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 /*
 337  * Write out chars from start to end - 1 inclusive
 338  */
 339 static void _call_console_drivers(unsigned long start,
 340                                 unsigned long end, int msg_log_level)
 341 {
 342         if (msg_log_level < console_loglevel &&
 343                         console_drivers && start != end) {
 344                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 345                         /* wrapped write */
 346                         __call_console_drivers(start & LOG_BUF_MASK,
 347                                                 log_buf_len);
 348                         __call_console_drivers(0, end & LOG_BUF_MASK);
 349                 } else {
 350                         __call_console_drivers(start, end);
 351                 }
 352         }
 353 }
 354
 355 /*
 356  * Call the console drivers, asking them to write out
 357  * log_buf[start] to log_buf[end - 1].
 358  * The console_sem must be held.
 359  */
 360 static void call_console_drivers(unsigned long start, unsigned long end)
 361 {
 362         unsigned long cur_index, start_print;
 363         static int msg_level = -1;
 364
 365         BUG_ON(((long)(start - end)) > 0);
 366
 367         cur_index = start;
 368         start_print = start;
 369         while (cur_index != end) {
 370                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 371                                 LOG_BUF(cur_index + 0) == '<' &&
 372                                 LOG_BUF(cur_index + 1) >= '0' &&
 373                                 LOG_BUF(cur_index + 1) <= '7' &&
 374                                 LOG_BUF(cur_index + 2) == '>') {
 375                         msg_level = LOG_BUF(cur_index + 1) - '0';
 376                         cur_index += 3;
 377                         start_print = cur_index;
 378                 }
 379                 while (cur_index != end) {
 380                         char c = LOG_BUF(cur_index);
 381
 382                         cur_index++;
 383                         if (c == '\n') {
 384                                 if (msg_level < 0) {
 385                                         /*
 386                                          * printk() has already given us loglevel tags in
 387                                          * the buffer.  This code is here in case the
 388                                          * log buffer has wrapped right round and scribbled
 389                                          * on those tags
 390                                          */
 391                                         msg_level = default_message_loglevel;
 392                                 }
 393                                 _call_console_drivers(start_print, cur_index, msg_level);
 394                                 msg_level = -1;
 395                                 start_print = cur_index;
 396                                 break;
 397                         }
 398                 }
 399         }
 400         _call_console_drivers(start_print, end, msg_level);
 401 }
 402
 403 static void emit_log_char(char c)
 404 {
 405         LOG_BUF(log_end) = c;
 406         log_end++;
 407         if (log_end - log_start > log_buf_len)
 408                 log_start = log_end - log_buf_len;
 409         if (log_end - con_start > log_buf_len)
 410                 con_start = log_end - log_buf_len;
 411         if (logged_chars < log_buf_len)
 412                 logged_chars++;
 413 }
 414
 415 /*
 416  * Zap console related locks when oopsing. Only zap at most once
 417  * every 10 seconds, to leave time for slow consoles to print a
 418  * full oops.
 419  */
 420 static void zap_locks(void)
 421 {
 422         static unsigned long oops_timestamp;
 423
 424         if (time_after_eq(jiffies, oops_timestamp) &&
 425                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 426                 return;
 427
 428         oops_timestamp = jiffies;
 429
 430         /* If a crash is occurring, make sure we can't deadlock */
 431         spin_lock_init(&logbuf_lock);
 432         /* And make sure that we print immediately */
 433         init_MUTEX(&console_sem);
 434 }
 435
 436 #if defined(CONFIG_PRINTK_TIME)
 437 static int printk_time = 1;
 438 #else
 439 static int printk_time = 0;
 440 #endif
 441 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 442
 443 static int __init printk_time_setup(char *str)
 444 {
 445         if (*str)
 446                 return 0;
 447         printk_time = 1;
 448         return 1;
 449 }
 450
 451 __setup("time", printk_time_setup);
 452
 453 __attribute__((weak)) unsigned long long printk_clock(void)
 454 {
 455         return sched_clock();
 456 }
 457
 458 /* Check if we have any console registered that can be called early in boot. */
 459 static int have_callable_console(void)
 460 {
 461         struct console *con;
 462
 463         for (con = console_drivers; con; con = con->next)
 464                 if (con->flags & CON_ANYTIME)
 465                         return 1;
 466
 467         return 0;
 468 }
 469
 470 /**
 471  * printk - print a kernel message
 472  * @fmt: format string
 473  *
 474  * This is printk.  It can be called from any context.  We want it to work.
 475  *
 476  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 477  * call the console drivers.  If we fail to get the semaphore we place the output
 478  * into the log buffer and return.  The current holder of the console_sem will
 479  * notice the new output in release_console_sem() and will send it to the
 480  * consoles before releasing the semaphore.
 481  *
 482  * One effect of this deferred printing is that code which calls printk() and
 483  * then changes console_loglevel may break. This is because console_loglevel
 484  * is inspected when the actual printing occurs.
 485  *
 486  * See also:
 487  * printf(3)
 488  */
 489
 490 asmlinkage int printk(const char *fmt, ...)
 491 {
 492         va_list args;
 493         int r;
 494
 495         va_start(args, fmt);
 496         r = vprintk(fmt, args);
 497         va_end(args);
 498
 499         return r;
 500 }
 501
 502 /* cpu currently holding logbuf_lock */
 503 static volatile unsigned int printk_cpu = UINT_MAX;
 504
 505 asmlinkage int vprintk(const char *fmt, va_list args)
 506 {
 507         unsigned long flags;
 508         int printed_len;
 509         char *p;
 510         static char printk_buf[1024];
 511         static int log_level_unknown = 1;
 512
 513         preempt_disable();
 514         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 515                 /* If a crash is occurring during printk() on this CPU,
 516                  * make sure we can't deadlock */
 517                 zap_locks();
 518
 519         /* This stops the holder of console_sem just where we want him */
 520         local_irq_save(flags);
 521         lockdep_off();
 522         spin_lock(&logbuf_lock);
 523         printk_cpu = smp_processor_id();
 524
 525         /* Emit the output into the temporary buffer */
 526         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 527
 528         /*
 529          * Copy the output into log_buf.  If the caller didn't provide
 530          * appropriate log level tags, we insert them here
 531          */
 532         for (p = printk_buf; *p; p++) {
 533                 if (log_level_unknown) {
 534                         /* log_level_unknown signals the start of a new line */
 535                         if (printk_time) {
 536                                 int loglev_char;
 537                                 char tbuf[50], *tp;
 538                                 unsigned tlen;
 539                                 unsigned long long t;
 540                                 unsigned long nanosec_rem;
 541
 542                                 /*
 543                                  * force the log level token to be
 544                                  * before the time output.
 545                                  */
 546                                 if (p[0] == '<' && p[1] >='0' &&
 547                                    p[1] <= '7' && p[2] == '>') {
 548                                         loglev_char = p[1];
 549                                         p += 3;
 550                                         printed_len -= 3;
 551                                 } else {
 552                                         loglev_char = default_message_loglevel
 553                                                 + '0';
 554                                 }
 555                                 t = printk_clock();
 556                                 nanosec_rem = do_div(t, 1000000000);
 557                                 tlen = sprintf(tbuf,
 558                                                 "<%c>[%5lu.%06lu] ",
 559                                                 loglev_char,
 560                                                 (unsigned long)t,
 561                                                 nanosec_rem/1000);
 562
 563                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 564                                         emit_log_char(*tp);
 565                                 printed_len += tlen;
 566                         } else {
 567                                 if (p[0] != '<' || p[1] < '0' ||
 568                                    p[1] > '7' || p[2] != '>') {
 569                                         emit_log_char('<');
 570                                         emit_log_char(default_message_loglevel
 571                                                 + '0');
 572                                         emit_log_char('>');
 573                                         printed_len += 3;
 574                                 }
 575                         }
 576                         log_level_unknown = 0;
 577                         if (!*p)
 578                                 break;
 579                 }
 580                 emit_log_char(*p);
 581                 if (*p == '\n')
 582                         log_level_unknown = 1;
 583         }
 584
 585         if (!down_trylock(&console_sem)) {
 586                 /*
 587                  * We own the drivers.  We can drop the spinlock and
 588                  * let release_console_sem() print the text, maybe ...
 589                  */
 590                 console_locked = 1;
 591                 printk_cpu = UINT_MAX;
 592                 spin_unlock(&logbuf_lock);
 593
 594                 /*
 595                  * Console drivers may assume that per-cpu resources have
 596                  * been allocated. So unless they're explicitly marked as
 597                  * being able to cope (CON_ANYTIME) don't call them until
 598                  * this CPU is officially up.
 599                  */
 600                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 601                         console_may_schedule = 0;
 602                         release_console_sem();
 603                 } else {
 604                         /* Release by hand to avoid flushing the buffer. */
 605                         console_locked = 0;
 606                         up(&console_sem);
 607                 }
 608                 lockdep_on();
 609                 local_irq_restore(flags);
 610         } else {
 611                 /*
 612                  * Someone else owns the drivers.  We drop the spinlock, which
 613                  * allows the semaphore holder to proceed and to call the
 614                  * console drivers with the output which we just produced.
 615                  */
 616                 printk_cpu = UINT_MAX;
 617                 spin_unlock(&logbuf_lock);
 618                 lockdep_on();
 619                 local_irq_restore(flags);
 620         }
 621
 622         preempt_enable();
 623         return printed_len;
 624 }
 625 EXPORT_SYMBOL(printk);
 626 EXPORT_SYMBOL(vprintk);
 627
 628 #else
 629
 630 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 631 {
 632         return -ENOSYS;
 633 }
 634
 635 static void call_console_drivers(unsigned long start, unsigned long end)
 636 {
 637 }
 638
 639 #endif
 640
 641 /*
 642  * Set up a list of consoles.  Called from init/main.c
 643  */
 644 static int __init console_setup(char *str)
 645 {
 646         char name[sizeof(console_cmdline[0].name)];
 647         char *s, *options;
 648         int idx;
 649
 650         /*
 651          * Decode str into name, index, options.
 652          */
 653         if (str[0] >= '0' && str[0] <= '9') {
 654                 strcpy(name, "ttyS");
 655                 strncpy(name + 4, str, sizeof(name) - 5);
 656         } else {
 657                 strncpy(name, str, sizeof(name) - 1);
 658         }
 659         name[sizeof(name) - 1] = 0;
 660         if ((options = strchr(str, ',')) != NULL)
 661                 *(options++) = 0;
 662 #ifdef __sparc__
 663         if (!strcmp(str, "ttya"))
 664                 strcpy(name, "ttyS0");
 665         if (!strcmp(str, "ttyb"))
 666                 strcpy(name, "ttyS1");
 667 #endif
 668         for (s = name; *s; s++)
 669                 if ((*s >= '0' && *s <= '9') || *s == ',')
 670                         break;
 671         idx = simple_strtoul(s, NULL, 10);
 672         *s = 0;
 673
 674         add_preferred_console(name, idx, options);
 675         return 1;
 676 }
 677 __setup("console=", console_setup);
 678
 679 /**
 680  * add_preferred_console - add a device to the list of preferred consoles.
 681  * @name: device name
 682  * @idx: device index
 683  * @options: options for this console
 684  *
 685  * The last preferred console added will be used for kernel messages
 686  * and stdin/out/err for init.  Normally this is used by console_setup
 687  * above to handle user-supplied console arguments; however it can also
 688  * be used by arch-specific code either to override the user or more
 689  * commonly to provide a default console (ie from PROM variables) when
 690  * the user has not supplied one.
 691  */
 692 int __init add_preferred_console(char *name, int idx, char *options)
 693 {
 694         struct console_cmdline *c;
 695         int i;
 696
 697         /*
 698          *      See if this tty is not yet registered, and
 699          *      if we have a slot free.
 700          */
 701         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 702                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 703                           console_cmdline[i].index == idx) {
 704                                 selected_console = i;
 705                                 return 0;
 706                 }
 707         if (i == MAX_CMDLINECONSOLES)
 708                 return -E2BIG;
 709         selected_console = i;
 710         c = &console_cmdline[i];
 711         memcpy(c->name, name, sizeof(c->name));
 712         c->name[sizeof(c->name) - 1] = 0;
 713         c->options = options;
 714         c->index = idx;
 715         return 0;
 716 }
 717
 718 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 719 /**
 720  * suspend_console - suspend the console subsystem
 721  *
 722  * This disables printk() while we go into suspend states
 723  */
 724 void suspend_console(void)
 725 {
 726         printk("Suspending console(s)\n");
 727         acquire_console_sem();
 728         console_suspended = 1;
 729 }
 730
 731 void resume_console(void)
 732 {
 733         console_suspended = 0;
 734         release_console_sem();
 735 }
 736 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 737
 738 /**
 739  * acquire_console_sem - lock the console system for exclusive use.
 740  *
 741  * Acquires a semaphore which guarantees that the caller has
 742  * exclusive access to the console system and the console_drivers list.
 743  *
 744  * Can sleep, returns nothing.
 745  */
 746 void acquire_console_sem(void)
 747 {
 748         BUG_ON(in_interrupt());
 749         if (console_suspended) {
 750                 down(&secondary_console_sem);
 751                 return;
 752         }
 753         down(&console_sem);
 754         console_locked = 1;
 755         console_may_schedule = 1;
 756 }
 757 EXPORT_SYMBOL(acquire_console_sem);
 758
 759 int try_acquire_console_sem(void)
 760 {
 761         if (down_trylock(&console_sem))
 762                 return -1;
 763         console_locked = 1;
 764         console_may_schedule = 0;
 765         return 0;
 766 }
 767 EXPORT_SYMBOL(try_acquire_console_sem);
 768
 769 int is_console_locked(void)
 770 {
 771         return console_locked;
 772 }
 773
 774 /**
 775  * release_console_sem - unlock the console system
 776  *
 777  * Releases the semaphore which the caller holds on the console system
 778  * and the console driver list.
 779  *
 780  * While the semaphore was held, console output may have been buffered
 781  * by printk().  If this is the case, release_console_sem() emits
 782  * the output prior to releasing the semaphore.
 783  *
 784  * If there is output waiting for klogd, we wake it up.
 785  *
 786  * release_console_sem() may be called from any context.
 787  */
 788 void release_console_sem(void)
 789 {
 790         unsigned long flags;
 791         unsigned long _con_start, _log_end;
 792         unsigned long wake_klogd = 0;
 793
 794         if (console_suspended) {
 795                 up(&secondary_console_sem);
 796                 return;
 797         }
 798
 799         console_may_schedule = 0;
 800
 801         for ( ; ; ) {
 802                 spin_lock_irqsave(&logbuf_lock, flags);
 803                 wake_klogd |= log_start - log_end;
 804                 if (con_start == log_end)
 805                         break;                  /* Nothing to print */
 806                 _con_start = con_start;
 807                 _log_end = log_end;
 808                 con_start = log_end;            /* Flush */
 809                 spin_unlock(&logbuf_lock);
 810                 call_console_drivers(_con_start, _log_end);
 811                 local_irq_restore(flags);
 812         }
 813         console_locked = 0;
 814         up(&console_sem);
 815         spin_unlock_irqrestore(&logbuf_lock, flags);
 816         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 817                 wake_up_interruptible(&log_wait);
 818 }
 819 EXPORT_SYMBOL(release_console_sem);
 820
 821 /**
 822  * console_conditional_schedule - yield the CPU if required
 823  *
 824  * If the console code is currently allowed to sleep, and
 825  * if this CPU should yield the CPU to another task, do
 826  * so here.
 827  *
 828  * Must be called within acquire_console_sem().
 829  */
 830 void __sched console_conditional_schedule(void)
 831 {
 832         if (console_may_schedule)
 833                 cond_resched();
 834 }
 835 EXPORT_SYMBOL(console_conditional_schedule);
 836
 837 void console_print(const char *s)
 838 {
 839         printk(KERN_EMERG "%s", s);
 840 }
 841 EXPORT_SYMBOL(console_print);
 842
 843 void console_unblank(void)
 844 {
 845         struct console *c;
 846
 847         /*
 848          * console_unblank can no longer be called in interrupt context unless
 849          * oops_in_progress is set to 1..
 850          */
 851         if (oops_in_progress) {
 852                 if (down_trylock(&console_sem) != 0)
 853                         return;
 854         } else
 855                 acquire_console_sem();
 856
 857         console_locked = 1;
 858         console_may_schedule = 0;
 859         for (c = console_drivers; c != NULL; c = c->next)
 860                 if ((c->flags & CON_ENABLED) && c->unblank)
 861                         c->unblank();
 862         release_console_sem();
 863 }
 864
 865 /*
 866  * Return the console tty driver structure and its associated index
 867  */
 868 struct tty_driver *console_device(int *index)
 869 {
 870         struct console *c;
 871         struct tty_driver *driver = NULL;
 872
 873         acquire_console_sem();
 874         for (c = console_drivers; c != NULL; c = c->next) {
 875                 if (!c->device)
 876                         continue;
 877                 driver = c->device(c, index);
 878                 if (driver)
 879                         break;
 880         }
 881         release_console_sem();
 882         return driver;
 883 }
 884
 885 /*
 886  * Prevent further output on the passed console device so that (for example)
 887  * serial drivers can disable console output before suspending a port, and can
 888  * re-enable output afterwards.
 889  */
 890 void console_stop(struct console *console)
 891 {
 892         acquire_console_sem();
 893         console->flags &= ~CON_ENABLED;
 894         release_console_sem();
 895 }
 896 EXPORT_SYMBOL(console_stop);
 897
 898 void console_start(struct console *console)
 899 {
 900         acquire_console_sem();
 901         console->flags |= CON_ENABLED;
 902         release_console_sem();
 903 }
 904 EXPORT_SYMBOL(console_start);
 905
 906 /*
 907  * The console driver calls this routine during kernel initialization
 908  * to register the console printing procedure with printk() and to
 909  * print any messages that were printed by the kernel before the
 910  * console driver was initialized.
 911  */
 912 void register_console(struct console *console)
 913 {
 914         int i;
 915         unsigned long flags;
 916
 917         if (preferred_console < 0)
 918                 preferred_console = selected_console;
 919
 920         /*
 921          *      See if we want to use this console driver. If we
 922          *      didn't select a console we take the first one
 923          *      that registers here.
 924          */
 925         if (preferred_console < 0) {
 926                 if (console->index < 0)
 927                         console->index = 0;
 928                 if (console->setup == NULL ||
 929                     console->setup(console, NULL) == 0) {
 930                         console->flags |= CON_ENABLED | CON_CONSDEV;
 931                         preferred_console = 0;
 932                 }
 933         }
 934
 935         /*
 936          *      See if this console matches one we selected on
 937          *      the command line.
 938          */
 939         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 940                         i++) {
 941                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 942                         continue;
 943                 if (console->index >= 0 &&
 944                     console->index != console_cmdline[i].index)
 945                         continue;
 946                 if (console->index < 0)
 947                         console->index = console_cmdline[i].index;
 948                 if (console->setup &&
 949                     console->setup(console, console_cmdline[i].options) != 0)
 950                         break;
 951                 console->flags |= CON_ENABLED;
 952                 console->index = console_cmdline[i].index;
 953                 if (i == selected_console) {
 954                         console->flags |= CON_CONSDEV;
 955                         preferred_console = selected_console;
 956                 }
 957                 break;
 958         }
 959
 960         if (!(console->flags & CON_ENABLED))
 961                 return;
 962
 963         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 964                 unregister_console(console_drivers);
 965                 console->flags &= ~CON_PRINTBUFFER;
 966         }
 967
 968         /*
 969          *      Put this console in the list - keep the
 970          *      preferred driver at the head of the list.
 971          */
 972         acquire_console_sem();
 973         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 974                 console->next = console_drivers;
 975                 console_drivers = console;
 976                 if (console->next)
 977                         console->next->flags &= ~CON_CONSDEV;
 978         } else {
 979                 console->next = console_drivers->next;
 980                 console_drivers->next = console;
 981         }
 982         if (console->flags & CON_PRINTBUFFER) {
 983                 /*
 984                  * release_console_sem() will print out the buffered messages
 985                  * for us.
 986                  */
 987                 spin_lock_irqsave(&logbuf_lock, flags);
 988                 con_start = log_start;
 989                 spin_unlock_irqrestore(&logbuf_lock, flags);
 990         }
 991         release_console_sem();
 992 }
 993 EXPORT_SYMBOL(register_console);
 994
 995 int unregister_console(struct console *console)
 996 {
 997         struct console *a, *b;
 998         int res = 1;
 999
1000         acquire_console_sem();
1001         if (console_drivers == console) {
1002                 console_drivers=console->next;
1003                 res = 0;
1004         } else if (console_drivers) {
1005                 for (a=console_drivers->next, b=console_drivers ;
1006                      a; b=a, a=b->next) {
1007                         if (a == console) {
1008                                 b->next = a->next;
1009                                 res = 0;
1010                                 break;
1011                         }
1012                 }
1013         }
1014
1015         /* If last console is removed, we re-enable picking the first
1016          * one that gets registered. Without that, pmac early boot console
1017          * would prevent fbcon from taking over.
1018          *
1019          * If this isn't the last console and it has CON_CONSDEV set, we
1020          * need to set it on the next preferred console.
1021          */
1022         if (console_drivers == NULL)
1023                 preferred_console = selected_console;
1024         else if (console->flags & CON_CONSDEV)
1025                 console_drivers->flags |= CON_CONSDEV;
1026
1027         release_console_sem();
1028         return res;
1029 }
1030 EXPORT_SYMBOL(unregister_console);
1031
1032 /**
1033  * tty_write_message - write a message to a certain tty, not just the console.
1034  * @tty: the destination tty_struct
1035  * @msg: the message to write
1036  *
1037  * This is used for messages that need to be redirected to a specific tty.
1038  * We don't put it into the syslog queue right now maybe in the future if
1039  * really needed.
1040  */
1041 void tty_write_message(struct tty_struct *tty, char *msg)
1042 {
1043         if (tty && tty->driver->write)
1044                 tty->driver->write(tty, msg, strlen(msg));
1045         return;
1046 }
1047
1048 /*
1049  * printk rate limiting, lifted from the networking subsystem.
1050  *
1051  * This enforces a rate limit: not more than one kernel message
1052  * every printk_ratelimit_jiffies to make a denial-of-service
1053  * attack impossible.
1054  */
1055 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1056 {
1057         static DEFINE_SPINLOCK(ratelimit_lock);
1058         static unsigned long toks = 10 * 5 * HZ;
1059         static unsigned long last_msg;
1060         static int missed;
1061         unsigned long flags;
1062         unsigned long now = jiffies;
1063
1064         spin_lock_irqsave(&ratelimit_lock, flags);
1065         toks += now - last_msg;
1066         last_msg = now;
1067         if (toks > (ratelimit_burst * ratelimit_jiffies))
1068                 toks = ratelimit_burst * ratelimit_jiffies;
1069         if (toks >= ratelimit_jiffies) {
1070                 int lost = missed;
1071
1072                 missed = 0;
1073                 toks -= ratelimit_jiffies;
1074                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1075                 if (lost)
1076                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1077                 return 1;
1078         }
1079         missed++;
1080         spin_unlock_irqrestore(&ratelimit_lock, flags);
1081         return 0;
1082 }
1083 EXPORT_SYMBOL(__printk_ratelimit);
1084
1085 /* minimum time in jiffies between messages */
1086 int printk_ratelimit_jiffies = 5 * HZ;
1087
1088 /* number of messages we send before ratelimiting */
1089 int printk_ratelimit_burst = 10;
1090
1091 int printk_ratelimit(void)
1092 {
1093         return __printk_ratelimit(printk_ratelimit_jiffies,
1094                                 printk_ratelimit_burst);
1095 }
1096 EXPORT_SYMBOL(printk_ratelimit);
1097
1098 /**
1099  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1100  * @caller_jiffies: pointer to caller's state
1101  * @interval_msecs: minimum interval between prints
1102  *
1103  * printk_timed_ratelimit() returns true if more than @interval_msecs
1104  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1105  * returned true.
1106  */
1107 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1108                         unsigned int interval_msecs)
1109 {
1110         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1111                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1112                 return true;
1113         }
1114         return false;
1115 }
1116 EXPORT_SYMBOL(printk_timed_ratelimit);