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
  35 #include <asm/uaccess.h>
  36
  37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  38
  39 #ifdef        CONFIG_DEBUG_LL
  40 extern void printascii(char *);
  41 #endif
  42
  43 /* printk's without a loglevel use this.. */
  44 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  45
  46 /* We show everything that is MORE important than this.. */
  47 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  48 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  49
  50 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  51
  52 int console_printk[4] = {
  53         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  54         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  55         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  56         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  57 };
  58
  59 EXPORT_UNUSED_SYMBOL(console_printk);  /*  June 2006  */
  60
  61 /*
  62  * Low lever drivers may need that to know if they can schedule in
  63  * their unblank() callback or not. So let's export it.
  64  */
  65 int oops_in_progress;
  66 EXPORT_SYMBOL(oops_in_progress);
  67
  68 /*
  69  * console_sem protects the console_drivers list, and also
  70  * provides serialisation for access to the entire console
  71  * driver system.
  72  */
  73 static DECLARE_MUTEX(console_sem);
  74 static DECLARE_MUTEX(secondary_console_sem);
  75 struct console *console_drivers;
  76 /*
  77  * This is used for debugging the mess that is the VT code by
  78  * keeping track if we have the console semaphore held. It's
  79  * definitely not the perfect debug tool (we don't know if _WE_
  80  * hold it are racing, but it helps tracking those weird code
  81  * path in the console code where we end up in places I want
  82  * locked without the console sempahore held
  83  */
  84 static int console_locked, console_suspended;
  85
  86 /*
  87  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  88  * It is also used in interesting ways to provide interlocking in
  89  * release_console_sem().
  90  */
  91 static DEFINE_SPINLOCK(logbuf_lock);
  92
  93 #define LOG_BUF_MASK    (log_buf_len-1)
  94 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  95
  96 /*
  97  * The indices into log_buf are not constrained to log_buf_len - they
  98  * must be masked before subscripting
  99  */
 100 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
 101 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
 102 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
 103
 104 /*
 105  *      Array of consoles built from command line options (console=)
 106  */
 107 struct console_cmdline
 108 {
 109         char    name[8];                        /* Name of the driver       */
 110         int     index;                          /* Minor dev. to use        */
 111         char    *options;                       /* Options for the driver   */
 112 };
 113
 114 #define MAX_CMDLINECONSOLES 8
 115
 116 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 117 static int selected_console = -1;
 118 static int preferred_console = -1;
 119
 120 /* Flag: console code may call schedule() */
 121 static int console_may_schedule;
 122
 123 #ifdef CONFIG_PRINTK
 124
 125 static char __log_buf[__LOG_BUF_LEN];
 126 static char *log_buf = __log_buf;
 127 static int log_buf_len = __LOG_BUF_LEN;
 128 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 129
 130 static int __init log_buf_len_setup(char *str)
 131 {
 132         unsigned long size = memparse(str, &str);
 133         unsigned long flags;
 134
 135         if (size)
 136                 size = roundup_pow_of_two(size);
 137         if (size > log_buf_len) {
 138                 unsigned long start, dest_idx, offset;
 139                 char *new_log_buf;
 140
 141                 new_log_buf = alloc_bootmem(size);
 142                 if (!new_log_buf) {
 143                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 144                         goto out;
 145                 }
 146
 147                 spin_lock_irqsave(&logbuf_lock, flags);
 148                 log_buf_len = size;
 149                 log_buf = new_log_buf;
 150
 151                 offset = start = min(con_start, log_start);
 152                 dest_idx = 0;
 153                 while (start != log_end) {
 154                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 155                         start++;
 156                         dest_idx++;
 157                 }
 158                 log_start -= offset;
 159                 con_start -= offset;
 160                 log_end -= offset;
 161                 spin_unlock_irqrestore(&logbuf_lock, flags);
 162
 163                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 164         }
 165 out:
 166         return 1;
 167 }
 168
 169 __setup("log_buf_len=", log_buf_len_setup);
 170
 171 /*
 172  * Commands to do_syslog:
 173  *
 174  *      0 -- Close the log.  Currently a NOP.
 175  *      1 -- Open the log. Currently a NOP.
 176  *      2 -- Read from the log.
 177  *      3 -- Read all messages remaining in the ring buffer.
 178  *      4 -- Read and clear all messages remaining in the ring buffer
 179  *      5 -- Clear ring buffer.
 180  *      6 -- Disable printk's to console
 181  *      7 -- Enable printk's to console
 182  *      8 -- Set level of messages printed to console
 183  *      9 -- Return number of unread characters in the log buffer
 184  *     10 -- Return size of the log buffer
 185  */
 186 int do_syslog(int type, char __user *buf, int len)
 187 {
 188         unsigned long i, j, limit, count;
 189         int do_clear = 0;
 190         char c;
 191         int error = 0;
 192
 193         error = security_syslog(type);
 194         if (error)
 195                 return error;
 196
 197         switch (type) {
 198         case 0:         /* Close log */
 199                 break;
 200         case 1:         /* Open log */
 201                 break;
 202         case 2:         /* Read from log */
 203                 error = -EINVAL;
 204                 if (!buf || len < 0)
 205                         goto out;
 206                 error = 0;
 207                 if (!len)
 208                         goto out;
 209                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 210                         error = -EFAULT;
 211                         goto out;
 212                 }
 213                 error = wait_event_interruptible(log_wait,
 214                                                         (log_start - log_end));
 215                 if (error)
 216                         goto out;
 217                 i = 0;
 218                 spin_lock_irq(&logbuf_lock);
 219                 while (!error && (log_start != log_end) && i < len) {
 220                         c = LOG_BUF(log_start);
 221                         log_start++;
 222                         spin_unlock_irq(&logbuf_lock);
 223                         error = __put_user(c,buf);
 224                         buf++;
 225                         i++;
 226                         cond_resched();
 227                         spin_lock_irq(&logbuf_lock);
 228                 }
 229                 spin_unlock_irq(&logbuf_lock);
 230                 if (!error)
 231                         error = i;
 232                 break;
 233         case 4:         /* Read/clear last kernel messages */
 234                 do_clear = 1;
 235                 /* FALL THRU */
 236         case 3:         /* Read last kernel messages */
 237                 error = -EINVAL;
 238                 if (!buf || len < 0)
 239                         goto out;
 240                 error = 0;
 241                 if (!len)
 242                         goto out;
 243                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 244                         error = -EFAULT;
 245                         goto out;
 246                 }
 247                 count = len;
 248                 if (count > log_buf_len)
 249                         count = log_buf_len;
 250                 spin_lock_irq(&logbuf_lock);
 251                 if (count > logged_chars)
 252                         count = logged_chars;
 253                 if (do_clear)
 254                         logged_chars = 0;
 255                 limit = log_end;
 256                 /*
 257                  * __put_user() could sleep, and while we sleep
 258                  * printk() could overwrite the messages
 259                  * we try to copy to user space. Therefore
 260                  * the messages are copied in reverse. <manfreds>
 261                  */
 262                 for (i = 0; i < count && !error; i++) {
 263                         j = limit-1-i;
 264                         if (j + log_buf_len < log_end)
 265                                 break;
 266                         c = LOG_BUF(j);
 267                         spin_unlock_irq(&logbuf_lock);
 268                         error = __put_user(c,&buf[count-1-i]);
 269                         cond_resched();
 270                         spin_lock_irq(&logbuf_lock);
 271                 }
 272                 spin_unlock_irq(&logbuf_lock);
 273                 if (error)
 274                         break;
 275                 error = i;
 276                 if (i != count) {
 277                         int offset = count-error;
 278                         /* buffer overflow during copy, correct user buffer. */
 279                         for (i = 0; i < error; i++) {
 280                                 if (__get_user(c,&buf[i+offset]) ||
 281                                     __put_user(c,&buf[i])) {
 282                                         error = -EFAULT;
 283                                         break;
 284                                 }
 285                                 cond_resched();
 286                         }
 287                 }
 288                 break;
 289         case 5:         /* Clear ring buffer */
 290                 logged_chars = 0;
 291                 break;
 292         case 6:         /* Disable logging to console */
 293                 console_loglevel = minimum_console_loglevel;
 294                 break;
 295         case 7:         /* Enable logging to console */
 296                 console_loglevel = default_console_loglevel;
 297                 break;
 298         case 8:         /* Set level of messages printed to console */
 299                 error = -EINVAL;
 300                 if (len < 1 || len > 8)
 301                         goto out;
 302                 if (len < minimum_console_loglevel)
 303                         len = minimum_console_loglevel;
 304                 console_loglevel = len;
 305                 error = 0;
 306                 break;
 307         case 9:         /* Number of chars in the log buffer */
 308                 error = log_end - log_start;
 309                 break;
 310         case 10:        /* Size of the log buffer */
 311                 error = log_buf_len;
 312                 break;
 313         default:
 314                 error = -EINVAL;
 315                 break;
 316         }
 317 out:
 318         return error;
 319 }
 320
 321 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 322 {
 323         return do_syslog(type, buf, len);
 324 }
 325
 326 /*
 327  * Call the console drivers on a range of log_buf
 328  */
 329 static void __call_console_drivers(unsigned long start, unsigned long end)
 330 {
 331         struct console *con;
 332
 333         for (con = console_drivers; con; con = con->next) {
 334                 if ((con->flags & CON_ENABLED) && con->write &&
 335                                 (cpu_online(smp_processor_id()) ||
 336                                 (con->flags & CON_ANYTIME)))
 337                         con->write(con, &LOG_BUF(start), end - start);
 338         }
 339 }
 340
 341 /*
 342  * Write out chars from start to end - 1 inclusive
 343  */
 344 static void _call_console_drivers(unsigned long start,
 345                                 unsigned long end, int msg_log_level)
 346 {
 347         if (msg_log_level < console_loglevel &&
 348                         console_drivers && start != end) {
 349                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 350                         /* wrapped write */
 351                         __call_console_drivers(start & LOG_BUF_MASK,
 352                                                 log_buf_len);
 353                         __call_console_drivers(0, end & LOG_BUF_MASK);
 354                 } else {
 355                         __call_console_drivers(start, end);
 356                 }
 357         }
 358 }
 359
 360 /*
 361  * Call the console drivers, asking them to write out
 362  * log_buf[start] to log_buf[end - 1].
 363  * The console_sem must be held.
 364  */
 365 static void call_console_drivers(unsigned long start, unsigned long end)
 366 {
 367         unsigned long cur_index, start_print;
 368         static int msg_level = -1;
 369
 370         BUG_ON(((long)(start - end)) > 0);
 371
 372         cur_index = start;
 373         start_print = start;
 374         while (cur_index != end) {
 375                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 376                                 LOG_BUF(cur_index + 0) == '<' &&
 377                                 LOG_BUF(cur_index + 1) >= '0' &&
 378                                 LOG_BUF(cur_index + 1) <= '7' &&
 379                                 LOG_BUF(cur_index + 2) == '>') {
 380                         msg_level = LOG_BUF(cur_index + 1) - '0';
 381                         cur_index += 3;
 382                         start_print = cur_index;
 383                 }
 384                 while (cur_index != end) {
 385                         char c = LOG_BUF(cur_index);
 386
 387                         cur_index++;
 388                         if (c == '\n') {
 389                                 if (msg_level < 0) {
 390                                         /*
 391                                          * printk() has already given us loglevel tags in
 392                                          * the buffer.  This code is here in case the
 393                                          * log buffer has wrapped right round and scribbled
 394                                          * on those tags
 395                                          */
 396                                         msg_level = default_message_loglevel;
 397                                 }
 398                                 _call_console_drivers(start_print, cur_index, msg_level);
 399                                 msg_level = -1;
 400                                 start_print = cur_index;
 401                                 break;
 402                         }
 403                 }
 404         }
 405         _call_console_drivers(start_print, end, msg_level);
 406 }
 407
 408 static void emit_log_char(char c)
 409 {
 410         LOG_BUF(log_end) = c;
 411         log_end++;
 412         if (log_end - log_start > log_buf_len)
 413                 log_start = log_end - log_buf_len;
 414         if (log_end - con_start > log_buf_len)
 415                 con_start = log_end - log_buf_len;
 416         if (logged_chars < log_buf_len)
 417                 logged_chars++;
 418 }
 419
 420 /*
 421  * Zap console related locks when oopsing. Only zap at most once
 422  * every 10 seconds, to leave time for slow consoles to print a
 423  * full oops.
 424  */
 425 static void zap_locks(void)
 426 {
 427         static unsigned long oops_timestamp;
 428
 429         if (time_after_eq(jiffies, oops_timestamp) &&
 430                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 431                 return;
 432
 433         oops_timestamp = jiffies;
 434
 435         /* If a crash is occurring, make sure we can't deadlock */
 436         spin_lock_init(&logbuf_lock);
 437         /* And make sure that we print immediately */
 438         init_MUTEX(&console_sem);
 439 }
 440
 441 static int printk_time = 0;
 442
 443 #ifdef CONFIG_PRINTK_TIME
 444
 445 /*
 446  * Initialize printk time. Note that on some systems sched_clock()
 447  * does not work until timer is initialized.
 448  */
 449 static int __init printk_time_init(void)
 450 {
 451         printk_time = 1;
 452
 453         return 0;
 454 }
 455 subsys_initcall(printk_time_init);
 456
 457 #else
 458
 459 static int __init printk_time_setup(char *str)
 460 {
 461         if (*str)
 462                 return 0;
 463         printk_time = 1;
 464         return 1;
 465 }
 466
 467 __setup("time", printk_time_setup);
 468
 469 #endif
 470
 471 __attribute__((weak)) unsigned long long printk_clock(void)
 472 {
 473         return sched_clock();
 474 }
 475
 476 /* Check if we have any console registered that can be called early in boot. */
 477 static int have_callable_console(void)
 478 {
 479         struct console *con;
 480
 481         for (con = console_drivers; con; con = con->next)
 482                 if (con->flags & CON_ANYTIME)
 483                         return 1;
 484
 485         return 0;
 486 }
 487
 488 /**
 489  * printk - print a kernel message
 490  * @fmt: format string
 491  *
 492  * This is printk.  It can be called from any context.  We want it to work.
 493  *
 494  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 495  * call the console drivers.  If we fail to get the semaphore we place the output
 496  * into the log buffer and return.  The current holder of the console_sem will
 497  * notice the new output in release_console_sem() and will send it to the
 498  * consoles before releasing the semaphore.
 499  *
 500  * One effect of this deferred printing is that code which calls printk() and
 501  * then changes console_loglevel may break. This is because console_loglevel
 502  * is inspected when the actual printing occurs.
 503  *
 504  * See also:
 505  * printf(3)
 506  */
 507
 508 asmlinkage int printk(const char *fmt, ...)
 509 {
 510         va_list args;
 511         int r;
 512
 513         va_start(args, fmt);
 514         r = vprintk(fmt, args);
 515         va_end(args);
 516
 517         return r;
 518 }
 519
 520 /* cpu currently holding logbuf_lock */
 521 static volatile unsigned int printk_cpu = UINT_MAX;
 522
 523 asmlinkage int vprintk(const char *fmt, va_list args)
 524 {
 525         unsigned long flags;
 526         int printed_len;
 527         char *p;
 528         static char printk_buf[1024];
 529         static int log_level_unknown = 1;
 530
 531         preempt_disable();
 532         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 533                 /* If a crash is occurring during printk() on this CPU,
 534                  * make sure we can't deadlock */
 535                 zap_locks();
 536
 537         /* This stops the holder of console_sem just where we want him */
 538         local_irq_save(flags);
 539         lockdep_off();
 540         spin_lock(&logbuf_lock);
 541         printk_cpu = smp_processor_id();
 542
 543         /* Emit the output into the temporary buffer */
 544         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 545
 546 #ifdef  CONFIG_DEBUG_LL
 547         printascii(printk_buf);
 548 #endif
 549
 550         /*
 551          * Copy the output into log_buf.  If the caller didn't provide
 552          * appropriate log level tags, we insert them here
 553          */
 554         for (p = printk_buf; *p; p++) {
 555                 if (log_level_unknown) {
 556                         /* log_level_unknown signals the start of a new line */
 557                         if (printk_time) {
 558                                 int loglev_char;
 559                                 char tbuf[50], *tp;
 560                                 unsigned tlen;
 561                                 unsigned long long t;
 562                                 unsigned long nanosec_rem;
 563
 564                                 /*
 565                                  * force the log level token to be
 566                                  * before the time output.
 567                                  */
 568                                 if (p[0] == '<' && p[1] >='0' &&
 569                                    p[1] <= '7' && p[2] == '>') {
 570                                         loglev_char = p[1];
 571                                         p += 3;
 572                                         printed_len -= 3;
 573                                 } else {
 574                                         loglev_char = default_message_loglevel
 575                                                 + '0';
 576                                 }
 577                                 t = printk_clock();
 578                                 nanosec_rem = do_div(t, 1000000000);
 579                                 tlen = sprintf(tbuf,
 580                                                 "<%c>[%5lu.%06lu] ",
 581                                                 loglev_char,
 582                                                 (unsigned long)t,
 583                                                 nanosec_rem/1000);
 584
 585                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 586                                         emit_log_char(*tp);
 587                                 printed_len += tlen;
 588                         } else {
 589                                 if (p[0] != '<' || p[1] < '0' ||
 590                                    p[1] > '7' || p[2] != '>') {
 591                                         emit_log_char('<');
 592                                         emit_log_char(default_message_loglevel
 593                                                 + '0');
 594                                         emit_log_char('>');
 595                                         printed_len += 3;
 596                                 }
 597                         }
 598                         log_level_unknown = 0;
 599                         if (!*p)
 600                                 break;
 601                 }
 602                 emit_log_char(*p);
 603                 if (*p == '\n')
 604                         log_level_unknown = 1;
 605         }
 606
 607         if (!down_trylock(&console_sem)) {
 608                 /*
 609                  * We own the drivers.  We can drop the spinlock and
 610                  * let release_console_sem() print the text, maybe ...
 611                  */
 612                 console_locked = 1;
 613                 printk_cpu = UINT_MAX;
 614                 spin_unlock(&logbuf_lock);
 615
 616                 /*
 617                  * Console drivers may assume that per-cpu resources have
 618                  * been allocated. So unless they're explicitly marked as
 619                  * being able to cope (CON_ANYTIME) don't call them until
 620                  * this CPU is officially up.
 621                  */
 622                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 623                         console_may_schedule = 0;
 624                         release_console_sem();
 625                 } else {
 626                         /* Release by hand to avoid flushing the buffer. */
 627                         console_locked = 0;
 628                         up(&console_sem);
 629                 }
 630                 lockdep_on();
 631                 local_irq_restore(flags);
 632         } else {
 633                 /*
 634                  * Someone else owns the drivers.  We drop the spinlock, which
 635                  * allows the semaphore holder to proceed and to call the
 636                  * console drivers with the output which we just produced.
 637                  */
 638                 printk_cpu = UINT_MAX;
 639                 spin_unlock(&logbuf_lock);
 640                 lockdep_on();
 641                 local_irq_restore(flags);
 642         }
 643
 644         preempt_enable();
 645         return printed_len;
 646 }
 647 EXPORT_SYMBOL(printk);
 648 EXPORT_SYMBOL(vprintk);
 649
 650 #else
 651
 652 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 653 {
 654         return 0;
 655 }
 656
 657 int do_syslog(int type, char __user *buf, int len)
 658 {
 659         return 0;
 660 }
 661
 662 static void call_console_drivers(unsigned long start, unsigned long end)
 663 {
 664 }
 665
 666 #endif
 667
 668 /*
 669  * Set up a list of consoles.  Called from init/main.c
 670  */
 671 static int __init console_setup(char *str)
 672 {
 673         char name[sizeof(console_cmdline[0].name)];
 674         char *s, *options;
 675         int idx;
 676
 677         /*
 678          * Decode str into name, index, options.
 679          */
 680         if (str[0] >= '0' && str[0] <= '9') {
 681                 strcpy(name, "ttyS");
 682                 strncpy(name + 4, str, sizeof(name) - 5);
 683         } else {
 684                 strncpy(name, str, sizeof(name) - 1);
 685         }
 686         name[sizeof(name) - 1] = 0;
 687         if ((options = strchr(str, ',')) != NULL)
 688                 *(options++) = 0;
 689 #ifdef __sparc__
 690         if (!strcmp(str, "ttya"))
 691                 strcpy(name, "ttyS0");
 692         if (!strcmp(str, "ttyb"))
 693                 strcpy(name, "ttyS1");
 694 #endif
 695         for (s = name; *s; s++)
 696                 if ((*s >= '0' && *s <= '9') || *s == ',')
 697                         break;
 698         idx = simple_strtoul(s, NULL, 10);
 699         *s = 0;
 700
 701         add_preferred_console(name, idx, options);
 702         return 1;
 703 }
 704 __setup("console=", console_setup);
 705
 706 /**
 707  * add_preferred_console - add a device to the list of preferred consoles.
 708  * @name: device name
 709  * @idx: device index
 710  * @options: options for this console
 711  *
 712  * The last preferred console added will be used for kernel messages
 713  * and stdin/out/err for init.  Normally this is used by console_setup
 714  * above to handle user-supplied console arguments; however it can also
 715  * be used by arch-specific code either to override the user or more
 716  * commonly to provide a default console (ie from PROM variables) when
 717  * the user has not supplied one.
 718  */
 719 int __init add_preferred_console(char *name, int idx, char *options)
 720 {
 721         struct console_cmdline *c;
 722         int i;
 723
 724         /*
 725          *      See if this tty is not yet registered, and
 726          *      if we have a slot free.
 727          */
 728         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 729                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 730                           console_cmdline[i].index == idx) {
 731                                 selected_console = i;
 732                                 return 0;
 733                 }
 734         if (i == MAX_CMDLINECONSOLES)
 735                 return -E2BIG;
 736         selected_console = i;
 737         c = &console_cmdline[i];
 738         memcpy(c->name, name, sizeof(c->name));
 739         c->name[sizeof(c->name) - 1] = 0;
 740         c->options = options;
 741         c->index = idx;
 742         return 0;
 743 }
 744
 745 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 746 /**
 747  * suspend_console - suspend the console subsystem
 748  *
 749  * This disables printk() while we go into suspend states
 750  */
 751 void suspend_console(void)
 752 {
 753         printk("Suspending console(s)\n");
 754         acquire_console_sem();
 755         console_suspended = 1;
 756 }
 757
 758 void resume_console(void)
 759 {
 760         console_suspended = 0;
 761         release_console_sem();
 762 }
 763 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 764
 765 /**
 766  * acquire_console_sem - lock the console system for exclusive use.
 767  *
 768  * Acquires a semaphore which guarantees that the caller has
 769  * exclusive access to the console system and the console_drivers list.
 770  *
 771  * Can sleep, returns nothing.
 772  */
 773 void acquire_console_sem(void)
 774 {
 775         BUG_ON(in_interrupt());
 776         if (console_suspended) {
 777                 down(&secondary_console_sem);
 778                 return;
 779         }
 780         down(&console_sem);
 781         console_locked = 1;
 782         console_may_schedule = 1;
 783 }
 784 EXPORT_SYMBOL(acquire_console_sem);
 785
 786 int try_acquire_console_sem(void)
 787 {
 788         if (down_trylock(&console_sem))
 789                 return -1;
 790         console_locked = 1;
 791         console_may_schedule = 0;
 792         return 0;
 793 }
 794 EXPORT_SYMBOL(try_acquire_console_sem);
 795
 796 int is_console_locked(void)
 797 {
 798         return console_locked;
 799 }
 800 EXPORT_UNUSED_SYMBOL(is_console_locked);  /*  June 2006  */
 801
 802 /**
 803  * release_console_sem - unlock the console system
 804  *
 805  * Releases the semaphore which the caller holds on the console system
 806  * and the console driver list.
 807  *
 808  * While the semaphore was held, console output may have been buffered
 809  * by printk().  If this is the case, release_console_sem() emits
 810  * the output prior to releasing the semaphore.
 811  *
 812  * If there is output waiting for klogd, we wake it up.
 813  *
 814  * release_console_sem() may be called from any context.
 815  */
 816 void release_console_sem(void)
 817 {
 818         unsigned long flags;
 819         unsigned long _con_start, _log_end;
 820         unsigned long wake_klogd = 0;
 821
 822         if (console_suspended) {
 823                 up(&secondary_console_sem);
 824                 return;
 825         }
 826
 827         console_may_schedule = 0;
 828
 829         for ( ; ; ) {
 830                 spin_lock_irqsave(&logbuf_lock, flags);
 831                 wake_klogd |= log_start - log_end;
 832                 if (con_start == log_end)
 833                         break;                  /* Nothing to print */
 834                 _con_start = con_start;
 835                 _log_end = log_end;
 836                 con_start = log_end;            /* Flush */
 837                 spin_unlock(&logbuf_lock);
 838                 call_console_drivers(_con_start, _log_end);
 839                 local_irq_restore(flags);
 840         }
 841         console_locked = 0;
 842         up(&console_sem);
 843         spin_unlock_irqrestore(&logbuf_lock, flags);
 844         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 845                 wake_up_interruptible(&log_wait);
 846 }
 847 EXPORT_SYMBOL(release_console_sem);
 848
 849 /**
 850  * console_conditional_schedule - yield the CPU if required
 851  *
 852  * If the console code is currently allowed to sleep, and
 853  * if this CPU should yield the CPU to another task, do
 854  * so here.
 855  *
 856  * Must be called within acquire_console_sem().
 857  */
 858 void __sched console_conditional_schedule(void)
 859 {
 860         if (console_may_schedule)
 861                 cond_resched();
 862 }
 863 EXPORT_SYMBOL(console_conditional_schedule);
 864
 865 void console_print(const char *s)
 866 {
 867         printk(KERN_EMERG "%s", s);
 868 }
 869 EXPORT_SYMBOL(console_print);
 870
 871 void console_unblank(void)
 872 {
 873         struct console *c;
 874
 875         /*
 876          * console_unblank can no longer be called in interrupt context unless
 877          * oops_in_progress is set to 1..
 878          */
 879         if (oops_in_progress) {
 880                 if (down_trylock(&console_sem) != 0)
 881                         return;
 882         } else
 883                 acquire_console_sem();
 884
 885         console_locked = 1;
 886         console_may_schedule = 0;
 887         for (c = console_drivers; c != NULL; c = c->next)
 888                 if ((c->flags & CON_ENABLED) && c->unblank)
 889                         c->unblank();
 890         release_console_sem();
 891 }
 892
 893 /*
 894  * Return the console tty driver structure and its associated index
 895  */
 896 struct tty_driver *console_device(int *index)
 897 {
 898         struct console *c;
 899         struct tty_driver *driver = NULL;
 900
 901         acquire_console_sem();
 902         for (c = console_drivers; c != NULL; c = c->next) {
 903                 if (!c->device)
 904                         continue;
 905                 driver = c->device(c, index);
 906                 if (driver)
 907                         break;
 908         }
 909         release_console_sem();
 910         return driver;
 911 }
 912
 913 /*
 914  * Prevent further output on the passed console device so that (for example)
 915  * serial drivers can disable console output before suspending a port, and can
 916  * re-enable output afterwards.
 917  */
 918 void console_stop(struct console *console)
 919 {
 920         acquire_console_sem();
 921         console->flags &= ~CON_ENABLED;
 922         release_console_sem();
 923 }
 924 EXPORT_SYMBOL(console_stop);
 925
 926 void console_start(struct console *console)
 927 {
 928         acquire_console_sem();
 929         console->flags |= CON_ENABLED;
 930         release_console_sem();
 931 }
 932 EXPORT_SYMBOL(console_start);
 933
 934 /*
 935  * The console driver calls this routine during kernel initialization
 936  * to register the console printing procedure with printk() and to
 937  * print any messages that were printed by the kernel before the
 938  * console driver was initialized.
 939  */
 940 void register_console(struct console *console)
 941 {
 942         int i;
 943         unsigned long flags;
 944
 945         if (preferred_console < 0)
 946                 preferred_console = selected_console;
 947
 948         /*
 949          *      See if we want to use this console driver. If we
 950          *      didn't select a console we take the first one
 951          *      that registers here.
 952          */
 953         if (preferred_console < 0) {
 954                 if (console->index < 0)
 955                         console->index = 0;
 956                 if (console->setup == NULL ||
 957                     console->setup(console, NULL) == 0) {
 958                         console->flags |= CON_ENABLED | CON_CONSDEV;
 959                         preferred_console = 0;
 960                 }
 961         }
 962
 963         /*
 964          *      See if this console matches one we selected on
 965          *      the command line.
 966          */
 967         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 968                         i++) {
 969                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 970                         continue;
 971                 if (console->index >= 0 &&
 972                     console->index != console_cmdline[i].index)
 973                         continue;
 974                 if (console->index < 0)
 975                         console->index = console_cmdline[i].index;
 976                 if (console->setup &&
 977                     console->setup(console, console_cmdline[i].options) != 0)
 978                         break;
 979                 console->flags |= CON_ENABLED;
 980                 console->index = console_cmdline[i].index;
 981                 if (i == selected_console) {
 982                         console->flags |= CON_CONSDEV;
 983                         preferred_console = selected_console;
 984                 }
 985                 break;
 986         }
 987
 988         if (!(console->flags & CON_ENABLED))
 989                 return;
 990
 991         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 992                 unregister_console(console_drivers);
 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         /* If last console is removed, we re-enable picking the first
1044          * one that gets registered. Without that, pmac early boot console
1045          * would prevent fbcon from taking over.
1046          *
1047          * If this isn't the last console and it has CON_CONSDEV set, we
1048          * need to set it on the next preferred console.
1049          */
1050         if (console_drivers == NULL)
1051                 preferred_console = selected_console;
1052         else if (console->flags & CON_CONSDEV)
1053                 console_drivers->flags |= CON_CONSDEV;
1054
1055         release_console_sem();
1056         return res;
1057 }
1058 EXPORT_SYMBOL(unregister_console);
1059
1060 /**
1061  * tty_write_message - write a message to a certain tty, not just the console.
1062  * @tty: the destination tty_struct
1063  * @msg: the message to write
1064  *
1065  * This is used for messages that need to be redirected to a specific tty.
1066  * We don't put it into the syslog queue right now maybe in the future if
1067  * really needed.
1068  */
1069 void tty_write_message(struct tty_struct *tty, char *msg)
1070 {
1071         if (tty && tty->driver->write)
1072                 tty->driver->write(tty, msg, strlen(msg));
1073         return;
1074 }
1075
1076 /*
1077  * printk rate limiting, lifted from the networking subsystem.
1078  *
1079  * This enforces a rate limit: not more than one kernel message
1080  * every printk_ratelimit_jiffies to make a denial-of-service
1081  * attack impossible.
1082  */
1083 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1084 {
1085         static DEFINE_SPINLOCK(ratelimit_lock);
1086         static unsigned long toks = 10 * 5 * HZ;
1087         static unsigned long last_msg;
1088         static int missed;
1089         unsigned long flags;
1090         unsigned long now = jiffies;
1091
1092         spin_lock_irqsave(&ratelimit_lock, flags);
1093         toks += now - last_msg;
1094         last_msg = now;
1095         if (toks > (ratelimit_burst * ratelimit_jiffies))
1096                 toks = ratelimit_burst * ratelimit_jiffies;
1097         if (toks >= ratelimit_jiffies) {
1098                 int lost = missed;
1099
1100                 missed = 0;
1101                 toks -= ratelimit_jiffies;
1102                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1103                 if (lost)
1104                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1105                 return 1;
1106         }
1107         missed++;
1108         spin_unlock_irqrestore(&ratelimit_lock, flags);
1109         return 0;
1110 }
1111 EXPORT_SYMBOL(__printk_ratelimit);
1112
1113 /* minimum time in jiffies between messages */
1114 int printk_ratelimit_jiffies = 5 * HZ;
1115
1116 /* number of messages we send before ratelimiting */
1117 int printk_ratelimit_burst = 10;
1118
1119 int printk_ratelimit(void)
1120 {
1121         return __printk_ratelimit(printk_ratelimit_jiffies,
1122                                 printk_ratelimit_burst);
1123 }
1124 EXPORT_SYMBOL(printk_ratelimit);