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/jiffies.h>
  27 #include <linux/nmi.h>
  28 #include <linux/module.h>
  29 #include <linux/interrupt.h>                    /* For in_interrupt() */
  30 #include <linux/config.h>
  31 #include <linux/delay.h>
  32 #include <linux/smp.h>
  33 #include <linux/security.h>
  34 #include <linux/bootmem.h>
  35 #include <linux/syscalls.h>
  36 #include <linux/vs_base.h>
  37 #include <linux/vs_cvirt.h>
  38
  39 #include <asm/uaccess.h>
  40
  41 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  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_SYMBOL(console_printk);
  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;
  85 int console_suspended;
  86
  87 /*
  88  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  89  * It is also used in interesting ways to provide interlocking in
  90  * release_console_sem().
  91  */
  92 static DEFINE_SPINLOCK(logbuf_lock);
  93
  94 #define LOG_BUF_MASK    (log_buf_len-1)
  95 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  96
  97 /*
  98  * The indices into log_buf are not constrained to log_buf_len - they
  99  * must be masked before subscripting
 100  */
 101 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
 102 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
 103 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
 104
 105 /*
 106  *      Array of consoles built from command line options (console=)
 107  */
 108 struct console_cmdline
 109 {
 110         char    name[8];                        /* Name of the driver       */
 111         int     index;                          /* Minor dev. to use        */
 112         char    *options;                       /* Options for the driver   */
 113 };
 114
 115 #define MAX_CMDLINECONSOLES 8
 116
 117 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 118 static int selected_console = -1;
 119 static int preferred_console = -1;
 120
 121 /* Flag: console code may call schedule() */
 122 static int console_may_schedule;
 123
 124 #ifdef CONFIG_PRINTK
 125
 126 static char __log_buf[__LOG_BUF_LEN];
 127 static char *log_buf = __log_buf;
 128 static int log_buf_len = __LOG_BUF_LEN;
 129 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 130
 131 static int __init log_buf_len_setup(char *str)
 132 {
 133         unsigned long size = memparse(str, &str);
 134         unsigned long flags;
 135
 136         if (size)
 137                 size = roundup_pow_of_two(size);
 138         if (size > log_buf_len) {
 139                 unsigned long start, dest_idx, offset;
 140                 char *new_log_buf;
 141
 142                 new_log_buf = alloc_bootmem(size);
 143                 if (!new_log_buf) {
 144                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 145                         goto out;
 146                 }
 147
 148                 spin_lock_irqsave(&logbuf_lock, flags);
 149                 log_buf_len = size;
 150                 log_buf = new_log_buf;
 151
 152                 offset = start = min(con_start, log_start);
 153                 dest_idx = 0;
 154                 while (start != log_end) {
 155                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 156                         start++;
 157                         dest_idx++;
 158                 }
 159                 log_start -= offset;
 160                 con_start -= offset;
 161                 log_end -= offset;
 162                 spin_unlock_irqrestore(&logbuf_lock, flags);
 163
 164                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 165         }
 166 out:
 167         return 1;
 168 }
 169
 170 __setup("log_buf_len=", log_buf_len_setup);
 171
 172 #ifdef CONFIG_BOOT_DELAY
 173
 174 extern unsigned int boot_delay; /* msecs to delay after each printk during bootup */
 175 extern long preset_lpj;
 176 extern unsigned long long printk_delay_msec;
 177
 178 static void boot_delay_msec(int millisecs)
 179 {
 180         unsigned long long k = printk_delay_msec * millisecs;
 181         unsigned long timeout;
 182
 183         timeout = jiffies + msecs_to_jiffies(millisecs);
 184         while (k) {
 185                 k--;
 186                 cpu_relax();
 187                 /*
 188                  * use (volatile) jiffies to prevent
 189                  * compiler reduction; loop termination via jiffies
 190                  * is secondary and may or may not happen.
 191                  */
 192                 if (time_after(jiffies, timeout))
 193                         break;
 194                 touch_nmi_watchdog();
 195         }
 196 }
 197
 198 #endif
 199
 200 /*
 201  * Commands to do_syslog:
 202  *
 203  *      0 -- Close the log.  Currently a NOP.
 204  *      1 -- Open the log. Currently a NOP.
 205  *      2 -- Read from the log.
 206  *      3 -- Read all messages remaining in the ring buffer.
 207  *      4 -- Read and clear all messages remaining in the ring buffer
 208  *      5 -- Clear ring buffer.
 209  *      6 -- Disable printk's to console
 210  *      7 -- Enable printk's to console
 211  *      8 -- Set level of messages printed to console
 212  *      9 -- Return number of unread characters in the log buffer
 213  *     10 -- Return size of the log buffer
 214  */
 215 int do_syslog(int type, char __user *buf, int len)
 216 {
 217         unsigned long i, j, limit, count;
 218         int do_clear = 0;
 219         char c;
 220         int error;
 221
 222         error = security_syslog(type);
 223         if (error)
 224                 return error;
 225
 226         if ((type >= 2) && (type <= 4)) {
 227                 error = -EINVAL;
 228                 if (!buf || len < 0)
 229                         goto out;
 230                 error = 0;
 231                 if (!len)
 232                         goto out;
 233                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 234                         error = -EFAULT;
 235                         goto out;
 236                 }
 237         }
 238         if (!vx_check(0, VX_ADMIN|VX_WATCH))
 239                 return vx_do_syslog(type, buf, len);
 240
 241         switch (type) {
 242         case 0:         /* Close log */
 243                 break;
 244         case 1:         /* Open log */
 245                 break;
 246         case 2:         /* Read from log */
 247                 error = wait_event_interruptible(log_wait,
 248                                                         (log_start - log_end));
 249                 if (error)
 250                         goto out;
 251                 i = 0;
 252                 spin_lock_irq(&logbuf_lock);
 253                 while (!error && (log_start != log_end) && i < len) {
 254                         c = LOG_BUF(log_start);
 255                         log_start++;
 256                         spin_unlock_irq(&logbuf_lock);
 257                         error = __put_user(c,buf);
 258                         buf++;
 259                         i++;
 260                         cond_resched();
 261                         spin_lock_irq(&logbuf_lock);
 262                 }
 263                 spin_unlock_irq(&logbuf_lock);
 264                 if (!error)
 265                         error = i;
 266                 break;
 267         case 4:         /* Read/clear last kernel messages */
 268                 do_clear = 1;
 269                 /* FALL THRU */
 270         case 3:         /* Read last kernel messages */
 271                 count = len;
 272                 if (count > log_buf_len)
 273                         count = log_buf_len;
 274                 spin_lock_irq(&logbuf_lock);
 275                 if (count > logged_chars)
 276                         count = logged_chars;
 277                 if (do_clear)
 278                         logged_chars = 0;
 279                 limit = log_end;
 280                 /*
 281                  * __put_user() could sleep, and while we sleep
 282                  * printk() could overwrite the messages
 283                  * we try to copy to user space. Therefore
 284                  * the messages are copied in reverse. <manfreds>
 285                  */
 286                 for (i = 0; i < count && !error; i++) {
 287                         j = limit-1-i;
 288                         if (j + log_buf_len < log_end)
 289                                 break;
 290                         c = LOG_BUF(j);
 291                         spin_unlock_irq(&logbuf_lock);
 292                         error = __put_user(c,&buf[count-1-i]);
 293                         cond_resched();
 294                         spin_lock_irq(&logbuf_lock);
 295                 }
 296                 spin_unlock_irq(&logbuf_lock);
 297                 if (error)
 298                         break;
 299                 error = i;
 300                 if (i != count) {
 301                         int offset = count-error;
 302                         /* buffer overflow during copy, correct user buffer. */
 303                         for (i = 0; i < error; i++) {
 304                                 if (__get_user(c,&buf[i+offset]) ||
 305                                     __put_user(c,&buf[i])) {
 306                                         error = -EFAULT;
 307                                         break;
 308                                 }
 309                                 cond_resched();
 310                         }
 311                 }
 312                 break;
 313         case 5:         /* Clear ring buffer */
 314                 logged_chars = 0;
 315                 break;
 316         case 6:         /* Disable logging to console */
 317                 console_loglevel = minimum_console_loglevel;
 318                 break;
 319         case 7:         /* Enable logging to console */
 320                 console_loglevel = default_console_loglevel;
 321                 break;
 322         case 8:         /* Set level of messages printed to console */
 323                 error = -EINVAL;
 324                 if (len < 1 || len > 8)
 325                         goto out;
 326                 if (len < minimum_console_loglevel)
 327                         len = minimum_console_loglevel;
 328                 console_loglevel = len;
 329                 error = 0;
 330                 break;
 331         case 9:         /* Number of chars in the log buffer */
 332                 error = log_end - log_start;
 333                 break;
 334         case 10:        /* Size of the log buffer */
 335                 error = log_buf_len;
 336                 break;
 337         default:
 338                 error = -EINVAL;
 339                 break;
 340         }
 341 out:
 342         return error;
 343 }
 344
 345 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 346 {
 347         return do_syslog(type, buf, len);
 348 }
 349
 350 /*
 351  * Call the console drivers on a range of log_buf
 352  */
 353 static void __call_console_drivers(unsigned long start, unsigned long end)
 354 {
 355         struct console *con;
 356
 357         for (con = console_drivers; con; con = con->next) {
 358                 if ((con->flags & CON_ENABLED) && con->write)
 359                         con->write(con, &LOG_BUF(start), end - start);
 360         }
 361 }
 362
 363 /*
 364  * Write out chars from start to end - 1 inclusive
 365  */
 366 static void _call_console_drivers(unsigned long start,
 367                                 unsigned long end, int msg_log_level)
 368 {
 369         if (msg_log_level < console_loglevel &&
 370                         console_drivers && start != end) {
 371                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 372                         /* wrapped write */
 373                         __call_console_drivers(start & LOG_BUF_MASK,
 374                                                 log_buf_len);
 375                         __call_console_drivers(0, end & LOG_BUF_MASK);
 376                 } else {
 377                         __call_console_drivers(start, end);
 378                 }
 379         }
 380 }
 381
 382 /*
 383  * Call the console drivers, asking them to write out
 384  * log_buf[start] to log_buf[end - 1].
 385  * The console_sem must be held.
 386  */
 387 static void call_console_drivers(unsigned long start, unsigned long end)
 388 {
 389         unsigned long cur_index, start_print;
 390         static int msg_level = -1;
 391
 392         BUG_ON(((long)(start - end)) > 0);
 393
 394         cur_index = start;
 395         start_print = start;
 396         while (cur_index != end) {
 397                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 398                                 LOG_BUF(cur_index + 0) == '<' &&
 399                                 LOG_BUF(cur_index + 1) >= '0' &&
 400                                 LOG_BUF(cur_index + 1) <= '7' &&
 401                                 LOG_BUF(cur_index + 2) == '>') {
 402                         msg_level = LOG_BUF(cur_index + 1) - '0';
 403                         cur_index += 3;
 404                         start_print = cur_index;
 405                 }
 406                 while (cur_index != end) {
 407                         char c = LOG_BUF(cur_index);
 408
 409                         cur_index++;
 410                         if (c == '\n') {
 411                                 if (msg_level < 0) {
 412                                         /*
 413                                          * printk() has already given us loglevel tags in
 414                                          * the buffer.  This code is here in case the
 415                                          * log buffer has wrapped right round and scribbled
 416                                          * on those tags
 417                                          */
 418                                         msg_level = default_message_loglevel;
 419                                 }
 420                                 _call_console_drivers(start_print, cur_index, msg_level);
 421                                 msg_level = -1;
 422                                 start_print = cur_index;
 423                                 break;
 424                         }
 425                 }
 426         }
 427         _call_console_drivers(start_print, end, msg_level);
 428 }
 429
 430 static void emit_log_char(char c)
 431 {
 432         LOG_BUF(log_end) = c;
 433         log_end++;
 434         if (log_end - log_start > log_buf_len)
 435                 log_start = log_end - log_buf_len;
 436         if (log_end - con_start > log_buf_len)
 437                 con_start = log_end - log_buf_len;
 438         if (logged_chars < log_buf_len)
 439                 logged_chars++;
 440 }
 441
 442 /*
 443  * Zap console related locks when oopsing. Only zap at most once
 444  * every 10 seconds, to leave time for slow consoles to print a
 445  * full oops.
 446  */
 447 static void zap_locks(void)
 448 {
 449         static unsigned long oops_timestamp;
 450
 451         if (time_after_eq(jiffies, oops_timestamp) &&
 452                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 453                 return;
 454
 455         oops_timestamp = jiffies;
 456
 457         /* If a crash is occurring, make sure we can't deadlock */
 458         spin_lock_init(&logbuf_lock);
 459         /* And make sure that we print immediately */
 460         init_MUTEX(&console_sem);
 461 }
 462
 463 #if defined(CONFIG_PRINTK_TIME)
 464 static int printk_time = 1;
 465 #else
 466 static int printk_time = 0;
 467 #endif
 468
 469 static int __init printk_time_setup(char *str)
 470 {
 471         if (*str)
 472                 return 0;
 473         printk_time = 1;
 474         return 1;
 475 }
 476
 477 __setup("time", printk_time_setup);
 478
 479 __attribute__((weak)) unsigned long long printk_clock(void)
 480 {
 481         return sched_clock();
 482 }
 483
 484 /**
 485  * printk - print a kernel message
 486  * @fmt: format string
 487  *
 488  * This is printk.  It can be called from any context.  We want it to work.
 489  *
 490  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 491  * call the console drivers.  If we fail to get the semaphore we place the output
 492  * into the log buffer and return.  The current holder of the console_sem will
 493  * notice the new output in release_console_sem() and will send it to the
 494  * consoles before releasing the semaphore.
 495  *
 496  * One effect of this deferred printing is that code which calls printk() and
 497  * then changes console_loglevel may break. This is because console_loglevel
 498  * is inspected when the actual printing occurs.
 499  *
 500  * See also:
 501  * printf(3)
 502  */
 503
 504 asmlinkage int printk(const char *fmt, ...)
 505 {
 506         va_list args;
 507         int r;
 508
 509         va_start(args, fmt);
 510         r = vprintk(fmt, args);
 511         va_end(args);
 512
 513 #ifdef CONFIG_BOOT_DELAY
 514         if (boot_delay && system_state == SYSTEM_BOOTING)
 515                 boot_delay_msec(boot_delay);
 516 #endif
 517
 518         return r;
 519 }
 520
 521 /* cpu currently holding logbuf_lock */
 522 static volatile unsigned int printk_cpu = UINT_MAX;
 523
 524 asmlinkage int vprintk(const char *fmt, va_list args)
 525 {
 526         unsigned long flags;
 527         int printed_len;
 528         char *p;
 529         static char printk_buf[1024];
 530         static int log_level_unknown = 1;
 531
 532         preempt_disable();
 533         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 534                 /* If a crash is occurring during printk() on this CPU,
 535                  * make sure we can't deadlock */
 536                 zap_locks();
 537
 538         /* This stops the holder of console_sem just where we want him */
 539         spin_lock_irqsave(&logbuf_lock, flags);
 540         printk_cpu = smp_processor_id();
 541
 542         /* Emit the output into the temporary buffer */
 543         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 544
 545         /*
 546          * Copy the output into log_buf.  If the caller didn't provide
 547          * appropriate log level tags, we insert them here
 548          */
 549         for (p = printk_buf; *p; p++) {
 550                 if (log_level_unknown) {
 551                         /* log_level_unknown signals the start of a new line */
 552                         if (printk_time) {
 553                                 int loglev_char;
 554                                 char tbuf[50], *tp;
 555                                 unsigned tlen;
 556                                 unsigned long long t;
 557                                 unsigned long nanosec_rem;
 558
 559                                 /*
 560                                  * force the log level token to be
 561                                  * before the time output.
 562                                  */
 563                                 if (p[0] == '<' && p[1] >='0' &&
 564                                    p[1] <= '7' && p[2] == '>') {
 565                                         loglev_char = p[1];
 566                                         p += 3;
 567                                         printed_len -= 3;
 568                                 } else {
 569                                         loglev_char = default_message_loglevel
 570                                                 + '0';
 571                                 }
 572                                 t = printk_clock();
 573                                 nanosec_rem = do_div(t, 1000000000);
 574                                 tlen = sprintf(tbuf,
 575                                                 "<%c>[%5lu.%06lu] ",
 576                                                 loglev_char,
 577                                                 (unsigned long)t,
 578                                                 nanosec_rem/1000);
 579
 580                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 581                                         emit_log_char(*tp);
 582                                 printed_len += tlen;
 583                         } else {
 584                                 if (p[0] != '<' || p[1] < '0' ||
 585                                    p[1] > '7' || p[2] != '>') {
 586                                         emit_log_char('<');
 587                                         emit_log_char(default_message_loglevel
 588                                                 + '0');
 589                                         emit_log_char('>');
 590                                         printed_len += 3;
 591                                 }
 592                         }
 593                         log_level_unknown = 0;
 594                         if (!*p)
 595                                 break;
 596                 }
 597                 emit_log_char(*p);
 598                 if (*p == '\n')
 599                         log_level_unknown = 1;
 600         }
 601
 602         if (!cpu_online(smp_processor_id())) {
 603                 /*
 604                  * Some console drivers may assume that per-cpu resources have
 605                  * been allocated.  So don't allow them to be called by this
 606                  * CPU until it is officially up.  We shouldn't be calling into
 607                  * random console drivers on a CPU which doesn't exist yet..
 608                  */
 609                 printk_cpu = UINT_MAX;
 610                 spin_unlock_irqrestore(&logbuf_lock, flags);
 611                 goto out;
 612         }
 613         if (!down_trylock(&console_sem)) {
 614                 console_locked = 1;
 615                 /*
 616                  * We own the drivers.  We can drop the spinlock and let
 617                  * release_console_sem() print the text
 618                  */
 619                 printk_cpu = UINT_MAX;
 620                 spin_unlock_irqrestore(&logbuf_lock, flags);
 621                 console_may_schedule = 0;
 622                 release_console_sem();
 623         } else {
 624                 /*
 625                  * Someone else owns the drivers.  We drop the spinlock, which
 626                  * allows the semaphore holder to proceed and to call the
 627                  * console drivers with the output which we just produced.
 628                  */
 629                 printk_cpu = UINT_MAX;
 630                 spin_unlock_irqrestore(&logbuf_lock, flags);
 631         }
 632 out:
 633         preempt_enable();
 634         return printed_len;
 635 }
 636 EXPORT_SYMBOL(printk);
 637 EXPORT_SYMBOL(vprintk);
 638
 639 #else
 640
 641 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 642 {
 643         return 0;
 644 }
 645
 646 int do_syslog(int type, char __user *buf, int len)
 647 {
 648         return 0;
 649 }
 650
 651 static void call_console_drivers(unsigned long start, unsigned long end)
 652 {
 653 }
 654
 655 #endif
 656
 657 /*
 658  * Set up a list of consoles.  Called from init/main.c
 659  */
 660 static int __init console_setup(char *str)
 661 {
 662         char name[sizeof(console_cmdline[0].name)];
 663         char *s, *options;
 664         int idx;
 665
 666         /*
 667          * Decode str into name, index, options.
 668          */
 669         if (str[0] >= '0' && str[0] <= '9') {
 670                 strcpy(name, "ttyS");
 671                 strncpy(name + 4, str, sizeof(name) - 5);
 672         } else {
 673                 strncpy(name, str, sizeof(name) - 1);
 674         }
 675         name[sizeof(name) - 1] = 0;
 676         if ((options = strchr(str, ',')) != NULL)
 677                 *(options++) = 0;
 678 #ifdef __sparc__
 679         if (!strcmp(str, "ttya"))
 680                 strcpy(name, "ttyS0");
 681         if (!strcmp(str, "ttyb"))
 682                 strcpy(name, "ttyS1");
 683 #endif
 684         for (s = name; *s; s++)
 685                 if ((*s >= '0' && *s <= '9') || *s == ',')
 686                         break;
 687         idx = simple_strtoul(s, NULL, 10);
 688         *s = 0;
 689
 690         add_preferred_console(name, idx, options);
 691         return 1;
 692 }
 693 __setup("console=", console_setup);
 694
 695 /**
 696  * add_preferred_console - add a device to the list of preferred consoles.
 697  * @name: device name
 698  * @idx: device index
 699  * @options: options for this console
 700  *
 701  * The last preferred console added will be used for kernel messages
 702  * and stdin/out/err for init.  Normally this is used by console_setup
 703  * above to handle user-supplied console arguments; however it can also
 704  * be used by arch-specific code either to override the user or more
 705  * commonly to provide a default console (ie from PROM variables) when
 706  * the user has not supplied one.
 707  */
 708 int __init add_preferred_console(char *name, int idx, char *options)
 709 {
 710         struct console_cmdline *c;
 711         int i;
 712
 713         /*
 714          *      See if this tty is not yet registered, and
 715          *      if we have a slot free.
 716          */
 717         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 718                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 719                           console_cmdline[i].index == idx) {
 720                                 selected_console = i;
 721                                 return 0;
 722                 }
 723         if (i == MAX_CMDLINECONSOLES)
 724                 return -E2BIG;
 725         selected_console = i;
 726         c = &console_cmdline[i];
 727         memcpy(c->name, name, sizeof(c->name));
 728         c->name[sizeof(c->name) - 1] = 0;
 729         c->options = options;
 730         c->index = idx;
 731         return 0;
 732 }
 733
 734 /**
 735  * acquire_console_sem - lock the console system for exclusive use.
 736  *
 737  * Acquires a semaphore which guarantees that the caller has
 738  * exclusive access to the console system and the console_drivers list.
 739  *
 740  * Can sleep, returns nothing.
 741  */
 742 void acquire_console_sem(void)
 743 {
 744         if (console_suspended) {
 745                 down(&secondary_console_sem);
 746                 return;
 747         }
 748
 749         BUG_ON(in_interrupt());
 750         down(&console_sem);
 751         console_locked = 1;
 752         console_may_schedule = 1;
 753 }
 754 EXPORT_SYMBOL(acquire_console_sem);
 755
 756 int try_acquire_console_sem(void)
 757 {
 758         if (down_trylock(&console_sem))
 759                 return -1;
 760         console_locked = 1;
 761         console_may_schedule = 0;
 762         return 0;
 763 }
 764 EXPORT_SYMBOL(try_acquire_console_sem);
 765
 766 int is_console_locked(void)
 767 {
 768         return console_locked;
 769 }
 770 EXPORT_SYMBOL(is_console_locked);
 771
 772 /**
 773  * release_console_sem - unlock the console system
 774  *
 775  * Releases the semaphore which the caller holds on the console system
 776  * and the console driver list.
 777  *
 778  * While the semaphore was held, console output may have been buffered
 779  * by printk().  If this is the case, release_console_sem() emits
 780  * the output prior to releasing the semaphore.
 781  *
 782  * If there is output waiting for klogd, we wake it up.
 783  *
 784  * release_console_sem() may be called from any context.
 785  */
 786 void release_console_sem(void)
 787 {
 788         unsigned long flags;
 789         unsigned long _con_start, _log_end;
 790         unsigned long wake_klogd = 0;
 791
 792         if (console_suspended) {
 793                 up(&secondary_console_sem);
 794                 return;
 795         }
 796
 797         for ( ; ; ) {
 798                 spin_lock_irqsave(&logbuf_lock, flags);
 799                 wake_klogd |= log_start - log_end;
 800                 if (con_start == log_end)
 801                         break;                  /* Nothing to print */
 802                 _con_start = con_start;
 803                 _log_end = log_end;
 804                 con_start = log_end;            /* Flush */
 805                 spin_unlock(&logbuf_lock);
 806                 call_console_drivers(_con_start, _log_end);
 807                 local_irq_restore(flags);
 808         }
 809         console_locked = 0;
 810         console_may_schedule = 0;
 811         up(&console_sem);
 812         spin_unlock_irqrestore(&logbuf_lock, flags);
 813         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 814                 wake_up_interruptible(&log_wait);
 815 }
 816 EXPORT_SYMBOL(release_console_sem);
 817
 818 /**
 819  * console_conditional_schedule - yield the CPU if required
 820  *
 821  * If the console code is currently allowed to sleep, and
 822  * if this CPU should yield the CPU to another task, do
 823  * so here.
 824  *
 825  * Must be called within acquire_console_sem().
 826  */
 827 void __sched console_conditional_schedule(void)
 828 {
 829         if (console_may_schedule)
 830                 cond_resched();
 831 }
 832 EXPORT_SYMBOL(console_conditional_schedule);
 833
 834 void console_print(const char *s)
 835 {
 836         printk(KERN_EMERG "%s", s);
 837 }
 838 EXPORT_SYMBOL(console_print);
 839
 840 void console_unblank(void)
 841 {
 842         struct console *c;
 843
 844         /*
 845          * console_unblank can no longer be called in interrupt context unless
 846          * oops_in_progress is set to 1..
 847          */
 848         if (oops_in_progress) {
 849                 if (down_trylock(&console_sem) != 0)
 850                         return;
 851         } else
 852                 acquire_console_sem();
 853
 854         console_locked = 1;
 855         console_may_schedule = 0;
 856         for (c = console_drivers; c != NULL; c = c->next)
 857                 if ((c->flags & CON_ENABLED) && c->unblank)
 858                         c->unblank();
 859         release_console_sem();
 860 }
 861
 862 /*
 863  * Return the console tty driver structure and its associated index
 864  */
 865 struct tty_driver *console_device(int *index)
 866 {
 867         struct console *c;
 868         struct tty_driver *driver = NULL;
 869
 870         acquire_console_sem();
 871         for (c = console_drivers; c != NULL; c = c->next) {
 872                 if (!c->device)
 873                         continue;
 874                 driver = c->device(c, index);
 875                 if (driver)
 876                         break;
 877         }
 878         release_console_sem();
 879         return driver;
 880 }
 881
 882 /*
 883  * Prevent further output on the passed console device so that (for example)
 884  * serial drivers can disable console output before suspending a port, and can
 885  * re-enable output afterwards.
 886  */
 887 void console_stop(struct console *console)
 888 {
 889         acquire_console_sem();
 890         console->flags &= ~CON_ENABLED;
 891         release_console_sem();
 892 }
 893 EXPORT_SYMBOL(console_stop);
 894
 895 void console_start(struct console *console)
 896 {
 897         acquire_console_sem();
 898         console->flags |= CON_ENABLED;
 899         release_console_sem();
 900 }
 901 EXPORT_SYMBOL(console_start);
 902
 903 /*
 904  * The console driver calls this routine during kernel initialization
 905  * to register the console printing procedure with printk() and to
 906  * print any messages that were printed by the kernel before the
 907  * console driver was initialized.
 908  */
 909 void register_console(struct console *console)
 910 {
 911         int i;
 912         unsigned long flags;
 913
 914         if (preferred_console < 0)
 915                 preferred_console = selected_console;
 916
 917         /*
 918          *      See if we want to use this console driver. If we
 919          *      didn't select a console we take the first one
 920          *      that registers here.
 921          */
 922         if (preferred_console < 0) {
 923                 if (console->index < 0)
 924                         console->index = 0;
 925                 if (console->setup == NULL ||
 926                     console->setup(console, NULL) == 0) {
 927                         console->flags |= CON_ENABLED | CON_CONSDEV;
 928                         preferred_console = 0;
 929                 }
 930         }
 931
 932         /*
 933          *      See if this console matches one we selected on
 934          *      the command line.
 935          */
 936         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 937                         i++) {
 938                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 939                         continue;
 940                 if (console->index >= 0 &&
 941                     console->index != console_cmdline[i].index)
 942                         continue;
 943                 if (console->index < 0)
 944                         console->index = console_cmdline[i].index;
 945                 if (console->setup &&
 946                     console->setup(console, console_cmdline[i].options) != 0)
 947                         break;
 948                 console->flags |= CON_ENABLED;
 949                 console->index = console_cmdline[i].index;
 950                 if (i == selected_console) {
 951                         console->flags |= CON_CONSDEV;
 952                         preferred_console = selected_console;
 953                 }
 954                 break;
 955         }
 956
 957         if (!(console->flags & CON_ENABLED))
 958                 return;
 959
 960         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 961                 unregister_console(console_drivers);
 962                 console->flags &= ~CON_PRINTBUFFER;
 963         }
 964
 965         /*
 966          *      Put this console in the list - keep the
 967          *      preferred driver at the head of the list.
 968          */
 969         acquire_console_sem();
 970         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 971                 console->next = console_drivers;
 972                 console_drivers = console;
 973                 if (console->next)
 974                         console->next->flags &= ~CON_CONSDEV;
 975         } else {
 976                 console->next = console_drivers->next;
 977                 console_drivers->next = console;
 978         }
 979         if (console->flags & CON_PRINTBUFFER) {
 980                 /*
 981                  * release_console_sem() will print out the buffered messages
 982                  * for us.
 983                  */
 984                 spin_lock_irqsave(&logbuf_lock, flags);
 985                 con_start = log_start;
 986                 spin_unlock_irqrestore(&logbuf_lock, flags);
 987         }
 988         release_console_sem();
 989 }
 990 EXPORT_SYMBOL(register_console);
 991
 992 int unregister_console(struct console *console)
 993 {
 994         struct console *a, *b;
 995         int res = 1;
 996
 997         acquire_console_sem();
 998         if (console_drivers == console) {
 999                 console_drivers=console->next;
1000                 res = 0;
1001         } else if (console_drivers) {
1002                 for (a=console_drivers->next, b=console_drivers ;
1003                      a; b=a, a=b->next) {
1004                         if (a == console) {
1005                                 b->next = a->next;
1006                                 res = 0;
1007                                 break;
1008                         }
1009                 }
1010         }
1011
1012         /* If last console is removed, we re-enable picking the first
1013          * one that gets registered. Without that, pmac early boot console
1014          * would prevent fbcon from taking over.
1015          *
1016          * If this isn't the last console and it has CON_CONSDEV set, we
1017          * need to set it on the next preferred console.
1018          */
1019         if (console_drivers == NULL)
1020                 preferred_console = selected_console;
1021         else if (console->flags & CON_CONSDEV)
1022                 console_drivers->flags |= CON_CONSDEV;
1023
1024         release_console_sem();
1025         return res;
1026 }
1027 EXPORT_SYMBOL(unregister_console);
1028
1029 /**
1030  * tty_write_message - write a message to a certain tty, not just the console.
1031  * @tty: the destination tty_struct
1032  * @msg: the message to write
1033  *
1034  * This is used for messages that need to be redirected to a specific tty.
1035  * We don't put it into the syslog queue right now maybe in the future if
1036  * really needed.
1037  */
1038 void tty_write_message(struct tty_struct *tty, char *msg)
1039 {
1040         if (tty && tty->driver->write)
1041                 tty->driver->write(tty, msg, strlen(msg));
1042         return;
1043 }
1044
1045 /*
1046  * printk rate limiting, lifted from the networking subsystem.
1047  *
1048  * This enforces a rate limit: not more than one kernel message
1049  * every printk_ratelimit_jiffies to make a denial-of-service
1050  * attack impossible.
1051  */
1052 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1053 {
1054         static DEFINE_SPINLOCK(ratelimit_lock);
1055         static unsigned long toks = 10 * 5 * HZ;
1056         static unsigned long last_msg;
1057         static int missed;
1058         unsigned long flags;
1059         unsigned long now = jiffies;
1060
1061         spin_lock_irqsave(&ratelimit_lock, flags);
1062         toks += now - last_msg;
1063         last_msg = now;
1064         if (toks > (ratelimit_burst * ratelimit_jiffies))
1065                 toks = ratelimit_burst * ratelimit_jiffies;
1066         if (toks >= ratelimit_jiffies) {
1067                 int lost = missed;
1068
1069                 missed = 0;
1070                 toks -= ratelimit_jiffies;
1071                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1072                 if (lost)
1073                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1074                 return 1;
1075         }
1076         missed++;
1077         spin_unlock_irqrestore(&ratelimit_lock, flags);
1078         return 0;
1079 }
1080 EXPORT_SYMBOL(__printk_ratelimit);
1081
1082 /* minimum time in jiffies between messages */
1083 int printk_ratelimit_jiffies = 5 * HZ;
1084
1085 /* number of messages we send before ratelimiting */
1086 int printk_ratelimit_burst = 10;
1087
1088 int printk_ratelimit(void)
1089 {
1090         return __printk_ratelimit(printk_ratelimit_jiffies,
1091                                 printk_ratelimit_burst);
1092 }
1093 EXPORT_SYMBOL(printk_ratelimit);