370  */
 371 static void call_console_drivers(unsigned long start, unsigned long end)
 372 {
 373         unsigned long cur_index, start_print;
 374         static int msg_level = -1;
 375
 376         BUG_ON(((long)(start - end)) > 0);
 377
 378         cur_index = start;
 379         start_print = start;
 380         while (cur_index != end) {
 381                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 382                                 LOG_BUF(cur_index + 0) == '<' &&
 383                                 LOG_BUF(cur_index + 1) >= '0' &&
 384                                 LOG_BUF(cur_index + 1) <= '7' &&
 385                                 LOG_BUF(cur_index + 2) == '>') {
 386                         msg_level = LOG_BUF(cur_index + 1) - '0';
 387                         cur_index += 3;
 388                         start_print = cur_index;
 389                 }
 390                 while (cur_index != end) {
 391                         char c = LOG_BUF(cur_index);
 392
 393                         cur_index++;
 394                         if (c == '\n') {
 395                                 if (msg_level < 0) {
 396                                         /*
 397                                          * printk() has already given us loglevel tags in
 398                                          * the buffer.  This code is here in case the
 399                                          * log buffer has wrapped right round and scribbled
 400                                          * on those tags
 401                                          */
 402                                         msg_level = default_message_loglevel;
 403                                 }
 404                                 _call_console_drivers(start_print, cur_index, msg_level);
 405                                 msg_level = -1;
 406                                 start_print = cur_index;
 407                                 break;
 408                         }
 409                 }
 410         }
 411         _call_console_drivers(start_print, end, msg_level);
 412 }
 413
 414 static void emit_log_char(char c)
 415 {
 416         LOG_BUF(log_end) = c;
 417         log_end++;
 418         if (log_end - log_start > log_buf_len)
 419                 log_start = log_end - log_buf_len;
 420         if (log_end - con_start > log_buf_len)
 421                 con_start = log_end - log_buf_len;
 422         if (logged_chars < log_buf_len)
 423                 logged_chars++;
 424 }
 425
 426 /*
 427  * Zap console related locks when oopsing. Only zap at most once
 428  * every 10 seconds, to leave time for slow consoles to print a
 429  * full oops.
 430  */
 431 static void zap_locks(void)
 432 {
 433         static unsigned long oops_timestamp;
 434
 435         if (time_after_eq(jiffies, oops_timestamp) &&
 436                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 437                 return;
 438
 439         oops_timestamp = jiffies;
 440
 441         /* If a crash is occurring, make sure we can't deadlock */
 442         spin_lock_init(&logbuf_lock);
 443         /* And make sure that we print immediately */
 444         init_MUTEX(&console_sem);
 445 }
 446
 447 #if defined(CONFIG_PRINTK_TIME)
 448 static int printk_time = 1;
 449 #else
 450 static int printk_time = 0;
 451 #endif
 452 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 453
 454 static int __init printk_time_setup(char *str)
 455 {
 456         if (*str)
 457                 return 0;
 458         printk_time = 1;
 459         return 1;
 460 }
 461
 462 __setup("time", printk_time_setup);
 463
 464 __attribute__((weak)) unsigned long long printk_clock(void)
 465 {
 466         return sched_clock();
 467 }
 468
 469 /* Check if we have any console registered that can be called early in boot. */
 470 static int have_callable_console(void)
 471 {
 472         struct console *con;
 473
 474         for (con = console_drivers; con; con = con->next)
 475                 if (con->flags & CON_ANYTIME)
 476                         return 1;
 477
 478         return 0;
 479 }
 480
 481 /**
 482  * printk - print a kernel message
 483  * @fmt: format string
 484  *
 485  * This is printk().  It can be called from any context.  We want it to work.
 486  *
 487  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 488  * call the console drivers.  If we fail to get the semaphore we place the output
 489  * into the log buffer and return.  The current holder of the console_sem will
 490  * notice the new output in release_console_sem() and will send it to the
 491  * consoles before releasing the semaphore.
 492  *
 493  * One effect of this deferred printing is that code which calls printk() and
 494  * then changes console_loglevel may break. This is because console_loglevel
 495  * is inspected when the actual printing occurs.
 496  *
 497  * See also:
 498  * printf(3)
 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 /* cpu currently holding logbuf_lock */
 514 static volatile unsigned int printk_cpu = UINT_MAX;
 515
 516 asmlinkage int vprintk(const char *fmt, va_list args)
 517 {
 518         unsigned long flags;
 519         int printed_len;
 520         char *p;
 521         static char printk_buf[1024];
 522         static int log_level_unknown = 1;
 523
 524         preempt_disable();
 525         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 526                 /* If a crash is occurring during printk() on this CPU,
 527                  * make sure we can't deadlock */
 528                 zap_locks();
 529
 530         /* This stops the holder of console_sem just where we want him */
 531         raw_local_irq_save(flags);
 532         lockdep_off();
 533         spin_lock(&logbuf_lock);
 534         printk_cpu = smp_processor_id();
 535
 536         /* Emit the output into the temporary buffer */
 537         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 538
 539         /*
 540          * Copy the output into log_buf.  If the caller didn't provide
 541          * appropriate log level tags, we insert them here
 542          */
 543         for (p = printk_buf; *p; p++) {
 544                 if (log_level_unknown) {
 545                         /* log_level_unknown signals the start of a new line */
 546                         if (printk_time) {
 547                                 int loglev_char;
 548                                 char tbuf[50], *tp;
 549                                 unsigned tlen;
 550                                 unsigned long long t;
 551                                 unsigned long nanosec_rem;
 552
 553                                 /*
 554                                  * force the log level token to be
 555                                  * before the time output.
 556                                  */
 557                                 if (p[0] == '<' && p[1] >='0' &&
 558                                    p[1] <= '7' && p[2] == '>') {
 559                                         loglev_char = p[1];
 560                                         p += 3;
 561                                         printed_len -= 3;
 562                                 } else {
 563                                         loglev_char = default_message_loglevel
 564                                                 + '0';
 565                                 }
 566                                 t = printk_clock();
 567                                 nanosec_rem = do_div(t, 1000000000);
 568                                 tlen = sprintf(tbuf,
 569                                                 "<%c>[%5lu.%06lu] ",
 570                                                 loglev_char,
 571                                                 (unsigned long)t,
 572                                                 nanosec_rem/1000);
 573
 574                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 575                                         emit_log_char(*tp);
 576                                 printed_len += tlen;
 577                         } else {
 578                                 if (p[0] != '<' || p[1] < '0' ||
 579                                    p[1] > '7' || p[2] != '>') {
 580                                         emit_log_char('<');
 581                                         emit_log_char(default_message_loglevel
 582                                                 + '0');
 583                                         emit_log_char('>');
 584                                         printed_len += 3;
 585                                 }
 586                         }
 587                         log_level_unknown = 0;
 588                         if (!*p)
 589                                 break;
 590                 }
 591                 emit_log_char(*p);
 592                 if (*p == '\n')
 593                         log_level_unknown = 1;
 594         }
 595
 596         if (!down_trylock(&console_sem)) {
 597                 /*
 598                  * We own the drivers.  We can drop the spinlock and
 599                  * let release_console_sem() print the text, maybe ...
 600                  */
 601                 console_locked = 1;
 602                 printk_cpu = UINT_MAX;
 603                 spin_unlock(&logbuf_lock);
 604
 605                 /*
 606                  * Console drivers may assume that per-cpu resources have
 607                  * been allocated. So unless they're explicitly marked as
 608                  * being able to cope (CON_ANYTIME) don't call them until
 609                  * this CPU is officially up.
 610                  */
 611                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 612                         console_may_schedule = 0;
 613                         release_console_sem();
 614                 } else {
 615                         /* Release by hand to avoid flushing the buffer. */
 616                         console_locked = 0;
 617                         up(&console_sem);
 618                 }
 619                 lockdep_on();
 620                 raw_local_irq_restore(flags);
 621         } else {
 622                 /*
 623                  * Someone else owns the drivers.  We drop the spinlock, which
 624                  * allows the semaphore holder to proceed and to call the
 625                  * console drivers with the output which we just produced.
 626                  */
 627                 printk_cpu = UINT_MAX;
 628                 spin_unlock(&logbuf_lock);
 629                 lockdep_on();
 630                 raw_local_irq_restore(flags);
 631         }
 632
 633         preempt_enable();
 634         return printed_len;
 635 }
 636 EXPORT_SYMBOL(printk);
 637 EXPORT_SYMBOL(vprintk);
 638
 639 #else
 640
 641 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 642 {
 643         return -ENOSYS;
 644 }
 645
 646 static void call_console_drivers(unsigned long start, unsigned long end)
 647 {
 648 }
 649
 650 #endif
 651
 652 /*
 653  * Set up a list of consoles.  Called from init/main.c
 654  */
 655 static int __init console_setup(char *str)
 656 {
 657         char name[sizeof(console_cmdline[0].name)];
 658         char *s, *options;
 659         int idx;
 660
 661         /*
 662          * Decode str into name, index, options.
 663          */
 664         if (str[0] >= '0' && str[0] <= '9') {
 665                 strcpy(name, "ttyS");
 666                 strncpy(name + 4, str, sizeof(name) - 5);
 667         } else {
 668                 strncpy(name, str, sizeof(name) - 1);
 669         }
 670         name[sizeof(name) - 1] = 0;
 671         if ((options = strchr(str, ',')) != NULL)
 672                 *(options++) = 0;
 673 #ifdef __sparc__
 674         if (!strcmp(str, "ttya"))
 675                 strcpy(name, "ttyS0");
 676         if (!strcmp(str, "ttyb"))
 677                 strcpy(name, "ttyS1");
 678 #endif
 679         for (s = name; *s; s++)
 680                 if ((*s >= '0' && *s <= '9') || *s == ',')
 681                         break;
 682         idx = simple_strtoul(s, NULL, 10);
 683         *s = 0;
 684
 685         add_preferred_console(name, idx, options);
 686         return 1;
 687 }
 688 __setup("console=", console_setup);
 689
 690 /**
 691  * add_preferred_console - add a device to the list of preferred consoles.
 692  * @name: device name
 693  * @idx: device index
 694  * @options: options for this console
 695  *
 696  * The last preferred console added will be used for kernel messages
 697  * and stdin/out/err for init.  Normally this is used by console_setup
 698  * above to handle user-supplied console arguments; however it can also
 699  * be used by arch-specific code either to override the user or more
 700  * commonly to provide a default console (ie from PROM variables) when
 701  * the user has not supplied one.
 702  */
 703 int __init add_preferred_console(char *name, int idx, char *options)
 704 {
 705         struct console_cmdline *c;
 706         int i;
 707
 708         /*
 709          *      See if this tty is not yet registered, and
 710          *      if we have a slot free.
 711          */
 712         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 713                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 714                           console_cmdline[i].index == idx) {
 715                                 selected_console = i;
 716                                 return 0;
 717                 }
 718         if (i == MAX_CMDLINECONSOLES)
 719                 return -E2BIG;
 720         selected_console = i;
 721         c = &console_cmdline[i];
 722         memcpy(c->name, name, sizeof(c->name));
 723         c->name[sizeof(c->name) - 1] = 0;
 724         c->options = options;
 725         c->index = idx;
 726         return 0;
 727 }
 728
 729 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 730 /**
 731  * suspend_console - suspend the console subsystem
 732  *
 733  * This disables printk() while we go into suspend states
 734  */
 735 void suspend_console(void)
 736 {
 737         printk("Suspending console(s)\n");
 738         acquire_console_sem();
 739         console_suspended = 1;
 740 }
 741
 742 void resume_console(void)
 743 {
 744         console_suspended = 0;
 745         release_console_sem();
 746 }
 747 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 748
 749 /**
 750  * acquire_console_sem - lock the console system for exclusive use.
 751  *
 752  * Acquires a semaphore which guarantees that the caller has
 753  * exclusive access to the console system and the console_drivers list.
 754  *
 755  * Can sleep, returns nothing.
 756  */
 757 void acquire_console_sem(void)
 758 {
 759         BUG_ON(in_interrupt());
 760         if (console_suspended) {
 761                 down(&secondary_console_sem);
 762                 return;
 763         }
 764         down(&console_sem);
 765         console_locked = 1;
 766         console_may_schedule = 1;
 767 }
 768 EXPORT_SYMBOL(acquire_console_sem);
 769
 770 int try_acquire_console_sem(void)
 771 {
 772         if (down_trylock(&console_sem))
 773                 return -1;
 774         console_locked = 1;
 775         console_may_schedule = 0;
 776         return 0;
 777 }
 778 EXPORT_SYMBOL(try_acquire_console_sem);
 779
 780 int is_console_locked(void)
 781 {
 782         return console_locked;
 783 }
 784
 785 void wake_up_klogd(void)
 786 {
 787         if (!oops_in_progress && waitqueue_active(&log_wait))
 788                 wake_up_interruptible(&log_wait);
 789 }
 790
 791 /**
 792  * release_console_sem - unlock the console system
 793  *
 794  * Releases the semaphore which the caller holds on the console system
 795  * and the console driver list.
 796  *
 797  * While the semaphore was held, console output may have been buffered
 798  * by printk().  If this is the case, release_console_sem() emits
 799  * the output prior to releasing the semaphore.
 800  *
 801  * If there is output waiting for klogd, we wake it up.
 802  *
 803  * release_console_sem() may be called from any context.
 804  */
 805 void release_console_sem(void)
 806 {
 807         unsigned long flags;
 808         unsigned long _con_start, _log_end;
 809         unsigned long wake_klogd = 0;
 810
 811         if (console_suspended) {
 812                 up(&secondary_console_sem);
 813                 return;
 814         }
 815
 816         console_may_schedule = 0;
 817
 818         for ( ; ; ) {
 819                 spin_lock_irqsave(&logbuf_lock, flags);
 820                 wake_klogd |= log_start - log_end;
 821                 if (con_start == log_end)
 822                         break;                  /* Nothing to print */
 823                 _con_start = con_start;
 824                 _log_end = log_end;
 825                 con_start = log_end;            /* Flush */
 826                 spin_unlock(&logbuf_lock);
 827                 call_console_drivers(_con_start, _log_end);
 828                 local_irq_restore(flags);
 829         }
 830         console_locked = 0;
 831         up(&console_sem);
 832         spin_unlock_irqrestore(&logbuf_lock, flags);
 833         if (wake_klogd)
 834                 wake_up_klogd();
 835 }
 836 EXPORT_SYMBOL(release_console_sem);
 837
 838 /**
 839  * console_conditional_schedule - yield the CPU if required
 840  *
 841  * If the console code is currently allowed to sleep, and
 842  * if this CPU should yield the CPU to another task, do
 843  * so here.
 844  *
 845  * Must be called within acquire_console_sem().
 846  */
 847 void __sched console_conditional_schedule(void)
 848 {
 849         if (console_may_schedule)
 850                 cond_resched();
 851 }
 852 EXPORT_SYMBOL(console_conditional_schedule);
 853
 854 void console_print(const char *s)
 855 {
 856         printk(KERN_EMERG "%s", s);
 857 }
 858 EXPORT_SYMBOL(console_print);
 859
 860 void console_unblank(void)
 861 {
 862         struct console *c;
 863
 864         /*
 865          * console_unblank can no longer be called in interrupt context unless
 866          * oops_in_progress is set to 1..
 867          */
 868         if (oops_in_progress) {
 869                 if (down_trylock(&console_sem) != 0)
 870                         return;
 871         } else
 872                 acquire_console_sem();
 873
 874         console_locked = 1;
 875         console_may_schedule = 0;
 876         for (c = console_drivers; c != NULL; c = c->next)
 877                 if ((c->flags & CON_ENABLED) && c->unblank)
 878                         c->unblank();
 879         release_console_sem();
 880 }
 881
 882 /*
 883  * Return the console tty driver structure and its associated index
 884  */
 885 struct tty_driver *console_device(int *index)
 886 {
 887         struct console *c;
 888         struct tty_driver *driver = NULL;
 889
 890         acquire_console_sem();
 891         for (c = console_drivers; c != NULL; c = c->next) {
 892                 if (!c->device)
 893                         continue;
 894                 driver = c->device(c, index);
 895                 if (driver)
 896                         break;
 897         }
 898         release_console_sem();
 899         return driver;
 900 }
 901
 902 /*
 903  * Prevent further output on the passed console device so that (for example)
 904  * serial drivers can disable console output before suspending a port, and can
 905  * re-enable output afterwards.
 906  */
 907 void console_stop(struct console *console)
 908 {
 909         acquire_console_sem();
 910         console->flags &= ~CON_ENABLED;
 911         release_console_sem();
 912 }
 913 EXPORT_SYMBOL(console_stop);
 914
 915 void console_start(struct console *console)
 916 {
 917         acquire_console_sem();
 918         console->flags |= CON_ENABLED;
 919         release_console_sem();
 920 }
 921 EXPORT_SYMBOL(console_start);
 922
 923 /*
 924  * The console driver calls this routine during kernel initialization
 925  * to register the console printing procedure with printk() and to
 926  * print any messages that were printed by the kernel before the
 927  * console driver was initialized.
 928  */
 929 void register_console(struct console *console)
 930 {
 931         int i;
 932         unsigned long flags;
 933         struct console *bootconsole = NULL;
 934
 935         if (console_drivers) {
 936                 if (console->flags & CON_BOOT)
 937                         return;
 938                 if (console_drivers->flags & CON_BOOT)
 939                         bootconsole = console_drivers;
 940         }
 941
 942         if (preferred_console < 0 || bootconsole || !console_drivers)
 943                 preferred_console = selected_console;
 944
 945         /*
 946          *      See if we want to use this console driver. If we
 947          *      didn't select a console we take the first one
 948          *      that registers here.
 949          */
 950         if (preferred_console < 0) {
 951                 if (console->index < 0)
 952                         console->index = 0;
 953                 if (console->setup == NULL ||
 954                     console->setup(console, NULL) == 0) {
 955                         console->flags |= CON_ENABLED | CON_CONSDEV;
 956                         preferred_console = 0;
 957                 }
 958         }
 959
 960         /*
 961          *      See if this console matches one we selected on
 962          *      the command line.
 963          */
 964         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 965                         i++) {
 966                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 967                         continue;
 968                 if (console->index >= 0 &&
 969                     console->index != console_cmdline[i].index)
 970                         continue;
 971                 if (console->index < 0)
 972                         console->index = console_cmdline[i].index;
 973                 if (console->setup &&
 974                     console->setup(console, console_cmdline[i].options) != 0)
 975                         break;
 976                 console->flags |= CON_ENABLED;
 977                 console->index = console_cmdline[i].index;
 978                 if (i == selected_console) {
 979                         console->flags |= CON_CONSDEV;
 980                         preferred_console = selected_console;
 981                 }
 982                 break;
 983         }
 984
 985         if (!(console->flags & CON_ENABLED))
 986                 return;
 987
 988         if (bootconsole) {
 989                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
 990                        bootconsole->name, bootconsole->index,
 991                        console->name, console->index);
 992                 unregister_console(bootconsole);
 993                 console->flags &= ~CON_PRINTBUFFER;
 994         }
 995
 996         /*
 997          *      Put this console in the list - keep the
 998          *      preferred driver at the head of the list.
 999          */
1000         acquire_console_sem();
1001         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1002                 console->next = console_drivers;
1003                 console_drivers = console;
1004                 if (console->next)
1005                         console->next->flags &= ~CON_CONSDEV;
1006         } else {
1007                 console->next = console_drivers->next;
1008                 console_drivers->next = console;
1009         }
1010         if (console->flags & CON_PRINTBUFFER) {
1011                 /*
1012                  * release_console_sem() will print out the buffered messages
1013                  * for us.
1014                  */
1015                 spin_lock_irqsave(&logbuf_lock, flags);
1016                 con_start = log_start;
1017                 spin_unlock_irqrestore(&logbuf_lock, flags);
1018         }
1019         release_console_sem();
1020 }
1021 EXPORT_SYMBOL(register_console);
1022
1023 int unregister_console(struct console *console)
1024 {
1025         struct console *a, *b;
1026         int res = 1;
1027
1028         acquire_console_sem();
1029         if (console_drivers == console) {
1030                 console_drivers=console->next;
1031                 res = 0;
1032         } else if (console_drivers) {
1033                 for (a=console_drivers->next, b=console_drivers ;
1034                      a; b=a, a=b->next) {
1035                         if (a == console) {
1036                                 b->next = a->next;
1037                                 res = 0;
1038                                 break;
1039                         }
1040                 }
1041         }
1042
1043         /*
1044          * If this isn't the last console and it has CON_CONSDEV set, we
1045          * need to set it on the next preferred console.
1046          */
1047         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1048                 console_drivers->flags |= CON_CONSDEV;
1049
1050         release_console_sem();
1051         return res;
1052 }
1053 EXPORT_SYMBOL(unregister_console);
1054
1055 /**
1056  * tty_write_message - write a message to a certain tty, not just the console.
1057  * @tty: the destination tty_struct
1058  * @msg: the message to write
1059  *
1060  * This is used for messages that need to be redirected to a specific tty.
1061  * We don't put it into the syslog queue right now maybe in the future if
1062  * really needed.
1063  */
1064 void tty_write_message(struct tty_struct *tty, char *msg)
1065 {
1066         if (tty && tty->driver->write)
1067                 tty->driver->write(tty, msg, strlen(msg));
1068         return;
1069 }
1070
1071 /*
1072  * printk rate limiting, lifted from the networking subsystem.
1073  *
1074  * This enforces a rate limit: not more than one kernel message
1075  * every printk_ratelimit_jiffies to make a denial-of-service
1076  * attack impossible.
1077  */
1078 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1079 {
1080         static DEFINE_SPINLOCK(ratelimit_lock);
1081         static unsigned long toks = 10 * 5 * HZ;
1082         static unsigned long last_msg;
1083         static int missed;
1084         unsigned long flags;
1085         unsigned long now = jiffies;
1086
1087         spin_lock_irqsave(&ratelimit_lock, flags);
1088         toks += now - last_msg;
1089         last_msg = now;
1090         if (toks > (ratelimit_burst * ratelimit_jiffies))
1091                 toks = ratelimit_burst * ratelimit_jiffies;
1092         if (toks >= ratelimit_jiffies) {
1093                 int lost = missed;
1094
1095                 missed = 0;
1096                 toks -= ratelimit_jiffies;
1097                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1098                 if (lost)
1099                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1100                 return 1;
1101         }
1102         missed++;
1103         spin_unlock_irqrestore(&ratelimit_lock, flags);
1104         return 0;
1105 }
1106 EXPORT_SYMBOL(__printk_ratelimit);
1107
1108 /* minimum time in jiffies between messages */
1109 int printk_ratelimit_jiffies = 5 * HZ;
1110
1111 /* number of messages we send before ratelimiting */
1112 int printk_ratelimit_burst = 10;
1113
1114 int printk_ratelimit(void)
1115 {
1116         return __printk_ratelimit(printk_ratelimit_jiffies,
1117                                 printk_ratelimit_burst);
1118 }
1119 EXPORT_SYMBOL(printk_ratelimit);
1120
1121 /**
1122  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1123  * @caller_jiffies: pointer to caller's state
1124  * @interval_msecs: minimum interval between prints
1125  *
1126  * printk_timed_ratelimit() returns true if more than @interval_msecs
1127  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1128  * returned true.
1129  */
1130 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1131                         unsigned int interval_msecs)
1132 {
1133         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1134                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1135                 return true;
1136         }
1137         return false;
1138 }
1139 EXPORT_SYMBOL(printk_timed_ratelimit);