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/smp_lock.h>
  24 #include <linux/console.h>
  25 #include <linux/init.h>
  26 #include <linux/module.h>
  27 #include <linux/moduleparam.h>
  28 #include <linux/interrupt.h>                    /* For in_interrupt() */
  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/jiffies.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 /*
  57  * Low lever drivers may need that to know if they can schedule in
  58  * their unblank() callback or not. So let's export it.
  59  */
  60 int oops_in_progress;
  61 EXPORT_SYMBOL(oops_in_progress);
  62
  63 /*
  64  * console_sem protects the console_drivers list, and also
  65  * provides serialisation for access to the entire console
  66  * driver system.
  67  */
  68 static DECLARE_MUTEX(console_sem);
  69 static DECLARE_MUTEX(secondary_console_sem);
  70 struct console *console_drivers;
  71 /*
  72  * This is used for debugging the mess that is the VT code by
  73  * keeping track if we have the console semaphore held. It's
  74  * definitely not the perfect debug tool (we don't know if _WE_
  75  * hold it are racing, but it helps tracking those weird code
  76  * path in the console code where we end up in places I want
  77  * locked without the console sempahore held
  78  */
  79 static int console_locked, console_suspended;
  80
  81 /*
  82  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  83  * It is also used in interesting ways to provide interlocking in
  84  * release_console_sem().
  85  */
  86 static DEFINE_SPINLOCK(logbuf_lock);
  87
  88 #define LOG_BUF_MASK    (log_buf_len-1)
  89 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  90
  91 /*
  92  * The indices into log_buf are not constrained to log_buf_len - they
  93  * must be masked before subscripting
  94  */
  95 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  96 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  97 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  98
  99 /*
 100  *      Array of consoles built from command line options (console=)
 101  */
 102 struct console_cmdline
 103 {
 104         char    name[8];                        /* Name of the driver       */
 105         int     index;                          /* Minor dev. to use        */
 106         char    *options;                       /* Options for the driver   */
 107 };
 108
 109 #define MAX_CMDLINECONSOLES 8
 110
 111 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 112 static int selected_console = -1;
 113 static int preferred_console = -1;
 114
 115 /* Flag: console code may call schedule() */
 116 static int console_may_schedule;
 117
 118 #ifdef CONFIG_PRINTK
 119
 120 static char __log_buf[__LOG_BUF_LEN];
 121 static char *log_buf = __log_buf;
 122 static int log_buf_len = __LOG_BUF_LEN;
 123 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 124
 125 static int __init log_buf_len_setup(char *str)
 126 {
 127         unsigned long size = memparse(str, &str);
 128         unsigned long flags;
 129
 130         if (size)
 131                 size = roundup_pow_of_two(size);
 132         if (size > log_buf_len) {
 133                 unsigned long start, dest_idx, offset;
 134                 char *new_log_buf;
 135
 136                 new_log_buf = alloc_bootmem(size);
 137                 if (!new_log_buf) {
 138                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 139                         goto out;
 140                 }
 141
 142                 spin_lock_irqsave(&logbuf_lock, flags);
 143                 log_buf_len = size;
 144                 log_buf = new_log_buf;
 145
 146                 offset = start = min(con_start, log_start);
 147                 dest_idx = 0;
 148                 while (start != log_end) {
 149                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 150                         start++;
 151                         dest_idx++;
 152                 }
 153                 log_start -= offset;
 154                 con_start -= offset;
 155                 log_end -= offset;
 156                 spin_unlock_irqrestore(&logbuf_lock, flags);
 157
 158                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 159         }
 160 out:
 161         return 1;
 162 }
 163
 164 __setup("log_buf_len=", log_buf_len_setup);
 165
 166 /*
 167  * Commands to do_syslog:
 168  *
 169  *      0 -- Close the log.  Currently a NOP.
 170  *      1 -- Open the log. Currently a NOP.
 171  *      2 -- Read from the log.
 172  *      3 -- Read all messages remaining in the ring buffer.
 173  *      4 -- Read and clear all messages remaining in the ring buffer
 174  *      5 -- Clear ring buffer.
 175  *      6 -- Disable printk's to console
 176  *      7 -- Enable printk's to console
 177  *      8 -- Set level of messages printed to console
 178  *      9 -- Return number of unread characters in the log buffer
 179  *     10 -- Return size of the log buffer
 180  */
 181 int do_syslog(int type, char __user *buf, int len)
 182 {
 183         unsigned long i, j, limit, count;
 184         int do_clear = 0;
 185         char c;
 186         int error = 0;
 187
 188         error = security_syslog(type);
 189         if (error)
 190                 return error;
 191
 192         switch (type) {
 193         case 0:         /* Close log */
 194                 break;
 195         case 1:         /* Open log */
 196                 break;
 197         case 2:         /* Read from log */
 198                 error = -EINVAL;
 199                 if (!buf || len < 0)
 200                         goto out;
 201                 error = 0;
 202                 if (!len)
 203                         goto out;
 204                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 205                         error = -EFAULT;
 206                         goto out;
 207                 }
 208                 error = wait_event_interruptible(log_wait,
 209                                                         (log_start - log_end));
 210                 if (error)
 211                         goto out;
 212                 i = 0;
 213                 spin_lock_irq(&logbuf_lock);
 214                 while (!error && (log_start != log_end) && i < len) {
 215                         c = LOG_BUF(log_start);
 216                         log_start++;
 217                         spin_unlock_irq(&logbuf_lock);
 218                         error = __put_user(c,buf);
 219                         buf++;
 220                         i++;
 221                         cond_resched();
 222                         spin_lock_irq(&logbuf_lock);
 223                 }
 224                 spin_unlock_irq(&logbuf_lock);
 225                 if (!error)
 226                         error = i;
 227                 break;
 228         case 4:         /* Read/clear last kernel messages */
 229                 do_clear = 1;
 230                 /* FALL THRU */
 231         case 3:         /* Read last kernel messages */
 232                 error = -EINVAL;
 233                 if (!buf || len < 0)
 234                         goto out;
 235                 error = 0;
 236                 if (!len)
 237                         goto out;
 238                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 239                         error = -EFAULT;
 240                         goto out;
 241                 }
 242                 count = len;
 243                 if (count > log_buf_len)
 244                         count = log_buf_len;
 245                 spin_lock_irq(&logbuf_lock);
 246                 if (count > logged_chars)
 247                         count = logged_chars;
 248                 if (do_clear)
 249                         logged_chars = 0;
 250                 limit = log_end;
 251                 /*
 252                  * __put_user() could sleep, and while we sleep
 253                  * printk() could overwrite the messages
 254                  * we try to copy to user space. Therefore
 255                  * the messages are copied in reverse. <manfreds>
 256                  */
 257                 for (i = 0; i < count && !error; i++) {
 258                         j = limit-1-i;
 259                         if (j + log_buf_len < log_end)
 260                                 break;
 261                         c = LOG_BUF(j);
 262                         spin_unlock_irq(&logbuf_lock);
 263                         error = __put_user(c,&buf[count-1-i]);
 264                         cond_resched();
 265                         spin_lock_irq(&logbuf_lock);
 266                 }
 267                 spin_unlock_irq(&logbuf_lock);
 268                 if (error)
 269                         break;
 270                 error = i;
 271                 if (i != count) {
 272                         int offset = count-error;
 273                         /* buffer overflow during copy, correct user buffer. */
 274                         for (i = 0; i < error; i++) {
 275                                 if (__get_user(c,&buf[i+offset]) ||
 276                                     __put_user(c,&buf[i])) {
 277                                         error = -EFAULT;
 278                                         break;
 279                                 }
 280                                 cond_resched();
 281                         }
 282                 }
 283                 break;
 284         case 5:         /* Clear ring buffer */
 285                 logged_chars = 0;
 286                 break;
 287         case 6:         /* Disable logging to console */
 288                 console_loglevel = minimum_console_loglevel;
 289                 break;
 290         case 7:         /* Enable logging to console */
 291                 console_loglevel = default_console_loglevel;
 292                 break;
 293         case 8:         /* Set level of messages printed to console */
 294                 error = -EINVAL;
 295                 if (len < 1 || len > 8)
 296                         goto out;
 297                 if (len < minimum_console_loglevel)
 298                         len = minimum_console_loglevel;
 299                 console_loglevel = len;
 300                 error = 0;
 301                 break;
 302         case 9:         /* Number of chars in the log buffer */
 303                 error = log_end - log_start;
 304                 break;
 305         case 10:        /* Size of the log buffer */
 306                 error = log_buf_len;
 307                 break;
 308         default:
 309                 error = -EINVAL;
 310                 break;
 311         }
 312 out:
 313         return error;
 314 }
 315
 316 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 317 {
 318         return do_syslog(type, buf, len);
 319 }
 320
 321 /*
 322  * Call the console drivers on a range of log_buf
 323  */
 324 static void __call_console_drivers(unsigned long start, unsigned long end)
 325 {
 326         struct console *con;
 327
 328         for (con = console_drivers; con; con = con->next) {
 329                 if ((con->flags & CON_ENABLED) && con->write &&
 330                                 (cpu_online(smp_processor_id()) ||
 331                                 (con->flags & CON_ANYTIME)))
 332                         con->write(con, &LOG_BUF(start), end - start);
 333         }
 334 }
 335
 336 static int __read_mostly ignore_loglevel;
 337
 338 static int __init ignore_loglevel_setup(char *str)
 339 {
 340         ignore_loglevel = 1;
 341         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 342
 343         return 1;
 344 }
 345
 346 __setup("ignore_loglevel", ignore_loglevel_setup);
 347
 348 /*
 349  * Write out chars from start to end - 1 inclusive
 350  */
 351 static void _call_console_drivers(unsigned long start,
 352                                 unsigned long end, int msg_log_level)
 353 {
 354         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 355                         console_drivers && start != end) {
 356                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 357                         /* wrapped write */
 358                         __call_console_drivers(start & LOG_BUF_MASK,
 359                                                 log_buf_len);
 360                         __call_console_drivers(0, end & LOG_BUF_MASK);
 361                 } else {
 362                         __call_console_drivers(start, end);
 363                 }
 364         }
 365 }
 366
 367 /*
 368  * Call the console drivers, asking them to write out
 369  * log_buf[start] to log_buf[end - 1].
 370  * The console_sem must be held.
 371  */
 372 static void call_console_drivers(unsigned long start, unsigned long end)
 373 {
 374         unsigned long cur_index, start_print;
 375         static int msg_level = -1;
 376
 377         BUG_ON(((long)(start - end)) > 0);
 378
 379         cur_index = start;
 380         start_print = start;
 381         while (cur_index != end) {
 382                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 383                                 LOG_BUF(cur_index + 0) == '<' &&
 384                                 LOG_BUF(cur_index + 1) >= '0' &&
 385                                 LOG_BUF(cur_index + 1) <= '7' &&
 386                                 LOG_BUF(cur_index + 2) == '>') {
 387                         msg_level = LOG_BUF(cur_index + 1) - '0';
 388                         cur_index += 3;
 389                         start_print = cur_index;
 390                 }
 391                 while (cur_index != end) {
 392                         char c = LOG_BUF(cur_index);
 393
 394                         cur_index++;
 395                         if (c == '\n') {
 396                                 if (msg_level < 0) {
 397                                         /*
 398                                          * printk() has already given us loglevel tags in
 399                                          * the buffer.  This code is here in case the
 400                                          * log buffer has wrapped right round and scribbled
 401                                          * on those tags
 402                                          */
 403                                         msg_level = default_message_loglevel;
 404                                 }
 405                                 _call_console_drivers(start_print, cur_index, msg_level);
 406                                 msg_level = -1;
 407                                 start_print = cur_index;
 408                                 break;
 409                         }
 410                 }
 411         }
 412         _call_console_drivers(start_print, end, msg_level);
 413 }
 414
 415 static void emit_log_char(char c)
 416 {
 417         LOG_BUF(log_end) = c;
 418         log_end++;
 419         if (log_end - log_start > log_buf_len)
 420                 log_start = log_end - log_buf_len;
 421         if (log_end - con_start > log_buf_len)
 422                 con_start = log_end - log_buf_len;
 423         if (logged_chars < log_buf_len)
 424                 logged_chars++;
 425 }
 426
 427 /*
 428  * Zap console related locks when oopsing. Only zap at most once
 429  * every 10 seconds, to leave time for slow consoles to print a
 430  * full oops.
 431  */
 432 static void zap_locks(void)
 433 {
 434         static unsigned long oops_timestamp;
 435
 436         if (time_after_eq(jiffies, oops_timestamp) &&
 437                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 438                 return;
 439
 440         oops_timestamp = jiffies;
 441
 442         /* If a crash is occurring, make sure we can't deadlock */
 443         spin_lock_init(&logbuf_lock);
 444         /* And make sure that we print immediately */
 445         init_MUTEX(&console_sem);
 446 }
 447
 448 #if defined(CONFIG_PRINTK_TIME)
 449 static int printk_time = 1;
 450 #else
 451 static int printk_time = 0;
 452 #endif
 453 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 454
 455 static int __init printk_time_setup(char *str)
 456 {
 457         if (*str)
 458                 return 0;
 459         printk_time = 1;
 460         return 1;
 461 }
 462
 463 __setup("time", printk_time_setup);
 464
 465 __attribute__((weak)) unsigned long long printk_clock(void)
 466 {
 467         return sched_clock();
 468 }
 469
 470 /* Check if we have any console registered that can be called early in boot. */
 471 static int have_callable_console(void)
 472 {
 473         struct console *con;
 474
 475         for (con = console_drivers; con; con = con->next)
 476                 if (con->flags & CON_ANYTIME)
 477                         return 1;
 478
 479         return 0;
 480 }
 481
 482 /**
 483  * printk - print a kernel message
 484  * @fmt: format string
 485  *
 486  * This is printk().  It can be called from any context.  We want it to work.
 487  *
 488  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 489  * call the console drivers.  If we fail to get the semaphore we place the output
 490  * into the log buffer and return.  The current holder of the console_sem will
 491  * notice the new output in release_console_sem() and will send it to the
 492  * consoles before releasing the semaphore.
 493  *
 494  * One effect of this deferred printing is that code which calls printk() and
 495  * then changes console_loglevel may break. This is because console_loglevel
 496  * is inspected when the actual printing occurs.
 497  *
 498  * See also:
 499  * printf(3)
 500  */
 501
 502 asmlinkage int printk(const char *fmt, ...)
 503 {
 504         va_list args;
 505         int r;
 506
 507         va_start(args, fmt);
 508         r = vprintk(fmt, args);
 509         va_end(args);
 510
 511         return r;
 512 }
 513
 514 /* cpu currently holding logbuf_lock */
 515 static volatile unsigned int printk_cpu = UINT_MAX;
 516
 517 asmlinkage int vprintk(const char *fmt, va_list args)
 518 {
 519         unsigned long flags;
 520         int printed_len;
 521         char *p;
 522         static char printk_buf[1024];
 523         static int log_level_unknown = 1;
 524
 525         preempt_disable();
 526         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 527                 /* If a crash is occurring during printk() on this CPU,
 528                  * make sure we can't deadlock */
 529                 zap_locks();
 530
 531         /* This stops the holder of console_sem just where we want him */
 532         raw_local_irq_save(flags);
 533         lockdep_off();
 534         spin_lock(&logbuf_lock);
 535         printk_cpu = smp_processor_id();
 536
 537         /* Emit the output into the temporary buffer */
 538         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 539
 540         /*
 541          * Copy the output into log_buf.  If the caller didn't provide
 542          * appropriate log level tags, we insert them here
 543          */
 544         for (p = printk_buf; *p; p++) {
 545                 if (log_level_unknown) {
 546                         /* log_level_unknown signals the start of a new line */
 547                         if (printk_time) {
 548                                 int loglev_char;
 549                                 char tbuf[50], *tp;
 550                                 unsigned tlen;
 551                                 unsigned long long t;
 552                                 unsigned long nanosec_rem;
 553
 554                                 /*
 555                                  * force the log level token to be
 556                                  * before the time output.
 557                                  */
 558                                 if (p[0] == '<' && p[1] >='0' &&
 559                                    p[1] <= '7' && p[2] == '>') {
 560                                         loglev_char = p[1];
 561                                         p += 3;
 562                                         printed_len -= 3;
 563                                 } else {
 564                                         loglev_char = default_message_loglevel
 565                                                 + '0';
 566                                 }
 567                                 t = printk_clock();
 568                                 nanosec_rem = do_div(t, 1000000000);
 569                                 tlen = sprintf(tbuf,
 570                                                 "<%c>[%5lu.%06lu] ",
 571                                                 loglev_char,
 572                                                 (unsigned long)t,
 573                                                 nanosec_rem/1000);
 574
 575                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 576                                         emit_log_char(*tp);
 577                                 printed_len += tlen;
 578                         } else {
 579                                 if (p[0] != '<' || p[1] < '0' ||
 580                                    p[1] > '7' || p[2] != '>') {
 581                                         emit_log_char('<');
 582                                         emit_log_char(default_message_loglevel
 583                                                 + '0');
 584                                         emit_log_char('>');
 585                                         printed_len += 3;
 586                                 }
 587                         }
 588                         log_level_unknown = 0;
 589                         if (!*p)
 590                                 break;
 591                 }
 592                 emit_log_char(*p);
 593                 if (*p == '\n')
 594                         log_level_unknown = 1;
 595         }
 596
 597         if (!down_trylock(&console_sem)) {
 598                 /*
 599                  * We own the drivers.  We can drop the spinlock and
 600                  * let release_console_sem() print the text, maybe ...
 601                  */
 602                 console_locked = 1;
 603                 printk_cpu = UINT_MAX;
 604                 spin_unlock(&logbuf_lock);
 605
 606                 /*
 607                  * Console drivers may assume that per-cpu resources have
 608                  * been allocated. So unless they're explicitly marked as
 609                  * being able to cope (CON_ANYTIME) don't call them until
 610                  * this CPU is officially up.
 611                  */
 612                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 613                         console_may_schedule = 0;
 614                         release_console_sem();
 615                 } else {
 616                         /* Release by hand to avoid flushing the buffer. */
 617                         console_locked = 0;
 618                         up(&console_sem);
 619                 }
 620                 lockdep_on();
 621                 raw_local_irq_restore(flags);
 622         } else {
 623                 /*
 624                  * Someone else owns the drivers.  We drop the spinlock, which
 625                  * allows the semaphore holder to proceed and to call the
 626                  * console drivers with the output which we just produced.
 627                  */
 628                 printk_cpu = UINT_MAX;
 629                 spin_unlock(&logbuf_lock);
 630                 lockdep_on();
 631                 raw_local_irq_restore(flags);
 632         }
 633
 634         preempt_enable();
 635         return printed_len;
 636 }
 637 EXPORT_SYMBOL(printk);
 638 EXPORT_SYMBOL(vprintk);
 639
 640 #else
 641
 642 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 643 {
 644         return -ENOSYS;
 645 }
 646
 647 static void call_console_drivers(unsigned long start, unsigned long end)
 648 {
 649 }
 650
 651 #endif
 652
 653 /*
 654  * Set up a list of consoles.  Called from init/main.c
 655  */
 656 static int __init console_setup(char *str)
 657 {
 658         char name[sizeof(console_cmdline[0].name)];
 659         char *s, *options;
 660         int idx;
 661
 662         /*
 663          * Decode str into name, index, options.
 664          */
 665         if (str[0] >= '0' && str[0] <= '9') {
 666                 strcpy(name, "ttyS");
 667                 strncpy(name + 4, str, sizeof(name) - 5);
 668         } else {
 669                 strncpy(name, str, sizeof(name) - 1);
 670         }
 671         name[sizeof(name) - 1] = 0;
 672         if ((options = strchr(str, ',')) != NULL)
 673                 *(options++) = 0;
 674 #ifdef __sparc__
 675         if (!strcmp(str, "ttya"))
 676                 strcpy(name, "ttyS0");
 677         if (!strcmp(str, "ttyb"))
 678                 strcpy(name, "ttyS1");
 679 #endif
 680         for (s = name; *s; s++)
 681                 if ((*s >= '0' && *s <= '9') || *s == ',')
 682                         break;
 683         idx = simple_strtoul(s, NULL, 10);
 684         *s = 0;
 685
 686         add_preferred_console(name, idx, options);
 687         return 1;
 688 }
 689 __setup("console=", console_setup);
 690
 691 /**
 692  * add_preferred_console - add a device to the list of preferred consoles.
 693  * @name: device name
 694  * @idx: device index
 695  * @options: options for this console
 696  *
 697  * The last preferred console added will be used for kernel messages
 698  * and stdin/out/err for init.  Normally this is used by console_setup
 699  * above to handle user-supplied console arguments; however it can also
 700  * be used by arch-specific code either to override the user or more
 701  * commonly to provide a default console (ie from PROM variables) when
 702  * the user has not supplied one.
 703  */
 704 int __init add_preferred_console(char *name, int idx, char *options)
 705 {
 706         struct console_cmdline *c;
 707         int i;
 708
 709         /*
 710          *      See if this tty is not yet registered, and
 711          *      if we have a slot free.
 712          */
 713         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 714                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 715                           console_cmdline[i].index == idx) {
 716                                 selected_console = i;
 717                                 return 0;
 718                 }
 719         if (i == MAX_CMDLINECONSOLES)
 720                 return -E2BIG;
 721         selected_console = i;
 722         c = &console_cmdline[i];
 723         memcpy(c->name, name, sizeof(c->name));
 724         c->name[sizeof(c->name) - 1] = 0;
 725         c->options = options;
 726         c->index = idx;
 727         return 0;
 728 }
 729
 730 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 731 /**
 732  * suspend_console - suspend the console subsystem
 733  *
 734  * This disables printk() while we go into suspend states
 735  */
 736 void suspend_console(void)
 737 {
 738         printk("Suspending console(s)\n");
 739         acquire_console_sem();
 740         console_suspended = 1;
 741 }
 742
 743 void resume_console(void)
 744 {
 745         console_suspended = 0;
 746         release_console_sem();
 747 }
 748 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 749
 750 /**
 751  * acquire_console_sem - lock the console system for exclusive use.
 752  *
 753  * Acquires a semaphore which guarantees that the caller has
 754  * exclusive access to the console system and the console_drivers list.
 755  *
 756  * Can sleep, returns nothing.
 757  */
 758 void acquire_console_sem(void)
 759 {
 760         BUG_ON(in_interrupt());
 761         if (console_suspended) {
 762                 down(&secondary_console_sem);
 763                 return;
 764         }
 765         down(&console_sem);
 766         console_locked = 1;
 767         console_may_schedule = 1;
 768 }
 769 EXPORT_SYMBOL(acquire_console_sem);
 770
 771 int try_acquire_console_sem(void)
 772 {
 773         if (down_trylock(&console_sem))
 774                 return -1;
 775         console_locked = 1;
 776         console_may_schedule = 0;
 777         return 0;
 778 }
 779 EXPORT_SYMBOL(try_acquire_console_sem);
 780
 781 int is_console_locked(void)
 782 {
 783         return console_locked;
 784 }
 785
 786 void wake_up_klogd(void)
 787 {
 788         if (!oops_in_progress && waitqueue_active(&log_wait))
 789                 wake_up_interruptible(&log_wait);
 790 }
 791
 792 /**
 793  * release_console_sem - unlock the console system
 794  *
 795  * Releases the semaphore which the caller holds on the console system
 796  * and the console driver list.
 797  *
 798  * While the semaphore was held, console output may have been buffered
 799  * by printk().  If this is the case, release_console_sem() emits
 800  * the output prior to releasing the semaphore.
 801  *
 802  * If there is output waiting for klogd, we wake it up.
 803  *
 804  * release_console_sem() may be called from any context.
 805  */
 806 void release_console_sem(void)
 807 {
 808         unsigned long flags;
 809         unsigned long _con_start, _log_end;
 810         unsigned long wake_klogd = 0;
 811
 812         if (console_suspended) {
 813                 up(&secondary_console_sem);
 814                 return;
 815         }
 816
 817         console_may_schedule = 0;
 818
 819         for ( ; ; ) {
 820                 spin_lock_irqsave(&logbuf_lock, flags);
 821                 wake_klogd |= log_start - log_end;
 822                 if (con_start == log_end)
 823                         break;                  /* Nothing to print */
 824                 _con_start = con_start;
 825                 _log_end = log_end;
 826                 con_start = log_end;            /* Flush */
 827                 spin_unlock(&logbuf_lock);
 828                 call_console_drivers(_con_start, _log_end);
 829                 local_irq_restore(flags);
 830         }
 831         console_locked = 0;
 832         up(&console_sem);
 833         spin_unlock_irqrestore(&logbuf_lock, flags);
 834         if (wake_klogd)
 835                 wake_up_klogd();
 836 }
 837 EXPORT_SYMBOL(release_console_sem);
 838
 839 /**
 840  * console_conditional_schedule - yield the CPU if required
 841  *
 842  * If the console code is currently allowed to sleep, and
 843  * if this CPU should yield the CPU to another task, do
 844  * so here.
 845  *
 846  * Must be called within acquire_console_sem().
 847  */
 848 void __sched console_conditional_schedule(void)
 849 {
 850         if (console_may_schedule)
 851                 cond_resched();
 852 }
 853 EXPORT_SYMBOL(console_conditional_schedule);
 854
 855 void console_print(const char *s)
 856 {
 857         printk(KERN_EMERG "%s", s);
 858 }
 859 EXPORT_SYMBOL(console_print);
 860
 861 void console_unblank(void)
 862 {
 863         struct console *c;
 864
 865         /*
 866          * console_unblank can no longer be called in interrupt context unless
 867          * oops_in_progress is set to 1..
 868          */
 869         if (oops_in_progress) {
 870                 if (down_trylock(&console_sem) != 0)
 871                         return;
 872         } else
 873                 acquire_console_sem();
 874
 875         console_locked = 1;
 876         console_may_schedule = 0;
 877         for (c = console_drivers; c != NULL; c = c->next)
 878                 if ((c->flags & CON_ENABLED) && c->unblank)
 879                         c->unblank();
 880         release_console_sem();
 881 }
 882
 883 /*
 884  * Return the console tty driver structure and its associated index
 885  */
 886 struct tty_driver *console_device(int *index)
 887 {
 888         struct console *c;
 889         struct tty_driver *driver = NULL;
 890
 891         acquire_console_sem();
 892         for (c = console_drivers; c != NULL; c = c->next) {
 893                 if (!c->device)
 894                         continue;
 895                 driver = c->device(c, index);
 896                 if (driver)
 897                         break;
 898         }
 899         release_console_sem();
 900         return driver;
 901 }
 902
 903 /*
 904  * Prevent further output on the passed console device so that (for example)
 905  * serial drivers can disable console output before suspending a port, and can
 906  * re-enable output afterwards.
 907  */
 908 void console_stop(struct console *console)
 909 {
 910         acquire_console_sem();
 911         console->flags &= ~CON_ENABLED;
 912         release_console_sem();
 913 }
 914 EXPORT_SYMBOL(console_stop);
 915
 916 void console_start(struct console *console)
 917 {
 918         acquire_console_sem();
 919         console->flags |= CON_ENABLED;
 920         release_console_sem();
 921 }
 922 EXPORT_SYMBOL(console_start);
 923
 924 /*
 925  * The console driver calls this routine during kernel initialization
 926  * to register the console printing procedure with printk() and to
 927  * print any messages that were printed by the kernel before the
 928  * console driver was initialized.
 929  */
 930 void register_console(struct console *console)
 931 {
 932         int i;
 933         unsigned long flags;
 934
 935         if (preferred_console < 0)
 936                 preferred_console = selected_console;
 937
 938         /*
 939          *      See if we want to use this console driver. If we
 940          *      didn't select a console we take the first one
 941          *      that registers here.
 942          */
 943         if (preferred_console < 0) {
 944                 if (console->index < 0)
 945                         console->index = 0;
 946                 if (console->setup == NULL ||
 947                     console->setup(console, NULL) == 0) {
 948                         console->flags |= CON_ENABLED | CON_CONSDEV;
 949                         preferred_console = 0;
 950                 }
 951         }
 952
 953         /*
 954          *      See if this console matches one we selected on
 955          *      the command line.
 956          */
 957         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 958                         i++) {
 959                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 960                         continue;
 961                 if (console->index >= 0 &&
 962                     console->index != console_cmdline[i].index)
 963                         continue;
 964                 if (console->index < 0)
 965                         console->index = console_cmdline[i].index;
 966                 if (console->setup &&
 967                     console->setup(console, console_cmdline[i].options) != 0)
 968                         break;
 969                 console->flags |= CON_ENABLED;
 970                 console->index = console_cmdline[i].index;
 971                 if (i == selected_console) {
 972                         console->flags |= CON_CONSDEV;
 973                         preferred_console = selected_console;
 974                 }
 975                 break;
 976         }
 977
 978         if (!(console->flags & CON_ENABLED))
 979                 return;
 980
 981         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 982                 unregister_console(console_drivers);
 983                 console->flags &= ~CON_PRINTBUFFER;
 984         }
 985
 986         /*
 987          *      Put this console in the list - keep the
 988          *      preferred driver at the head of the list.
 989          */
 990         acquire_console_sem();
 991         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 992                 console->next = console_drivers;
 993                 console_drivers = console;
 994                 if (console->next)
 995                         console->next->flags &= ~CON_CONSDEV;
 996         } else {
 997                 console->next = console_drivers->next;
 998                 console_drivers->next = console;
 999         }
1000         if (console->flags & CON_PRINTBUFFER) {
1001                 /*
1002                  * release_console_sem() will print out the buffered messages
1003                  * for us.
1004                  */
1005                 spin_lock_irqsave(&logbuf_lock, flags);
1006                 con_start = log_start;
1007                 spin_unlock_irqrestore(&logbuf_lock, flags);
1008         }
1009         release_console_sem();
1010 }
1011 EXPORT_SYMBOL(register_console);
1012
1013 int unregister_console(struct console *console)
1014 {
1015         struct console *a, *b;
1016         int res = 1;
1017
1018         acquire_console_sem();
1019         if (console_drivers == console) {
1020                 console_drivers=console->next;
1021                 res = 0;
1022         } else if (console_drivers) {
1023                 for (a=console_drivers->next, b=console_drivers ;
1024                      a; b=a, a=b->next) {
1025                         if (a == console) {
1026                                 b->next = a->next;
1027                                 res = 0;
1028                                 break;
1029                         }
1030                 }
1031         }
1032
1033         /* If last console is removed, we re-enable picking the first
1034          * one that gets registered. Without that, pmac early boot console
1035          * would prevent fbcon from taking over.
1036          *
1037          * If this isn't the last console and it has CON_CONSDEV set, we
1038          * need to set it on the next preferred console.
1039          */
1040         if (console_drivers == NULL)
1041                 preferred_console = selected_console;
1042         else if (console->flags & CON_CONSDEV)
1043                 console_drivers->flags |= CON_CONSDEV;
1044
1045         release_console_sem();
1046         return res;
1047 }
1048 EXPORT_SYMBOL(unregister_console);
1049
1050 /**
1051  * tty_write_message - write a message to a certain tty, not just the console.
1052  * @tty: the destination tty_struct
1053  * @msg: the message to write
1054  *
1055  * This is used for messages that need to be redirected to a specific tty.
1056  * We don't put it into the syslog queue right now maybe in the future if
1057  * really needed.
1058  */
1059 void tty_write_message(struct tty_struct *tty, char *msg)
1060 {
1061         if (tty && tty->driver->write)
1062                 tty->driver->write(tty, msg, strlen(msg));
1063         return;
1064 }
1065
1066 /*
1067  * printk rate limiting, lifted from the networking subsystem.
1068  *
1069  * This enforces a rate limit: not more than one kernel message
1070  * every printk_ratelimit_jiffies to make a denial-of-service
1071  * attack impossible.
1072  */
1073 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1074 {
1075         static DEFINE_SPINLOCK(ratelimit_lock);
1076         static unsigned long toks = 10 * 5 * HZ;
1077         static unsigned long last_msg;
1078         static int missed;
1079         unsigned long flags;
1080         unsigned long now = jiffies;
1081
1082         spin_lock_irqsave(&ratelimit_lock, flags);
1083         toks += now - last_msg;
1084         last_msg = now;
1085         if (toks > (ratelimit_burst * ratelimit_jiffies))
1086                 toks = ratelimit_burst * ratelimit_jiffies;
1087         if (toks >= ratelimit_jiffies) {
1088                 int lost = missed;
1089
1090                 missed = 0;
1091                 toks -= ratelimit_jiffies;
1092                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1093                 if (lost)
1094                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1095                 return 1;
1096         }
1097         missed++;
1098         spin_unlock_irqrestore(&ratelimit_lock, flags);
1099         return 0;
1100 }
1101 EXPORT_SYMBOL(__printk_ratelimit);
1102
1103 /* minimum time in jiffies between messages */
1104 int printk_ratelimit_jiffies = 5 * HZ;
1105
1106 /* number of messages we send before ratelimiting */
1107 int printk_ratelimit_burst = 10;
1108
1109 int printk_ratelimit(void)
1110 {
1111         return __printk_ratelimit(printk_ratelimit_jiffies,
1112                                 printk_ratelimit_burst);
1113 }
1114 EXPORT_SYMBOL(printk_ratelimit);
1115
1116 /**
1117  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1118  * @caller_jiffies: pointer to caller's state
1119  * @interval_msecs: minimum interval between prints
1120  *
1121  * printk_timed_ratelimit() returns true if more than @interval_msecs
1122  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1123  * returned true.
1124  */
1125 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1126                         unsigned int interval_msecs)
1127 {
1128         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1129                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1130                 return true;
1131         }
1132         return false;
1133 }
1134 EXPORT_SYMBOL(printk_timed_ratelimit);